Tuning oxygen vacancy for efficient CO2 electroreduction over CeO2 supported SnO2

CO₂ electroreduction is favorable in neutral or alkaline aqueous solutions, where H₂O serves as the proton source, suffering from sluggish dynamics. Herein, we synthesize a series of SnO₂-CeO₂ with different oxygen vacancy (O_v) concentration, regulating the H₂O dissociation, to synchronize with the CO₂ reduction. The optimal SnO₂-CeO₂ catalyst, with a moderate O_v concentration, exhibits a formate Faradic efficiency of nearly 93% and maintains for more than 46 h at a current density of 100 mA/cm². The catalyst with lower O_v concentration results in weak H₂O dissociation, thus enhancing the energy barrier of *OCHO generation, while higher O_v concentration leads to excessive proton, exacerbating the hydrogen evolution reaction (HER), as supported by DFT calculation and in situ attenuated total reflection-Fourier transform infrared spectra (ATR-FTIR). This study underscores the significance of O_v concentration in determining the ability of water dissociation over supported electrocatalysts, providing valuable insights for the development of more efficient electrocatalyst.