Impedance Spectroscopy of Dielectric Relaxation in a Perfluorosulfonic Acid Ionomer Nafion Membrane

We have employed impedance spectroscopy in order to study the intrinsic dielectric properties and dynamics of a perfluorosulfonic acid ionomer Nafion (NR-211) membrane. Distinct dielectric relaxation processes involving ionic and chain motions were elucidated by using a frequency-temperature contour plot analysis of the dielectric loss. Furthermore, the low-frequency dielectric loss data that reflect the fractal chain structure of the Nafion system indicated the least topological imperfection of the ionic clusters at the temperature of the maximum loss tangent, Tg = 325 K. An equivalent circuit analysis of the complex impedance manifested a drastic motional slowing down that was apparently associated with a relaxation process around Tg.