Atomically Engineered SnO _x ‐Cu Interfacial Sites Regulate Water Dissociation toward Highly Selective CO ₂ to C ₂ Conversion

ABSTRACT Electrochemical CO 2 reduction reaction (CO 2 RR) offers a sustainable strategy to convert CO 2 into value‐added chemicals, yet achieving selective C─C coupling remains challenging because water‐derived protons predominantly drive the competing hydrogen evolution reaction (HER). Here, we develop a porous carbon‐confined Cu catalyst decorated with atomically dispersed SnO x clusters (SnO x ‐Cu@C) that achieves highly selective CO 2 ‐to‐C 2 conversion, achieving a maximum Faradaic efficiency of 66.3% for C 2 product while substantially suppressing H 2 generation to 7.4%. In situ ATR‐SEIRAS uncover strengthened * CO adsorption and accelerated * CO‐ * COH coupling, accompanied by enriched weakly hydrogen‐bonded interfacial water species that preferentially dissociate into reactive * H for subsequent protonation. Density functional theory further shows that SnO x anchoring induces interfacial charge redistribution, lowers the * CO to * COH activation barrier, and restrains proton‐proton coupling. These mechanistic insights demonstrate that precise atomic‐level engineering of oxide‐metal interfaces is an effective strategy to modulate water activation and intermediate energetics, enabling efficient and highly selective CO 2 to C 2 conversion.