{"Affiliation":[{"label":"Affiliation","value":"Applied Science, Faculty of","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","classmap":"vivo:EducationalProcess","property":"vivo:departmentOrSchool"},"iri":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","explain":"VIVO-ISF Ontology V1.6 Property; The department or school name within institution; Not intended to be an institution name."},{"label":"Affiliation","value":"Chemical and Biological Engineering, Department of","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","classmap":"vivo:EducationalProcess","property":"vivo:departmentOrSchool"},"iri":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","explain":"VIVO-ISF Ontology V1.6 Property; The department or school name within institution; Not intended to be an institution name."}],"AggregatedSourceRepository":[{"label":"Aggregated Source Repository","value":"DSpace","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider","classmap":"ore:Aggregation","property":"edm:dataProvider"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider","explain":"A Europeana Data Model Property; The name or identifier of the organization who contributes data indirectly to an aggregation service (e.g. Europeana)"}],"Campus":[{"label":"Campus","value":"UBCV","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#degreeCampus","classmap":"oc:ThesisDescription","property":"oc:degreeCampus"},"iri":"https:\/\/open.library.ubc.ca\/terms#degreeCampus","explain":"UBC Open Collections Metadata Components; Local Field; Identifies the name of the campus from which the graduate completed their degree."}],"Creator":[{"label":"Creator","value":"Delima, Roxanna","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/creator","classmap":"dpla:SourceResource","property":"dcterms:creator"},"iri":"http:\/\/purl.org\/dc\/terms\/creator","explain":"A Dublin Core Terms Property; An entity primarily responsible for making the resource.; Examples of a Contributor include a person, an organization, or a service."}],"DateAvailable":[{"label":"Date Available","value":"2021-10-25T18:48:06Z","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/issued","classmap":"edm:WebResource","property":"dcterms:issued"},"iri":"http:\/\/purl.org\/dc\/terms\/issued","explain":"A Dublin Core Terms Property; Date of formal issuance (e.g., publication) of the resource."}],"DateIssued":[{"label":"Date Issued","value":"2021","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/issued","classmap":"oc:SourceResource","property":"dcterms:issued"},"iri":"http:\/\/purl.org\/dc\/terms\/issued","explain":"A Dublin Core Terms Property; Date of formal issuance (e.g., publication) of the resource."}],"Degree":[{"label":"Degree (Theses)","value":"Doctor of Philosophy - PhD","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#relatedDegree","classmap":"vivo:ThesisDegree","property":"vivo:relatedDegree"},"iri":"http:\/\/vivoweb.org\/ontology\/core#relatedDegree","explain":"VIVO-ISF Ontology V1.6 Property; The thesis degree; Extended Property specified by UBC, as per https:\/\/wiki.duraspace.org\/display\/VIVO\/Ontology+Editor%27s+Guide"}],"DegreeGrantor":[{"label":"Degree Grantor","value":"University of British Columbia","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#degreeGrantor","classmap":"oc:ThesisDescription","property":"oc:degreeGrantor"},"iri":"https:\/\/open.library.ubc.ca\/terms#degreeGrantor","explain":"UBC Open Collections Metadata Components; Local Field; Indicates the institution where thesis was granted."}],"Description":[{"label":"Description","value":"Hydrogenation is a class of chemical manufacturing widely used for applications including fine chemicals, food, fertilizer, and fuels. Conventional thermochemical hydrogenation requires large amounts of hydrogen gas and heat derived from fossil fuel combustion to enable reaction. This process is highly carbon intensive. In this thesis, I present the electrocatalytic palladium membrane reactor (ePMR) as a technology that can reduce this carbon footprint by producing hydrogenated chemicals using water and renewable electricity. In this architecture, reactive hydrogen atoms are produced from water electrolysis on one side of a palladium membrane. These hydrogen atoms are then transported through the membrane to react with an unsaturated bond of a substrate on the other side. This technology eliminates the use of hydrogen gas and fossil fuels, and operates under ambient temperatures and pressures.\r\nIn this thesis, I first demonstrate the utility of the ePMR to pair two organic reactions. Electrochemical synthesis generally forms a useful product at one electrode and a waste product at the other electrode. The palladium membrane acts as a physical barrier between the two electrodes, enabling optimized reaction conditions of two reactions simultaneously. I also investigate the effect of catalyst surface area, applied current, and electrolyte on reaction selectivity in the ePMR.\r\nI then focus on reducing the palladium content in an ePMR through a supported palladium membrane design. I show that a thin layer of palladium (<2 \u03bcm) deposited onto a porous support can enable a >20-fold reduction in palladium content compared to palladium foil membranes (25 \u03bcm) often used in the ePMR. The supported membrane design enables faster 1-hexyne hydrogenation rates than palladium foil and provides a strategy for designing cost-effective and potentially scalable membranes.\r\nFinally, I show that furfural (an important biomass derivative) can be hydrogenated into higher value products, furfuryl alcohol and tetrahydrofurfuryl alcohol at selectivities >84%. I also compare the ePMR to conventional electrochemical hydrogenation reactors. I find that furfural hydrogenation in the ePMR proceeds at higher selectivity, suppresses side product formation, and lowers operating voltages. This work presents an opportunity to decarbonize a >350,000 ton year-1 hydrogenation industry.","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/description","classmap":"dpla:SourceResource","property":"dcterms:description"},"iri":"http:\/\/purl.org\/dc\/terms\/description","explain":"A Dublin Core Terms Property; An account of the resource.; Description may include but is not limited to: an abstract, a table of contents, a graphical representation, or a free-text account of the resource."}],"DigitalResourceOriginalRecord":[{"label":"Digital Resource Original Record","value":"https:\/\/circle.library.ubc.ca\/rest\/handle\/2429\/80044?expand=metadata","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO","classmap":"ore:Aggregation","property":"edm:aggregatedCHO"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO","explain":"A Europeana Data Model Property; The identifier of the source object, e.g. the Mona Lisa itself. This could be a full linked open date URI or an internal identifier"}],"FullText":[{"label":"Full Text","value":"  EFFICIENT, CARBON-NEUTRAL HYDROGENATION USING A PALLADIUM MEMBRANE REACTOR  by  Roxanna Delima  B.Eng., McMaster University, 2017    A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF   DOCTOR OF PHILOSOPHY   in   THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES  (Chemical and Biological Engineering)    THE UNIVERSITY OF BRITISH COLUMBIA  (Vancouver)      October 2021   \u00a9 Roxanna Delima, 2021     ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the dissertation entitled: Efficient, Carbon-Neutral Hydrogenation Using a Palladium Membrane Reactor  submitted by Roxanna Delima in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical and Biological Engineering  Examining Committee: Curtis Berlinguette, Professor, Chemical and Biological Engineering, UBC Supervisor  Elod Gynge, Professor, Chemical and Biological Engineering, UBC Supervisory Committee Member  Heather Trajano, Professor, Chemical and Biological Engineering, UBC University Examiner Edouard Asselin, Professor, Materials Engineering, UBC University Examiner Additional Supervisory Committee Members: Kevin Smith, Professor, Chemical and Biological Engineering, UBC Supervisory Committee Member     iii Abstract Hydrogenation is a class of chemical manufacturing widely used for applications including fine chemicals, food, fertilizer, and fuels. Conventional thermochemical hydrogenation requires large amounts of hydrogen gas and heat derived from fossil fuel combustion to enable reaction. This process is highly carbon intensive. In this thesis, I present the electrocatalytic palladium membrane reactor (ePMR) as a technology that can reduce this carbon footprint by producing hydrogenated chemicals using water and renewable electricity. In this architecture, reactive hydrogen atoms are produced from water electrolysis on one side of a palladium membrane. These hydrogen atoms are then transported through the membrane to react with an unsaturated bond of a substrate on the other side. This technology eliminates the use of hydrogen gas and fossil fuels, and operates under ambient temperatures and pressures.   In this thesis, I first demonstrate the utility of the ePMR to pair two organic reactions. Electrochemical synthesis generally forms a useful product at one electrode and a waste product at the other electrode. The palladium membrane acts as a physical barrier between the two electrodes, enabling optimized reaction conditions of two reactions simultaneously. I also investigate the effect of catalyst surface area, applied current, and electrolyte on reaction selectivity in the ePMR.  I then focus on reducing the palladium content in an ePMR through a supported palladium membrane design. I show that a thin layer of palladium (<2 \u00b5m) deposited onto a porous support can enable a >20-fold reduction in palladium content compared to palladium foil membranes (25 \u00b5m) often used in the ePMR. The supported membrane design enables faster 1-hexyne hydrogenation rates than palladium foil and provides a strategy for designing cost-effective and potentially scalable membranes.   iv  Finally, I show that furfural (an important biomass derivative) can be hydrogenated into higher value products, furfuryl alcohol and tetrahydrofurfuryl alcohol at selectivities >84%. I also compare the ePMR to conventional electrochemical hydrogenation reactors. I find that furfural hydrogenation in the ePMR proceeds at higher selectivity, suppresses side product formation, and lowers operating voltages. This work presents an opportunity to decarbonize a >350,000 ton year-1 hydrogenation industry.    v Lay Summary Approximately 10\u201320% of chemical manufacturing including the production of food, pharmaceuticals, fertilizers, and fuels involves at least one hydrogenation step. Hydrogenation is the addition of two hydrogen atoms to a widely available unsaturated chemical (e.g., vegetable oil) to make useful products (e.g., margarine). A key shortcoming of hydrogenation reactors is that they require high temperatures, and flammable and explosive hydrogen gas. Both of these inputs are derived from fossil fuels in an energy-intensive process that has a large carbon footprint. This thesis presents an alternative hydrogenation method using a \u201cpalladium membrane reactor\u201d that uses only water and renewable electricity to drive reactions. Other methods that source hydrogen from water have not yet been developed for industry because many unsaturated chemicals (e.g., oil) separate from water and cannot mix to react. The work presented in this thesis provides strategies for developing the membrane reactor technology to decarbonize the hydrogenation industry.   vi Preface Chapter 3 is adapted from the paper \u201cComplete electron economy by pairing electrolysis with hydrogenation,\u201d Nat. Catal. 2018, 1, 501-507.1 This work was supervised by Prof. Curtis Berlinguette. The concept was developed by Dr. Rebecca Sherbo, Ben MacLeod, and Prof. Berlinguette. Dr. Sherbo and I designed the experimental plan. I performed gas\u2013chromatography (GC) experiments. Dr. Sherbo and I carried out all proof-of-concept experiments and developed the gas chromatography\u2013mass spectrometry (GC\u2013MS) method. Dr. Sherbo performed paired electrolysis experiments and Dr. Valerie Chiykowski performed nuclear magnetic resonance (NMR) experiments. GC\u2013MS experiments were carried out under the supervision of Dr. Yun Ling in the UBC Mass Spectrometry Centre and scanning electron microscopy (SEM) experiments were carried out under the supervision of Dr. Gethin Owen in the Centre for High-Throughput Phenogenomics (CHTP) at UBC. The manuscript was written by Dr. Sherbo with contributions from all authors.  Chapter 4 is adapted from the paper \u201cSupported palladium membrane reactor architecture for electrocatalytic hydrogenation,\u201d J. Mater. Chem. A. 2019, 7, 26586.2   This work was supervised by Prof. Berlinguette. I developed the concept and designed the experiments with input from Dr. Sherbo and David Dvorak. I performed all experiments with the exception of sputter-deposition and SEM imaging performed by David and NMR experiments performed by Dr. Aiko Kurimoto. GC\u2013MS experiments were carried out under the supervision of Dr. Ling in the UBC Mass Spectrometry Centre and SEM experiments were carried out under the supervision of Dr. Owen in the CHTP at UBC. Dr. Sherbo, Prof. Berlinguette, and I wrote the manuscript.   vii  Chapter 5 is adapted from the paper \u201cSelective hydrogenation of furfural in a membrane reactor,\u201d In Review. This work was supervised by Prof. Berlinguette. The reactor concept, \u201cMultiThor\u201d, was developed by Ben MacLeod and I. Michael Rooney designed and built MultiThor with input from Ben and me. I developed the experimental plan. Mia Stankovic and I performed all MultiThor experiments. I developed the GC\u2013MS method and performed data analysis with help from Arthur Fink and Aoxue Huang. David Dvorak and Mia performed all sputter-deposition and membrane characterization experiments. GC\u2013MS experiments were carried out under the supervision of Ben Herring in the Shared Instrument Facility and SEM experiments were carried out under the supervision of Dr. Owen in the CHTP at UBC. Fraser Parlane assisted with X-ray fluorescence (XRF) spectroscopy, and Dr. Camden Hunt assisted with electrocatalytic surface area (ECSA) measurements. I wrote the draft manuscript with contributions from all authors in the construction of the final manuscript.    viii Table of Contents  Abstract ......................................................................................................................................... iii\tLay Summary .................................................................................................................................v\tPreface ........................................................................................................................................... vi\tTable of Contents ....................................................................................................................... viii\tList of Tables .............................................................................................................................. xiv\tList of Figures ...............................................................................................................................xv\tList of Abbreviations ...................................................................................................................xx\tAcknowledgements ................................................................................................................ xxviii\tChapter 1: Introduction ................................................................................................................1\t1.1\t Motivation ....................................................................................................................... 1\t1.2\t Thesis Structure .............................................................................................................. 4\tChapter 2: Literature Review .......................................................................................................7\t2.1\t The Palladium\u2013Hydrogen System .................................................................................. 7\t2.1.1\t The Formation of an Interstitial Alloy .................................................................... 7\t2.1.2\t Hydrogen Absorption into Palladium ..................................................................... 9\t2.2\t Hydrogen Permeation Through a Palladium Membrane .............................................. 11\t2.2.1\t Gas-Phase Hydrogen Permeation ......................................................................... 12\t2.2.2\t Electrochemical Hydrogen Permeation ................................................................ 15\t2.3\t Thermochemical Palladium Membrane Reactors ......................................................... 17\t2.3.1\t Applications of Thermochemical Palladium Membrane Reactors ....................... 18\t2.3.1.1\t Hydrogen Gas Separation and Purification ....................................................... 18\t  ix 2.3.1.2\t Dehydrogenation ............................................................................................... 19\t2.3.1.3\t Hydrogenation ................................................................................................... 20\t2.3.2\t Membrane and Reactor Designs ........................................................................... 21\t2.3.2.1\t Membrane Designs ........................................................................................... 21\t2.3.2.2\t Reactor Engineering .......................................................................................... 24\t2.3.2.3\t Commercialization of Thermochemical Palladium Membrane Reactors ......... 25\t2.4\t Methods of Hydrogenation ........................................................................................... 26\t2.4.1\t Thermochemical Hydrogenation .......................................................................... 27\t2.4.2\t Electrocatalytic Hydrogenation ............................................................................ 29\t2.4.3\t Electrocatalytic Palladium Membrane Reactor Hydrogenation ........................... 31\tChapter 3: Paired Electrolysis and Hydrogenation in a Palladium Membrane Reactor .....35\t3.1\t Introduction ................................................................................................................... 35\t3.2\t Results and Discussion ................................................................................................. 38\t3.2.1\t Palladium Membrane Properties ........................................................................... 38\t3.2.2\t Catalytic Hydrogenation ....................................................................................... 42\t3.2.3\t Paired Electrolysis ................................................................................................ 44\t3.2.4\t Tunable Reaction Selectivity ................................................................................ 48\t3.3\t Conclusions ................................................................................................................... 51\t3.4\t Experimental Methods .................................................................................................. 52\t3.4.1\t Materials ............................................................................................................... 52\t3.4.2\t Electrochemical Measurements ............................................................................ 52\t3.4.3\t Hydrogen Quantification ...................................................................................... 53\t3.4.4\t Palladium Membrane Preparation ......................................................................... 54\t  x 3.4.4.1\t Palladium Foil Preparation ............................................................................... 54\t3.4.4.2\t Catalyst Preparation .......................................................................................... 54\t3.4.5\t Scanning Electron Microscopy ............................................................................. 55\t3.4.6\t Product Quantification .......................................................................................... 55\tChapter 4: Supported Palladium Membrane Architecture for Electrocatalytic Hydrogenation ..............................................................................................................................57\t4.1\t Introduction ................................................................................................................... 57\t4.2\t Results ........................................................................................................................... 58\t4.2.1\t Membrane and Design Fabrication ....................................................................... 58\t4.2.2\t Wettability and Liquid Permeation ....................................................................... 60\t4.2.3\t Hydrogen Permeation ........................................................................................... 62\t4.2.4\t Catalytic Hydrogenation ....................................................................................... 64\t4.3\t Discussion ..................................................................................................................... 67\t4.4\t Conclusions ................................................................................................................... 71\t4.5\t Experimental ................................................................................................................. 71\t4.5.1\t Materials ............................................................................................................... 71\t4.5.2\t Material Preparation .............................................................................................. 72\t4.5.2.1\t PTFE Support Preparation ................................................................................ 72\t4.5.2.2\t Palladium Sputter-Deposition ........................................................................... 73\t4.5.3\t Liquid Permeation Measurements ........................................................................ 73\t4.5.4\t Scanning Electron Microscopy ............................................................................. 73\t4.5.5\t Brunauer-Emmett-Teller (BET) Analysis ............................................................. 74\t4.5.6\t Electrochemical Measurements ............................................................................ 74\t  xi 4.5.6.1\t Electrochemical Surface Area ........................................................................... 75\t4.5.6.2\t Atmospheric\u2013Mass Spectrometry ..................................................................... 75\t4.5.7\t Product Quantification .......................................................................................... 76\t4.5.7.1\t Gas Chromatography\u2013Mass Spectrometry ....................................................... 76\t4.5.7.2\t 1H Nuclear Magnetic Resonance ...................................................................... 76\t4.5.8\t Palladium Leaching Quantification ...................................................................... 77\tChapter 5: Selective Hydrogenation of Furfural in a Palladium Membrane Reactor ..........78\t5.1\t Introduction ................................................................................................................... 78\t5.2\t Results ........................................................................................................................... 81\t5.2.1\t Proof-of-Principle Reactions ................................................................................ 81\t5.2.2\t Effect of Solvent on Selectivity ............................................................................ 84\t5.2.3\t Effect of Catalyst and Current on Selectivity ....................................................... 85\t5.3\t Discussion ..................................................................................................................... 90\t5.4\t Conclusions ................................................................................................................... 94\t5.5\t Experimental ................................................................................................................. 94\t5.5.1\t Materials ............................................................................................................... 94\t5.5.2\t MultiThor Design .................................................................................................. 95\t5.5.3\t Electrochemistry ................................................................................................... 96\t5.5.4\t Palladium Membrane Preparation ......................................................................... 96\t5.5.5\t Hydrogen Permeation ........................................................................................... 97\t5.5.6\t Product Quantification .......................................................................................... 98\tChapter 6: Conclusions and Future Directions ........................................................................99\t6.1\t Conclusions ................................................................................................................... 99\t  xii 6.2\t Future Directions ........................................................................................................ 101\t6.2.1\t Industrial Applications ........................................................................................ 101\t6.2.1.1\t Renewable Fuels ............................................................................................. 102\t6.2.1.2\t Hydrogen Peroxide ......................................................................................... 103\t6.2.1.3\t Hydrogen Storage ........................................................................................... 104\t6.2.2\t Reactor Designs .................................................................................................. 105\t6.2.3\t Membrane Designs ............................................................................................. 108\t6.2.4\t Catalyst Design ................................................................................................... 110\tReferences ...................................................................................................................................112\tAppendices ..................................................................................................................................124\tAppendix 1: Chapter 3 ............................................................................................................ 124\tA1.1 \t Supplementary Figures ....................................................................................... 124\tAppendix 2: Chapter 4 ............................................................................................................ 131\tA2.1 \t Supplementary Figures ....................................................................................... 131\tAppendix 3: Chapter 5 ............................................................................................................ 144\tA3.1 \t Furfural Proof-of-Concept Reaction in an H-cell ............................................... 144\tA3.2 \t MultiThor Construction and Assembly .............................................................. 144\tA3.3 \t MultiThor Control Experiments ......................................................................... 147\tA3.4 \t Additional Membrane Preparation and Characterization ................................... 149\tA3.5 \t Product Quantification by Gas Chromatography\u2013Mass Spectrometry ............... 154\tA3.6 Influence of current and charge passed on furfural hydrogenation rates ................... 156\tA3.7 Influence of sputter-deposited catalyst thickness on reactivity ................................. 158\tA3.7 Furfural Hydrogenation Without an Electrochemical Bias ........................................ 159\t  xiv List of Tables Table 4.1 Comparison of mass of palladium and 1-hexyne consumption rates using Pd\/Pd foil and Pd\/PTFE membranes in the electrocatalytic palladium membrane reactor and compared to conventional thermochemical hydrogenation Pd\/C catalysts.152\u2026\u2026\u2026\u2026\u2026\u2026\u2026\u2026\u2026\u2026\u2026\u2026\u202670   xv List of Figures Figure 1.1 Outline of thesis goals relating to the electrocatalytic palladium membrane reactor. .. 4\t Figure 2.1 (a) Palladium lattice structure (fcc unit cube) with H atoms absorbed into octahedral interstitial holes. The maximum ratio of H to Pd atoms is ~0.7. (b) Pressure\u2013composition isotherms and (c) schematic depiction of H absorption in a palladium lattice. The \u0251-phase occurs at low H concentrations (left side of curve in b), \u03b1- and \u03b2-phases exists at medium H concentrations (under dotted line in b), and only the \u03b2-phase exists at high H concentrations (right side of curve in b). Pressure\u2013composition isotherms plot adapted from Grashoff.62 ........... 9  Figure 2.2 Comparison of (a) gas-phase and (b) electrochemical hydrogen absorption and desorption. (a) H2 gas is homolytically cleaved at the Pd surface to form two adsorbed H atoms that either absorb into the metal or desorb to form H2 gas. (b) H+ are reduced at a Pd cathode surface to form an adsorbed H atom (Volmer step). The H atom can recombine with a second H atom (Tafel step) or recombine with a H+ (Heyrovsky step) to form H2 gas. (b) Effective H2 partial pressure as a function of overpotential for a palladium cathode, adapted from Maoka and Enyo.63 Effective H2 pressure was determined by correlating the atomic ratio of H:Pd to the equivalent H2 pressure using literature data on the gas-phase hydrogen absorption isotherm. The dashed line shows the theoretical slope based on the Nernst equation. ........................................ 11  Figure 2.3 (a) Hydrogen permeation through a palladium membrane, where x1 is the \u201cabsorption side\u201d of the membrane and x2 is the \u201cdesorption side\u201d. Hydrogen atoms: (1) adsorb onto the Pd surface; (2) transition from the surface to the bulk metal through absorption; (3) diffuse through the membrane; (4) transition from Pd bulk to the surface; and (5) desorbs from the surface. (b) Gas-phase hydrogen permeation, where H2 gas dissociates at the Pd membrane, permeates through the membrane, and recombines on the other side. (c) Electrochemical hydrogen permeation, where two H+ formed from water electrolysis are reduced to H atoms on one side of a palladium membrane and permeate to the other side. On the other side, H atoms are oxidized to H+ and migrate to a cathode to react in the Heyrovsky step of the HER. ..................................... 12\t Figure 2.4 Gas-phase hydrogen permeation. (a) Effect of temperature on desorption-limited hydrogen flux. Reaction conditions: 1 \u00b5m thick palladium membrane; pressure is held at 1 atm at x1 and 0 atm at x2, where x1 is the hydrogen absorption side of the palladium membrane and x2 is the hydrogen desorption side. (b) Effect of partial pressure at x1 on hydrogen flux for no external mass transport resistance (pink), mass transport resistance at x1 (blue), and mass transport resistance at x2 (purple). Reaction conditions: 10 \u00b5m thick palladium membrane and reactor temperature is 673 K. Plots adapted from Ward and Dao.66 ......................................................... 15\t Figure 2.5 Thermochemical palladium membrane reactors for: (a) hydrogen purification; (b) dehydrogenation; and (c) hydrogenation using H2 gas as a hydrogen source. (a) For hydrogen purification, a mix of gases (CO2, CO, H2) is fed at one side of the membrane and only H atoms selectively permeate through to the other side to form pure H2 gas. (b) For dehydrogenation, saturated reactants are stripped of their H atoms using a packed-bed catalyst. H atoms are then transported to the other side of the membrane to form H2 gas. (c) For hydrogenation, H2 gas is   xvi fed into one side of the membrane and H atoms that permeate to the other side react with unsaturated reactants to form saturated products. ......................................................................... 18\t Figure 2.6 Comparison of palladium membrane designs for tPMRs: (a) Pd foils (<1960s); (b) Pd alloy foil (1960\u20131970); (c) Pd alloy film deposited on a metal support (1960\u20131990); and (d) Pd alloy film deposited on a porous support (>1990). (a)\u2013(c) H permeates the entire membrane and (d) H permeates the Pd alloy film only. ........................................................................................ 22\t Figure 2.7 Palladium membrane reactor designs for industrial use, where palladium is deposited on a porous support tube with catalyst packed (a) inside the tube or (b) outside the tube. (c) Multi-tubular design implemented to improve membrane surface area. Sweep gas (e.g., N2) is used to improve mass transport. .................................................................................................... 