Rapid microwave synthesis of δ-MnO2 microspheres and their electrochemical property

The delta-MnO2 microspheres as well as the delta-MnO2 microspheres/ delta-MnO2 nanorods mixture were synthesized by reduction of KMnO4 under microwave irradiation. The morphology and structure of the as-prepared products were characterized by powder X-ray diffraction (PXRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) measurements and Raman spectra. Electrochemical performances of the samples were examined using cyclic voltammetry (CV) and galvanostatical discharge-charge test in Na2SO4 and Li2SO4 aqueous electrolyte, respectively. It was found that the nearly ideal rectangular shapes of the CV curves show that these samples exhibited good pseudo-capacitor properties in the voltage range from 0.0 to 1.0 V. The test of long-term cycling stability indicated that two samples all have a reasonably good stability. However, the delta-MnO2 microspheres possessed a lower specific surface area while a higher supercapacitance than those of the delta-MnO2 micropheres/alpha-MnO2 nanorods mixture did. The presence a few fraction delta-MnO2 impurities reduces the specific capacitance of delta-MnO2 electrode. Because of the crystal structure and morphologies are two such important parameters that have to be taken into account in this work.