Preparation of novel conductive polymer ligand-coated carbon particles by electropolymerization of pyridylthiophene and application as metal complex catalysts for oxygen reduction

Conductive polymer ligand-coated carbon particles were prepared by a fluid-bed electrolysis of 2-(3-pyridyl)thiophene using carbon particles as a working electrode. The resulting particles were suspeneded in a DMF solution of cobalt acetate. The surface of carbon particles was successfully modified with the highly dispersed cobalt complex. The modified carbon particles were suspended in an alcoholic solution of Nafion, and a pseudo-MEA was prepared on an electrode by casting the solution. The electrocatalytic reduction of dissolved O₂ was examined using the modified electrode. When the catalyst was prepared using a carbon black with a large surface area and pyrrole was added as a complementary ligand, the catalytic potential for the reduction of O₂ appeared at E_p = 0.37 V vs. SCE. The catalyst was found to reduce O₂ mainly with four electrons (n=3.1). This activity was superior to that of the previously reported carbon nanoparticles modified with a cobalt polypyrrole complex. It was clearly shown that nitrogen atoms of the pyridine-type ligand contribute to accumulate cobalt ions on the surface of the catalyst. It was also revealed that the catalytic activity improved remarkably after heat treatment of the catalyst under argon. The catalyst revealed the possibility of its use as a cathode catalyst for platinum-free fuel cells.