Effect of monomer concentration on the performance of Polyaniline based redox capacitors

Supercapacitors are promising alternatives for answering the thirst for ever increasing demand for power. They bridge the gap between the batteries and the conventional capacitors. Redox capacitors in the family of supercapacitors consist of conducting polymers or transition metal oxide electrodes. In this study, symmetric redox capacitors have been fabricated utilizing Polyaniline electrodes and a Polyvinylidenefluoride based gel polymer electrolyte. The effect of aniline concentration on the performance of redox capacitors was investigated. Aniline concentration was varied from 0.20 M to 0.50 M. Capacitors were characterized using Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and Galvanostatic Charge-Discharge tests. Redox capacitor with 0.40 M aniline concentration showed the highest performance. From EIS measurements it was shown that the lowest relaxation time was 0.22 s. This implies that 0.40 M aniline system has the fastest ion movement behavior. Cyclic Voltammetry (CV) test of this capacitor resulted 81% of specific capacity retention between the 1^st and the 200^th cycle. Galvanostatic Charge-Discharge (GCD) for 1000 cycles showed an average discharging capacity of 323 F g^-1, power density of 760 W kg^-1 and energy density of 6.5 Wh kg^-1. The results of this study confirm that aniline concentration has a significant effect on the performance of PANI films when they are served as electrodes in redox capacitors.