Composite proton exchange membranes from zirconium-based solid acids and PVDF/acrylic polyelectrolyte blends

Organicinorganic composite proton exchange membranes (PEMs) are of interest in fuel cell applications because of potential benefits in conductivity, mechanical, and transport properties that may be imparted by the inorganic component. Our previous work showed that polymeric membranes based on blends of poly(vinylidene fluoride) (PVDF) and cross-linked sulfonated acrylic polyelectrolytes (PE) compare favorably against the proton conductivity and mechanical properties of commercial perfluorosulfonic acid-based PEMs. One problem found in the previous study was that crystalline regions in homopolymers of PVDF interfered with the formation of proton conducting pathways by the PE component. In this study, we explore the ability to use proton-conductive zirconium-based inorganic particles to improve conductivity in such PVDF/PE membranes. Three different particles were considered, namely, zirconium oxide, zirconium hydroxide sulfate, and zirconium hydrogen phosphate. Dispersion of particles in the polymer matrix was limited, resulting in severe aggregation at particle loadings above 5 wt %. Nevertheless, a general improvement in proton conductivity was evidenced in composite membranes with 0.5 to 1 wt % particle loadings. This beneficial effect was particularly noticeable in membranes manufactured from highly crystalline PVDF homopolymers (7 to 14% increase). We propose that the surface of zirconium particles act to provide proton conducting pathways between PE regions that otherwise would become blocked due to PVDF crystallization. In addition to conductivity, composite membranes exhibited enhancement of tensile properties at identical particle loadings, especially in membranes containing more flexible PVDF:HFP copolymers, where a reinforcing stiffening effect was evident (19 to 22% elastic modulus increment). (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012