花状δ-MnO_2和线状α-MnO_2的制备及其电容性能研究

Synthesis and Capacitive Properties of Flower-like δ-MnO_2 and Wire-like α-MnO_2

以KMn O4为锰源,尿素为还原剂,在水热温度120℃和180℃下分别合成了花状δ-Mn O2和线状α-Mn O2。利用XRD和SEM对样品的结构和形貌进行了分析;利用循环伏安、交流阻抗和恒流充放电测试研究其电化学性能。测试结果表明,Mn O2的晶型和形貌对其电化学性能影响较大,花状δ-Mn O2比线状α-Mn O2展现出更好的电容性能。在扫速5 m V/s时,花状δ-Mn O2和线状α-Mn O2电极比电容分别为193.9 F/g和152.0 F/g。在与活性炭组成的非对称超级电容器中,AC//δ-Mn O2和AC//α-Mn O2电容器初始比电容分别为31.2 F/g和25.4 F/g;1000次充放电循环后,AC//δ-Mn O2循环性能更好。因此,花状δ-Mn O2更适合做非对称超级电容器的正极活性材料。

Flower-like δ-MnO2 and wire-like α-MnO2 were synthesized at the hydrothermal temperature of 120℃ and 180℃ with adding urea into KMnO4. Their crystal structures and morphologies were analyzed by XRD and SEM. Their capacitive properties were investigated by cyclic voltammeter, electrochemical impedance spectroscopy and galvanostatie charge- discharge test. The results showed that the crystal structure and morphology had an important influence on its electrochemical properties. Flower-like δ-MnO2 showed better capacitive behavior than wire-like α- MnO2. The specific capacitance values of δ-MnO2 and ct-MnO2 electrode were 193.9 F/g and 152. 0 F/g at the scan rate of 5 mV/s. After asymmetric supercapacitors were fabricated by MnO2 positive electrode and AC negative electrode, the initial specific capacitance values of AC//δ-MnO2 and AC//α-MnO2 supercapacitors were 31.2 F/g and 25.4 F/g. After 1000 cycles, AC//δ-MnO2 exhibited better cyclic stability. Therefore, flower-like δ-MnO2 was more suitable for the positive electrode material of the asymmetric supercapacitor.