Construction of hierarchical Co₉S₈@NiO synergistic microstructure for high-performance asymmetric supercapacitor

Metal-organic frameworks (MOFs) become a research hot-spot owing to their unique properties originating from the ultra-high porosity and large specific surface area with highly accessible active sites. However, the electrochemical performance of a single component is unsatisfied when MOFs are applied as electrode material in a supercapacitor. In this work, the hierarchical hollow framework involving interconnected Co₉S₈ structure and NiO nanosheets (Co₉S₈@NiO) are successfully prepared by MOFs derived methods and proposed to electrode materials. As a result, the prepared Co₉S₈@NiO electrode materials exhibit a superior specific capacitance of 1627 F g^-1 at a current density of 1 A g^-1. Moreover, an assembled hybrid supercapacitor shows a high energy density of 51.65 Wh Kg^-1 at a power density of 749.8 W Kg^-1 as well as excellent long-term cycling stability with 81.79% capacity retention after 10,000 cycles. Meanwhile, we concluded that the marvelous electrochemical performance is closely associated with the unique structure of NiO, in particular, the nanosheet surface provides a superior specific surface area and rich accessible redox reaction sites, thus enlarged the contact between the surface and interface of the electrode material. Finally, two supercapacitor devices connected in series can light up four light-emitting diodes (LEDs) for about 30 min. Hence, the presented strategy represents a general route for supercapacitor electrode material with promising electrochemical performance, which can combine the MOFs template and other hierarchical nanosheets together.