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

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_xS_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, CoS₂, Co₉S₈, 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_xS_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_xS_y/CNF//AC asymmetric supercapacitor device is assembled using C,N-Co_xS_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_xS_y/CNF composite material may also be used as a potential electrode for future lithium-ion batteries, zinc-ion batteries, lithium-sulfur batteries, etc.