25\t Figure 2.8 Comparison of TCH, ECH, and ePMR hydrogenation. TCH is performed with H2 gas that is dissociated to surface-adsorbed H atoms that react with an unsaturated substrate to form hydrogenated products. ECH is performed with H+ derived from water that are reduced to H atoms and react with an unsaturated substrate to form hydrogenated products. Hydrogenation in an ePMR is performed with H+ derived from water that are reduced to H atoms, permeate the Pd membrane, and resurface on the opposing side to react with an unsaturated substrate to form hydrogenated products. ................................................................................................................. 27\t Figure 2.9 Hydrogenation of industrially-relevant applications ranked by functional groups that are generally easiest to hardest to hydrogenate. The functional group trend is adapted from Clayden and can vary depending on the catalyst.115 ..................................................................... 28\t Figure 2.10 Reaction conditions that control reaction rates in an ePMR: (a) current density; (b) Pd surface area; and (c) additional metal catalysts deposited on electrodeposited Pd. ................ 34\t Figure 3.1. Three-compartment cell configuration designed for paired electrolysis. (1) A current is applied to the palladium. (2) An alcohol is oxidized to an aldehyde at the platinum anode with an electron-transfer mediator and protons are released. (3) The protons cross a Nafion proton exchange membrane. (4) The protons are reduced to adsorbed hydrogen atoms at the palladium foil cathode. (5) The adsorbed hydrogen atoms permeate through the palladium lattice to the opposite surface of the foil. (6) The hydrogen atoms hydrogenate an unsaturated bond. ............ 37\t Figure 3.2 Cyclic voltammograms demonstrating isolation of the hydrogenation (hydro) and electrochemical (echem) compartments. (a) A comparison between an empty hydrogenation compartment and one with 1 M H2SO4 when 0.1 M TBAPF6 in DCM is the electrolyte in the electrochemical compartments and (b) 1 M H2SO4 in the hydrogenation compartment and a comparison between 0.1 M TBAPF6 in DCM and 1 M H2SO4 electrolyte in the electrochemical compartments. Pd foil was used as the working electrode, Pt mesh as the counter electrode, and Ag\/AgCl as the reference electrode. ............................................................................................. 39\t Figure 3.3 Hydrogen evolution on both sides of the palladium membrane. (a\u2013d) Three- compartment cell setup (a,c) and gas chromatography measurements of hydrogen evolution from   xvii the hydrogenation and electrochemical compartments at an applied current (b,d) with 1 M H2SO4 in both compartments (a,b) and with pentane replacing 1 M H2SO4 in the hydrogenation compartment (c,d). Error bars indicate standard deviations of triplicate gas chromatography measurements. ............................................................................................................................... 41\t Figure 3.4 Catalyst morphology and product distribution for palladium membrane chemical hydrogenation. (a\u2013f) Three-compartment cell setup (a,d) 1-hexyne consumption into hexenes and hexanes (b,e) and SEM images (c,f) with a palladium foil membrane (a\u2013c) and with electrodeposited palladium on the hydrogenation side of the palladium foil membrane (d\u2013f). A current of 50 mA (40.1 mA cm-2) is applied in both cases. .......................................................... 44\t Figure 3.5 Product conversion and distribution in paired electrolysis. (a) Three-compartment cell setup for paired electrolysis. (b) Hydrogenation reactions of 1-hexyne and oxidation reactions of anisyl alcohol. (c,d) Product consumption and reactant formation for the 1-hexyne hydrogenation reaction (c) and the anisyl alcohol oxidation (d) at a 50 mA applied current (40.1 mA cm-2) over a 5 hour period. (e) The current efficiencies for the desired product for both the anodic and cathodic reactions. ......................................................................................................................... 46\t Figure 3.6 Hydrogenation and oxidation current efficiencies at varied applied currents.  (a) Three-compartment cell setup for paired electrolysis. (b,c) Current efficiencies for the desired reaction product for the 1-hexyne hydrogenation reaction (b) and the anisyl alcohol oxidation reaction (c) at 25, 50, and 75 mA applied currents corresponding to current densities of 20.5, 40.1, and 61.5 mA cm-2, respectively. .......................................................................................... 48\t Figure 3.7 Hydrogenation selectivity with applied current and electrolyte. (a) Three- compartment cell setups for hydrogenation selectivity measurements. (b,c) Maximum 1-hexene conversion before the formation of n-hexane product at 25, 50 and 75 mA applied currents corresponding to current densities of 20.5, 40.1, and 61.5 mA cm-2, respectively, in 1 M KHCO3 electrolyte (b) and at 50 mA applied current (40.1 mA cm-2) in 1 M KHCO3 and 1 M H2SO4 electrochemical electrolyte (c). ..................................................................................................... 50\t Figure 4.1 (a) Cross-sectional SEM and (b) top-view SEM of a fabricated Pd\/PTFE membrane. SEM images show ~1.9 \u00b5m Pd sputtered on a PTFE support. The PTFE support has a 0.05 \u00b5m pore size and 25.4 \u00b5m thickness. (c) Schematic diagram of the electrocatalytic Pd membrane reactor using a supported Pd\/PTFE membrane as a cathode to perform hydrogenation chemistry. A current is applied to the Pd\/PTFE cathode (1) and water is oxidized at the Pt anode to form protons (2). Protons are reduced to surface-adsorbed hydrogen at the Pd surface (3), which permeate through the Pd layer to the chemical compartment (4). In the hydrogenation compartment, the organic reactant diffuses through the porous PTFE support and reacts with surface-adsorbed hydrogen at the Pd\u2013PTFE interface to form hydrogenated products (5). ......... 60\t Figure 4.2 (a) Electrocatalytic Pd\/PTFE membrane reactor setup to measure hydrogen evolution and flux through the membrane. (b) Hydrogen flux through the Pd layer for solvents with different polarities in the hydrogenation compartment (pentane being the most non-polar and H2SO4 being the most polar). A current of 100 mA (82 mA cm-2) was applied and an   xviii atmospheric\u2013mass spectrometer was used to measure H2 evolved on the hydrogenation and electrochemical sides. ................................................................................................................... 63\t Figure 4.3 (a) Hydrogenation reaction of 1-hexyne to 1-hexene and n-hexane using (b) Pd\/Pd foil and (c) Pd\/PTFE membranes in the ePMR. 1-hexyne consumption and product formation using the (d) Pd\/Pd foil membrane and (e) Pd\/PTFE membrane over an 8-h period. A current of 50 mA (40.1 mA cm-2) was applied in both cases. The Pd foil is 25 \u00b5m thick and the Pd layer (of the Pd\/PTFE membrane) is 1\u20132 \u00b5m thick. .................................................................................... 66\t Figure 4.4 (a) Hydrogenation reaction of 6-chloro-1-hexyne to 6-chloro-1-hexene and 6-chlorohexane. (b) Cell architecture using the Pd\/PTFE membrane reactor and (c) 6-chloro-1-hexyne consumption rates in pentane, DCM, and MeOH with the Pd\/Pd foil membrane (light purple) and Pd\/PTFE membrane (dark purple). A current of 50 mA (40.1 mA cm-2) was applied in both cases and consumption rate was determined for the first 3 h of reaction. ........................ 67\t Figure 4.5 Schematic depictions of hydrogen flux through the palladium layer demonstrate the difference between (a) a polar solvent (H2SO4) and (b) a non-polar solvent (pentane) in the hydrogenation compartment measured by an atmospheric mass spectrometer. For a polar solvent, there is no liquid permeation through the PTFE support which results in a gas-phase PTFE layer that enables hydrogen evolution to occur freely at the palladium\u2013PTFE interface. For a non-polar solvent, liquid diffuses through the PTFE support layer to the palladium\u2013PTFE interface and can affect the rate of hydrogen recombination. ................................................................................... 69\t Figure 5.1 Furfural hydrogenation pathways and methods. (a) Reaction pathways of furfural hydrogenation. (b) Comparison of thermochemical hydrogenation (TCH), electrochemical hydrogenation (ECH), and electrocatalytic Pd membrane reactor (ePMR) hydrogenation. TCH is performed with H2 gas that is dissociated to surface-adsorbed hydrogen atoms (H) that react with furfural to form hydrogenated products. ECH is performed with protons (H+) derived from protic electrolyte that are reduced to H and react with furfural to form hydrogenated products. Hydrogenation in an ePMR is performed with H+ derived from protic electrolyte that are reduced to H, permeate the Pd membrane, and resurface on the opposing side to react with furfural to form hydrogenated products. Note: reaction pathways in (a) and main products differ for the three methods. ............................................................................................................................... 81\t Figure 5.2 MultiThor architecture. (a) A rendering of the MultiThor design with six hydrogenation wells and an electrochemical compartment separated by a Pd foil cathode\/membrane with electrodeposited Pd catalyst. A Pt anode is used as a counter electrode in the electrochemical compartment, Cu tape is attached to the Pd cathode to provide electrical contact, and Fluorosilicone gaskets are used to seal intercompartmental interfaces. (b) Illustration of hydrogen pathway through MultiThor. (c) External MultiThor set-up showing pump, electrochemical reservoir, and electrode leads that are connected to a potentiostat. An applied current across the Pd cathode and Pt anode results in water oxidation to form H+. These H+ are reduced to surface-adsorbed H atoms at the Pd surface, H permeate through the Pd membrane, and resurface on the other side where they are poised to react on the high surface area Pd catalyst. ......................................................................................................................................... 83\t  xix  Figure 5.3 Effect of solvent on furfural hydrogenation selectivity. (a) MultiThor setup for solvent measurements. (b) Product selectivity of furfural hydrogenation to FA, THFA, and any other products formed during reaction (other) in CHCl3, t-BuOH, n-BuOH, i-PrOH, EtOH, and MeOH after 2 h of reaction at 150 mA. (c) Furfural consumption during hydrogenation in CHCl3, t-BuOH, i-PrOH, and n-BuOH. Note: MeOH and EtOH are not shown in (c) due to solvent attack on furfural to form 2-furaldehyde diethyl acetal and 2-furaldehyde dimethyl acetal (Fig. A3.7). .................................................................................................................................... 85\t Figure 5.4 Effect of catalyst identity and applied current on furfural selectivity. (a) MultiThor setup for catalyst identity measurements for furfural hydrogenation to FA and THFA. Selectivity of (b) FA and (c) THFA for 75, 150, and 225 mA applied current corresponding to current densities of 18.75, 37.5, and 56.25 mA cm-2, respectively with M\/Pd\/Pd membrane (10 nm; M = Cu, Ni, Pd, Ir, Pt, Au, and Ag). Coloured bars represent selectivity of >50% and white bars represent selectivity of <50%. Samples were taken after 8 h of applied current. ......................... 87\t Figure 5.5 Effects of catalyst thickness on furfural selectivity. (a) Furfural hydrogenation rate calculated for the first 2 h of reaction for Pt and Ir with different thicknesses. (b) Furfuryl alcohol (FA) selectivity for 10 to 50 nm of Pt and Ir sputter-deposited on a Pd\/Pd membrane measured after 8 h of reaction. (c) SEM images of 10, 20, and 50 nm of Pt on a Pd\/Pd membrane. (d) Comparison of consumption of starting material furfural to furfuryl alcohol (FA) and tetrahydrofurfuryl alcohol (THFA), and starting material FA to THFA with a Pd\/Pd membrane. ....................................................................................................................................................... 89\t Figure 6.1 Summary of future research directions for the ePMR. ............................................. 101\t Figure 6.2 (a) Comparison of liquid hydrogen (cryogenic), liquid organic hydrogen carriers, and gaseous dihydrogen. (b) Schematic diagram of hydrogenation and dehydrogenation of LOHCs in the ePMR for hydrogen fuel cell vehicles. .................................................................................. 105\t Figure 6.3 (a) Rendering of flow cell developed for developing a scalable ePMR. (b) Comparison of hydrogenation reaction of 0.1 M phenylacetlyene in an H-cell and flow cell ePMR demonstrating a 15-fold increase in reaction rates. (c\u2013e) Schematic diagram showing the upgrades that are required for the flow cell reactor to enable higher energy efficiencies. Plots in (b) and (c) were adapted from Jansonius et al.47 ........................................................................ 108\t   xx List of Abbreviations % Percent \u2206H Enthalpy \u2206x Palladium membrane thickness \u00d7 Times < Less than > Greater than ~ Approximately \u2264 Less than or equal to \u2265 Greater than or equal to $ Dollars A Amperes \u00c5 Angstroms Ag\/AgCl Silver\/silver chloride atm Atmospheres atm-MS Atmospheric-mass spectrometry \u0251 Alpha-phase bar Bar BET Brunauer-Emmett-Teller C Coulombs C\u2013C Alkane C=C Alkene   xxi C=O Carbonyl C\u2261C Alkyne CAD Computer aided design CE Counter electrode CE Current efficiency Ch. Chapter CH4 Methane CHCl3 Chloroform cm Centimeters CO Carbon monoxide CO2 Carbon dioxide cps Counts per second CV Cyclic voltammetry D Diffusion coefficient D2O Deuterated water dc\/dx Concentration gradient DCM Dichloromethane e\u2013 Electron e.g., For example ECH Electrocatalytic hydrogenation echem Electrochemical compartment ECSA Electrocatalytic surface area   xxii Ep Activation energy of permeation ePMR Electrocatalytic palladium membrane reactor Eq. Equation EtOH Ethanol eV Electronvolt F Farad F Faraday\u2019s constant  FA Furfuryl alcohol FAME Fatty acid methyl ester fcc Face-centered cubic FF Furfural Fig. Figure fold Multiplied by G Giga g Gram GC Gas chromatography GC\u2013MS Gas chromatography\u2013mass spectrometry gPd Grams of palladium h Hour(s) H atoms Hydrogen atoms H-cell Batch-style electrochemical cell H:Pd Hydrogen to palladium ratio   xxiii H+ Proton H2 gas Hydrogen gas H2O Water H2O2 Hydrogen peroxide H2SO4 Sulfuric acid Habs Absorbed H atoms Hads Surface-adsorbed H atoms HCl Hydrochloric acid Hconsumed H atoms consumed HDO Hydrodeoxygenation HER Hydrogen evolution reaction HFW Horizontal field width HNO3 Nitric acid HOR Hydrogen oxidation reaction Hproduced H atoms produced hydro Hydrogenation compartment i Applied current i-PrOH iso-propanol i.e., That is ICP\u2013OES Inductively coupled plasma\u2013optical emission spectroscopy in operando During operation in situ On site   xxiv J Joule JH2 Hydrogen flux  K Kelvin k Kila KCl Potassium chloride KHCO3 Potassium bicarbonate LOHCs Liquid organic hydrogen carriers m Milli M Molar M\/Pd\/Pd membrane Metal (M) sputter-deposited on a Pd\/Pd membrane m\/z Mass to charge ratio MEA Membrane electrode assembly MeOH Methanol min Minute(s) mm Millimeter mol Mole Mt Megaton n Rate-limiting step of permeation n-BuOH n-Butanol N2 Nitrogen gas NaOH Sodium hydroxide nH2 Moles of H2   xxv NIST National Institute of Standards and Technology nm Nanometers NMR Nuclear magnetic resonance nproduct Moles of product o Degrees O2 Oxygen gas oC Degree Celsius OER Oxygen evolution reaction oz Ounce Pa Pascals pA Picaamperes Pd\/Pd foil or membrane High surface area Pd black electrodeposited Pd foil membrane Pd\/PTFE membrane Pd (1\u20132 \u00b5m) deposited on a porous PTFE support membrane PdCl2 Palladium chloride PdHx Palladium hydride, where x is the concentration of H atoms  Pe Permeability rate  Pe0 Pre-exponential factor PEEK Polyetheretherketone  PEM Proton exchange membrane PH2 H2 partial pressure  PMR Palladium membrane reactor ppb Parts per billion   xxvi ppm Parts per million PTFE Polytetrafluoroethylene px1  Partial pressure at x1 px2 Partial pressure at x2 QCM Quartz crystal microbalance R Gas constant  RDS Rate-determining step RE Reference electrode s Second(s) SA Surface area SEM Scanning electron microscopy SLA Stereolithography  SMR Steam\u2013methane reforming t Reaction time T Temperature  t-BuOH tert-Butanol TBAPF6 Tetrabutylammonium hexafluorophosphate Tc Critical temperature TCH Thermochemical hydrogenation TEMPO 2,2,6,6-tetramethylpiperidine-1-oxyl THFA Tetrahydrofurfuryl alcohol TLD Through-the-lens detector   xxvii ton Tonne torr Torr tPMR Thermochemical palladium membrane reactor USD United states dollars V Volts V Volume vide infra See below W Watts WE Working electrode WGS Water-gas shift  wt.% Weight percentage x1 Absorption side of palladium membrane x2 Desorption side of palladium membrane XRF X-ray fluorescence \u03b2 Beta-phase \u03b4 Delta \u03b7 Overpotential \u00b5 Micro \u00b5m Micron \u03a9 Ohms    xxviii Acknowledgements I would like to start off by saying thank you to my supervisor, Curtis Berlinguette. You have taught me so many skills that go beyond anything I would have imagined I would learn in graduate school from how to become a more effective communicator, presenter, and writer to how to snowboard through tight glades and find the best lift lines on powder days. Your ambition and perseverance, especially towards difficult reviewers, are qualities I hope to emulate. Thank you for investing so much into me and encouraging me to pursue my PhD and ThorTech.  I would also like to thank my supervisory committee members, Elod Gynge and Kevin Smith. Thank you for your guidance and thoughtful feedback throughout my degree. Your expertise in electrochemistry and reactor design provided a foundation for much of the work I developed in this thesis. Thank you to all the mentors and industrial collaborators who made my PhD experience meaningful and strengthened the scope of my research work. Thank you to Michael Jones, Kris Begic, Katie Birdsall, Marianna Trujillo Vaccari, Carlyn McGeean, and Renate Schwiedernoch. Thank you to the incredible ThorTech mentors and colleagues that instilled in me a desire to pursue a career in entrepreneurship. Thank you to David Weekes, Gabe Kalmar, Francis Steiner, Udi Daon, Cynthia Shippam, Brett Sharp, and Dave Summers. A special thank you to Rebecca Sherbo for mentoring me in my first year of graduate school. The completion of my PhD degree would have not been possible without the incredible support group and friendships that I have formed along the way. Thank you to Caroline Krzyszkowski and Thomas Morrissey for becoming my first friends in Vancouver and lifelong adventure buddies. Thank you to Danielle Salvatore for teaching me so much about chemistry,   xxix engineering, art, snowboarding, and life. Thank you to Max Goldman for the endless happy hour drinks and electrochemistry lectures. Thank you to Eric Lees for always being there to provide feedback when I needed it, and for inspiring me to understand the fundamentals of chemical engineering. Thank you to Fraser Parlane for showing me that chemistry can be used in everyday life from making cocktails to engineering solar-powered cameras. Thank you to Aoxue Huang for providing me with your friendship during one of the hardest times of my PhD. Your thoughtfulness and methodological way of performing experiments continue to inspire me to be better. Thank you to Arthur Fink for being someone I could rely on for anything and everything over the past few years, including camping at Whistler in \u201310 oC. Thank you to Mia Stankovic for making the last year of my PhD incredibly fulfilling. It has been such a pleasure to mentor and be mentored by you. Thank you to Ryan Jansonius for the long late-night walks, indulging in my endless rants, and being the partner that I did not want at first, but eventually grew to need. I would also like to thank many others in the Berlinguette group including Michael Elliot for always making me laugh, Danika Wheeler for inspiring me to become a climber, Mike Rooney for motivating me to try surfing, Karry Ocean for teaching me how to do a proper handstand, Paloma Prieto for helping me become a better communicator, Ben MacLeod for teaching me how to combine imagination and science, Camden Hunt for helping me design effective experiments, and Fae Habib Zadeh for always being there to provide feedback on life and science. Thank you to Kevan Dettleback and David Dvorak for your ruthlessness on board game nights, Ken Hu and Laura Sloboda for helping me get through first year, Phil Schauer for always keeping me on my toes, Aiko Kurimoto for letting me into CHBE the endless number of times I was locked out, and Natalie Lesage for our thought-provoking conversations.   xxx I would also like to thank my family for their unconditional love and support. Thank you to my father, Royce Delima, for always encouraging me to strive for more. Your ambition and drive have shaped me into the person I am today. Thank you to my mother, Pauline Delima for teaching me how to balance my work and personal needs, and for always being there for me in times of high stress. Thank you to my sister, Hayley Delima for helping me through all my anxiety attacks, for saying yes to all my adventure ideas, and for continually inspiring me to be better. Thank you to all my extended family members for being such an incredible community of love and support, particularly Clare Doty, Shania Lobo, and Abigail Luxton. Thank you to Harold Eyster \u2013 this thesis would have been more challenging to complete without you. Thank you for being there for me during all the highs and lows of the past few years. Thank you for reading and editing much of the work written in this thesis. Thank you for all our writing retreats, backpacking adventures, ski endeavors, and road trips. And most importantly, thank you for helping me grow into the person I am today. Our discussions about veganism, climate change, communication, reflection, and human interactions will continue to impact the way I move through the world. Finally, I would like to thank the friends that have made the past 4 years of my life incredibly fulfilling. Thank you for indulging in my endless rants about my research and going on skiing, climbing, backpacking, eating adventures with me. Thank you to Fiona Dickson, Logan Timmins, Jacqueline DeSantis, Eleanor Yang, Megan Simpson, Chad Davis, Emma Carscadden, Joel Smith, Alex Ianovski, Emma Kent, Leandra Cusimano, Brittany King, Lauren Renee, Maureen Fitzpatrick, and many more.   1 Chapter 1: Introduction 1.1 Motivation  Chemical manufacturing is the largest industrial consumer of oil and gas, responsible for 10% of energy consumed worldwide and >5.5% of global carbon emissions.3 This large carbon footprint is due to the nature of chemical manufacturing processes, which require thermal energy derived from fossil fuel combustion to drive reactions.4 Environmental regulations are being implemented to require chemical manufacturers to source energy from renewable resources instead of fossil fuels.4,5  Electrochemical synthesis provides an opportunity for circumventing the use of thermal energy by using electricity to drive chemical transformations.6\u20139 Thermochemical hydrogenation (TCH) is a particularly attractive process for electrification because it makes up 20% of all fine chemical manufacturing,10 and is widely used in the food,11 petrochemical,12 and pharmaceutical industries.13 Conventional TCH relies heavily on H2 gas derived from methane, a highly energy intensive process, and requires high temperatures and pressures to enable reaction.14 This high energy intensity translates to annual carbon emissions of 1.4 Gt.15 Hydrogen derived from renewable sources has the potential to reduce these carbon emissions to 0 Gt, the largest potential process improvement in the chemical manufacturing industry.15  Electrocatalytic hydrogenation (ECH) is analogous to TCH, but uses hydrogen derived from protic electrolyte (e.g., water) and electricity to facilitate the hydrogenation of organic molecules without H2 gas.16,17 In ECH, protons (H+) are produced electrolytically at an anode and migrate to a cathode where they combine with an electron (e\u2013) to form surface-adsorbed hydrogen atoms (denoted herein as \u201cH atoms\u201d). These H atoms then react with unsaturated bonds of organic substrates to form hydrogenated products under ambient conditions. The use of   2 hydrogen derived from renewable sources is intriguing, however, there are several fundamental challenges that need to be addressed before this method can be considered for industry. ECH reactions require a protic electrolyte to enable the electrochemical production of H atoms and subsequent hydrogenation to occur simultaneously in the same reaction chamber. This requirement significantly limits the scope of solvents that can be used for the reaction, adds formidable challenges to product separation, and lowers product selectivity.18     This thesis showcases the electrocatalytic palladium membrane reactor (ePMR, Fig. 1.1) as an enabling technology to overcome the challenges with conventional thermochemical and electrocatalytic hydrogenation reactors. The defining feature of an ePMR is that a dense palladium membrane acts as: (i) a cathode for reducing H+ (produced from water electrolysis) to form reactive H atoms; (ii) a hydrogen-selective membrane to transport H atoms to an isolated reaction vessel; and (iii) a catalyst for the hydrogenation reaction. In this architecture, H+ produced at a platinum anode migrate to the palladium cathode, where they are reduced to surface-adsorbed H atoms. H atoms subsequently absorb into interstitial octahedral sites of the palladium face-centered cubic (fcc) lattice,19 permeate across the membrane, and resurface on the opposite face of the membrane where they react with unsaturated bonds of organic molecules to form hydrogenated products. The palladium membrane therefore acts as a physical barrier to separate the electrochemical production of H atoms from the hydrogenation reaction. Consequently, ePMR hydrogenation can be performed in any solvent (including protic and organic solvents) and without product separation challenges. Despite these advantages, the ePMR has not yet been widely explored. The ePMR was first reported by Iwakura, Inoue, and coworkers in 1996,20 and since then there have been ~25 publications demonstrating proof-of-concept hydrogenations of various functional groups (e.g.,   3 alkynes, alkenes, quinones, aromatic rings, and CO2).20\u201344 The Berlinguette group independently began studying the ePMR in 2018, with a focus on developing an ePMR that is competitive with conventional TCH for industrially relevant applications.1,2,45\u201349 In this thesis, I will discuss the research that I have undertaken to advance our understanding of factors that impact reaction rates and activity, membrane designs, and reaction scope to develop a scalable ePMR.              4 1.2 Thesis Structure The goals of this thesis are shown in Fig. 1.1. There are three main objectives: (i) to advance our understanding of the variables that govern reactivity and selectivity in the ePMR (Ch. 3); (ii) to reduce palladium loading to develop a scalable reactor (Ch. 4); and (iii) to demonstrate the hydrogenation of an industrially-relevant molecule (Ch. 5). In Chapter 6, I discuss future opportunities for the ePMR technology and a roadmap for continued development.    Figure 1.1 Outline of thesis goals relating to the electrocatalytic palladium membrane reactor.   Chapter 3 is the first report of the ePMR by the Berlinguette group. In this chapter, the ePMR is used to couple two reactions that are otherwise incompatible: electrochemical oxidation and chemical hydrogenation. Electrosynthesis is generally performed at either an anode or cathode and the other half reaction forms a waste product. Paired electrolysis forms useful products at both electrodes, however, this process is limited to reactions that operate at similar   5 conditions. The ePMR offers a method for separating the two reactions, enabling each transformation to be performed at different reaction conditions. In this chapter, catalyst surface area, solvent, applied current, and electrolyte are modified to enable >98% product selectivity, and the mechanisms that govern hydrogen permeation in the ePMR are discussed. Chapter 4 focuses on reducing the palladium content in an ePMR by depositing a thin layer of palladium (1\u20132 \u00b5m) onto a porous polytetrafluoroethylene (PTFE) support (herein denoted \u201cPd\/PTFE membrane\u201d). All previous embodiments of ePMRs utilized thick expensive palladium foil membranes (\u226525 \u00b5m), which are not cost-competitive with conventional TCH catalysts. The Pd\/PTFE membranes enable a 20-fold reduction in palladium content, while still facilitating fast solution transport to the palladium layer and comparable reaction rates to palladium foil membranes. I also show how deposition on porous supported membranes can directly increase catalyst surface area. This work demonstrates a pathway for designing supported membranes that can lead to a cost-effective and potentially scalable ePMR.  Chapter 5 demonstrates the hydrogenation of furfural, an important biomass derivative, into higher value products (e.g., furfuryl alcohol and tetrahydrofurfuryl alcohol) with >84% selectivities. To reach these high selectivities, I design and build a novel ePMR that enables high-throughput testing of combinations of solvents, catalysts, and applied currents. This empirical approach reveals that bulky solvents with weak nucleophilicities suppress the formation of side products. Notably, these solvents are not compatible with standard ECH reactor architectures, yet they are compatible with the ePMR. This work highlights the utility of the ePMR for selective furfural hydrogenation without H2 gas, and presents a possible pathway for decarbonizing this >350,000 ton\/year hydrogenation industry.   6 Chapter 6 provides my vision of next steps for developing the ePMR. While there has been tremendous progress in the last 4 years, there are still limitations that need to be addressed before this technology can be cost-competitive with TCH. In this chapter, I discuss: (i) a broad product scope to demonstrate the value of the ePMR; (ii) reactor engineering to improve energy efficiencies; (iii) membrane design to reduce reactor cost; and (iv) catalyst design to improve reactivity and selectivity. The roadmap I present seeks to elaborate on the opportunities and challenges that the ePMR will face as a disruptive technology in the chemical manufacturing industry.      7 Chapter 2: Literature Review This literature review first describes the unique interactions between palladium and hydrogen (Ch. 2.1) and how this relationship has been utilized to permeate hydrogen through a palladium membrane (Ch. 2.2). I then discuss the development of thermochemical palladium membrane reactors (tPMRs) for H2 gas related applications, and the challenges that this 60-year-old technology has had with commercialization (Ch. 2.3). Finally, I detail how an ePMR fed with electrolytic hydrogen instead of H2 gas can address the limitations of tPMRs to enable a carbon-neutral hydrogenation industry (Ch. 2.4).  2.1 The Palladium\u2013Hydrogen System 2.1.1 The Formation of an Interstitial Alloy Palladium is one of few metals that is capable of reversibly absorbing large amounts of H atoms into its lattice to form an interstitial alloy (i.e., palladium hydride, PdHx).50\u201352 Other metals (Ti, V, Y, Nb, Ta, La, and Th) can also form interstitial alloys with hydrogen, however, these metals undergo multiple phase transitions during hydrogen absorption that leads to irreversible damage to the lattice structure.53,54 The palladium fcc lattice has octahedral interstitial holes that can perfectly accommodate single H atoms up to a hydrogen-to-palladium ratio of H:Pd ~0.7 (Fig. 2.1a).19,55 The unique ability of palladium to absorb hydrogen reversibly has been widely implemented for applications such as hydrogen storage,56 high sensitivity hydrogen sensors,57 palladium membrane reactors (PMRs, Ch. 2.2, 2.3),58 heterogeneous catalysts in chemical manufacturing (Ch. 2.4), and membrane electrodes in fuel cells.59  Palladium hydride can exist at two crystalline phases at room temperature: (i) \u0251-phase (\u0251-PdHx) exists when low concentrations of H atoms (x < 0.008) are absorbed into palladium; and (ii) \u03b2-phase (\u03b2-PdHx) exists at high concentrations of H atoms (x < 0.61, Fig. 2.1b, c). Both \u0251-   8 and \u03b2-PdHx are present when an intermediate amount of H atoms are absorbed (0.008 < x < 0.61).19 This relatively small number of phases enables PdHx to outperform other metals for reversible hydrogen absorption.19 However, the Pd lattice still undergoes changes during phase transitions. When pure Pd transitions to \u0251-PdHx and \u03b2-PdHx at room temperature the lattice expands from 3.890 \u00c5 to 3.894 \u00c5 and 4.025 \u00c5, respectively.19 This expansion corresponds to a 3.4% increase in lattice size from Pd to \u03b2-PdHx.60 During hydrogen cycling, the expansion and contraction of the palladium lattice can lead to internal stresses in the metal that result in fractures and, ultimately, deactivation of the palladium\u2013hydrogen system (see Ch. 2.3.2 for more details).61  Pressure\u2013composition isotherms of hydrogen absorption into the palladium lattice highlight this failure mechanism (Fig. 2.1b). At temperatures below ~295 oC (marked by the dashed line in Fig. 2.1b), all three phases of PdHx exist, while above this critical temperature (Tc) only \u0251-PdHx exists. These data suggest that at temperatures above 295 oC, there are fewer internal stresses on the palladium lattice and the lattice is therefore less prone to deactivation.61 The trade-off at these high temperatures, however, is that the palladium lattice absorbs less H atoms. In this thesis, I take advantage of the ability of palladium to absorb large amounts of H atoms at room temperature to perform unique chemistry in the ePMR (Ch. 3\u20135). However, in order to develop a commercially viable ePMR, the expansion and contraction of the palladium lattice at ambient conditions that inevitably leads to mechanical failure must also be considered (Ch. 2.3.2, 4.2.4, 6.2.3).    