Hierarchical NiCoO@NiCoS Nanocomposite on Ni Foam as an Electrode for Hybrid Supercapacitors.

In this work, NiCoO@NiCoS nanocomposite with a hierarchical structure is prepared by a multistep process. First, NiCoO nanowires array on Ni foam is prepared by a hydrothermal and a subsequent calcination process. Then, the NiCoO nanowires array is converted to NiCoO@NiCoS nanocomposite through a vapor-phase hydrothermal process. The NiCoO@NiCoS/Ni foam electrode exhibits a specific capacitance of 1872 F g at 1 A g, a capacitance retention of 70.5% at 10 A g, and a retention ratio of 65% after 4000 charge-discharge cycles. The capacitance of NiCoO@NiCoS nanocomposite is much higher than that of the NiCoO nanowires array. The excellent electrochemical capacitive performances of the NiCoO@NiCoS nanocomposite can be attributed to the hierarchical nanostructure, which can provide large surface areas and short diffusion pathways for electrons and ions. By using the NiCoO@NiCoS/Ni foam as the positive electrode and activated carbon/Ni foam as the negative electrode, a hybrid supercapacitor device is fabricated. The device achieves an energy density of 35.6 W h kg and a power density of 1.5 kW kg at 2 A g.