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Solid-state NMR Investigations of Proton Conducting Membranes

  • Author(s): Dodd, Matthew Ryan
  • Advisor(s): Reimer, Jeffrey A
  • et al.
Abstract

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

ionic liquids.

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.

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