Development of solid state NMR to understand materials involved in catalytic technology used in fuel cells

The utility of the little used Field Sweep Fourier transform (FSFT) method is demonstrated for recording wideline nuclear magnetic resonance (NMR) of 195Pt resonances for various sized platinum nanoparticles, as well as platinum-tin bimetallics used in fuel cell catalysts, and various other related platinum (Pt3X; X = Al, Sc, Nb, Ti, Hf and Zr) alloys. The lineshapes observed from PtSn for both 195Pt and 119Sn suggest that it is more ordered than other closely related intermetallics, which might be expected from other measurements (e.g. XRD linewidths). From these reconstructed spectra the mean number of platinum atoms in the nanoparticle can be accurately determined along with detailed information regarding the number of atoms present effectively in each layer from the surface. This can be compared with theoretical predictions of the number of platinum atoms in these various layers for cubo-octahedral nanoparticles, thereby providing an estimate of the particle size. A comparison of the common NMR techniques used to acquire wideline spectra from spin I = 1 2 nuclei shows the advantages of the automated FSFT technique over the spin echo height/integration approach that dominates the literature. A study of small 13 atom platinum clusters, with variable particle size dispersion for which there is no experimental characterisation in the literature, provides evidence for an isotropic chemical shift of these platinum nanoparticles and provides a better basis for determining the Knight shift when compared to referencing against the primary IUPAC standard which has a different local structure. Rare earth apatite oxide ion conductors are novel candidates for electrolytes in solid oxide fuel cells. It has been shown that La8Y2Ge6O27 is an excellent oxide conductor at lower temperatures when compared to the market leader yttrium stabilised zirconia (YSZ). To understand the mechanism of its conduction 17O-labelled water was allowed to conduct through the sample and 17O solid state NMR was employed to comment on this pathway in a series of germanium and silicon substituted apatites. The linear channels running through the centre of the structure were believed to contain vacancies and as with perovskites it was commonly believed these allowed hopping of the oxygen to enable the apatite to conduct. It was shown that a limited amount of the 17O-oxygens made it to the channel and almost all of the label was located in the tetrahedra. This suggested that the mechanism of conduction was via the tetrahedral backbone. Molecular dynamics studies on these systems confirmed this SN2 mechanism of conduction as the excess oxygen hopped onto the tetrahedral site to form a five coordinate bridging oxygen which then forced a neighbouring oxygen to hop onto another tetrahedra. A comparison of analytical techniques used to characterise hydrogen bonding in benzoic acid and its corresponding group IA hemibenzoates indicates the need to draw upon multiple methods to fully understand the nature of the bond. The X-ray diffraction (XRD) data cannot confirm precisely the position of the hydrogen in the complex and hence cannot comment on the nature of the bond. Traditionally the angle at the central bonded proton and the oxygen-oxygen bond distance are used to comment on the strength of the hydrogen bonding, the results present here show the limitations of these analysis methods. Due to the oxygen-proton-oxygen bond angle variations commenting on the oxygen-oxygen length and correlating it to the hydrogen bonding is not feasible. There is heavy literature present on correlating the 1H isotropic shifts to the hydrogen bond strength, here we show a step wise change in hydrogen bonding from benzoic acid and lithium hemibenzoate down the periodic table to potassium, rubidium and cesium hemibenzoate. We show that the anisotropic tensor, 22, is pointed along the carbonyl bond and changes with the hydrogen bonding strength. However this method of characterising the bonding interaction gives a linear correlation from benzoic acid to cesium hemibenzoate. The 17O MAS of the carbonyl groups show an in ated quadrupole coupling constant when compared to the hydroxyls. There is a correlation between the anisotropic 13C 22 parameter and the quadrupole coupling (CQ), as the 22 decreases the CQ seems to give an overall increase. These oxygen results have been confirmed by multiple field double rotation results. All the crystallographic and solid state NMR data present is tied together by density functional theory calculations which show varying degrees of agreement with the achieved results

