Facile preparation of hexagonal WO3 nanopillars and its reduced graphene oxide nanocomposites for high-performance supercapacitor

One-dimensional (1D) nanostructures are extremely important due to better charge transport capabilities. The ability to anchor 1D semiconductor nanostructures on graphene may give advantages in electrochemical charge storage applications. In this study, the authors explored the synthesis, growth mechanism, and insertion-type pseudocapacitive properties of 1D hexagonal (h) phase-WO3 (h-WO3) nanopillars and h-WO3/rGO nanocomposite. The nanocomposite is composed of h-WO3 nanopillars uniformly grown on a reduced graphene oxide (rGO) matrix and the resulting h-WO3/rGO nanocomposite shows the hexagonal structure and, 3D networks gathered during a hydrothermal process. XRD confirms the phase purity and crystalline nature, SEM confirms the hexagonal bundled nanopillar morphology of h-WO3 and its graphene composites, and rGO offered crumpled two-dimensional sheet-like morphologies. HRTEM and SAED analysis confirmed the highly oriented growth of h-WO3 nanowire along the [001] zone axis. XPS analysis confirms the presence of tungsten in +6 and + 5 oxidation states, indicating the formation of the oxygen-deficient h-WO3-x structure. The electrochemical characterizations are performed using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and stability tests. From the CV measurements, the outperformed exceptional h-WO3 and h-WO3/rGO nanocomposites exhibit specific capacitance (Csp) of ∼545 Fg−1 and ∼926 Fg−1, respectively, at a 5 mVs−1 scan rate, and from GCD measurements Csp found to be ∼504 Fg−1 and ∼991 Fg−1, respectively at 0.1 Ag−1 current density. Supercapacitor capacitances with carbon and metal oxide electrodes are typically related to the accessible surface areas. However, this work indicates that proton insertion, a rare capacitive charge storage mechanism, may significantly increase the capacitance of metal oxides with a limited surface area but a particular structure. Nonetheless, using the proton insertion process, scientists have shown that the electrodes made from an assembly structure of h-WO3 nanopillars have enhanced charge storage performance. According to detailed investigations, the electrochemical behavior of h-WO3 is dominated by the proton insertion mechanism and is critical in achieving high capacitance by eliminating alternative mechanisms. This research work presents a novel method for attaining extraordinary charge storage contribution into the ordered tunnels in crystalline metal oxides due to efficient proton insertion, which is especially significant for the construction of high-performance electrochemical energy storage systems: batteries and supercapacitors.