Template-free synthesis of hierarchical hollow NiS microspheres for supercapacitor.

Hierarchical nickel sulfide (NiS) hollow microspheres can be successfully synthesized with a template-free method using α-Ni(OH) microspheres as a precursor by calcination and sulfidation. The intermediate Ni hollow spheres, formed at different calcination temperatures (300°C and 400°C) under H/N atmosphere, can be easily transformed into NiS with similar morphology and mixed phases of NiS and NiS during the followed sulfidation process. The formation processes for the hollow structure of NiS are also discussed in this work. Particularly, the NiS prepared from Ni intermediate spheres at 300°C show a high specific capacity of 153.6mAhg at 0.5Ag at high mass loading due to its small crystal size, hierarchically porous structure and high electrical conductivity. A hybrid capacitor was assembled by using it as positive electrode and activated carbon as negative electrode to examine their practical applications in a full-cell configuration. The hybrid capacitor exhibited excellent comprehensive performances in 1.6V. The hybrid capacitor also showed good cycling stability, with 81.25% of the initial specific capacitance after 1000 cycles at 2Ag. Above results indicate the great potential of the NiS hollow spheres as a promising electrode material for supercapacitor applications.