<p>Rapid
improvements in polymer-electrolyte fuel-cell (PEFC) performance have been
driven by the development of commercially available ion-conducting polymers
(ionomers) that are employed as membranes and catalyst binders in membrane-electrode
assemblies. Commercially available ionomers are based on a perfluorinated
chemistry comprised of a polytetrafluoroethylene (PTFE) matrix that imparts low
gas permeability and high mechanical strength but introduces significant
mass-transport losses in the electrodes. These transport losses currently limit
PEFC performance, especially for low Pt loadings. In this study, we present a
novel ionomer incorporating a glassy amorphous matrix based on a
perfluoro(2-methylene-4-methyl-1,3-dioxolane) (PFMMD) backbone. The novel
backbone chemistry induces structural changes in the ionomer, restricting
ionomer domain swelling under hydration while disrupting matrix crystallinity.
These structural changes slightly reduce proton conductivity while
significantly improving gas permeability. The performance implications of this
tradeoff are assessed, which reveal the potential for substantial performance
improvement by incorporation of highly permeable ionomers as the functional catalyst
binder. These results underscore the significance of tailoring material chemistry
to specific device requirements, where ionomer chemistry should be rationally
designed to match the local transport requirements of the device architecture.</p>