Tailoring oxygen vacancies on bismuth using one-dimensional BiSI for efficient CO₂ electrolysis to formate

The electrochemical reduction of CO₂ to formate represents a promising strategy for carbon mitigation and energy storage. However, achieving selectivity and productivity at industrially relevant current densities remains a critical challenge. Herein, we report a defect-engineered bismuth electrocatalyst with abundant surface oxygen vacancies (O_V-Bi), synthesized via electrochemical reduction of exfoliated one-dimensional BiSI—a van der Waals materials. The facile removal of sulfur and iodine during reduction promotes the formation of oxygen vacancies, which lower the energy barrier for *OCHO intermediate formation, thereby steering the reaction pathway toward formate. The resulting OV-Bi electrode exhibits a record-high partial current density for formate production of 465.7 mA cm⁻² on a 5 cm² electrode, while maintaining Faradaic efficiency above 90 % and stable operation for over 24 h at 100 mA cm⁻². Electron spin resonance spectroscopy confirmed a substantial increase in oxygen vacancy concentration, and in situ/Operando X-ray absorption spectroscopy revealed dynamic electronic structure evolution under CO₂RR conditions. These findings demonstrate that oxygen vacancy engineering significantly enhances catalytic CO₂ adsorption and reduction, offering a viable strategy for designing next-generation high-performance electrocatalysts for scalable CO₂-to-formate electrolysis.