dc Proton conductivity at low‐frequency in Nafion conductivity spectrum probed by time‐resolved SAXS measurements and impedance spectroscopy

The electric transport properties of Nafion membranes are investigated by impedance spectroscopy (IS) and correlated with small angle X-ray scattering (SAXS). Detailed IS measurements in a wide range of temperature and frequencies (f) allowed separating contributions from different charge carriers in Nafion. At controlled relative humidity and temperature, Nafion IS spectrum exhibits at T > 160 °C two distinct frequency-independent conductivities occurring at high f ∼ 106 Hz and low f < 10−2 Hz. Such IS measurements were combined with time-dependent SAXS measurements under applied dc electric potential, which provided compelling evidence that the low-f dc conductivity is related to the motion of protons via ion-hopping in hydrated Nafion membranes. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 822–828