Atomically dispersed Fe/Zn synergy in sulfur-modified nitrogen-doped carbon for boosting oxygen reduction activity†

Single-atom catalysts (SACs) stabilized by multiple nitrogen-coordination architectures exhibit superior catalytic activity in pivotal electrocatalytic reactions, owing to their highly unsaturated coordination environments and robust metal-substrate interactions. Herein, atomically dispersed Fe and Zn species stabilized in specific Fe-N₄ and Zn-N₄ configurations without dimer formation were synthesized, confirmed by X-ray absorption near-edge structure analysis. Moderate S-doping strategically modulates the electronic structure of metal active sites, which advantageously regulates the adsorption/desorption characteristics of the atomic center towards the reaction intermediate. Electrochemical evaluations reveal remarkable oxygen reduction reaction (ORR) enhancement in the S-doped Fe₁Zn₁-NC catalyst (denoted as the Fe₁Zn₁-SNC-X series). The optimal catalyst Fe₁Zn₁-SNC-II demonstrates an exceptional onset potential of 0.999 V and half-wave potential of 0.871 V in 0.1 M KOH, surpassing the performance of Fe₁Zn₁-NC (S free). When assembled in zinc–air batteries (ZABs), the Fe₁Zn₁-SNC-II-ZAB outperforms the Pt/C-ZAB in both power density and cycling stability. This work provides fundamental insights into catalytic enhancement mechanisms through precisely tailoring the local coordination environment of M₁-N₄/M₂-N₄ moieties, establishing a paradigm for designing high-performance SACs by synergistic heteroatom engineering.