ELECTROCATALYTIC REDUCTION OF DIOXYGEN AT MACROCYCLE CONDUCTING POLYMER ELECTRODES IN ACID-MEDIA

Functionalized transition metal macrocyclic monomers were synthesized in order to prepare electron-conducting polymer-based electrodes. Coba lt tetra(o-aminophenyl)porphyrin and cobalt 4,4',3'',4'''-tetraaminoph thalocyanine macrocycles were electropolymerized at a vitreous carbon electrode to give, respectively, poly(CoTAPP) and poly(CoTAPc). The el ectrocatalytic behaviour of such electrodes, particularly the influenc e of the macrocyclic skeleton towards dioxygen reduction, was examined . Both electrodes are active in oxygen reduction. However, the modifie d electrode containing cobalt phthalocyanine seems to be the most acti ve. The Tafel slope determined at 20 degrees C at the onset of the red uction wave for both modified electrodes was 58 +/- 5 mV/decade, while in a higher overpotential region it was close to 116 +/- 20 mV/decade . The number of electrons involved during the reduction of dioxygen wa s determined using the Koutecky-Levich equation. The main reaction pro duct at a poly(CoTAPP) electrode is hydrogen peroxide, whereas at a po ly(CoTAPc) electrode the product is mainly water, since the last elect rode allows a four-electron reduction process to occur at higher overp otentials. (C) 1997 Elsevier Science S.A.