ELECTRON-TRANSFER AT CONDUCTING POLYMER FILM ELECTRODES - MECHANISM AND KINETICS OF FERROCENE OXIDATION AT POLY(3-OCTYLTHIOPHENE)

Oxidation of ferrocene at a poly(3-octylthiophene) (POT) film electrod e has been investigated by using cyclic voltammetry, rotating disc ele ctrode voltammetry and electrochemical impedance spectroscopy. The POT film electrode wats prepared by galvanostatic electropolymerization o f 3-octylthiophene on a rotating Pt disc electrode. In the medium used i.e. 0.1 M LiBF4 + propylene carbonate, the formal redox potentials o f ferrocene and POT are 0.4 and 1.1 V vs. Ag/AgCl respectively. This m akes it possible to study the oxidation of ferrocene at both undoped ( semiconducting) POT and at doped (electronically conducting) POT. The voltammetric data show that the oxidation of ferrocene is kinetically controlled at undoped or lightly doped POT while ferrocene is oxidized at a diffusion limited rate at highly doped POT. Impedance data on th e POT film electrode in solutions containing different concentrations of supporting electrolyte and ferrocene indicate that the ferrocene ox idation occurs in parallel with the doping process, resulting in a com petition between ferrocene and doping ions for the available 'sites' a t the polymer/solution interface. The kinetics of electron transfer at the polymer/solution interface are discussed based on the Butler-Volm er formulation of electrode kinetics. (C) 1997 Elsevier Science S.A.