CO2 Electrochemical Reduction via Adsorbed Halide Anions

The electrochemical reduction of CO2 was studied utilizing halide ions as electrolytes, specifically, aqueous solutions of KCl, KBr, and KI. The objective was to investigate the reaction mechanism for CO2 reduction with halides and understand how they influence electron transfer processes. A laboratory-made, divided H-type cell was employed for electrochemical experiments, using a copper mesh as the working electrode and Pt wire with an Ag/AgCl electrode as counter and reference electrodes. Results indicated that the presence of Cu-X as a catalytic layer facilitated electron transfer from the electrode to CO2 via the formed X– (Br–, Cl–, I–) bond. Higher adsorption of halide anions correlated with stronger restraint of CO2, leading to increased reduction current. Moreover, specifically adsorbed halide anions appeared to suppress proton adsorption, resulting in a higher hydrogen overvoltage. This synergy may reduce the overpotential necessary for CO2 reduction, effectively enhancing the electrochemical CO2 reduction rate. These findings highlight the significant role of halide ions in improving electrochemical processes for CO2 utilization.