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Reversible hydrogenation of Mg(B3H8)2·2THF (obtained by addition of BH3·THF to Mg/Hg amalgam) is investigated in the presence of MgH2, LiH, or NaH.

Complex hydrides have energy storage-related functions such as i) solid-state hydrogen storage, ii) electrochemical Li storage, and iii) fast Li- and Na-ionic conductions. Here, recent progress on the development of fast Li-ionic conductors based on the complex hydrides is reported. The validity of using them as electrolytes in all-solid-state lithium rechargeable batteries is also examined. Not only coated oxides but also bare sulfides are found to be applicable as positive electrode active materials. Results related to fast Na-ionic conductivity in the complex hydrides are presented. In the last section, the future prospects for battery assemblies with high-energy densities, and Mg ion batteries with the liquid and the solid-state electrolytes are discussed.

The multimode reversible hydriding/dehydriding reactions of CaPd are investigated over the temperature range 273—773 K.

We have developed new composite materials for hydrogen storage containing ZrFe1.4Cr0.6 or TiMn1.5 as a storage material and magnesium as a binder. The influences of composition, compacting pressure and heat treatment on hydrogen capacity, kinetics and cyclic durability of the composite pellets were examined by repeating absorption-desorption cycles. The pellets obtained by sintering the mixtures at 773 K for 20–40 h absorb hydrogen readily and very quickly under a hydrogen pressure of less than 1 MPa without any activation treatment, and exhibit no disintegration after 1000 hydriding—dehydriding cycles. Observations of the microstructure and distribution of metals and oxygen atoms in the composites, using scanning electron microscopy, electron probe microanalysis and electron spectroscopy for chemical analysis, indicate that the heat treatment at 773 K not only promotes the so-called magnesium reduction and makes the surface of the hydride clean, but it also helps to form a new thin composite phase on the boundary between the original hydride and unreacting magnesium metal which acts as a binder, keeping the pellet intact upon hydrogenation.

We have investigated the hydriding properties and microstructures of the new composite material Ti 0.6 Zr 0.4 Mn 0.8 CrCu 0.2 /Mg which contains elemental Mg as a binder. The hydriding properties of the host compound are improved owing to the Mg reduction effect in the process of heat treatment. In addition, we observed that in the process of heat treatment the Cu in the host compound Ti 0.6 Zr 0.4 Mn 0.8 CrCu 0.2 diffuses into the Mg region and Mg 2 Cu is formed. After hydriding and dehydriding cycles, hydrogen in the host compound diffuses into the Mg region through the Mg 2 Cu phase. Consequently, MgH 2 is formed even at temperatures below 373 K under hydrogen pressures of less than 1 MPa.

The intermetallic compound Mg 2 Ni was mechanically ground under a hydrogen atmosphere. Its hydrogen content reaches 1.6 wt.% (Mg 2 NiH 1.8 ) without changing the crystal structure of the matrix Mg 2 Ni phase, and the dehydriding reaction starts at around 440 K. Its properties are most likely to originate from the formation of a nano-scale composite material which is composed of the crystalline matrix phase and the disordered interface phase.

The title compound is prepared by milling of a mixture of (1-x)LiNH2 and xLiI (x = 0.06—0.75) for 5 h under Ar followed by heating at 423 K for 12 h.

The binary intermetallic superconductor MgB 2 was synthesized for the first time under a hydrogen atmosphere of 1.0 MPa. The synthesis reaction between elemental Mg and B was completed after only 10 min at 1173 K (about 4 h over 1000 K). The particle size of the sample synthesized in this way is comparable to that of the elemental Mg used as a starting material, while in a sample synthesized under an argon atmosphere the particle size is drastically decreased by cracking during the synthesis of MgB 2 . Hydrogen solubility was estimated to be less than 0.01 mass% at around room temperature. However, the lattice constant a is nearly 0.1% larger and thus the critical temperature for the superconductivity T c is ∼0.6 K higher in the sample synthesized under hydrogen than in the sample synthesized under argon. Therefore, the synthesis under hydrogen is a promising process to optimize the superconducting properties of MgB 2 and related systems.

