Solar-Driven Sulfide Oxidation Paired With CO₂ Reduction Based on Vacancies Engineering of Copper Selenide

Photovoltaic-driven electrochemical (PV-EC) carbon dioxide reduction (CO₂R) coupled with sulfide oxidation (SOR) can efficiently convert the solar energy into chemical energy, expanding its applications. However, developing low-cost electrocatalysts that exhibit high selectivity and efficiency for both CO₂R and SOR remains a challenge. Herein, a bifunctional copper selenide catalyst is developed with copper vacancies (v-CuSe₂) for the CO₂R-SOR. The Faradaic efficiency (FE) of 62.4% for methane at -200 mA cm^-2 is achieved in the cathodic CO₂R. In a two-electrode CO₂R-SOR system with 16 h of long-term operation at a current density of 200 mA cm^-2, an average Faradaic efficiency of 57.2% for methane and 97.7% for sulfur powder generation is achieved at cathode and anode, respectively. Compared to the coupling of CO₂R with oxygen evolution reaction (OER), the energy efficiency (EE) of the CO₂R-SOR system can be increased to 22.9%. The mechanism study has found that the synergistic effect of copper vacancies and introduced Se significantly enhances the selectivity toward methane. Driven by silicon solar cells, a solar-to-methane conversion efficiency of 2% is achieved.