Fine Morphology of Proton-Conducting Ionomers

Abstract

The key factors that control the performance of perfluorinated sulfonic acid polymer electrolyte membranes cannot be deeply understood without a structural model of the material. Models of different complexity have been discussed in the literature. In this paper, we suggest a more detailed structural model of Nafion-type membranes, which results from a combined analysis of the ionomer molecular structure, data on swelling, small-angle diffraction, and conductivity as a function of water content. The analysis focuses on geometrical constraints on the self-organization of the polymer and possible patterns of phase segregation within it. The model identifies the percolation bottlenecks for proton transport and resolves controversies about the water-content dependence of the activation energy of proton mobility. It also suggests a new framework for molecular dynamics simulations of proton and water transport in such media.

Surface orientation of hydrophilic groups in sulfonated poly(ether ether ketone) membranes

“…The unique properties and performance of perfluorinated sulfonic acid polymer electrolyte membranes result from their complex microstructure. Exposed to water or other hydrophilic solvents, a polymer electrolyte exhibits nanoscale segregation into two sub-phases, i.e., hydrophilic domains and hydrophobic domains [42]. Employing small-angle X-ray scattering (SAXS) data and water self-diffusion coefficients obtained by pulsed-field-gradient (PFG-NMR), a microstructure model of sulfonated poly (aryl ether ether ketone ketone) (SPEEKK) was proposed, involving a cubic hydrophilic channel system in a hydrophobic matrix [38].…”

Backbone Dynamics of the Nafion Ionomer Studied by 19F‐13C Solid‐State NMR

“…[7] Another model that takes into account the chain stiffness is that of Ioselevitch et al, which attempts to form multifaceted clusters from straight chains. [55] However, the finite thickness of the chains was disregarded in this model; in reality, each of the four or more ''points'' where three chains ''intersect'' would have a diameter of >2 nm. Together, these intersection regions would make the cluster significantly larger than the size indicated by SAXS.…”

Preparation and Characterization of Nafion Composite Membranes Containing 1-ethyl-3-methylimidazolium Tetracyanoborate

“…Ionic cluster network is a proposed structure comprised of spherical ionic clusters and connection between ionic clusters. [10][11][12][13][14] The formation of spherical ionic clusters in membranes is done by the reorganization of hydrophilic side chains solvated by solvents such as water (in general) or ionic liquids (in this study). SASX is usually being used to study scattering of intermolecular like scattering between clusters.…”