In this paper, we report an experimental study of the mixed alkali metal and alkaline-earth metal borohydrides. It was found that dual-cation (Li, Mg) borohydride was in situ formed during the mechanical milling and subsequent heating process of 1:1 LiBH(4)/Mg(BH(4))(2) mixture. Compared with the constituent phases, the dual-cation borohydride exhibits lower onset dehydrogenation temperature. Furthermore, property examination results showed that the dehydrogenation reaction of the dual-cation borohydride may involve different mechanistic pathway from that of the constituent borohydrides. These findings suggest a viable approach for tailoring the dehydrogenation property of borohydrides, and should be of significance for better understanding the structure and property of ionic borohydrides. (C) 2009 Elsevier B.V. All rights reserved.

Calcium borohydride Ca(BH4)2 is one of the promising new hydrogen storage materials because of its large amount of hydrogen desorption capability (9.6 mass%). The crystal structures of α-Ca(BH4)2 (space group: Fddd, lattice constants: a = 8.7782(2) A, b = 13.129(1) A, c = 7.4887(9) A) and β-Ca(BH4)2 (P42/m, a = 6.9509(5) A, c = 4.3688(3) A) were refined by synchrotron X-ray diffraction at 300 and 433 K, respectively. The unsolved structures of γ-Ca(BH4)2 (Pbca, a = 7.525(1) A, b = 13.109(2) A, c = 8.403(1) A) and Ca(BH4)2·H2O (Pnma, a = 8.200(1) A, b = 5.8366(7) A, c = 11.851(2) A) were determined. In α-, β- and γ-Ca(BH4)2 structures, six boron atoms around a calcium atom construct CaB6 octahedron. The polymorphism of Ca(BH4)2 is formed by the different connection with adjacent octahedrons sharing vertexes and edges of the CaB6 octahedron. Furthermore, the charge density distribution in α-Ca(BH4)2 was experimentally determined by maximum entropy method. It is clarified that the bonding nature in α-Ca(BH4)2 ionic crystal is constructed from Ca2+ cation and BH4− anion.

Solid state lithium conductors are attracting much attention for their potential applications to solid-state batteries and supercapacitors of high energy density to overcome safety issues and irreversible capacity loss of the currently commercialized ones. Recently, we discovered a new class of lithium super ionic conductors based on lithium borohydride (LiBH4). LiBH4 was found to have conductivity as high as 10−2 Scm−1 accompanied by orthorhombic to hexagonal phase transition above 115 °C. Polarization to the lithium metal electrode was shown to be extremely low, providing a versatile anode interface for the battery application. However, the high transition temperature of the superionic phase has limited its applications. Here we show that a chemical modification of LiBH4 can stabilize the superionic phase even below room temperature. By doping of lithium halides, high conductivity can be obtained at room temperature. Both XRD and NMR confirmed room-temperature stabilization of superionic phase for LiI-d...

LiNH2, a new candidate of reversible hydrogen storage materials, was synthesized by vacuum evaporation of elemental Li with 99.9%-purity onto a metallic substrate, and subsequent nitrogenation and hydrogenation using high-purity gases. Depending on the evaporation time, the sample morphologies change from an island-shape with nearly 50 μm (873 K for 0 min; just heated-up to the set temperature) to a homogeneously flat film (873 K for 30 min) with a thickness of nearly 500 μm. The preliminary thermal desorption measurement implies a lower temperature hydrogen desorption from the film than that from bulk (powder) sample.

The hole-doped Li x BC ( x x BC ( x =0.5 and 1.0), using Li hydride as a starting material. The hydrogen concentration in Li x BC ( x =0.5) is about 0.7 mass% (Li 0.5 BC-H 0.18 ), and the hydrogen desorption occurs around 700 K. The absence of superconductivity might originate from the modified atomistic structure, detected by Raman spectroscopy. We propose that the hydrogen concentrations can be varied for realizing superconductivity in Li x BC ( x

A new intermetallic compound MgYNi4 with C15b(AuBe5)-type Laves phase structure was successfully synthesized by both mechanical milling and casting methods. The structural and hydriding properties of the samples were examined by X-ray diffraction measurement, thermal analysis and hydrogen pressure–composition (p–c) isotherm measurement. The lattice parameter of MgYNi4 was estimated to be a=0.701 nm, which is ca. 2% smaller than that of YNi2. A plateau (miscibility-gap) pressure was clearly observed in the p–c isotherm during the dehydriding process of the sample synthesized by casting. The maximum hydrogen content is ∼1.05 mass% (H/M∼0.6) under a hydrogen pressure of 4.0 MPa at 313 K, and the enthalpy of hydride formation was calculated to be −35.8 kJ/mol H2. The study in this paper reveals, for the first time, an application potential of MgNi2-based Laves phase structure for practical use as hydrogen storage and transport materials.