Thick active layers of electrochemically modified glassy carbon - Electrochemical impedance studies

Glassy carbon electrodes were electrochemically modified by an anodization/cathodization procedure in aqueous H2SO4. Depending on the anodization time, the active-layer thickness could be controlled from less than a micrometer to nearly 100 mu m. Electrochemical impedance measurements indicated that the capacitance per unit volume of the active layer was similar to various other porous carbons and sufficient for application as an electrochemical capacitor material. The small-signal ac capacitance was found to be 80-460 F/cm(3) (single-electrode capacitance), depending on potential, for the higher-pyrolysis-temperature carbon, and 25-420) F/cm(3) for the lower-pyrolysis-temperature carbon. The resistance of the active layer depended even more strongly on the pyrolysis temperature of the glassy carbon. The active layer on the carbon pyrolyzed at a temperature of 2200 degrees C had a resistance which was about 1000 times lower than that of a corresponding layer grown on glassy carbon pyrolyzed at 1000 degrees C. (C) 2000 The Electrochemical Society. S0013-4651(99)04-111-7. All rights reserved.