Ideal supercapacitor behavior of amorphous V2O5•nH2O in potassium chloride (KCl) aqueous solution

Amorphous a-V2O5. nH(2)O in mild KCI 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 Fig, respectively, On short-circuit, a-V2O5. nH(2)O in 2 M KCI aqueous solution at pH 2.32 gave an initial current density of 0.28 A/cm(2) and a total released charge of 4.5 C/cm(2), which is to be compared with 0.32 A/cm(2) and 11.1 C/cm(2) for RuOOH nH(2)O in 5.3 M H2SO4. Moreover, half the stored charge was released 1.6 times faster from the a-V2O5. nH(2)O 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. (C) 1999 Academic Press.