Nanostructuring Polyaniline Using Non-Substituted Imidazolium-Based Ionic liquid as Polymerization Medium Enabling Faster Supercapacitor Operation

Non-substituted imidazolium-based protic ionic liquid, namely imidazolium hydrogen sulfate [Imi][HSO₄], has been investigated as a polymerization medium for PANI (designated as PANI/PIL). The resulting material was then investigated as electrode materials for supercapacitors. [Imi][HSO₄] was prepared via a one-step acid-base reaction, and its structure was confirmed by ¹H NMR. [Imi][HSO₄] displayed full miscibility with water owing to the charge density distribution of its ions. Furthermore, the binary mixture [Imi][HSO₄]/water is highly acid (e.g. pH ~ 0.1 for [Imi][HSO₄]/water in a weight ratio of 70/30). As the polymerization medium for PANI/PIL, [Imi][HSO₄] plays the role of a soft template agent and induces nanostructured PANI formation with fibrillar morphology (as shown by SEM images) without affecting the typical structure of PANI (as confirmed by FT-IR analysis). Furthermore, PANI/PIL was obtained in emeraldine salt form without any undesirable byproduct. Moreover, the electrical conductivity was seven times superior to that of the conventional PANI (i.e. PANI/HCl) when measured by the four-probe technique of PANI/PIL (~ 21.8 S/cm). This improvement in the PANI/PIL’s electrical conductivity of as well as the fibrillar morphology of PANI/PIL positively influences its electrochemical performances and highlights the suitability of [Imi][HSO₄] as a polymerization medium for PANI material.