Enhanced ORR/OER activities and stability of nitrogen-doped CNTs decorated with MnO2 as electrocatalysts in rechargeable Zn-air batteries

It is the key to develop an efficient and durable bifunctional electrocatalyst that can catalyze both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in rechargeable Zn-air batteries. In this study, nitrogen-doped carbon nanotubes (NCNTs) decorated with MnO2 were synthesized by metal organic chemical vapor deposition of manganese carbonyl. MnO2 and nitrogen species as active sites showed enhanced ORR/OER activities compared to NCNTs. A small amount of MnO2 can catalyze the disproportionation of hydrogen peroxide resulted in an overall four-electron reduction of oxygen. The electrochemical stability studies revealed that NCNTs decorated with MnO2 exhibited a slower decrease in OER activity and maintained a relatively higher ORR activity than NCNTs, which proves its high potential in ORR and OER catalysis under alkaline conditions. Furthermore, the NCNTs decorated with MnO2 catalyst exhibited excellent performance in Zn-air batteries.