Hydrothermal synthesis of hierarchical microstructure tungsten oxide/carbon nanocomposite for supercapacitor...

A hierarchical nanocomposite of carbon microspheres decorated with tungsten oxide (WO₃) nanocrystals resulted from the hydrothermal treatment of a precursor solution containing glucose and tungstic acid. The dehydration of glucose molecules formed oligosaccharides, which consequently carbonized, turning into carbon microspheres. The carbon microspheres then acted as a spherical nucleus onto which WO₃ nanocrystals grew via heterogeneous nucleation. The reaction product showed a phase junction of orthorhombic and monoclinic WO_3, which transitioned to mix-phase of tetragonal and monoclinic WO₃ after a subsequent heat treatment at 600 °C in an inert condition. The electrochemical tests showed that incorporating WO₃ onto the carbon (WO₃/C) resulted in a three-fold increase in the specific capacitance compared to WO₃ alone and a high coulombic and energy efficiencies of 98.2% and 92.8%, respectively. The nanocomposite exhibited supercapacitance with both Faradaic and non-Faradaic charge storage mechanisms. Electrochemical impedance spectroscopy showed a lower charge transfer resistance for the composite at R_ct = 11.7Ω.