Cobalt-Doped MnFe2O4 Spinel Coupled with Nitrogen-Doped Reduced Graphene Oxide: Enhanced Oxygen Electrocatalytic Activity for Zinc-Air Batteries

MFCO spinel anchored on N-rGO is synthesized by a two-step hydrothermal method as a bifunctional electrocatalyst. Its physicochemical properties have been characterized and tested, and it is applied to zinc-air batteries. The experimental and theoretical calculations show that the MFCO is uniformly distributed on the surface of N-rGO. When MFCO is anchored on the conducting N-rGO, a synergistic effect occurs between the Co–N bonds, which changes the arrangement of the C–N bonds from the sp² orientation to the sp³ form. The ORR catalytic pathway of the MFCO/N-rGO electrocatalyst is dominated by 4-electron transfer, with a half-wave potential of 0.8003 V, an overpotential value of 352 mV, and a small potential difference (ΔE = 0.78 V). With a charge/discharge voltage difference of about 0.88 V, the voltage gap remains almost unchanged for a long period after 650 h, showing excellent stability. The improved catalytic performance is attributed to Co acting as an active site, and the doping of Co induces the Jahn–Teller effect, which alters the electronic structure of spinel, shifts the d-band center upward, enhances the adsorption of oxygen intermediates, and promotes the oxygen electrocatalytic reaction. This study provides a low-cost and promising bifunctional oxygen electrocatalyst for zinc-air batteries.