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.