Novel vanadium oxide/carbon nanotube composite and its charge storage properties

To over the low conductivity of VO₂, metastable VO₂ nanolayer is deposited onto conductive carbon nanotubes (CNTs) forming a nano-porous structure via a facile redox method. Seven different CNTs/VO₂ nanocomposites are prepared with seven different weight percent (20, 30, 40, 50, 60, 70 and 80) of VO₂. Scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and thermogravimetric analyses confirm the surface morphology, microstructure, crystallinity and loading of VO₂ in the nanocomposite, respectively. Prominently, the nanocomposites also show very reversible conversion in the negative potential region between the V(III) and V(IV) states. The optimal specific capacitance is achieved at the loading of 60 wt% of VO₂. The high surface area and very thin layer of the VO₂ in the nanocomposite contribute to the increase in the specific capacitance, due to the increased electrochemical utilization of VO₂. The highest specific capacitance of 307.82 F/g is attained via the galvanostatic charge–discharge technique at a normalized current of 0.4 A/g in the potential range of −0.8 to −0.1 V (vs. Ag/Ag/Cl). The CNTs/VO₂ 60 wt% nanocomposite, when subjected to charging-discharging over 1000 cycles at a scan rate of 20 mV/s, shows excellent stability with a gain in specific capacitance of 0.19 F/g as compared to the initial capacitance after a loss of 5.1% in the first 450 cycles. With the improved specific capacitance and excellent cycling stability, the CNTs/VO₂ nanocomposite could be used as a promising electrode material in the application of supercapacitors.