Characterization of high porosity carbon electrodes derived from mesophase pitch for electric double-layer capacitors

High porosity carbons prepared from mesophase pitch with KOH etching to different extents were used to fabricate electrodes for electric double-layer capacitors. Nitrogen adsorption was used to characterize the porous structure of the carbon electrodes. The performance of the capacitors in 1 M H2SO4 was investigated with voltage sweep cyclic voltammetry and constant current charge-discharge cycling. These two electrochemical methods gave fairly close results for capacitance measurements and demonstrated that distributed capacitance along a micropore path affected the capacitor performance. The specific capacitance of the electrodes was found to increase with the specific surface area. However, the capacitance per unit carbon area showed a decreasing trend with the specific area, and this has been attributed to the increased electrode resistance that would probably result from the deepening of the pores upon etching. The highest specific capacitance of 130 F g(-1) was achieved with an electrode consisting of 80% carbon powders with a specific surface area of 2860 m(2) g(-1) and 20% polyvinylidenefluoride as the binder. (C) 2001 The Electrochemical Society. Ail rights reserved.