9  Figure 2.1 (a) Palladium lattice structure (fcc unit cube) with H atoms absorbed into octahedral interstitial holes. The maximum ratio of H to Pd atoms is ~0.7. (b) Pressure\u2013composition isotherms and (c) schematic depiction of H absorption in a palladium lattice. The \u0251-phase occurs at low H concentrations (left side of curve in b), \u03b1- and \u03b2-phases exists at medium H concentrations (under dotted line in b), and only the \u03b2-phase exists at high H concentrations (right side of curve in b). Pressure\u2013 composition isotherms plot adapted from Grashoff.62  2.1.2 Hydrogen Absorption into Palladium Palladium absorbs H atoms by: (i) a spontaneous reaction with H2 gas; or (ii) an electrochemical reduction of H+ in an aqueous medium.63,64 For reactions with H2 gas, H2 is homolytically cleaved at the palladium surface to form two adsorbed H atoms (Fig. 2.2a). These H atoms can either absorb into the bulk of the palladium lattice or recombine to form H2 gas. Hydrogen concentration in H2 gas systems is controlled by modifying H2 pressure, temperature, and flow rate.  For reactions with H+ in an electrochemical system, H+ produced through an oxidation reaction at an anode, migrate to the palladium cathode and react with an e\u2013 to form surface-adsorbed H atoms at the palladium surface (Fig. 2.2b). This reduction is the first step of the hydrogen evolution reaction (HER) known as the Volmer step. The adsorbed H atom can further   10 absorb into the lattice bulk or react on the surface to form H2 gas through either a faradaic or non-faradaic process. The combination of two adsorbed H atoms is a non-faradaic process (the Tafel step), while the combination of a second H+ in close proximity to the adsorbed H atom is a faradaic process (the Hyrovsky step). The electrochemical hydrogen absorption and desorption steps is one key distinguishing feature between ePMR hydrogenation and ECH, which I will discuss in Chapters 2.4.1 and 2.4.2.  Hydrogen concentration in electrochemical systems is controlled by modifying electrolyte identity, concentration, and applied potential (or current).63 One key advantage of controlling electrochemical absorption using electricity is that the applied potential directly influences H2 partial pressure (PH2, Fig 2.2c). This relationship (i.e., the overpotential, \u03b7) is derived from the Nernst equation:          ! = #$%& ln\t(+,%)              (Eq. 2.1) where R represents the gas constant (8.314 J K-1 mol-1), T represents temperature, and F represents Faraday\u2019s constant (96,485 C mol-1). Studies of hydrogen absorption into palladium have demonstrated this relationship, and have shown that a strikingly small overpotential (~0.2\u20130.3 V) applied to a palladium cathode at room temperature (293 K) can yield an effective H2 pressure of 1,000\u201310,000 atm.63     11  Figure 2.2 Comparison of (a) gas-phase and (b) electrochemical hydrogen absorption and desorption. (a) H2 gas is homolytically cleaved at the Pd surface to form two adsorbed H atoms that either absorb into the metal or desorb to form H2 gas. (b) H+ are reduced at a Pd cathode surface to form an adsorbed H atom (Volmer step). The H atom can recombine with a second H atom (Tafel step) or recombine with a H+ (Heyrovsky step) to form H2 gas. (c) Effective H2 partial pressure as a function of overpotential for a palladium cathode, adapted from Maoka and Enyo.63 Effective H2 pressure was determined by correlating the atomic ratio of H:Pd to the equivalent H2 pressure using literature data on the gas-phase hydrogen absorption isotherm. The dashed line shows the theoretical slope based on the Nernst equation.  2.2 Hydrogen Permeation Through a Palladium Membrane  Similarly to hydrogen absorption, hydrogen permeation has been studied with both H2 gas and electrochemical methods (Fig. 2.3). Although electrochemical hydrogen permeation is more relevant for the work in this thesis, gas-phase hydrogen permeation has been more widely studied due to its broad use in tPMRs (Ch. 2.3) and there have only been a handful of studies performed with electrochemical hydrogen permeation. For these reasons, key takeaways from both methods are discussed in this section to better understand the mechanisms that govern hydrogen permeation in the ePMR.   12   Figure 2.3 (a) Hydrogen permeation through a palladium membrane, where x1 is the \u201cabsorption side\u201d of the membrane and x2 is the \u201cdesorption side\u201d. Hydrogen atoms: (1) adsorb onto the Pd surface; (2) transition from the surface to the bulk metal through absorption; (3) diffuse through the membrane; (4) transition from Pd bulk to the surface; and (5) desorbs from the surface (5). (b) Gas-phase hydrogen permeation, where H2 gas dissociates at the Pd membrane, permeates through the membrane, and recombines on the other side. (c) Electrochemical hydrogen permeation, where two H+ formed from water electrolysis are reduced to H atoms on one side of a palladium membrane and permeate to the other side. On the other side, H atoms are oxidized to H+ and migrate to a cathode to react in the Heyrovsky step of the HER.   2.2.1 Gas-Phase Hydrogen Permeation  Gas-phase hydrogen permeation through a palladium membrane is driven by a difference in chemical potential resulting from a partial pressure gradient across the membrane.65 H2 gas is homolytically cleaved to form surface-adsorbed H atoms (Hads) on the palladium membrane. Once adsorbed to the surface, Hads freely transition to the bulk of the metal to form absorbed H atoms (Habs), Habs diffuse through the bulk, and transition from bulk-to-surface on the other side of the membrane and resurface as Hads (Fig. 2.3a). Two Hads atoms then desorb to produce H2 gas, which is transported away from the palladium surface (Fig. 2.3b). The rate at which hydrogen permeates through a palladium membrane is known as the hydrogen flux (JH2 in mol H cm-2 s-1). Hydrogen flux is directly correlated to the amount of hydrogen available for reaction, relevant for all PMR architectures (Ch. 2.3, 2.4.3), with a higher   13 hydrogen flux being more desirable. Hydrogen flux is affected by: (i) the concentration of hydrogen in the system; and (ii) the rate-limiting step of permeation.66 While hydrogen concentration is directly influenced by temperature, pressure, and H2 flow rate, the factors that affect rate-limiting step of permeation are more challenging to discern. The rate-limiting step of permeation can be influenced by hydrogen surface coverage on both sides of the membrane, surface poisoning, number of available surface and bulk palladium atoms, grain sizes and boundaries, membrane thickness, hydrogen concentration near both surfaces, and activation energy of each step.66 The complexity of these processes has given rise to theoretical models that use empirical data to investigate the mechanisms that govern the rate-limiting step and thus enable high hydrogen fluxes to be achieved. For metal membranes, JH2 is often modelled using Fick\u2019s first law:                .,% = \u22120 1213             (Eq. 2.2)  where D is the diffusion coefficient and 1213 represents the concentration gradient across the membrane. Under steady-state flow of hydrogen, hydrogen flux can be expressed as:       .,% = +4 5678 956:8\u22063              (Eq. 2.3)  where \u2206x represents the thickness of the palladium membrane, px1 and px2 represent the partial pressures at x1 and x2 in Figure 2.3a, respectively. The exponential n represents the rate-limiting step of permeation, and Pe is permeability. Eq. 2.3 suggests that palladium membrane thickness inversely affects hydrogen flux and therefore a higher flux can be achieved by decreasing membrane thickness. However, theoretical models based on empirical data have shown that this effect only holds true for tPMRs that are diffusion-limited (step 3 in Fig 2.3a). For these systems, there is an approximate square root   14 dependence on partial pressure suggesting that n = 0.5 for diffusion-limited membranes according to Sievert\u2019s law.67 Substantial deviations from Eq. 2.3 occur when surface interactions change the rate-limiting step (to dissociative adsorption or recombinative desorption), or thin palladium membranes are implemented (<5 \u00b5m, Ch. 2.3.2.1).66  Theoretical models of gas-phase hydrogen permeation have shown that hydrogen flux through palladium membranes is diffusion-limited at high temperatures (\u2265573 K), desorption-limited at low temperatures, and adsorption-limited at very low hydrogen partial pressures or in the presence of substantial surface contamination.66 The ePMR developed in this thesis operates at room temperature under high hydrogen pressures and therefore the desorption-limited case is most relevant. When desorption is rate-limiting, increasing the number of palladium surface sites to increase hydrogen surface coverage at x2 or decreasing the activation energy of desorption result in an increase in hydrogen flux. Moreover, a desorption-limited ePMR implies that hydrogen flux is not dependent on palladium thickness for palladium thicknesses >5 \u00b5m. In Chapter 3, I perform experiments to study the rate-limiting step of hydrogen permeation in the ePMR inspired by these gas-phase studies. This approach also informed my design of efficient membranes in Chapter 4 and reactor architectures in Chapters 5. The gas-phase studies also demonstrated that higher hydrogen fluxes can be achieved by modifying temperature, pressure, and mass transport resistance. An increase in temperature generally means an increase in hydrogen flux, however, the extent to which temperature influences hydrogen flux is dependent on rate-limiting step.66 Desorption-limited hydrogen flux has a logarithmic relationship with increasing temperature (Fig. 2.5a). An increase in pressure at x1 results in an increase in hydrogen flux, while an increase in pressure at x2 results in a decrease in hydrogen flux. This effect of pressure is directly correlated to the pressure difference across   15 the membrane described by the diffusion-limited flux (Eq. 2.3), suggesting that a larger pressure differential across the membrane results in greater hydrogen flux. Finally, mass-transport resistance at both x1 and x2 leads to a reduced hydrogen flux, with resistance at x1 resulting in a 2-fold reduction in flux compared to at x2 (Fig. 2.5b).66 This reduction in hydrogen flux due to mass transport resistance is even more prominent in liquid-phase systems compared to gas-phase systems,68 and can lead to substantial reduction in reaction rates in the ePMR. In Chapter 4, I show the significant impact mass transport resistance has in the ePMR and highlight the importance of designing palladium membranes that reduce this resistance.   Figure 2.4 Gas-phase hydrogen permeation. (a) Effect of temperature on desorption-limited hydrogen flux. Reaction conditions: 1 \u00b5m thick palladium membrane; pressure is held at 1 atm at x1 and 0 atm at x2, where x1 is the hydrogen absorption side of the palladium membrane and x2 is the hydrogen desorption side. (b) Effect of partial pressure at x1 on hydrogen flux for no external mass transport resistance (pink), mass transport resistance at x1 (blue), and mass transport resistance at x2 (purple). Reaction conditions: 10 \u00b5m thick palladium membrane and reactor temperature is 673 K. Plots adapted from Ward and Dao.66  2.2.2 Electrochemical Hydrogen Permeation Hydrogen permeation proceeds in an electrochemical cell when a potential (or current) is applied across an anode and palladium cathode submersed in aqueous electrolyte (e.g., 0.1 M NaOH, Fig. 2.3c).69\u201373 These electrochemical experiments have confirmed that the palladium metal is not ionically conductive (e.g., no ions or electrolyte pass through) and thus the membrane enables permeation of H atoms only.69,70,74 In this configuration, two H+ are reduced   16 to Hads when a potential is applied to a palladium cathode in the Volmer step of the HER. These Hads then transition to the bulk to form Habs as a result of a chemical potential across the membrane. The absorption, diffusion, bulk-to-surface transition of H atoms are the same in electrochemical and gas-phase systems. Once Hads atoms are formed on the opposing side of the membrane, these atoms are oxidized to form H+ at the palladium anode surface, and are transported away to proceed in the Heyrovsky step of the HER at the cathode. The main goal of electrochemical hydrogen permeation studies has been to determine the diffusion coefficient of palladium.70\u201372 The diffusion coefficient can be measured by making diffusion the rate-limiting step of hydrogen permeation, such that the concentration of surface hydrogen on one side of a palladium membrane is fixed and the amount of hydrogen that surfaces on the opposing side is measured. Devanathan and Stachurski showed that this rate-limiting diffusion can be achieved electrochemically by applying a cathodic potential at x1, holding an anodic potential at x2 of 0 V, and measuring the corresponding current at x2.70  For palladium foil membranes (50\u2013500 \u00b5m thick), the diffusion coefficient of palladium has been determined to be ~7\u00d710\u20137 cm2 s-1 (at 293 K).69,71 These measurements have shown that the currents at both sides of the membrane reach steady-state, indicating that 100% of the hydrogen reduced at x1 permeates through the membrane.69 A very low current density of <10\u20135 A cm-2 is applied to ensure that the concentration of hydrogen in palladium remained in the \u03b1-phase, \u03b1-PdHx, and the corresponding hydrogen flux is also very low (~1.5\u00d710\u201313 mol H cm-2 s\u20131).69,70 Higher current densities (to enable higher hydrogen concentrations) are easily achievable electrochemically, however, higher concentrations of hydrogen may favour H2 gas formation over H permeation resulting in anomalies in the diffusion coefficient measurement.70   17 Unlike in gas-phase systems, electrochemical techniques have not been used to study the hydrogen flux mechanisms or the hydrogen concentration profile through palladium membranes. This situation is in part due to difficulties with decoupling interactions at the liquid\u2013metal interface. Solvent can adsorb onto the palladium surface and block hydrogen adsorption and desorption leading to a hydrogen flux that is lower than expected.75,76 Mass transport to and away from the palladium surface has a larger effect in liquid-phase systems than in gas-phase systems, which can also result in a reduced hydrogen flux.68,77 Hydrogen permeation rates have been observed to be at least 4-fold lower in liquid-phase than gas-phase systems.77 Solvent polarity also plays a role in hydrogen interactions with palladium, with polar solvents binding more strongly to the metal than non-polar solvents.75 This observation suggests that solvents that adsorb less strongly to palladium (e.g., non-polar solvents) may improve hydrogen fluxes in the ePMR and inspired the investigation of solvent polarity and nucleophilicity in Chapters 4 and 5. 2.3 Thermochemical Palladium Membrane Reactors In this section, tPMR applications, membrane and reactor designs, and commercialization pathways are discussed. These reactors have been developed for over 60 years for 3 main industrial applications: (i) H2 gas separation and purification; (ii) dehydrogenation; and (iii) hydrogenation (Fig. 2.5). The membrane and reactor designs have been extensively studied with ~6000 articles on the topic, and played a key role in inspiring the supported palladium membranes designed in Chapter 4. The commercialization pathway undertaken by tPMR research can provide a better understanding of the advantages and challenges that the ePMR technology will face as a disruptive technology to conventional thermochemical methods, and help facilitate an easier path to market for the ePMR.   18  Figure 2.5 Thermochemical palladium membrane reactors for: (a) hydrogen purification; (b) dehydrogenation; and (c) hydrogenation using H2 gas as a hydrogen source. (a) For hydrogen purification, a mix of gases (CO2, CO, H2) is fed at one side of the membrane and only H atoms selectively permeate through to the other side to form pure H2 gas. (b) For dehydrogenation, saturated reactants are stripped of their H atoms using a packed-bed catalyst. H atoms are then transported to the other side of the membrane to form H2 gas. (c) For hydrogenation, H2 gas is fed into one side of the membrane and H atoms that permeate to the other side react with unsaturated reactants to form saturated products.  2.3.1 Applications of Thermochemical Palladium Membrane Reactors 2.3.1.1 Hydrogen Gas Separation and Purification The most widely studied application of tPMRs is H2 gas separation and purification in steam\u2013methane reforming (SMR, Fig. 2.5a).32\u201335 Conventional SMR reactors comprise of two reversible processes: (i) a methane reforming reaction, which requires a high temperature and low pressure to produce H2 and CO (Eq. 2.4); and (ii) a water\u2013gas shift (WGS) reaction, which involves the separation of H2, is favored by low temperatures (Eq. 2.5).78\u201381  CH4 + H2O \u2194 CO + 3H2 \u2206H = \u2013205 kJ mol-1            (Eq. 2.4) CO + H2O \u2194 CO2 + H2 \u2206H = \u201341 kJ mol-1           (Eq. 2.5) There are several challenges associated with conventional SMR reactors. The methane reforming reaction (an endothermic process) requires temperatures that are 100\u2013200 oC higher than the WGS reaction (an exothermic process). The WGS reaction must therefore be performed   19 in a separate unit to ensure that the reaction equilibrium does not move in the reverse direction (i.e., become endothermic). Even with separated units, expensive alloy steel tubing is required due to high mechanical stress on the tubes between the two reactors.40 SMR reactors enable ~80% methane conversion to H2 gas. The 20% unconverted methane and an additional methane stream are burnt in order to supply heat to the system, which is equivalent to >10 MW of heat for an industrial plant.82 SMR processes are therefore thermodynamically unfavourable and highly energy intensive.  These challenges can be overcome by using a tPMR to selectively permeate ~100% of the H atoms (Fig. 2.5a). The removal of H atoms from the reaction interface through the membrane shifts the chemical equilibrium towards the products, thereby circumventing the thermodynamic limitations of conventional SMR. In comparison to SMR reactors, tPMRs have been shown to enable high H2 purities (99.89% at 330 \u00b0C),83 >1.5-fold higher methane conversion,84 and operate at milder reaction conditions (<450 oC instead of >800 oC).81 Technoeconomic analyses have shown that implementing a tPMR for H2 separation could enable a 10% reduction in capital expenditure due to a reduced energy intensity.81 However, tPMRs for H2 separation have not yet been developed beyond pilot scales due to challenges with membrane durability, cost, and deactivation. These limitations and potential solutions are discussed in detail in Chapters 2.3.2 and 2.3.3. 2.3.1.2 Dehydrogenation tPMRs have also been used for dehydrogenation (Fig 2.5b).30,58,85\u201387 For dehydrogenation reactions, C\u2013C or C=C bonds are stripped of their H atoms to form saturated products (C=C, C\u2261C). This process is conventionally performed in a packed-bed reactor at high temperatures and low pressures (>800 oC, 1 atm).88 Dehydrogenation in a tPMR is also performed in a packed-bed   20 architecture, but the membrane removes H atoms from the reaction site enabling the reaction to become limited by kinetics instead of thermodynamics.89 Dehydrogenation in tPMRs have enabled a >2-fold improvement in reaction rates ascribed to an increase in thermodynamic equilibrium88,89 and can enable energy savings of 50\u2013300%.89 Similarly to H2 separation, tPMRs developed for dehydrogenation also have challenges associated with membrane durability, cost, and deactivation (Ch. 2.3.2 and 2.3.3). 2.3.1.3 Hydrogenation For hydrogenation in a tPMR, H atoms sourced from H2 gas permeate through the membrane to react with an unsaturated bond of an organic substrate on the other side of the membrane (Fig. 2.5c).58,90\u201392 benefits of a tPMR for hydrogenation is that the palladium membrane can simultaneously act as: (i) a hydrogen-selective membrane to transport H atoms to the reaction site; and (ii) a hydrogenation catalyst. The use of a palladium membrane to deliver H atoms to the reaction site enables hydrogenation to proceed in gas-phase or organic solvent without concern for hydrogen solubility. Moreover, studies using tPMRs have shown that hydrogen permeation through the membrane yields faster reaction rates than hydrogen reacting on the same side of the membrane.91,93,94 These faster rates are ascribed to the lack of competition between substrate and hydrogen for surface binding sites during activation and reaction.91,93,94 Another possible explanation is that subsurface hydrogen is more energetic and accesses different orbital pathways enabling higher reactivity and selectivity.95,96 Despite these benefits, tPMRs have a smaller available surface area compared to conventional thermochemical hydrogenation catalysts that are highly dispersed (e.g., high surface area nanoparticles are deposited on porous pellets).58 This challenge has limited the applicability of tPMRs for   21 hydrogenation and led to the focus of tPMR studies on other applications (i.e., H2 purification and dehydrogenation).  2.3.2 Membrane and Reactor Designs H2 purification and dehydrogenation in tPMRs have the potential to improve energy efficiency, selectivity, and reaction rates compared to conventional processes (Ch. 2.3.1.1, 2.3.1.2). However, in order for tPMRs to be commercially viable, the membranes must have a low cost (e.g., reduced palladium content), enable high H2 flux, and exhibit high mechanical stability over a long period of time under harsh working conditions.97 These requirements all point to the importance of membrane properties for enabling a competitive technology. A number of economic studies confirmed that highly stable and cheap membranes are required to ensure tPMRs have favourable investment and operational costs.98,99 In this section, tPMR membrane and reactor designs as well as their implications for ePMR designs are discussed.  2.3.2.1 Membrane Designs Before the 1960s, tPMRs employed unsupported Pd foils (>75 \u00b5m thick) capable of permeating H atoms at ~100% purity, and withstanding the high temperature and pressure differentials between the units in an H2 purification reactor (Fig. 2.6a). These foils were implemented in pilot-scale reactors, however, due to the high cost of Pd, these reactors were never scaled-up further. This limitation of using pure Pd led to the development of Pd alloys, with some alloys (PdAg, PdCu, PdY, PdPt, PdAu) demonstrating a higher mechanical stability than pure Pd (Fig. 2.6b). The higher stability of the Pd alloys is ascribed to the reduction in Tc of the \u03b1\u2013\u03b2 phase transformation (Ch. 2.1.1) from 295 oC to below room temperature.67  The champion Pd alloy membrane was discovered to be PdAg (23 wt.% Ag) because it improves H2 fluxes by almost 2-fold, and reduces the membrane cost.67 PdCu (40 wt.% Cu) was   22 also seen as a potential candidate for commercial-use due to its significantly lower cost, high mechanical stability, and H2 fluxes comparable to pure Pd. Although these Pd alloy foils demonstrated improvements over pure Pd, relative to catalysts for conventional steam\u2013methane reforming, these membranes were still not cost-competitive.81  Figure 2.6 Comparison of palladium membrane designs for tPMRs: (a) Pd foils (<1960s); (b) Pd alloy foil (1960\u20131970); (c) Pd alloy film deposited on a metal support (1960\u20131990); and (d) Pd alloy film deposited on a porous support (>1990). (a)\u2013(c) H permeates the entire membrane and (d) H permeates the Pd alloy film only.      This situation prompted the development of membranes that were cheap, while still enabling a high mechanical stability. These next generation membranes (developed between 1960\u20131990) were composed of thin Pd alloy films deposited on a secondary metal with H permeation properties (e.g., Nb, Ta, and V, Fig. 2.6c).100 As discussed in Chapter 2.1.1, these secondary metals undergo phase changes during hydrogen absorption that lead to irreversible lattice degradation.53,54 The secondary metals do have some advantages over Pd and Pd alloys   23 including higher diffusion coefficients and lower cost.100 By depositing a thin Pd alloy onto the surface of the secondary metal, the distortions caused by hydrogen absorption into the secondary metal could be eliminated.100 The thin Pd alloy film was effectively a mediator to enable H absorption, where H atoms would subsequently permeate through the secondary metals to form H2 gas on the other side (Fig 2.6c). This membrane design enabled high mechanical stability and reduced cost of palladium membranes by 10- to 20-fold.100 Unfortunately, supported metal membranes suffered from H2 fluxes that were too low to be economically feasible.101 The largest breakthrough for palladium membrane designs was the development of thin (<5 \u00b5m) films of palladium deposited on rigid supports composed of porous glass or ceramic materials (>25 \u00b5m, Fig 2.6d).102\u2013104 This design enabled a 20- to 50-fold reduction in cost, while improving H2 flux in part due to the reduced membrane thickness (i.e., the >25 \u00b5m palladium foils that came before this were diffusion-limited, see Ch. 2.2.1).89 These Pd and Pd alloy films deposited on porous supports also demonstrated high mechanical stability, with studies showing efficient H2 purification performance for up to 10 months at temperatures ranging between 623\u2013773K.89  To date, supported palladium membranes on porous supports continue to be developed for tPMRs. This membrane design is effective in the harsh working conditions of gas-phase tPMRs, but may not amenable for liquid-phase ePMRs developed in this thesis. This limitation of tPMR membranes in ePMRs can be attributed to the substantial reduction in mass transport in liquid-phase systems compared to gas-phase systems (see Ch. 2.2.2).68,77 Design principles for supported membranes in the ePMR therefore differ quite substantially from gas-phase systems. Factors that influence membrane design in an ePMR are discussed in detail in Chapters 4 and 6.2.3, and potential membrane designs for industrial applications are suggested.   24 2.3.2.2 Reactor Engineering tPMRs are designed to ensure that: (i) membrane surface area is high; and (ii) mass transport to the surface occurs quickly. The most important design consideration is the membrane surface area because it directly influences reactivity and hydrogen flux, and it is the most expensive component of tPMRs. In order to achieve a high surface area, membranes are implemented in tubular configurations (planar configurations are used on the research-scale).105 In some cases, the tubes are packed with a catalyst either inside the tube (Fig. 2.7a) or in the shell of the tube (Fig. 2.7b) to speed up the reaction, and H2 gas is collected on the other side of the membrane. Multi-tubular configurations are commonly implemented to increase catalyst surface area even more and improve efficiencies (Fig. 2.7c). In order to ensure high mass transport, a sweep gas (e.g., N2) is used on the side of the membrane where pure H2 gas is collected, which reduces the partial pressure and promotes high hydrogen permeation.80 A tPMR plant demonstrated that a reduced pressure on the H2-collection side of the membrane could be achieved by implementing a packed-bed catalyst deposited on a foam support.80 The decrease in pressure was ascribed to a reduction in energy costs associated with reducing gas compression and recirculation of gas streams.80   25  Figure 2.7 Palladium membrane reactor designs for industrial use, where palladium is deposited on a porous support tube with catalyst packed (a) inside the tube or (b) outside the tube. (c) Multi-tubular design implemented to improve membrane surface area. Sweep gas (e.g., N2) is used to improve mass transport.    2.3.2.3 Commercialization of Thermochemical Palladium Membrane Reactors  Commercialization of tPMRs has been ongoing for over 60 years with the first tPMRs being developed in 1964 by Johnson Matthey for H2 separation using a PdAg foil membrane (75 \u00b5m thick).106 This tPMR plant was successfully used at a small pilot-scale until 1975. However, even today, the entire tPMR market is still limited to lab-scale or small pilot plants.107,108 A pilot plant built in 2011 demonstrated the production of pure H2 at a rate of 20 m3 h-1.109 This plant demonstrated that tPMRs could be used to produce high purity H2 with a 20\u201350% reduction in energy consumption and 10% reduction in cost compared to conventional SMR processes.109 The next step for assessing the feasibility of tPMRs for H2 purification is to develop a semi-industrial test plant, but there are no current scale-up plans in place. This is due to the limited number of companies (<5) that currently produce high surface area palladium membranes.110 Moreover, in   26 order to be economically viable, the palladium membranes must cost less than $2000 m-2, a >2-fold reduction in cost, which is difficult to achieve due to challenges associated with deposition methods.110 To date, there are no companies that produce supported palladium membranes that are >1 m2.110 These limitations notwithstanding, PMRs may offer a bigger opportunity than is being realized by H2 gas-driven, thermochemical applications. If coupled with a water electrolyzer as the hydrogen source, a PMR can operate using a carbon-free energy source to produce in-situ H atoms without ever requiring H2 gas. Consider, for example, that the largest application of tPMRs is H2 separation and purification for displacing conventional steam\u2013methane reforming. Steam\u2013methane reforming accounts for ~50% of the total H2 produced worldwide, of which >80% is used by the chemical manufacturing industry particularly for processes such as hydrogenation (i.e., ammonia, food, fuel, and fine chemical production).111 An ePMR offers a method for eliminating the production of H2 gas to directly feed hydrogen to arguably one of the largest consumers of H2 gas in the world, the hydrogenation industry.  2.4 Methods of Hydrogenation In this section, I detail conventional thermochemical hydrogenation and applications. I then discuss two alternative methods, electrocatalytic hydrogenation and hydrogenation in an electrocatalytic palladium membrane reactor. Both methods enable hydrogenation chemistry to be performed using electricity and water, and have the potential to enable carbon-free hydrogenation, but neither have been developed for industrial-use yet (Fig. 2.8).    27  Figure 2.8 Comparison of TCH, ECH, and ePMR hydrogenation. TCH is performed with H2 gas that is dissociated to surface-adsorbed H atoms that react with an unsaturated substrate to form hydrogenated products. ECH is performed with H+ derived from water that are reduced to H atoms and react with an unsaturated substrate to form hydrogenated products. Hydrogenation in an ePMR is performed with H+ derived from water that are reduced to H atoms, permeate the Pd membrane, and resurface on the opposing side to react with an unsaturated substrate to form hydrogenated products.  2.4.1 Thermochemical Hydrogenation Thermochemical hydrogenation reactions are generally performed by flowing H2 gas and a substrate into a batch-style reactor containing a high surface area heterogeneous catalyst (Fig 2.8a).112 H2 gas and an unsaturated bond of the substrate adsorb onto the catalyst surface, where they react to form a saturated product. The choice of catalyst depends on the functional group being hydrogenated. Pd is most commonly used to reduce C=C and C\u2261C bonds, while catalysts such as Ru and Pt are required for C=O bonds.113 The reaction is controlled by modifying the catalyst, H2 pressure, temperature, and flow rate.  