Multilayer-structured, SiO2/sulfonated poly(phenylsulfone) composite membranes for proton exchange membrane fuel cells

In an effort to improve the dimensional change and proton conductivity of sulfonated poly(phenylsulfone) (SPPSU) membranes and facilitate their application to proton exchange membrane fuel cells (PEMFC), we develop a new composite membrane featured with a multilayer structure. The multilayer structure consists of a SPPSU-impregnated SiO2 ceramic layer and a SPPSU layer. In contrast to a bulk composite membrane containing randomly dispersed SiO2 nanoparticles, this unusual multilayer-structured composite membrane has an independent ceramic layer comprising close-packed SiO2 nanoparticles and polyetherimide (PEI) binders. On the basis of structural characterization of the composite membranes, the effects of the multilayer structure on the membrane properties are investigated. The introduction of the SiO2 ceramic layer is found to be effective in not only suppressing dimensional change but also enhancing proton conductivity of the multilayered composite membrane. Another intriguing finding is that the decrease of proton conductivity at a low humidity condition encountered in conventional water-swollen membranes is retarded in the multilayered composite membrane. These improvements in the proton conductivity of the multilayered composite membrane are discussed by considering the morphological uniqueness and the water retention capability of hygroscopic SiO2 nanoparticles.