Suppression of Hydrogen Evolution over Oxidized Cu_<i>X</i>Co_<i>Y</i> in an Ionic Liquid Electrolyte for CO₂ Electrochemical Reduction

Hydrogen evolution reaction (HER) is the dominant competitive side reaction for the carbon dioxide electrochemical reduction reaction (CO2RR). In the present study, it was the first time that 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) as an electrolyte was utilized in the CO2RR on oxidized CuXCoY to suppress hydrogen evolution. The as-prepared oxidized CuXCoY electrodes that were fabricated via electrodeposition and subsequent thermal oxidation processes had extended surface area and small charge transfer resistance, resulting in better catalytic activity and high C2+ selectivity compared to the oxidized CuX and oxidized CoY electrodes. Relatively high C2+ Faradaic efficiency, more than 40% at −0.77 V vs RHE, and superior long-term stability over 48 h in a traditional aqueous 0.5 M KHCO3 solution were achieved. Instead of using an aqueous KHCO3 solution as an electrolyte, experimental and density functional theory (DFT) calculation results showed that the HER was dramatically suppressed in [AMIM]Cl, especially over oxidized CuXCoY at low and high overpotentials, because proton diffusion and adsorption could be prevented.