Changing, priming, and acting on values: Effects via motivational relations in a circular model

Circular models of values and goals suggest that some motivational aims are consistent with each other, some oppose each other, and others are orthogonal to each other. The present experiments tested this idea explicitly by examining how value confrontation and priming methods influence values and value-consistent behaviors throughout the entire value system. Experiment 1 revealed that change in 1 set of social values causes motivationally compatible values to increase in importance, whereas motivationally incompatible values decrease in importance and orthogonal values remain the same. Experiment 2 found that priming security values reduced the better-than-average effect, but priming stimulation values increased it. Similarly, Experiments 3 and 4 found that priming security values increased cleanliness and decreased curiosity behaviors, whereas priming self-direction values decreased cleanliness and increased curiosity behaviors. Experiment 5 found that priming achievement values increased success at puzzle completion and decreased helpfulness to an experimenter, whereas priming with benevolence values decreased success and increased helpfulness. These results highlight the importance of circular models describing motivational interconnections between values and personal goals

Development of solid state NMR to understand materials involved in catalytic technology used in fuel cells

The utility of the little used Field Sweep Fourier transform (FSFT) method is demonstrated for recording wideline nuclear magnetic resonance (NMR) of 195Pt resonances for various sized platinum nanoparticles, as well as platinum-tin bimetallics used in fuel cell catalysts, and various other related platinum (Pt3X; X = Al, Sc, Nb, Ti, Hf and Zr) alloys. The lineshapes observed from PtSn for both 195Pt and 119Sn suggest that it is more ordered than other closely related intermetallics, which might be expected from other measurements (e.g. XRD linewidths). From these reconstructed spectra the mean number of platinum atoms in the nanoparticle can be accurately determined along with detailed information regarding the number of atoms present e�ectively in each layer from the surface. This can be compared with theoretical predictions of the number of platinum atoms in these various layers for cubo-octahedral nanoparticles, thereby providing an estimate of the particle size. A comparison of the common NMR techniques used to acquire wideline spectra from spin I = 1 2 nuclei shows the advantages of the automated FSFT technique over the spin echo height/integration approach that dominates the literature. A study of small 13 atom platinum clusters, with variable particle size dispersion for which there is no experimental characterisation in the literature, provides evidence for an isotropic chemical shift of these platinum nanoparticles and provides a better basis for determining the Knight shift when compared to referencing against the primary IUPAC standard which has a di�erent local structure. Rare earth apatite oxide ion conductors are novel candidates for electrolytes in solid oxide fuel cells. It has been shown that La8Y2Ge6O27 is an excellent oxide conductor at lower temperatures when compared to the market leader yttrium stabilised zirconia (YSZ). To understand the mechanism of its conduction 17O-labelled water was allowed to conduct through the sample and 17O solid state NMR was employed to comment on this pathway in a series of germanium and silicon subsituted apatites. The linear channels running through the centre of the structure were believed to contain vacancies and as with perovskites it was commonly believed these allowed hopping of the oxygen to enable the apatite to conduct. It was shown that a limited amount of the 17O-oxygens made it to the channel and almost all of the label was located in the tetrahedra. This suggested that the mechanism of conduction was via the tetrahedral backbone. Molecular dynamics studies on these systems con�rmed this SN2 mechanism of conduction as the excess oxygen hopped onto the tetrahedral site to form a �ve coordinate bridging oxygen which then forced a neighbouring oxygen to hop onto another tetrahedra. A comparison of analytical techniques used to characterise hydrogen bonding in benzoic acid and its corresponding group IA hemibenzoates indicates the need to draw upon multiple methods to fully understand the nature of the bond. The X-ray di�raction (XRD) data cannot con�rm precisely the position of the hydrogen in the complex and hence cannot comment on the nature of the bond. Traditionally the angle at the central bonded proton and the oxygen-oxygen bond distance are used to comment on the strength of the hydrogen bonding, the results present here show the limitations of these analysis methods. Due to the oxygen-proton-oxygen bond angle variations commenting on the oxygen-oxygen length and correlating it to the hydrogen bonding is not feasible. There is heavy literature present on correlating the 1H isotropic shifts to the hydrogen bond strength, here we show a step wise change in hydrogen bonding from benzoic acid and lithium hemibenzoate down the periodic table to potassium, rubidium and cesium hemibenzoate. We show that the anisotropic tensor, �22, is pointed along the carbonyl bond and changes with the hydrogen bonding strength. However this method of characterising the bonding interaction gives a linear correlation from benzoic acid to cesium hemibenzoate. The 17O MAS of the carbonyl groups show an in ated quadrupole coupling constant when compared to the hydroxyls. There is a correlation between the anisotropic 13C �22 parameter and the quadrupole coupling (CQ), as the �22 decreases the CQ seems to give an overall increase. These oxygen results have been con�rmed by multiple �eld double rotation results. All the crystallographic and solid state NMR data present is tied together by density functional theory calculations which show varying degrees of agreement with the achieved results.EThOS - Electronic Theses Online ServiceEngineering and Physical Sciences Research Council (EPSRC)Johnson Matthey Plc.University of WarwickGBUnited Kingdo

