In this work, three kinds of ultrathin tremella-like MnO 2 have been simply synthesized by decomposing KMnO 4 under mild hydrothermal conditions. When applied as electrode materials, they all exhibited excellent electrochemical performance. The asprepared MnO 2 samples were characterized by means of XRD, SEM, TEM and XPS. Additionally, the relationship of the crystalline nature with the electrochemical performance was investigated. Among the three samples, the product with the poorest crystallinity had the highest capacitance of 220 F/g at a current density of 0.1 A/g. It is thought that the ultrathin MnO 2 nanostructures can serve as promising electrode materials for supercapacitors.
Manganese oxide/carbon sphere composites (MnO 2 /C) with suitable pore structure and coating layer have been synthesized through a self-limiting redox reaction between carbon spheres and permanganate at room temperature in neutral-pH solutions. The asprepared composites were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption techniques. Their capacitance performances were evaluated using both cycle voltammetry and galvanostatic charge-discharge methods. It was found that the specific capacitance of the composites firstly increased with the reaction time, and then it slightly decline and leveled off finally. The highest specific capacitance (170 F/g at a current density of 0.1 A/g) is obtained when the reaction time is 6 h.
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