Numerical Analysis of Proton Conductivity in Hydrated Nafion Membrane Contaminated with Iron Ion

We performed a numerical analysis of the influences of contaminated metal ion on the dynamic properties of proton in a polymer electrolyte membrane (PEM). It was revealed that the nanostructure of the PEM was changed greatly with increasing the concentration of ferric ions. The diffusion coefficient of hydronium ions increases larger at higher water contents with increasing the concentration of ferric ions because of the lower concentration of cations. At higher water contents, the hydronium diffusion coefficient increases largely because ferric ions reduce the electrostatic interactions between hydronium ions and sulfonate groups. At lower water contents, by contrast, the structures between ferric ions and sulfonate groups hinder the hydronium motions resulting in a small increase in the hydronium diffusion coefficient