Co-Doped Ni3V2O8 Nanofibers Achieving d–d Orbital Coupling for Electrocatalytic Oxygen Reduction

Efficient and robust non-platinum-group metal electrocatalysts for O₂ reduction are a prerequisite for practical high-performance fuel cells and metal-air batteries. Herein, we reported an integrated principle of gradient electrospinning and controllable pyrolysis to fabricate various Co-doped Ni₃V₂O₈ nanofibers with high oxygen reduction reaction (ORR) activity. The representative Co_1.3Ni_1.7V₂O₈ nanofibers showed outstanding ORR performance in an alkaline solution with a half-wave potential (E_1/2) of 0.874 V vs RHE, along with high long-term stability. Furthermore, the introduction of Co could effectively restrain the growth of nanoparticles and change the electronic structure of Ni₃V₂O₈. Control experiments and theoretical calculations demonstrated that upon Co-doping, the hybridization between the 3d orbital for both Co and Ni guaranteed the stable adsorption interaction with O₂ over Ni and Co metal centers. Meanwhile, the weakened binding ability of Ni₃V₂O₈ to OH* reduced the ORR free energy. Overall, the synergistic effect of Co and Ni metal cations essentially reflected the origin of ORR activity on the Co-doped Ni₃V₂O₈ nanofibers. This work offers new insights and practical guidance for designing highly active ORR catalysts for electrochemical clean energy conversion and storage.