(Digital Presentation) Electrochemical CO₂-to-Formate Conversion on Metastable Tin Oxide Catalyst in a Catholyte-Free Electrolyzer

Abstract

Designing an efficient electrocatalysis system for CO2 conversion to desired value-added products with high selectivity and activity holds promise to enable carbon neutrality and industrial application. Herein, we construct and test two hypotheses: (1) metastable tin oxides play a critical role in enhancing CO2-to-formate conversion rather than metallic tin, and (2) a catholyte-free electrolyzer, where no electrolyte is present on the cathode side, enables highly concentrated formate generation. We prepare tin oxide thin films on a gas diffusion layer by thermal evaporation and confirm the co-existence of SnO and SnO2 on the as-prepared tin oxide films. Annealing in air is used to increase the oxidation of tin prior to starting CO2 electrolysis. In subsequent CO2 electrolysis, we demonstrate that the selectivity for formate is substantially enhanced while parasitic hydrogen evolution reaction is suppressed on the annealed tin oxide electrodes as compared to the as-prepared. The increased selectivity for formate would suggest the presence of metastable tin oxide species during electrolysis favors formation of *OCHO, a key intermediate of formate generation, while suppressing *H and *COOH formation. We also achieve a concentration of formate at the end of 3 hrs electrolysis is > 1 mol L-1. We will describe our latest understanding of the change in surface chemistry modulated by post-heat treatment, providing insights into the role of metastable tin oxide on the highly selective CO2-to-formate conversion.