Charge transport in activated carbon electrodes: the behaviour of three electrolytes vis-a-vis their specific conductance

In this study, the electrochemical performances of different aqueous electrolytes (6 M KOH, 2 M KCl and 0.5 M K2SO4) in activated carbon electrodes are evaluated with regard to their use in electrochemical double layer capacitor (EDLC). The results from cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) were analysed. The lowest value of equivalent series resistance (ESR) and the highest values of specific capacitance and coulombic efficiency were observed, when KOH was the electrolyte. The impedance spectroscopy plots were fitted to an equivalent circuit of ladder type to evaluate the resistances to ion transport at different levels of hierarchies in the pore network. Also, the quality of the double layer capacitance at lower hierarchy that primarily contributes to the overall capacitance of the device was evaluated from the leakage resistance in the equivalent circuit. The fitted circuit parameters were further reviewed vis-a-vis the specific conductance of chosen electrolyte, and the number of successive charge-discharge cycles prior to the EIS measurements.