Suppression of Hydrogen Evolution over Oxidized Cu_XCo_Y 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 Cu_XCo_Y to suppress hydrogen evolution. The as-prepared oxidized Cu_XCo_Y 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 Cu_X and oxidized Co_Y 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 Cu_XCo_Y at low and high overpotentials, because proton diffusion and adsorption could be prevented.