Template-free synthesis of hierarchical hollow NiSx microspheres for supercapacitor

Abstract Hierarchical nickel sulfide (NiS x ) hollow microspheres can be successfully synthesized with a template-free method using α-Ni(OH) 2 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 2 /N 2 atmosphere, can be easily transformed into NiS x with similar morphology and mixed phases of Ni 3 S 2 and NiS during the followed sulfidation process. The formation processes for the hollow structure of NiS x are also discussed in this work. Particularly, the NiS x prepared from Ni intermediate spheres at 300 °C show a high specific capacity of 153.6 mAh g −1 at 0.5 A g −1 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 1.6 V. The hybrid capacitor also showed good cycling stability, with 81.25% of the initial specific capacitance after 1000 cycles at 2 A g −1 . Above results indicate the great potential of the NiS x hollow spheres as a promising electrode material for supercapacitor applications.