Nobuhiko Takeichi

“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.

Indigo carmine: An organic crystal as a positive-electrode material for rechargeable sodium batteries

Using sodium, instead of lithium, in rechargeable batteries is a way to circumvent the lithiums resource problem. The challenge is to find an electrode material that can reversibly undergo redox reactions in a sodium-electrolyte at the desired electrochemical potential. We proved that indigo carmine (IC, 5,5′-indigodisulfonic acid sodium salt) can work as a positive-electrode material in not only a lithium-, but also a sodium-electrolyte. The discharge capacity of the IC-electrode was ~100 mAh g−1 with a good cycle stability in either the Na or Li electrolyte, in which the average voltage was 1.8 V vs. Na+/Na and 2.2 V vs. Li+/Li, respectively. Two Na ions per IC are stored in the electrode during the discharge, testifying to the two-electron redox reaction. An X-ray diffraction analysis revealed a layer structure for the IC powder and the DFT calculation suggested the formation of a band-like structure in the crystal.

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.

Observation of helical water chains reversibly inlayed in magnesium imidazole-4,5-dicarboxylate

A helical water chain, reversibly inlayed in a magnesium imidazole-4,5-dicarboxlylate, was characterized by single-crystal X-ray diffraction, thermogravimetric analysis, as well as temperature-variable Fourier transform infrared spectroscopy and powder X-ray diffraction techniques.

Rational assembly of a 3D metal–organic framework for gas adsorption with predesigned cubic building blocks and 1D open channels

A novel 3D metal-organic framework with predesigned cubic building blocks and 1D open channels exhibiting significant N2 adsorption has been synthesized and characterized by single crystal X-ray diffraction analysis.

Hydrogen Storage Properties of Mg-Al Alloy Prepared by Super Lamination Technique

Microstructures and hydrogen storage properties of Mg-Al super laminate composite alloys were investigated. The laminated sample was made by alternately stacking Mg films and Al films. The laminate was subjected to repetition of stacking and cold-rolling under an ambient condition (super lamination technique), combined with final heat treatment under an argon gas atmosphere. The number of films and thickness was nearly 15000 layers and about 50μm, respectivery. Their microstructures and hydrogen storage properties were studied by scanning electron microscopy, X-ray diffractometry and volumetric method by use of a Sieverts-type apparatus. In heat treatment process at 673K, Mg17Al12 intermetallic compound was formed by interdiffusion. This compound absorbed and desorbed hydrogen reversibly through the disproportionation and recombination react at 673K.

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.

Hydrogenation characteristics of mg based alloy prepared by super lamination technique

In order to improve the hydrogenation property of Mg/Ti laminate composite, Ni was added as a third element. Hydrogen storage properties of the laminated Mg/Ti/Ni alloy films were studied. Laminated Mg/Ti/Ni multilayer alloy films were prepared by cold rolling of stacked Mg, Ti and Ni under ambient conditions. The stacked foils were subjected to repetition of rolling and stacking, resulting in super-laminated foils with the thickness less than 0.3mm, containing more than 15000 layers. Microstructures of the super-laminates were studied by scanning electron microscopy and X-ray diffractometry. Their hydrogenation behaviors were investigated by use of a Sieverts type apparatus. The hydrogen storage capacity (H/M) of the laminate with composition Mg/Ti/Ni=9.0/0.9/0.1 amounted H/M=1.6 at 573K, 0.4MPa. Initial activation property was improved by controlling the amount of Ni appropreately.

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.

Phase transformation in Ti–Cr alloys by mechanical grinding

Abstract The effect of mechanical grinding on phase transformation in Ti–Cr alloys with nominal compositions of TiCr 2− x ( x =0, 0.2 and 0.5) was studied on phase transformation by mechanical grinding (MG). An X-ray diffraction (XRD) technique was applied for the identification of the constituent phases in the samples ground for various periods ranging from 0 to 12 h. The results indicated that the constituent phases changed from the mixture of a C15 and C14 Laves phases stable at ambient temperatures to a bcc phase stable at high temperatures such as 1643 K with an increase in grinding time. It was also found that, after 12 h of grinding, we could obtain samples composed of only a bcc phase within the detection ability of the X-ray diffraction apparatus.