Trace Iodine Modified Copper Catalyst Drives Asymmetric C─C Coupling in Stable CO₂ Electroreduction

Abstract Cu‐based catalysts efficiently catalyze the electrochemical conversion of CO₂ into high‐value multicarbon (C₂₊) products. However, it remains a challenge to achieve optimal structural stability, product selectivity, and long‐term catalytic durability. In this study, a well‐active oxide‐derived Cu surface consisting predominantly of Cu₂O(111) facets is developed, which contains trace amounts of iodine (I). The Cu₂O(111) surface enhances the hydrogenation of *CO and facilitates the asymmetric coupling of *CO and *CHO, while the intercalated iodine boosts the adsorption of CO₂ and CO. During the reaction, the release of excess I increases the surface roughness, while the remaining iodine controls the chemical state of the surface Cu. These effects together lead to a Faradaic efficiency of 79.0% and a cathodic energy efficiency of 43.5% for C₂₊ products at a current density of 300 mA cm⁻². Moreover, it is found that periodic electrode treatment with iodide prevents the agglomeration of catalysts and preserves sufficient active iodine sites, ensuring improved catalytic stability for C₂₊ production. This study provides new insights into the synergistic interactions between Cu─O compounds and iodine and offers a promising route for the development of highly active and durable catalytic systems for long‐term CO₂ electroreduction.