Redox-active electrolyte for carbon nanotube-based electric double layer capacitors

The specific capacitance of the MWCNTs was improved by the addition of an electrochemically active compound (Indigo carmine) to an electrolyte generally used in electric double layer capacitors. The pseudocapacitive contribution of the IC trebled the specific capacitance values of the MWCNTs at low current densities (from 17 Fg to 50 Fg). The good resistance obtained for the MWCNT-based capacitor was not modified with the use of this novel redox-active electrolyte. A reversible process associated to the redox reaction of IC was found to be responsible for the capacitance increase observed. Therefore, a combined effect of double layer formation and pseudocapacitive phenomena is presented. Long-term cycling experiments performed showed good stability with a reduction of the initial capacitance values of 30 % after 10,000 galvanostatic cycles at 360 mAg. The efficiency of the cell was close to 100 % throughout the experiment.