The Study Of Preparation And Electrochemical Performance Of Plant-based Porous Carbon

Supercapacitor is a new device for electric energy storage. It has not only much more energy than conventional capacitors, but also much higher power density than batteries. Electrode material is one of the most important components of supercapacitor. It is a key factor influencing the performance of supercapacitor. The research and development of electrode materials have been the focus in the recent years.In this dissertation, the preparation, modification and electrochemical performance of plant-based porous activated carbon (AC) were studied in detail. In addition, Fe3O4 nano-particles, prepared by microwave method, were used as the electrode material of hybrid supercapacitor together with AC for the first time. The electrochemical properties of the hybrid capacitor were studied. The properties of ACs and Fe3O4 nano-particles were investigated by modern instruments, such as SEM, XRD, N2 adsorption, FTIR, XPS and so on. The performance of the resultant electrode materials and testing supercapacitors were tested by electrochemical measurements through constant current charge-discharge, cyclic voltammogram, impedance spectrum etc. The relationship between the structure and surface properties of electrode materials and its electrochemical performance was studied. In this paper, main works were done as following:Microporous activated carbon fibers (ACFs) with high surface area and high yield were successfully prepared by chemical using ramee as raw materials and ZnCl2 as activating agents. The activation was carried under low temperature and short activation time. The effects of activation parameters on the structure, surface and capacity properties of ACFs were systematically studied. The results showed that the ACF, which specific area is more than 1600 m2/g, pore size distributes in 0.5~2 nm and specific capacitance can reach to 253 F/g in 30wt.% KOH, can be produced under optimal condition. In addition, it also showed good power and cyclic properties.Apricot shell-based AC and coconut shell-based AC were modified by concentrated nitric acid. The results showed that after modification, the specific area and pore volume of ACs decreased while the content of oxygen functional groups, especially which of hydroxyl, increased obviously. The contribution of hydroxyl to the specific capacitance of AC is the most among all of functional groups. At the same time, the increase of functional group content is also benefit to the improvement of capacitance at high current density.Iron oxide nanoparticles, prepared by microwave method, was used as anode material of the hybrid supercapacitor for the first time, in which coconut shell-based activated carbon was used as cathode material. The electrochemical performances of the hybrid supercapacitor were studied. The results showed that the asymmetric capacitor has an operating voltage of 1.2 V and energy density up to 9.25 Wh/kg, 53.4% higher than the coconut shell-based activated carbon double-layer capacitor. At the same time, the asymmetric capacitor also showed stable cycle performance.