All-optical hyperpolarization of electron and nuclear spins in diamond

Low thermal polarization of nuclear spins is a primary sensitivity limitation for nuclear magnetic resonance. Here we demonstrate optically pumped (microwave-free) nuclear spin polarization of $^{13}\mathrm{C}$ and $^{15}\mathrm{N}$ in $^{15}\mathrm{N}$-doped diamond. $^{15}\mathrm{N}$ polarization enhancements up to $-2000$ above thermal equilibrium are observed in the paramagnetic system $\mathrm{N_s}^{0}$. Nuclear spin polarization is shown to diffuse to bulk $^{13}\mathrm{C}$ with NMR enhancements of $-200$ at room temperature and $-500$ at $\mathrm{240~K}$, enabling a route to microwave-free high-sensitivity NMR study of biological samples in ambient conditions.Comment: 5 pages, 5 figure

Facile silane functionalization of graphene oxide

The facile silane functionalization of graphene oxide (GO) was achieved yielding vinyltrimethoxysilane-reduced graphene oxide (VTMOS-rGO) nanospheres located in the inter-layer spacing between rGO sheets via an acid–base reaction using aqueous media. The successful grafting of the silane agent with pendant vinyl groups to rGO was confirmed by a combination of Fourier-transform infrared (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The structure and speciation of the silane-graphene network (nanosphere) and, the presence of free vinyl groups was verified from solid-state magic angle spinning (MAS) and solution 13C and 29Si nuclear magnetic resonance (NMR) measurements. Evidence from Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HRTEM) and TEM-High-Angle Annular Dark-Field (TEM-HAADF) imaging showed that these silane networks aided the exfoliation of the rGO layers preventing agglomeration, the interlayer spacing increased by 10 Å. The thermal stability (TGA/DTA) of VTMOS-rGO was significantly improved relative to GO, displaying just one degradation process for the silane network some 300 °C higher than either VTMOS or GO alone. The reduction of GO to VTMOS-rGO induced sp2 hybridization and enhanced the electrical conductivity of GO by 105 S m−1

