Supercapacitor Behavior with KCl Electrolyte

Amorphous MnO2·nH2O in a mild 2 M KCl aqueous electrolyte proves to be an excellent electrode for a faradaic electrochemical capacitor cycled between −0.2 and +1.0 V versus SCE. In this potential range, it had ideal behavior with a specific capacitance ofca. 200 F/g, excellent cyclability at 2 mA/cm2over 100 cycles, and a short-circuit initial current density of 0.23 A/cm2with a total released charge of 3.8 C/cm2as compared to 0.32 A/cm2and 11.1 C/cm2for RuO·nH2O in 5.3 M H2SO4.