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

Copper–silica‐based catalysts have drawn much attention for the remarkable product selectivity in the electrochemical CO 2 reduction reaction, particularly toward CH 4 and C 2 H 4 . However, systematic studies exploring the underlying reasons for the selectivity differences are lacking. Herein, Cu/SiO 2 catalysts with different Cu/Si ratio are controllably synthesized by fine‐tuning the precursor ratio, enabling selective CO 2 electroreduction to CH 4 /C 2 H 4 . Specifically, at a current density of 200 mA cm −2 , Cu/SiO 2 ‐10 including majority of CuSiO 3 facilitates the electroreduction of CO 2 to CH 4 with a Faradaic selectivity ratio of CH 4 /C 2 H 4 (9.3/1), whereas Cu/SiO 2 ‐50 primarily consisting of CuO exhibits a Faradaic selectivity ratio of C 2 H 4 /CH 4 (16.7/1). X‐ray photoelectron spectroscopy and in situ Raman spectroscopic characterization reveal that CuSiO 3 in the catalysts remains stable and no valve state change occurs during the reaction, while CuO in the catalysts is reduced in situ to Cu 0 /Cu + during the reaction. In situ infrared spectroscopic and temperature‐programmed desorption of CO characterization further reveal that CuSiO 3 has a stronger protonation capacity and promotes the direct protonation of adsorbed *CO species to CH 4 , while Cu 0 /Cu + is more conducive to the CC coupling between the intermediate species *CHO with adsorbed *CO species to form C 2 H 4 due to the stronger CO adsorption capacity and higher coverage.