Study On Phenolic Resin Based Activated Carbon Fibers As Electric Double Layer Capacitor Electrode Material

The object of this research is to develop a new type of carbon electrode material-phenolic based activated carbon fibers (PACFs) with high specific surface area and pore volume, suitable pore size distribution, and good conductivity for the electric double layer capacitors (EDLC). PACFs were prepared by carbonization and activated by CO2, H2O and KOH at different temperatures, respectively. The effects of the specific surface areas and pore structures on the electrochemical performances of EDLC were discussed in detail. The BET specific surface area and pore structure parameter of all PACF samples were determined by the low temperature N2 adsorption isotherm method. The electrochemical properties of EDLCs using PACF as electrodes are systematically studied by cyclic voltammetry, AC impedance and galvanostatic charge/discharge.It was found that PACFs activated by KOH were typical micropores structure. Although the PACFs activated with different conditions showed different specific surface areas and specific capacitances, the pore size distributions were similar for all samples, within the range of 0.5nm to 3.0nm. With the increase of activation temperature, the resulting PACFs showed the decrease in terms of resistance expressed by AC impedance as well as increase specific capacitance and power capability. The capacitance and resistance strongly depend on the porous structure, the bigger the pore, the easier and faster being accessed electrochemically, the less resistance should be, and it can be discharge/charged at higher current density. PACFs with larger pore and surface area are desirable for those applications either as energy devices or as power storage devices. In addition, when the activation temperatures lower than 900℃, the PACFs electrodes showed better cyclic properties and lower resistance.However, the higher carbonization temperature, the lower specific capacitance, the lower resistance and the better cyclic properties. In hence, PACFs carbonized at 600℃for 1 hour and activated by KOH (the ratio of alkali to the PACFs was 4) at 900℃for 1 hour, which is the optimal condition in this work, shows the best electrochemical characteristics. When it was discharged at bigger current density, the specific capacitance can keep at 264.1 F·g^-1.