Electrochemical Behavior of Graphite Fiber-Polymer Composites

Graphite fiber-polymer matrix composites containing about 40 w/o fibers have specific resistivities on the order of 1 to 10 ohm-cm. Such resistivity values are low enough for these materials to be considered for a wide range of electrochemical applications. Three graphite fiber-epoxy matrix composite electrodes were investigated in this study; a randomly oriented composite containing 38 v/o (50 w/o) pitchbased 15 micrometer diameter fibers, a parallel oriented composite containing 50 v/o (65 wo) PAN precursor 7 micrometer diameter fibers, and a perpendicularly oriented composite containing 50 v/o (65 w/o) PAN percursor 7 micrometer diameter fibers. For the purpose of comparison, three additional carbon containing electrodes were the purpose of comparison, three additional carbon containing electrodes were also investigated in this study, namely, pyrolitic carbon, anode-grade bulk graphite, and a specially prepared graphite fiber 'brush' electrode containing 12 micrometer diameter pitch-based fibers. With the exception of the graphite fiber brush electrode, all electrodes were used in a stationary flat plate configuration, Cyclic voltammetry (between oxygen and hydrogen evolution) was performed on each carbon containing electroder in 1 N H2SO4, 30 w/o KOH, and 2M KCl. From the cyclic voltammograms, surface functional groups were identified, and the double layer capacitance was measured for each electrode. Chronoamperometry was used to study two diffusion-controlled electrode processes on each electrode.