Synthesis and Electrochemical Properties of α and β Modifications of MnO₂ for Supercapacitors Application

Abstract

In this study, the α and β modifications of MnO2 have been successfully synthesized by the hydrothermal method. The obtained materials have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and low-temperature nitrogen adsorption. In addition, the supercapacitor performance of the materials has been pre-tested to assess their suitability for practical applications. The average particle size of the α modification is 12-15 nm, and the β modification is 14-18 nm. The surface areas of the α and β modifications of MnO2 are 200 m2/g and 70 m2/g, respectively. The average pore sizes are 3.2 nm and 5.3 nm, respectively. The specific capacitance of 40 F/g is observed at 1 mV/s, which has been recorded using cyclic voltammetry and constant current charge-discharge cycling in 30 % aqueous KOH solutions. It has been determined that the specific capacitance of the β - MnO2/electrolyte system decreases from 40 F/g to 15 F/g with an increase in the scan rate from 1 to 30 mV/s. In addition, the total capacitance of the material was divided into the electric double layer capacitance and the diffusion-controlled redox capacitance due to the Faraday reverse redox reactions. Finally, the pseudocapacitance contribution has been determined to be 90 % of the total specific capacitance.