The main advantages of TCH is that methods for controlling yield, selectivity, and purification are well-established, and H2 gas is relatively inexpensively sourced from fossil fuel (e.g., compared to H2 gas produced from water electrolysis).113 The main challenges with TCH reactors are: (i) the use of H2 gas and (ii) the large amount of CO2 emitted. H2 gas is highly   28 flammable and explosive and requires expensive infrastructure to enable safe storage and handling.111,114 The CO2 emissions from TCH arise from the use of H2 gas derived from natural gas reforming,14 and high temperatures and pressures required to run the reaction.  Despite these challenges, almost all industrial hydrogenation processes are performed using TCH to produce commodity chemicals (e.g., food, fuels, fertilizer) and fine chemicals (e.g., pharmaceuticals, electronics, fragrances). The carbon footprint for each application depends on the difficulty of the hydrogenation and the scale of the reaction (e.g., commodity or fine chemical scale). The difficulty of hydrogenation depends on functional group (Fig. 2.9), with more challenging hydrogenations requiring harsher reaction conditions to enable reaction. Commodity chemicals are low-value products (<$1000 USD ton-1) produced at a large scales (>10,000 tons year-1), and make up ~60% of the total hydrogenation market.15 Fine chemicals are high-value products (>$2000 USD ton-1) produced at small scales (100\u201310,000 tons year-1).15   Figure 2.9 Hydrogenation of industrially-relevant applications ranked by functional groups that are generally easiest to hardest to hydrogenate. The functional group trend is adapted from Clayden and can vary depending on the catalyst.115   TCH of vegetable oils produces margarine (a commodity chemical) by hydrogenating poly-unsaturated fatty acids containing cis-alkenes chains at relatively low temperatures and   29 pressures (<100 oC, <50 atm).116 Hydrogenation of fine chemicals is used to transform a variety of functional groups (e.g., alkynes, imines, carbonyls, and nitriles), with each application requiring completely different reaction conditions to enable high selectivity, yield, functional group tolerance, and purity.10 Petrochemicals and biofuels are produced from the hydrogenation (or hydrodeoxygenation, HDO) of functional groups that are relatively more difficult to hydrogenate such as the fatty acid methyl ester (FAME) molecule. These reactions require relatively higher temperatures and pressures (e.g., >200 oC and >200 atm),117 and consume the second largest amount of H2 gas worldwide (Ch. 6.2.1.1).118 TCH of N2 to ammonia for use in fertilizer applications (i.e., the Haber\u2013Bosch process) is the largest H2 gas consumer.111 This highly energy intensive process consumes >1% of energy worldwide and is responsible for ~2% of carbon emissions.119 The hydrogenation (and dehydrogenation) of aromatic compounds for hydrogen storage and transportation is an up and coming technology. Although this process does not currently make up a large fraction of the industrial hydrogenation market, it has the potential to play a significant role in a future H2 economy (Ch. 6.2.1.3).111  2.4.2 Electrocatalytic Hydrogenation  Electrocatalytic hydrogenation is an alternative method to TCH that sources hydrogen from water instead of H2 gas (Fig. 2.8b). A reductive current or potential is applied across two electrodes which forms protons from water or hydronium ions at the anode.120 These protons then migrate to the cathode, where they are reduced to surface-adsorbed hydrogen that then react with unsaturated bonds of organic substrates dissolved in the electrolyte. ECH can therefore use renewable electricity to drive heterogeneous hydrogenation chemistry at ambient pressures and temperatures, without ever requiring H2 gas.16,17 For this reason, ECH can circumvent the use of fossil fuels and eliminate the capital intensive infrastructure required for H2 gas handling.120   30 Moreover, the hydrogen fugacity can be controlled by the applied electrochemical potential rather than H2 gas pressure.63  One major difference between ECH and TCH is that for ECH there is a direct correlation between power supplied to the system (e.g., applied potential or current) and hydrogen available for reaction. This means that any competing HER that forms H2 gas at the surface will negatively impact hydrogenation rates. Current efficiency (CE) is the metric used to measure the formation of a hydrogenated product over H2 gas. CE is defined as:            => = ,?@8ABCDE,FG@EB?DE = ( HFG@EB?IHJ)&K\u00d7M              (Eq. 2.6) where the amount of hydrogen consumed (Hconsumed) is equivalent to the sum of moles of product formed (nproduct) multiplied by the number of H atoms (nH) required for that particular product formation. The hydrogen produced (Hproduced) is equivalent to the product of applied current (i) and reaction time (t).  An effective ECH system has a current efficiency of 100% during peak reaction. Current efficiency begins to decrease once a bulk concentration of organic substrate is consumed and reaches 0% once the reaction is complete.120 This is because ECH is generally performed in a stirred electrochemical cell and surface-adsorbed H atoms begin to form H2 gas once the catalyst surface is no longer saturated with substrate. Current efficiency is affected by applied current, cathode surface morphology, substrate, and hydrogen adsorption rates, and any other factors that affect adsorption (e.g., electrolyte, cosolvents, etc.).120 An increase in current in ECH is analogous to increasing H2 partial pressure in TCH and leads to a higher hydrogen concentration on the cathode surface due to fast electron transfer reactions. This results in higher hydrogenation rates, reduced H2 gas formation, and a high (ideally 100%) current efficiency.   31 However, increasing current over a threshold value increases electron transfer to an extent that favours H2 gas formation, and current efficiency and hydrogenation rates are compromised.120 This trade-off between applying a high current and ensuring low H2 gas formation is one of many optimization challenges that ECH faces.   Although the advantage of an alternative hydrogen source makes ECH intriguing, this method has not yet been adopted on an industrial scale because of several fundamental challenges. ECH must be performed in a protic electrolyte, which leads to poor solubility of most organic substrates that are non-polar.120 Organic cosolvents are added to the electrolyte to improve substrate solubility, but these additives increase solution resistance making it difficult for protons to reach the cathode surface. This leads to high voltages and can reduce energy consumption tremendously. Finally, confining the organic substrate, products, cosolvents, and electrolyte in the same electrochemical cell leads to unwanted byproducts at the cathode and a complicated product purification process.121 These challenges prompted us to explore alternative ways to utilize electrochemistry to source hydrogen, while bypassing the issues that surround working in aqueous media for ECH, which inevitably led to our development of the ePMR. In Chapter 5, I demonstrate the benefits of the ePMR architecture for overcoming the challenges of conventional ECH for furfural hydrogenation.   2.4.3 Electrocatalytic Palladium Membrane Reactor Hydrogenation  Hydrogenation in an electrocatalytic palladium membrane reactor is performed using a hydrogen-permeable palladium membrane that physically separates the electrochemical and hydrogenation reactions (Fig. 2.8c), enabling electrolysis to proceed in protic electrolyte and the hydrogenation to proceed in organic solvent. In this configuration, H atoms produced from water electrolysis in the electrochemical compartment are reduced to surface adsorbed H atoms at the   32 surface of a palladium membrane. These H atoms then permeate through the palladium membrane to react with an unsaturated substrate in the hydrogenation compartment on the opposite face of the membrane. Notably, the substrate on the hydrogenation side adsorbs to the palladium catalyst in an analogous way as conventional thermochemical hydrogenation (e.g., chemisorption for alkene hydrogenation).   The ePMR architecture enables hydrogenation chemistry to be performed using hydrogen sourced from a water in a faradaic process (unlike TCH) and hydrogenation to be performed in a non-faradaic process (unlike ECH, see Ch. 2.1.2). Moreover, hydrogenation in an ePMR can be performed in solvents without any solubilizing agents or organic electrolyte, which expands the substrate scope, substrate concentrations, electrolyte identities, and solvents that can be tested. The ePMR configuration also minimizes side reactions, bypasses challenges of product purification, and enables electrolyte recyclability compared to conventional ECH.45   Although the ePMR presents the opportunity to replace conventional electrochemical and thermochemical hydrogenation, prior to the work being presented in this thesis, there were a limited number of studies using the ePMR by one research group.1,2,20\u201347 These studies have shown proof-of-concept experiments using a palladium foil membrane to hydrogenate alkynes,1,21,22,27,45 alkenes,22 aldehydes,34 ketones,37 quinones,38 and aromatic rings.40 These reports demonstrated that reaction rates can be increased by increasing applied current from 1 mA to 10 mA due to a higher H2 flux across the palladium membrane (Fig. 2.10a, surface area of 0.28 cm2).92,122 However, the mechanism of hydrogen permeation in the ePMR have not previously been studied. In Chapters 3\u20136, I present a deeper understanding of the factors that govern hydrogen permeation in the ePMR based on experiments performed by our research group.   33 Iwakura and coworkers have also previously shown that the addition of a high surface area Pd electrodeposited catalyst (metal loading ~45 mg cm-2) on the hydrogenation side of the membrane improved reaction rates of 4-methylstyrene by 40-fold, and enabled a high current efficiency of 98% (Fig 2.10b).123 In Chapters 3, I use a similar electrodeposition procedure to increase the catalytic surface area of the palladium membrane by 250-fold based on electrocatalytic surface area (ECSA) measurements. However, the hydrogenation rates achieved are merely ~10-fold higher than a bare palladium due to the use of an \u201cH-cell\u201d architecture (a batch-style electrochemical configuration, Fig. A1.1). This relatively low conversion compared to the active surface area suggests that the active catalyst surface area is not being fully accessed, and that the rate-limiting step in the ePMR is likely the hydrogenation reaction (e.g., step 5 in Fig. 2.3a). In Chapters 4.2.4 and 6.2.2, I show how membrane and reactor architectures can be modified to maximize the active catalyst surface area and thereby improve hydrogenation rates.  Another key advancement from prior art is that adding a metal catalyst layer (e.g., Au, Pt) deposited on top of the high surface area Pd could also improve reaction rates.26 In this study, metal loading of ~5 mg cm-2 improved reaction rates, while higher loadings resulted in a reduction in reaction rate due to hydrogen blockage (Fig 2.10c).26 It is worth noting that an electroless plating method was used to deposit these additional metals, which made catalyst loading difficult to control. In Chapter 5, I show that a sputter-deposition method can enable facile control over metal loading of various catalysts (Pt, Ir, Au, Ni, Cu, and Ag) for thicknesses varying from 10 to 50 nm.          34  Figure 2.10 Reaction conditions that control reaction rates in an ePMR: (a) current; (b) Pd surface area; and (c) additional metal catalysts deposited on electrodeposited Pd.   While prior art has demonstrated the advantages of the ePMR for a variety of functional groups, in order to be competitive with conventional thermochemical methods, the following aspects of the ePMR must be explored: (i) the influence of H permeation on hydrogenation; (ii) methods for developing a scalable ePMR; and (iii) molecules that can be produced on an industrial-scale in the ePMR. In Chapters 3 to 6, I explore strategies for advancing our understanding of the ePMR to develop this unique technology towards an efficient, carbon-neutral hydrogenation industry.     35 Chapter 3: Paired Electrolysis and Hydrogenation in a Palladium Membrane Reactor 3.1 Introduction Organic electrochemical synthesis is a potentially cost-effective, scalable, and green method of synthesizing organic products using renewable electricity.6,124,125 In most cases, however, the chemistry that occurs at the counter-electrode yields a waste product. In the case of the oxygen evolution reaction (OER), for example, the O2 product not only holds little economic value, but also suffers from slow kinetics and requires strikingly high overpotentials.  Paired electrolysis forms useful products at both electrodes. Known examples of paired electrolysis have focused on pairing gas production or conversion (e.g., HER, CO2 reduction) with an organic transformation126\u2013130 or on pairing two organic transformations.6,124,131,132 A major challenge for paired electrolysis is ensuring that the reaction conditions are suitable for both chemical transformations. The scope of feasible reactions is limited by the compatibility of the reactants and products with each other, the supporting electrolyte and the solvent medium. Product separation also needs to be considered. Paired electrolysis reactions are often performed with an ion permeable membrane between the anode and cathode which means the solvent and ions used for the two transformations must be similar. To overcome this limitation, a dense palladium membrane in an electrocatalytic palladium membrane reactor was used as an alternative (see Ch. 2.4.3). An ePMR architecture places the hydrogen content of palladium under electrochemical control to enable facile tuning of interstitial hydrogen content. Unlike conventional thermochemical hydrogenation systems, which require catalyst and pressure modifications to enable reaction, in the ePMR, current, voltage, or electrolyte   36 choice can be tuned. The ePMR therefore offers a means of controlling reaction rate and selectivity over the degree of chemical hydrogenation.  Here, I report the use of an ePMR to pair a hydrogenation reaction at a palladium membrane with an electrochemical oxidation reaction. The architecture of the reactor (Fig. 3.1, A1.1) consists of a hydrogenation compartment and two electrochemical compartments. A current is applied which drives electrochemical oxidation of an alcohol in the anode compartment. The two H+ released from this reaction pass through a proton-conducting membrane (Nafion) separating the anode and cathode compartments. These H+ are reduced at the electrochemical surface of the palladium foil cathode to form adsorbed H atoms that are then absorbed into the bulk of the palladium lattice. Absorbed H atoms that diffuse through the foil can transition from the bulk to the surface on the opposite side of the foil and are poised for reaction with an unsaturated bond. The palladium foil therefore acts as a cathode for proton reduction and a hydrogen permeation membrane. In this report, I examine the oxidation of 4-methoxybenzyl alcohol (anisyl alcohol) to 4-methoxybenzaldehyde (anisaldehyde) in tandem with the hydrogenation of 1-hexyne to 1-hexene as proof-of-concept reactions. These reactions were selected not only to study the pairing between two typically incompatible reactions, but also to examine product selectivity as both reactions can proceed past the desired product (4-methoxybenzoic acid, anisic acid; n-hexane).   37   Figure 3.1. Three-compartment cell configuration designed for paired electrolysis. (1) A current is applied to the palladium. (2) An alcohol is oxidized to an aldehyde at the platinum anode with an electron-transfer mediator and protons are released. (3) The protons cross a Nafion proton exchange membrane. (4) The protons are reduced to adsorbed hydrogen atoms at the palladium foil cathode. (5) The adsorbed hydrogen atoms diffuse through the palladium lattice to the opposite surface of the foil. (6) The hydrogen atoms hydrogenate an unsaturated bond.  This reactor has a number of advantages for paired electrolysis. The electrochemical reaction on palladium is isolated to the side of the foil in contact with the electrolyte133,134 so the hydrogenation reaction on the other side of the foil is exclusively a chemical reaction. This enables an organic solvent to be paired with an aqueous electrolyte without the mixing of the two immiscible solvents. Product purification is also simplified because the hydrogenation reaction requires no supporting electrolyte. The separation of two distinct reaction compartments by a dense palladium foil mediates simultaneous chemical hydrogenation and electrochemical organic transformations that are typically incompatible. This separation enabled co-optimization of selectivity, current efficiency, and reaction rate was possible and that the paired reactions could   38 simultaneously achieve high yield and high selectivity. This reactor assembly offers the opportunity to utilize electricity to drive hydrogenation reactions without the complications associated with handling H2 gas.  3.2 Results and Discussion 3.2.1 Palladium Membrane Properties  The selective permeability of the palladium membrane to H atoms and the separation of the hydrogenation and electrochemical compartments is fundamental to the success of this device. Electrochemical experiments were performed to validate that the hydrogenation side of the cell was not in ionic contact with the cathode compartment and that the electrochemical response was only due to reactions on the electrochemical side of the foil. The electrochemical side of the cell was filled with a 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) in DCM electrolyte, an organic electrolyte with very little current response in a wide potential window, and the hydrogenation side of the cell was left empty and open to air. Cyclic voltammetry (CV) measurements were performed with the palladium foil acting as the working electrode. Figure 3.2a shows the current response is in the \u00b5A cm-2 range, consistent with the wide electrochemical window of the organic electrolyte. The hydrogenation compartment of the cell was then charged with 1 M H2SO4 and a CV was recorded. The CV was superimposable with that recorded when the hydrogenation compartment was empty. This observation and the lack of bubbles formed on the hydrogenation side of the foil led us to conclude that electrochemical reactions do not occur within the hydrogenation compartment of the cell in this configuration. However, the expected aqueous electrochemical response of the palladium electrode (water electrolysis, H absorption, and   39 H desorption) was observed when the electrolyte in the electrochemical compartments were changed from an organic electrolyte to an aqueous electrolyte (1 M H2SO4, Fig. 3.2b). These experiments demonstrate that the solvent and the electrolyte in the hydrogenation and electrochemical compartments, respectively, are in isolation of one another.  Figure 3.2 Cyclic voltammograms demonstrating isolation of the hydrogenation (hydro) and electrochemical (echem) compartments. (a) A comparison between an empty hydrogenation compartment and one with 1 M H2SO4 when 0.1 M TBAPF6 in DCM is the electrolyte in the electrochemical compartments and (b) 1 M H2SO4 in the hydrogenation compartment and a comparison between 0.1 M TBAPF6 in DCM and 1 M H2SO4 electrolyte in the electrochemical compartments. Pd foil was used as the working electrode, Pt mesh as the counter electrode, and Ag\/AgCl as the reference electrode.   I then set out to test whether hydrogen absorption and diffusion through the palladium foil or the HER at the surface of the foil dominates when no unsaturated reactant is present. Adsorbed hydrogen must transition into the bulk of the palladium lattice, diffuse through the lattice, and transition to the surface on the other side of the cell to react with an unsaturated organic substrate (Ch 2.2, Fig. 2.3a). If the kinetics of HER on the electrochemical side of the palladium are faster than the competing absorption and diffusion steps, hydrogen would evolve only on the electrochemical side of the foil and would not hydrogenate the substrate on the hydrogenation side.   40 GC was used to measure the relative production of H2 gas on the electrochemical and hydrogenation sides of the foil. A constant current was applied to the foil and measurements were taken after hydrogen evolution had reached equilibrium (i.e., GC measurements of evolved hydrogen were consistent after multiple runs). Hydrogen measured on the hydrogenation side of the cell gives a measurement of the hydrogen flux across the membrane. Acidic electrolyte (1 M H2SO4) was added to both the hydrogenation (hydro) and electrochemical (echem) compartments for the first measurement (Fig. 3.3a). Measurements at 10 mA and 25 mA applied currents (or 8.1 mA cm-2 and 20.5 mA cm-2 current densities, respectively based on geometric surface area) showed that in both cases more hydrogen was released on the hydrogenation side of the foil than the electrochemical side (Fig. 3.3b). At higher current (e.g., 50 mA), however, 90% of the hydrogen was released on the electrochemical side of the cell (Fig. 3.3b) and only a small hydrogen flux across the membrane was observed.    41  Figure 3.3 Hydrogen evolution on both sides of the palladium membrane. (a\u2013d) Three- compartment cell setup (a,c) and gas chromatography measurements of hydrogen evolution from the hydrogenation and electrochemical compartments at an applied current (b,d) with 1 M H2SO4 in both compartments (a,b) and with pentane replacing 1 M H2SO4 in the hydrogenation compartment (c,d). Error bars indicate standard deviations of triplicate gas chromatography measurements.  Experiments were then carried out with pentane in the hydrogenation compartment and 1 M H2SO4 in the electrochemical compartments (Fig. 3.3c). The majority of the total evolved H2 gas was detected on the hydrogenation side of the foil at every applied current (Fig. 3.3d). Even at 50 mA applied current (40.1 mA cm-2), 90% of H2 gas was detected on the hydrogenation side of the foil indicating that almost all the protons being reduced at the cathode are diffusing and   42 recombining on the opposite side of the foil. These results confirm that palladium is acting effectively as a selectively-permeable membrane for H atoms. It should also be noted that the flux of hydrogen across the membranes increases in a linear fashion within this range of current densities, suggesting more hydrogen may be available to hydrogenate a substrate at higher applied currents.  There is a large increase in flux across the palladium membrane when the solvent is changed from sulfuric acid to pentane. This increase in flux can be attributed to a faster reaction rate of hydrogen formation in a non-coordinating solvent. Coordinating ions do not hinder the recombination of two H atoms in a non-polar solvent and\/or do not block the transition of H atoms from bulk to surface. These data together suggest that when 1 M H2SO4 is used on the hydrogenation side the rate-limiting step is the formation of H2 gas or the transition of hydrogen from bulk to surface (see Ch. 2.2.1).66 Changing the solvent to pentane either increases the rate of this step or changes the rate-limiting step to diffusion through the foil. Pentane is therefore a suitable reaction solvent because it enables a high flux of hydrogen through the foil. Notably, hydrogen gas formation in the hydrogenation compartment is lowest at the highest applied current when sulfuric acid is used as the solvent. These data suggest the increasing current past a threshold value leads to excessive HER formation in the electrochemical compartment that results in less hydrogen permeation through the membrane and less H2 gas formation in the hydrogenation compartment.    3.2.2 Catalytic Hydrogenation The hydrogenation of 1-hexyne in pentane in the hydrogenation compartment was tested in tandem with OER at the anode in 1 M H2SO4 in the electrochemical compartment (Fig. 3.4a).   43 This reaction was performed without the alcohol oxidation to verify that the permeation of H atoms through the palladium foil could be leveraged to perform useful organic chemistry. The detection of 1-hexene and n-hexane confirmed that chemical hydrogenation does indeed occur, however, the rates of reaction are slow, merely 6% of the starting material was converted to 1-hexene and 2% to n-hexane (the over-reduction product) after 8 h of continuous reaction (Fig. 3.4b).  These sluggish kinetics for hydrogenation can be attributed to the low surface area of the planar palladium foil. The surface area of the foil within the hydrogenation compartment was therefore increased by electrodepositing an additional layer of palladium from a PdCl2 solution in 1 M HCl.92,135 This procedure increases the surface area of the hydrogenation side of the palladium foil by 250-fold relative to the planar surface according to double-layer capacitance electrochemical surface area measurements (Fig. A1.2). The hydrogenation of 1-hexyne using the electrodeposited palladium accelerates the rate of the reaction significantly (Fig. 3.4d, e, and A1.3), as exhibited by complete consumption of 1-hexyne after 6 h of electrolytically-driven electrolysis, compared to merely 8% conversion with the planar palladium catalyst. Scanning electron microscopy images of the foil with and without the electrodeposited palladium highlight the stark difference in morphologies between the two surfaces (Fig. 3.4c, f).     44  Figure 3.4 Catalyst morphology and product distribution for palladium membrane chemical hydrogenation. (a\u2013f) Three-compartment cell setup (a,d) 1-hexyne consumption into hexenes and hexanes (b,e) and SEM images (c,f) with a palladium foil membrane (a\u2013c) and with electrodeposited palladium on the hydrogenation side of the palladium foil membrane (d\u2013f). A current of 50 mA (or current density of 40.1 mA cm-2) is applied in both cases.  3.2.3 Paired Electrolysis The three-compartment cell was set up to test a paired electrolysis reaction by adding anisyl alcohol dissolved in 1 M KHCO3 containing a redox mediator 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)126,128,136 to the anode compartment and 1 M KHCO3 to the cathode compartment. The reaction conditions in the hydrogenation compartment were maintained (Fig. 3.5a, b). The oxidation of anisyl alcohol is intended to bypass the prohibitive OER reaction and instead generate useful oxidation products. The anode and cathode sides of the electrochemical compartment were   45 separated by a Nafion membrane. The reaction was run with an applied current of 50 mA (current density of 40.1 mA cm-2) for 5 h. All starting material in both reactions was consumed within 5 h of continuous electrolysis (Fig. 3.5c, d). Notably, both the hydrogenation and oxidation reactions can over-react to form undesired products: 1-hexene can further hydrogenate to n-hexane or can isomerize at the palladium surface to (E)- and (Z)-3-hexene, while anisaldehyde can further oxidize to anisic acid (Fig. 3.5b). The reaction produced the desired anisaldehyde product in 96% yield, with merely 4% of the solution containing anisic acid (Fig. 3.5d). The concurrent hydrogenation of 1-hexyne in the hydrogenation compartment of the cell was found to form 1-hexene with 86% conversion 4 h into the reaction, however, the formation of n-hexane was triggered over the last hour of the reaction leaving a solution containing a ratio of 83:17 1-hexene to n-hexane (Fig. 3.5c). Notably, the oxidation reaction can be performed without the electron transfer mediator but the reaction does not proceed to completion and the current efficiencies are lower (A1.4).     46  Figure 3.5 Product conversion and distribution in paired electrolysis. (a) Three-compartment cell setup for paired electrolysis. (b) Hydrogenation reactions of 1-hexyne and oxidation reactions of anisyl alcohol. (c,d) Product consumption and reactant formation for the 1-hexyne hydrogenation reaction (c) and the anisyl alcohol oxidation (d) at a 50 mA applied current (or current density of 40.1 mA cm-2) over a 5 hour period. (e) The current efficiencies for the desired product for both the anodic and cathodic reactions.  The current efficiency (Fig. 3.5e) describes how many of the electrons used at the cathode and anode yield the desired organic product (instead of hydrogen evolution, oxygen evolution, and the over-reaction product, Eq. 2.6). The current efficiencies for the hydrogenation reaction were measured to be 60\u201380%, generally greater than the anodic current efficiencies that were consistently measured to be ~60%. These reactions are significant but are not yet optimized at this proof-of-concept stage of reactor development, and higher conversion efficiencies can be obtained in future investigations.   47 Paired electrolysis was also performed at applied currents of 25 and 75 mA (or current densities of 20.5 mA cm-2 and 61.5 mA cm-2, respectively) to determine how current affects reaction rate, efficiency, and selectivity (Fig. 3.6, 3.7, A1.5). The rate of the oxidation reaction did not change considerably at different applied currents, however, the rate of the hydrogenation reaction varied widely. The increase in hydrogenation rate changes with current suggesting that increased flux at different current densities affects hydrogenation rate. The data also suggests a rate-limiting step involving surface hydrogen. These results are promising for the general utility of the device because they suggest that applied current can be used to tune the concentration of hydrogen, similar to increasing pressure in a typical hydrogenation system.  The current efficiencies for 1-hexene and anisaldehyde show the opposite trend to reaction rates and generally decreased with increased applied current (Fig. 3.6). The remainder of the current can be attributed to HER (at both sides of the foil cathode) and OER at the anode. The decrease in current efficiencies over time is ascribed to diminishing reactant concentrations.    48  Figure 3.6 Hydrogenation and oxidation current efficiencies at varied applied currents.  (a) Three-compartment cell setup for paired electrolysis. (b,c) Current efficiencies for the desired reaction product for the 1-hexyne hydrogenation reaction (b) and the anisyl alcohol oxidation reaction (c) at 25, 50, and 75 mA applied currents corresponding to current densities of 20.5, 40.1, and 61.5 mA cm-2, respectively.  3.2.4 Tunable Reaction Selectivity Both the alcohol oxidation product and the alkyne hydrogenation product could be further converted to another product. Our next goal of this study was to achieve tunable selectivity for both reactions, in which a single reduction\/oxidation product in the short-term and a double reduction\/oxidation product if desired in the long-term could be achieved. This tunable selectivity   49 would be completely successful if 100% of the singly reduced\/oxidized product was made before the doubly reduced\/oxidized product was formed.  The selectivities of the hydrogenation and oxidation reactions were tested at applied currents of 25, 50, and 75 mA (current densities of 20.5, 40.1, and 61.5 mA cm-2, respectively; Fig. 3.7a, A1.6\u2013A1.9). The alcohol oxidation produced 95\u201398% anisaldehyde before the production of anisic acid at all three currents. By contrast, the product selectivity of the cathodic hydrogenation reaction was found to be sensitive to applied current. The 1-hexene product was formed in 95% yield before the formation of n-hexane at 25 mA (20.5 mA cm-2), but merely 60% was formed at 75 mA (61.5 mA cm-2, Fig. 3.7b). The choice of electrolyte in the electrochemical compartments was also found to affect hydrogenation selectivity (Fig. 3.7c). The hydrogenation product 1-hexene was produced in 56% yield before the onset of n-hexane production in the case where 1 M H2SO4 was employed as the electrolyte. Conversely, it was observed that 85% 1-hexene could be produced when 1 M KHCO3 was used. This large improvement in selectivity (30\u201335%) that we observed when changing the electrolyte demonstrates the benefit of the ePMR for enabling simple modifications to reaction conditions. The change in selectivity seen from varying electrolyte and applied current may be attributed to different hydrogen absorption characteristics of the system under these varying conditions. Both the electrolyte pH and the applied current affect proton reduction rate at the surface of the palladium which will affect absorption. This data is consistent with previous reports on the effect of subsurface hydrogen in the palladium lattice on alkyne hydrogenation.96 It should be noted that this temporal type of selectivity has advantages and disadvantages. While the timeframe of the reaction must be known in order to prevent an undesired product from forming unlike some selective catalysts that will never proceed to over-reaction, temporal selectivity   50 enables the production of either product under the right conditions depending on the context and desired outcome.    