Uniform Co9S8 nanosheets on carbon nanotube arrays grown on Ni mesh as free-standing electrodes for asymmetric supercapacitors

A free-standing 3D core/shell composite material CNTs@Co 9 S 8 on nickel mesh has been prepared by a simple two-step method. Carbon nanotubes (CNTs) grown vertically on the surface of nickel mesh by chemical vapor deposition (CVD) method act as conductive skeleton. Then Co 9 S 8 nanosheets uniformly aligned on the surface of the CNTs by solvothermal method are interconnected to form a honeycomb structure . Owing to the close contact of the CNTs@Co 9 S 8 hybrid with the nickel mesh and the hierarchical 3D porous structure , the prepared Ni@CNTs@Co 9 S 8 electrodes exhibit low resistance and excellent charge storage capability with a specific capacitance of 1305.4 F g −1 at 1 A g −1 . The composite delivers an excellent rate capability with 84.3 % capacitance retention at 10 A g −1 . An asymmetric supercapacitor composed of Ni@CNTs@Co 9 S 8 and nitrogen-doped carbon nanotubes (NCNTs) shows an energy density of 23.8 Wh kg −1 and a high power density of 8007.4 W kg −1 . The specific capacitance of the ASC device remained 87.31 % after 10,000 charge-discharge cycles and two tandem ASCs can power two red LED diodes for at least 7 min, suggesting the potential application of the obtained free-standing electrode for supercapacitors .