| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系 === 102 === Nanostructured MnO2 was synthesized using a simple and rapid (5min)microwave-assisted hydrothermal technique through the decomposition of KMnO4 in various hydrochloric acid conditions. The hydrothermal solution consisted of KMnO4
and HCl. The effects of hydrothermal temperature and ramp rate were addressed. The temperature was varied from 140 to 200 o C at a ramp rate of 20 o C /min. It was found
that a lower temperature favors the formation of flower-like δ-MnO2 while a higher temperature favors alfa-MnO2 nanorod. The flower-like δ-MnO2 has a higher specific surface area of 114.9 m2/g than the alfa-MnO2 nanorods (25-30 m2/g). The flower-like δ-MnO2 has a larger pore size of 2.13 nm than the alfa-MnO2 nanorods. At a fixed temperature of 140 o C, the ramp rate was varied from 5 to 40 o C /min and found two kinds of characteristic, 5 and 20 o C /min samples have poor crystallinity the morphology is flower and few whiskers. Samples 10 and 40 o C /min which have good crystallinity the
morphology is pure flower without whiskers. At a fixed temperature of 200 o C, the ramp rate was varied from 7 to 40 o C /min and found that the length and diameter of the MnO2 nanorod become shorter and larger with the raising ramp rate. The obtained MnO2 was made into electrodes for use in supercapacitors. The supercapacitors were evaluated using
cyclic voltammetry and electrochemical impedance spectroscopy in 1M Na2SO4 within potential window -0.1~0.9V. The samples at fixed temperature 140 o C, 5 and 20 o C /min
ramp rate which have flower and whiskers morphology obtain the best specific capacitance performance (201.7F/g and 175.5F/g) due to their high surface area, much more pore
volume structure, low K+ ion exist in matrix and even may be the poor crystallinity cause more water adsorption. The other effects of characteristics on the capacitance performance will also be addressed.
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