Orr, Simon Timothy (2010) Multinuclear solid-state NMR of fuel cell materials. PhD thesis, University of Warwick.

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Abstract

This thesis describes the application of multinuclear solid-state NMR to three
materials systems: first, components of polymer-based proton-exchange fuel cells
including the fluoropolymer membranes (Chapter 4) and the precious metal supported
catalysts (Chapter 5); secondly, the formation of a complex bismuth niobium
aluminoborosilicate glass-ceramic with novel dielectric properties (Chapter 6);
finally, platinum (II) dialkyldithiophosphates which belong to a class of compounds
(metal dialkyldithiophosphates) some of which are used in mineral separation
processing (Chapter 7).
A full investigation into the effects of different conditions during sample
preparation and 19F NMR experiments on fluoropolymer membranes recommended
unmilled preparation, dry storage and magic angle spinning below 24 kHz for the
study of structural differences between membranes. The application of 19F NMR to a
range of commercial and experimental fluoropolymer membranes revealed that the
equivalent weight does not affect the mobility of the polymer molecules such that can
be detected by this technique. Calculations of equivalent weight from 19F NMR
differed with quoted values by up to 14%. Discrepancies were smallest in the short
sidechain polymers, as low as 3%. The assignment of spectra was invariant with
sidechain structure apart from a change in the number of ester links. The presence or
absence of oxygen affected chemical shielding even around nuclei separated by
several bonds. Differences in 1H linewidths between membranes could not be
interpreted without the control and comparison of manufacturing techniques. It is
desirable to remove the necessity for organic solvents in membrane casting. However,
membranes cast from aqueous solution do not possess the same properties as those
from propanol. It had been proposed that rapid drying of water cast membranes would
result in a structure more similar to those from organic solvent. 1H NMR revealed that
the opposite is the case, rapid drying makes the ordinarily more inhomogeneous
aqueous membranes even more so. The application of both 19F and 1H NMR revealed
that the monomolecular layers of fluoropolymer deposited on the surface of fuel cell
catalysts to aid proton conductivity are categorically different in nature to the same
materials in the bulk state. 19F NMR suggests a polymer structure either more
disordered, greatly less mobile or both. 1H NMR displayed water environments that
could not be reconciled to the standard model of rapid exchange between bulk water
and water associated with acid groups. Spectral differences caused by solvent and
polymer loading were discussed.
The first complete and quantitative Fourier transformed 195Pt NMR spectra of
platinum fuel cell catalysts, acquired using a field sweeping method, are analysed for
deviation from the cubooctohedral particle model and surface oxidation.
A combination of 11B, 27Al and 29Si studies of the BN1 ceramic system after
different temperature heat treatments confirmed much of the previous work on phase
evolution. However, it was shown that kyanite does not make up a significant
proportion of the material until heat treatment reaches 1000 ºC and that aluminium
impurities in bismuthbiobate crystals appear to increase with treatment temperature.
The nature and abundance of glassy phases in the system are explored for the first
time.
Field sweep 195Pt NMR was employed to characterise the 195Pt chemical shift
anisotropy of five platinum (II) dialkyldithiophosphates complexes. Additionally the
31P chemical shift anisotropies of two of the complexes, previously unpublished are
presented.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Nuclear magnetic resonance, Proton exchange membrane fuel cells, Glass-ceramics -- Analysis, Platinum compounds -- Analysis
Official Date:	October 2010
Dates:	Date Event October 2010 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Smith, Mark E. ; Hanna, John V. ; Fisher, J. ; Thompsett, D.
Sponsors:	Engineering and Physical Sciences Research Council (EPSRC) ; Johnson Matthey Plc.
Extent:	xvi, 151 leaves : ill., charts
Language:	eng

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