Mark A. Roberts

In situ X-ray absorption spectroscopy and X-ray diffraction of fuel cell electrocatalysts

The utility of in situ X-ray absorption spectroscopy (XAS) in determining structural parameters, through analysis of the extended X-ray absorption fine structure (EXAFS), and electronic perturbations, through a white line analysis of the X-ray absorption near edge structure (XANES), is demonstrated for Pt/C, PtRu/C and PtMo/C fuel cell electrodes. The results provide verification that the enhancement of CO tolerance of the alloy catalysts occurs via an intrinsic mechanism for the PtRu alloy, whilst a promotion mechanism is in operation for the PtMo alloy. Preliminary results of an in situ powder X-ray diffraction (XRD) method which utilises synchrotron radiation (SR) and a curved image plate detector are also presented, using Pd/C as an example. The lattice expansion upon formation of the β-hydride is clearly observed.

Molecular and mesoscale structures in hydrophobically driven aqueous solutions.

Since Kauzmanns seminal 1959 paper, the hydrophobic interaction has dominated thinking on the forces that control protein folding and stability. Despite its wide importance in chemistry and biology, our understanding of this interaction at the molecular level remains poor, with little experimental evidence to support the idea of water ordering close to a non-polar group that is at the centre of the standard model for the source of the entropic driving force. Developments over recent years in neutron techniques now enable us to see directly how a non-polar group actually affects the molecular structure of the water in its immediate neighbourhood. On the basis of such work on aqueous solutions of small alcohols, the generally accepted standard model is found to be wanting, and alternative sources of the entropic driving force are suggested. Moreover, the fact that we can now follow changes in hydrogen bonding as the alcohol concentration is varied gives us the possibility of explaining the concentration dependence of the enthalpy of mixing. Complementary studies of solute association on the mesoscopic scale show a rich concentration and temperature behaviour, which reflects a complex balance of polar and non-polar interactions. Unravelling the detailed nature of this balance in simple aqueous amphiphiles may lead to a better understanding of the forces that control biomolecular structural stability and interactions.

Effects of composition on structure and activity of PtRu/C catalysts

A series of carbon supported PtRu bimetallic catalysts with varying Pt:Ru ratio were prepared and characterised using ex situ and in situ XRD, in situ EXAFS at 0 V vs. RHE, ex situ XPS and monolayer CO stripping voltammetry. Although the catalysts were found to be well mixed/alloyed, with no evidence of unalloyed Ru (oxides) present, the surfaces of the electrocatalyst nanoparticles were found to be enriched with Pt compared to the nominal bulk composition. The methanol oxidation activities of the catalysts were determined in 1.0 mol dm(-3) H2SO4. In agreement with published studies of polycrystalline bulk PtRu alloys the catalyst with a 0.6 surface fraction of Pt was found to give the best methanol oxidation activity at 30 degrees C. However, at 80 degrees C a greater surface fraction of Ru could be tolerated, with some activity at low current densities found for a Pt surface fraction as low as 0.2. The results support the conclusion that a limited amount of methanol dehydrogenation occurs at Ru sites or Ru dominated surface ensembles at 80 degrees C.

The effect of large magnetic fields on solid state combustion reactions: novel microstructure, lattice contraction and reduced coercivity in barium hexaferrite

Combustion reactions of BaO2, Fe2O3 and Fe performed in large applied fields have revealed unexpected modifications in the microstructure of the multiphase combustion product, and in the lattice parameters and coercivity of monophase BaFe12O19 obtained by post-production grinding and sintering.

A novel facility using a Laue focusing monochromator for high-pressure diffraction at the SRS, Daresbury, UK

A novel Laue focusing monochromator has been developed to provide intense X-radiation for high-pressure diffraction experiments. A beamline using this monochromator has been successfully developed on station 9.5 at the SRS, Daresbury Laboratory. Contributions to resolution from monochromator bandpass and divergence due to focusing have been quantified and are used to assess experimental diffraction data from diamond-anvil cells recorded using image plates with X-rays at approximately 30 keV. This optical and beamline design could be readily adapted to use X-rays from a bending magnet on a third-generation synchrotron source.

X-Ray absorption spectroscopy investigations of the hydrophobic hydration of krypton at high pressure

The development of third-generation synchrotron radiation sources has created considerable opportunities for the investigation of systems under extreme sample conditions of pressure and temperature. This paper presents the application of a recently developed pressure cell and pressurization and circulation system to the investigation of the hydrophobic hydration of noble gases by X-ray absorption spectroscopy. This system operates in the pressure range from 1 bar to 1 kbar, and allows for mixing of gaseous and liquid components and the control of the ultimate gas in liquid concentration. First results demonstrate the remarkable resilience of the first hydration shell of a nonpolar solute (krypton) to the application of pressure in the 150 bar to 700 bar range. These results suggest questioning the conclusions of some recent computer simulations, in particular with regards to the potential impact of such studies on our understanding of pressure induced protein denaturation.

Cryosolvents useful for protein and enzyme studies below −100°C

Abstract For the study of protein structure, dynamics, and function, at very low temperatures it is desirable to use cryosolvents that resist phase separation and crystallisation. We have examined these properties in a variety of cryosolvents. Using visual and X-ray diffraction criteria, methanol:ethanediol (70%:10%), methanol:glycerol (70%:10%), acetone:methoxyethanol:ethanediol (35%:35%:10%), dimethylformamide:ethanediol (70%:10%), dimethylformamide (80%), methoxyethanol (80%), and methoxyethanol:ethanediol (70%:10%) were all found to be free of phase-changes down to at least −160°C. The least viscous of these, methanol:ethanediol (70%:10%), was miscible down to −125°C and showed no exo or endothermic transitions when examined using DSC. It is therefore potentially particularly suitable for very low temperature cryoenzymology.

Software for automatic calibration of synchrotron powder diffractometers.

An automatic procedure to calibrate angular-dispersive monochromatic diffraction instruments has been developed at the Daresbury Synchrotron Radiation Source. The procedure uses a macro Language to control the powder diffraction instruments to locate Bragg reflections and perform peak-centre refinement from a standard reference material. The information obtained is used to refine the wavelength of the radiation used and the angular offset of the detector arm. The concept and implementation of the new software are described with applications to demonstrate its viability. The results of a reliability and accuracy study are also presented.

A Multidisciplinary Approach to Pigment Analysis: King’s Yellow and Dragon’s Blood From the Winsor and Newton Pigment Box at the Victoria and Albert Museum

A 19thcentury box of unused watercolour pigment cakes, manufactured by Winsor and Newton and currently at the Victoria and Albert Museum, was analysed using several techniques. The box and its contents are in remarkably good condition, with most of the watercolour cakes being still intact; thus a unique opportunity was made available to study unadulterated artists’ materials. Two interesting results obtained by using Raman microscopy and synchrotron radiation X-ray diffraction are reported here for the pigment cakes labelled king’s yellow and dragon’s blood.

A Focusing Laue Monochromator Optimised for Diamond Anvil Cell Diffraction Experiments

We have developed a sagittally bent Laue monochromator that is optimised for diffraction experiments on samples in diamond anvil cells. Test measurements have shown that the bandwidth of the monochromatic beam can be broadened with simultaneous focusing of the X‐rays. A gain in X‐ray flux of over 100 is achieved.