In Situ/Operando Insights into the Selectivity of CH/CH in CO Electroreduction by Fine-Tuning the Composition of Cu/SiO Catalysts.

Copper-silica-based catalysts have drawn much attention for the remarkable product selectivity in the electrochemical CO reduction reaction, particularly toward CH and CH. However, systematic studies exploring the underlying reasons for the selectivity differences are lacking. Herein, Cu/SiO catalysts with different Cu/Si ratio are controllably synthesized by fine-tuning the precursor ratio, enabling selective CO electroreduction to CH/CH. Specifically, at a current density of 200 mA cm, Cu/SiO-10 including majority of CuSiO facilitates the electroreduction of CO to CH with a Faradaic selectivity ratio of CH/CH (9.3/1), whereas Cu/SiO-50 primarily consisting of CuO exhibits a Faradaic selectivity ratio of CH/CH (16.7/1). X-ray photoelectron spectroscopy and in situ Raman spectroscopic characterization reveal that CuSiO 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/Cu during the reaction. In situ infrared spectroscopic and temperature-programmed desorption of CO characterization further reveal that CuSiO has a stronger protonation capacity and promotes the direct protonation of adsorbed *CO species to CH, while Cu/Cu is more conducive to the CC coupling between the intermediate species *CHO with adsorbed *CO species to form CH due to the stronger CO adsorption capacity and higher coverage.