Reductive Treatment of δ-MnO2 with Sodium Borohydride: Method for Increasing the Electrode Material Capacitance

Abstract

The effect of reductive treatment on the phase composition, morphology, and electrochemical parameters of δ-MnO2 produced by the hydrothermal method from KMnO4 at a temperature of 160°C in the presence of HNO3 was studied. δ-MnO2 processing with 3 M NaBH4 aqueous solution leads to partial reduction of Mn(IV) to Mn(III) and Mn(II). The electrochemical characteristics of the obtained electrode materials were examined by cyclic voltammetry, galvanostatic charge–discharge measurements, and impedance spectroscopy. Reductive treatment increases the specific capacitance of δ-MnO2 in 1 M Na2SO4 up to 204 F g–1 at a current density of 0.1 A g–1, and also reduces diffusion limitations during cycling due to an increase in the specific surface area. The loss of specific capacitance after 2000 charge–discharge cycles does not exceed 2.6%, which confirms the high electrochemical stability of the obtained electrode materials.