Polymer electrolyte membrane (PEM) based devices such as fuel cells, electrolyzers, or redox flow batteries rely on high ionic conductivity under differing hydration conditions and temperatures. These materials are often operated under conditions where their structures are far from equilibrium. In order to fully understand these materials, we have undertaken a dynamic study of the morphological changes observed. One of the key tools that we use is small angle X-ray scattering (SAXS) using synchrotron radiation to study the dynamics of PEMs during hydration changes and also to establish the morphology of the films at known set points for comparison with data from other measurements such as electrochemical impedance spectroscopy, dynamic water sorption, IR and NMR spectroscopy .Over the years perfected an environmental chamber for SAXS measurements of polymer samples in which the temperature and relative humidity can be controlled.<br/>Two classes of polymers will be discussed, anion exchange membranes (AEMs) and proton conductors based on the heteropolyacids (HPAs). There has been a large resurgence of interest in AEMs as they could facilitate electrocatlysis utilizing non-precious metals and the utilization of fuels more complex than hydrogen or ethanol. We have primarily studied random and structured block co-polymer AEMs ( see image) based on hydrocarbons. In general we see modest water swelling on the nanometer scale when the IEC is &lt; 2.0 meq g-1, and with out cross-linking a large uptake at higher IECs. Interestingly we almost always see a heterogeneous distribution of the water in these materials and evidence of cation clustering at higher temperatures when the films are wet. The SAXS of the HPA functionalized materials is dominated by the tungsten in the samples. These proton conductors rely on the distribution of HPA being amorphous and we have shown that the water prefers to solvate the HPA. Currently HPA clustering is compromising hot and dry proton conductivity.

Using small angle x-ray scattering as a key tool to develop next generation polymer electrolyte membrane for electrochemical energy conversion

253rd National Meeting (2017)

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