Hydrothermal synthesis of ZnWO4–MnO2 nanopowder doped with carbon black nanoparticles for high-performance supercapacitor applications

Abstract

A two-step hydrothermal method was employed to synthesize ZnWO4–MnO2 nanopowder with a high degree of crystallinity as revealed by X-ray diffraction studies. The synthesized nanopowder exhibits nanorod-type structure as revealed by high-resolution transmission microscopy with selected area electron diffraction pattern, confirming the crystalline behaviour. The electrochemical behaviour of the symmetrically fabricated electrodes using ZnWO4–MnO2 as active materials along with doped carbon black was investigated by means of cyclic voltammetry (CV), galvanostatic charge/discharge profiling and electrochemical impedance spectroscopy in the potential window of 0–1 V. The electrochemical analysis was carried out using 2 M KOH electrolyte. The fabricated electrodes showed better electrochemical behaviour with maximum specific capacitance of 714 F g−1 at a scan rate of 5 mV s−1 as demonstrated by CV curves. The capacitance obtained from CV measurements depicts dominant electrostatic double layer behaviour. The maximum specific capacitance of 690.6 F g−1 at a current density of 1 A g−1 was attained from charge/discharge profiling. In addition, the electrodes showed an energy density of 289.17 Wh kg−1 at a power density of 547.90 W kg−1 at the same current density. Furthermore, after undergoing 5000 charging/discharging cycles, the fabricated electrodes retained 94.5% of its initial capacity, thereby yielding Coulombic efficiency of 81.7%.