Study On Preparation And Application Of Carbon Material For Electrochemical Double-layer Capacitors

As new energy storage devices, electrochemical capacitors possess high power density, high energy density, quick charge-discharge capability, long cycle-life, maintenance free, friendly to the environment, et al. And have been applied in many fields. Based on different charge-storage mechanism two basic types of electrochemical capacitors can be realized: faradaic pseudocapacitors and electrochemical double-layer capacitors. The electrode material is a key factors to determine capacitive properties of electrochemical capacitors. There are three kinds of the electrode materials: metal oxide, carbon, and conductng polymers. In this thesis, various carbons were prepared, and they were applied as the electrode materials in electrochemical capacitors. The details are summarized as follows:(1) high surface area activated carbon was prepared from lotus root by ZnCl2 chemical activation with high temperature under nitrogen atmosphere. It was used as electrode materials for electrochemical double-layer capacitor. The specific surface area and pore diameter distribution of activated carbon was characterised by ASAP2020 and the related morphology was investigated by scanning electron microscopy(SEM). The capacitive behavior of the activated carbon electrode was investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge method in 6 mol·L-1 KOH aqueous solutions. The results show that activated carbon electrode shows excellent capacitive properties: ideal CV performance and specific capacitance as high as 210 F·g-1 in 6 mol·L-1 KOH aqueous solution from -1.0 V to 0.0 V when the charge–discharge current load is 0.2 A·g-1. Additionally, the activated carbon electrode shows excellent power characteristics and long-term cycle stability.(2) Peasecod-based carbons from peasecod treated with KOH and ZnCl2 as pore formers have been successfully prepared by the simple pyrolysis process. The specific surface area and pore diameter distribution of activated carbon was characterised by ASAP2020. The capacitive behavior of the peasecod-based carbon electrode was investigated by CV and galvanostatic charge-discharge method in 6 mol·L-1 KOH aqueous solutions. The results demonstrate that compared with the untreated peasecod-based carbons, the activated carbons shows an enhancement in specific surface area of up to 1323 times for the KOH activation (2237m2·g?1) and 367 times for the ZnCl2 treatment (621m2·g?1). Furthermore, the peasecod-based carbons treated by KOH have a high ratio of mesopores, show the best performance with a specific capacitance of 297.5 F·g?1 in 6 mol·L-1 KOH electrolyte at 2 mV·s-1and has 91.4 % capacitance retention for 500 charge/discharge cycles at a high current density of 5 A·g-1. Peasecod-based carbons electrode exhibit good capacitive properties.(3) Hollow nitrogen-doped carbon microspheres (HNCM) prepared from dopamine have been prepared by simple template method and their electrochemical capacitive properties have been investigated. The specific surface area and pore diameter distribution of HNCM were characterised by ASAP2020 and the related morphology was investigated by SEM and transmission electron microscopy (TEM). Nitrogen content in HNCM was determined by elemental analyzer. The capacitive behavior of the HNCM electrode was investigated by CV and galvanostatic charge-discharge method in 1 mol·L-1 H2SO4 aqueous solutions. The results indicate that the specific surface area of HNCM is 767 m2·g-1. It shows the best performance with a specific capacitance of 473 F·g?1 in 1 mol L-1 H2SO4 electrolyte at the current density of 0.5 A·g-1 and the specific capacitance almost remains constant after 3000 charge/discharge cycles at a high current density of 30 A·g-1. The results show that the hollow nitrogen-doped carbon microspheres electrode exhibit good capacitive properties and long-term cycle stability.