SPECTROSCOPIC INVESTIGATIONS OF POLYMER-MODIFIED ELECTRODES CONTAINING COBALT PHTHALOCYANINE - APPLICATION TO THE STUDY OF OXYGEN REDUCTION AT SUCH ELECTRODES

Polymer films such as polypyrrole (PPy), polypyrrole modified by cobalt tetrasulphonated phthalocyanine (PPy-CoTsPc), polyaniline and polyaniline modified by cobalt tetrasulphonated phthalocyanine were electrosynthesized at gold electrodes by cyclic voltammetry. A UV-visible differential reflectance spectroscopic investigation of the behaviour of these electrodes as a function of their potential was carried out in acid electrolyte. II was shown that the insertion of cobalt phthalocyanine rakes place into such polymer films and that it is possible to follow the variation in the UV-visible spectra of cobalt phthalocyanine with the electrode potential. The cobalt tetrasulphonated phthalocyanine appears as the Co(III)TsPc species at higher potentials and becomes the Co(II)TsPc species when the potential decreases. An electron spin resonance investigation was performed at PPy and PPy-CoTsPc electrodes in deoxygenated and oxygen-saturated solutions. It was shown that the Co(III)TsPc species is effective in the electroreduction of oxygen and that this species is more stable in oxygen-saturated medium than in deoxygenated medium, certainly because of its stabilization under the following form: Co(III)TsPc-O-2(-). In the case of the PPy-CoTsPc film, the polypyrrole matrix undergoes strong interactions with oxygen species, and more probably with hydrogen peroxide.