  The physio-chemical properties of Nafion 115 and a composite Nafion
115/Zirconium Phosphate (25wt%) membranes are compared. The composite membrane
takes up more water than Nafion at the same water activity. However, the proton
conductivity of the composite membrane is slightly less than that for Nafion
115. Small angle X-ray scattering shows the hydrophilic phase domains in the
composite membrane are spaced further apart than in Nafion 115, and the
composite membrane shows less restructuring with water uptake. Despite the
lower proton conductivity of the composite membranes they display better fuel
cell performance than Nafion 115 when the fuel cell is operated
under-humidified. It is suggested that the composite membrane has a greater
rigidity that accounts for its improved fuel cell performance.
