Study on the ion transport of polyaniline thin film using electrogravimetric impedance technique

Abstract

Recently developed elctrogravimetric impedance technique, which combines the EQCM and electrochemical impedance technique, is very useful method in the study of ion transport in conducting polymer. It makes no morphological change of the polymer film and can separate the respective information of anion and cation. In this study, elctrogravimetric impedance technique was constructed and applied to the study of polyaniline, which is one of the most promising conducting polymers. The respective contribution to ion transport and the diffusion coefficients of anion($ClO_4{^-},HSO_4^{-},Cl^{-}$) and proton($H_3O^{+}$) were obtained and their dependence on the electrode potential and pH of bathing solution was investigated. The proton contribution increases with the decreasing dc potential and the decreasing solution pH, which is consistent with others`` reports that proton transport largely takes place at the initial stage of oxidation process and the proton contribution increases as PAN film is more protonated. The diffusion coefficients of proton and anion show the same order of magnitude. These values decrease with decreasing dc potential and increasing solution pH, which can be explained by the facts that ion transport is harder as the conducting polymer is in its insulating state and diffusion coefficients increase with the increment of ionic concentration in bathing solution resulting in that in the film.