Ion and Solvent Effects on Aquivion Perflourosulfonic Acid Ionomer Infrared Spectra with Respect to State-of-Solvation

Thursday, 5 October 2017: 11:40
National Harbor 8 (Gaylord National Resort and Convention Center)
R. O'Hagan, N. Loupe, J. Doan, and E. S. Smotkin (Northeastern University)
The impact of solvent polarity and ion exchange on Aquivion perfluorosulfonic acid ionomer (PFSI) infrared spectra were probed as a function of sorbed solvent content. Aquivion membranes were exchanged with lithium or sodium ions, dehydrated, and then solvated in methanol or ethanol. These samples were installed in a controlled temperature/pressure IR sample compartment that enabled acquisition of time dependent spectra as the membranes were desolvated. In all cases, the local symmetry of the ionomer exchange site retained a 3-fold axis of symmetry during desolvation. The spectra were interpreted in terms of local symmetry based IR band assignments. The bandwidths of peaks directly associated with the exchange site functional group progressively increase (solvated PFSI-H < solvated PFSI-Li < solvated PFSI-Na). FWHM trends are explained in terms of electric field induced exchange site polarization. The smaller Stokes Einstein radius of solvated Na+ enables closer proximity to the exchange site and thus greater induced band broadening as compared to Li+ and H+.