Cationic-group-functionalized electrocatalysts enable stable acidic CO 2 electrolysis

Acidic electrochemical CO 2 reduction (CO 2 R) addresses CO 2 loss and thus mitigates the energy penalties associated with CO 2 recovery; however, acidic CO 2 R suffers low selectivity. One promising remedy—using a high concentration of alkali cations—steers CO 2 R towards multi-carbon (C 2+ ) products, but these same alkali cations result in salt formation, limiting operating stability to <15 h. Here we present a copper catalyst functionalized with cationic groups (CG) that enables efficient CO 2 activation in a stable manner. By replacing alkali cations with immobilized benzimidazolium CG within ionomer coatings, we achieve over 150 h of stable CO 2 R in acid. 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 CO 2 R with a C 2+ Faradaic efficiency of 80 ± 3%. As a result, we report an energy efficiency of 28% for acidic CO 2 R towards C 2+ products and a single-pass CO 2 conversion efficiency exceeding 70%.