Hiroyuki T. Takeshita

Hydriding properties of LaNi3 and CaNi3 and their substitutes with PuNi3-type structure

Abstract The PuNi 3 -type intermetallic compounds LaNi 3 , CaNi 3 , La 0.5 Ca 0.5 Ni 3 , LaCaMgNi 9 , La 0.5 Ca 1.5 MgNi 9 , CaTiMgNi 9 , LaCaMgNi 6 Al 3 and LaCaMgNi 6 Mn 3 have been prepared using a powder–metallurgy–sintering method. The hydrogenation behaviour of these materials has been studied through the gas–solid reaction. The as-prepared compounds were easily activated at room temperature under a hydrogen pressure of 3.3 MPa. The pressure–composition–temperature ( P – C – T ) curves show a single plateau region with the exception of LaNi 3 -H, which shows no plateau, and La 0.5 Ca 1.5 MgNi 9 -H, which shows two plateaus. All of these alloys can absorb/desorb hydrogen by 1.8 wt.% under the conditions studied. X-ray diffraction (XRD) analysis reveals that LaNi 3 H 4.5 is in the amorphous state, and the other hydrides are accompanied by different expansions of the unit cell volume of the host alloy.

X-ray diffraction studies of titanium and zirconium doped NaAlH4: elucidation of doping induced structural changes and their relationship to enhanced hydrogen storage properties

Abstract X-ray diffraction patterns of NaAlH4 doped with up to 10 mol.% of either titanium or zirconium do not contain Bragg peaks for the bulk metals or their aluminum alloys. Instead the hydride lattice parameters a and c undergo significant contraction upon 2 mol.% doping and then expand as the doping level increases from 2 to 5 mol.%. These results are explained by a model that entails substitution of sodium cations by variable valence transition metal cations and the creation of Na+ vacancies in the bulk hydride lattice.

“Hybrid hydrogen storage vessel”, a novel high-pressure hydrogen storage vessel combined with hydrogen storage material

Abstract Potential of a novel hydrogen storage vessel, “hybrid hydrogen storage vessel”, combining an aluminum–carbon fiber reinforced plastic (Al–CFRP) composite vessel and hydrogen storage alloy, is reported through calculation of the weight and volume of the hydrogen storage system for 5 kg of hydrogen. Evaluation of this system showed that the concept of the hybrid hydrogen storage vessel allowed us to realize a hydrogen storage system advantageous in both gravimetric and volumetric hydrogen density compared with conventional hydrogen storage techniques. The hybrid vessel requires a hydrogen storage alloy with a higher volumetric hydrogen density as well as a higher gravimetric density, and with a higher equilibrium hydrogen pressure than the hydrogen storage alloys which have been used for conventional hydrogen storage vessels.

Hydrogen Storage and Electrode Properties of V‐Based Solid Solution Type Alloys Prepared by a Thermic Process

A vanadium-based solid-solution-type alloy V 4 TiNi 0.65 Co 0.05 Nb 0.047 Ta 0.047 with a large discharge capacity was obtained using a low-cost precursor of V 4 Ni 0.65 Nb 0.047 produced by aluminothermic reduction from V 2 O 5 , Nb 2 O 5 , and Ni, The alloy was deoxidized to a low level by adding mischmetal as a reducing agent when the precursor was alloyed with Ti, Co, and Ta. The alloy showed a hydrogen absorption behavior similar to an alloy prepared from high-purity constituent metals. Moreover, the Mm-Ni-O phase was precipitated as spherical particles along the TiNi network phase in the alloy, remarkably improving the electrode rate capability because of enhanced catalytic ability of the network phase.

Hydrogen adsorption in carbonaceous materials

A volumetric apparatus for gas phase hydrogen/helium adsorption and desorption measurement aimed at carbon materials was constructed. The performance of the apparatus was assessed using activated carbons and vapor grown carbon nanofibers, and was proved to be applicable for these materials of low apparent densities with sufficient accuracy. Materials used in this study did not show a significant storage capacity of hydrogen. The obtained result, however, will provide reference data for future study to develop the carbon material for hydrogen storage.

