Investigations on electrochemical supercapacitors using polypyrrole redox electrodes and PMMA based gel electrolytes

Polypyrrole based solid state electrochemical redox supercapacitors have been fabricated using the polymeric gel electrolytes comprising of poly methyl methacrylate (PMMA)-propylene carbonate (PC)-ethylene carbonate (EC)-perchlorate salts of different cations [Li⁺, Na⁺ and (C₂H₅)₄N⁺ (TEA⁺)]. A comparative study has been carried out using linear sweep reversal voltammetry, complex impedance spectroscopy and constant current charge-discharge tests. The capacitance values of the cells have been observed to be in the range of 15.3-22.5 mF cm⁻² (equivalent to single electrode specific capacitance of 120-178 F g⁻¹ of polypyrrole). This corresponds to the values of energy density 16.7-24.7 Wh kg⁻¹ and power density 1.6-2.8 kW kg⁻¹ calculated for the working voltage of 1.0 V limited for polypyrrole based redox capacitors. Substantial improvements in the coulombic efficiency of the cells have been observed (close to 100%) due to the application of gel electrolytes showing flexible and liquid like behaviour. Further, the types and sizes of the cations in the gel electrolytes do not play any dominant role in the capacitive behaviour of the redox cells.