Electronic Delocalization of Bismuth Oxide Induced by Sulfur Doping for Efficient CO₂ Electroreduction to Formate

Developing efficient electrocatalysts for electrochemical CO2 reduction (ECR) to fuels and chemicals with high product faradaic efficiency (FE) and current density is desirable but remains challenging. Herein, S-doped Bi2O3 electrocatalysts coupled with carbon nanotubes (S-Bi2O3-CNT) are synthesized for efficient ECR to formate. The obtained S2-Bi2O3-CNT (with a S doping amount of 0.7 at. %) is highly active for formate production (FE > 90%) over a wide current density range (2.77–48.6 mA cm–2), and a maximum formate FE of 97.06% can be achieved at −0.9 V. The significantly enhanced selectivity and activity is originated from the fast electron transfer, enhanced CO2 adsorption, and more undercoordinated Bi sites induced by the S doping. More importantly, density functional theory calculations revealed that S doping can lead to an electronic delocalization of Bi, which benefits the binding of *CO2 and *HCOO for ECR, while significantly inhibiting the hydrogen evolution reaction via weakening the adsorption of *H, thus helping achieve high current density and FE. This work paves a promising way to tuning ECR activities at the atomic level.