Three dimensional hollow sulphide nanocomposites for supercapacitor electrodes

The transition metal sulphides have gained sufficient attraction due to their high theoretical capacitance, low electronegativity, good thermal and electrical conductivity and good redox behaviour. In the present work, nanocomposites of nickel cobalt sulphide (NiCoS), zinc cobalt sulphide (ZnCoS), copper cobalt sulphide (CuCoS) and nickel-zinc-copper cobalt sulphide (NiZnCuCoS) have been prepared, by hydrothermal synthesis method, for their use as the supercapacitor electrode material. The X-ray diffraction analysis, Field Emission Scanning Electron Microscopy images and UV–Visible studies suggest the formation of quantum dots (as the crystallite size is in the range of 3.5 nm–6.0 nm) in all the nanocomposites. The aim of this study is to observe the change in the electrochemical properties of the transition metal sulphides by multi-metal doping. The electrochemical measurements reveal that among all the prepared nanocomposites, highest specific capacitance (150 F g−1 at 5 mV s−1) has been exhibited by CuCoS nanocomposites (nanowires like structure) whereas highest potential window (1.7 V) and hence highest energy density (16.5 W h kg−1 at 0.1 A g−1) has been exhibited by NiZnCuCoS nanocomposites. Presently, the main goal of supercapacitors is to provide high energy density. It is observed that multi-metal sulphides (NiZnCuCoS), when used as the supercapacitor electrode, provide better electrochemical performance which may be owing to the specific nanosheets like structures as well as good synergism between Ni, Zn, Cu and Co transition metals. Hence it is observed that by multi-metal doping, the supercapacitive behaviour of transition metal sulphides has improved.