High Density Arrayed Ni/NiO Core-shell Nanospheres Evenly Distributed on Graphene for Ultrahigh Performance Supercapacitor.

A novel NiO/Ni/RGO three-dimensional core-shell architecture consisting of Ni nanoparticles as core, NiO as shell and reduced graphene oxide (RGO) as conductivity layer, has been constructed by redox reactions with hydrothermal method and heat treatment. High density arrayed nickel nanoparticles (20 nm diameter) semi-coated by a 3 nm thick layer of NiO are evenly distributed on the surface of graphene. This elaborate design not only uses abundant NiO surfaces to provide a wealth of active sites, but also bridges electrochemical active NiO shell and graphene by Ni core to construct an interconnected 3D conductive network. Since both electrochemical activity and excellent conductivity are reserved in this Ni/NiO core-shell/graphene layer 3D structure, the as-prepared electrode material exhibits an extremely high specific capacitance (2048.3 F g at current density of 1 A g) and excellent cycle stability (77.8% capacitance retention after 10000 cycles at current density of 50 A g). The novel method presented here is easy and effective and would provide reference for the preparation of other high performance supercapacitor electrodes.