Abstract
Ionic conductivity and water transport through alkaline Anion Exchange Membranes (AEM) are key properties for application in Alkaline Membrane Fuel Cells (AMFC), Redox-Flow-Cells, or Alkaline Membrane Electrolysis. AEMs consist of a polymer domain with cationic side groups and a pervading water domain through which anions are conducted. In this study, Quasielastic Neutron Scattering (QENS) is employed to study water rotational and diffusive dynamics in the hydroxide form of a model AEM (Fumatech FAA-3) at water contents relevant for application. Two distinct diffusion time- and length-scales are accessed: “Localized” diffusion at the lower Ångstrom/tens of picosecond scale and “extended” diffusion at the higher Ångstrom/hundreds of picosecond scale. The localized diffusion length scale is smaller than the membrane's water domain thickness and its diffusion coefficients remain close to the value of bulk water even at decreasing water content. Extended diffusion approaches the thickness of the water domain and its diffusion coefficients decrease strongly with decreasing water content. A master curve links water domain thickness to the extended water diffusion coefficients for the alkaline hydrocarbon model AEM and literature data on acidic per-fluorinated Proton Exchange Membranes.
Original language | English |
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Pages (from-to) | 240-247 |
Number of pages | 8 |
Journal | Journal of Membrane Science |
Volume | 586 |
DOIs | |
State | Published - Sep 15 2019 |
Funding
Time-of-flight QENS was conducted at the TOFTOF spectrometer (operated by Technische Universität München, at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany). High-resolution backscattering QENS was conducted at the SPHERES spectrometer (operated by Jülich Centre for Neutron Science at the Heinz Maier-Leibnitz Zentrum). Parts of this work have been funded through LDRD 8264 as part of the Laboratory Directed Research and Development program at ORNL U.S. Department of Energy (DOE) . JPM likes to thank Anibal Ramirez-Cuesta and Robert W. Smith for support with the QClimax fitting suite. QClimax [ 40 ] is a part of the ICE-MAN (LDRD 8237) project, funded by the Laboratory Directed Research and Development program at ORNL U.S. Department of Energy (DOE).