In Situ/Operando Insights into the Selectivity of CH4/C2H4 in CO2 Electroreduction by Fine-Tuning the Composition of Cu/SiO2 Catalysts.

Abstract

Copper-silica-based catalysts have drawn much attention for the remarkable product selectivity in electrochemical CO2 reduction reaction, particularly towards CH4 and C2H4. However, there has been a lack of systematic studies exploring the underlying reasons for the selectivity differences. Herein, Cu/SiO2 catalysts with different Cu/Si ratio were controllably synthesized, enabling a selective CO2 electroreduction from CH4 to C2H4. Specifically, at a current density of 200 mA cm-2, Cu/SiO2-10 including majority of CuSiO3 facilitates the selective reduction of CO2 to CH4 with a high Faradaic ratio of CH4/C2H4 (7.2/1), whereas Cu/SiO2-50 primarily consisting of CuO exhibits a higher Faradaic ratio of C2H4/CH4 (17.9/1). XPS and in-situ Raman characterization revealed that CuSiO3 component in the catalysts serves as the active site remains stable and no valve state change occurred, while CuO component was reduced in situ to Cu0/Cu+ as active sites during the reaction. In-situ infrared spectroscopic and CO-TPD characterization further revealed that CuSiO3 has a stronger protonation capacity and promotes the direct protonation of adsorbed *CO species to CH4, while Cu0/Cu+ is more conducive to the C-C coupling between the intermediate species *CHO with adsorbed *CO species to form C2H4 due to the stronger CO adsorption capacity and higher coverage.