(Invited) NiCo₂O₄/MnO₂ Microsphere as Efficient Bi-functional Electrocatalyst for Zinc-air Battery

Microsphere-like NiCo 2 O 4 /MnO 2 composite was synthesized via hydrothermal route as an efficient electrocatalyst with dual functionality, facilitating oxygen electrocatalysis reactions and serving as an air cathode in zinc-air batteries (ZABs) applications. The as-synthesized NiCo 2 O 4 /MnO 2 demonstrated adaptable kinetics for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Specifically, it displayed a half-wave potential of 0.692 V for ORR and an overpotential of 218 mV for OER at a current density of 10 mA·cm -2 . The double layer capacitance for NiCo 2 O 4 /MnO 2 was experimentally calculated to be 31.67 mF.cm -2 , suggesting a substantial level of electrochemical activity in the synthesized composite. The ZAB device assembled with a NiCo 2 O 4 /MnO 2 cathode in a 6 M KOH electrolyte achieved an open circuit voltage of 1.48 V. It demonstrated a maximum power density of 127.04 mW·cm –2 at a current density of 190.64 mA·cm -2 and exhibited a notable specific discharge capacity of 756.62 mAh·g -1 at a current density of 5 mA·cm -2 . The ZAB exhibited remarkable stability over 200 hours (equivalent to 600 cycles) of charge-discharge cycling at 5 mA·cm -2 , with an almost negligible decrease in voltaic efficiency (~1.58%). Moreover, the practical applicability of Zn//NiCo 2 O 4 /MnO 2 battery was assessed by powering a 2 V light-emitting diode for 20 hours employing two ZAB devices connected in series. This study establishes a foundation for the feasible application of ZABs incorporating cathodes based on Ni-Co-Mn.