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UBC Theses and Dissertations

Fast CO₂ conversion by molecular electrocatalysts Ren, Shaoxuan

Abstract

CO₂ reduction in electrolysers is a promising method to produce carbon-neutral chemicals and fuels. A significant challenge for commercializing this technology is the development of durable and efficient catalysts that selectively generate a single product. Molecular electrocatalysts can potentially mitigate this challenge because of the acute synthetic control over the electronic environment of the active site. These catalysts, however, are typically tested and studied at rates and voltages orders of magnitude lower than what is required for industrial operation. This thesis first demonstrates that a molecular electrocatalyst, cobalt phthalocyanine (CoPc), can mediate fast and selective CO₂-to-CO conversion in a flow cell. This process is made possible by the direct supply of gaseous CO₂ to a customized flow cell architecture. The configuration accommodated current densities exceeding 150 milliamperes per square centimetre (mA/cm²). After this proof-of-concept work, this thesis investigates the mechanism of CO₂ reduction mediated by CoPc molecular catalysts by the use of a marriage of electrochemistry and operando Raman spectroscopy. The mechanistic insights provided clear design principles for immobilized molecular catalysts used in a flow cell. This study also demonstrates that catalyst aggregation is a deciding variable with regard to the distribution of active species in a flow cell. Finally, this thesis studies the CO conversion to higher-value multi carbon product (C₂₊) production mediated by the copper phthalocyanine (CuPc) catalyst layer in a CO electrolyser. A gas diffusion electrode coated with CuPc can effectively electrolyze CO into C₂₊ products at high rates of product formation (i. e., current densities ≥ 200 mA/cm²), and high faradaic efficiencies for C₂₊ production (FEc₂₊; >70 % at 200 mA/cm²). The active species generated during the electrolysis were identified using series of in-situ and ex-situ characterization techniques. These results open the door to use the rich library of metal-complex catalysts accessible in the literature, as well as novel analogues, for efficient CO electrolysis and C₂₊ formation.

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Attribution-NonCommercial-NoDerivatives 4.0 International