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

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%.