Electrode Kinetics of Metal Complexes Confined in Perfluoro Polycarboxylate and Polysulfonate Coatings on Graphite Electrodes

A heterogeneous electron-transfer process of [Os(bpy)3]2+⁄3+ (bpy: 2,2′-bipyridine) and [(trimethylammonio)methyl]ferrocene/ferricinium (TAF+⁄2+) redox couples, which were confined in perfluoro polycarboxylate and polysulfonate polyelectrolyte coatings on graphite electrodes, at the electrode/film interfaces as well as a homogeneous charge-transport process within the coating films were examined by means of potential-step chronoamperometry and chronocoulometry, normal pulse voltammetry and ac impedance measurements. The relevant kinetic parameters (i.e., the standard rate constant k° and the transfer coefficient of the heterogeneous electron-transfer process and the apparent diffusion coefficient Dapp for the homogeneous charge-transport process) were determined at various concentrations of the redox species in the films at various pH’s. The temperature dependences of Dapp, k° and the formal potentials of the [Os(bpy)3]2+⁄3+ and TAF+⁄2+ couples confined in the films were also examined and the relevant activation parameters for the heterogeneous electron-transfer and homogeneous charge-transport processes and the reaction entropies of these redox couples were evaluated. On the basis of the kinetic and thermodynamic data obtained, the mechanism of the charge-transport process within the films, the effects of polymer domain and pH on the rates of the heterogeneous electron-transfer and homogeneous charge-transport processes and on the incorporation of the redox species into the films, etc. are discussed.