Hierarchical NiCo(2)O(4)@NiCo(2)S(4) Nanocomposite on Ni Foam as an Electrode for Hybrid Supercapacitors

[Image: see text] In this work, NiCo(2)O(4)@NiCo(2)S(4) nanocomposite with a hierarchical structure is prepared by a multistep process. First, NiCo(2)O(4) nanowires array on Ni foam is prepared by a hydrothermal and a subsequent calcination process. Then, the NiCo(2)O(4) nanowires array is converted to NiCo(2)O(4)@NiCo(2)S(4) nanocomposite through a vapor-phase hydrothermal process. The NiCo(2)O(4)@NiCo(2)S(4)/Ni foam electrode exhibits a specific capacitance of 1872 F g(–1) at 1 A g(–1), a capacitance retention of 70.5% at 10 A g(–1), and a retention ratio of 65% after 4000 charge–discharge cycles. The capacitance of NiCo(2)O(4)@NiCo(2)S(4) nanocomposite is much higher than that of the NiCo(2)O(4) nanowires array. The excellent electrochemical capacitive performances of the NiCo(2)O(4)@NiCo(2)S(4) 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 NiCo(2)O(4)@NiCo(2)S(4)/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(–1) and a power density of 1.5 kW kg(–1) at 2 A g(–1).