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

Co-doped Ni3V2O8 nanofibersare prepared by electrospinning and pyrolysis with high ORR activity.It is noteworthy that the Co1.3Ni1.7V2O8 nanofibers show outstanding ORR performance in an alkalinesolution with a half-wave potential (E (1/2)) of 0.874 V vs RHE, outperforming that of the commercial Pt/C benchmark.The synergistic effect of Co and Ni metal cations reflects the originof ORR activity on the Co-doped Ni3V2O8 nanofibers. Efficient and robust non-platinum-group metal electrocatalystsfor O-2 reduction are a prerequisite for practical high-performancefuel cells and metal-air batteries. Herein, we reported anintegrated principle of gradient electrospinning and controllablepyrolysis to fabricate various Co-doped Ni3V2O8 nanofibers with high oxygen reduction reaction (ORR)activity. The representative Co1.3Ni1.7V2O8 nanofibers showed outstanding ORR performancein 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 thegrowth of nanoparticles and change the electronic structure of Ni3V2O8. Control experiments and theoreticalcalculations demonstrated that upon Co-doping, the hybridization betweenthe 3d orbital for both Co and Ni guaranteed the stable adsorptioninteraction with O-2 over Ni and Co metal centers. Meanwhile,the weakened binding ability of Ni3V2O8 to OH* reduced the ORR free energy. Overall, the synergistic effectof Co and Ni metal cations essentially reflected the origin of ORRactivity on the Co-doped Ni3V2O8 nanofibers.This work offers new insights and practical guidance for designinghighly active ORR catalysts for electrochemical clean energy conversionand storage.