Inhibiting Hydrogen Evolution using a Chloride Adlayer for Efficient Electrochemical CO2 Reduction on Zn Electrodes

A challenge in electrochemical CO2 reduction is inhibiting hydrogen evolution reaction (HER). Herein, a bulk Zn electrode was chosen to reveal the effect of specifically adsorbed Cl– ions on HER during CO2 reduction. We found that in the Cl– ion-containing electrolyte, the Zn–Cl adlayer formed because the weakly solvated Cl– ions can strip the solvation shell and form a direct chemical bond with the metal Zn. As a result, the Zn–Cl bonds on the Zn electrode notably blocked the hydrogen evolution and significantly facilitated the electron transfer process via the Cl to the vacant orbitals of inert CO2, therefore stabilizing the CO2– radical and leading to a four times higher CO Faradaic efficiency for CO2 reduction in the KCl electrolyte than that in the KHCO3 electrolyte at a moderate potential of −1.2 V versus a reversible hydrogen electrode.