Figure 3.7 Hydrogenation selectivity with applied current and electrolyte. (a) Three- compartment cell setups for hydrogenation selectivity measurements. (b,c) Maximum 1-hexene conversion before the formation of n-hexane product at 25, 50 and 75 mA applied currents corresponding to current densities of 20.5, 40.1, and 61.5 mA cm-2 in 1 M KHCO3 electrolyte (b) and at 50 mA applied current or 40.1 mA cm-2 current density in 1 M KHCO3 and 1 M H2SO4 electrochemical electrolyte (c).  The pairing of these two reactions that proceed under normally incompatible reaction conditions is only possible with the three-compartment electrocatalytic palladium membrane reactor.  Reactions that occur at similar rates at a specific current while also achieving optimal current efficiencies and selectivities are fundamental to the success of a paired electrolytic system.   51 The hydrogenation of 1-hexyne in tandem with anisyl alcohol oxidation results in 85\u201395% conversion and selectivity at a 60\u201370% current efficiency over 5 h of electrolysis, thereby serving as a meaningful proof-of-concept demonstration of this device. In order to optimize the system, I leveraged the ability to tune the reaction rate and current efficiency of each reaction with the tandem hydrogenation\/electrochemical tool. At 50 mA (40.1 mA cm-2, Fig. 3.5c, d), both reactions achieve maximum product conversion before over-reaction occurs between 4 and 5 h of electrolysis. The hydrogenation reaction is more selective at 25 mA (20.5 mA cm-2) than at 50 mA (40.1 mA cm-2) but the reaction proceeds much more slowly than the alcohol oxidation. The maximum product conversion for 1-hexyne hydrogenation is achieved after 10 h at 25 mA (40.1 mA cm-2, Fig. A1.5), while anisyl alcohol oxidation is achieved at a maximum after 6 h (Fig. A1.5). Although both reactions have higher current efficiencies at 25 mA (20.5 mA cm-2), the mismatch in reaction rates make this current density impractical for these two reactions. At 75 mA (61.5 mA cm-2), the reactions proceed more quickly, however, the hydrogenation over-reaction product has already been formed in 35% yield by the time the alcohol oxidation has reached completion (Fig. A1.5). While the selectivities of these reactions were controlled by current and electrolyte, the choice of catalyst, membrane thickness, and overpressure represent other conditions that are expected to control device performance. 3.3 Conclusions In summary, I have developed a three-compartment cell that enables paired electrolysis using a dense palladium membrane for separation of two otherwise incompatible reactions. The oxidation of anisyl alcohol at the anode compartment in tandem with chemical hydrogenation of 1-hexyne in the hydrogenation compartment proceed at current efficiencies ranging between 50\u201380% and selectivities between 85\u201398% with 100% starting material conversion. This electrolytic   52 device enables the use of organic solvents for chemical hydrogenation and does not require the addition of H2 gas. The reaction rate has been shown to increase with increased applied currents, an effect similar to increasing pressure in a typical hydrogenation reaction. The tunable selectivity of the hydrogenation reaction by altering current and electrolyte may also enable the ability to change product selectivity under operando conditions without having to modify the catalyst or the system. This paired system bypasses the parasitic OER reaction that produces a dioxygen product with no economic value. The entire system uses electricity to drive the formation of hydrogen that is utilized without the formation of H2 gas, an expensive factor that needs to be considered during conventional electrolysis. Future experiments will focus on expanding the scope of this device to other organic oxidation and hydrogenation reactions to show the broad utility of this device and demonstrate the advantages it provides over systems.  3.4 Experimental Methods 3.4.1 Materials Palladium foil (99.9%) and KHCO3 were purchased from Alfa Aesar. PdCl2 (99.9%) was purchased from Strem Chemicals. 1-hexyne (>97%) was purchased from TCI Chemicals. Pentane (\u226599%), D2O (99.9 atom% D), 1-hexene (99%), 4-methoxybenzyl alcohol (98%), 4-methoxybenzaldehyde (98%), n-hexane (99+%), tetrabutylammonium hexafluorophosphate (>99%), (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (98%) and Pt mesh (99.9%) were purchased from Sigma Aldrich. Nafion 117 membranes were purchased from Fuel Cell Store. Ag\/AgCl reference electrodes (RE5B) were purchased from BASi. 3.4.2 Electrochemical Measurements A Metrohm Autolab PGSTAT302N (organic reactions) or CHI 660D (gas chromatography experiments) potentiostat was used for electrochemical experiments with the designed three-  53 compartment cell. A palladium foil was pressed between the hydrogenation and cathode compartments of the cell. A Nafion PEM was used between the cathode and anode compartments. Each compartment contained a total 30 mL solution volume. The electrochemical compartments contained either 1 M H2SO4 or 1 M KHCO3 and the hydrogenation compartment contained either 1 M H2SO4 or pentane. An Ag\/AgCl electrode (3.0 M NaCl) was used as the reference electrode and a Pt mesh was used as the counter electrode or anode. Experiments were conducted under constant current conditions where a reductive current was applied by the potentiostat to the cathode and the working electrode potential was measured. In all cases, the surface area of the foil on both the hydrogenation and electrochemical sides was 1.22 cm2. Electrochemical surface area measurements on the palladium foil and palladium catalyst were performed by running cyclic voltammograms at various scan rates (10 to 100 mV s-1) and plotting current versus scan rate. A potential range of 0.25 to 0.65 V versus Ag\/AgCl with the plotted current taken at 0.5 V versus Ag\/AgCl was used for the palladium foil. A potential range of 0.25 to 0.55 V versus Ag\/AgCl with plotted current taken at 0.4 V versus Ag\/AgCl was used for the electrodeposited palladium. The slope was used as a measure for comparing double-layer capacitance\/electrochemically active surface area. 3.4.3 Hydrogen Quantification Gas chromatography measurements were carried out on a PerkinElmer Clarus 580 gas chromatograph equipped with a flame ionization detector and thermal conductivity detector. An Agilent MolSieve 5A column with an inner diameter of 2 mm and a 0.274 m length was used. Argon (Praxair, 99.999%) was used as a carrier gas with a flow rate of 20 sccm. N2 (99.999%) was used as a dilution gas to keep the hydrogen concentration within the calibration range and remove H2 from the headspace. The thermal conductivity detector was used to quantify H2. Quantification   54 was done by using a constant flow rate for both compartments at the specified applied current and using the ratio of hydrogen evolution on the hydrogenation and cathode compartments. The ratios were converted into mmol h-1 with coulombs of charge passed over an hour of the reaction period. Each measurement was taken three times after the cell had equilibrated (the GC peak areas were consistent for long time periods) and the standard deviations are reported as error bars on the data. 3.4.4 Palladium Membrane Preparation 3.4.4.1 Palladium Foil Preparation A 1 oz Pd wafer bar was used to roll 1 mm Pd strips that were then annealed at 850 \u00b0C for 1.5 hours. The 1 mm strips of Pd were rolled into 25 \u00b5m Pd foils and again annealed at 850 \u00b0C for 1.5 hours. Thickness of Pd foils were determined by a Mitutoyo digital micrometer. Pd foils were cleaned using a 0.5:0.5:1 concentration of HNO3:H2O:H2O2 solution mixture for ~45 min or until vigorous bubbling resided. Solution mixture changed from clear to yellow during the cleaning procedure. 3.4.4.2 Catalyst Preparation The Pd catalyst was prepared by electrodeposition. The Pd foil substrate was clamped into the middle compartment of the three-compartment cell as the working electrode. A 15.9 mM PdCl2 solution in 1 M HCl was used for electrodeposition. A Ag\/AgCl electrode was used as the reference electrode and a Pt mesh electrode was used as the counter electrode. A \u22120.2 V versus Ag\/AgCl potential was applied until 9 C of charge (7.38 C cm-2) for an estimated total of 5 mg of palladium on the surface.   55 3.4.5 Scanning Electron Microscopy SEM images were acquired on an FEI Helios NanoLab 650 dual beam SEM at 1 kV voltage and current of 50 pA. A through-the-lens detector (TLD) was employed in secondary electron mode. A horizontal field width (HFW) of 5.97 \u00b5m was shown in both cases. 3.4.6 Product Quantification Gas chromatography\u2013mass spectrometry was used for product quantification of the hydrogenation reactions in the hydrogenation compartment of the cell (Fig. A1.3, A1.7\u2013A1.9). Samples of 100 \u00b5L were taken every 1\u20132 h during the reaction and diluted in 900 \u00b5L pentane. GC\u2013MS samples were further diluted with 100 \u00b5L of dilute reaction mixture with 900 \u00b5L pentane. GC\u2013MS experiments were conducted on an Agilent GC\u2013MS using a HP\u20135ms column and electron ionization. The prepared samples were run on an autosampler with a 1 \u00b5L injection volume and a split ratio of 20:1. The oven temperature began at 30 \u00b0C for 2 min and ramped to 40 \u00b0C at 2 \u00b0C min-1 then to 200 \u00b0C at 40 \u00b0C min-1. A solvent delay of 2.15 min was employed. Peaks for 1-hexyne, 1-hexene and n-hexane were identified by searching the National Institute of Standards and Technology (NIST) database for matching mass spectra and confirmed by using standards for each of the compounds. Proton nuclear magnetic resonance measurements of the electrochemical anodic products were collected on a Bruker Avance 400inv or 400sp Spectrometer (Fig. A1.4, A1.7\u2013A1.9). Benzene- 1,3,5-tricarboxylic acid was used as an internal standard and added to all samples. For each NMR sample, 30 \u00b5L of reaction mixture, 120 \u00b5L of 0.0125 M benzene-1,3,5-tricarboxylic acid and 450 \u00b5L of D2O were used. The water signal from solvent remaining from the reaction mixture was suppressed by a watergate W5 pulse sequence with double gradient echos. The relative amounts of reactant and products were calculated as percentages by comparing the   56 integrations of the anisyl alcohol reactant (\u03b4 = 7.34 (d, 2H), 7.0 (d, 2H), 3.82 (s, 5H)), the singly oxidized anisaldehyde product (\u03b4 = 9.79 (s, 1H), 7.92 (d, 2H), 7.14 (d, 2H), 3.91 (s, 3H)) and the doubly oxidized anisic acid product (\u03b4 = 7.84 (d, 2H), 7.0 (d, 2H), 3.86 (s, 3H) at peaks corresponding to 2 H+ for each molecule. The internal standard peak was integrated to 1 in all spectra to ensure total integrations for reactant and products remained constant throughout the duration of experiment and no other products were forming.  The amount of product formed was calculated by multiplying the moles of reactant (determined from the amount of starting material used in the electrochemical cell) by the percentage product formation as determined by relative NMR and GC\u2013MS integrations. Current efficiencies for the reactions were calculated by dividing the amount of product formed by the theoretical moles of product, determined from the charge passed at that time point in the experiment converted to moles with Faraday\u2019s constant and the moles of electrons needed to perform the hydrogenation reaction (Eq. 2.6).    57 Chapter 4: Supported Palladium Membrane Architecture for Electrocatalytic Hydrogenation  4.1 Introduction A key shortcoming of ePMRs is the high cost of the palladium foil (see Ch. 2.3.2.1).1,45,92 While this challenge can be addressed by decreasing foil thickness, the mechanical integrity cannot be maintained for membranes with thicknesses <20 \u00b5m.137 This thickness is still too expensive to be economically feasible, based on technoeconomic assessments that have shown that a thickness of <15 \u00b5m is required for related dehydrogenation tPMR technologies89,98,138 to be cost-competitive with thermochemical dehydrogenation catalysts. Indeed, the tPMR catalyst costs >60-fold more than that of the thermochemical dehydrogenation, which uses pellets or supported nanoparticles with high surface areas139,140 and inexpensive supports89 to reduce palladium content. On this basis, the high catalyst\/membrane cost needs to be addressed in order to fully leverage the 4-fold faster reaction rates achieved for the PMR.141 The palladium content can be reduced in tPMRs by deposition of thin palladium films onto rigid, porous supports.58,102,104,142\u2013146 As discussed in Chapter 2.3.2.1, tPMRs typically employ rigid materials such as porous glass,104 alumina,102,143\u2013145 or stainless steel.147 Kikuchi, Uemiya, and coworkers have demonstrated that high hydrogen permselectivity is achievable under high temperature and pressure flow conditions using thick (>1 mm), small pore size (<0.1 \u00b5m) supports that provide high mechanical strength and thermal resistance.102,104,142 These supports also provide good adhesion for the palladium film and enable a pinhole-free palladium membrane.148 While there have been extensive reports on supported palladium membranes for gas-fed systems, they   58 are not amenable to the ePMR architecture, where solvent and\/or electrolyte transport to the palladium layer is crucial for reactor success.  I report here that a thin layer of palladium sputter-deposited on a thin, porous PTFE support (Pd\/PTFE membrane) is capable of matching the performance of a palladium foil in an electrocatalytic palladium membrane reactor (Fig. 4.1). I demonstrate that a dense, pinhole-free, 1\u20132 \u00b5m palladium layer adheres to the PTFE membrane and that fast solvent transport occurs through the thin (<100 \u00b5m) PTFE support, but does not occur through a thick (<1 mm) porous alumina support. In a proof-of-concept hydrogenation reaction, I show that the Pd\/PTFE membrane reduces the mass of palladium used by 20-fold compared to a palladium foil membrane, while maintaining similar 1-hexyne consumption rates of 0.72 mmol h-1 (compared to 0.91 mmol h-1). I also resolve the effect of support properties (e.g., pore size, thickness, hydrophobicity), catalytic surface area, and solvent polarity on the membrane design and report on a cost-effective solution for designing supported palladium membranes for ePMRs.  4.2 Results  4.2.1 Membrane and Design Fabrication The supported palladium membranes used in this study were fabricated by sputter-deposition of 1\u20132 \u00b5m of palladium onto prepared PTFE supports (Fig. 4.1a, b). PTFE supports were prepared by sealing a PTFE membrane (0.05 mm average pore size, 25.4 mm thickness, 104.7 m2 g-1 BET surface area) between two Kapton masks with circular cutouts and a geometric surface area of 1.22 cm2 (Fig. A2.1). The Pd\/PTFE membranes were tested in a three-compartment membrane reactor,1 and used to separate the two electrochemical compartments from the hydrogenation compartment (Fig. 4.1c). The Pd\/PTFE membrane was configured such that the PTFE support faced the hydrogenation compartment to match the hydrophobicity of the   59 membrane to that of the organic solvents used in the hydrogenation compartment (vide infra). The hydrogenation compartment was filled with 35 mL of solvent with or without unsaturated reactant. The two electrochemical compartments each contained 35 mL of 1 M H2SO4 as the electrolyte. A Nafion PEM was used to separate the outer electrochemical compartment containing a 1 cm2 Pt mesh anode from the middle electrochemical compartment containing a Ag\/AgCl reference electrode and the Pd (on PTFE) cathode. In each experiment, a reductive current was applied to the system and protons formed at the Pt anode from water oxidation passed through the Nafion membrane to be reduced to surface-adsorbed hydrogen on the Pd cathode.     60  Figure 4.1 (a) Cross-sectional SEM and (b) top-view SEM of a fabricated Pd\/PTFE membrane. SEM images show ~1.9 \u00b5m Pd sputtered on a PTFE support. The PTFE support has a 0.05 \u00b5m pore size and 25.4 \u00b5m thickness. (c) Schematic diagram of the electrocatalytic Pd membrane reactor using a supported Pd\/PTFE membrane as a cathode to perform hydrogenation chemistry. A current is applied to the Pd\/PTFE cathode (1) and water is oxidized at the Pt anode to form protons (2). Protons are reduced to surface-adsorbed hydrogen at the Pd surface (3), which diffuse through the Pd layer to the chemical compartment (4). In the hydrogenation compartment, the organic reactant diffuses through the porous PTFE support and reacts with surface-adsorbed hydrogen at the Pd\u2013PTFE interface to form hydrogenated products (5).   4.2.2 Wettability and Liquid Permeation I tested the wettability and liquid permeation through bare PTFE supports with different pore sizes and thicknesses (pore size, thickness = 0.05 \u00b5m, 25.4 \u00b5m; 0.1 \u00b5m, 74 \u00b5m; 0.2 \u00b5m, 66 \u00b5m) and found that lower-polarity solvents yielded faster liquid permeation in all cases. Solvent droplet images show a trend in wettability consistent with the polarities of the solvent, with non-  61 polar solvents fully wetting the support (Fig. A2.2). Liquid permeation experiments showed the same trend, where pentane had the fastest permeation rates of \u22655.5 mL h-1 and no water transported through any of the PTFE supports tested over the 24-h period (Fig. A2.3, Table A2.1). Liquid permeation measurements on porous alumina supports (0.1 \u00b5m pore size, 1 mm thickness), commonly used in tPMRs,102,143\u2013145 yielded rates of <0.15 mL h-1 for all solvents tested. These data show that alumina exhibits slower permeation rates than PTFE in each case, with the exception of water. I then tested the effect of depositing a thin palladium film on PTFE supports with different pore sizes and under different sputtering pressures. The amount of palladium required to achieve a pinhole-free, continuous palladium film is dependent on pore size, surface roughness, and surface chemistry of the porous support layer.146 A 1 \u00b5m film of palladium was sputter-deposited onto PTFE supports with 0.05 \u00b5m, 0.1 \u00b5m, and 0.2 \u00b5m pore sizes and palladium surface coverage on each support was examined by SEM (Fig. A2.4). SEM images confirmed that a reduction in support pore size resulted in higher palladium surface coverage (Fig. A2.4), and a palladium layer with no visible pinholes >100 nm was obtained using the 0.05 \u00b5m pore-sized PTFE support (Fig. 4.1b, A2.4a). A ~1.5 \u00b5m film of palladium was then sputtered using three working pressures: 1\u00d710\u20133 torr, 2\u00d710\u20133 torr, and 2\u00d710\u20132 torr to study the effect of Ar pressure on palladium surface morphology. SEM images showed that reducing sputtering pressure resulted in smaller Pd crystals and a more continuous film (Fig. A2.5). A pressure of 1\u00d710-3 torr resulted in large cracks across the membrane while a pressure of 2\u00d710\u20132 torr did not provide full surface coverage. A sputtering pressure of 2\u00d710\u20133 torr was used for all Pd\/PTFE membranes hereafter since it provided a continuous palladium layer without any cracks, which is   62 consistent with observations made for sputter-deposition of thin Pd films on supports in gas-phase systems.149 I next performed electrochemical experiments on these dense Pd\/PTFE membranes to demonstrate that the hydrophobic PTFE support should be oriented toward the hydrogenation compartment and the palladium toward the electrochemical compartment. The membrane was first tested with the PTFE support facing the electrochemical compartment, and both compartments were filled with 1 M H2SO4 (Fig. A2.6a). A current of 100 mA was applied (corresponding to a current density of 82 mA cm-2) and the voltage immediately dropped to the \u221210 V limit of the instrument, suggesting that the electrolyte was not able to diffuse through the PTFE and make contact with the palladium layer. The Pd\/PTFE was then reversed such that the PTFE layer faced the hydrogenation side (Fig. A2.6b) and a constant potential of ~\u20130.6 V was recorded over 1 h (Fig. A2.6c). In all experiments hereafter, the Pd\/PTFE membrane was orientated such that the PTFE layer faced the hydrogenation side to ensure ionic contact between the electrolyte and the palladium cathode and to ensure PTFE wettability by organic solvents. 4.2.3 Hydrogen Permeation Hydrogen evolution experiments were performed to confirm that the Pd\/PTFE membrane was selectively permeable to H atoms and blocked passage of solvents. For these tests, the electrochemical compartment was filled with 1 M H2SO4, the solvent was varied in the hydrogenation compartment, and 100 mA of current was applied (82 mA cm-2, Fig. 4.2a). An atmospheric\u2013mass spectrometer (atm\u2013MS) was used to measure the relative production of H2 gas evolved on the hydrogenation and electrochemical sides of the membrane (Fig. 4.2b, A2.7), with hydrogen flux being defined as the amount of H2 gas evolved on the hydrogenation side per unit time. Experiments performed with pentane, DCM, MeOH, and H2SO4 in the hydrogenation   63 compartment (Fig. 4.2b, A2.7) resulted in 55%, 80%, 88%, and 96% of H2 gas released on the hydrogenation side, indicating successful hydrogen permeation. Solution resistances did not change before and after the experiment (~4\u20136 \u03a9), suggesting that the organic solvent did not pass through the palladium layer into the electrochemical compartment. These results confirm that only hydrogen (and not solution) permeates the Pd\/PTFE membrane in all solvents tested and that this hydrogen is available for hydrogenation reactions. Hydrogen permeation measurements were also performed on the Pd\/PTFE membranes to study the effect of Pd layer thickness and Pd morphology on hydrogen flux. A palladium layer of 1 \u00b5m, 1.5 \u00b5m, 2 \u00b5m, and 3.5 \u00b5m was sputter-deposited onto the 0.05 pore-sized PTFE membrane. All Pd thicknesses resulted in a hydrogen flux of ~1.7 mmol cm-2 h-1, under 100 mA applied current (82 mA cm-2) with 1 M H2SO4 in both compartments (Fig. A2.8). These data suggest that hydrogen flux is independent of thickness in our electrocatalytic Pd\/PTFE membrane reactor.    Figure 4.2 (a) Electrocatalytic Pd\/PTFE membrane reactor setup to measure hydrogen evolution and flux through the membrane. (b) Hydrogen flux through the Pd layer for solvents with different polarities in the hydrogenation compartment (pentane being the most non-polar and H2SO4 being the most polar). A current of 100 mA was applied corresponding to a current density of 82 mA cm-2 and an atmospheric\u2013mass spectrometer was used to measure H2 evolved on the chemical and electrochemical sides.     64 4.2.4 Catalytic Hydrogenation The hydrogenation of 1-hexyne in the hydrogenation compartment of the ePMR was used as a proof-of-concept reaction to demonstrate that the Pd\/PTFE membrane has comparable reaction rates to a palladium foil with palladium catalyst (Pd\/Pd foil) membrane (Fig. 4.3a, A2.9). In Chapter 3, I showed that electrodepositing a layer of palladium black catalyst (~5 mg) onto a planar palladium foil can lead to an increase in catalytic surface area that results in a ~10-fold increase in 1-hexyne consumption rate of Pd\/Pd foil compared to Pd foil (Ch. 3.2.2 and 3.4.4 for details).1 In all cases, the hydrogenation compartment was filled with 0.1 M 1-hexyne dissolved in pentane, the electrochemical compartment was filled with 1 M H2SO4, and a 50 mA current (40.1 mA cm-2) was applied (Fig. 4.3b, c). I measured the 1-hexyne to be completely consumed after 6 and 8 h for Pd\/PTFE and Pd\/Pd foil, respectively (Fig. 4.3d, e), with similar working electrode voltages for both reactors (Fig. A2.10). ECSA measurements were used as an approximation for the palladium catalytic surface area, and a comparison between a planar Pd foil membrane, Pd\/Pd foil, and Pd\/PTFE (Fig. A2.11) indicated that the catalytic surface areas were 1.22 cm2, 64.2 cm2, and 14.9 cm2 for the three membranes, respectively. These results demonstrate that a supported palladium membrane is effective for hydrogenation in an ePMR.  Three 1-hexyne hydrogenation reactions were also completed using a single Pd\/Pd foil and Pd\/PTFE membrane to study stability after multiple reaction cycles. For a Pd\/Pd foil membrane, the starting 1-hexyne material was completely consumed after 6 h during the first two cycles, but took 8 h to reach completion by the third cycle (Fig. A2.12a). These data suggest that multiple hydrogenation cycles may result in an accumulation of surface poisons on the Pd\/Pd foil surface, which results in a reduced reaction rate.29 For this reason, the electrodeposited Pd black on the Pd foil is replaced every \u22643 uses to ensure any surface poisons are removed. The removal of Pd black   65 using HNO3 (see Ch. 3.4.4) reduces the mechanical stability of the palladium foil and over ~3 cleaning procedures, pinholes begin to form in the foil and the foil is no longer usable (Fig. A2.12b, A2.12c). Thus, a Pd foil membrane lasts ~9 hydrogenation cycles before it must be replaced with a new foil. For Pd\/PTFE, the reaction rates also diminish over three hydrogenation cycles (Fig. A2.12d), and after 3\u20135 cycles the membranes begin to form small cracks and must be replaced (Fig. A2.12e, A2.12f). The reaction mixtures after each hydrogenation cycle were analyzed by inductively coupled plasma\u2013optical emission spectroscopy (ICP\u2013OES) to determine residual palladium after reaction and very small quantities of palladium (<27\u00b17 ppb) outside the detectible limit on the instrument were found (Fig. A2.13).        66  Figure 4.3 (a) Hydrogenation reaction of 1-hexyne to 1-hexene and n-hexane using (b) Pd\/Pd foil and (c) Pd\/PTFE membranes in the ePMR. 1-hexyne consumption and product formation using the (d) Pd\/Pd foil membrane and (e) Pd\/PTFE membrane over an 8-h period. A current of 50 mA (40.1 mA cm-2) was applied in both cases. The Pd foil is 25 \u00b5m thick and the Pd layer (of the Pd\/PTFE membrane) is 1\u20132 \u00b5m thick.   Hydrogenation experiments were then performed in various solvents to examine how solvent polarity affects reaction rates. The reactant 6-chloro-1-hexyne (Fig. 4.4a) was used because it could be solubilized in a wide range of solvents (pentane, DCM, and MeOH). The electrochemical compartment was filled with 1 M H2SO4, the solvent was varied in the hydrogenation compartment, and 50 mA (40.1 mA cm-2) was applied (Fig. 4.4b). Experiments were carried out on both Pd\/Pd foil and Pd\/PTFE to determine if solvent polarity impacted rates of non-supported membranes (Fig. 4.4c, A2.14\u2013A2.17). Consumption rates of 6-chloro-1-hexyne was determined by the slope of the initial 3 h of consumption (mmol h-1). Consumption rates were   67 the highest for the most non-polar solvent, pentane (0.58 mmol h-1) and lowest for the most polar solvent, MeOH (0.47 mmol h-1) when Pd\/PTFE was used, and 0.6\u20130.63 mmol h-1 for all solvents when Pd\/Pd foil was used. These data suggest that the hydrophobicity of the support does affect the hydrogenation reaction and the high hydrophobicity of the PTFE support enables the fastest hydrogenation rates in non-polar solvents.   Figure 4.4 (a) Hydrogenation reaction of 6-chloro-1-hexyne to 6-chloro-1-hexene and 6-chlorohexane. (b) Cell architecture using the Pd\/PTFE membrane reactor and (c) 6-chloro-1-hexyne consumption rates in pentane, DCM, and MeOH with the Pd\/Pd foil membrane (light purple) and Pd\/PTFE membrane (dark purple). A current of 50 mA (40.1 mA cm-2) was applied in both cases and consumption rate was determined for the first 3 h of reaction.   4.3 Discussion Supports used in tPMRs that are designed to enable fast H2 gas permeation under high temperature and pressure flow conditions97 are not necessarily amenable to ePMRs. In the ePMR, replacing the Pd foil membrane with Pd deposited on a porous support introduces a resistive layer that reduces how quickly the electrolyte or reactant (depending on membrane   68 orientation) can diffuse to the palladium catalyst. This extra layer can hinder permeation rates,150 negatively impacting the rate of hydrogenation and performance of the reactor. For these reasons, a support layer that enables fast liquid permeation is fundamental to the success of the reactor. tPMR studies have shown that sputtering <10 nm of palladium onto an intermediate PTFE support layer (on porous glass) can enable better adhesion than without PTFE.151 Moreover, the liquid permeation experiments I performed on porous alumina supports show that solvent permeation rates through the PTFE supports were faster than with the alumina supports in all cases, except for water (Fig. A2.3, Table A2.1), with a 50-fold increase in rate for the most non-polar solvent (pentane). These data demonstrate that the supported Pd membranes developed up to this point are not amenable for ePMRs and highlight the importance of developing membranes with thin supports (<200 \u00b5m thick) and good liquid permeation. The hydrogen flux through the membrane and the 6-chloro-1-hexyne hydrogenation reaction rates were both affected by the polarity of the solvent in the hydrogenation compartment (Fig. 4.2b, 4.4c). These effects can be attributed to the high hydrophobicity and solvent-dependent wettability of the PTFE support (shown schematically in Fig. 4.5). While 96% of the hydrogen permeated through the Pd when H2SO4 was placed in the hydrogenation compartment, merely 55% of hydrogen permeated when pentane was used. Polar solvents like H2SO4 (or water) cannot diffuse through the PTFE support, and the PTFE support layer acts effectively as a gas-phase layer (Fig. 4.5a, A2.3). In contrast, pentane fully wets the PTFE support (Fig. 4.5b, A2.3). Hydrogen permeation into the liquid-phase is known to be less favoured than permeation into the gas-phase because a liquid layer can affect both hydrogen transition from bulk to surface and hydrogen recombination at the Pd\u2013PTFE interface.77    69 Faster permeation of non-polar solvents and therefore the 6-chloro-1-hexyne reactant, to the catalyst surface also enabled faster hydrogenation rates. The hydrogenation rates of 6-chloro-1-hexyne followed a solvent polarity trend (Fig. 4.4c, A2.18), confirming the effect of PTFE wettability in the hydrogenation compartment on hydrogenation rates. These experiments also demonstrated that, even in polar solvents, substrate and solvent can diffuse through the PTFE support to participate in hydrogenation at the palladium layer. Moreover, these findings suggest that hydrophobicity of the support is an important factor to consider when designing supported membranes for ePMRs, and that the hydrophobicity of the support needs to be tuned to match the polarity of the solvent\/reactant being studied.    Figure 4.5 Schematic depictions of hydrogen flux through the palladium layer demonstrate the difference between (a) a polar solvent (H2SO4) and (b) a non-polar solvent (pentane) in the hydrogenation compartment measured by an atmospheric mass spectrometer. For a polar solvent, there is no liquid permeation through the PTFE support which results in a gas-phase PTFE layer that enables hydrogen evolution to occur freely at the palladium-PTFE interface. For a non-polar solvent, liquid diffuses through the PTFE support layer to the palladium-PTFE interface and can affect the rate of hydrogen recombination.  Hydrogenation of 1-hexyne proceeded at comparable reaction rates using the Pd\/PTFE membranes compared to Pd\/Pd foil membranes (Fig. 4.3d, e), even with 20-fold less palladium metal. Mass-independent and -dependent (normalized) consumption rates were calculated using the slope of the initial 3 h of consumption (mmol h-1) divided by mass of palladium content (mmol   70 gPd-1 h-1 (Table 4.1)). The normalized 1-hexyne consumption rates of the Pd\/PTFE and Pd\/Pd foil were 18 \u00b5mol gPd-1 s-1 and 1 \u00b5mol gPd-1 s-1, respectively. This comparison is particularly stark when comparing the mass of catalyst against conventional thermochemical hydrogenation Pd\/C catalysts, which generally have a normalized consumption rate of ~50 \u00b5mol gPd-1 s-1.152 These results demonstrate that the palladium content in Pd\/Pd foil membranes are not practical for industrial, but the Pd\/PTFE membranes have a significantly higher reaction rate per mass of palladium compared to Pd\/Pd foil membranes that is comparable to conventional standards. Table 4.1 Comparison of mass of palladium and 1-hexyne consumption rates using palladium foil with palladium catalyst (Pd\/Pd foil) and Pd\/PTFE membranes in the electrocatalytic palladium membrane reactor and compared to conventional thermochemical hydrogenation Pd\/C catalysts.152 Membrane Pd mass (g) \u00b1 0.005  Consumption rate  (mmol h-1) Normalized consumption rate  (mmol gPd-1 h-1) Normalized consumption rate  (\u00b5mol gPd-1 s-1) Pd\/Pd foil 0.257 0.91 3.5  1 Pd\/PTFE 0.011 0.72 65.5  18 Conventional  TCH Pd\/C \u2013 \u2013 \u2013 ~50a a This value was obtained from on Cecilia R et al. as a qualitative comparison for the amount of catalyst used for the hydrogenation of 1-heptyne with 5% Pd\/C (i.e., a conventional thermochemical hydrogenation catalyst).152  The comparable consumption rates (before normalization) by Pd\/PTFE and Pd\/Pd foil may be attributed, in part, to the catalytic surface area at the Pd\u2013PTFE interface. ECSA measurements recorded on both sides of the Pd\/PTFE membrane show that the catalytic surface area of palladium at the Pd\u2013PTFE interface is ~3-fold higher than that at the Pd interface (Fig. A2.19). The higher ECSA at the Pd\u2013PTFE interface is attributed to the surface structure of the porous PTFE layer which creates palladium-filled pores (as shown by cross-sectional SEM in Fig. 4.1a) that results in a non-planar palladium layer. In Chapter 3, I showed that 1-hexyne hydrogenation rates are affected by catalytic surface area, and that electrodeposition of a   71 palladium catalyst on a planar palladium foil leads to faster reaction rates.1 The catalytic surface area of the palladium at the Pd\u2013PTFE interface was measured to be 14.9 cm2 compared to 1.22 cm2 for planar Pd foil. The higher catalytic surface area of Pd at the Pd\u2013PTFE interface compared to a planar palladium electrode (Fig. A2.11) suggests that the surface area is one factor that contributes to the performance of the Pd\/PTFE membranes in hydrogenation reactions. These data also indicate that catalytic surface area can be increased by deposition of palladium directly onto a high-surface area porous support without the need for additional catalyst.  