Synthesis of β-MnO 2 nanowires and their electrochemical capacitive behavior

γ-MnOOH nanowires have been synthesized using the hydrothermal process in which MnSO4 is oxidized by (NH4)2S2O8 at 130 °C for 10 h in aqueous LiOH solution. The synthesized γ-MnOOH nanowires are transformed to β-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 γ-MnOOH and β-MnO2 nanowires with 20-30 nm diameter and >5 μm length. Electrochemical capacitive behavior of the synthesized β-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.