Nafion® membranes have outstanding proton conductivities attributed to its unique assembled structures[1-2]. Unfortunately, structure models for Nafion membranes are still in hot debates[3-4]. We carried out statistical analysis and molecular dynamics simulation to address the unique structure and its correlation with proton conductivity. The statistical analysis revealed that water in the membrane is crucial as distributed like typical fluid in porous material. It can be fitted using the Brunauer–Emmett–Teller equation, and the saturation of water molecules around a sulfonate group is about 20. Further integration of Nernst-Einstein equation provides a quantitative understanding for proton conductivity in Nafion membranes as a function of water content and temperature. Fillers to construct Nafion composite membranes were also investigated and most potent types are circled out accounting for Robeson upper bound[5], DOE standard and active energy. To clarify the microstructure in Nafion membranes, the anisotropy in the backbone of polymers in molecular dynamics simulations was introduced. It has well matched morphologies and intensity profiles comparing with those characterized by electron microscopy and small angle X-ray scattering experiments.

Insight into the structure and proton conductivity of Nafion® membranes using simulation and statistical approaches

256th National Meeting (2018)

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