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The hydrogenation of NaF/9NaH + 5MgB2and NaF/2NaH + 1.5MgB2reactive hydride composites (RHC) was studied by volumetric titration (kinetics and PCI curves), in situ synchrotron radiation powder X-ray diffraction (SR-PXD), high-pressure differential scanning calorimetry (HP-DSC), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM). A hydrogen uptake between 4.1 and 4.8 wt % was observed when the H2pressure was in the range between 25 and 50 bar, and the temperature was kept constant at 325 °C. PCI curves indicate a hydrogenation equilibrium pressure of 2 and 8 bar at 325 °C for NaF/9NaH + 5MgB2and NaF/2NaH + 1.5MgB2, respectively. Synchrotron radiation powder X-ray diffraction revealed the formation of solid solutions of NaF–NaH after milling and a change in the reaction pathway compared to a reported nondoped 2NaH + MgB2reactive hydride composite. Formation of the stable side-product NaMgH2F was found as a drawback for hydrogen storage capacity and reversibility. FT-IR indicates no hydrogen to fluorine substitution in the NaBH4product.

The reactive hydride composites 9CaH2+ CaF2+ 10MgB2, 10Ca(BH4)2+ 9MgH2+ MgF2, and 9Ca(BH4)2+ Ca(BF4)2+ 10MgH2were prepared by ball milling. Their properties toward hydrogen absorption/desorption were tested by means of manometric measurements. The highest hydrogen storage capacity was obtained for 9CaH2+ CaF2+ 10MgB2(7.6 wt %) at the first cycle. The effects of CaF2, MgF2, or Ca(BF4)2on the dehydrogenation reaction were studied by means of in situ synchrotron radiation powder X-ray diffraction (in situ SR-PXD) and differential scanning calorimetry (DSC). The high resolution SR-PXD technique was used to confirm the formation of hydrogenated products and side products in the 9CaH2+ CaF2+ 10MgB2reactive hydride composites. These studies indicate the formation of a complex mixture of phases.

In this work the effect of a partial replacement of CaH2with CaF2on the sorption properties of the system CaH2+ MgB2has been studied. The first five hydrogen absorption and four desorption reactions of the CaH2+ MgB2and 3CaH2+ CaF2+ 4MgB2systems were investigated by means of volumetric measurements, high-pressure differential scanning calorimetric technique (HP-DSC), 11B and 19F MAS NMR spectroscopy, and in situ synchrotron radiation powder X-ray diffraction (SR-PXD). It was observed that already during the mixing of the reactants formation of a nonstoichiometric CaF2–xHxsolid solution takes place. Formation of the CaF2–xHxsolid solution sensibly affects the overall hydrogen sorption reactions of the system CaH2+ MgB2.

A reactive hydride composite (RHC) with initial composition 3CaH2+ 4MgB2+ CaF2was studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and X-ray absorption near edge structure (XANES) at the B K-edge and at the Ca K-edge. The hydrogenation reaction proceeds by an unknown intermediate. No evidence of intermediates was observed during the dehydrogenation reaction. B and Ca K-edge XANES results hint to a closed interaction of CaF2and Ca(BH4)2. The main function of CaF2in the 3CaH2+ 4MgB2+ CaF2RHC is as a dopant for the hydrogenation and dehydrogenation reactions.

LiF−MgB2composites are proposed for reversible hydrogen storage. With respect to pure LiBH4, a significantly kinetic destabilization regarding hydrogenation and dehydrogenation is accomplished. The reversible hydrogen storage capacity is up to 6.4 wt %. The kinetic properties are improved significantly during cycling. The formations of the hydridofluoride phases (LiBH4−yFyand LiH1−xFx) are observed by in situ synchrotron X-ray diffraction (XRD) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Hydrogenation and dehydrogenation mechanisms are described on the basis of the formation and decomposition of the hydridofluoride phases, respectively.

