Deciphering the Role of Au in CO Reduction on Cu: From Atomic Sites to a Stabilized Proton-Transfer Interface

Abstract Incorporating gold (Au) into copper (Cu)-based electrocatalysts effectively enhances the conversion of CO into multicarbon products, yet the fundamental role of Au remains elusive due to limited mechanistic insight. Using a Au-doped basic copper chloride as a platform precatalyst, we demonstrate that the in situ formation of stable Cu3Au intermetallics during operation substantially alters the CO electroreduction pathway. Using multispectroscopic analyses combined with theoretical calculations, we find that the in situ-formed Cu3Au structure likely plays a synergistic role by (i) optimizing *CO adsorption and surface coverage to promote C–C coupling and (ii) restructuring the interfacial water network to strengthen hydrogen bonding, thereby shifting the dominant proton-transfer pathway from a Langmuir–Hinshelwood mechanism to an Eley–Rideal mechanism. This reconfiguration suppresses the hydrogen evolution reaction and adsorbed hydrogen-mediated pathways while promoting direct proton donation from interfacial water for the formation of acetate. Consequently, the optimized catalyst achieves an acetate Faradaic efficiency of 80.3% at −1.05 V versus the reversible hydrogen electrode with a partial current density of −492.7 mA cm–2. These findings underscore how adaptive electrochemical reconstruction can design active sites and modulate interfacial proton-transfer dynamics to steer CO valorization toward targeted products.