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.