EFFECT OF ELECTROLYTES ON THE KINETICS AND MECHANISM OF THE ELECTROPOLYMERIZATION OF PYRROLE ON TO CARBON-FIBERS

The effect of reaction conditions on the kinetics of aqueous electropo lymerization of pyrrole on to carbon fibers has been studied. The rate of electropolymerization of pyrrole, R(p), varied with the electrolyt e concentration, [R(+)X(-)], applied voltage, E(pa), and monomer conce ntration, [M], raised to a power of 0.8, 1.1-1.3 and 0.8-1.7, respecti vely (R(p) alpha [R(+)X(-)](0.8) E(pa)(0.9-1.2) [M](0.8-1.0). The orde r of aqueous electropolymerization with respect to the monomer concent ration, 0.8-1.0, and applied voltage, 0.9-1.2, varied slightly with th e concentration and type of electrolyte used. The pH of the reaction m edium decreased with increased reaction time. Correspondingly, the amo unt of polypyrrole coatings formed into graphite fibers increased with decreased pH and increased reaction time. In fact at a pH of less tha n or equal to 3, a sharp rise in the amount of polypyrrole coatings fo rmed occurred. Elemental analysis and infrared spectroscopy were used to show that supporting electrolyte was embedded in the coatings. In a ddition, infrared spectroscopy and the pH of the reaction medium, yiel ded information in support of the anodic oxidation of pyrrole with the associated dehydrogenation (removal of the 2,5 hydrogens of the pyrro le ring) and the consequent 2,5 pyrrole ring coupling. Copyright (C) 1 996 Elsevier Science Ltd