One-Step Hydrothermal Synthesis of CoNi2S4 for Hybrid Supercapacitor Electrodes

In this study, a simple one-step hydrothermal method was developed to prepare a novel hierarchical CoNi 2 S 4 nanostructure similar to rambutan fruit. The surface microstructural study clearly visualized that the rambutan-like CoNi 2 S 4 consists of nanorods grown directly on the surface of spherical core structures. The close attachment of the nanorods to the spheres increased the active areas of the electrode, which facilitates efficient charge transport from the nanorods to the spherical core structure. CoNi 2 S 4 with a rambutan-like hierarchical structure showed an excellent specific capacitance of 944 F g − 1 at 1 A g − 1 , considerable rate capacitance (75.6% retention at 10 A g − 1 ) and excellent cycling life (91.1% retention after 5000 circulations) in the three-electrode system. Besides, the assembled hybrid supercapacitor based on CoNi 2 S 4 and reduced graphene oxide exhibited a high specific energy density of 23.58 Wh kg − 1 at the power density of 800 W kg − 1 .