Sulfur‐Mediated Microenvironment Modulation of High‐Density Fe‐N ₄ Sites for High‐Efficiency Oxygen Reduction and Cryotolerant Quasi‐Solid‐State Zinc‐Air Batteries

Abstract Single‐atom catalysts (SACs) featuring Fe‐N ₄ active sites hold significant potential for the oxygen reduction reaction (ORR). However, achieving high‐density Fe‐N ₄ active sites while precisely modulating their microenvironment to enhance ORR activity remains a formidable challenge. Here, an S‐mediated strategy is presented for the preparation of Fe single‐atom‐loaded S,N‐doped carbon (FeNSC). This strategy leverages the interactions between S and N during pyrolysis to significantly suppress N loss, thereby achieving a high density of Fe‐N ₄ sites. Concurrently, the precise doping of S into the second coordination shell of Fe‐N ₄ centers modulates their electronic structure, leading to a significant weakening of ^* O and ^* OH intermediates adsorption during the ORR. Consequently, the FeNSC catalyst exhibits excellent pH‐universal ORR performance with half‐wave potentials of 0.928 V (0.1 M KOH), 0.806 V (0.1 M HClO ₄ ), and 0.755 V (0.1 M phosphate buffer solution). A FeNSC‐based quasi‐solid‐state zinc‐air battery (QSS‐ZAB) achieves smooth operation over a broad temperature range of −40 to 60 °C. Notably, it sustains continuous operation for over 940 h at −40 °C, showcasing unprecedented cryotolerance. This work provides novel insights into the electronic microenvironment engineering of Fe‐N ₄ sites in SACs for high‐efficiency ORR and cryotolerant QSS‐ZABs.