MECHANISM OF OXYGEN ELECTROREDUCTION AT POLYPYRROLE ELECTRODES MODIFIED BY COBALT PHTHALOCYANINE

Polypyrrole (PPy) films containing cobalt tetrasulphonated phthalocyan ine (CoTsPc) were electrosynthesized at gold electrodes by cyclic volt ammetry. Oxygen reduction at the cobalt phthalocyanine modified polypy rrole gold electrodes (Au/PPy/CoTsPc) was investigated mainly in acid solutions because of the non-conductivity of the polymer matrix in alk aline electrolytes. The number of electrons transferred during the oxy gen reduction was determined using the rotating disk electrode techniq ue. The ability of the Au/PPy/CoTsPc electrode to reduce hydrogen pero xide to water was also investigated. It is shown that several mechanis ms, depending on the potential, may be involved in oxygen reduction at such electrodes. For potentials greater than 0.4 V(RHE), the mechanis m involved two exchanged electrons and the main product formed was hyd rogen peroxide, while for potentials lower than 0.4 V(RHE), four elect rons were transferred during oxygen reduction, giving water as the mai n product.