Preparation of microporous activated carbon and its electrochemical performance for electric double layer capacitor

Microporous activated carbons were prepared by microwave heating petroleum coke with potassium hydroxide as activation agent. Microporous activated carbons were characterized by infrared spectroscopy, X-ray diffraction and nitrogen adsorption/desorption isotherms. Electrochemical properties of an electric double layer capacitor using microporous activated carbon as electrode materials were investigated by constant current charge-discharge and electrochemical impedance spectroscopic techniques. The results show that the specific surface area and the pore volume of microporous activated carbon increase with increasing activation time before the activation time reaches 37 min. The microporous volume totals 94.0% in the microporous activated carbons and the average pore diameter of microporous activated carbon is 2.00 nm. Microporous activated carbons prepared in the activation time of 31, 35 and 37 min are named as AC-31, AC-35 and AC-37, respectively. Compared with AC-27 electrode, the internal resistance for ions transferring in AC-31, AC-35 or AC-37 electrode is relatively small. The specific capacitance of AC-31 is the biggest among the microporous activated carbons, and it retains 279.6 F g(-1) maintaining 93.5% capacity after 200 recycling number. (C) 2009 Published by Elsevier Ltd.