Effects of thermal treatment on the electrochemical behavior of manganese dioxide

Abstract

Manganese dioxide (MnO2) was synthesized using a fluid phase method with potassium permanganate and manganous acetate as precursors. The obtained MnO2 was treated thermally at different temperatures. The structural transformation of MnO2, its electrochemical behavior as an electrode material for use in a supercapacitor were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 physical adsorption, thermogravimetry (TG), cyclic voltammetry, and galvanostastic charge-discharge. The results indicate that the synthesized MnO2 can be assigned to its α phase and that it possesses a mesoporous feature with a high surface area of up to 253 m2·g-1. After a low temperature thermal treatment (<350 ° C), the manganese oxide retained its α-MnO2 crystal structure and its specific surface area was found to be approximately 170 m2·g-1. The specific capacitance of the single electrode increased from 267 F·g-1 for untreated MnO2 to 286 F·g-1 for the sample treated at 250 °C. However, high temperature thermal treatment (>450 ° C) results in a transformation of the manganese oxide structure to α-Mn2O3 and then to α-Mn3O4. Additionally, the surface area reduced to ca 30 m2·g-1 and this lead to a dramatic decrease in the specific capacitance of manganese oxide. The electrochemical cycling stability of manganese oxide improved noticeably after low temperature thermal treatment and the electrode retained a good rate performance at a scan rate of 50 mV·s-1. © Editorial office of Acta Physico-Chimica Sinica.