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Letter

Increased Water Retention in Polymer Electrolyte Membranes at Elevated Temperatures Assisted by Capillary Condensation

Supporting Info

Moon Jeong Park,^†^‡ Kenneth H. Downing,^§ Andrew Jackson,^£ Enrique D. Gomez,^†^‡ Andrew M. Minor,^# David Cookson, Adam Z. Weber,⁺ and Nitash P. Balsara*^†^‡⁺

Department of Chemical Engineering, Materials Sciences Division, Life Sciences Division, National Center for Electron Microscopy, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, and Australian Synchrotron Research Program, Building 343, Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439

Nano Lett., 2007, 7 (11), pp 3547–3552

DOI: 10.1021/nl072617l

Publication Date (Web): October 26, 2007

†

Department of Chemical Engineering, University of California.

‡

Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California.

Life Sciences Division, Lawrence Berkeley National Laboratory, University of California.

National Institute of Standards and Technology.

University of Maryland.

National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, University of California.

Argonne National Laboratory.

Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, University of California.

To whom correspondence should be addressed.

Abstract

We establish a new systematic methodology for controlling the water retention of polymer electrolyte membranes. Block copolymer membranes comprising hydrophilic phases with widths ranging from 2 to 5 nm become wetter as the temperature of the surrounding air is increased at constant relative humidity. The widths of the moist hydrophilic phases were measured by cryogenic electron microscopy experiments performed on humid membranes. Simple calculations suggest that capillary condensation is important at these length scales. The correlation between moisture content and proton conductivity of the membranes is demonstrated.

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