Morphology and Transport of Multivalent Cation-Exchanged Ionomer Membranes Using Perfluorosulfonic Acid–Ce Z+as a Model System

Morphology and Transport of Multivalent Cation-Exchanged Ionomer Membranes Using Perfluorosulfonic Acid–Ce Z+as a Model System

TitleMorphology and Transport of Multivalent Cation-Exchanged Ionomer Membranes Using Perfluorosulfonic Acid–Ce Z+as a Model System
Publication TypeJournal Article
Year of Publication2020
AuthorsAndrew M Baker, Andrew R Crothers, Kavitha Chintam, Xiaoyan Luo, Adam Z Weber, Rodney L Borup, Ahmet Kusoglu
JournalACS Applied Polymer Materials
Volume2
3642
Issue8
Pagination3642 - 3656
Date Published08/2020
ISSN2637-6105
Abstract

Perfluorosulfonic acids (PFSAs) are commonly used as solid polymer electrolyte membranes (PEMs) in electrochemical energy devices, where they are vulnerable to attack by radical species during operation. A popular strategy to combat this problem is to introduce radical scavengers like cerium (Ce) ions that neutralize these species before they attack the PFSA. Such cation doping creates a multi-ion system, in which understanding the mechanisms of cation solvation and transport becomes important for the effective design and utilization of PFSA–cation systems. Ce ions also provide a representative model system for multication-exchanged ionomers in electrochemical systems. In this study, hydration and conductivity measurements, along with X-ray fluorescence and scattering, are employed to elucidate how Ce ion exchange alters PFSA’s ionic solvation, as well as nano- and mesoscale morphologies, which ultimately control its ion transport properties. A molecular transport model is used to deconvolute the impact of Ce ions on the local solvation structure of water in the membrane from mesoscale changes of the transport pathways. The combined experimental and theoretical analysis reveals a nonlinear decrease in conductivity driven by cation solvation at the molecular level and morphological changes at longer length scales. Migration–diffusion coupling, its nonlinear dependence on ion exchange and hydration, and its overall implications for ionomer performance are also discussed. These findings have the potential to be translated into other mixed cation–ionomer systems for a wide range of energy and environmental devices.

URLhttps://pubs.acs.org/doi/10.1021/acsapm.0c00633https://pubs.acs.org/doi/pdf/10.1021/acsapm.0c00633https://pubs.acs.org/doi/suppl/10.1021/acsapm.0c00633/suppl_file/ap0c00633_si_001.pdf
DOI10.1021/acsapm.0c0063310.1021/acsapm.0c00633.s001
Short TitleACS Appl. Polym. Mater.
Refereed DesignationRefereed