Duncan H. Gregory

Modern Microwave Methods in Solid-State Inorganic Materials Chemistry: From Fundamentals to Manufacturing

Chemistry: From Fundamentals to Manufacturing Helen J. Kitchen,† Simon R. Vallance,†,‡ Jennifer L. Kennedy,†,§ Nuria Tapia-Ruiz,† Lucia Carassiti,† Andrew Harrison, A. Gavin Whittaker, Timothy D. Drysdale, Samuel W. Kingman,‡ and Duncan H. Gregory*,† †WestCHEM, School of Chemistry, University of Glasgow, Joseph Black Building, Glasgow G12 8QQ, United Kingdom ‡Department of Chemical and Environmental Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom School of Engineering, University of Glasgow, James Watt South Building, Glasgow G12 8QQ, United Kingdom Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, F 38042, Grenoble, Cedex 9, France Tan Delta Microwaves Limited, 7 Nettlingflat, Heriot EH38 5YF, United Kingdom

Emerging concepts in solid-state hydrogen storage: the role of nanomaterials design

This perspective highlights the state-of-the-art solid-state hydrogen storage and describes newly emerging routes towards meeting the practical demands required of a solid-state storage system. The article focuses both on the physical and chemical aspects of hydrogen storage. Common to both classes of storage material is the concept of nanostructure design to tailor kinetics and thermodynamics; whether this be control of functionalised porosity or crystalline growth on the nanoscale. In the area of chemical storage, different processing and nanostructuring techniques that have been employed to overcome the barriers of slow kinetics will be discussed in addition to new chemical systems that have emerged. The prospects of porous inorganic solids, coordination polymers (metal organic frameworks; MOFs) and other polymeric matrices for physical storage of hydrogen will be highlighted. Additionally the role of inorganic nanostructures as evolving materials “intermediate” between physical and chemical storage systems will be discussed and their place within the fine thermodynamic balance for optimum hydrogen uptake and release considered.

Characterization and catalytic behavior of VOx-CeO2 catalysts for the oxidative dehydrogenation of propane

A series of ceria-supported vanadium catalysts was prepared via impregnation of the support with an ammonium metavanadate solution. The 723 K calcined samples were tested for propane oxydehydrogenation (ODH) activity and selectivity. The sample exhibiting the highest propane conversion was found to be the ceria support material itself, although this showed essentially no selectivity towards propene. An optimum propene yield of 4.2% was obtained at 673 K for the 6 wt% V2O5-CeO2 sample. Conversion decreased with increasing V loading which was attributed to the formation of cerium vanadate (CeVO4). This phase was found in all samples after calcination, its abundance rising in proportion to the V loading. In the 6 wt% V2O5 catalyst hydrated surface VOx species were present, although they underwent conversion to CeVO4 at temperatures above 573 K. The low reducibility of these surface vanadates was linked to the oxidation activity. It is inferred that surface polyvanadate species are responsible for the selective ODH of propane with V-O-V and/or V-O-Ce being the active oxygen species.

Sol-gel formation of ordered nanostructured doped ZnO films

A novel sol-gel route to c-axis oriented undoped and Co, Fe and Mn doped ZnO films is reported. Sols were prepared from a hydrated zinc acetate precursor and dimethylformamide (DMF) solvent. Films were spin-coated on to hydrophilic sapphire substrates then dried, annealed and post-annealed, producing almost purely uniaxial ZnO nanocrystallites and a high degree of long-range structural order. Specific orientation of hexagonal crystallites is demonstrated both perpendicular and parallel to the substrate surface. Cobalt doping resulted in the formation of disconnected oriented ZnO nanocrystals. Vanadium doped films formed the spinel oxide ZnAl2O4. Structural, optical and morphological characterisation demonstrated the high quality of the films and shows the suitability of the method for cost-effective fabrication studies in areas of oxide research that traditionally employ epitaxial growth techniques.

Nitride chemistry of the s-block elements

Abstract The highly electropositive s-block elements combine with nitrogen in the solid state to form some of the most ionic nitride compounds known. Also, however, these elements can combine in binary and higher systems to form compounds with partially covalent character, predominantly metallic bonds or low dimensional structural hybrids of metallic and ionic components. The crystal and coordination chemistry of both binary and ternary s-block nitrides is unusual and provides the basis for unexpected and exploitable physical properties and a range of exotic reaction chemistry.

Lithium nitrides, imides and amides as lightweight, reversible hydrogen stores

Complex “chemical hydrides” present new families of materials for high gravimetric capacity hydrogen uptake. Such high capacity storage is offered reversibly with potentially rapid sorption kinetics and good cyclability by systems taking materials containing lithium and nitrogen as a basis. Such nitrides, imides and amides also present vast opportunities for doping, catalysis and morphology/size control. This feature article highlights how the materials chemistry of these hydrides has developed at a rapid rate from conception and discovery through to modification and optimisation.

