Tuning oxygen vacancy for efficient CO2 electroreduction over CeO2 supported SnO2

[Display omitted] •A series of SnO2-CeO2 with different Ov concentration were prepared for CO2RR to formate.•SnO2-CeO2 with a moderate Ov concentration exhibited moderate H2O dissociation capacity, enhancing formate production.•The stability of the catalyst decreased with increasing Ov concentration.•The optimal SnO2-CeO2 catalyst exhibits a FEformate of nearly 93% for more than 46 h at a current density of 100 mA/cm2. 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 (Ov) concentration, regulating the H2O dissociation, to synchronize with the CO2 reduction. The optimal SnO2-CeO2 catalyst, with a moderate Ov 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 Ov concentration results in weak H2O dissociation, thus enhancing the energy barrier of *OCHO generation, while higher Ov 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 Ov concentration in determining the ability of water dissociation over supported electrocatalysts, providing valuable insights for the development of more efficient electrocatalyst.