Nitrogen, sulfur co-coordinated iron single-atom catalysts with the optimized electronic structure for highly efficient oxygen reduction in Zn-air battery and fuel cell

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-N₃S 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).