Identification of Multiple Diffusion Rates in Mixed Solvent Anion Exchange Membranes Using High Resolution MAS NMR

Abstract

High resolution magic angle spinning (HRMAS) 1H NMR in combination with 2D exchange NOESY and pulsed field gradient (PFG) NMR diffusion experiments have been used to characterize 1 N methanol swollen polymer anion exchange membranes (AEM) presently being developed for alkaline fuel cells. Standard static 1H NMR experiments on these materials have proven unsuccessful due to severe signal broadening. New experimental methods for increased resolution are needed to determine distinct solvent environments and transport properties. Using HRMAS NMR, resonances from water and methanol in both a free (bulk-like) environment and membrane-associated environment within the AEM were observed. 1H HRMAS PFG NMR experiments identified different molecular diffusion environments in the solvent, while 1H 2D NOESY exchange NMR experiments confirmed spatial contacts between membrane-associated species and the membrane. These results demonstrate that 1H HRMAS is an ideal technique for the characterization of individual environments and diffusion rates in polymer membranes with mixed solvent systems.