## 3 Results and Discussion
The voltage distance of the charge-discharge of the V(acac)\({}_{3}\) under acetonitrile electrolytes with the aromatic and aliphatic  
Figure 4: Cyclic voltammograms (CV) of 0.01 M V(acac)\({}_{3}\) under acetonitrile with 0.1 M aromatic N-heterocyclic salts on a glassy carbon working electrode with a scan rate of 100 mV/s. N-heterocyclic salts as supporters reached 2.2 V. Unfortunately, the charge-discharge cycles could not be measured more than 20 times because the commercial anion-exchange membrane was dissolved due to the usage of electrolytes. Figure 5: Electrochemical capacitor performance of 0.1M V(acac)\({}_{3}\) in acetonitrile in the presence of 0.1 M N-heterocyclic aromatic salts (Working condition: set voltage = 2.5 V, I\({}_{\text{c}}\) = 0.1 mA, and I\({}_{\text{d}}\) = \(-\)0.1 mA, Neosepta® AFN). Figure 6: Electrochemical capacitor performance in acetonitrile with 0.01M V(acac)\({}_{3}\) and 0.1 M electrolyte salts (Working condition: set voltage = 2.5 V, I\({}_{\text{c}}\) = 0.1 mA, and I\({}_{\text{d}}\) = \(-\)0.1 mA, Neosepta® AFN). According to previous studies, the solubility of energy-storage chemicals increases with the use of a mixture of solvents [17]. In these cases, a phenomenon known as preferential solvation occurs, and it can be used to explain how interactions between different types of solvents affect solute-solvent interactions. In addition, [PERSON] et al. were successful in using a solvent-mixture approach for other storage systems, such as lithium-ion batteries [18]. Therefore, for energy-storage systems such as electrochemical capacitors, this approach can provide better active species. The investigation of the solubility of V(acac)\({}_{3}\) was performed with different binaries as well as an increase in energy density due to the improved solubility of the ternary mixtures in the presence of aromatic and aliphatic N-heterocyclic salts (Table 1). According to the results of the solubility of the vanadium complex, the higher solubility was observed when using mixed solvents with high donor numbers or higher polarizability, such as dimethyl sulfoxide (DMSO). A ternary mixture solution with DMSO and 1,4-Di to AN or PC has a solubility almost as high as that of V(acac)\({}_{3}\), as shown in Table 1. It is known from previous reports that DMSO interacts preferentially with dissolved species because of its high donor and acceptor numbers [19]. We examined charge-discharge performance using the electrolyte mixtures; however, we could not obtain charge-discharge profiles because the assembled commercial membrane in the test cell dissolved in the electrolyte mixtures. For commercialization, these results indicate the need for an advanced anion-exchange membrane that is insoluble in electrolyte mixtures. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**No. ** & **ACN** & **PC** & **DMSO** & **1,4-Di** & **[MPy]\({}^{+}\)[I]\({}^{-}\)** & **[MPy]\({}^{+}\)[BF\({}_{4}\)]\({}^{-}\)** & **[MPy]\({}^{+}\)[PF\({}_{6}\)]\({}^{-}\)** \\ \hline
1 & 100 & - & - & - & 0.88 M & 0.88 M & 0.88 M \\ \hline
2 & 94.1 & - & 5.90 & - & 0.85 M & 0.85 M & 0.85 M \\ \hline
3 & 76.2 & - & 4.80 & 19.0 & 0.90 M & 0.90 M & 0.90 M \\ \hline
4 & - & 100 & - & - & 0.06 M & 0.06 M & 0.06 M \\ \hline
5 & - & 94.1 & 5.90 & - & 0.07 M & 0.07 M & 0.07 M \\ \hline
6 & - & 76.2 & 4.80 & 19.0 & 0.82 M & 0.82 M & 0.82 M \\ \hline No. & ACN & PC & DMSO & 1,4-Di & [DI]\({}^{+}\)[Br]\({}^{-}\) & [DI]\({}^{+}\)[BF\({}_{4}\)]\({}^{-}\) & [DI]\({}^{+}\)[PF\({}_{6}\)]\({}^{-}\) \\ \hline
7 & 100 & - & - & - & 0.60 M & 0.60 M & 0.60 M \\ \hline
8 & 94.1 & - & 5.90 & - & 0.60 M & 0.60 M & 0.60 M \\ \hline
9 & 76.2 & - & 4.80 & 19.0 & 0.70 M & 0.70 M & 0.70 M \\ \hline
10 & - & 100 & - & - & 0.07 M & 0.07 M & 0.07 M \\ \hline
11 & - & 94.1 & 5.90 & - & 0.09 M & 0.09 M & 0.09 M \\ \hline
12 & - & 76.2 & 4.80 & 19.0 & 0.12 M & 0.12 M & 0.12 M \\ \hline No.