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

Abstract Heteroatom‐doping in metal‐nitrogen‐carbon single‐atom catalysts (SACs) is considered a powerful strategy to promote the electrocatalytic CO 2 reduction reaction (CO 2 RR), but the origin of enhanced catalytic activity is still elusive. Here, we disclose that sulfur doping induces an obvious proton‐feeding effect for CO 2 RR. The model SAC catalyst with sulfur doping in the second‐shell of FeN 4 (Fe 1 −NSC) was verified by X‐ray absorption spectroscopy and aberration‐corrected scanning transmission electron microscopy. Fe 1 −NSC exhibits superior CO 2 RR performance compared to sulfur‐free FeN 4 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 H 2 O activation and feeds sufficient protons for promoting CO 2 conversion to *COOH, which is also corroborated by the theoretical results. This work deepens the understanding of the CO 2 RR mechanism based on SAC catalysts.