A REVISED MODEL TO ACCOUNT FOR THE KINETICS OF THERMODYNAMICALLY DISFAVORED ELECTRON-TRANSFER CROSS-REACTIONS AT THE INTERFACE BETWEEN REDOX POLYMERS AND SOLUTIONS

Previously applied procedures for the analysis of the kinetics of electron-transfer cross-reactions at electrodes coated with redox polymers require reconsideration when the cross-reactions involved are thermodynamically disfavored. A revised procedure is described for treating kinetic data which takes account of the observation that redox couples incorporated in coatings on electrodes often behave as an ensemble of couples exhibiting a range of formal potentials extending over hundreds of millivolts. The application of this procedure is described for two experimental systems, the oxidation of IrCl63- by Os(bpy)33+ and the oxidation of Fe(DPP)34- by Fe(bpy)33+ with the cationic reactants incorporated in Nafion coatings on rotating-disk electrodes. The revised procedure provides better agreement between calculated and experimental currents than could be obtained with previously applied approaches which assume that a redox couple incorporated in a Nafion coating can be characterized by a single formal potential.