Halide-guided carbon-affinity active sites in BimOnBrp-derived Bi2O2CO3 for efficient electrocatalytic CO2 reduction to formate†

Bismuth oxyhalides (Bi_mO_nX_p, where X represents Cl, Br, and I) present a promising family of template catalysts for in situ Bi₂O₂CO₃ synthesis to achieve the highly efficient CO₂ electrochemical reduction reaction (CO₂RR) toward formate. However, the specific mechanism behind Bi_mO_nX_ps' structural reconstruction and their subsequent effects on CO₂RR performance remain unresolved inquiries. In this study, a comprehensive investigation into how halogens (Cl, Br, and I) influence Bi_mO_nX_p CO₂RR performance was conducted. It is suggested that Br is capable of introducing a bismuth-rich phase (Bi₂₄O₃₁Br₁₀) in BiOBr, which promotes the formation of external Bi–O structural characteristics and leads to exceptional CO₂RR performance, with a faradaic efficiency (FE_{HCOO −}) of 90.67% and a formate partial current density (J_{HCOO −}) of 52.31 mA cm⁻², surpassing those of BiOCl and BiOI. Kinetic simulations suggest that the alternative Bi–O structure will promote the combination of the Bi–O structure and carbon-based intermediates, leading to the improved kinetics of the rate-determining step, and ultimately resulting in better CO₂RR performance.