Identifying the Impact of Fe Nanoparticles Encapsulated by Nitrogen-Doped Carbon to Fe Single Atom Sites for Boosting Oxygen Reduction Reaction Toward Zn-Air Batteries

•A highly efficient Fe SAs/NPs@NC catalyst for boosting the ORR is developed.•A synergistic effect stemming from the isolated Fe-Nx and metallic Fe is uncovered.•The catalyst showed high ORR activity and stability superior to the commercial Pt/C.•The Zn-air battery exhibits high power density and excellent cycling stability.