A Hollow Tube-on-Tube Architecture of Carbon-Tube-Supported Nickel Cobalt Sulfide Nanotubes for Advanced Supercapacitors

The nanotube structure has unique advantages, such as a large electroactive surface area and shorter diffusion pathway for ions/electrons for energy storage. In this paper, we fabricated a novel supercapacitor electrode material based on a composite material with a hollow tube-on-tube architecture. This architecture, which was derived from the sustainable Juncus roemerianus, consisted of nickel cobalt sulfide nanotubes coating the exterior and interior of carbon tubes. The obtained hollow tube-on-tube structure is similar to a reservoir, in which ions/electrons can diffuse via a bi-directional method and supply and transfer to the carbon tube interface. Consequently, this structure can probably provide more electrochemically active sites for its application in high-performance asymmetric supercapacitors (ASCs). The assembled ASC device also presents superior specific capacitance (83Fg(-1) at the current density of 0.5Ag(-1)), high energy density (27.7Whkg(-1) at a power density of 263.6Wkg(-1)), and good cycling stability (72.23% capacitance retention after 3000cycles). Therefore, the NiCo2S4/bio-carbon electrode with hollow tube-on-tube structure is not only a promising electrode material, but also can be applicable to energy storage and conversion devices.