Acidic electrochemical CO2 reduction reaction (CO2RR) offers an attractive route to store intermittent renewables as valuable chemicals with high carbon efficiency but suffers from low selectivity due to predominant hydrogen evolution reaction. Utilizing concentrated alkali cations steers the acidic CO2RR to multicarbon (C2+) products but leads to salt precipitation. Here we report a molecular tuning strategy to facilitate acidic CO2RR to ethylene under a low K+ concentration by modifying tetraphenylporphyrin-based molecules onto a Cu surface. At 200 mA cm-2, we achieve a record ethylene Faradaic efficiency (FE) of 53% on 5,10,15,20-tetraphenyl-21H,23H-porphine zinc functionalized Cu catalysts (a 1.2× improvement compared to the best reports at above 100 mA cm-2 under an acidic electrolyte having a low alkali cation concentration) and a high C2+ FE of 85%, as well as a high CO2 single-pass utilization of 72%. This work presents a catalyst design strategy for efficient acidic CO2-to-ethylene electrolysis under low alkali-cation availability.
Zhang et al. (2026) studied this question.