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Selva Ochoa, Ángela Gabriela

University of British Columbia

Electrochemical reduction of carbon dioxide (CO₂) to useful products could alleviate emissions from industrial processes. To do so, CO₂ electroreduction requires selective and stable catalysts that can be easily synthesized and are cost-effective for their scalability. This thesis investigates the importance of Bi CAU-17 metal-organic framework (MOF) as an electrocatalyst for CO₂ reduction to formate. The advantage of using CAU-17 for its possible application in CO₂ electrolyzers or redox flow batteries is discussed, aiming to reduce carbon emissions and obtain useful products such as chemicals or energy. A novel synthesis method is developed to obtain the Bi-CAU-17, which in situ transforms into a highly active Bi₂O₂CO₃ during the CO₂ reduction to formate. The experimental tests in different electrochemical cells show that this material can successfully perform the CO₂ reduction with an outstanding performance. High formate faradaic efficiencies (FE_{HCOO⁻} = 85–100%) at current densities up to 1 A cm⁻² in a gas diffusion electrode, at low catalytic loading (0.5 mg cm⁻²) are achieved in a GDE H-cell device. Compared with common catalysts, the Bi CAU-17 shows superior electrocatalytic performance at high current densities (>300 mA cm⁻²). Results in a flow cell at 100 mA cm⁻² demonstrate the CAU-17 scalability capacity and the importance of the system's dynamics, such as CO₂ pressure and electrolyte flow rates, reaching a formate selectivity over 80%. The Bi MOF forms a robust and versatile material whose activity stays unaffected in different electrolytes in a broad pH range (8–14) for long periods of time. Intensive characterization analysis (XRD, EDX, SEM) pre- and post-electrolysis highlight the importance of the CAU-17, indicating that this material generates abundant Bi/Bi-O vacancies that promote a selective electroreduction of CO₂ to formate. This thesis finally clarifies the advantages of using this MOF in CO₂ electrolysis to promote the formation of an active Bi₂O₂CO₃ with improved performance compared to previously reported materials. The synthesis methodology to obtain the CAU-17 coupled with the incorporation of a gas diffusion electrode, allows the formation of a stable and reliable structure that explains the advantage of this material over others, a problem that remained undefined until now.

Text

2025-04-22

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90867

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/