Improved accessibility of porous carbon electrodes with surfactant ionic liquids for supercapacitors


Ionic liquids (ILs) are promising electrolytes for supercapacitors due to their wide electrochemical window. However, most ILs are viscous in nature and require diffusional and rotational transformations to access the pore space of common supercapacitor electrodes. In this study, novel anionic surfactant ILs (ASILs) are synthesized to lubricate the electrode surface to improve pore accessibility by IL ions. ASIL composition (0–10 wt%) and temperature (22–150 °C)-dependent capacitances, as a measure of pore accessibility and wettability, are determined by cyclic voltammetry. 10 wt% 1-butyl-1-methylpyrrolidinium docusate, [PYR14][AOT], in the base IL 1-propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [PYR13][TFSI], exhibits the highest specific capacitance (202 F g−1 at 150 °C and 10 mV s−1), compared to [PYR13][TFSI] (160 F g−1). Electrochemical impedance spectroscopy measurements indicate resistive charging for ASIL/IL electrolyte compared to the base IL at 22 °C due to reduced conductivity—a consequence of larger non-polar domains. However, at elevated temperatures (> 100 °C), electrolyte resistance is circumvented as the viscosity is reduced. The wide voltage window of ILs and improved wettability by ASILs can be coupled to maximize energy storage capability of supercapacitors for high-temperature power applications.

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Authors would like to thank the Case Western Reserve University Capacitor Facility, specifically Dr John Miller, Mirko Antloga, and Becca Segeel for supplying the electrodes.

Author information




NX synthesized ASILs and performed the physical property and electrochemical measurements. JMK carried out the EIS fit and analysis. PH performed TGA and DSC measurements. HA measured surface tension. EM supervised surface tension measurements. BEG designed the experiments and supervised all activities. All authors contributed to writing the manuscript.

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Correspondence to Burcu E. Gurkan.

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Xu, N., Klein, J.M., Huang, P. et al. Improved accessibility of porous carbon electrodes with surfactant ionic liquids for supercapacitors. J Appl Electrochem 49, 151–162 (2019).

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  • Anionic surfactant ionic liquid
  • Ion accessibility
  • Electrode wettability
  • Capacitance
  • Impedance