Hexagonal prism-like hierarchical Co9S8@Ni(OH)2 core–shell nanotubes on carbon fibers for high-performance asymmetric supercapacitors

Abstract

In this work, novel hierarchical cobalt sulfide@nickel hydroxide [Co₉S₈@Ni(OH)₂] core–shell nanotube arrays supported on carbon fibers have been designed logically and synthesized for use as supercapacitors. The one-dimensional Co₉S₈ nanotubes (NTs) serve as an ideal backbone to improve the electrical conductivity of Ni(OH)₂ nanosheets, whereas the ultrathin and redox active Ni(OH)₂ nanosheets electrodeposited on the Co₉S₈ NTs greatly enhance the surface area and provide more electroactive sites for faradaic reaction. The optimized Co₉S₈@Ni(OH)₂ electrode shows high specific capacitances of 149.44 mA h g⁻¹ at the current density of 1 A g⁻¹ and 75 mA h g⁻¹ even at 10 A g⁻¹. An asymmetric supercapacitor was successfully assembled with this unique hybrid nanostructure as the anode and an active carbon film as the cathode. The as-fabricated device shows high energy density (31.35 W h kg⁻¹ at 252.8 W kg⁻¹), high power density (2500 W kg⁻¹ at 12.5 W h kg⁻¹), as well as a long-term cycle stability (97.3% retention of its initial capacitance after 5000 cycles). The as-prepared hierarchical nanostructure shows great potential as a promising electrode material for energy storage applications.