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

• Published in: Journal of polymer science. Part B, Polymer physics Vol. 53; no. 11; pp. 822 - 828
• Main Authors: Matos, Bruno R., Santiago, Elisabete I., Rey, Jose Fernando Q., Scuracchio, Carlos H., Mantovani, Gerson L., Hirano, Laos A., Fonseca, Fabio C.
• Format: Journal Article
• Language: English
• Published: Hoboken Blackwell Publishing Ltd 01.06.2015; Wiley Subscription Services, Inc
• Subjects: Direct current; Electric potential; Exchange; Impedance spectroscopy; Ion exchangers; ionomers; Membranes; Relative humidity; relaxation; SAXS; structure-property relations
• ISSN: 0887-6266; 1099-0488
• DOI: 10.1002/polb.23704

ABSTRACT 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 Nafion has been extensively used as the electrolyte in proton exchange membrane fuel cells due to its high proton conductivity and diffusion coefficient. Numerous efforts have been focused on disentangling the intricate relation between the physical properties and morphology of perfluorosulfonate ionomers. Here, an additional dc proton conductivity at low frequencies in Nafion is identified by small‐angle X‐ray spectroscopy (SAXS) and impedance spectroscopy.