Nickel foam supported hierarchical Co9S8 nanostructures for asymmetric supercapacitors

Abstract

In this work, nickel foam supported Co₉S₈ nanostructures are fabricated by a facile two-step hydrothermal process. The Co₉S₈ nanostructures have a hierarchical structure in which the Co₉S₈ nanotubes are wrapped by Co₉S₈ nanosheets. The Co₉S₈ nanostructures are in situ grown on nickel foam by the hydrothermal process and can be directly used as electrodes for supercapacitors without any further treatment. The Co₉S₈ electrode exhibits a high specific capacitance up to 2166 F g⁻¹ at a discharge current density of 1 A g⁻¹ and a capacitance retention of 74% at 20 A g⁻¹. Furthermore, the Co₉S₈ electrode shows a good cycling stability with 75.8% capacitance retention after 4000 charge–discharge cycles. An asymmetric supercapacitor device was assembled by using Co₉S₈ and porous carbon as the positive and negative electrode materials, respectively. The device displays an excellent electrochemical capability. This work demonstrates that the hierarchical Co₉S₈ nanostructures are desirable for application as advanced supercapacitor electrode materials.