Short communication Organo-redox shuttle promoted protic ionic liquid electrolyte for supercapacitor S. Sathyamoorthi a , V. Suryanarayanan a, b , D. Velayutham a, b, * a Electrochemical Process Engineering Division, CSIR-Central Electrochemical Research Institute, Karaikudi 630 006, India b CSIR-Network Institutes of Solar Energy (CSIR-NISE), CSIR-Central Electrochemical Research Institute, Karaikudi 630 006, India highlights  Hydroquinone is employed as an organic redox shuttle in PIL for supercapacitor.  HQ enhances the ionic conductivity of electrode in PIL.  The specific capacitance increases upto 71.0% at 0.57 mA cm 2 .  The specific energy increases from 18.40 to 31.22 W h Kg 1 . article info Article history: Received 8 July 2014 Received in revised form 17 October 2014 Accepted 18 October 2014 Available online 29 October 2014 Keywords: Redox-mediated electrolyte Hydroquinone Protic ionic liquid Triethylammonium bis(trifluoromethane) sulfonimide Supercapacitor abstract Performance of activated charcoal based supercapacitor (SC) containing hydroquinone (HQ), as an organic redox shuttle, is evaluated in triethylammonium bis(trifluoromethane)sulfonimide (TEATFSI). Cyclic voltammograms of the SC show pseudocapacitive contribution of HQ and the galvanostatic charge edischarge measurement shows enhanced specific capacitance (72.0 F g 1 ) and specific energy (31.22 Wh Kg 1 ). The presence of HQ shows low charge transfer resistance, as confirmed by electro- chemical impedance spectroscopy. Cyclic stability of the SC in the redox mediated electrolyte is com- parable with that of the protic ionic liquid. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Electrical double layer capacitors (EDLC) have been considered as one of the promising energy devices attributing swift char- geedischarge, specific power, durable cycle life and low cost [1]. They had been fabricated with different types of carbon materials and their energy storage is based on the interaction between charged electrode and ions in the electrolyte. However, the specific energy of the EDLC is still lower than other storage devices. Reversible faradic reaction is incorporated in the EDLC which may enhances the performance through additional contributions from pseudocapacitance. This can be achieved by employing different electrode materials such as transition metal oxides/hydroxides [2e4], metal chalcogenides [5] and conducting polymers [6]. The capacitance of the EDLC can also be improved by introducing small amount of organic or inorganic reversible redox couple in the aqueous electrolyte. Few examples are iodide [7e9], quinone/hy- droquinone [10e13], anthraquinone [14], p-phenylenediamine [15e17], m-phenylenediamine [18], methylene blue [19] and indigo carmine [20]. In general, aqueous electrolytes limit the operational potential of the supercapacitor at around 1.0 V, whereas, non-aqueous sol- vent systems provide wide potential window. However, their po- tential utility has been restricted due to inherent volatility, restricted operational temperature limit and inflammability. Ionic liquids (ILs) are a class of low temperature organic melts. They are considered as an alternative for both aqueous and non-aqueous solvents, on account of their excellent physico-chemical * Corresponding author. Electrochemical Process Engineering Division, CSIR- Central Electrochemical Research Institute, Karaikudi 630 006, India. E-mail addresses: dvelayutham@rediffmail.com, dvelayutham@cecri.res.in (D. Velayutham). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour http://dx.doi.org/10.1016/j.jpowsour.2014.10.166 0378-7753/© 2014 Elsevier B.V. All rights reserved. Journal of Power Sources 274 (2015) 1135e1139