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

Electrochemical CO₂ reduction reaction (CO₂RR) 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 CO₂RR, that is Cu₂₉Ag₇₁ 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 Cu₂₉Ag₇₁ during acidic CO₂RR and also indicates that the evolved interface structure enhances the proton activity for CO₂RR. Cu₂₉Ag₇₁ 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 Cu₉₀Al₁₀ surface to act as a protective and CO overflow layer. The tandem configuration suppresses dealloying in Cu₉₀Al₁₀ 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.