Synergistic regulation of nickel doping/hierarchical structure in cobalt sulfide for high performance zinc-air battery

Reduced-graphene-nanoribbon supported nickel doped Co9S8 spheres (Ni-Co9S8/rGN) have been successfully constructed. The hierarchical structured sphere assembles by spindle-type nanorods features high surface area and good hydrophilicity property. Excellent OER/ORR activities and long-term stabilities are obtained on Ni-Co9S8/rGN relative to Pt/C and RuO2. Density functional theory calculations demonstrate that nickel dopants in Co9S8 structure effectively optimizes the adsorption properties at the rate-determining steps. Therefore, the synergistic regulation between the rGN covered hierarchical structure and nickel dopants by promoting the intrinsic ORR/OER properties, electrical conductivity, and mass transfer is responsible to the superior catalytic performance. Moreover, as a bi-functional catalyst for liquid and flexible Zn–air batteries, Ni-Co9S8/rGN based battery exhibits excellent battery performance, especially high power density, superior rate performance and long-term cycling stability, providing a new vision for the preparation of high-efficiency catalysts in energy conversion.