GLASSY-CARBON ELECTRODE MODIFIED BY CONDUCTIVE, POLYMERIC NICKEL(II) PORPHYRIN COMPLEX AS A 3D HOMOGENEOUS CATALYTIC-SYSTEM FOR METHANOL OXIDATION IN BASIC-MEDIA

The voltammetric behaviour in alkaline solution of a nickel-based chem ically modified electrode (poly-NiTMHPP) prepared by oxidative electro polymerization of a nickel tetrakis(3-methoxy-4-hydroxyphenyl)porphyri n for electro-oxidation of methanol was investigated by cyclic voltamm etry and the rotating disk technique. The oxidation of methanol occurs at 0.61 V vs. SCE, where oxidation is not observed at the bare electr ode. The dependence of the oxidation current on the methanol concentra tion and on the number of redox centres Ni(II)/Ni(III) is discussed. F rom the fact that the oxidation current increases with increasing film thickness it is evident that the electrocatalytic reaction occurs ins ide the polymer film. The system examined is a typical example of a re dox polymer with 3D properties. It is also concluded that the reaction mechanism of methanol electro-oxidation is of the so-called ''R'' cas e, according to the concept of Saveant and Andrieux, i.e, a cross-exch ange reaction is the limiting step. (C) 1997 Elsevier Science S.A.