Effect of growth time on solvothermal synthesis of vanadium dioxide for electrochemical supercapacitor application

Abstract

In this work, we report the time-dependent morphological evolution of the as-prepared vanadium dioxide (VO2) and its electrochemical performance for supercapacitor applications. VO2 with different morphologies (microspheres and nanosheets) were successfully synthesised by solvothermal method for time growth ranging from 2 h 30min to 12 h at a temperature of 200 °C. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), gas adsorption/desorption analysis and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure, morphology, composition and the oxidation state of the as-prepared samples. The electrochemical behaviour of the as-prepared VO2 samples were analysed in a three-electrode cell configuration using 6 M KOH aqueous electrolyte. The VO2 samples revealed monoclinic crystal structure (with VO2 (B) monoclinic phase for the samples prepared for 4 h and 6 h and VO2 (A) monoclinic phase for the samples grown for 2 h 30min and 12 h). The VO2 samples grown for 4 h and 6 h displayed nanoflakes and nanosheets-like morphology, respectively, whereas VO2 samples grown for 2 h 30min and 12 h revealed nanorods-like morphology. The 6 h grown sample also showed more porous structure leading to much higher specific surface area, pore volume and enhanced electrochemical performance with highest specific discharge capacity of 49.28 mA h g−1 at current density of 0.5 A g−1 and the corresponding specific capacitance of 663 F g−1 at a scan rate of 5 mV s−1 with excellent cycling stability as compared to others samples. Accordingly, the 6 h is considered to be optimal growth time for VO2 nanosheets for considerable potential as an electrode material for supercapacitor applications.