Unveiling the synergistic promotion mechanism of vanadium nitride nanoparticles on single-atom Fe sites for enhanced oxygen reduction reaction

The development of high-performance non-noble metal catalysts for the oxygen reduction reaction (ORR) is critical for advancing electrochemical energy conversion devices. Herein, a series of Fe 1 NC-VX catalysts (X = 1, 3, 5) were synthesized via a two-step process involving solvothermal polymerization of formamide with Fe 3+ and V 5+ salts, followed by pyrolysis under N 2 atmosphere, where the content of vanadium nitride (VN) nanoparticles was regulated by adjusting the V precursor concentration. Physicochemical characterizations confirmed that Fe exists as atomically dispersed Fe N 4 sites, while VN nanoparticles are formed in V-doped samples, with Fe 1 NC-V3 exhibiting optimal Fe V synergistic interactions and a reduced Fe oxidation state. Electrochemical evaluations in 0.1 M KOH showed that Fe 1 NC-V3 delivers superior ORR activity with an onset potential of 1.02 V, half-wave potential of 0.89 V, a dominant 4-electron transfer pathway, and a low Tafel slope of 55.4 mV dec −1 , outperforming commercial Pt/C. It also exhibits excellent methanol tolerance and durability. Density functional theory (DFT) calculations revealed that VN modulates the electronic structure of Fe N 4 sites via a d -band center downshift, optimizing intermediate adsorption and reducing the rate-determining step overpotential to 0.58 eV. In practical zinc-air batteries (ZABs), Fe 1 NC-V3-based ZAB achieved a high open-circuit voltage (1.578 V), peak power density (214.1 mW cm −2 ), specific capacity (813.8 mAh g Zn − 1 ), and exceptional cycling stability. These findings demonstrate that Fe 1 NC-V3 is a competitive noble metal substitute for efficient electrochemical energy conversion.