Abstract: Manganese dioxides were prepared by direct thermal decomposition of KMnO₄ at different temperatures. XRD
and TEM measurements show that the materials contain a large amorphous/crystalline ratio and have layered structures with K⁺ ions between them.
Cyclic voltammetry tests indicate that the materials prove to be excellent electrodes for electrochemical capacitors in a mild 0.5mol/L Na₂SO₄ aqueous electrolyte. A sample decomposed at 550℃ gives a specific
capacitance of 243F·g^-1 between --0.2 and +1.0V(vs. SCE), and an excellent cyclability after 200 cycles at constant current 40mA and its specific capacitance
remains over 95%.

Key words: electrochemical capacitor, manganese dioxide, KMnO₄, direct thermal decomposition, specific capacitance