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.