Surface Defects Induced Polarization Manipulation in Cu2SnS3 for Boosting Electrochemical CO2 Reduction

Abstract

Controlling the electrocatalyst's surface polarization is crucial for the interfacial CO2 electrolysis that takes place. Here, we propose an efficient way to increase the electrochemical reduction of CO2 to formate by controlling the Cu2SnS3 surface polarization. This results in a formate partial current density of 408.3 mA cm-2 at an applied bias of -1.2 V vs. RHE and a Faradaic efficiency of 91.7%. More specifically, the concentration of sulfur vacancies is controlled to alter the surface polarization of Cu2SnS3. Theoretical computations and experimental characterizations emphasize the importance of sulfur vacancies in controlling Cu2SnS3's surface polarization. Additionally, the altered CO2 evolution pathway is explained by the local charge redistribution caused by sulfur vacancies, and the lower Gibbs free energy for the formation of intermediate *OCHO which guarantees its high selectivity toward formate is explained by the coordination structural changes of the Cu and Sn atoms involved in deficient Cu2SnS3. This study presents a practical approach to surface polarization regulation-based CO2-to-formate electrocatalyst design.