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Nanometer-Scale Water Dynamics in Nafion Polymer Electrolyte Membranes: Influence of Molecular Hydrophobicity and Water Content Revisited
Version 2 2020-06-26, 14:33
Version 1 2020-06-23, 17:03
journal contribution
posted on 2020-06-26, 14:33 authored by Seung-Bo Saun, JiWon Kim, Ryeo Yun Hwang, Yeonho Ahn, Dukjoon Kim, Daniel K. Park, Soonchil Lee, Oc Hee HanThe ionic conductivity of polymer
electrolyte membranes (PEMs) is an essential parameter for their device
applications. In water-swollen PEMs, protons and other ions are transferred
through hydrophilic channels of a few nanometers in diameter at most.
Thus, optimizing the chemical and physical properties of the channels
can enhance the conductivity of PEMs. However, the factors controlling
the conductivity have not been completely clarified. Here, we report
that measurements taken near the channel walls by a special nuclear
magnetic resonance technique with ≤1 nm spatial resolution
showed the largest water diffusivity when ∼80% of hydrophilic
sulfonic acid groups were blocked, but the proton conductivity was
low. The water diffusivity was much less affected by differences in
water content. Our results provide a concept for changing the properties
of PEMs and a challenge to implement the improved diffusivity in a
way that enhances net ion conductivity.