Suppression of radical attack in polymer electrolyte membranes using a vinyl polymer blend interlayer with low oxygen permeability

Decomposition of polymer electrolyte membranes (PEMs) by radical species is a significant issue related to the chemical durability of polymer electrolyte fuel cells (PEFCs). A major contributor to radical formation is the oxygen crossover through the membrane from cathode to anode. Therefore, suppression of oxygen diffusion through the PEM is predicted to effectively mitigate the chemical degradation via radical formation. To confirm this, a simple high oxygen barrier PEM is prepared by sandwiching a thin gas barrier interlayer in between two Nafion 211 membranes. The interlayer consists of poly (vinyl alcohol) (PVA) and poly (vinyl sulfonic acid) (PVS) with various molar ratio. The sandwich PEM can show 286 times lower oxygen permeability than Nafion 212 membrane, which corresponds to 1.7 times longer survival time than Nafion 212 in a chemically accelerated stress test for PEMs known as open circuit voltage (OCV) holding test. Furthermore, the SEM image of the sandwich PEM cross-section shows that the interlayer could survive the OCV holding test despite its lower resistance against radical attack. The results in this study indicate that the addition of high oxygen barrier interlayer can reduce radical formation in PEFC and improve chemical durability.