Ion-conductive polymers (ionomers) have been widely used as the solid-electrolyte in energy conversion devices, such as polymer-electrolyte fuel cells and electrolyzers, to facilitate selective transport of ionic and gaseous species. In most energy conversion devices, an ionomer’s role is not limited to polymer-electrolyte membrane (PEM), but also extends to the porous electrodes structure where ionomers exist as nanometer-thick electrolyte “thin films” binding the catalytic particles and facilitating transport of ionic and gaseous species therein. Once confined to these thicknesses (&lt; 100 nm), ionomer properties change drastically from the bulk (membrane) and are significantly more influenced by interfacial and ionic interactions. Thus, throughout this thickness range, an ionomer’s functionality is controlled by the relationship between chemistry and phase-separated morphology, which is challenging to characterize and control. This talk explores the structure-property relationships of perfluorosulfonic-acid (PFSA) as well as a new class of 3M ionomer based on PFSA containing bis(sulfonyl)imide groups on the side-chain in addition to a terminal sulfonic acid group, which shows higher ion conductivity. Using advanced in situ synchrotron characterization techniques such as transmission and grazing-incidence x-ray scattering, relationship between molecular structure and morphology of ionomers has been examined at different length scales. In particular, energy-tunable and resonant X-rays with sensitivity to sulfur can decipher the unique bonding environment of different protogenic groups in the ionomer membrane. Through structural and transport characterization of ionomers, we revealed how an ionomer’s phase-separated morphology and hydration behavior can be controlled through chemical modifications for optimizing their functionality as both a membrane or as an electrode ionomer. Overall, these results provide guidelines to design new ionomers with optimized transport properties in both bulk (membrane) and thin-film (electrode) regime to examine how chemistry-confinement interplay governs ionomer functionality and provide insight into tuning and optimization of their performance for energy conversion devices.

Structure-transport relationship in sulfonated ionomers for energy conversion devices: From membranes to electrodes

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.