High-performance non-spinel cobalt–manganese mixed oxide-based bifunctional electrocatalysts for rechargeable zinc–air batteries

Highlights: • A new type of non-spinel MnCo oxide on N-doped carbon nanotube was prepared. • It simultaneously exhibited high activity for the ORR and OER in alkaline media. • Primary Zn-air battery showed a gravimetric energy density of 695 Wh/kgZn. • Rechargeable Zn-air battery exhibits high round-trip efficiency and good stability. Development of efficient bifunctional electrocatalysts from earth abundant elements, simultaneously active for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), remains to be a grand challenge for electrocatalysis. Herein we firstly synthesized a new type of bifunctional catalyst (NCNT/Co_xMn_1−xO) consisting of non-spinel cobalt–manganese oxide supported on N-doped carbon nanotubes through a simple non-surfactant assistant hydrothermal method. This hybrid catalyst exhibits much higher OER activity than that of IrO₂, and comparable ORR activity to Pt/C with identical onset potential (0.96 V) in alkaline media. Furthermore, the NCNT/Co_xMn_1−xO catalyst was studied as a cathode in both primary and rechargeable zinc–air batteries demonstrating similar performance to commercial Pt/C or (Pt/C+IrO₂), respectively. Primary zinc–air battery tests show a gravimetric energy density of 695 W h ${\mathrm{kg}}_{\mathrm{Zn}}^{-1}$, and the rechargeable battery exhibits a high round-trip efficiency evidenced by a low discharge–charge voltage gap (0.57 V) at a current density of 7 mA cm⁻².