Hierarchical composite electrodes of nickel oxide nanoflake 3D graphene for high-performance pseudocapacitors

NiO nanoflakes are created with a simple hydrothermal method on 3D (three-dimensional) graphene scaffolds grown on Ni foams by microwave plasma enhanced chemical vapor deposition (MPCVD). Such as-grown NiO-3D graphene hierarchical composites are then applied as monolithic electrodes for a pseudo-supercapacitor application without needing binders or metalbased current collectors. Electrochemical measurements impart that the hierarchical NiO-3D graphene composite delivers a high specific capacitance of ≈1829 F g^-1 at a current density of 3 A g^-1 (the theoretical capacitance of NiO is 2584 F g^-1). Furthermore, a full-cell is realized with an energy density of 138 Wh kg^-1 at a power density of 5.25 kW kg^-1, which is much superior to commercial ones as well as reported devices in asymmetric capacitors of NiO. More attractively, this asymmetric supercapacitor exhibits capacitance retention of 85% after 5000 cycles relative to the initial value of the 1^st cycle.