Co-Doped Ni 3 V 2 O 8 Nanofibers Achieving d-d Orbital Coupling for Electrocatalytic Oxygen Reduction.

Efficient and robust non-platinum-group metal electrocatalysts for O ₂ 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 Ni ₃ V ₂ O ₈ nanofibers with high oxygen reduction reaction (ORR) activity. The representative Co _1.3 Ni _1.7 V ₂ O ₈ 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 Ni ₃ V ₂ O ₈ . 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 O ₂ over Ni and Co metal centers. Meanwhile, the weakened binding ability of Ni ₃ V ₂ O ₈ 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 Ni ₃ V ₂ O ₈ nanofibers. This work offers new insights and practical guidance for designing highly active ORR catalysts for electrochemical clean energy conversion and storage.