MONOMOLECULAR FILMS OF A NICKEL(II) PENTAAZAMACROCYCLIC COMPLEX FOR THE ELECTROCATALYTIC OXIDATION OF HYDROGEN-PEROXIDE AT GOLD ELECTRODES

Self-assembled monolayers (SAMs) of a redox active nickel(II) pentaaza macrocyclic complex 1 and mixed monolayers of 1 with ethyl disulfide h ave been fabricated on a gold electrode, and their electrochemical beh avior has been studied by cyclic voltammetry in aqueous solutions of N a2SO4 and NaNO3. The results demonstrate that the redox behavior as we ll as the electrocatalytic activity towards the oxidation of H2O2 of t he SAM and mixed monolayers of 1 largely depend on the electrolyte ani ons, i.e. SO42- and NO3-: the formal potential in the SO42- electrolyt e is about 220 mV less positive than that in the NO3- electrolyte, and the SAM and mixed monolayers of 1 possess an efficient electrocatalys is for the oxidation of H2O2 in the NO3- electrolyte, but not in the S O42- electrolyte. In addition, a unique cyclic voltammogram with a sha rp peak of inverted 'V' shape has been observed in the cathodic scan f or the electrocatalytic oxidation of H2O2, largely depending on the co ncentration of the NO3- electrolyte anion and the solution pH. These e lectrolyte anion-dependent redox behaviors have been discussed on the basis of different coordinating tendencies of SO42- and NO3- to the ni ckel(III) centre of the complex and a possible reaction mechanism for the observed electrocatalytic reaction. (C) 1998 Elsevier Science S.A. All rights reserved.