Morphological Factors Affecting the Behavior of Water in Proton Exchange Membrane Materials

Perfluorosulfonic acid ionomers (PFSAs), such as Nafion®, have become the benchmark membrane material for proton exchange membrane fuel cells (PEMFCs). Despite their commercial success, little is known about the complex morphology-property relationships governing the chemical and physical properties. For example, the detailed structure of PFSA crystallites within the amorphous phase and the spatial arrangement of the crystallites around the ionic aggregates of PFSA materials are virtually unknown. In addition, the effect of processing on the membrane performance and durability in PEMFC applications is not yet fully understood. The first part of this work focuses on the significance of the crystalline component with respect to polymer-water interactions. The second part of this work addresses the impact on changes in morphology that could occur during long-term operation in a fuel cell including the effects of heat and humidity.