Through-space contributions to two-dimensional double-quantum J correlation NMR spectra of magic-angle-spinning solids

A routinely used assumption when interpreting two-dimensional NMR spectra obtained with a commonly used double-quantum (DQ) magic-angle-spining (MAS) pulse sequence referred to as the refocused incredible natural abundance double-quantum transfer experiment (INADEQUATE) [A. Lesage, M. Bardet, and L. Emsley, J. Am. Chem. Soc. 121, 10987 (1999)] has been that correlation peaks are only observed for pairs of nuclei with a through-bond connectivity. The validity of this assumption is addressed here by theory, experiment, and computer simulations. If the isotropic chemical shifts of the two nuclei are different and the MAS frequency is far from rotational resonance, the theoretical description demonstrates that DQ correlation peaks are indeed indicative of a J coupling. However, if the isotropic chemical shifts are the same, it is shown that DQ peaks can appear for pairs of nuclei even in the absence of a through-bond J coupling. These peaks appear in the specific case of a pair of nuclei with a nonzero through-space dipole-dipole coupling and chemical shift anisotropy tensors having different principal magnitudes or orientations, provided that the MAS frequency is comparable to or smaller than the chemical shift anisotropies. Experimental 31P spectra recorded on a sample of TiP2O7 and computer simulations show that the magnitude of these anomalous peaks increases with increasing B0 magnetic field and that they decrease with increasing MAS frequency. This behavior is explained theoretically.

Hydrogen: A future energy vector for sustainable development:

Abstract The rapid exhaustion of fossil fuel reserves and the adverse effects of climate change have attracted global attention and pose serious threats to mankind. The emergence of new energy technologies based on new materials discovery is crucial if the world is to arrest the adverse effects of climate change and secure the global energy security based on sustainable and renewable energy sources. Hydrogen is thought to be the solution as a clean and renewable future energy vector. The use of hydrogen in a polymer electrolyte membrane fuel cell is likely to be at the centre of power generation for stationary and mobile applications. This review describes the present state of contemporary research on modes of hydrogen generation and storage on the basis of research carried out during the last decade. The article focuses particularly on the key aspects of fuel cells and materials based on the physical and chemical storage of hydrogen. A high storage density together with favourable sorption thermodynamics and kinetics and prolonged cycleability and lifetime are the key requirements for a practical storage material. This review emphasizes both how the engineering of fuel cells and our understanding of solid state hydrogen storages impact on the future of hydrogen storage research and the prospects for the implementation of the hydrogen economy.

One‐Step Synthesis of Bismuth Telluride Nanosheets of a Few Quintuple Layers in Thickness

Strictly two dimensional (2D) crystals were previously believed to be non-existent due to inherent thermodynamical instability. Thin films of quasi 2D crystals had been limited until recently to epitaxial growth on single-crystal substrates with lattice matching achieved by routes such as molecular beam epitaxy (MBE). Graphene, 2D monolayers of graphite, was first observed experimentally in 2004 to exist as single layer (or 2–3 layer) freestanding films. It was explained that 2D crystals become intrinsically stable by gentle “crumpling” in the third dimension. Some inorganic, quasi-2D compounds, such as dichalcogenides (WS2 and MoS2), [5] boron nitride (BN) 7] and some complex oxides have been prepared by mechanical cleavage or chemical intercalation/ exfoliation methods. Bismuth telluride, Bi2Te3, as one of the best known thermoelectric materials, possesses the highest figure of merit and power factor at room temperature. 10] Calculations have shown that 2D Bi2Te3 layers in a quantum well structure have the potential to increase the figure of merit by a factor of 13 over the bulk telluride. Very recently, mechanical exfoliation techniques similar to those used in the preparation of graphene were employed by Teweldebrhan et al. to prepare the first 2D Bi2Te3 crystals. [12] Experiments indicate that these 2D Bi2Te3 crystals possess a high electrical conductivity and low thermal conductivity and Bi2Te3 2D thin films present a new class of topological insulators. 15] Also, very recently, rigid triangular and hexagonal Bi2Q3 (Q = Se,Te) nanoplates of 6 nm or less in thickness were deposited from the respective bulk chalcogenide powders. Here, we report the facile, one-step synthesis and growth of 2D Bi2Te3 nanosheets using chemical vapor transport (CVT) methods in a sealed tube. The surface-assisted CVT (SACVT) technique used here is a low-cost and uncomplicated synthesis method that can be used for producing a relatively high yield of nanomaterials. Performing the reaction in a closed container means that departures from the target stoichiometry of the products can be minimized. The folded edges of the nanometer scale sheets in the reactions described here provide a clear high-resolution transmission electron microscopy (HRTEM) signature for the exact thickness of the 2D Bi2Te3 crystals. Figure 1 shows a (negative) SEM image of the products deposited on the as-received Si wafer after the reaction. From the SEM image we can see that most of the particles have a thin sheet-like morphology and many edges of the particles

Lithium nitrides as sustainable energy materials.

Lithium nitride is an exceptional yet simple compound with remarkable properties that can be tuned with judicious chemical modifications. A unique structure coupled with high ionic mobility present both a fundamental model and an advanced material for energy applications, involving either storage of charge (lithium) or storage of hydrogen. In the former case, and as an electrode material, the system can be modified to increase defects and the number of charge carriers, both ionic and electronic. In so doing, one can create anodes of high reversible capacity. In the latter context, tailoring structure, microstructure, and composition has profound effects on both the amount of hydrogen one can store in the solid state and the rate at which this process (uptake and release) can be achieved.