High performance hybrid supercapacitors by using para-Benzoquinone ionic liquid redox electrolyte

• Redox electrolyte based on quinone species dissolved in ionic liquid was developed.
• Hybrid Supercapacitors with 3 times higher values of Cam were achieved.
• Hybrid Supercapacitors with 3 times higher values of Ereal were achieved.
• The nature of carbon electrode has strong influence in electrochemical performance.
• Faradaric contribution is more relevant in non-microporous carbon.

A solution of 0.4M para-Benzoquinone (p-BQ) in the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI) was used as a redox electrolyte in hybrid supercapacitors. Two carbons with very different textural properties, Pica carbon and Vulcan carbon, were used as electrode material. Electrochemical performance of these energy storage systems was investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge (CD). Unlike SCs with pure IL electrolyte, new battery-like features appeared in the CV curves and CD profiles. This electrochemical performance, associated with the faradaic contribution of the redox electrolyte, results in a significant improvement of the electrochemical performance of the hybrid system. For Vulcan carbon with low specific surface area (SBET = 240 m2 g-1), specific capacitance (Cs) and specific real energy (Ereal) values as high as 70 Fg-1 and 10.3 WhKg−1 were obtained at 5 mAcm−2 with hybrid SC operating at 3 V. This represents an increment of 300% in Cs and Ereal with respect to the SC based on pure PYR14TFSI. For high surface area carbon such as Pica (SBET = 2410 m2g-1), the addition of the redox quinone molecule resulted in a moderate enhancement reaching values of 156 Fg-1 and 30 WhKg−1 under the same experimental conditions (36% and 10% increment, respectively).