Oxygen Reduction Intermediates Facilitate Stable and Efficient CO2 Electroreduction to Multicarbon Products in an Acidic Electrolyte.

CO2 electroreduction in an acidic electrolyte with low alkali cation concentrations is an effective approach to mitigate the salting-out effect and achieve stable catalysis. However, the competitive hydrogen evolution reaction (HER) becomes more significant due to the high proton concentration. In this study, we introduce, for the first time, O2 generated at the anode into the CO2 gas feed during electroreduction to enhance C2+ products formation. Compared with pure CO2, the addition of 1% O2 to the gas phase increases the Faradaic efficiency (FE) for C2+ products from 31.2% to 77.6% over a Cu&Fe-N4C electrode at a current density of 400 mA cm-2 in an acidic electrolyte containing 0.5 M K+ (pH = 1). The low K+ concentration effectively suppresses the salting-out effect, enabling stable operation for 100 h. Mechanistic studies reveal that •OH and •OOH radicals, derived from the oxygen reduction reaction (ORR), play distinct roles, with •OH promoting C-C coupling and •OOH selectively inhibiting HER, together accounting for the high FEC2+ achieved in an acidic electrolyte.