Abstract: The charge transport of Fe(Ⅱ/Ⅲ) ions within the Nafion film and in solutions has theoretically been derived. The diffusion coefficients and standard rate constants of Fe(Ⅱ/Ⅲ) ions in the film were evaluated to be 2.9×10~(-7) cm~2·s~(-1) and 1.1×10~(-3) cm·s~(-1), respectively, by analyzing the system impedance based on the small amplitude potential step. Obtained value of k°′ is less than an order of magnitude to uncoated electrodes, which is correlated with large diffusion rate of Fe(Ⅱ/Ⅲ) ions within the Nafion film. Effects of electrode potentials and concentrations of supporting electrolytes on the system impedances have been discussed. Results are reasonably agreed with theoretical derivations.

Key words: Nafion film, Iron ions, Charge transport, Diffusion, Impedance measurement