Tandem Electrocatalysis With Cu‐Based Alloy Catalysts for Efficient Multi‐Carbon Formation in Strongly Acidic Conditions

Abstract Electrochemical CO 2 reduction reaction (CO 2 RR) in acidic electrolyte enables high single‐pass carbon efficiency (SPCE), while highly corrosive acidic electrolytes typically cause catalyst degradation. It is reported that the dealloying of Cu/Ag and Cu/Al alloys, as well as the increased C─C coupling energy barrier, are reasons that advances in neutral/alkaline electrolysis do not translate to acidic conditions. Detailed characterizations reveal the dynamic evolution of the alloy in acidic CO 2 RR, that is Cu 29 Ag 71 undergoes dealloying, re‐deposition, and surface restructuration, ultimately forming the stable Ag/Cu interfacial structure. In situ Raman spectroscopy reveals the dynamic evolution of interfacial water structures on Cu 29 Ag 71 during acidic CO 2 RR and also indicates that the evolved interface structure enhances the proton activity for CO 2 RR. Cu 29 Ag 71 achieves a CO Faradaic efficiency (FE) of 93.1% with stable electrolysis of 45 h at 250 mA cm −2 . Based on this stable, high CO‐selective catalyst, a tandem electrode is designed by deploying it on the Cu 90 Al 10 surface to act as a protective and CO overflow layer. The tandem configuration suppresses dealloying in Cu 90 Al 10 and creates a localized alkaline environment, thereby promoting C─C coupling. This tandem electrode exhibits a multi‐carbon FE of 81.2% at 648 mA cm −2 , a SPCE of 70.4%, and stable electrolysis of 30 h.