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UBC Theses and Dissertations

Photodeposited functional thin films Dettelbach, Kevan

Abstract

The conversion of electrical energy derived from clean, renewable, and intermittent sources such as wind and solar into transportable and storable fuels is a means of matching energy supply and demand. Effective electrocatalysts can facilitate these conversions in an economical manner. Our group has developed photodeposition techniques for synthesizing amorphous thin-film metal oxide electrocatalysts. The thicknesses of amorphous metal oxide films were determined by cross-sectional scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). XRF measurements recorded on the films provided a strong linear correlation with the thicknesses determined by cross-sectional SEM. The electrochemical surface area (ECSA) determined by double-layer capacitance measurements did not universally show a linear relationship with film thicknesses. These results highlight the limitations of using ECSA to determine electrocatalyst film thickness. The noninvasive XRF technique is demonstrated to be a superior method for reporting on the thickness and loadings of thin metal oxide films. XRF measurements were made on iron-nickel oxy/hydroxide (FeNiOx) films that are widely known to mediate the oxygen evolution reaction at modest current densities (10 mA cm-²). These measurements enabled the determination of the electrochemical stability and metal composition of these electrocatalyst films when subjected to sustained electrolysis in strong base at a current density J = 200 mA cm-². Most of the iron in the film was liberated during the first 24 h of electrolysis and deposited on the cathode. These results show that one must account for the instability of this mixed-metal composition when drawing structure-property relationships and when considering the scale-up of electrocatalysts. Finally, modifications to the photodeposition technique are demonstrated that enables access to metal and metal alloy thin films. Silver and copper are widely studied metals for catalyzing the CO₂ reduction reaction (CO₂RR), yet studies of Ag-Cu alloys are rare due to the immiscibility of the metals. I report that our photodeposition procedure provides access to Ag-Cu alloys at ambient pressures and temperatures. Our photodeposition procedure is shown to furnish metastable alloys with ~10 atomic weight % (at-%) copper incorporated into the silver lattice. These results provide proof that photodeposition can be used to access kinetic phases of alloys.

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