Prepared MnO2 with different crystal forms as electrode materials for supercapacitors: experimental research from hydrothermal crystallization process to electrochemical performances

Abstract

The aim of this study was to prepare manganese dioxide with different crystal forms through hydrothermal treatment of MnSO₄·H₂O–KMnO₄ precursors at various precursor ratios, temperatures, time periods, and pH values. The effect of the preparation parameters on the crystal structure and electrochemical performance of MnO₂ was also studied. The conditions for the preparation of each crystal of MnO₂ were experimentally optimized. The results indicate that the varied parameters affect the crystal form of MnO₂; the ratio of the precursor and reaction temperature are the significant factors affecting the crystal form of MnO₂, and the reaction time and pH value mainly affect the integrity of crystallization. Moreover, the presence of the cations K⁺ and NH₄⁺ assists the crystallization of α-MnO₂. δ-MnO₂ and amorphous MnO₂ have higher specific capacitance. The specific capacitance is determined not only by the crystal form, but also by the parameters of hydrothermal treatment.