Electrochemical Assembly of a Defective Cu Catalyst for High Current CO₂ Electrolysis to Methane in a Zero-Gap...

CO₂ electrolysis to methane offers a promising route toward enabling long-term storage of renewable energy. However, electrolysis in zero-gap membrane electrode assembly (MEA) systems using conventional Cu-based electrocatalysts is typically limited by relatively low methane productivity and Faradaic efficiency (FE). Here, we conceived an electrochemical assembly strategy that forms a Cu(111)-dominant catalyst with vacancy defects. In an MEA system at a total current of 1.5 A, the catalyst (Def-Cu₆) achieved a record methane FE of 71.46% and production rate of 0.28 µmol s^-1 cm^-2, with relatively stable operation over 10 h. Density functional theory calculations reveal the crucial role of vacancy defects in a Cu(111) surface, which favors the hydrogenation of CO* and promotes methane formation over the competing CO* coupling pathway that leads to multicarbon products. Our findings demonstrate how vacancy defects can be tuned to control catalytic outcomes.