## 4 Conclusions  
In this study, aromatic N-heterocyclic chemical salts ([MPy]\({}^{+}\)[BF\({}_{4}\)]\({}^{-}\), [MPy]\({}^{+}\)[PF\({}_{6}\)]\({}^{-}\), [DI]\({}^{+}\)[BF\({}_{4}\)]\({}^{-}\), [DI]\({}^{+}\)[PF\({}_{6}\)]\({}^{-}\), [BMTA]\({}^{+}\)[BF\({}_{4}\)]\({}^{-}\), and [BMTA]\({}^{+}\)[PF\({}_{6}\)]\({}^{-}\)) and aliphatic N-heterocyclic chemical salts ([DMP]\({}^{+}\)[BF\({}_{4}\)]\({}^{-}\), [DMP]\({}^{+}\)[PF\({}_{6}\)]\({}^{-}\), [DMPy]\({}^{+}\)[BF\({}_{4}\)]\({}^{-}\), [DMPy]\({}^{+}\)[PF\({}_{6}\)]\({}^{-}\), [E-TEDA]\({}^{+}\)[BF\({}_{4}\)]\({}^{-}\), and [E-TEDA]\({}^{+}\)[PF\({}_{6}\)]\({}^{-}\)) were synthesized and applied in an organic electrochemical capacitor as a supporting electrolyte. The synthesized aromatic and aliphatic N-heterocyclic chemical salts were confirmed successfully by \({}^{1}\)H-NMR, FT-IR, and GC/MS.  
The CV results for V(acac)\({}_{3}\) were found to be stable from \(-\)2.5 to 1.0 V when using electrolytes as aromatic N-heterocyclic chemical salts with acetonitrile. However, CV results were unstable or not detected when using electrolytes as aliphatic N-heterocyclic chemical salts with acetonitrile because the anion-exchange membrane was dissolved during the redox process. The electrochemical potential of V(acac)\({}_{3}\) was determined to be approximately 2.2 V under aromatic and aliphatic N-heterocyclic chemical salts (electrolytes) from its CV. The charge-discharge voltage distance of the V(acac)\({}_{3}\) in the acetonitrile electrolyte with the aromatic and aliphatic N-heterocyclic salts as supporters was 2.2 V; however, charge-discharge cycles could not be performed more than 20 times because the commercial membrane dissolved with the usage of acetonitrile electrolytes. In the solubility test with the vanadium complex, it was observed that the highest solubility was achieved in solvent mixtures with solvents of high donor numbers or higher polarizability, but charge-discharge profiles could not be obtained because the assembled commercial membrane dissolved in the electrolyte mixtures. From the above results, we conclude that the synthesized electrolyte supporters could be used as electrolyte additives in an electrochemical capacitor system.  
Conceptualization, S.-H.C.; validation, S.-Y.K. and Y.-J.K.; investigation, Y.-J.K.; writing--original draft preparation, Y.-J.K.; writing--review and editing, J.-Y.C., S.-Y.K. and S.-H.C.; supervision, J.-Y.C., S.-Y.K. and S.-H.C.; project administration, S.-Y.K. and S.-H.C. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data used to support the findings of this study are available within the article. The data are also available from the corresponding author upon reasonable request.  
This work was supported by the 2021 HannNAM University Innovation Research Program. Hannam University and Innovation Research Program have agreed to the publication of this manuscript.  
\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
23 & - & 94.1 & 5.90 & - & 0.05 M & 0.05 M & 0.05 M \\ \hline
24 & - & 76.2 & 4.80 & 19.0 & 0.08 M & 0.08 M & 0.08 M \\ \hline No. & ACN & PC & DMSO & 1,4-Di & [DMP]\({}^{+}\)[I]\({}^{-}\) & [DMP]\({}^{+}\)[BF\({}_{4}\)]\({}^{-}\) & [DMP]\({}^{+}\)[PF\({}_{6}\)]\({}^{-}\) \\ \hline
25 & 100 & - & - & - & 0.15 M & 0.15 M & 0.15 M \\ \hline
26 & 94.1 & - & 5.90 & - & 0.15 M & 0.15 M & 0.15 M \\ \hline
27 & 76.2 & - & 4.80 & 19.0 &