| Summary: | 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][HSO<sub>4</sub>], 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][HSO<sub>4</sub>] or [Pyrr][PTS]), in mixture with water, were also investigated as alternatives to the conventional electrolyte (i.e., aqueous H<sub>2</sub>SO<sub>4</sub>) for PANI electrodes. Walden plots of binary mixture ionic liquid–water weight ratios with the optimal ionic conductivity (i.e., [Imi][HSO<sub>4</sub>]/water 48/52 wt% (195.1 mS/cm), [Pyrr][HSO<sub>4</sub>]/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][HSO<sub>4</sub>]<sub>aq</sub> or [Imi][HSO<sub>4</sub>]<sub>aq</sub> are convenient electrolytes for PANI/PIL, as opposed to [Pyrr][PTS]<sub>aq</sub>. Furthermore, replacing the conventional aqueous electrolyte H<sub>2</sub>SO<sub>4</sub> with [Imi][HSO<sub>4</sub>] <sub>aq</sub> 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][HSO<sub>4</sub>]<sub>aq</sub> (the correction factor of CPE<sub>4</sub> 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.
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