Heterogeneous cobalt polysulfide leaf-like array/carbon nanofiber composites derived from zeolite imidazole framework for advanced asymmetric supercapacitors.

A unique cobalt polysulfide/carbon nanofibers (C, N -Co x S y /CNF) film derived from zeolitic imidazolate framework is first prepared by a facile strategy. The hierarchical structure material is compose of CoS, CoS 2 , Co 9 S 8 , N -doped carbon nanosheets, and carbon nanofibers. The C, N -Co x S y /CNF electrode displays high specific capacitance and good rate performance due to the synergistic effect of cobalt polysulfide and carbon nanofibers. An asymmetric supercapacitor based on C, N -Co x S y /CNF and AC electrodes is assembled and exhibits high energy density and power density. [Display omitted] Developing new electrode materials is one of the keys to improving the energy density of supercapacitors. In this article, a novel cobalt polysulfide/carbon nanofibers (C, N -Co x S y /CNF) film derived from zeolitic imidazolate framework is first prepared by a facile strategy. The composite material with two-dimensional leaf-shaped nanoarray neatly grown on the surface of carbon nanofibers is composed of CoS, CoS 2 , Co 9 S 8 , N -doped carbon nanosheets, and carbon nanofibers. It is found that the composite can not only increase the contact area with the electrolyte but also provide abundant redox-active sites and a Faraday capacitance for the entire electrode. The C, N -Co x S y /CNF composite exhibits excellent electrochemical properties, including a high capacity of up to 1080F g -1 at 1 A g -1 and a good rate capability (80.4 % from 1 A g -1 to 10 A g -1). A C, N -Co x S y /CNF//AC asymmetric supercapacitor device is assembled using C, N -Co x S y /CNF as the positive electrode and activated carbon as the negative electrode, showing high energy density (37.29 Wh kg -1@813.6 W kg -1) and good cycle stability (90.5% of initial specific capacitance at 10 g−1 after 5000 cycles). This C, N -Co x S y /CNF composite material may also be used as a potential electrode for future lithium-ion batteries, zinc-ion batteries, lithium-sulfur batteries, etc. [ABSTRACT FROM AUTHOR]