Non-Substituted Imidazolium-Based Electrolytes as Potential Alternatives to the Conventional Acidic Electrolytes of Polyaniline-Based Electrode Materials for Supercapacitors

Abstract

Although disubstituted imidazolium cation is sterically crowded, hundreds of ionic liquids based on this cation have been reported as electrolytes for energy storage devices. In contrast to disubstituted imidazolium, non-substituted imidazolium is uncrowded sterically and has not yet been investigated as an electrolyte, to the best of our knowledge. Hence, imidazolium hydrogen sulfate [Imi][HSO₄], in mixture with water, was studied as an electrolyte for PANI-based electrode materials. For comparison, pyrrolidinium with hydrogen sulfate or <i>p</i>-toluene sulfonate ([Pyrr][HSO₄] or [Pyrr][PTS]), in mixture with water, were also investigated as alternatives to the conventional electrolyte (i.e., aqueous H₂SO₄) for PANI electrodes. Walden plots of binary mixture ionic liquid-water weight ratios with the optimal ionic conductivity (i.e., [Imi][HSO₄]/water 48/52 wt% (195.1 mS/cm), [Pyrr][HSO₄]/water 41/59 wt% (186.6 mS/cm), and [Pyrr][PTS]/water 48/52 wt% (43.4 mS/cm) along with the electrochemical performances of PANI in these binary mixtures showed that [Pyrr][HSO₄]_aq or [Imi][HSO₄]_aq are convenient electrolytes for PANI/PIL, as opposed to [Pyrr][PTS]_aq. Furthermore, replacing the conventional aqueous electrolyte H₂SO₄ with [Imi][HSO₄] _aq increased the specific capacitance of PANI/PIL from 249.8 to 268.5 F/g at 15 mV/s. Moreover, PANI/PIL electrodes displayed a quasi-ideal capacitive behavior in [Imi][HSO₄]_aq (the correction factor of CPE₄ was 0.99). This primary study has shown that non-substituted imidazolium as an electrolyte could enhance the electrochemical performances of PANI electrodes and could be a good alternative to the conventional electrolyte.