4.4 Conclusions In this chapter, I have demonstrated that a supported Pd\/PTFE membrane can reduce the mass of palladium by 20-fold compared to Pd\/Pd foil membranes in electrocatalytic palladium membrane reactors. I have shown that supports used in gas-fed reactors are incompatible with the electrocatalytic environment, and therefore the design of ePMRs are subject to different constraints compared to gas-fed PMRs. Palladium deposition onto the porous PTFE support enabled a higher catalytic surface area at the Pd\u2013PTFE interface compared to planar palladium membranes and fast liquid permeation of organic solvents to the palladium layer. The supported membranes yielded similar hydrogenation rates to palladium foil membranes and improved reaction rates per mass of catalyst. This study shows that supported palladium membranes can be designed to provide a more cost-effective and potentially scalable palladium membrane reactor for electrolytic environments. 4.5 Experimental 4.5.1 Materials Pd 2\u2033 target (99.95%) was purchased from ACI Alloys. Kapton (500 HN) substrates were purchased from American Durafilm. Tetratex Microfiltration PTFE membranes (TX1301, TX1302, TX1325; A4 size, 8.5\u2033 \u00d7 11\u2033) were purchased from Donaldson Membranes. EpoxySet   72 Resin and EpoxySet Hardener were purchased from Allied High Tech Products. A 1 oz wafer bar of Pd (99.95%) was purchased from Silver Gold Bull. PdCl2 (99.9%) was purchased from Strem Chemicals. Porous alumina discs (0.1 \u00b5m pore size, 1 mm thickness) were purchased from Coorstek. 1-hexyne (>97%) was purchased from TCI Chemicals. Pentane (\u226599%), DCM (HPLC grade, \u226599.8%), CD3OD (\u226599.8% D), dimethylsulfone (quantitative NMR standard, TraceCERT), MeOH (\u226599.8%), HCl (37%), H2SO4 (95\u221298%), CH3CN (>99.8%), tetrabutylammonium hexafluorophosphate (>99%), and H2O2 solution (30 wt. % in H2O) were purchased from Sigma Aldrich. Pt gauze (52 mesh, 99.9%), Pt wire (0.5 mm, 99.95%), 6-chloro-1-hexyne (98%) were purchased from Alfa Aesar. Nitric acid (68\u201370%) was purchased from VWR. Nafion 117 membranes were purchased from Fuel Cell Store. Ag\/AgCl reference electrodes (RE5B) were purchased from BASi. Viton foam gasket (\u215b\u2033 thickness) was purchased from McMaster Carr.  4.5.2 Material Preparation 4.5.2.1 PTFE Support Preparation  A Kapton substrate was cut into two circular 4\u2033 diameter masks each with 16 circular cut outs using a Cricut (Cut Smart 20). A 1:1 concentration of EpoxySet Resin and EpoxySet Hardener was combined to make epoxy that was spread on one Kapton mask. Tetratex PTFE was carefully placed on one of the Kapton masks and cured at 120 oC for 24 h. After 24 h, epoxy was spread onto the second Kapton mask and the mask was attached to the opposite side of the Tetratex PTFE for mechanical support. The complete PTFE (with Kapton) support (Fig. A2.1) was cured at 120 oC for 24 h and cleaned by sonication in deionized water, acetone, and IPA for 1 min each and then blow dried with N2.    73 4.5.2.2 Palladium Sputter-Deposition Palladium was deposited onto prepared PTFE supports by D.C. magnetron sputtering. The process chamber had a base pressure of 3\u00d710\u20136 torr and an Ar gas working pressure of 2\u00d710\u20133 torr. Pd deposition was carried out at 100 W after pre-sputtering for 3.5 min. The target\u2013substrate distance was 10 cm. The deposition rate was 2.5\u20133.0 A s\u20131 and resulted in films with thicknesses ranging from 1000\u20131900 nm. Pd mass was quantified using a Sartorius analytical balance (\u00b10.001 resolution) before and after deposition.  4.5.3 Liquid Permeation Measurements Liquid permeation experiments were carried out in a cell with two compartments: one with a solvent inlet and the other with an outlet (Fig. A2.2). Prepared PTFE supports and porous alumina supports were sandwiched between the two compartments. Viton foam gaskets were used to seal the support and prevent leaking. The inlet compartment was filled with 5 mL of solvent and measurements of solvent permeation were made by marking the inlet compartment at regular time intervals. Interval length depended on the solvent and support. Markings for alumina with all solvents and PTFE with MeOH and water were made every 1\u20132 h for 8 h and at 24 h. Markings for PTFE with pentane were made every 15 min and with DCM every 30 min until the inlet compartment was empty. 4.5.4 Scanning Electron Microscopy SEM images were acquired with an FEI Helios NanoLab 650 dual beam SEM at 1 kV and 50 pA using a through-lens detector in secondary electron mode. Cross-sectional images were taken at an angle of 52 o after a focused ion beam was used to evacuate a pit and expose a cross-sectional area. A HFW of 5.97 \u00b5m was exposed in both cases.   74 4.5.5 Brunauer-Emmett-Teller (BET) Analysis The BET surface area of the PTFE membrane was determined from N2 adsorption\u2013desorption on a Micrometrics ASAP 2020 instrument measured at 70 K. Prior to analysis, the PTFE was pretreated at 373 K under a vacuum pressure of 40 Pa for 8 h to remove any adsorbed moisture from the pores. 4.5.6 Electrochemical Measurements A Metrohm Autolab PGSTAT302N potentiostat and ePMR were used for electrochemical experiments. The ePMR used has a three-compartment cell configuration consisting of two electrochemical compartments and one hydrogenation compartment. All three compartments were filled with 35 mL solution volume. The chemical and middle electrochemical compartment were separated by Pd\/PTFE (or Pd\/Pd foil) cathode\/working electrode. A Nafion membrane was used between the two electrochemical compartments. Viton foam gaskets were used to seal both the palladium membrane and the Nafion membrane in place and prevent leaking. A Ag\/AgCl electrode (3.0 M NaCl) was used as a reference electrode and placed in the middle electrochemical compartment. A 1 cm2 Pt mesh was used as an anode\/counter electrode and placed in the outer electrochemical compartment. The thickness of the Pd layer of the Pd\/PTFE cathode was 1\u20132 \u00b5m (or 25 \u00b5m for the Pd foil cathode) and the geometric surface area of the cathode was 1.22 cm2 on both sides. The PTFE support was 25.4 \u00b5m thick with 0.05 \u00b5m pore size. Experiments were chronopotentiometric where a reductive current was applied by the potentiostat to the Pd\/PTFE (or Pd foil) working electrode (cathode) and the potential was measured between the Pd cathode and the reference electrode.   75 4.5.6.1 Electrochemical Surface Area  ECSA measurements of the Pd\/PTFE, Pd foil, and Pd\/Pd foil were performed by running cyclic voltammograms at various scan rates (10 to 100 mV s\u22121) and plotting current versus scan rate. The middle electrochemical compartment was filled with 0.15 M TBAPF6 in CH3CN with the other two compartments left empty. A Ag\/AgCl reference electrode and Pt mesh counter electrode were used. For Pd\/PTFE, ECSA measurements were done on both sides of the membrane to study the electrochemical surface area at the Pd\u2013PTFE interface and Pd interface. The liquid permeation of the organic electrolyte through the PTFE layer was confirmed by a relatively low uncompensated resistance of ~95\u201398 \u03a9 (compared to ~74\u201376 \u03a9 for Pd foil). A potential range of 0.05 to 0.25 V versus Ag\/AgCl with the plotted current taken at 0.15 V versus Ag\/AgCl (the open circuit voltage) was used for all three cases. The slope was used to compare double-layer capacitance and electrochemically active surface area, and to give a relative approximation of the surface area available for chemical reaction. 4.5.6.2 Atmospheric\u2013Mass Spectrometry  Hydrogen evolution measurements were made using the three-compartment cell with no substrate in the hydrogenation compartment. The electrochemical compartments were filled with 1 M H2SO4, a Nafion membrane was placed in between, and the solvent in the hydrogenation compartment was changed for each experiment. The Pd\/PTFE membrane was placed with the PTFE facing the hydrogenation compartment. Both the hydrogenation and middle electrochemical compartments were attached to the atm\u2013MS. Both compartments were closed to air and stirred at a consistent rate. The flow rate into the instrument was 10 mL min-1. The potentiostat was used to apply 100 mA (82 mA cm-2) of reductive current and an ESS CatalySys atm\u2013MS was used to measure 2 m\/z current ratio over time, switching between the chemical and electrochemical   76 compartment every 2 s with 5 s of purge to detect H2 gas evolution on both sides of the cell. The equilibrated ion current values were used to calculate the ratio of chemical:electrochemical H2 gas evolution. 4.5.7 Product Quantification 4.5.7.1 Gas Chromatography\u2013Mass Spectrometry GC\u2013MS was used to quantify products for the hydrogenation of 1-hexyne in pentane and 6-chloro-1-hexyne in pentane and DCM. Aliquots of 300 \u00b5L were taken every 2\u20134 h during the reaction and diluted in 700 \u00b5L pentane or DCM. GC\u2013MS samples were further diluted with 300 \u00b5L of dilute reaction mixture with 700 \u00b5L pentane or DCM. GC\u2013MS experiments were conducted on an Agilent GC\u2013MS using a HP\u20135ms column and electron ionization. The prepared samples were run on an autosampler with a 1 \u00b5L injection volume and a split ratio of 20:1. Reactions in pentane:  The oven temperature began at 30 \u00b0C for 2 min and ramped to 40 \u00b0C at 2 \u00b0C min\u22121 then to 200 \u00b0C at 40 \u00b0C min\u22121. A solvent delay of 2.15 min was employed. Peaks for 1-hexyne, 1-hexene, n-hexane, 6-chloro-1-hexyne, 6-chloro-1-hexene, and 6-chlorohexane were identified by searching the NIST database for matching mass spectra.  Reactions in DCM:  The oven temperature began at 70 \u00b0C for 1 min and ramped to 80 \u00b0C at 5 \u00b0C min\u22121 and held for 1 min. The temperature was then ramped to 81 \u00b0C at 1 \u00b0C min\u22121 then to 200 \u00b0C at 50 \u00b0C min\u22121. A solvent delay of 2.80 min was employed. Peaks for 6-chloro-1-hexyne, 6-chloro-1-hexene, and 6-chlorohexane were identified by searching the NIST database for matching mass spectra. 4.5.7.2 1H Nuclear Magnetic Resonance NMR was used for product quantification of 6-chloro-1-hexyne hydrogenation in MeOH in the hydrogenation compartment. 500 \u00b5L of the reaction mixture (0.1 M), 500 \u00b5L of methanol-d4 with   77 0.1 M dimethylsulfone internal standard were added to an NMR tube. 1H NMR spectra were acquired on a Bruker Avance 400inv spectrometer at 298 K. Relative concentrations were determined by comparing methylene signals (2H) of 6-chloro-1-hexyne (~1.83 ppm) and 6-chloro-1-hexene (~2.11 ppm) and methyl signal (3H) of 6-chlorohexane (~0.90 ppm). In each case the internal standard was integrated to 6.  4.5.8 Palladium Leaching Quantification  Inductively Coupled Plasma\u2013Optical Emission Spectroscopy (ICP\u2013OES) studies were performed with the electrocatalytic Pd\/PTFE membrane reactor to determine whether any palladium content was leached from the membrane after multiple hydrogenation cycles. The Pd\/PTFE membrane was used for three hydrogenation reaction cycles (8 h cycle-1) with 1-hexyne in pentane in the hydrogenation compartment under an applied current of 50 mA. The sample was prepared by removing the final 30 mL reaction mixture from the hydrogenation compartment after each cycle. Substrate and solvent were removed using a rotary evaporator under vacuum and the vial was treated with 500 \u00b5L of 70% HNO3 for 72 h. Subsequently, 6 mL of dH2O was added to yield <5% HNO3 concentration matrix mixture. A calibration curve was prepared using a 1000 mg\/L Pd in 5% HNO3 stock standard solution. The calibration curve ranged from 0 to 2.5 ppm with 3 emission lines (340 nm, 361 nm, and 324 nm). ICP\u2013OES measurements of the samples yielded results of 0.021 \u00b1 0.007 ppm for the first cycle, 0.011 \u00b1 0.003 ppm for the second cycle, and 0.014 \u00b1 0.005 ppm for the third cycle in the initial 30 mL reaction mixtures.   78 Chapter 5: Selective Hydrogenation of Furfural in a Palladium Membrane Reactor 5.1 Introduction The conversion of biomass feedstocks into fuels and chemicals provides a route to decarbonize chemical manufacturing.153,154 Furfural is a promising chemical feedstock to target because it can be derived from low-value agricultural biomass155 and upgraded to value-added chemicals through the process of hydrogenation.156,157 Hydrogenation of furfural can produce a variety of products, including furfuryl alcohol (FA), tetrahydrofurfuryl alcohol (THFA), and other furan-containing derivatives (Fig. 5.1a). FA accounts for >65% of the ~$800 million furfural market,158 and is widely used in foundry binders, lubricating oils, fragrances, and as a chemical intermediate for pharmaceuticals.159 THFA is a green solvent used in paint-stripping agents, industrial cleaners, epoxy resins, herbicides, dyes, and inks.159 The high miscibility and biodegradability of THFA make it a promising candidate to displace conventional polar solvents (e.g., alcohols) for a wide range of applications. These furfural derivatives are also important building blocks for the emerging bioplastics market.5  Furfural provides the opportunity to make industrial chemicals renewably, yet the current method for producing furfural derivatives, thermochemical hydrogenation, requires large amounts of H2 gas derived from fossil fuels (Fig. 5.1b).159 In addition to this high carbon intensity, H2 gas is difficult to handle and store, particularly in the remote locations where biomass is plentiful and inexpensive.160 Electrocatalytic hydrogenation is appealing because H atoms are derived from protic electrolyte enabling furfural hydrogenation to be performed at ambient temperatures and pressures without H2 gas (Fig. 5.1b, see Ch. 2.4.2 for details on ECH).18,161\u2013167  Unlike many substrates, furfural is soluble in an ECH environment (e.g., acidic electrolyte), and is therefore a main candidate for an ECH industrial-scale reactor. However, there are several   79 fundamental limitations to ECH that need to be addressed before this technology can be considered for industry. For example, the use of protic electrolyte to enable the electrochemical production of H atoms and subsequent hydrogenation significantly limits the scope of solvents that can be used for the reaction (Fig. 5.1b). This requirements leads to additional challenges such as product separation from solution164,168 and byproduct formation (e.g., furfural products reacting with electrolyte to form polymerized byproducts).163,169 Finally, the low furfural concentrations (\u2264100 mM) that are recommended to prevent oligomer formation and electrode fouling are not conducive to commercial reactors.169  These challenges prompted us to explore hydrogenation in an ePMR (Ch. 2.4.4) as an alternative to ECH architecture for furfural hydrogenation.1,2,39,45,47,48,122,170 The ePMR architecture is appealing for furfural hydrogenation because the physical separation of the electrochemical and hydrogenation chambers enables hydrogenations to be performed in any solvent (including protic and organic solvents) and at any concentration of furfural (i.e., not constrained to \u2264100 mM).  In this chapter, I report the first demonstration of hydrogenation of furfural using an ePMR. These experiments were performed successfully with furfural dissolved in n-BuOH in the hydrogenation compartment, and 1 M H2SO4 in the electrochemical compartment. While this result was important, the reaction was not selective for a single hydrogenation product. This issue is common to furfural hydrogenation chemistry because the large number of products (>10) that can form are sensitive to reaction conditions (e.g., temperature, pressure, catalyst, H2 flow rate, solvent, etc.).157 The challenge I faced is that the extensive literature linking reaction conditions to furfural selectivity does not translate effectively to the ePMR: the ePMR sources monoatomic hydrogen from water and hydrogenation occurs through a non-faradaic process, which is fundamentally different from both thermochemical hydrogenation (which involves the   80 dissociation of H2 gas at the catalyst surface) and ECH (which involves faradaic processes; see Ch. 2.1.2). We needed to empirically build a new database for reaction chemistry in the ePMR.  I therefore designed and built a customized high throughput ePMR platform to rapidly screen furfural hydrogenation reaction chemistries. This platform, called \u201cMultiThor\u201d, enabled a ~60-fold faster testing of furfural hydrogenation conditions (e.g., H atom supply at the surface, solvent, and catalyst). These accelerated experiments revealed to us that the reaction chemistry in the ePMR occurs in two successive steps: (i) the carbonyl bond is first hydrogenated to form FA (rate-limiting step); and (ii) the furan ring is subsequently hydrogenated to form THFA. The outcome of these experiments is that I identified the reaction conditions necessary to hydrogenate furfural to produce FA and THFA with selectivities of 84% and 98%, respectively. Although the production of FA and THFA generally requires an entirely different set of conditions for each product,159 I showed that the ePMR can selectively produce both without changing the system. This study highlights the opportunity for using the ePMR to selectively hydrogenate furfural without carbon-intensive H2 gas.     81  Figure 5.1 Furfural hydrogenation pathways and methods. (a) Reaction pathways of furfural hydrogenation. (b) Comparison of thermochemical hydrogenation (TCH), electrochemical hydrogenation (ECH), and electrocatalytic Pd membrane reactor (ePMR) hydrogenation. TCH is performed with H2 gas that is dissociated to surface-adsorbed hydrogen atoms (H) that react with furfural to form hydrogenated products. ECH is performed with protons (H+) derived from protic electrolyte that are reduced to H and react with furfural to form hydrogenated products. Hydrogenation in an ePMR is performed with H+ derived from protic electrolyte that are reduced to H, permeate the Pd membrane, and resurface on the opposing side to react with furfural to form hydrogenated products. Note: reaction pathways in (a) and main products differ for the three methods.   5.2 Results 5.2.1 Proof-of-Principle Reactions For the first stage of this study, I set out to demonstrate that furfural could be hydrogenated in the ePMR. This proof-of-concept reaction was performed in an H-cell, an electrochemical reactor architecture previously demonstrated for ePMR experiments (Fig. A3.1a; see Appendix   82 3.1.1 for details).1,2,45,48,170 The hydrogenation compartment was filled with 30 mL of 0.25 M furfural dissolved in n-BuOH, the electrochemical compartment with 30 mL of 1 M H2SO4, and a 45 mA (37 mA cm-2) was applied to drive the reaction. Reaction progress monitored by GC\u2013MS showed that furfural was hydrogenated to form FA and THFA, as well as >6 other side products with higher boiling points (Fig. A3.1b). Although this proof-of-concept study demonstrated furfural hydrogenation in the ePMR, the large number of products formed and the slow reaction rates (6.3 \u00b5mol h-1) highlighted the shortcomings of the H-cell architecture for studying furfural hydrogenation.  To address these challenges, I designed and constructed MultiThor (Fig. 5.2, A3.2, A3.3) in order to enable 6 reactions to be performed in parallel and at ~10-fold faster furfural hydrogenation rates than the H-cell (64.8 \u00b5mol h-1 compared to 6.3 \u00b5mol h-1). This faster hydrogenation rate was made possible by using a lower-volume hydrogenation compartment with a 10-fold higher catalyst surface area exposed to the furfural solution (Table A3.1). MultiThor was also designed such that a bulk water electrolysis chamber (i.e., electrochemical compartment) provided H atoms to all six isolated wells. Control experiments showed that hydrogen permeation and hydrogenation were evenly distributed across the six wells at the reaction conditions tested (Fig A3.4, A3.5; see Appendix 3 for details). These results confirmed that MultiThor could be used to study furfural hydrogenation at a ~60-fold faster rate of testing.   83  Figure 5.2 MultiThor architecture. (a) A rendering of the MultiThor design with six hydrogenation wells and an electrochemical compartment separated by a Pd foil cathode\/membrane with electrodeposited Pd catalyst. A Pt anode is used as a counter electrode in the electrochemical compartment, Cu tape is attached to the Pd cathode to provide electrical contact, and Fluorosilicone gaskets are used to seal intercompartmental interfaces. (b) Illustration of hydrogen pathway through MultiThor. (c) External MultiThor setup showing pump, electrochemical reservoir, and electrode leads that are connected to a potentiostat. An applied current across the Pd cathode and Pt anode results in water oxidation to form H+. These H+ are reduced to surface-adsorbed H atoms at the Pd surface, H permeate through the Pd membrane, and resurface on the other side where they are poised to react on the high surface area Pd catalyst.      84 5.2.2 Effect of Solvent on Selectivity  I used MultiThor to study the effect of different solvents on furfural selectivity and hydrogenation rate. For each experiment, furfural was dissolved into 1 mL of solvent (CHCl3, t-BuOH, n-BuOH, i-PrOH, EtOH, MeOH; 0.25 M) and a current of 150 mA (37.5 mA cm-2) was applied for 2 h (Fig. 5.3a). The production of FA, THFA, and any side products that were formed during reaction (labelled \u201cother\u201d) for each solvent are plotted in Fig. 5.3b. These results showed that solvents with lower nucleophilicity generally produced fewer side products (<15%), while more nucleophilic solvents (i.e., EtOH and MeOH) resulted in the formation of >40% side products (particularly 2-furaldehyde diethyl acetal and 2-furaldehyde dimethyl acetal, respectively; Fig. A3.8, A3.9). This finding is consistent with previous studies showing the formation of 74% acetal products during furfural hydrogenation, which was ascribed to EtOH and MeOH nucleophilic attack of the solvent on furfural.171  For reactions where furfural was not consumed by the solvent, furfural consumption rates decreased as follows:  n-BuOH ~ i-PrOH > t-BuOH > CHCl3 (Fig. 5.3c). This observed trend is similar to those found in literature that correlate hydrogenation rate to H-donating ability of the alcohol solvent.172 For all experiments hereafter, t-BuOH was used as the solvent because of the effectiveness of side product suppression (Fig. 5.3b, A3.8).     85  Figure 5.3 Effect of solvent on furfural hydrogenation selectivity. (a) MultiThor setup for solvent measurements. (b) Product selectivity of furfural hydrogenation to FA, THFA, and any other products formed during reaction (other) in CHCl3, t-BuOH, n-BuOH, i-PrOH, EtOH, and MeOH after 2 h of reaction at 150 mA. (c) Furfural consumption during hydrogenation in CHCl3, t-BuOH, i-PrOH, and n-BuOH. Note: MeOH and EtOH are not shown in (c) due to solvent attack on furfural to form 2-furaldehyde diethyl acetal and 2-furaldehyde dimethyl acetal (Fig. A3.9).  5.2.3 Effect of Catalyst and Current on Selectivity  The selective hydrogenation of furfural in t-BuOH was tested for six different catalysts to examine the effect of metal identity on FA and THFA selectivity. For each experiment, a Pd\/Pd membrane was prepared with six sputter-deposited catalysts (10 nm; Ni, Cu, Ag, Ir, Pt, and Au) using a masking technique such that one catalyst was deposited in each well (see Experimental for details). The M\/Pd\/Pd membrane was secured in MultiThor, 1 mL of 0.25 M furfural in t-BuOH was placed into each well, and a current of 75, 150, or 225 mA was applied across the electrochemical compartment (Fig. 5.4a). Product selectivity measured after 8 h of reaction showed that FA selectivity increased with decreasing current (i.e., highest selectivity of 67% was   86 achieved with Pt at 75 mA), while THFA selectivity increased with increasing current (i.e., highest selectivity of 98% achieved with Pt at 225 mA).  The trend for highest to lowest selectivity for FA production at 75 mA was Pt > Ir ~ Cu > Pd ~ Au > Ni > Ag, while for THFA at 225 mA the trend was Pt ~ Ir > Pd > Au ~ Ni > Cu > Ag (Fig. 5.4b, 5.4c, A3.8\u2013A3.12). These data highlight that reactivity can be enhanced by the addition of a catalyst layer in an ePMR, and show that reactivity for FA and THFA generally follow a similar catalyst trend (e.g., Pt and Ir enabled the highest reactivity and Ag the lowest). Importantly, a selectivity of 98% THFA was achieved with a 10 nm Pt\/Pd\/Pd membrane, which demonstrates the ability to perform selective furfural hydrogenation in the ePMR.  The effect of applied current was further investigated by comparing FA and THFA production at equivalent charge passed (Fig. A3.12). A current of 75 mA applied for 8 h is equivalent (in terms of charge passed) to a current of 225 mA applied for 2.7 h. The observed FA selectivity at these two applied currents varied by at least 2- to 6-fold depending on the catalyst tested (Fig. A3.13a). These results show that applied current (and not just charge passed) influences reaction selectivity. A second experiment performed for a longer amount of time at each applied current (e.g., 75 mA for 24 h and 225 mA for 8 h) showed that THFA selectivity varied by merely ~10% at the two applied currents because almost all furfural and FA is consumed over this time period with our apparatus (Fig. A3.13b). It is worth noting that ~14% MTHF was observed after 24 h of reaction at 225 mA (Fig. A3.10d), indicating that THFA can be further hydrodeoxygenated to form MTHF.32     87  Figure 5.4 Effect of catalyst identity and applied current on furfural selectivity. (a) MultiThor setup for catalyst identity measurements for furfural hydrogenation to FA and THFA. Selectivity of (b) FA and (c) THFA for 75, 150, and 225 mA applied current corresponding to current desities of 18.75, 37.5, and 56.25 mA cm-2, respectively with M\/Pd\/Pd membrane (10 nm; M = Cu, Ni, Pd, Ir, Pt, Au, and Ag). Coloured bars represent selectivity of >50% and white bars represent selectivity of <50%. Samples were taken after 8 h of applied current.   I then tested how catalyst thickness affects FA selectivity. I chose different thicknesses of Pt and Ir because these catalysts enabled the highest selectivity towards FA in our initial catalyst experiments (Fig. 5.4b). A 10-, 20-, and 50-nm thick layer of Pt and Ir was sputter-deposited on the Pd\/Pd membrane (using the same masking technique as before), t-BuOH was used as the solvent in all hydrogenation wells, and a current of 75 mA (18.75 mA cm-2) was applied to drive the hydrogenation reaction. Furfural consumption rates were calculated using the slopes of the initial 2 h of the reactions (\u00b5mol h-1; Fig. A3.14). For both the Pt and Ir catalysts, thicknesses of   88 20 nm enabled a >30% increase in furfural consumption rates (Fig. 5.5a). Moreover, samples recorded after 8 h of reaction showed a 17% increase in FA selectivity when the catalyst thicknesses were increased from 10 to 50 nm (Fig. 5.5b). Notably, SEM images and ECSA measurements for all thicknesses demonstrate that there are negligible changes in catalytic surface area, suggesting that the rough morphology of the underlying Pd is retained during sputter-deposition (Fig. 5.5c, A3.6). FA selectivity was highest for Pt\/Pd\/Pd membranes, which showed a selectivity of 84% at 50 nm. These results highlight how reaction selectivity can be adjusted by catalyst thickness.  I also performed a control experiment using 0.25 M FA in t-BuOH as the starting material instead of 0.25 M furfural to define the reaction mechanisms that govern furfural hydrogenation in the ePMR. I observed a 4-fold faster reaction rate when FA was used as the starting material instead of furfural (Fig. 5.5d). This result points to furfural hydrogenation being rate-limiting, and the subsequent hydrogenation of FA to THFA being a relatively fast step (Eq. 6.1).                                 (Eq. 6.1)   89   Figure 5.5 Effects of catalyst thickness on furfural selectivity. (a) Furfural hydrogenation rate calculated for the first 2 h of reaction for Pt and Ir with different thicknesses. (b) Furfuryl alcohol (FA) selectivity for 10 to 50 nm of Pt and Ir sputter-deposited on a Pd\/Pd membrane measured after 8 h of reaction. (c) SEM images of 10, 20, and 50 nm of Pt on a Pd\/Pd membrane. (d) Comparison of consumption of starting material furfural to furfuryl alcohol (FA) and tetrahydrofurfuryl alcohol (THFA), and starting material FA to THFA with a Pd\/Pd membrane.      90 5.3 Discussion Furfural hydrogenation to FA and THFA is typically performed using a series of reactors to enable: (i) H2 production; (ii) H2 purification; (iii) hydrogenation of FA; and (iv) hydrogenation of THFA.159 These reactors require expensive infrastructure to ensure safe handling of H2 gas.114 The H2 gas is first produced by steam\u2013methane reforming (SMR), a process that requires large amounts of heat and fossil fuels to reduce water and methane into H2 gas and CO.14 The H2 gas is then purified to 99.999% to ensure that the H2 feed is not contaminated with CO which is known to poison many hydrogenation catalysts. Large amounts of purified H2 gas are then transported into a rector containing furfural to produce FA at ~120 oC in the presence of Cu-based catalysts.159 This CO2-intensive process produces FA at high yields of >95% in a solvent-free environment. FA is further hydrogenated into THFA using a separate reactor vessel in the presence of H2 gas and Ni-based catalysts at ~100 oC.159 These reactions are well-established; however, the high infrastructure costs and large carbon footprint associated with conventional TCH,15 as well as the expanding furfural market158 have resulted in a growing interest in furfural hydrogenation using renewable methods.  Electrochemical hydrogenation achieves this goal by sourcing hydrogen from renewable electricity and water (or protic media), but there are limitations to performing electrolysis and hydrogenation in the same environment (Fig. 5.1b). Consider, for example, that the two most common products for ECH of furfural (furfuryl alcohol and 2-methylfuran) undergo side reactions in acidic environments that can result in product polymerization.163 Moreover, 2-methylfuran, which has a low boiling point (64 oC) and high hydrophobicity relative to the surrounding protic solution, can evaporate during ECH of furfural.163 This evaporation can be suppressed with cosolvents, but these cosolvents increase the cell potential and can also trap furfural to reduce the   91 amount of available reactant.168 Low furfural concentrations (\u2264100 mM) are also required to prevent oligomer formation and electrode fouling,169 a constraint that does not exist for ePMR hydrogenation. Finally, an ePMR can enable operation at significantly lower voltages (~1 V) than ECH.45  These factors led us to hypothesize that the ePMR could be used to hydrogenate furfural using electricity and water. I first tested this hypothesis by performing electrolytic furfural hydrogenation in a proof-of-concept ePMR \u201cH-cell\u201d architecture (Fig. A3.1a). I validated this hypothesis by observing the successful conversion of furfural to FA and THFA during these experiments (Fig 3.1b), which proceeded without an external H2 gas supply. Notably, the reaction was performed in n-BuOH, a solvent that is not compatible with ECH.  