Hydrogenation characteristics of ternary alloys containing Ti4Ni2X (X=O, N, C)

Abstract Ti 2 Ni-based alloys containing oxygen, nitrogen and carbon were investigated regarding their metallographic structures and hydrogenation characteristics. The alloy samples containing these non-metal elements had multi-phase structures composed of Ti 4 Ni 2 X, TiNi and TiX (X=O, N, C) phases. The ternary alloy samples reversibly absorbed and desorbed hydrogen under moderate conditions such as room temperature and atmospheric pressure. The hydrogenation properties of the alloy samples containing the non-metal elements were compared with those of the binary Ti 2 Ni compound.

Synthesis and characterization of nanocrystalline Mg2CoH5 obtained by mechanical alloying

The stoichiometric mixture of 2MgH2 + Co was ball milled under a hydrogen atmosphere to synthesize nanocrystalline metal hydride Mg2CoH5. Upon milling, the mixture was analyzed by X-ray powder diffraction (XRD) and thermal methods employing the techniques of differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermal analysis (DTA). Hydrogen absorption and desorption measured by pressure-composition-temperature (P-C-T) curves indicated that the capacity loss was small after 20 consecutive cycling tests. The enthalpies associated with hydride formation and decomposition were measured to be −69.5 and −83.2 kJ mol−1 H2, respectively. At the temperatures of this study (553 to 653 K), hysteresis decreases with increasing temperature.

Another unusual phenomenon for Zr7Ni10: structural change in hydrogen solid solution and its conditions

Zr7Ni10 has three hydrogen occlusion phases, α, β and γ, and the following unusual features are known for the phase transitions in the Zr7Ni10–H2 system: (1) The intermediate hydride phase (β) appears only during dehydrogenation but not during hydrogenation, and (2) The continuous hydrogen solid solution phase (α) exhibits a much higher hydrogen solubility during hydrogenation than during dehydrogenation. In order to clarify the mechanism about the difference in the hydrogen solubility of the α phase, the relation between the pressure-composition isotherms and corresponding structural change has been examined by a conventional volumetric method and X-ray diffraction. Through the examination, we discovered that the crystal structure of the α phase, which undergoes hydrogenation followed by dehydrogenation, is different from that of its pure metal phase, where the crystal structure of the dehydrogenated α phase changes from an orthorhombic structure to a tetragonal structure. The conditions causing the structural change were then examined, and it has been found that the α phase maintains its original orthorhombic structure as long as it is hydrogenated so as not to absorb enough hydrogen to change it to the hydride with a higher hydrogen content (γ). The phenomenon can be understood as one of the hydrogen-assisted phase transitions such as hydrogen-induced amorphization (HIA) in the sense that the phase transition requires hydrogenation under special conditions.

Nanocrystalline Ti-doped Li3AlH6 as a reversible hydrogen storage material

Here, the authors reports nanocrystalline titanium-doped lithium aluminium hydride(Ti-doped Li32AlH6) obtained by a high-energy ball milling technique and its potential utilization as a reversible hydrogen storage medium

Hydrogenation characteristics of Ti2Ni and Ti4Ni2X (X=O, N, C)

Ternary Ti4Ni2X (X=O, N, C) compounds and a binary Ti2Ni compound were compared based on their hydrogen pressure–composition–temperature (PCT) relations. It was demonstrated that the ternary compounds desorbed most of the absorbed hydrogen under moderate conditions such as room temperature and atmospheric pressure. The hydrogen desorption pressures of the Ti4Ni2X compounds were more than two orders of magnitude higher than the desorption pressure of the binary compound. In spite of the significant increase in the hydrogen desorption pressure, the slope of the PCT curve of each ternary compound was not large compared with that of the Ti2Ni one. These four Ti2Ni-based compounds and their corresponding hydrogen occlusion ones were discussed in terms of their relative thermal stability.