Room-temperature ionic liquids (RTILs), i.e. organic molten salts with melting points below 100 ^◦C, have been intensively developed for electrolytic media in various electrochemical systems due to the fact that RTILs have unique physicochemical properties such as favorable solubility of organic and inorganic compounds, relatively high ionic conductivity, no measurable vapor pressure, high thermal stability, low flammability, etc. Particularly, RTILs have been regarded as potential electrolytic media for electropolymerization processes.¹ Many kinds of RTILs have been investigated for the electropolymerizations; however, highly conductive and stable RTILs based on quaternary phosphonium cations² have been rarely employed for this application. In this work, we report the electrooxidative polymerization of aniline in triethylpentylphosphonium bis(trifluoromethylsulfonly)amide (P₂₂₂₅-TFSA) and tributylmethylphosphonium bis(trifluoromethylsulfonly)amide (P₄₄₄₁-TFSA) in comparison with the other type of RTILs, characterizing the obtained polyaniline films.

The preparation of the phosphonium RTILs was performed by aqueous ion exchange reaction of the precursor quaternary phosphonium halides with lithium TFSA. The electrooxidative polymerization of aniline in phosphonium RTILs containing 0.1 M H-TFSA was carried out by cyclic voltammetry (CV) method using a three-electrode cell equipped with a Pt disk working electrode. The electrochemical activity of the polyaniline films were evaluated by extended CV scanning technique.

Figure 1 shows typical cyclic voltammograms for the electrooxidative pocesses of aniline. As shown in Fig. 1, it was found that relatively large voltammetric response was observed in P₂₂₂₅-TFSA when compared to that in P₄₄₄₁-TFSA. This seems to be attributed to the relatively low viscosity and high conductivity of P₂₂₂₅-TFSA. In addition, the voltammetric responses were enhanced by cycling, which indicates that ionic species could be efficiently doped into the polyaniline film. The surface morphology based on SEM images of the polyaniline films will be also discussed.

References

1  K. Sekiguchi, et al, J. Electroanal. Chem., 557, 1 (2003).

2  K. Tsunashima, et al, Electrochem. Commun., 9, 2353 (2007).