Engineering of Nanostructured WO(3) Powders for Asymmetric Supercapacitors

Transition metal oxide nanostructures are promising materials for energy storage devices, exploiting electrochemical reactions at nanometer solid–liquid interface. Herein, WO(3) nanorods and hierarchical urchin-like nanostructures were obtained by hydrothermal method and calcination processes. The morphology and crystal phase of WO(3) nanostructures were investigated by scanning and transmission electron microscopy (SEM and TEM) and X-ray diffraction (XRD), while energy storage performances of WO(3) nanostructures-based electrodes were evaluated by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) tests. Promising values of specific capacitance (632 F/g at 5 mV/s and 466 F/g at 0.5 A/g) are obtained when pure hexagonal crystal phase WO(3) hierarchical urchin-like nanostructures are used. A detailed modeling is given of surface and diffusion-controlled mechanisms in the energy storage process. An asymmetric supercapacitor has also been realized by using WO(3) urchin-like nanostructures and a graphene paper electrode, revealing the highest energy density (90 W × h/kg) at a power density of 90 W × kg(−1) and the highest power density (9000 W/kg) at an energy density of 18 W × h/kg. The presented correlation among physical features and electrochemical performances of WO(3) nanostructures provides a solid base for further developing energy storage devices based on transition metal oxides.