| dc.description.abstract | The vanadium oxides were prepared by anodic deposition in this study. Follow the method in the literature, the deposited vanadium oxides from VOSO4･xH2O solution with or without H2O2 were not uniform, and the time of deposition was too long. As a consequence, acetate (lithium acetate, sodium acetate, potassium acetate) were added into the VOSO4･xH2O solution to improve the vanadium oxide deposition. The vanadium oxides deposited from the solutions with acetate were uniform, and the depositing rates were faster. According to the results, three factors were discussed to clarify the reason for uniform and fast vanadium oxide deposition: pH values, cations, and CH3COO－. The experimental results showed that the plating solutions containing CH3COO－ at the pH around 3.8 produced vanadium oxide deposition fast and uniformly. On the other hand, the FESEM images confirmed that the cations affected the morphology of vanadium oxides. The XRD analyses explained that the cations could distort the lattice structure and change the d spacing and grain size. According to the XPS data, there were cations on the surface of vanadium oxides. In the electrochemical characterization, the cyclic voltammogtry showed that the cations could affect pseudocapacitive performance. The specific capacitance of Li-doped, Na-doped, K-doped vanadium oxide was 220, 238, 350 F/g, respectively.
As the previous results, the K-doped vanadium oxide deposition had the best quality. The pseudocapacitive performances and discharge-charge tests of the K-doped vanadium oxide were measured in the ionic liquids. And the ionic liquids included BMP-NTf2, EMI-NTf2, BMI-PF6, EMI-BF4, EMI-SCN, EMI-DCA, and BMP-DCA. The results showed that the specific capacitance was related to the anion of ionic liquids. And the vanadium oxides in the DCA-based ionic liquids had the best capacitance performance. In particular, in BMP-DCA, the specific capacitance of vanadium oxide was 90 F/g, the potential window of vanadium oxide was 3.4 V, and the cycle life performance in BMP-DCA was better than in other ionic liquids and aqueous solutions. Then, the capacitive behavior of the vanadium oxide in BMP-DCA was compared with that in 3 M KCl. At low scan rate, the specific energy of vanadium oxide was 13 Wh/kg in 3 M KCl and 132 Wh/kg in BMP-DCA. At the same specific energy (~10 Wh/kg), the specific power of vanadium oxide was was 9556 W/kg in 3 M KCl and 27840 W/kg in BMP-DCA. The results indicated that the ionic liquid electrolytes could promote the specific energy and the specific power. With the ionic liquid electrolytes, vanadium oxides may become a potential supercapacitor.
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