Coordinating the Edge Defects of Bismuth with Sulfur for Enhanced CO₂ Electroreduction to Formate

Bismuth-based materials have been recognized as promising catalysts for the electrocatalytic CO₂ reduction reaction (ECO₂ RR). However, they show poor selectivity due to competing hydrogen evolution reaction (HER). In this study, we have developed an edge defect modulation strategy for Bi by coordinating the edge defects of bismuth (Bi) with sulfur, to promote ECO₂ RR selectivity and inhibit the competing HER. The prepared catalysts demonstrate excellent product selectivity, with a high HCOO^- Faraday efficiency of ≈95 % and an HCOO^- partial current of ≈250 mA cm^-2 under alkaline electrolytes. Density function theory calculations reveal that sulfur tends to bind to the Bi edge defects, reducing the coordination-unsaturated Bi sites (*H adsorption sites), and regulating the charge states of neighboring Bi sites to improve *OCHO adsorption. This work deepens our understanding of ECO₂ RR mechanism on bismuth-based catalysts, guiding for the design of advanced ECO₂ RR catalysts.