ANALYSIS OF CHARGE-TRANSPORT IMPEDANCE IN THE REDUCTION OF THIN-FILMS OF CONDUCTING POLYANILINE IN AQUEOUS TRICHLOROACETIC-ACID SOLUTIONS

Some theoretical predictions of the charge transport properties of mixed electronic-ionic conductors are compared with experimental results for a thin-film polyaniline electrode in aqueous trichloroacetic acid solutions. The transport capacitance and characteristic time were determined from the impedance/admittance frequency dispersions. The supporting electrolyte concentration and film-thickness dependences were studied at several de potentials corresponding to various reduction levels of conducting polyaniline. The general form of the theoretical equation for the diffusion-migration impedance is found to give a good description of the system under study, i.e. a thin-film electrode in the first redox system of polyaniline. A very thin polymer layer that contacts the substrate electrode and so has different charge transport characteristics from the thicker polymer films is postulated. The enhanced ionic conductivity due to incorporation of excess supporting electrolyte in the porous conducting polyaniline is observed. The specific transport capacitances and apparent anion diffusion coefficients of thin polyaniline films in trichloroacetic acid solutions were found to be of the order of 10(2)F cm(-3) and 10(-12)-10(-11) cm(2) s(-1) respectively.