Tuning the subsurface oxygen of Ag2O-derived Ag nanoparticles to achieve efficient CO2 electroreduction to CO

Abstract Electrochemical CO2 reduction reaction (CO2RR) to value-added chemicals at low cost is highly attractive in mitigating the environmental issues caused by excessive greenhouse gases emission. In this work, Ag2O-derived Ag nanoparticles (OD-Ag NPs) with the optimized subsurface oxygen were obtained through steering the reducing current density (ire) upon in situ Galvano-statically reducing Ag2O NPs to metallic Ag, and it is found that the OD-Ag NPs thus obtained exhibit high catalytic activity and selectivity towards CO production. Specifically, the OD-Ag NPs derived from an intermediate ire of ‒1 mA•cm‒2 achieve the high Faradaic efficiencies (FECO) of over 90% in a wide potential window over 450 mV, whereas either smaller (‒0.1 mA•cm‒2) or larger (‒10 mA•cm‒2) ire reduces the overall CO2RR performance. This suggests that tuning the ire to change the subsurface oxygen of oxide-derived catalysts is beneficial to improve their selectivity. Theoretical DFT calculations and analysis rationalize the experimental observation, and reveal that the outstanding performance of the OD-Ag NPs benefits from the suitable concentration of subsurface oxygen which not only enhances the adsorption of intermediate *COOH, but also optimizes the free energy of the reaction pathways.