Facile synthesis of NiCo2O4 nanosphere-carbon nanotubes hybrid as an efficient bifunctional electrocatalyst for rechargeable Zn–air batteries

•One-pot synthesis of NiCo2O4 nanosphere and carbon nanotubes hybrid catalysts is reported.•NiCo2O4-CNTs hybrid exhibited highly catalytic activity for both ORR and OER.•The primary Zn–air battery reached a discharge peak power density of 320 mW cm−2.•The rechargeable Zn–air battery showed a stability of 100 h at 10 mA cm−2 with 10 min per cycle.

Developing low-cost non-precious metal catalysts for high-performance oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desirable. In this work, both the primary and rechargeable Zn–air batteries with NiCo2O4 nanosphere and carbon nanotubes hybrid (NiCo2O4-CNTs) as cathode catalyst are reported. The catalysts are synthesized through a facile one-pot precipitation reaction and hydrothermal process, which exhibited highly active bi-functional catalytic activity for both ORR and OER. Using NiCo2O4-CNTs hybrid as a cathode catalyst, the resulting practical primary and electrochemically rechargeable Zn–air batteries give a promising discharge peak power density as high as 320 mW cm−2, and a high current density 210 mA cm−2 at 1.0 V. Also, the rechargeable Zn–air batteries in a two-electrode configuration exhibits an unprecedented small charge–discharge voltage polarization of ∼0.75 V at 10 mA cm−2, high reversibility and stability over long charge and discharge cycles. The high performance is believed to be induced by the hybrid effect (coupling effect) among NiCo2O4 and CNTs, which can produce a synergy enhancement for both catalytic ORR and OER.