UC San Diego

Transforming carbon dioxide (CO2) into valuable chemical feedstocks through electrochemical processes powered by renewable electricity shows promise in achieving carbon neutrality. However, the development of effective and selective catalysts is essential for enabling energy-efficient conversion. The activity and selectivity of the reaction towards formic acid production are governed by the stabilization of the *OCHO intermediate on the catalyst surface. This thesis presents strategies for designing active electrocatalysts that exhibit improved selectivity towards formic acid in CO2 electrolysis by manipulating the chemical environment surrounding the catalyst. Introducing a partial positively charged copper species on the surface in the form of copper sulfide stabilizes the *OCHO intermediate on the catalyst surface. The ligand plays a key role in supplying the proton required for the reduction of CO2 to formate, and that an optimum pKa value ligand is beneficial for improved selectivity towards formate. Another aspect involves tuning the chemical state of tin oxide catalyst surfaces. By favoring a Sn (II) rich initial surface oxidation state, the selectivity and energy efficiency of formate generation are improved, offering a potential near-term solution for carbon-negative CO2 electrolysis. Optimal design of electrolyzers is also crucial for facilitating the mass transport of CO2, thereby increasing industrial relevance. These discoveries underscore the importance of chemical environment surrounding the catalyst, and chemical state in the efficient design of CO2 reduction catalysts to formic acid and providing fundamental guidelines and direction towards achieving carbon- neutral CO2 conversion.