Revealing the Dynamic Microenvironment of the Ag/CeO₂ Surface for Robust Electrocatalytic CO₂ Reduction

The microenvironment during CO2 electroreduction critically influences product selectivity, yet its structural composition and dynamic evolution remain challenging to study due to the bulk water interface. Herein, we report an acid-regulated CeO2-modified nanoporous Ag strategy to achieve a localized alkaline microenvironment at the interface to promote the conversion of CO2 to CO. By exploiting the intrinsic surface-enhanced Raman spectroscopy (SERS) activity of the nanoporous Ag architecture, we directly track the dynamic structural evolution of interfacial water within the electrochemical double layer using in situ SERS techniques. Furthermore, we reveal that high concentrations of K•H2O induce self-dissociation of HCO3– to form OH– and CO2. The readsorption of hydroxyl groups is beneficial in reducing the adsorption energy of the key intermediate *COatop, as confirmed by theoretical calculations, thus promoting the production of CO. In an anion exchange membrane (AEM) electrolyzer, the catalyst achieves a maximum Faradaic efficiency of nearly 98.8% for CO and a high CO current density of 248.4 mA cm–2, exceeding industrial requirements. This work highlights the importance of microenvironment engineering in optimizing intermediate adsorption and provides a scalable strategy for efficient CO2-to-CO conversion.