Ideal Supercapacitor Behavior of Amorphous V2O5·nH2O in Potassium Chloride (KCl) Aqueous Solution

Amorphous a-V2O5·nH2O in mild KCl aqueous electrolyte proves to be an excellent electrode for a faradaic electrochemical capacitor. Cyclic voltammograms versus SCE give ideal capacitor behavior between 0.0 and +0.8 V at pH 6.67 and between 0.2 and +0.8 V at pH 2.32 with, respectively, a constant specific capacitance over 100 cycles of ca. 350 and 290 F/g, respectively. On short-circuit, a-V2O5·nH2O in 2 M KCl aqueous solution at pH 2.32 gave an initial current density of 0.28 A/cm2 and a total released charge of 4.5 C/cm2, which is to be compared with 0.32 A/cm2 and 11.1 C/cm2 for RuOOH·nH2O in 5.3 M H2SO4. Moreover, half the stored charge was released 1.6 times faster from the a-V2O5·nH2O electrode. These results demonstrate that the K+ ion can be used as the working ion in a faradaic capacitor, which frees the search for new materials from the constraint of working in a strong acid aqueous medium.