Nowadays, the technological utilization of reactive hydride composites (RHC) as hydrogen storage materials is limited by their reaction kinetics. However, addition of transition-metal-based additives, for instance titanium isopropoxide (Ti-iso), to the 2LiBH4+MgH2system, results in a significant improvement of sorption kinetics. In this work, the evolution of chemical state and local structure of the Ti-based additive has been investigated by means of X-ray absorption (XAS) and photoemission (XPS) spectroscopy. X-ray absorption near-edge structure (XANES) as well as extended X-ray absorption fine structure (EXAFS) analysis have been undertaken at the Ti K-edge. The measurements reveal the formation of a highly dispersed and disordered TiO2-like phase during ball milling. During first desorption reduced titanium oxide and titanium boride are formed and remain stable upon cycling. The surface analysis performed by XPS shows that the reduction processes of the Ti-based additive during first desorption is coupled to the migration of the Ti species from the surface to the bulk of the material. Several factors, related to favoring heterogeneous nucleation of MgB2and the increase of interfacial area through grain refinement are proposed as potential driving force, among other effects, for the observed kinetic improvement.

In the framework of the EC project STORHY (Hydrogen Storage for Automotive Applications), the prototype of a solid storage tank for hydrogen based on sodium alanate was developed. A storage tank containing 8 kg sodium alanate was designed and manufactured with the objective of fast refueling. To obtain the optimum design of the storage tank a simulation tool was developed and validated by experiments with a laboratory‐scale tubular reactor. Application of the simulation tool to different storage concepts and geometries yielded the final design. The chosen concept is modular, enabling simple scale‐up. This is the basis for the future development of fuel cell vehicle storage tanks containing 5 kg of hydrogen.

Im Rahmen des EUProjekts STORHY ist der Prototyp eines Metallhydridspeichers auf Natriumalanatbasis für automobile Anwendungen entwickelt worden. Besonderes Merkmal ist die Größe im Vergleich zu bisher vorhandenen Laborreaktoren. Mit Hilfe einer modellgestützten Simulation wird sein Beladungsverhalten für verschiedene Betriebsbedingungen berechnet. Anhand der Ergebnisse werden die Wirksamkeit der Kühlung und ihr Optimierungspotenzial diskutiert.

A breakthrough in hydrogen storage technology was achieved by preparing nanocrystalline hydrides using high‐energy ball milling and the use of suitable catalysts/additives. These new materials show fast or in case of Mg‐based hydrides very fast absorption and desorption kinetics within minutes, thus qualifying lightweight Mg‐ or Al‐based hydrides for storage applications. This article summarizes our current understanding of the kinetics of Mg‐based light metal hydrides, describes an approach for a cost‐effective processing technology and highlights some promising new developments in lightweight metal hydride research.

Abstract:: An in situ synchrotron radiation study of quasi-free five nanometer-sized palladium clusters during hydrogen absorption is combined with molecular dynamics simulations to investigate the structural development. In the diffraction patterns, strong intensity changes are found that provide evidence for a structural phase transformation that is significantly different from the α--Pd-H bulk phase transition. The structural transition is reversible and driven by the hydrogen concentration. The intensity changes are consistent with a cubic-to-icosahedral structural phase transition obtained in molecular dynamical simulations using embedded-atom-method potentials.

For Ge layers on Si(111) surfaces the energy of coherent and semicoherent interfaces with misfit dislocations is numerically analyzed by use of the atomistic anharmonic bond charge model and the Stillinger-Weber approach. For the semicoherent interface, three configurations are considered, differing in the dissociation of the misfit dislocations into Shockley partials and in the partial dislocation patterns. The calculations yield a slight energetic preference of the so-called B variant while the literature reports observation of all three configurations. The deduced critical thickness for the coherent interface is in fair accordance with experimental estimates.

For Ge films on (001)- and (111)-Si the energy of coherent and semicoherent interfaces with misfit dislocations is numerically analyzed by use of the atomistic, anharmonic bond charge model. The model describes correctly the elastic properties of the Ge film and the Si substrate, the bond angle stiffness reduction for short wavelength deformations as found in the dislocation cores, and the third order elastic constants. A generalization of the model to deal with mixed Ge–Si bonds is provided. For Ge/(001)Si misfit dislocations of 90° Lomer type are considered, for Ge/(111)Si a trigonal network of 90° glide-set partials with stacking faults between them. In both cases, the estimated critical thickness for the coherent interface is in fair accordance with experimental observations.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.