Improved CO₂ Electroreduction Performance on Plasma-Activated Cu Catalysts via Electrolyte Design: Halide Effect

As a sustainable pathway for energy storage and to close the carbon cycle, CO2 electroreduction has recently gained significant interest. We report here the role of the electrolyte, in particular of halide ions, on O2 electroreduction over plasma-oxidized polycrystalline Cu foils. It was observed that halide ions such as I− can induce significant nanostructuring of the oxidized Cu surface, even at open circuit potential, including the formation of Cu crystals with welldefined shapes. Furthermore, the presence of Cl−, Br−, and I− was found to lower the overpotential and to increase the CO2 electroreduction rate on plasma-activated preoxidized Cu catalyst in the order Cl−, Br− −, without sacrificing their intrinsically high C2−C3 product selectivity (∼65% total Faradaic efficiency at −1.0 V vs RHE). This enhancement in catalytic performance is mainly attributed to the specific adsorption of halides with a higher coverage on our oxidized Cu surface during the reaction, which have been previously reported to facilitate the formation and stabilization of the carboxyl (*COOH) intermediate by partial charge donation from the halide ions to CO2