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

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.