CO 2 attraction by specifically adsorbed anions and subsequent accelerated electrochemical reduction

Abstract

The electrochemical reduction of CO 2 was studied on a copper mesh electrode in aqueous solutions containing 3 M solutions of KCl, KBr and KI as the electrolytes in a two and three phase configurations. Electrochemical experiments were carried out in a laboratory-made, divided H-type cell. The working electrode was a copper mesh, while the counter and reference electrodes were Pt wire and Ag/AgCl electrode, respectively. Results of our work suggest a reaction mechanism for the electrochemical reduction of CO 2 in the two phase configuration where the presence of Cu-X as the catalytic layer facilitates the electron transfer from the electrode to CO 2. Electron-transfer to CO 2 may occur via the X ad −(Br −, Cl −, I −)–C bond, which is formed by the electron flow from the specifically adsorbed halide anion to the vacant orbital of CO 2. The stronger the adsorption of the halide anion to the electrode, the more strongly CO 2 is restrained, resulting in higher CO 2 reduction current. Furthermore, it is suggested that specifically adsorbed halide anions could suppress the adsorption of protons, leading to a higher hydrogen overvoltage. These effects may synergistically mitigate the overpotential necessary for CO 2 reduction, and thus increase the rate of electrochemical CO 2 reduction.