<p>Bismuth-based catalysts are widely regarded as one of the most promising materials for the electrocatalytic carbon dioxide reduction reaction to formate. Among these, BiOI is a representative example. However, achieving a high selectivity for formate and maintaining long-term durability during the reaction remain significant challenges for BiOI. In this study, an S-doping strategy was employed to synthesize S-doped BiOI catalysts with a nanosheet structure enriched with oxygen vacancies. The S-doped BiOI catalyst exhibited outstanding performance in carbon dioxide reduction reaction to formate, reaching a maximum faradaic efficiency of 96.47% in an H-cell. Furthermore, in a flow cell, the faradaic efficiency remained remarkably high at 96.98% over 800&#xa0;h of continuous operation at a high current density of 100&#xa0;mA&#xa0;cm⁻², demonstrating an exceptional durability. DFT calculations have revealed that S doping modifies the electronic structure around Bi atoms and creates oxygen vacancies, which enhance CO₂ adsorption and activation. This structural modification reduces the reaction energy barrier for the key intermediate (*OCHO), thereby significantly improving the catalytic performance of S-doped BiOI for the electrocatalytic reduction of CO₂ to formate.</p> Graphical Abstract <p>S-BiOI with oxygen vacancies synthesized using S-doping strategy for efficient electrocatalytic CO₂ reduction reaction to formate.</p> <p></p>