Modulating interfacial ion flux via electrode coatings enables efficient acidic CO2 electrolysis

Abstract

Acidic CO₂ electrolysis offers great potential for high-efficiency single-pass CO₂ conversion to valuable fuels and chemicals, yet is challenged by the kinetically favorable hydrogen evolution reaction. Electrode coatings can engineer a favorable electrode–electrolyte interface by regulating interfacial ion flux to steer the reaction pathway toward CO₂ electroreduction; however, rational design rules for such coatings remain elusive. Here, we decouple the roles of binders and inorganic fillers in the coatings and demonstrate that coupling a cation-exchange ionomer (CEI) with a proton-blocking oxide yields a durable coating that enables efficient acidic CO₂ electrolysis. Combined experimental and simulation results reveal that this optimal formulation promotes inward K⁺ transport while restricting H⁺ influx and outward OH⁻ transport, thereby establishing a K⁺-enriched and alkaline interfacial microenvironment that enhances CO₂/CO adsorption and lowers the *CO dimerization barrier. As a representative demonstration, an Al₂O₃/CEI-coated Cu electrode achieves a maximum Faradaic efficiency (FE) of 81.3% for multi-carbon (C₂₊) products at 600 mA cm⁻² and remarkably durable operation for 200 h at 200 mA cm⁻². Furthermore, this proposed electrode coating strategy demonstrates the broad generality in engineering interfacial microenvironments across distinct catalyst platforms.