Differences in the oxygen permeation behavior of perfluorinated and hydrocarbon-type polymer electrolyte membranes at elevated temperatures

• Gas permeation and pathways of HC-type and perfluorinated PEMs are essentially different.
• Gas permeation behavior of HC-type PEMs is dependent of free volume inside membrane.
• Gas permeation behavior of perfluorinated PEMs is dependent of ionic-water channel networks.
• Ionic-water channel networks induce slight stiffening in perfluorinated PEMs at α-transition.

Differences in the oxygen permeation behavior of perfluorinated and hydrocarbon (HC)-type polymer electrolyte membranes (PEMs) were systematically investigated at 80 and 90 °C under controlled relative humidity. We evaluated oxygen permeability under different humidity conditions, using dry–wet and wet–wet configurations, which correspond to the dry H2–wet (humidified) O2, and wet H2–wet O2 conditions, respectively. For perfluorinated PEMs, permeation behavior was significantly dependent on the growth of ionic-water channel networks, and an unusual depression of permeability at 90 °C and 70% RH (wet–wet) compared to that at 80 °C under the same humidity conditions was also observed due to slight stiffening of the membrane. For HC-type PEMs, on the other hand, the permeation behavior was likely to depend on the free volume inside the membrane, which undergoes a large dimensional change with swelling. The gas permeation behavior and gas diffusion pathways of perfluorinated and HC-type PEMs are essentially different because of differences in the structural changes between the membranes.

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