Efficiently optimizing the oxygen catalytic properties of the birnessite type manganese dioxide for zinc-air batteries

It is of great significance to design and develop the high-efficiency and low-cost bifunctional oxygen catalysts. Manganese dioxide (MnO2) is one of the most widely studied catalysts for oxygen reduction reaction (ORR) on account of the high reserves and environmental friendliness. Whereas, the catalytic activity of MnO2 for oxygen evolution reaction (OER) is so inferior that it cannot be used as the bifunctional oxygen catalysts. In this work, the assembled nanospheres of cobalt ion intercalated birnessite type MnO2 with a unique lamellar structure are synthesized by a very facile one-step liquid-phase method under mild conditions. Importantly, compared with the pristine MnO2, the optimized cobalt ion intercalated δ-MnO2 (24Co–MnO2) shows the greatly enhanced OER catalytic activity and stability. Specially, 24Co–MnO2 displays a low OER overpotential of 430 mV at 10 mA cm−2 in 0.1 M KOH. In addition, 24Co–MnO2 shows much higher bifunctional oxygen catalytic activity than most of the manganese oxide based catalysts. Moreover, 24Co–MnO2 as the bifunctional oxygen catalyst is assembled in the aqueous and flexible solid-state zinc-air batteries (ZABs), showing the high peak power density and outstanding cycling stability.