Charge transport properties of polythionine films dependent on electrode potential and solution pH

The charge-transport properties of polythionine film were studied by cyclic voltammetry and ac impedance spectroscopy. The redox reaction of polythion ine proceeded by a two-electron, two-proton transfer mechanism. Both the lo w-frequency resistance and the low-frequency capacitance obtained from the ac impedance response were proportional to the film thickness. The former s howed 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 tran sport in the film may be controlled by electron transport. A decrease in th e diffusion coefficient with increasing pH implied electron hopping accompa nied with intermolecular proton exchange.