Mass Transport Investigated with the Electrochemical and Electrogravimetric Impedance Techniques. 1. Water Transport in PPy/CuPTS Films

Water transport in poly(pyrrole/copper phthalocyaninetetrasulfonate) (PPy/CuPTS) films, where cation transport prevails, has been investigated by employing the electrochemical quartz crystal microbalance (EQCM) technique, the electrochemical impedance technique, and the electrogravimetric impedance technique. The approximate numbers of accompanying waters per cation for PPy/CuPTS films have been obtained from both cyclic EQCM experiment and impedance experiment. It is shown that the number of accompanying waters depends on the nature and concentration of an electrolyte solution as well as the redox state of the film. It increases with the hydration number of cation in an aqueous electrolyte solution and exhibits hysteresis behavior during redox cycle. It is found that ionic conductivity of cation in a film depends on the number of accompanying waters and the ion-ion interactions inside the film. It is also found that a substantial amount of water moves with the cation during the break-in process at the first cathodic scan. Moreover, the electromechanical impedance technique has been employed to verify the relation between mass and resonant frequency of an oscillating quartz crystal and to monitor morphology changes (viscoelastic change and volume change) during the redox reaction of PPy/CuPTS films. It is found that mass change can be obtained from resonant frequency without consideration of morphology changes of PPy films. It is also found that morphology changes of PPy/CuPTS films relate to the amount of water moving into or out of the film.