UBC Theses and Dissertations
Electrode design for reversible CO₂ reduction and formate oxidation Hakim, Andrew
Scalable carbon dioxide (CO₂) utilization solutions are urgently needed as a result of the continual rise in atmospheric CO₂ concentration brought on by the extensive usage of fossil fuels. To address these issues, the emerging field of electrochemical technologies offers promising solutions for scalable CO₂ utilization. This thesis investigates the design of high-performance bifunctional electrocatalysts for the CO₂ reduction reaction to formate, and formate oxidation reaction in a CO₂ redox flow battery (CRB), in a goal to reduce CO₂ emissions while simultaneously storing renewable energy. A CO₂/formate redox pair at the negative electrode is employed in the CRB. Herein, molecular approaches to heterogenous catalysis are explored for improving the performance of PdSnO₂-based bifunctional catalysts by incorporating polyethyleneimine (PEI) groups to the catalyst layer to increase CO₂ adsorption, stabilize key reaction intermediates, and improve intrinsic catalytic properties. Experimental tests on a variety of electrochemical cells show that PEI-incorporated PdSnO₂ catalysts show superior electrochemical performance compared to pristine PdSnO₂ catalysts. In preliminary batch cell tests, PEI modified catalysts show an increase in formate faradaic efficiency during charge by up to 60% at a 20 mA/cm² current density and increases in peak power densities during battery discharge by 15%. Additionally, under flow cell conditions, the incorporation of PEI to bare PdSnO₂ also shows enhanced discharge power densities and much improved stabilities. The catalytic performance is also further examined in relation to PEI loading, current density, and CO₂ flow rate. Surface characterization techniques including SEM, XPS, XRD and contact angle analysis were performed on several as-prepared and electro-reduced catalytic samples. XPS confirmed the addition of PEI groups in the catalytic layers. It was found that while PEI modification can improve several catalytic properties, it can exacerbate challenges such as flooding and salt precipitation on the electrode surface, especially under flow cell conditions. Despite these difficulties, the bifunctional performance of PdSnO₂ catalysts can be enhanced with PEI modifications and shows good prospects for sustainable energy storage, CO₂ utilization, and mitigating climate change impacts.
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