ac-Electrogravimetry study of ionic and solvent motion in polypyrrole films doped with an heteropolyanion, SiMo12O404−

Determination of the diffusion coefficient of protons in Nafion thin films by ac-electrogravimetry

This letter deals with an adaptation of the ac-electrogravimetry technique to extract separately the dynamic properties of H(+) and water in Nafion nanometric thin films (average thickness of 400 nm). An original theoretical approach was developed to extract the representative parameters from ac-electrogravimetry data. The concentration change of the exchanged species and the diffusion coefficient of the protons in a Nafion nanometric thin film (D = 0.5 × 10(-6) cm(2) s(-1) at 0.3 V vs SCE) were estimated for the first time according to the applied potential. The conductivity value of Nafion thin films was calculated from the Nernst-Einstein equation using diffusion coefficients and concentration values extracted from ac-electrogravimetry data. The calculated conductivity results agree well with the experimental proton conductivity values of Nafion thin films.

Redox switching of heteropolyanions entrapped in polypyrrole films investigated by ac electrogravimetry

In this work, the global kinetics and the exchange of protons and free solvent at the film/electrolyte interface were investigated when a PPy film doped with HPA (heteropolyanions) is polarized. The ionic and electronic transfers for the PPy-HPA system are fast because the determined values of the resistances are relatively low (a few ohms). Depending on the applied potential, the global kinetics is controlled by both the ionic and electronic transfers. The transport effects were neglected here because the prepared films were very thin. Protons play an important role in charge compensation whatever the imposed potential on the PPy-HPA film. This phenomenon results from the acidic-basic properties of the SiMo(12)O(40)(4-) reduced species. A small quantity of water was also shown to be involved in the film reaction process.