One-sided jet at milliarcsecond scales in LSI+61303

We present Very Long Baseline Interferometry (VLBI) observations of the high mass X-ray binary LSI+61303, carried out with the European VLBI Network (EVN). Over the 11 hour observing run, performed 10 days after a radio outburst, the radio source showed a constant flux density, which allowed sensitive imaging of the emission distribution. The structure in the map shows a clear extension to the southeast. Comparing our data with previous VLBI observations we interpret the extension as a collimated radio jet as found in several other X-ray binaries. Assuming that the structure is the result of an expansion that started at the onset of the outburst, we derive an apparent expansion velocity of 0.003 c, which, in the context of Doppler boosting, corresponds to an intrinsic velocity of at least 0.4 c for an ejection close to the line of sight. From the apparent velocity in all available epochs we are able to establish variations in the ejection angle which imply a precessing accretion disk. Finally we point out that LSI+61303, like SS433 and Cygnus X-1, shows evidence for an emission region almost orthogonal to the relativistic jet.Comment: 7 pages, 4 figures, LaTeX, uses aa.cls. Accepted for publication in A&

O- vs. N-protonation of 1-dimethylaminonaphthalene-8-ketones: formation of a peri N–C bond or a hydrogen bond to the pi-electron density of a carbonyl group

X-ray crystallography and solid-state NMR measurements show that protonation of a series of 1-dimethylaminonaphthalene-8-ketones leads either to O protonation with formation of a long N–C bond (1.637–1.669 Å) between peri groups, or to N protonation and formation of a hydrogen bond to the π surface of the carbonyl group, the latter occurring for the larger ketone groups (C(O)R, R = t-butyl and phenyl). Solid state 15N MAS NMR studies clearly differentiate the two series, with the former yielding significantly more deshielded resonances. This is accurately corroborated by DFT calculation of the relevant chemical shift parameters. In the parent ketones X-ray crystallography shows that the nitrogen lone pair is directed towards the carbonyl group in all cases

Structural and chemical heterogeneity in ancient glass probed using gas overcondensation, X-ray tomography, and solid-state NMR

Rare ancient glasses have complex, multi-scale structures requiring more sophisticated and non-destructive pore characterisation techniques than usual. Homotattic patch models for nitrogen adsorption gave better fits to the isotherm data, more accurate void space descriptors, and also greater understanding of the underlying physical factors affecting adsorption, than standard BET. These homotattic patch models revealed the critical role of iron impurities in determining adsorption behaviour. Non-destructive sodium-23 NMR relaxometry validated the homotattic patch model for some natron glasses, and, in turn, was validated using multiple quantum magic-angle spinning (MQMAS) 23Na NMR. X-ray tomography images of the glasses showed the presence of large macroporous bubbles, while FEG-SEM revealed nanopores within the glass matrix. A newly-developed, gas overcondensation technique, suitable for small amounts of low porosity material, assessed the inter-relationship between the disparate levels in this hierarchical porosity. This technique demonstrated that the nanoporosity did not form a ‘corona’ around the bubbles, due to leaching from the glass, as initially supposed from tomography data, but was completely disconnected, and, thus, is probably associated with glass alkalinity. Gas overcondensation is demonstrated as a non-destructive alternative to mercury porosimetry for probing multi-scale porosity in rare artefacts

Multimodal characterization of the visual network in Huntington's disease gene carriers

Objective A sensorimotor network structural phenotype predicted motor task performance in a previous study in Huntington’s disease (HD) gene carriers. We investigated in the visual network whether structure – function – behaviour relationship patterns, and the effects of the HD mutation, extended beyond the sensorimotor network. Methods We used multimodal visual network MRI structural measures (cortical thickness and white matter connectivity), plus visual evoked potentials and task performance (Map Search; Symbol Digit Modalities Test) in healthy controls and HD gene carriers. Results Using principal component (PC) analysis, we identified a structure – function relationship common to both groups. PC scores differed between groups indicating white matter disorganization (higher RD, lower FA) and slower, and more disperse, VEP signal transmission (higher VEP P100 latency and lower VEP P100 amplitude) in HD than controls while task performance was similar. Conclusions HD may be associated with reduced white matter organization and efficient visual network function but normal task performance. Significance These findings indicate that structure – function relationships in the visual network, and the effects of the HD mutation, share some commonalities with those in the sensorimotor network. However, implications for task performance differ between the two networks suggesting the influence of network specific factors