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Heteroatoms-modified Fe–N–C catalysts have garnered significant attention for enhancing the oxygen reduction reaction (ORR). However, revealing the correlation between the type of heteroatoms used for doping and catalytic performance still faces significant challenges. Herein, based on the density functional theory (DFT), a series of heteroatom-modified Fe–N–C models with the tailored Fe–N 4 -X (X = S, P or B) site are constructed to explore the regulatory mechanism of heteroatoms on the electronic structure and adsorption behavior of Fe centers. Theoretical calculations reveal that the doping of S atoms can optimize the electronic environment of Fe atoms, thus leading the favorable interaction between Fe–N 4 –S site and OH intermediates. As a result, the Fe–N 4 –S site possess a lower energy barrier for the desorption of OH* than that of Fe–N 4 –B and Fe–N 4 –P, indicating higher catalytic activity and kinetics of S-modified Fe–N–C catalysts. [Display omitted] • Heteroatom-modified Fe–N 4 models are analyzed by theoretical calculations. • S doping can optimize the electronic structure around Fe–N 4 sites. • S doping promotes the OH* desorption, thus leading to enhanced kinetics process. • Fe–N 4 –S model exhibits higher activity and stability than Fe–N 4 –B and Fe–N 4 –P. [ABSTRACT FROM AUTHOR]

Coordination environment engineering is developed to synthesize Fe SA /NSC catalysts with the tailored N, S co-coordinated Fe atomic site. [Display omitted] • The Fe-N 3 S active site with the optimized electronic structure is constructed. • S doping promotes the OH* desorption, thus leading to enhanced kinetics process. • The catalyst displays impressive ORR activity in both alkaline and acidic mediums. • The catalyst exhibits excellent performance in Zn-air batteries and fuel cells. Atomically dispersed iron–nitrogen-carbon (FesbndNsbndC) materials have been considered ideal catalysts for the oxygen reduction. Unfortunately, designing and adjusting the electronic structure of single-atom Fe sites to boost the kinetics and activity still faces grand challenges. In this work, the coordination environment engineering is developed to synthesize the Fe SA /NSC catalyst with the tailored N, S co-coordinated Fe atomic site (Fe-N 3 S site). The structural characterizations and theoretical calculations demonstrate that the incorporation of sulfur can optimize the charge distribution of Fe atoms to weaken the adsorption of OH* and facilitate the desorption of OH*, thus leading to enhanced kinetics process and intrinsic activity. As a result, the S-modified Fe SA /NSC exhibits outstanding catalytic activity with the half-wave potentials (E 1/2) of 0.915 V and 0.797 V, as well as good stability, in alkaline and acidic electrolytes, respectively. Impressively, the excellent performance of Fe SA /NSC is further confirmed in Zn-air batteries (ZABs) and fuel cells, with high peak power densities (146 mW cm−2 and 0.259 W cm−2). [ABSTRACT FROM AUTHOR]

The systematic summarization of the synthesis-structure-performance-mechanism correlations provides guidance for the rational design of S-doped M-N-C catalysts for ORR. [Display omitted] • Recent review on preparation of S-doped M-N-C catalysts for ORR. • Effects of doping S atoms on the ORR performance of M-N-C catalysts. • The advanced characterization methods and computational methods for S-doped M-N-C catalysts are introduced. • The future development direction of M-N-C catalysts is described. Due to the strong electronegativity of the N atom, the adsorption energy of the transition metal –nitrogen active site for the ORR intermediate is too high to facilitate the subsequent elementary reactions. It is worth noting that introducing sulfur atoms in transition metal–nitrogen–carbon catalysts can optimize the charge distribution of nitrogen atoms around metal sites to improve the electronic structure and structural defects of the catalysis, so as to boost the adsorption and transfer of oxygen-containing intermediates. Meanwhile, sulfur-doping can also inhibit metal nanoparticle formation and promote hierarchical porous carbon formation. This review will afford the S-doped M-N-C catalysts rational design principle and strategies and introduce the corresponding ORR electrochemical properties. We will combine advanced characterization techniques and DFT calculation to discuss the coordination environment of active sites and the ORR mechanism of S-doped M-N-C catalysts. Finally, a general perspective on the challenges and opportunities for S-doped M-N-C catalysts will be proposed to facilitate further development. [ABSTRACT FROM AUTHOR]