A bimetallic-activated MnO2 self-assembly electrode with a dual heterojunction structure for high-performance rechargeable zinc-air batteries

A major challenge in developing zinc-air batteries (ZABs) is to exploit suitable cathodes to efficiently accelerate the key electrocatalytic processes involved. Herein, a bifunctional oxygen catalytic self-supported MnO2-based electrode is designed that displays superior oxygen reduction and evolution reaction performance over noble metal electrodes with a total overpotential of 0.69 V. In addition, the as-synthesized NiCo2O4@MnO2/carbon nanotube (CNT)-Ni foam self-supported electrode can be directly used as an oxygen electrode without externally adding carbon or a binder and shows reasonable battery performance with a high peak power density of 226 mW cm-2 and a long-term charge-discharge cycling lifetime (5 mA for 160 h). As expected, the rapid oxygen catalytic intrinsic kinetics and high battery performance of the NiCo2O4@MnO2/CNTs-Ni foam electrode originates from the unique three-dimensional hierarchical structure, which effectively promotes mass transfer. Furthermore, the CNTs combined with Ni foam form a unique “meridian” conductive structure that enables rapid electron conduction. Finally, the abundant Mn3+ active sites activated by bimetallic ions shorten the oxygen catalytic reaction distance between the active sites and reactant and reduce the surface activity of MnO2 for the O, OH, and OOH species. This work not only offers a high-performance bifunctional self-supported electrode for ZABs but also opens new insights into the activation of Mn-based electrodes.