Cationic-group Functionalized Electrocatalysts Enable Stable Acidic CO2 Electrolysis

Acidic electrochemical CO2 reduction (CO2R) addresses CO2 loss, and thus mitigates the energy penalties associated with CO2 recovery; however, acidic CO2R suffers low selectivity. One promising remedy – using a high concentration of alkali cations – steers CO2R towards multi-carbon (C2+) products; but these same alkali cations result in salt formation, limiting operating stability to <15 hours. Here we present cationic groups (CG) functionalized copper that enables efficient CO2 activation in a stable manner: by replacing alkali cations with immobilized benzimidazolium cationic groups within ionomer coatings, we achieve over 150 hours of stable CO2R. We find the water-management property of CG minimizes proton migration that enables operation at a modest voltage of 3.3 V with mildly alkaline local pH, leading to more energy-efficient CO2R with a C2+ Faradaic efficiency of 80%±3%. As a result, we report an energy efficiency of 28% for acidic CO2R towards C2+ products, and a single-pass CO2 conversion efficiency exceeding > 70%.