Unveiling Ag-Modulated Cu Active Sites for Enhanced Multicarbon Product Formation in CO₂ Electroreduction

The development of innovative electrocatalysts for CO₂ reduction reaction (CO₂RR) is essential for producing high-value chemicals and fuels. Here, we report a simple surfactant- and solvent-free strategy to fabricate Cu-Ag bimetallic gas diffusion electrodes (GDEs) via sputtering of Cu onto a carbon substrate, followed by galvanic replacement with Ag. This method yields highly pure and tunable electrodes with minimal processing steps. The resulting CuAg GDEs exhibit a marked enhancement in CO₂RR performance compared to monometallic Cu, particularly in promoting C₂ (mainly ethanol and ethylene) product formation. This improvement is most pronounced when the galvanic replacement is carried out at 75 °C, yielding an optimal Ag/Cu ratio that maximizes electrochemical performance. Under these optimized conditions, Faradaic efficiencies (FE) for C₂ products reach 73% and 69% at high current densities of 400 and 600 mA cm^-2, respectively. Notably, the introduction of Ag markedly improves operational stability, with the system maintaining a FE of 49% for C₂ products after 3 h of continuous electrolysis. In situ X-ray absorption spectroscopy (XAS) reveals that Ag plays a key role in stabilizing of Cu⁺ species under reaction conditions, which correlates with the C-C coupling and long-term selectivity. These findings provide valuable insights for rational design of advanced Cu-based catalysts for high-performance CO₂ conversion.