Solid-state NMR Investigations of Proton Conducting Membranes
This thesis applies magnetic resonance techniques to novel and traditional proton conducting
materials in order to gain a better understanding of the molecular aspects of their
performance. An array of experiments and techniques are used. One material is a morphologically
designed block copolymer/ionic liquid system. Simple 1-D variable temperature
(VT) 1H magic angle spinning (MAS) NMR is used to catalogue the dynamic chemical
shifts, which relates to the prevalence of hydrogen bonding. Relaxation data are used
to measure the relative mobilities of conduction protons, and these data are related to
polymer physics phenomena. The effect of morphology is investigated by comparing block
copolymer data to a series of homopolymer analogues with no morphological structure.
The role of entropy in these systems is discussed as well as the effect of a non-symmetric
NMR techniques were also applied to more traditional materials, namely perfluorosulfonic
acid membranes modified with amphoteric imidazole compounds. The chemical
environments of the imidazole as well as the dynamics of proton transfer are measured
with Solid-state 1H NMR. The effect of imidazole concentration is also considered. 1H
-13C cross polarization (CP) MAS NMR is used to reveal the presence of both fast and
slow moving imidazole in the membranes. Pulsed field gradient (PFG) NMR is used to
quantify the diffusion of protons and methanol through the material.
The goal of replacing gaseous hydrogen with organic virtual carrier molecules as a
proton source for proton exchange membranes (PEM) fuel cells is investigate by testing
the effect of model organic liquids in contact with typical membrane materials. A suite
of data, including 19F NMR relaxation data of the polymer backbone and sidechains, are
used to explain bulk phenomena and membrane performance.