These positive results notwithstanding, reactivity was slow (6.3 \u00b5mol h-1) and there were >6 side products formed (Fig 3.1b). A powerful feature of the ePMR is that multiple experimental parameters can be varied to optimize for reaction rate and selectivity (e.g., solvents, current densities, electrolytes, co-additives, catalysts). In order to accelerate the testing of myriad experimental variables, I designed and constructed a high throughput testing platform, MultiThor (Fig. 5.2). This platform enabled a 10-fold faster hydrogenation rate (64.8 \u00b5mol h-1) and a ~60-fold higher throughput of testing reaction conditions than the H-cell (Table A3.1). For this study, I tested furfural hydrogenation using 6 different solvents and 7 catalyst formulations (two of which were selected for testing at 3 different thicknesses and 3 different applied electrical currents).  I observed the highest reaction rates and selectivities when using the bulky weakly nucleophilic solvent, t-BuOH (Fig. 5.3). Solvents of high nucleophilicities (e.g., EtOH, MeOH) reacted immediately with furfural to form undesirable acetal byproducts, while non-bulk weakly nucleophilic solvents (e.g., n-BuOH, i-PrOH) reacted with hydrogenation products FA and THFA   92 (Fig. 5.3b, A3.8, A3.9). In contrast, no byproducts were observed when the reaction was run in t-BuOH (Fig. A3.8, A3.10). This observation can be attributed to the steric bulk of the solvent inhibiting undesirable reaction chemistry.173 In terms of reaction rates, the observed trend tracks the H-donating ability of the solvent (n-BuOH ~ i-PrOH > t-BuOH > CHCl3; Fig. 5.3c). This observation is consistent with the TCH literature, where H-donating solvents are known to accelerate the rate of furfural hydrogenation by affecting the hydrogen transfer process or by activating the carbonyl of furfural.174,175 For the parameter space I tested, t-BuOH was identified as the optimal solvent for both reaction rate and selectivity. Importantly, this solvent is not compatible with ECH reactors.  I also observed that both applied current and catalyst identity influence selectivity and rate of furfural hydrogenation (Fig. 5.4, A3.11\u2013A3.13). Lower applied currents mediated faster FA formation (maximum selectivity of 67% at 75 mA), while higher currents resulted in higher THFA production (maximum selectivity of 98% at 225 mA). Plots of equivalent charge passed at applied currents of 75 mA and 225 mA (measured at 8 h and 2.7 h, respectively) for FA selectivity demonstrated two different trends (Fig. A3.13a), while measurements taken after 24 h and 8 h, respectively for THFA selectivity showed two similar trends (Fig. A3.13b). These results suggest that applied current (and not only charge passed) influences selectivity, particularly for intermediate products such as FA. We ascribe the observed trend for FA selectivity to a change in effective pressure across the palladium membrane mediated by changing the applied current. This observation is supported by studies that have shown that a small applied voltage of \u20130.2 to 0.3 V can lead to a large effective pressure of 1,000 to 10,000 atm.63 This feature is made even more pronounced by applying the current directly to the palladium membrane (as opposed to a producing hydrogen at   93 a secondary Pd cathode and then fed through a Pd membrane). Hydrogenation rates were 6-fold faster when hydrogen was fed through the palladium membrane directly (Fig. A3.17). These results highlight a stark advantage of the ePMR for direct hydrogenation compared to producing H2 gas using conventional water electrolysis and then using that H2 gas to perform hydrogenation. The FA production rates at 75 mA for different catalysts followed the trend Pt > Ir > Cu > Pd > Au > Ni > Ag. The rate of THFA production at 225 mA followed the trend Pt > Ir > Pd > Au > Ni > Cu > Ag. The rate of FA production (i.e., hydrogenation of the furfural C=O bond) tracks the substrate-metal adsorption energies,41 but the trend for THFA production (i.e., hydrogenation of the FA C=C bond) did not.42   This result points to furfural hydrogenation being rate-limiting, and the subsequent hydrogenation of FA to THFA being a relatively fast step (Eq. 6.1). This hypothesis was supported by an experiment with 0.25 M FA (instead of furfural) in t-BuOH as the starting material occurring at a rate that was ~4-fold faster (Fig. 5.5d, A3.15). A higher activation energy for furfural hydrogenation relative to FA hydrogenation is also supported by activation energy calculations.178  Our data demonstrates that FA hydrogenation rates decreased with increasing Pt thicknesses because Pt can passivate the superior catalytic properties of Pd hydrogenating C=C bonds (Fig. A3.15). These results taught us that adding a thicker layer of sputter-deposited catalyst would slow down the FA to THFA hydrogenation reaction and increase selectivity towards FA. I measured the effects of three thicknesses (10, 20, 50 nm) of Pt and Ir (i.e., catalysts that enabled the highest reactivity to FA). I found that 50 nm Pt improved FA by 17% (Fig. 5.5a). Furfural   94 hydrogenation rates also increased at 20 nm catalyst thicknesses, indicating that the 10 nm catalyst thicknesses used for much of this study were not optimal (Fig. 5.5b).  The thickness of the catalyst layer influences two variables: (i) hydrogen permeation; and (ii) furfural reactivity. Hydrogen permeation experiments with 10, 20, and 50 nm of Ir at 75 mA (18.75 mA cm-2) showed >96% hydrogen permeation for the thinner films but only ~78% hydrogen permeation for the 50-nm film (Fig. A3.16). The thicker 50-nm films reduce furfural hydrogenation rates and increase FA selectivity by limiting the amount of hydrogen permeating through the membrane. These findings highlight the important role of catalyst thickness on catalytic rates and substrates in the ePMR. 5.4 Conclusions  I have demonstrated that the ePMR can hydrogenate furfural with high selectivities and activities, using water as the H atom source. This system is driven by electricity rather than thermal energy, making it an appealing option for decarbonizing the industry. A powerful feature of the ePMR is that it enables electrolysis to be combined with reaction chemistry in organic media at high current densities. I leveraged the ability to tune product selectivity by adjusting solvent, current, catalyst identity, and catalyst thickness in operando without modifying the system. I also demonstrate the use of a high-throughput ePMR platform, which enabled us to identify the industrially relevant conditions for furfural hydrogenation. I anticipate that this platform will also accelerate the deployment of this membrane reactor to help decarbonize the chemical industry. 5.5 Experimental  5.5.1 Materials Wafer bars (1 oz) of Pd (99.95%) were obtained from Silver Gold Bull. PdCl2 (99.9%) was purchased from Strem Chemicals. DCM (\u226599.8%), H2SO4, HNO3, H2O2 solution (30 wt. % in   95 H2O), MeOH (\u226599.8%), EtOH (95%), n-BuOH (99.4%), i-PrOH (99.5%), t-BuOH (\u226599.7%), 2-methylfuran (99%), and 2-methyltetrahydrofuran (\u226599%) were purchased from Sigma Aldrich. Furfural (98%), FA (98%), Pt gauze (52 mesh, 99.9%), and Pt wire (0.5 mm, 99.95%) were obtained from Alfa Aesar. Ag\/AgCl reference electrodes (RE5B) were purchased from BASi. Viton gasket material (\u215b\u2033 thick), quick turn polycarbonate plastic couplings (\u00bc-28\u2033 thread), M3 and M4 socket head 18-8 stainless steel bolts, 304 stainless sheet metal (\u215c\u2033 thick), acrylic sheet (\u215c\u2033 thick), and M5 dowel pins were purchased from McMaster Carr. Kapton (500 HN) substrates and tape were purchased from American Durafilm. Copper tape (\u00bc\u2033 thick) manufactured by 3M was purchased from Digikey. A low-flow chemical metering pump (part no. 4049K55) was purchased from McMaster-Carr.  5.5.2 MultiThor Design The MultiThor design consisted of: (i) an 8-mL electrochemical compartment; (ii) six 2-mL isolated hydrogenation \u201cwells\u201d; and (iii) a 30-\u00b5m thick Pd foil membrane that separated the hydrogenation wells from the electrochemical compartment (Fig. 5.2, A3.2, A3.3). Inert Fluorosilicone gaskets were used to seal the interfaces between compartments. The electrochemical compartment contained a 1 cm2 Pt mesh anode that acted as the counter electrode against the Pd foil cathode\/working electrode. The Pd foil membrane had an exposed geometric surface area of 4 cm2 at the electrochemical compartment interface and 0.43 cm2 at each hydrogenation well interface. A high surface area Pd catalyst was electrodeposited on the Pd foil membrane (Pd\/Pd membrane) facing the hydrogenation side of the reactor with electrochemical surface area measurements showing a ~218-fold increase in catalytic surface area (Fig. A3.11).1 An additional 10\u201350 nm layer of metal catalyst (Ni, Cu, Ag, Ir, Pt, or Au) was sputter-deposited   96 on top of the Pd\/Pd membrane based on previously reported procedures to enhance reactivity for carbonyl functionalities (Fig. A3.14).49  5.5.3 Electrochemistry All experiments were performed with a Metrohm Autolab PGSTAT302N potentiostat coupled with MultiThor, with the exception of the initial proof-of-concept reaction where an H-cell was used (Appendix 3.1). Experiments were chronopotentiometric, where a reductive current was applied across the Pd foil cathode and Pt anode, and the cell potential was measured. For all experiments performed with MultiThor, the electrochemical compartment was filled with 25 mL of 1 M H2SO4 and operated under flow conditions (250 mL min-1) with inlet tubing directing electrolyte to the Pd membrane to remove H2 bubbles formed during electrolysis (Fig. A3.2). A small hole (2 mm diameter) over each hydrogenation well enabled excess H2 bubbles to escape and provided access for aliquots to be taken periodically during the reaction. Upon completion of each experiment, an oxidative potential (chronoamperometric, +0.2 V) was applied across the cell for 30 min to draw out any H atoms that remained in the Pd lattice.  5.5.4 Palladium Membrane Preparation Pd foils were rolled from a 1 oz Pd wafer bar using an MTI MR-100A electric rolling mill. The bar was rolled to achieve a thickness of 30 \u00b5m determined by a Mitutoyo digital micrometer. The resulting Pd foil was cut into ~3\u00d73 cm2 squares and annealed at 850 \u00b0C for 1.5 h under N2. The foils were then cleaned using 1:2:1 concentration HNO3:H2O:H2O2 v\/v ratio solution until vigorous bubbling subsided (~40 min), rinsed with acetone and Milli-Q water, and dried with N2. Pd catalyst was electrodeposited on Pd foils using a one-compartment electrochemical cell. A Pd foil was clamped into the cell with an exposed geometric surface area of 2\u00d72 cm2. The Pd foil served as a working electrode in reference to a Ag\/AgCl reference electrode and Pt mesh   97 counter electrode. The compartment was filled with 15 mL of 15.9 mM PdCl2 in 1 M HCl electrolyte. A voltage of \u20130.3 V vs. Ag\/AgCl was applied to the Pd foil working electrode to reduce Pd ions in solution. The electrodeposition ended when a charge of 30 C had been passed, corresponding to a catalyst loading of approximately 7.5 C cm-2, similar to a previously reported procedure.1 This Pd layer increased the catalytic surface area of the hydrogenation side of the Pd membrane by ~218-fold (Fig. A3.6).  An additional layer of catalyst was deposited on the Pd\/Pd membranes by sputter-deposition (M\/Pd\/Pd membranes). A Kapton mask with 6 cut-outs (0.5 cm2 each) that aligned with the 6 wells of MultiThor was used to enable customized deposition of catalysts in each well. A Leica EM MED020 coating system was used to sputter-deposit Pt, Ir, Cu, Ag, and Au and a Univex 250 RF magnetron sputtering system with an Onyx-2 IC Mag II cathode was used to deposit Ni. More details on sputter-deposition conditions can be found in Appendix 3. The catalyst coated Pd\/Pd membranes containing up to 6 sputter-deposited catalysts were used for hydrogen permeation and hydrogenation experiments without any further processing. 5.5.5 Hydrogen Permeation  Hydrogen permeation experiments were conducted in MultiThor with 1 M H2SO4 flowing through the electrochemical compartment and solvent without any furfural in all hydrogenation wells. All compartments were closed to air. The potentiostat was used to apply a constant applied current (75 \u2013300 mA). The production of gaseous H2 (2 m\/z current ratio over time; 10 mL min-1 flow rate) in the hydrogenation wells and electrochemical compartment was monitored by an ESS CatalySys atm\u2013MS. H2 evolution measurements were taken by alternating between one hydrogenation well and the electrochemical compartment every 2 s with a purge time of 5 s between measurements for 30 min for each well. Current was applied for 60 min prior to each set   98 of measurements and the ion current value was taken once the signal had equilibrated. The equilibrated ion current was used to determine the ratio of H2 evolution in the hydrogenation:electrochemical compartments. 5.5.6 Product Quantification Gas chromatography\u2013mass spectrometry was used to quantify products for the hydrogenation of furfural. GC\u2013MS measurements were conducted on an Agilent GC\u2013MS using a HP\u20135ms column and electron ionization. Aliquots of 30 \u00b5L diluted in 1 mL DCM were taken at time intervals for up to 24 h of reaction. The prepared samples were run on an autosampler with a 1 \u00b5L injection volume and a split ratio of 20:1. The oven temperature began at 40 \u00b0C for 1 min and ramped to 80 \u00b0C at 10 \u00b0C min\u22121 then to 200 \u00b0C at 25 \u00b0C min\u22121. A solvent delay of 2 min was employed. Furfural, FA, THFA, 2-methylfuran, and 2-methyltetrahydrofuran peaks were identified by searching the NIST database for matching mass spectra and confirmed with standards of each of the compounds.    99 Chapter 6: Conclusions and Future Directions 6.1 Conclusions The ePMR is a disruptive technology that can eliminate carbon emissions from conventional thermochemical hydrogenation. This reactor produces H atoms in situ with water and renewable electricity to drive hydrogenation in an organic solvent without ever requiring heat derived from fossil fuels or H2 gas produced from steam\u2013methane reforming. The ePMR also overcomes several limitations of conventional electrosynthesis architectures to increase the scope of solvents that can be used for reactions, reduce steps required for product purification, and improve product selectivities and reactor efficiencies. To date, the ePMR has been demonstrated for a variety of functional groups including industrially-relevant products for pharmaceuticals, green solvents, and fine chemicals industries. However, there are a few advances that must occur before ePMRs can compete with thermochemical hydrogenation on an industrial scale. The ePMR must have: (i) a broadened product scope; (ii) higher reactor efficiencies; (iii) efficient palladium membranes; and (iv) improved catalyst stability. This thesis moves us closer to these objectives by improving our understanding of the variables that govern reactivity and selectivity (Ch. 3), providing palladium membrane design strategies (Ch. 4), and broadening product scope to industrially-relevant molecules (Ch. 5).  Chapter 3 showed how the ePMR could be used to couple two reactions, an electrochemical oxidation and chemical hydrogenation, that are otherwise incompatible. This architecture enabled the oxidation of anisyl alcohol at the anode in tandem with chemical hydrogenation of 1-hexyne in the at current efficiencies of up to 80% and selectivities up to 98%.  I demonstrated these current efficiencies and selectivities could be achieved by modifying catalyst surface area, current density, solvent, and electrolyte identity. These reactions were   100 performed in a proof-of-concept H-cell, and demonstrated how an ePMR can serve to enable electrosynthesis without the formation of any byproducts (e.g., H2 or O2 gas). Chapter 4 provided an alternative membrane design to the palladium foil membranes (\u226525 \u00b5m thick) used in all previous embodiments of the ePMR. In this work, I sputter-deposited thin palladium films (1\u20132 \u00b5m thick) onto PTFE supports and benchmarked these membranes against palladium foil membranes. The Pd\/PTFE membranes enabled a 20-fold reduction in palladium content, with similar reaction rates to the palladium foils. I chose a porous support layer to provide fast solution transport to the palladium film and increase the catalytic surface area on the hydrogenation side without requiring any additional Pd catalyst. The design principles I described in this study provide a foundation for future membrane designs for developing a cost-effective and scalable ePMR. Chapter 5 demonstrated the hydrogenation of furfural, a low-value biomass derivative, into higher value products, furfuryl alcohol and tetrahydrofurfuryl alcohol. I designed a high-throughput MultiThor reactor that enabled us to test a combination of solvents, catalysts, and applied currents. This empirical approach revealed that bulky solvents with weak nucleophilicities suppressed the formation of side products to enable FA and THFA formation at selectivities of >84%. This work was the first demonstration of an industrially-relevant molecule produced by the ePMR, and highlighted the benefits of the ePMR for decarbonizing the furfural hydrogenation industry.       101 6.2 Future Directions  The next steps in developing the ePMR are to: (i) expand reaction scope to demonstrate more industrially-relevant molecules; (ii) engineer a reactor to improve energy and current efficiencies; (iii) develop membranes that are cheap, robust, and scalable; and (iv) design catalysts that facilitate long-term membrane stability and fast reaction rates (Fig. 6.1). In this section, I highlight the progress that has been made towards each of these steps and elaborate on future opportunities.   Figure 6.1 Summary of future research directions for the ePMR.  6.2.1 Industrial Applications  Over one year ago, we began developing the ePMR for industrial applications through a spin-out company from the Berlinguette group called \u201cThorTech\u201d. During this time, we have   102 investigated the business case for the ePMR for a variety of scales from a bench-top reactor for the production of pharmaceutical precursors at the lab scale (~1\u2013100 g\/day) to production of fuels at a commodity scale (>1000 kg\/day). Through this process we have interviewed >75 stakeholders and found that there is interest at the medium- and large- scales (>100 kg\/day) to replace current thermally-driven hydrogenation reactions. We are currently developing the ePMR for applications spanning renewable fuel production, hydrogen peroxide production, and hydrogen storage using liquid organic hydrogen carriers (LOHCs).   6.2.1.1 Renewable Fuels Renewable fuels are a promising alternative to conventional petroleum-based fuels; the former does not rely on new fossil fuel extraction, but can still be used in existing energy infrastructure as well as cars, heavy haul trucks, and airplanes.12 Production of renewable fuels from HDO of waste vegetable oils, animal fats, or biocrude oil has the added benefit of transforming these low-value products into an economic asset.12,179 Key challenges associated with incumbent processing methods include: i) large energy requirements to drive diesel production; ii) high capital costs to build reactors that can sustain high-temperature and -pressure conditions (up to 400 oC and 200 bar); and iii) safety considerations resulting from handling heated and pressurized H2 gas together with flammable feedstocks and products.180\u2013182  The advantage of using the ePMR for renewable fuel production is that this reactor could enable reaction at low temperature and pressure conditions. If successful, renewable diesel production in an ePMR would have a 95% lower carbon emissions than renewable diesel produced by conventional thermochemical methods. This estimate is based on a preliminary technoeconomic analysis conducted in our research group. Our group has also shown that Pd nanoparticles could be used to mediate HDO of benzaldehyde (a biomass model compound) with   103 selectivity greater than 90%.48 However, renewable fuel production generally requires HDO of esters and carboxylic acid functional groups,183 which are difficult to hydrogenate (see Ch. 2.4.2, Fig. 2.9) and have not been demonstrated in the ePMR yet. In order for the ePMR to be a viable consideration for the development of renewable fuel production, catalysts must be designed that reduce the activation energy such that HDO of these challenging functional groups can proceed (Ch. 6.2.4). 6.2.1.2 Hydrogen Peroxide  Hydrogen peroxide (H2O2) is a strong, environmentally-friendly oxidizing agent that can be used in a variety of applications including in low concentrations as a disinfectant or sanitizer. The conventional method for producing H2O2 (called the indirect method) involves thermochemical hydrogenation of a secondary molecule, anthraquinone, that then reacts with O2 to form H2O2.184,185 The indirect method sources H2 gas from SMR and leads to an annual energy consumption of >8.6 GW and carbon footprint of >2.8 Mt.186,187 An alternative method is the direct synthesis of H2O2 produced by reacting H2 and O2.188 The direct synthesis significantly simplifies the infrastructure by converting H2 and O2 without the use of the secondary molecule, and can reduce capital cost by 50% compared to the conventional method.189 However, the direct synthesis of hydrogen peroxide uses large quantities of hydrogen and oxygen gas which are highly explosive when combined.  The ePMR is capable of enabling both direct and indirect production of H2O2 without the large carbon footprint and without the dangers of H2 gas. In the ePMR, H atoms fed through the membrane can react with O2 directly at the membrane surface (direct method) or indirectly to regenerate a quinone with two H atoms. Both methods are currently being developed in the Berlinguette group in collaboration with an industrial partner.    104 6.2.1.3 Hydrogen Storage  Hydrogen storage using an LOHC presents an opportunity to store large quantities of hydrogen in a high volumetric energy density molecule under ambient conditions (Fig. 6.2a). In this hydrogen storage architecture: (i) H atoms are added to an LOHC molecule through thermochemical hydrogenation (150 oC, 50 bar); (ii) H atoms are stored and transported in the LOHC in existing liquid-fuel infrastructure; and (iii) H atoms are stripped from the LOHC through thermochemical dehydrogenation (300 oC, 1 bar) at the location of use.190 The LOHCs that are generally employed are aromatic hydrocarbons because they have high energy storage capacities (e.g., can store >6 H atoms per molecule). This process is currently being developed at pilot scales (e.g., Hydrogenious HydroStore system).   An alternative infrastructure to conventional LOHC storage could include the incorporation of an ePMR for producing H atoms and the subsequent hydrogenation step, and the dehydrogenation of the LOHC (Fig. 6.2b). The benefits of an ePMR for this application is that the hydrogenation and dehydrogenation could be performed at lower temperatures and pressures, and implemented at smaller scales (e.g., at H2 gas fueling stations). Studies have shown that hydrogenation of aromatic hydrocarbons such as toluene to benzene proceeded at conversions of >90% at 100 oC.39 There has only been one example of dehydrogenation in an ePMR for the conversion of formic acid to CO2. While this study confirms that dehydrogenation in ePMRs is possible, further studies on dehydrogenation in an ePMR are necessary for this application. Moreover, model compounds with favourable thermodynamics will likely be necessary for enabling dehydrogenation in the ePMR.    105  Figure 6.2 (a) Comparison of liquid hydrogen (cryogenic), liquid organic hydrogen carriers, and gaseous dihydrogen. (b) Schematic diagram of hydrogenation and dehydrogenation of LOHCs in the ePMR for hydrogen fuel cell vehicles  6.2.2 Reactor Designs  One key requirement for each ePMR application discussed in Chapter 6.2.1 is designing reactors that can produce chemicals at a scale of >100 kg\/day. The work described in Chapters 3\u20135 of this thesis have all focused on the use of batch-type reactors (the H-cell and MultiThor architectures), but our research group has also developed a flow cell reactor designed to enable a scalable ePMR (Fig 6.3a).47 The flow cell architecture was inspired by commercial water electrolyzers and hydrogen fuel cell designs. The key benefit of the flow cell architecture is that reactants are delivered to the membrane surface using a pump. This architecture delivers reactant through convection rather than diffusion, improving mass transport kinetics and increasing transport rate by 1000-fold.68 Flow cells are particularly appealing for reactions that are surface limited. For electrochemical reactions, flow cell architectures reduce overpotentials and improve   106 reaction rates without increasing the electrode surface area. The flow cell ePMR has enabled a 15-fold faster reaction rate for alkyne hydrogenation than the H-cell (Fig. 6.3b). Moreover, the flow cell was designed to reduce the gap between the platinum anode and palladium cathode to decrease voltage losses from electrolyte resistance and improve energy efficencies.191 This design enabled water electrolysis to be performed at 400 mA cm-2 instead of 100 mA cm-2 with similar applied voltages (~5.8 and 5.6 V respectively, Fig. 6.3c).47  While the flow cell developed enabled hydrogenation of alkynes and alkenes with no limitations,47 we have had limited success with using the flow cell to hydrogenate other model compounds that are easily hydrogenated in the H-cell (e.g., furfural and propiophenone). Notably, the only modification between the H-cell and flow cell ePMR is the use of a flow plate and pump on the hydrogenation side. The limitations of the flow cell can therefore be attributed to a residence time that is too short. Residence time can be increased in the ePMR by using shallower and wider channels, or by reducing the flow rate of the pump. The former is likely a more significant design consideration in the ePMR because, unlike CO2 or water electrolyzers, an increased number of channel and therefore channel \u201cribs\u201d in the ePMR reduces the active surface area of the palladium thereby reducing activity.   The next step in the ePMR engineering is to scale up the flow cell design based on established water and CO2 electrolyzers. This includes increasing the flow plate geometry to a 5-stack cell that is both energy efficient (<2.2 V, 11 V for the 5-cell stack) and can operate at high current densities (>100 mA cm-2, 50 A for the stack). In order to achieve these parameters, high surface area electrodes that are placed close together are required to ensure low internal resistances, and optimized flow plate channel geometries are required to accommodate high solution viscosities and flow rates (Fig 6.3d, e, f). A flow plate added to the electrochemical compartment   107 can also facilitate removal of O2 formed at the anode and ensure electrolyte volume is kept constant.  A key design consideration for the scaled-up ePMR will be mitigating excess H2 gas formation on both sides of the Pd membrane. While >98% H permeation is possible at current densities <50 mA cm-2,1 as current density is increased, HER in the electrochemical compartment occurs, even in the flow cell architecture.47 A low pressure applied to the electrochemical compartment (e.g., <9 bar) can reduce HER on the electrochemical side by 5-fold to enable a higher H permeation and hydrogenation rates in the ePMR.39 Another option for removing H2 formed in the electrochemical compartment is to ensure the anode and cathode are close together such that the H2 produced at the cathode is consumed in a hydrogen oxidation reaction (HOR) at the anode. This process would effectively reduce the overpotential of the cell and remove any excess H2 formed.    108  Figure 6.3 (a) Rendering of flow cell developed for developing a scalable ePMR. (b) Comparison of hydrogenation reaction of 0.1 M phenylacetlyene in an H-cell and flow cell ePMR demonstrating a 15-fold increase in reaction rates. (c\u2013e) Schematic diagram showing the upgrades that are required for the flow cell reactor to enable higher energy efficiencies. Plots in (b) and (c) were adapted from Jansonius et al.47  6.2.3 Membrane Designs  The palladium membrane in ePMRs must enable high hydrogen permeation, high mechanical stability, and low cost. These criteria can be achieved by developing porous supported Pd alloy membranes similar to those developed for tPMRs (see Ch. 2.3.2.1, Fig. 2.6). An key   109 additional requirement for the ePMR is that liquid transport on both sides of the palladium layer must occur quickly to ensure low voltages and high hydrogen permeation.2 An ideal supported palladium membrane would have a thin layer of palladium (<1 \u00b5m) deposited on a support layer (<50 \u00b5m) that must be compatible with the solution in the electrochemical or hydrogenation compartments.  I performed a simple technoeconomic analysis and found that a Pd membrane with 1 \u00b5m thickness and geometric surface area of 1 m2 could achieve a hydrogenation rate of 0.3 M gPd\u20131 s\u20131. This rate suggests that a reactor that produces 1 L h\u20131 requires 600 g of palladium. The current cost of palladium is ~$62 g\u20131, and a 1 L h\u20131 reactor would therefore cost ~$40k. In Chapter 5, a hydrophobic support layer in combination with a non-polar solvent was shown to enable hydrogenation rates comparable to a 25 \u00b5m palladium foil membrane.2 However, the Pd\/PTFE membranes had to be replaced after ~3 days of reaction suggesting that this design would not be feasible at large scales. Moreover, the support layer would not transport polar solvents (e.g., MeOH or water) meaning that it could only be set up in one configuration (i.e., support facing the hydrogenation side). This is a limitation of the Pd\/PFE membranes because the hydrogen desorption or hydrogenation steps of hydrogen permeation are known to be rate-limiting in the ePMR (see Ch. 3). Therefore, a support layer that faces the electrochemical side would likely be more effective.  A palladium membrane designed with the support facing the electrochemical compartment must enable: (i) fast proton transport to the Pd cathode; and (ii) high energy efficiencies at current densities >100 mA cm-2. One method for achieving high energy efficiencies and current densities is to develop an ePMR membrane electrode assembly (MEA). In this configuration, a polymer electrolyte (<125 \u00b5m) is sandwiched in between an anode composed of a high surface area catalyst   110 and the palladium membrane.192 MEAs designed for water electrolyzers have been shown to operate at high current densities (>1 A cm2) while enabling low cell voltages (<2 V).193 MEA designs implemented in the ePMR flow cell architecture with a high surface area catalyst on both sides may enable operation at similar current densities and voltages to established water electrolyzers. 6.2.4 Catalyst Design There have been a number of studies (including Ch. 5) that demonstrate the benefits of modifying the catalyst layer on the hydrogenation side of the ePMR.48,49 One key finding was that depositing Pd nanocubes of varying sizes onto a bare Pd foil could enable control over reaction selectivity.48 Our group has also found that sputter-deposition of a thin layer (10 nm) of secondary Pt catalyst on the high surface Pd black layer could enable an increase in acetophenone reactivity from 5% to 55% after 8 h of reaction.49 This increase in reactivity may be due to the stronger adsorption of hydrogen to the bimetallic PdPt catalyst relative to Pd.176 These studies demonstrate the importance of catalyst design for improving reactivity and selectivity, which is crucial for hydrogenating the more challenging substrates discussed in Chapter 6.2.1.  An additional advantage of secondary catalysts (which has not yet been explored in the ePMR) is the ability to prevent catalyst deactivation and poisoning. The deposition of Pt, Au, or Cu on a palladium catalyst to form a Pd surface alloy has been shown to reduce poisoning and deactivation of various contaminants (e.g., CO, sulfur) in tPMRs.194,195 These secondary catalysts will be particularly important for ePMR applications such as hydrogenation of biomass derivatives (e.g., biocrude oil and furfural) because the starting materials can contain significant impurities that poison palladium.159 Hydrogen peroxide production (specifically through the direct method) also suffers from catalyst design challenges due to catalyst degradation that   111 occurs due to H2O2 reaction with the catalyst.196 These challenges have been addressed by established industrial thermochemical reactor designs, and can inform the development of catalysts for the ePMR.     112 References (1)  Sherbo, R. 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A Pt mesh anode is used in the right electrochemical compartment.    125  Figure A1.2 Impact of electrodeposited palladium catalyst on electrochemical surface area.  Double-layer capacitance measurements of (a) the palladium foil membrane and (b) electrodeposited palladium on palladium foil to demonstrate that the 2 electrochemically active surface area of the foil increases by a factor of 277 after palladium electrodeposition. The dotted lines represent lines of best fit for the five data points.   