Sulfur boosting CO2 reduction activity of bismuth subcarbonate nanosheets via promoting proton-coupled electron transfer

Highlights: • S-doping boosts CO₂ reduction activity of bismuth subcarbonate (BiOC) nanosheets to formate. • S modifies electron density around Bi active site, promoting proton-coupled electron transfer to CO₂ intermediate. • Cost-effective CO₂ conversion could be obtained by tuning the content of S-doping. • The optimum S-BiOC exhibits good catalytic activity and high formate selectivity over a broad potential window. Bismuth (Bi) based nanomaterials are attractive catalysts for electrochemical CO₂ reduction to formate, while both high selectivity and high activity still need further investigation. Herein, we report a facile strategy, via introducing sulfur (S) atoms to modulate the electronic structure of two-dimensional (2D) bismuth subcarbonate Bi₂O₂CO₃ (BiOC) nanosheets, to improve their catalytic activity meanwhile maintain high formate selectivity. The lower electronegativity of the substituted S than O enhances the local electron density around Bi active sites, promoting the proton-coupled electron transfer to the CO₂ intermediate, and thus contributing to the superior CO₂ reduction performance with the selectivity of formate >90% in a wide negative potential range and high partial current density up to 29.0 mA cm⁻² at −0.9 vs RHE. This study provides an in-depth understanding on the design of advanced CO₂ reduction electrocatalysts via heteroatom doping.