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

Abstract

As a sustainable pathway for energy storage and to close the carbon cycle, CO 2 electroreduction has recently gained significant interest. We report here the role of the electrolyte, in particular of halide ions, on CO 2 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 well-defined shapes. Furthermore, the presence of Cl –, Br –, and I – was found to lower the overpotential and to increase the CO 2 electroreduction rate on plasma-activated preoxidized Cu catalyst in the order Cl – < Br – < I –, without sacrificing their intrinsically high C 2 –C 3 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 CO 2 .