Carbon-coated MnCo2O4 nanowire as bifunctional oxygen catalysts for rechargeable Zn-air batteries

Abstract

The catalytic activity of spinel-type MnCo2O4 is often limited by the poor electronic conductivity, limited specific surface area and inferior stability in oxygen reduction reaction and oxygen evolution reaction. In this study, carbon-coated MnCo2O4 nanowire (MnCo2O4@C) is prepared by a self-template method from MnCo2-NTA nanowire precursor. MnCo2O4@C shows excellent electrocatalytic performance and improved circulation stability, with an onset potential of 0.92 V and current retention rate of 99% within 10000 s at 0.80 V vs. RHE, better than the commercial Pt/C (Eonset = 0.94 V, current retention rate 94%). Further study shows that the oxygen reduction mechanism of MnCo2O4@C follows quasi-four-electron transfer process. The carbon provides conductive network and promotes the fast transfer of electrons in between the carbon network and MnCo2O4 nanoparticles. Meanwhile, under the limitation of rigid carbon shell, the growth of MnCo2O4 nanoparticle is impeded. These make MnCo2O4@C excellent electrochemical properties, and endow rechargeable Zn-air battery with high open-circuit voltage of 1.43 V and long-term cycling performance over 70 h with high efficiency and stability. MnCo2O4@C holds great promise as highly active bifunctional electrocatalyst in the practical application of rechargeable metal-air batteries and other fuel cells.