The Synergy between Bromine and Oxygen Vacancies in the Reconstruction of Bi 2 WO 6 for Electrocatalytic CO 2 Reduction to Formate

The electrochemical reduction of CO2 to formate provides a dual-purpose pathway to mitigate emissions and generate valuable fuels and chemicals. In this work, halide doping strategies (Cl–, Br–, and I–) were employed to prepare Bi2WO6 nanosheets with tunable oxygen vacancy (Ov) concentrations for the electrocatalytic reduction of CO2. The bromine-doped Bi2WO6 nanosheets (BWO-Br) achieve a Faradaic efficiency for formate (FEformate) exceeding 90% over a wide potential window in an H-cell and reach a high current density of 496 mA cm–2 in a flow cell. Density functional theory calculations reveal that bromine synergizes with Ov to generate electron-rich bismuth sites, thereby weakening the Bi–O bonds. In situ ATR-SEIRAS and Raman spectroscopy investigations further demonstrate that Br doping induces a rapid and favorable reconstruction during the reaction. This accelerated reconstruction process generates substantial tensile strain in the catalyst structure, which significantly enhances the adsorption of the *OCHO intermediate and ultimately boosts the performance of electrocatalytic CO2 reduction to formate. This work provides valuable insights into the reconstruction dynamics jointly guided by Br and Ov, offering a rational principle for the design of high-performance CO2 reduction electrocatalysts.