Unveiling the Proton-Feeding Effect in Sulfur-Doped Fe-N-C Single-Atom Catalyst for Enhanced CO2 Electroreduction

Heteroatom-doping in metal-nitrogen-carbon single-atom catalysts (SACs) is considered a powerful strategy to promote the electrocatalytic CO2 reduction reaction (CO2RR), but the origin of enhanced catalytic activity is still elusive. Here, we disclose that sulfur doping induces an obvious proton-feeding effect for CO2RR. The model SAC catalyst with sulfur doping in the second-shell of FeN4 (Fe-1-NSC) was verified by X-ray absorption spectroscopy and aberration-corrected scanning transmission electron microscopy. Fe-1-NSC exhibits superior CO2RR performance compared to sulfur-free FeN4 and most reported Fe-based SACs, with a maximum CO Faradaic efficiency of 98.6 % and turnover frequency of 1197 h(-1). Kinetic analysis and in situ characterizations confirm that sulfur doping accelerates H2O activation and feeds sufficient protons for promoting CO2 conversion to *COOH, which is also corroborated by the theoretical results. This work deepens the understanding of the CO2RR mechanism based on SAC catalysts.

Automated summary

Sulfur doping in metal-nitrogen-carbon single-atom catalysts enhances the electrocatalytic CO2 reduction reaction (CO2RR) by accelerating H2O activation and providing sufficient protons.