Oxide-derived low-coordination Ag catalysts enable efficient photovoltaic-driven electrochemical CO₂ reduction in MEA electrolyzers

Oxide-derived silver (Ag) catalysts have emerged as promising candidates for achieving highly efficient electrochemical CO₂ reduction reaction (eCO₂RR) to CO at industrial current densities. However, the evolution of active site configurations, the atomic-level coordination–activity relationship, and the design of practical solar-driven systems remain insufficiently explored. In this work, we report the facile in situ electrochemical synthesis of Ag₂O-derived Ag (Ag₂O-D-Ag), where the presence of unsaturated (low-coordination) Ag sites is revealed through operando X-ray absorption spectroscopy. The Ag₂O-D-Ag catalyst exhibits a CO faradaic efficiency of 90% at 500 mA cm⁻² and maintains a stability over 100 hours at 200 mA cm⁻² in a 4-cm² membrane electrode assembly (MEA) electrolyzer. In situ Fourier-transform infrared spectroscopy, combined with theoretical calculations, shows that these optimally low-coordinated Ag sites reduce the formation energy barrier of the *COOH intermediate, thereby accelerating CO production. Integration of this catalyst with a photovoltaic module enables a 100-cm² MEA prototype to operate stably for more than 30 hours, achieving a solar-to-CO energy efficiency of 4.87%. This study provides mechanistic insight into active site dynamics and demonstrates a scalable, renewable-energy-driven eCO₂RR system.