title: Water, proton, and oxygen transport in high IEC, short side chain PFSA ionomer membranes: consequences of a frustrated network.
abstract: The effect of ion exchange capacity (IEC) on the water sorption properties of high IEC, short side chain (SSC) PFSA ionomer membranes, and the relationships between water content, proton conductivity, proton mobility, water permeation, oxygen diffusion, and oxygen permeation are investigated. SSC PFSA ionomer membranes possessing 1.3, 1.4, and 1.5 mmol g(-1) IEC are compared to a series of long side chain (LSC) PFSA ionomer membranes ranging in IEC from 0.9 to 1.13 mmol g(-1). At 25 °C, fully-hydrated SSC ionomer membranes are characterized as possessing higher water contents (56-75 vol%), moderate λ values (15-18), high analytical acid concentrations (2-2.8 M), and moderate conductivity (88-115 mS/cm); but lower than anticipated effective proton mobility. Complementary measurements of water permeability, oxygen diffusion, and oxygen permeability also yield lower than expected values given their much higher water contents. Potential benefits afforded by reducing the side chain length of PFSA ionomer membranes, such as increased crystallinity, higher IEC, and high hydrated acid concentration are offset by a less-developed, frustrated hydrophilic percolation network, which provides a motivation for future improvements of transport properties for this class of material.
authors.affiliation: Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Luo
authors.forename: Steven
authors.initials: S
authors.lastname: Holdcroft
authors.forename: Ana
authors.initials: A
authors.lastname: Mani
authors.forename: Yongming
authors.initials: Y
authors.lastname: Zhang
authors.forename: Zhiqing
authors.initials: Z
authors.lastname: Shi