Fine-tuning copper dispersion in Cu/SiO2 core-shell particles regulates electrochemical CO2 reduction product selectivity

The wide product spectrum resulting from the intricate reactions of electrochemical CO2 reduction reaction (CO2RR) makes CO2RR unfavorable for industrial electrolysis. Herein, we demonstrate a hydrogen-feeding effect from copper-silica catalysts that can regulate CO2RR product selectivity via modulation of Cu dispersion in the copper-silica core-shell particles. We found electromethanation of CO2 is greatly enhanced on Cu-Si catalyst with optimally dispersed Cu nanoparticles, resulting in a high methane Faradaic efficiency of 72.9 %. In contrast, a lower or higher Cu dispersion correlated to a preferential (co-)production of methane and ethylene or hydrogen. Combining density functional theory (DFT) calculations and spectroscopic analysis, we show Cu dispersion affects the Cu coverage on SiO2 and the exposure of Cu-O-Si interfacial sites for CO2RR and water dissociation. An optimum Cu dispersion creates abundant Cu-O-Si sites with reduced energy barriers for both the hydrogenation of *CHO and water dissociation, leading to selective methane formation.