Co/Co9S8@carbon nanotubes on a carbon sheet: facile controlled synthesis, and application to electrocatalysis in oxygen reduction/oxygen evolution reactions, and to a rechargeable Zn-air battery

The development of efficient and cheap bifunctional catalysts for oxygen reduction and oxygen evolution reactions, is vital for the design of rechargeable Zn-air batteries. Herein, a facile strategy to fabricate Co/Co9S8 nanoparticles-encapsulated in carbon nanotubes, on an N-doped porous graphene sheet (Co/Co9S8@CNTs) via pyrolysis of a mixture of Co(NO3)2, melamine and L-cysteine is reported, the composition can be facile controlled using the molar ratio of melamine and L-cysteine. By controlling the molar ratio of melamine and L-cysteine and the pyrolysis temperature, Co/Co9S8@CNTs obtained at 900 °C (Co/Co9S8@CNTs-900) perform with high activities in oxygen reduction and oxygen evolution reactions, which promotes their application for rechargeable Zn-air batteries. Furthermore, the rechargeable Zn-air battery assembled with Co/Co9S8@CNTs-900 shows a high peak power density of 184.7 mW cm−2 and good long-term durability, holding great potential in practical applications.