Electrospun phosphonated poly(pentafluorostyrene) nanofibers as a reinforcement of Nafion membranes for fuel cell application

Nafion is a well-known perfluorosulfonic acid membrane widely used in fuel cells. However, despite its excellent properties, Nafion has limitations, including high hydrogen crossover. Reducing the hydrogen crossover is crucial since the H2 permeating through the membrane can directly react with O2 and produce radicals that can degrade Nafion. The hydrogen crossover can be minimized by increasing membrane thickness or by embedding nanostructures into Nafion. In this work, we report Nafion membranes reinforced by electrospun fibers made from phosphonated polypentafluorostyrene (PWN70) and, for comparison, unmodified polypentafluorostyrene (PPFSt). Composite membranes were obtained by spray-coating of Nafion onto the nanofiber meshes to fill the voids. From tensile tests, we found that PWN70/Nafion and PPFSt/Nafion composite membranes show higher Young's modulus and higher yield stress than pure Nafion. Fuel cell tests showed that PPFSt/Nafion composite membranes suffer from performance losses with increasing fiber loading, whereas PWN70/Nafion composite membranes perform similarly with non-reinforced Nafion. Furthermore, the use of PWN70/Nafion resulted in an H2 crossover reduction by 37–40% for atmospheric pressure, while it was not improved when using PPFSt/Nafion composite membranes. These results show the advantages of PWN70 nanofibers as a reinforcement for Nafion, which reduce the hydrogen crossover without sacrificing proton conductivity.