Synthesis of cross-linked Ni-Co oxide nanowires on graphene hydrogel with high capacitive performance for hybrid supercapacitors

Herein, Ni-Co oxide nanowire arrays on graphene supported by Ni foam are fabricated by a simple strategy. In this strategy, the Ni-Co oxide nanosheets are induced to evolve into ultra-fine nanowires with high length/diameter ratio through two-step hydrothermal process, which can effectively increase the surface area, enhance electrochemical activity and improve electron/charge transfer efficiency, thereby resulting in enhanced charge storage performance. It is worth noting that the graphene as a support help to optimize capacitive performance of Ni-Co oxides nanowires. As expected, Ni-Co oxide nanowires anchored on graphene show enhanced specific capacitance of 2619.4 F g(-1), due to high-efficient synergistic effect of graphene. However, Ni-Co oxides nano-wires directly anchored on Ni foam without graphene have a relatively low specific capacitance of 1950.7 F g(-1) at 1 A g(-1), but still higher that that of Ni-Co oxides nanosheets arrays (1632.4 F g(-1)). Furthermore, the hybrid supercapacitor assembled by the Ni-Co oxides nanowires anchored on graphene and nitrogen doped graphene materials shows a specific energy of 24.8 Wh kg(-1) and great cycle stability of 90.3% retention after 8000 cycles. This work also provides a strategy to construct novel Ni-Co oxides materials with high charge storage perfor-mance for supercapacitor.