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

The electrochemical reduction of CO 2 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 cm 2 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 CO 2 RR conditions. These findings demonstrate that oxygen vacancy engineering significantly enhances catalytic CO 2 adsorption and reduction, offering a viable strategy for designing next-generation high-performance electrocatalysts for scalable CO 2 -to-formate electrolysis. Electrochemical reduction of 1D BiSI generates oxygen-vacancy-rich Bi (O V -Bi), which promotes efficient and selective CO 2 -to-formate conversion at high current densities with excellent stability. • 1D BiSI yields oxygen-vacancy-rich Bi (O V -Bi) electrocatalyst for CO 2 -to-formate conversion. • O V -Bi achieves 465.7 mA cm −2 formate partial current density with >90 % selectivity. • O V -Bi maintains high formate selectivity over 24 h of continuous operation. • Oxygen vacancies enhanced *OCHO intermediate formation and suppressed H 2 evolution.