Synergism between oxygen vacancies and Fe-Nx in N-doped Fe3O4@CNTs for enhanced oxygen reduction reaction

·N-doped Fe 3 O 4 @CNTs with Fe-Nx and oxygen vacancies was fabricated for efficient ORR electrocatalysis. • The catalyst shows onset potential of 0.87 V and superior stability toward oxygen reduction reaction. • Zinc–air battery delivers 173.90 mW·cm −2 power density and stable running for 280 h. • Synergy of oxygen vacancies and Fe-Nx sites boosts ORR activity and structural stability. A composite catalyst consisting of Fe 3 O 4 nanoparticles coated with nitrogen-doped carbon nanotubes (Fe 3 O 4 @CNTs) was synthesized via in situ pyrolysis using heme-modified CNTs. Benefiting from the CNT coating and oxygen vacancies, the catalyst exhibits a half-wave potential of 0.88 V for oxygen reduction in alkaline media, with stability surpassing commercial Pt/C. In zinc-air batteries, it achieves a power density of 173.90 mW·cm −2 and maintains stable operation over 280 h. Experimental and theoretical studies reveal that the CNT coating provides a 3D conductive network, prevents Fe 3 O 4 agglomeration, and modulates the electronic structure of the active-sites via Fe–N interactions. Meanwhile, abundant oxygen vacancies are introduced into Fe 3 O 4 , optimizing O 2 adsorption and reducing reaction barriers. This work offers new insights into the design of iron-based oxide electrocatalysts with high activity and durability for renewable energy applications.