Layered zirconium alkylphosphates: Suitable materials for novel PFSA composite membranes with improved proton conductivity and mechanical stability

Nanosized ?-layered monohydrogen zirconium phosphate (ZP) has been organically modified by reacting the monohydrogen phosphate groups with of 1,2 epoxydodecane solutions in tetrahydrofuran. The materials thus obtained (ZP(C12)x, with x in the range 0.74-2.1) have been characterized by TEM, thermogravimetric analysis, X-ray powder diffraction and solid state 13C CPMAS NMR. The functionalization leads to a disordered layer packing without substantial alteration of the inorganic framework of the ?-layer of pristine ZP. Samples with x=0.74 and 1.15 have been used as fillers of membranes based on a recast short side chain perfluorinated ionomer with EW=830. Composite membranes with 5-15 wt% filler loadings have been characterized by stress-strain mechanical tests, proton conductivity measurements and water uptake determinations under controlled conditions of temperature and relative humidity (RH). The presence of the filler results in a significant increase in the Young?s modulus of the neat ionomer up to a maximum of 55% and 67% at room temperature and at 80 °C/70% RH, respectively. At 100 °C and in the RH range 50-90%, the conductivity of the composite membranes is higher than that of the neat ionomer, and the proportional increase in conductivity (+72% for RH=50% and +32% for RH=90%) is maximum for 10 wt% filler loading. Surprisingly, under the same conditions of temperature and RH, the hydration of the most conductive composite membrane is lower than the hydration of the neat ionomer.