Synthesis of beta-MnO2 nanowires and their electrochemical capacitive behavior

gamma-MnOOH nanowires have been synthesized using the hydrothermal process in which MnSO4 is oxidized by (NH4)(2)S2O8 at 130 C for 10 h in aqueous LiOH solution. The synthesized gamma-MnOOH nanowires are transformed to 13-MnO2 nanowires on calcination at 300 C. X-ray powder diffraction, thermal gravimetric analysis, field emission scanning electron microscopy and high resolution transmission electron microscopy examinations of the synthesized nanostructures confirm the formation of gamma-MnOOH and beta-MnO2 nanowires with 20-30 nm diameter and >5 mu m length. Electrochemical capacitive behavior of the synthesized beta-MnO2 nanowires has shown specific capacitance as 404 F/m which is nearly three times higher than the capacitance reported for commercial grade MnO2 particles. Increase in calcination period from 3 h to 6 h is found to decrease the specific capacitance but increase electrochemical reactivity.