Electrodes modified by conducting polymers bearing redox sites: Ni- and Co-cyclam complexes on polypyrrole

Cyclam has been N-functionalized and linked to the nitrogen of pyrrole thro ugh an alkyl spacer. After complexation of the ligand by nickel(II) or coba lt(II), the complexes have been electropolymerized on the surface of electr odes, by cyclic voltammetry or at constant potential. The Ni(III)/Ni(II) re dox system is very distinctly visible on the voltammogram of the poly[Ni(II )-cyclam-N-(CH2)(5)-pyrrole] film,even after over-oxidation of the polypyrr ole backbone; from this observation it is obvious that the electron transfe r between nickel sites occurs through hopping. The electropolymerization of Co(III)-cyclam-N-(CH2)(5)-pyrrole is more difficult and the films are thin and brittle; those obtained from the electropolymerization of the Co(II) c omplex are of a better quality. The Co modified glassy carbon electrodes ar e active for the electrocatalytic reduction of dioxygen in acidic media. A gold electrode modified by poly[Co(III)-cyclam-N-(CH2)(5)-pyrrole] catalyse s the nitrate ion reduction at -1.0 V versus saturated calomel electrode (S CE) in a strongly basic medium, after amalgamation. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.