Surface defect 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 characterization studies 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.