Sulfur Changes the Electrochemical CO Reduction Pathway over Cu Electrocatalysts.

Electrochemical CO reduction to value-added chemicals or fuels offers a promising approach to reduce carbon emissions and alleviate energy shortage. Cu-based electrocatalysts have been widely reported as capable of reducing CO to produce a variety of multicarbon products (e.g., ethylene and ethanol). In this work, we develop sulfur-doped Cu O electrocatalysts, which instead can electrochemically reduce CO to almost exclusively formate. We show that a dynamic equilibrium of S exists at the Cu O-electrolyte interface, and S-doped Cu O undergoes in situ surface reconstruction to generate active S-adsorbed metallic Cu sites during the CO reduction reaction (CO RR). Density functional theory (DFT) calculations together with in situ infrared absorption spectroscopy measurements show that the S-adsorbed metallic Cu surface can not only promote the formation of the *OCHO intermediate but also greatly suppress *H and *COOH adsorption, thus facilitating CO -to-formate conversion during the electrochemical CO RR.