## 3 Results and Discussion
Therefore, the results of Raman and infrared spectroscopy are consistent with those of XRD and EDS. The nitrogen adsorption-desorption isotherms of VO\({}_{2}\)(B) nanobelts is shown in Figure 5b. The isotherms show that the phenomenon of capillary condensation occurs at high P/P\({}_{0}\), which is a type IV isotherm in accordance with the IUPAC classification, and VO\({}_{2}\)(B) nanobelts exhibits mesoporous material characteristics [31]. The BET surface area of VO\({}_{2}\)(B) nanobelts is 10.4 m\({}^{2}\cdot\)g\({}^{-1}\) and the Barrett-Joyner-Halenda (BJH) method (insert in Figure 5b) was used to obtain the sample with a pore volume of 0.0687 cm\({}^{3}\)/g and an average pore size of 42.7 nm. The porous characteristic of VO\({}_{2}\)(B) nanobelts indicates potential excellent electrochemical properties, which can be used as SC [32] or lithium ion battery electrodes [33] in the future. The CV curves of the VO\({}_{2}\)(B) nanobelts are shown in Figure 6. The results indicate that there is a large capacity at the potential limit of \(-\)0.8-1.0 V among a different potential limit. Hence, electrochemical curves of VO\({}_{2}\)(B) nanobelts were measured from \(-\)0.8 V to 1.0 V.  
CV curves of the VO\({}_{2}\)(B) nanobelts at \(-\)0.8-1.0 V are shown in Figure 7a, and the scan rate is from 5 to 100 mV\(\cdot\)s\({}^{-1}\). The results indicate that the redox peaks are seen, disclosing  
Figure 5: (a) IR and Raman spectra of VO\({}_{2}\)(B) nanobelts; (b) N\({}_{2}\) adsorption-desorption isotherms of the VO\({}_{2}\)(B) nanobelts at 77 K.  
Figure 6: CV curves of the VO\({}_{2}\)(B) nanobelts at different potential limit (20 mV\(\cdot\)s\({}^{-1}\), 1 M Na\({}_{2}\)SO\({}_{4}\) electrolyte). storing charges are mainly on basis of a redox mechanism [34]. The corresponding redox reaction is described as follows: VO\({}_{2}\) + \(x\)Na\({}^{+}\) + \(x\)e\({}^{-}\)\(\rightarrow\) Na\({}_{x}\)VO\({}_{2}\). The \(x\) denotes mole fraction of inserted Na\({}^{+}\). Original shapes of the CV curves remain almost unchanged as the increment of scan rate, which indicates there are excellent ionic and electronic conductivity in the VO\({}_{2}\)(B) nanobelts. Meanwhile, the peak moves to a higher potential for the electrode polarization effect. Furthermore, the peak current enlarges as scan rate increases, which shows the faradic redox reactions at surface is rapid enough, as well as the rates of ionic and electronic transport [35]. Figure 7b shows GCD curves of the VO\({}_{2}\)(B) nanobelts. When the discharge current densities are 0.5, 1 and 10 A\(\cdot\)g\({}^{-1}\), the specific capacitance are 287, 246, and 222 F\(\cdot\)g\({}^{-1}\). As the discharge current density increases (0.5-10 A\(\cdot\)g\({}^{-1}\)), the specific capacitance decreases. One reason is that a lower use rate of VO\({}_{2}\)(B) occurs at the high current density in the process of charge-discharge, and the other one is that the incremental voltage drop is involved in the redox reaction [36; 37]. The value of capacitance at current density of 10 A\(\cdot\)g\({}^{-1}\) remains 77% of that at current density of 0.5 A\(\cdot\)g\({}^{-1}\).The good rate capability is ascribed to the belt-like (Figures 2 and 3) and porous (Figure 5b) structures of the VO\({}_{2}\)(B) nanobelts. Table 2 displays the electrochemical properties of the VO\({}_{2}\)(B) nanobelts with other materials discovered previously. Although the stability is not as good as some materials, the specific capacitance of porous VO\({}_{2}\)(B) nanobelts (287 F\(\cdot\)g\({}^{-1}\)) outperforms other materials, for example, VO\({}_{2}\)(B) particles (136 F\(\cdot\)g\({}^{-1}\)) [36], VO\({}_{2}\)(B) nanofibers (174 F\(\cdot\)g\({}^{-1}\)) [38], VO\({}_{2}\)(B)/CNTs (229 F\(\cdot\)g\({}^{-1}\)) [38], RG/VO\({}_{2}\)(B) hybrid composites (225 F\(\cdot\)g\({}^{-1}\)) [36], etc. Furthermore, it is concluded from Table 2 that porous VO\({}_{2}\)(B) nanobelts can be used as a large voltage window compared to the previous reports.