Preparation process optimization and properties of manganese dioxide micro/nano spheres and microrods

MnO₂ powders with micro/nano spheres simple, quick and low-temperature hydrothermal method and microrods for supercapacitors were synthesized via a Their preparation process was optimized by orthorhombic test and single factor experiment. The crystalline structure, surface morphology and supercapacitive properties of the as-prepared MnO₂ powders were studied by X-ray diffraction, scanning electron microscopy and electrochemical measurement. Experimental results show that the optimal reaction conditions are the reaction temperature of 150℃, the KMnO₄/MnCl₂ molar ratio of 2.5:1.0, the reaction time of 3 h, and the filling factor of 40%. Under the optimal conditions, the as-prepared MnO₂ powders have typical α-MnO₂ structure with hollow and porous micro/nano spheres and microrods. The α-MnO₂ micro/nano sphere diameter is about from 0.2 to 0.8 μm, while the α-MnO₂ microrods have the diameter of 30 nm and the length of 5 μm. The discharge specific capacitance of products at the 5th discharge cycle retains 255, 170, 133, 105 and 88 F·g^-1 at current densities of 100, 150,200,250 and 300 mA·g^-1, respectively. Moreover, the values of equivalent series resistance and charge transfer resistance decrease to 0.37 Ω and 0.40 Ω, respectively.