Multilayer Sulfonated Polyhedral Oligosilsesquioxane (S-POSS)-Sulfonated Polyphenylsulfone (S-PPSU) Composite Proton Exchange Membranes

Single-layer proton exchange membranes (PEMs) have been under development for several decades. The current use of conductive polymers in PEM fuel cells has been limited primarily to single layered sulfonated fluoro polymers, e.g. Nafion. Although this architecture has certain positive characteristics, it lacks the robust properties required for use in high-temperature, low=humidity conditions. In this work, a multilayer composite PEM consisting of outer layers of sulfonated polyphenylsulfone (S-PPSU) and an inner layer blend of octa-sulfonated octaphenyl-POSS (S-POSS) and S-PPSU has been developed and shown to exhibit good conductivity, physical and chemical durability, and high strength. The multilayer composite PEM showed improved conductivity at 90 °C and 25% RH relative to analogous single-layer S-POSS-S-PPSU PEMs and to the typical sulfonated fluoro polymers currently in use.