Correlation of energy storage performance of supercapacitor with iso-propanol improved wettability of aqueous electrolyte on activated carbon electrodes of various apparent densities

Abstract

Addition of iso-propanol in the aqueous electrolyte of 1.0mol/L Na2SO4 was found to be most effective at about 8vol.% to minimise electrolyte surface tension, and hence maximise electrolyte wetting on a commercial supercapacitor grade activated carbon powder. The wetting improvement was further studied on die-pressed cylindrical thin pellets of polytetrafluoroethylene bonded activated carbon powder at three different apparent densities (0.70, 0.55 and 0.35g/cm3) using adsorption isotherm, cyclic voltammetry and electrochemical impedance spectroscopy. Enhanced charge storage performance of the activated carbon at 0.70 and 0.55g/cm3 in apparent density was observed in electrolyte containing iso-propanol. The effect of iso-propanol became more prominent at high polarisation potentials. However, at the lowest density (0.35g/cm3) studied, the capacitance decreased in the presence of iso-propanol, which can be attributed to the iso-propanol molecules entering the nano-pores of the activated carbon particles. In symmetrical supercapacitors with the dense activated carbon electrodes, addition of iso-propanol to the aqueous electrolyte increased the cell voltage, specific energy and maximum specific power from 1.5 to 2.0V, 7.34 to 12.44Wh/kg, and 3.96 to 12.35kW/kg, respectively, under comparable conditions.