THE REDUCTION OF DIOXYGEN AND THE OXIDATION OF HYDROGEN AT POLYPYRROLE FILM ELECTRODES CONTAINING NANODISPERSED PLATINUM PARTICLES

Polypyrrole (ppy) films containing a three-dimensional array of nanometer-sized platinum catalyst particles have recently been developed in this laboratory. The catalytic activity of these ''nanocomposite'' (ppy+Pt) films towards the dioxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR) was tested in 0.05 M H3PO4 and 0.5 M H2SO4 respectively, with the polymer film thickness and platinum catalyst loading as variables. In both cases an increase in the reaction cross-section with the polymer film thickness was noted, consistent with the facile permeation of the substrates into the polymer+catalyst framework. The hydrodynamic voltammetry data were analyzed and found to be diagnostic of rate control being exercised by the bimolecular catalyst-substrate charge-transfer reaction for both the ORR and HOR. For the HOR, the ppy + Pt films exhibited a remarkable enhancement (five times) in the reaction rate relative to a massive platinum comparison standard. While polypyrrole itself showed negligible catalytic activity towards the HOR. the ORR proceeded at a fast rate at the polymer matrix even in the absence of the platinum catalyst. Comparisons with available data on the ORR and HOR at other types of platinum modified polypyrrole samples are presented.