Nafion membranes with a porous surface

Nafion membranes with a porous surface
헨켄스마이어디억DANG Quoc Khanh장종현김형준
polymer membranes
Issue Date
European Fuel Cell Forum
When ortho-dichlorobenzene (ODB) containing Nafion SE-20092 dispersions are cast into a film, evaporation leads to dense membranes with one highly porous surface layer. An annealing step improves the mechanical stability while maintaining the porous structure. In the case of solution casting for filtration membranes, wrong procedures can lead to an unwanted dense skin. Our process leads to the opposite morphology, rather resembling breath figures. However, assembly of water droplets on a solidifying Nafion dispersion is not probable. Therefore, we propose the following process: the solubility of ODB in the casting solution decreases with increasing water content by evaporation of ethanol and n-propanol, leading to phase separation of Nafion solution and ODB. Due to the high density of Nafion (Nafion: 1.97 g/ml, Nafion dispersion SE-20092: ca. 1 g/ml, ODB: 1.31 g/ml), the density of the Nafion dispersion increases continuously during solvent evaporation, and ODB droplets rise to the surface before the membrane solidifies. The obtained cavities might enhance the product water back diffusion at low humidity conditions. In fact, a MEA based on porous Nafion (P-Nafion) showed a performance superior to Nafion 211 in a hydrogen / air fuel cell at non-humidified conditions at 95°C.
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