Figure A1.3 Hydrogenation reaction with and without a catalyst on the hydrogenation side. Gas chromatography-mass spectrometry (G-CMS) measurements of the hydrogenation reaction of 1-hexyne to 1-hexene, n-hexane and (E)- and (Z)-3-hexene with (a) bare palladium foil and (b) palladium foil with an electrodeposited palladium catalyst on the hydrogenation side of the foil. Aliquots were sampled every 2 h starting at t=0 (teal) to t=8 (pink) (a) and every 1 h starting at t=1 (teal) to t=4 (pink) (b) . The reaction was run at 50 mA (40.1 mA cm-2) applied current with 1 M H2SO4 electrolyte and pentane solvent.   126   Figure A1.4 Oxidation reaction with and without the TEMPO redox mediator. 1H NMR measurements (400 MHz, D2O, 298 K) of the alcohol oxidation of anisyl alcohol (pink) to anisaldehyde (blue) during paired electrolysis without TEMPO. Aliquots were sampled every hour for 5 h. Benzene-1,3,5-tricarboxylic acid was added as an internal standard (green).     127  Figure A1.5 Product conversion and distribution in paired electrolysis at varied applied currents.  Reactant consumption and product formation for (a) the 1-hexyne hydrogenation reaction and (b) the anisyl alcohol oxidation reaction for paired electrolysis at a 25 mA applied current (20.5 mA cm-2) over the course of a 12 hour experiment; (c) the 1-hexyne hydrogenation reaction and (d) the anisyl alcohol oxidation reaction for paired electrolysis at a 75 mA applied current (61.5 mA cm-2) over the course of a 4 hour experiment. 1 M KHCO3 was used as the electrolyte and pentane was used as the solvent.    128  Figure A1.6 Hydrogenation reaction rate in paired electrolysis at varied applied current. The reaction rate at an individual applied current is determined by plotting 1-hexyne consumption (the inverse slope of 1hexyne concentration) vs. time during the initial 24 h of the experiment. The reaction rate for each experiment is plotted vs. applied current. The dotted line represents a line of best fit for the four data points.   Figure A1.7 Paired electrolysis reaction progress with 50 mA applied current (40.1 mA cm-2). (a) GC-MS measurements of the hydrogenation reaction of 1-hexyne to 1-hexene, n-hexane and (E)- and (Z)-3-hexene during paired electrolysis. Aliquots were sampled every hour starting at t=0 (teal) to t=5 (pink). (b) 1H NMR measurements (400 MHz, D2O, 298 K) of the alcohol oxidation of anisyl alcohol (pink) to anisaldehyde (blue) during paired electrolysis. Aliquots were sampled every hour for 5 h. Benzene-1,3,5-tricarboxylic acid was added as an internal standard (green). The reaction was run at 50 mA applied current (40.1 mA cm-2) with 1 M KHCO3 electrolyte and pentane solvent.   129  Figure A1.8 Paired electrolysis reaction progress with 25 mA (20.5 mA cm-2) applied current. (a) GC-MS measurements of the hydrogenation reaction of 1-hexyne to 1-hexene, n--hexane and (E) and (Z)-3-hexene during paired electrolysis. Aliquots were sampled every 2 h starting at t=0 (teal) to t=12 (pink). (b) 1H NMR measurements (400 MHz, D2O, 298 K) of the alcohol oxidation of anisyl alcohol (pink) to anisaldehyde (blue) and anisic acid (orange) during paired electrolysis. Aliquots were sampled every 2 h for 12 h. Benzene-1,3,5-tricarboxylic acid was added as an internal standard (green). The reaction was run at 25 mA applied current (20.5 mA cm-2) with 1 M KHCO3 electrolyte and pentane solvent.   Figure A1.9 Paired electrolysis reaction progress with 75 mA (61.5 mA cm-2) applied current. (a) GCMS measurements of the hydrogenation reaction of 1-hexyne to 1-hexene, n--hexane and (E)- and (Z)-3-hexene during paired electrolysis. Aliquots were sampled every hour starting at t=0 (teal) to t=4 (pink). (b) 1H NMR measurements (400 MHz, D2O, 298 K) of the   130 alcohol oxidation of anisyl alcohol (pink) to anisaldehyde (blue) during paired electrolysis. Aliquots were sampled every hour for 4 h. Benzene-1,3,5-tricarboxylic acid was added as an internal standard (green). The reaction was run at 75 mA applied current (61.5 mA cm-2) with 1 M KHCO3 electrolyte and pentane solvent.      131 Appendix 2: Chapter 4 A2.1  Supplementary Figures  Figure A2.1 Prepared PTFE supports attached to a Kapton mask (4\u2033 diameter) for mechanical support. The Tetratex PTFE support shown has a 0.05 \u00b5m pore size and 25.4 \u00b5m thickness. Circular cutouts in the Kapton mask correspond to one testable membrane (geometric surface area = 1.22 cm2).  Figure A2.2 Solvent droplet images demonstrating the wettability of the PTFE support to solvents with varying polarities (H2SO4 being the most polar and pentane being the most non-polar). The Tetratex PTFE support shown has a 0.05 \u00b5m pore size and 25.4 \u00b5m thickness. The Kapton mask was attached for mechanical support.    132  Figure A2.3 Liquid permeation measurements through porous alumina supports (commonly used in gas-fed palladium membrane reactors) and porous PTFE supports (proposed for electrocatalytic palladium membrane reactors). (a) Photograph of experimental setup and (b) liquid permeation rates through each support in solvents with varying polarities (H2O being the most polar and pentane being the most non-polar). Error bars indicate standard deviations of measurements (n=6 replicates). The Tetratex PTFE and Coorstek alumina supports both have 0.1 \u00b5m pore size and 74 \u00b5m and 1 mm thicknesses, respectively.  Table A2.1 Liquid permeation measurements of solvents with different polarities through alumina and through PTFE supports with different pore sizes and thicknesses. PTFE  (pore size, thickness) Permeation rate (mL\/h) H2O MeOH DCM Pentane 0.05 \u00b5m, 25.4 \u00b5m 0.0 0.25 1.1 6.7 0.1 \u00b5m, 74 \u00b5m 0.0 0.32 1.1 5.5 0.2 \u00b5m, 66 \u00b5m 0.0 0.30 1.3 7.5 Alumina  (0.1 \u00b5m, 1 mm) 0.13 0.08 0.15 0.11    133  Figure A2.4 SEM images demonstrating relationship between palladium layer surface coverage and support pore size. 1 \u00b5m palladium sputter-deposited on Tetratex PTFE with support pore sizes (a) 0.05 \u00b5m, (b) 0.1 \u00b5m, and (c) 0.2 \u00b5m. Corresponding PTFE thicknesses are 25.4 \u00b5m, 74 \u00b5m, and 66 \u00b5m, respectively. No visible pinholes >100 nm were seen on the 0.05 \u00b5m pore size, 25.4 \u00b5m thickness PTFE support.  Figure A2.5 SEM images demonstrating the relationship between palladium layer surface coverage and sputtering pressure. ~1.5 \u00b5m palladium sputter-deposited on a 0.05 \u00b5m pore size PTFE membrane with sputtering pressures (a) 1\u00d710\u20133 torr, (b) 2\u00d710\u20133 torr, and (c) 2\u00d710\u20132 torr. Both 1\u00d710\u20133 torr and 2\u00d710\u20133 torr sputtering pressures resulted in a continuous palladium film with no pinholes >100 nm and sputtering pressure of 2\u00d710\u20132 torr produced a non-continuous film with columnar Pd grains. Sputtering pressure of 1\u00d710\u20133 torr resulted in a brittle film with cracks across the entire membrane.    134  Figure A2.6 Electrocatalytic palladium membrane cell architecture with Pd\/PTFE configured such that the PTFE support faced (a) the electrochemical compartments and (b) the hydrogenation compartment. (c) Voltage of cell for Pd\/PTFE configuration shown in (b). The Pd\/PTFE configuration in (a) caused a termination of program and \u201310 V limit (not shown). A 100 mA current (82 mA cm-2) was applied in both cases.   135  Figure A2.7 Hydrogen flux measurements in the electrolytic Pd\/PTFE membrane reactor. (a) Cell setup for atmospheric mass spectrometer data. Ion current at 2 m\/z (H2) as a function of time in both compartments with (b) pentane, (c) H2SO4, (d) MeOH, and (e) DCM in the chemical compartment. 100 mA current (82 mA cm-2) was applied at t=0\u2013300 s. Equilibrated ion currents were used to calculate the ratio of chemical:electrochemical H2 evolution.     136   Figure A2.8 (a) Cell architecture and (b) measurements for hydrogen flux in the electrolytic Pd\/PTFE membrane reactor for different thicknesses of Pd (1 \u00b5m, 1.5 \u00b5m, 2 \u00b5m, and 3.5 \u00b5m) with 1 M H2SO4 on both sides of the membrane.   Figure A2.9 GC\u2013MS measurements of the hydrogenation reaction of 1-hexyne to 1-hexenes (labelled -ene) and n-hexane (labelled -ane) using (a) Pd\/Pd foil and (b) Pd\/PTFE membranes. Aliquots were sampled every 2 h starting at t=0 (teal) to t=8 (orange). The reaction was run at 50 mA applied current (40.1 mA cm-2) with 1 M H2SO4 in the electrochemical compartments and pentane in the chemical compartment.     137  Figure A2.10 (a) Cell architecture and (b) voltages required to hydrogenate using Pd\/Pd foil and Pd\/PTFE membranes in 1-hexyne reaction. A 50 mA current was applied (40.1 mA cm-2).     Figure A2.11 (a) Cell configurations and (b) double-layer capacitance measurements of Pd foil, Pd\/Pd foil and Pd\/PTFE cathodes. (c) Specific capacitance values calculated from measured data in (b). The dotted lines represent lines of best fit for the five data points. The geometric surface area of all cathodes was 1.22 cm2.     138  Figure A2.12 Stability tests for a single Pd\/Pd foil (a, b, c) and Pd\/PTFE membrane (d, e, f) in the electrolytic membrane reactor. (a, d) Three hydrogenation cycles of 1-hexyne in pentane for 8 hours of reaction. (b, c) Photographs of the Pd foil membrane before and after 3 cleaning\/electrodeposition cycles (~9 hydrogenation cycles). A small pinhole formed in the foil during the third cleaning cycle. (e, f) SEM images of the Pd\/PTFE membrane before and after 3 reaction cycles showing cracks on the membrane after the third cycle. All reactions were run at 50 mA applied current (40.1 mA cm-2) with 1 M H2SO4 in the electrochemical compartments.        139  Figure A2.13 ICP\u2013OES measurements after 1\u20133 hydrogenation cycles with the Pd\/PTFE membranes (hollow dots) and calibration curves (solid dots) for three emission spectra at 361 nm (blue), 340 nm (purple), and 324 nm (orange). (a) Calibration curves used to determine sample concentration. (b) A region between 0 and 0.125 ppm Pd concentration in which all three samples reside. A line of best fit is plotted on each of the calibration curves and was used to determine the sample concentrations.    140  Figure A2.14 (a) Initial 3 h of consumption of 6-chloro-1-hexyne in pentane, DCM, and MeOH using the Pd\/Pd foil membrane. Corresponding product quantification in (b) pentane, (c) DCM, and (d) MeOH. GC\u2013MS chromatograms in (c & d) show hydrogenation of 6-chloro-1-hexyne (labelled -yne) to 6-chloro-1-hexene (labelled -ene) and 6-chlorohexane (labelled -ane). 1H NMR (25 \u00b0C, 400 MHz) in (d) shows hydrogenation of 6-chloro-1-hexyne (blue) to 6-chloro-1-hexene (purple) and 6-chlorohexane (orange). Green peaks indicate a mixture of alkyne, alkene, and alkane. A dimethylsulfone internal standard is shown as a singlet peak at ~3 ppm. A 50 mA current (40.1 mA cm-2) was applied in all cases.   141  Figure A2.15 (a) Reaction progress and (b) GC\u2013MS chromatograms for hydrogenation of 6-chloro-1-hexyne (labelled -yne) to 6-chloro-1-hexene (labelled -ene) and 6-chlorohexane (labelled -ane) in pentane using the Pd\/PTFE membrane. A 50 mA current (40.1 mA cm-2) was applied.   Figure A2.16 (a) Reaction progress and (b) GC\u2013MS chromatograms for hydrogenation of 6-chloro-1-hexyne (labelled -yne) to 6-chloro-1-hexenes (labelled -ene) and 6-chlorohexane (labelled -ane) in pentane using the Pd\/PTFE membrane. A 50 mA current (40.1 mA cm-2) was applied.   142  Figure A2.17 (a) Reaction progress and (b) 1H NMR (25 \u00b0C, 400 MHz) for hydrogenation of 6-chloro-1-hexyne (blue) to 6-chloro-1-hexenes (purple) and 6-chlorohexane (orange) in MeOH using the Pd\/PTFE membrane. Green peaks indicate a mixture of alkyne, alkene, and alkane. A dimethylsulfone internal standard is shown as a singlet peak at ~3 ppm. A 50 mA current (40.1 mA cm-2) was applied.   Figure A2.18 Normalized 6-chloro-1-hexyne hydrogenation data. (a) Cell architecture using the Pd\/PTFE membrane reactor and (b) normalized 6-chloro-1-hexyne consumption rates in pentane, DCM, and MeOH with the Pd\/Pd foil membrane (light purple) and Pd\/PTFE membrane (dark purple). Plot inset in (b) shows small variation in Pd\/Pd foil consumption rates. A 50 mA current (40.1 mA cm-2) was applied in both cases and normalized consumption rate was determined for the first 3 h of reaction.      143  Figure A2.19 Measurements of electrochemical surface area (ECSA) on both sides of the Pd\/PTFE membrane. Cell configurations for measurements of ECSA at (a) the Pd\u2013PTFE interface and (b) the Pd interface. (c) Double-layer capacitance measurements using both configurations. The dotted lines represent lines of best fit for the five data points. The specific capacitance values of the Pd\u2013PTFE and Pd interfaces were 0.451 mF cm-2 and 0.139 mF cm-2, respectively. The geometric surface area of the Pd\/PTFE cathode was 1.22 cm2.       144 Appendix 3: Chapter 5 A3.1  Furfural Proof-of-Concept Reaction in an H-cell   Initial proof-of-concept hydrogenation of furfural was performed in a two-compartment H-cell reactor consisting of an electrochemical and hydrogenation compartment (Fig. A3.1a). These compartments were filled with 30 mL of 1 M H2SO4 and 0.25 M furfural dissolved in n-BuOH, respectively. A current of 45 mA was applied across the Pd foil cathode (geometric surface area of 1.22 cm2 on both sides, 37 mA cm-2) and Pt anode. A sample taken after 12 h of reaction showed that ~30% furfural was hydrogenated to form FA, THFA, and >6 products with higher retention time.   Figure A3.1: Proof-of-concept furfural hydrogenation experiment in an H-cell. (a) Schematic diagram of the H-cell electrocatalytic palladium membrane reactor architecture. (b) Gas chromatography\u2013mass spectrometry measurements of furfural (FF) hydrogenation to furfuryl alcohol (FA), tetrahydrofurfuryl alcohol (THFA), and other products. A current of 45 mA was applied (37 mA cm-2) for 12 h. The Pd foil membrane had a geometric surface area of 1.22 cm2.     A3.2  MultiThor Construction and Assembly The custom components of MultiThor were designed in Solidworks computer aided design (CAD) software, and manufactured in-house (Fig. A3.2). The hydrogenation compartment was machined from a block of polyetheretherketone (PEEK), and the electrochemical compartment was printed with a stereolithography (SLA) 3D Form 3 printer (made by Formlabs). The 3D print   145 enabled the inclusion of complex internal features and flow channels that otherwise would not be possible to manufacture from conventional machining techniques. The electrochemical compartment contained an inlet flow channel that split into six individual tubes to direct electrolyte vertically towards each of the six wells (to aid H2 bubble dispersion). The electrochemical compartment also contained 2 mm diameter horizontal flow channels that directed bubbles away from the Pd surface towards the electrolyte outlet (Fig. A3.3). The electrochemical compartment was printed from Formlabs proprietary clear V4 resin. The resin was chosen for its transparent optical properties, chemical resistance to the electrolyte, and watertight surface finish. Post-processing (e.g., wet sanding, thread chasing, and hole reaming) was required to fit and finish the compartment after printing and curing. Quick-turn polycarbonate couplings (\u00bc-28\u2033) were used to attach tubing from the electrochemical compartment to the pump and reservoir. Female threads were printed into the cell to fit these couplings (metal threaded inserts were not used because they are incompatible with the electrochemical process). The catalyst coated Pd membrane was sealed between the hydrogenation and electrochemical compartments by custom laser-cut 1\u204416\u2033 thick Fluorosilicone gaskets. Two \u215c\u2033 thick stainless steel plates sandwiched the two compartments, and eight 4 mm diameter bolts provided the clamping force to seal the internal gaskets (these bolts thread into the bottom plate). Two internal 5 mm diameter stainless steel locating pins were pressed into the bottom plate; these allowed precise assembly and disassembly of the cell. The Pt anode was shielded by a Teflon body (\u00bc\u2033 outer diameter), which was press-fitted into one side of the electrochemical compartment to provide a water-tight seal (a Viton o-ring and bracket was used to provide an additional seal against the Teflon body of the electrode). A \u215c\u2033 thick laser-cut acrylic panel was bolted to the bottom face of the electrochemical compartment to provide a viewing   146 window (sealed with a Viton o-ring). The viewing window enabled visual monitoring of H2 bubble dispersion during experiments.   Figure A3.2: Exploded view of MultiThor assembly.   Figure A3.3: Electrochemical compartment of MultiThor with electrolyte flow channels: (a) side view; (b) top view; and (c) bottom view. Electrolyte flow to the Pd foil is highlighted in blue. Arrows indicate direction of electrolyte flow into and out of MultiThor. The pump is set at a flow rate of 250 mL min-1. The flow channels were designed to remove excess H2 bubbles formed during water electrolysis at the Pd foil surface on the electrochemical side of the reactor.     147  A3.3  MultiThor Control Experiments Table A3.1: A qualitative comparison of the MultiThor and H-cell electrocatalytic palladium membrane reactor architectures based on the exposure of the hydrogenation solution to the catalyst surface.   H-cell MultiThor Geometric surface area (SA) 1.22 cm2 0.43 cm2 Hydrogenation compartment volume (V) 30 mL 1 mL Ratio of surface area:volume (SA\/V) ~0.04 cm2 mL-1 0.43 cm2 mL-1 SA\/V for MultiThor:H-cell \u2013 ~10 Initial furfural consumption rate 6.3 \u00b5mol h-1 64.8 \u00b5mol h-1  A3.3.1 Hydrogen Distribution  I tested hydrogen evolution on both sides of the Pd membrane to confirm that hydrogen permeation was evenly distributed across the six wells of the reactor (Fig. A3.4a). For these tests, a Pd\/Pd membrane was placed in MultiThor, the hydrogenation wells were filled with 1 mL of n-BuOH, and a current of 75, 150, 225, or 300 mA (18.75, 37.5, 56.25, 75 mA cm-2, respectively) was applied for 1 h. An atm-MS was used to measure the relative amount of H2 evolved in each hydrogenation well and the electrochemical compartment, with hydrogen flux being defined as the amount of H2 evolved in each well per unit time (Fig. A3.4b). Experiments performed with applied currents of 75, 150, and 225 mA (18.75, 37.5, 56.25 mA cm-2, respectively) showed hydrogen fluxes within error for each applied current (0.23 \u00b1 0.01 mmol h-1, 0.45 \u00b1 0.03 mmol h-1, and 0.65 \u00b1 0.03 mmol h-1, respectively). An applied current of 300 mA (75 mA cm-2) resulted in hydrogen fluxes ranging from 0.62 mmol h-1 to 0.78 mmol h-1 for wells 1\u20136. Although the hydrogen flux between wells fluctuated at 300 mA, fluxes within each well were still consistent (e.g., well 1 consistently showed a hydrogen flux of ~0.76 mmol h-1 for 3 different foils). I also found that   148 ~15% of H2 evolved in the electrochemical compartment at 300 mA, compared to <5% H2 at \u2264225 mA. One possible explanation for these results is that at 300 mA, H2 bubble formation blocked hydrogen from permeating, particularly the middle wells (well 3 and 4; Fig. A3.4c). Based on this finding, applied currents of \u2264225 mA (\u226456.25 mA cm-2) were used for all hydrogenation experiments.  Figure A3.4: Hydrogen flux measurements for the 6 wells of MultiThor at different applied currents. (a) Schematic diagram of reactor setup with inset showing well position labelled 1\u20136. (b) Hydrogen (H2) flux for each well at 75, 150, 225, and 300 mA (18.75, 37.5, 56.25, 75 mA cm-2, respectively). (c) Schematic diagram showing ~15% H2 bubble build up at an applied current of 300 mA (75 mA cm-2) compared to <5% bubble build up at \u2264225 mA (\u226456.25 mA cm-2). H2 flux was determined by atm\u2013MS measurements of the ratio of H2 evolved on the hydrogenation:electrochemical compartments.  A3.3.2  Hydrogenation Distribution The hydrogenation of 0.25 M furfural in n-BuOH was used as a proof-of-concept reaction to confirm that the rate of reaction was similar between wells (Fig. A3.5). A Pd\/Pd membrane was placed in the MultiThor and a current of 150 mA (37.5 mA cm-2) was applied for 2 h. Reaction   149 progress was monitored using gas chromatography\u2013mass spectrometry (GC\u2013MS) by taking 30-\u00b5L aliquots from each well after 0, 0.5, 1, and 2 h. GC\u2013MS measurements showed that hydrogenation proceeded at similar rates (<3% difference in furfural consumption) for wells 1\u20136, respectively (Fig. A3.5). These data confirmed that hydrogenation occurs at similar rates across the six wells under the stated reaction conditions.   Figure A3.5: Furfural hydrogenation in the 6 wells of MultiThor. (a) Schematic diagram of reactor setup and (b) initial furfural consumption for 2 h of reaction in each well.  A3.4  Additional Membrane Preparation and Characterization  A3.4.1  Sputter-Deposition Procedure An additional layer of catalyst was sputter-deposited on the Pd\/Pd membranes based on previously reported procedures.49 A Leica EM MED020 coating system was used to sputter-deposit Pt, Ir, Cu, Ag, and Au and a Univex 250 RF magnetron sputter system with an Onyx-2 IC Mag II cathode was used to deposit Ni. Pd\/Pd membranes were placed at a working distance of 6   150 cm and the chamber was evacuated to a base pressure of 1.5\u00d710\u20134 mbar (and 12 cm, 5\u00d710\u20136 mbar, respectively for Ni). After the base pressure was reached, Ar was directed into the chamber at a continuous flow rate to maintain a pressure of 1\u00d710\u20132 mbar, the plasma was ignited, and voltage was adjusted to maintain a constant current of 80 mA for Ir, and 30 mA for Au, Ag, Cu, and Pt. The RF power was held at 100 W for Ni. A pre-sputter of 30 s (1 min for Ag and 6 min for Ni) was followed by the opening the target shutter and sputter-deposition of 10, 20, or 50 nm of metal catalyst onto the Pd\/Pd membrane. The sputter rates were 0.2 nm\/s (Pt, Cu, and Ni) and 0.3 nm\/s (Ir, Au, and Ag), as determined by in situ quartz crystal microbalance. Once deposition was complete, the shutter was closed, chamber vented, and catalyst coated Pd membranes were removed from the deposition plate. A3.4.2  Electrochemical Surface Area Measurements ECSA measurements of three different Ir\/Pd\/Pd membranes (geometric surface area of 4 cm2) with 0, 20, and 50 nm of sputter-deposited Ir catalyst were performed in the one-compartment electrochemical cell. The compartment was filled with 15 mL of 0.15 M TBA-PF6 in acetonitrile. A leak-free Ag\/AgCl reference electrode using a leakless junction (eDAQ ET072) was used for ECSA measurements. The electrode was rinsed with Milli-Q water prior to use and referenced vs. 4.0 M KCl glass-body Ag\/AgCl master reference electrode (Fisher Scientific 13-620-53) by measuring the open circuit potential between both electrodes in a saturated KCl solution. The master electrode was stored in a KCl solution when not in use. A 1 cm2 Pt mesh counter electrode was used and cyclic voltammograms were performed at various scan rates (10 to 100 mV s\u22121) with a potential range of 0.05 to 0.25 V versus Ag\/AgCl. Current versus scan rates were plotted at 0.49,   151 0.47, and 0.52 V versus Ag\/AgCl (the open circuit voltages) for 0, 20, and 50 nm, respectively. The slope of the plot was used to measure double-layer capacitance (Fig. A3.6).  I have previously reported double-layer capacitance values for Pd\/Pd membranes with no additional sputter-deposited catalysts (i.e., 0 nm) of ~8.0 mF cm-2 using the same deposition method and parameters, and ECSA measurement procedure.1,2 ECSA measurements performed on 0 nm catalyst on Pd\/Pd membranes in this study demonstrated a double-layer capacitance of 6.6 mF cm-2 (Fig. A3.6). These collective results indicate that the electrodeposited Pd catalyst on Pd membranes can vary in surface area by approximately \u00b11.7 mF cm-2. The double-layer capacitance values for 0, 20, and 50 nm thick sputter-deposited catalysts on the Pd\/Pd membranes were within an error of \u00b10.6 mF cm-2. These findings suggest that the difference in double-layer capacitance values can be attributed to the underlying high surface area Pd catalyst, with little to no change in surface area from the sputter-deposited catalysts. Based on these results, ECSA was calculated for Pd\/Pd membranes by dividing double-layer capacitance by specific capacitance of Pd. Specific capacitance was calculated using bare Pd foil because it embodies an atomically smooth planar Pd surface.197,198 ECSA calculations indicated that the Pd\/Pd membranes have a chemical surface area that is 218 \u00b1 23\u00d7 larger than bare Pd foil.       152  Figure A3.6: Electrocatalytic surface area (ECSA) measurements for different thicknesses of Ir sputter-deposited on Pd\/Pd membranes. (a) CV scans near the open circuit potential (OCP; 0.52 V) for Ir catalyst (50 nm). (b) Double-layer capacitance measurements of Ir\/Pd\/Pd membrane (0, 20, and 50 nm Ir thicknesses). The open circuit voltages were 0.49, 0.47, and 0.52 V for 0, 20, and 50 nm, respectively. Double-layer capacitance values were calculated based on measured data. The dotted lines represent lines of best fit for the 9 data points. The geometric surface area of all cathodes was 4 cm2.   A3.4.3  X-ray Fluorescence Spectroscopy   Hyperspectral XRF images of the catalyst coated Pd membranes were taken using a Bruker M4 TORNADO XRF microscope (Fig. A3.7). The XRF microscope has a Rh X-ray source operated at 50 kV\/600 \u00b5A\/30 W and polycapillary X-ray optics yielding a 25-\u00b5m spot size on the sample. The instrument employs twin 30 mm2 silicon SSD detectors and achieves an energy resolution of 10 eV. Hyperspectral images were taken over a 641\u00d7231 mm2 area at a resolution of 750\u00d7270 pixels. The instrument generates a peak at exactly zero energy which is used for energy calibration. Each point measurement was integrated for 50 ms. The spectral energy is binned at 10 eV. Spectra was acquired from 0 to 40 keV and integrated over the following ranges: Pd: 2.632 to 2.892 keV (K\u03b1); Ni: 7.358 to 7.588 keV (K\u03b1); Au: 9.579 to 9.830 (L\u03b1); Cu: 7.925 to 8.162 keV (K\u03b1); Ir: 9.106 to 9.232 keV (L\u03b1); Pt: 9.374 to 9.498 keV (L\u03b1). Each element was visualized with a colour scale extending to the data bounds, with the exception of the following elements where   153 the maximum was set manually for an improved visualization: Ni: 2.5\u00d7105 cps; Cu: 2\u00d7106 cps; Au: 5\u00d7105 cps. XRF images of Ag were not obtained because the L\u03b1 Ag lines were obscured by the higher intensity L\u03b1 Pd lines.     Figure A3.7: X-ray fluorescence (XRF) images for three prepared Pd foils. (a)\u2013(f) XRF images of: (i) electrodeposited Pd catalyst on Pd foil membrane (Pd\/Pd membrane); (ii) Pd\/Pd membrane with 20 and 50 nm of sputtered catalysts (Ir  (b), Pt (f)); and (iii) Pd\/Pd membrane with 10 nm of sputtered catalysts (Ir (b), Au (c), Cu (d), Ni (e), Pt (f), Ag (now shown)).   A3.4.4  Scanning Electron Microscopy  SEM images of 10, 20, and 50 nm of sputter-deposited Pt on Pd\/Pd membranes (Fig. 3.5c) were taken with an FEI Helios NanoLab 650 dual beam SEM at 1 kV and 50 pA using a through-lens detector in secondary electron mode. A HFW of 5.97 mm was exposed in all cases.   154 A3.5  Product Quantification by Gas Chromatography\u2013Mass Spectrometry  Figure A3.8: GC\u2013MS measurements of furfural hydrogenation dissolved in: (a) CHCl3; (b) EtOH; (c) MeOH (d) i-PrOH; (e) n-BuOH; and (f) t-BuOH. Furfural (FF; purple) is hydrogenated to form furfuryl alcohol (FA; blue), tetrahydrofurfuryl alcohol (THFA; green), and other side products (gray). These experiments were performed in MultiThor at 150 mA applied current and Pd\/Pd membrane after 2 h of reaction.      155  Figure A3.9: Furfural reaction pathway in the electrocatalytic palladium membrane reactor showing the acetal products formed when MeOH and EtOH are used as the solvent.           156  Figure A3.10. (a) GC\u2013MS of standard solution containing 2-methylfuran (MF), 2-methyltetrahydrofuran (MTHF), furfural (FF), furfuryl alcohol (FA), and tetrahydrofurfuryl alcohol (THFA). (b) GC\u2013MS of furfural hydrogenation with THFA selectivity at 225 mA using 10 nm Pt\/Pd\/Pd membrane after 8 h of reaction. (c) GC\u2013MS of furfural hydrogenation with FA selectivity at 75 mA using 50 nm Pt\/Pd\/Pd membrane after 8 h of reaction. (d) GC\u2013MS of furfural hydrogenation, where THFA hydrodeoxygenation leads to MTHF production after 24 h at 225 mA using 10 nm Pt\/Pd\/Pd membrane.   A3.6 Influence of current and charge passed on furfural hydrogenation rates  Figure A3.11. Plot of a reaction concentration profile for hydrogenation reaction reaction of furfural to furfuryl alcohol (FA) and tetrahydrofurfuryl alcohol (THFA) carried out at: a) 75 mA; b) 150 mA; and c) 225 mA. The reaction was run with 0.25 M furfural in t-BuOH in the hydrogenation wells, and 10 nm Pd\/Pd membrane.   157  Figure A3.12. (a) Plot of selectivity for furfuryl alcohol (FA) at 75 mA after 8 h. (b) Plot of selectivity for tetrahydrofurfuryl alcohol (THFA) at 225 mA after 8 h of reaction. The reaction was run with 0.25 M furfural in t-BuOH in the hydrogenation wells. The error bars show triplicate experiments.    Figure A3.13. (a) Plot of selectivity for furfuryl alcohol (FA) at equivalent charge passed at 75 mA after 8 h and 225 mA after 2.7 h. (b) Plot of selectivity for tetrahydrofurfuryl alcohol (THFA) at equivalent charge passed at 75 mA after 24 h of reaction and 225 mA after 8 h of reaction. The observed trends suggest that charge passed is not the only factor that influences reactivity and selectivity. The reaction was run with 0.25 M furfural in t-BuOH in the hydrogenation wells and 10 nm of each sputter-deposited on a Pd\/Pd membrane.    158 A3.7 Influence of sputter-deposited catalyst thickness on reactivity   Figure A3.14: Initial consumption rate of furfural for different thicknesses (0, 10, 20, and 50 nm) of (a) Pt and (b) Ir sputter-deposited on a Pd\/Pd membrane. The reaction was run at 75 mA with 0.25 M furfural in t-BuOH in the hydrogenation wells.   Figure A3.15: FA hydrogenation rates with 0, 10, 20, and 50 nm Pt\/Pd\/Pd membrane. The reaction was run at 75 mA applied current with 0.25 M furfural in t-BuOH in the hydrogenation wells.    159  Figure A3.16: Hydrogen flux measurements for 10\u201350 nm of sputter deposited Ir on Pd\/Pd membrane. The reaction was run at 75 mA with t-BuOH in the hydrogenation wells. H2 flux was determined by atmospheric\u2013mass spectrometer measurements of the ratio of evolved H2 on the hydrogenation:electrochemical compartments.  A3.7 Furfural Hydrogenation Without an Electrochemical Bias  A control experiment designed to study whether applying current directly to the palladium membrane affected hydrogenation rates was performed. A 75 mA current was applied across a Pt anode and secondary Pd cathode (i.e., not directly to the palladium membrane) in the MultiThor electrochemical reservoir called \u201cwithout bias\u201d in Fig. A3.17. The pump was set to a flow rate of  250 mL min-1 for 1 h before current was applied to ensure the solution was saturated with H2. The hydrogenation wells were filled with 0.25 M furfural in t-BuOH. The key difference between this configuration and our conventional ePMR setup was that H atoms produced from proton reduction would then form H2 gas in the hydrogen evolution reaction. This H2 gas could then: (i) spontaneously dissociate to form surface-adsorbed H atoms at the Pd membrane surface that then permeate through and participate in furfural hydrogenation; or (ii) bubble away in the electrochemical reservoir. Fig. A3.17 demonstrates that the conversion after 2 h of reaction with and without electrochemical bias was 36% and 6%, respectively. We ascribe this low conversion when a secondary Pd cathode is used to the fact that only a fraction of the hydrogen produced permeates the palladium membrane. Moreover, the use of coordinating electrolyte, H2SO4, has   160 previously been shown to lead to low H2 permeation across the palladium membrane in the ePMR, which may have also led to the low furfural consumption rates.2 This low conversion highlights the importance of applying current directly to the palladium membrane.   Figure A3.17: (a) Schematic diagram showing furfural hydrogenation with and without an electrochemical bias across the palladium membrane. (b) Furfural consumption over 2 h for both cases. For experiments with a bias, a 75 mA current was applied across a Pt anode and the Pd\/Pd membrane in the electrochemical compartment. For experiments without a bias, a 75 mA current was applied across a Pt anode and a secondary Pd cathode placed in the electrochemical reservoir. Both reactions were run with 1 M H2SO4 in the electrochemical compartment and 0.25 M furfural in t-BuOH in the hydrogenation wells.      ","attrs":{"lang":"en","ns":"http:\/\/www.w3.org\/2009\/08\/skos-reference\/skos.html#note","classmap":"oc:AnnotationContainer"},"iri":"http:\/\/www.w3.org\/2009\/08\/skos-reference\/skos.html#note","explain":"Simple Knowledge Organisation System; Notes are used to provide information relating to SKOS concepts. 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