Charge Transport Properties of Polythionine Films Dependent on Electrode Potential and Solution pH

Abstract

The charge-transport properties of polythionine film were studied by cyclic voltammetry and ac impedance spectroscopy. The redox reaction of polythionine proceeded by a two-electron, two-proton transfer mechanism. Both the low-frequency resistance and the low-frequency capacitance obtained from the ac impedance response were proportional to the film thickness. The former showed a minimum, and the latter showed a maximum, at the half-wave potential. The coupled diffusion coefficient of electrons and protons also showed a maximum at the half-wave potential. This relationship between the oxidation level and the diffusion coefficient indicated that the rate of charge transport in the film may be controlled by electron transport. A decrease in the diffusion coefficient with increasing pH implied 1electron hopping accompanied with intermolecular proton exchange.