Synthesis And Electrochemical Properties Of MnO₂for Supercapacitors

Abstract:MnO2as a electrode material for supercapacitors, is considered as one of the most promising materials with merits including abound resources, cheap price and so on. Although many years have been spent on the research of MnO2, most of work still remains in the lab. The main restriction for its application is how to synthesize the ideal products by simple and controllable methods, and the low conductivity of MnO2is the other problem for its application. In this paper, the electrode materials with the specific morphology were synthesized by hydrothermal method and so on. In order to improve the capacitive properties of single MnO2, the composite MnO2/PANI was prepared by chemical method. Several techniques such as SEM, XRD, cyclic voltammetry (CV), EIS etc. were used to study on the structure properties and electrochemical performances of the synthesized materials.Urchin MnO2was synthesized by the reaction of KMnO4and Cu foil. There are the effects considered including the molar rate, concentration of KMnO4and the addition of sulfuric acid. The results show that the sample synthesized with1:5of molar rate,0.05mol L-1KMnO4and16mL sulfuric acid is composed of urchin α-MnO2with high crystallinity. The second discharge capacitance is288.02F g-1under65mAg-1。The spherical MnO2was prepared by hydrothermal reaction of KMnO4and self-made MnC03. There are three facts studied on, including the morphology of MnCO3, concentration of KMnO4and the temperature of hydrothermal reaction. The result of the preparation of MnCO3shows that the hollow spherical MnCO3was obtained under190℃while block particles of MnCO3above200℃. Furthermore, spherical MnO2synthesized by hollow structure MnCO3prepared at160℃has prior capacitive performance.Under hydrothermal conditions, high concentration of KMnO4or high temperature of synthesis was not beneficial for preparation of spherical MnO2with high purity. Uniform spherical MnO2with diameter2μm prepared with0.07mol L-1KMnO4and150℃has the highest specific capacitance355.40F g-1under65mA g-1which improves23.4% comparing with urchin MnO2. Under250mA g-1, it increases nearly37.1%, and keeps70%after100th cycles. However, urchin MnO2has less Rct than that of spherical MnO2.In order to improve the capacitive properties of MnO2, there was the synthesis of composite MnO2/PANI doped with H+from H2SO4. The results suggest that the degree of oxidation of aniline could be strengthened with the increase of initial acidity of solution, and polyaniline prepared with3mol L-1H+has the optimal capacitive performance.Compared with the simple MnO2, pseudocapacitance of composite material is more evident, and it has the promising specific capacitance388.67F g-1at65mA g-1, which is more30F g-1than the simple MnO2. With the rise of current density, it is still above300F g-1, which exhibits better rate performance than the simple MnO2.