Supercapacitive properties of ultra-fine MnO2 prepared by a solid-state coordination reaction

An ultra-fine MnO2 powder was synthesized by a novel route of solid-state coordination reaction. The structure and morphology were characterized by X-ray diffraction, scanning electron microscope and infrared spectroscopy. The MnO2 powder with a primary particle size of ∼200 nm was composed of α-MnO2 and γ-MnO2. Electrochemical properties of the MnO2 electrode were examined by cyclic voltammetry, and galvanostatic charge/discharge and electrochemical impedance spectroscopy measurements in 6 mol L−1 KOH electrolyte. The MnO2 electrode exhibited good supercapacitive performance. Specific capacitance values of 337 and 197 F g−1 were obtained for the MnO2 electrode at scan rates of 2 and 50 mV s−1, respectively. The MnO2 electrode subjected to 500 cycles at a current density of 800 mA g−1 delivered a specific capacitance of 228 F g−1, retaining 75% of its initial specific capacitance.