Synthesis of hierarchically porous NiCo2S4 core-shell hollow spheres via self-template route for high performance supercapacitors

The synthesis of hierarchical nickel cobalt sulfide with core-shelled hollow structures is greatly desired for electrochemical energy storage. Here we report a simple self-template route to synthesize hierarchical NiCo2S4 core-shell hollow spheres. Hierarchical Ni-Co precursor solid spheres are first prepared and utilized as the templates. After a sulfidation process, the solid precursor spheres can be transformed into hierarchical NiCo2S4 hollow spheres with a core-shelled hollow interior. The hierarchical NiCo2S4 core-shell hollow spheres possess a large specific surface area (98.8 m(2) g(-1)) and mesoporous (about 12 nm in sizes) structure. In view of the large specific surface areas, porosities, and novel hollow structures, the hierarchically porous NiCo2S4 core-shell hollow spheres as electrode materials present a high specific capacitance of 1870.2 F g(-1) at 2.0 A g(-1) and an excellent long-duration cycling performance (about 9% loss after 3000 repeated charging-discharging cycles). Additionally, an asymmetric supercapacitor device using the NiCo2S4 as a positive electrode and activated carbon as a negative electrode is assembled, which delivers an energy density of 52.9 W h kg(-1) at power density of 374.9 W kg(-1). This work not only suggests the promising electrode materials of the hierarchically porous NiCo2S4 core-shell hollow spheres for application in electrochemical energy storage, but also provides an effective strategy on the metal sulfides design and preparation. (C) 2018 Elsevier B.V. All rights reserved.