Sulfur Changes the Electrochemical CO2 Reduction Pathway over Cu Electrocatalysts

Abstract Electrochemical CO 2 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 2 to produce a variety of multicarbon products (e.g., ethylene and ethanol). In this work, we develop sulfur‐doped Cu 2 O electrocatalysts, which instead can electrochemically reduce CO 2 to almost exclusively formate. We show that a dynamic equilibrium of S exists at the Cu 2 O‐electrolyte interface, and S‐doped Cu 2 O undergoes in situ surface reconstruction to generate active S‐adsorbed metallic Cu sites during the CO 2 reduction reaction (CO 2 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 2 ‐to‐formate conversion during the electrochemical CO 2 RR.