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We studied reproducibility of discharge capacity, dischargeability, activation behavior, activity and porosity for charge–discharge reaction of a pellet-type electrode consisting of one part by weight of Ti 0.5 Zr 0.5 Ni 1.3 V 0.7 Mn 0.1 Cr 0.1 and three parts of the copper powder. We examined electrodes immediately after preparation and electrodes stored for 1 month under the following conditions: vacuum, dry air and humid air. Electrolyte impregnation in vacuo was found to be very effective in improving the reproducibility of electrochemical measurements, reducing measuring effects due to the storage conditions of the electrodes.

Two-dimensional model and simulation programs for designing a hydrogen storage vessel using hydrogen absorbing alloy with tubular heat exchanger were developed with the “Flow-3D” program in which physical properties of the hydrogen storage alloy were incorporated. The calculated results showed good agreement with experimental data obtained from 10 Nm 3 scale hydrogen storage vessel with MmNi 4.64 Al 0.36 alloy. It was concluded that this simulation program could be an adequate tool to design a practical scale hydrogen storage system for hydrogen from solid polymer electrolyte water electrolysis and to evaluate its hydrogen storage performance.

Alloy samples with a single phase structure of Ti 4 Cu 2 O were prepared and their hydrogenation characteristics were investigated. Pressure–composition isotherms of hydrogen absorption and desorption at 273, 303 and 313 K for the oxometallic alloys were measured over the range of hydrogen pressure from 0.004 to 2 MPa. The Ti 4 Cu 2 O alloys absorbed hydrogen up to 0.47 in the atomic ratio of hydrogen to metal at 273 K and under 2 MPa and reversibly desorbed at 313 K more than half of hydrogen absorbed. No distinct pressure plateau was observed in the isotherms. For all the samples after hydrogenation at temperatures and pressures below 523 K and 3 MPa, no phase other than Ti 4 Cu 2 O was observed in the X-ray diffraction profiles. The thermodynamic properties for the hydrogenation of the alloys were discussed.

Lattice expansion, contraction and degradation were investigated in two types of LaNi5-based alloys to identify the dominant factors in the mechanism of intrinsic degradation. Alloys were subjected to hydriding–dehydriding cycling tests up to 1000 cycles in pure hydrogen. Lattice expanding behaviour was studied by in-situ X-ray powder diffractometry, focusing on discrete lattice expansion of the crystal lattice between the α phase and the β phase in the plateau region. The alloy with a wider plateau region showed larger discrete expansion and lattice strain. The difference in degradation behaviour between the two alloys was related to the discrete expansion, especially in the c axis direction. This phenomenon is considered to be the dominant factor in the intrinsic degradation mechanism.

Cycling performance of hydrogen storage LaNi5−x alloys under O2 and H2O was investigated to develop a hydrogen storage system connected with a solid polymer electrolyte water electrolysis device. The best Al content was found to be between 0.5 and 0.8 through analysis of the initial hydrogen storage capacity decaying curves measured under impure hydrogen gas containing 100 ppm of O2, introducing a criteria for maximizing the total amount of hydrogen storage for long-term utilization of up to 10 000 cycles.

This paper outlines Japan's current activities in the research and development (R&D) and commercialization of metal hydrides for applications in hydride electrodes and batteries, hydrogen storage, hydrogen purification and effective utilization of thermal energy. Representative and notable activities and technologies promoted by private corporations and national projects are briefly covered.

Efforts to improve performance of metal hydride electrodes such as substitution of alloy components, heat treatment, and surface treatment intended to change surface and bulk structure of hydrogen storage alloys, mainly LaN 5 based alloys, are reviewed. The importance of control of morphology is emphasized.

Alloy samples with a single phase structure of Ti 4 Cu 2 O were prepared and their hydrogenation characteristics were investigated. Pressure–composition isotherms of hydrogen absorption and desorption at 273, 303 and 313 K for the oxometallic alloys were measured over the range of hydrogen pressure from 0.004 to 2 MPa. The Ti 4 Cu 2 O alloys absorbed hydrogen up to 0.47 in the atomic ratio of hydrogen to metal at 273 K and under 2 MPa and reversibly desorbed at 313 K more than half of hydrogen absorbed. No distinct pressure plateau was observed in the isotherms. For all the samples after hydrogenation at temperatures and pressures below 523 K and 3 MPa, no phase other than Ti 4 Cu 2 O was observed in the X-ray diffraction profiles. The thermodynamic properties for the hydrogenation of the alloys were discussed.

Yttrium tricopper dialuminium, YCu3Al2, is isostructural with hexagonal CaCu5, in which each Cu atom at the 3g(½,0,½) position in space group P6/mmm (No. 191) is partially replaced by an Al atom. The hydrogen-uptake properties are usually enhanced in other AB5 structures by aluminium substitution. YCu5 does not show any hydrogen absorption, and the goal of the present work is to investigate whether aluminium substitution could expand the metal-atom lattice enough to provide better interstitial positions for hydrogen storage. However, no enthalpy change was observed up to 773 K under 3 MPa static H2 pressure by differential thermal analysis (DTA) for the title compound. The compound does not show any significant hydrogen absorption/desorption in the pressure-composition isotherms (P–C–T diagrams) in the temperature range 298–673 K under 3.3 MPa H2 pressure.

Enhancement of the electrochemical activity of a LaNi 4.7 Al 0.3 electrode was observed subsequent to some charge–discharge cycles in a KOH solution containing hydrogen peroxide. Metallic nickel is enriched at the alloy surface after the treatment, and the concentration of lanthanum decreased during the treatment. The change in the distribution of elements at the alloy surface is expected to lead to a different dispersion state of nickel particles in the region, resulting in improvement of the catalytic activity for the charge-transfer process on the alloy surface.

Hydrogenation behavior and phase structures of some Ti–Fe–V ternary alloys were studied. Three different crystal structures, namely, a bcc, a CsCl-type and a C14 Laves phase structure were found. The atoms in the C14 Laves phase TiFe2 could be partially substituted by vanadium atoms without changing its structure. It was found that the C14 Laves phase structure region was expanded nearly to the center of the Ti–Fe–V ternary phase diagram. Lattice parameters of the alloys increased almost in proportion with increasing average atomic size of the constituent elements. It was also found that hydrogen storage capacity at a constant pressure increased with increasing the degree of vanadium substitution. The pressure–composition (P–C) isotherms of the C14 Ti–Fe–V alloys strongly sloped and they had no flat plateau. The storage capacity of C14 Laves phase Ti–Fe–V alloy was optimized to be 1.0 at the chemical composition of TiFeV0.7.

Yttrium tricopper dialuminium, YCu(3)Al(2), is isostructural with hexagonal CaCu(5), in which each Cu atom at the 3g((1/2),0,(1/2)) position in space group P6/mmm (No. 191) is partially replaced by an Al atom. The hydrogen-uptake properties are usually enhanced in other AB(5) structures by aluminium substitution. YCu(5) does not show any hydrogen absorption, and the goal of the present work is to investigate whether aluminium substitution could expand the metal-atom lattice enough to provide better interstitial positions for hydrogen storage. However, no enthalpy change was observed up to 773 K under 3 MPa static H(2) pressure by differential thermal analysis (DTA) for the title compound. The compound does not show any significant hydrogen absorption/desorption in the pressure-composition isotherms (P-C-T diagrams) in the temperature range 298-673 K under 3.3 MPa H(2) pressure.

LaMg2Ni9 has been redetermined from single-crystal diffraction data. The structure is isostructural with the hexagonal PuNi3, in which each Pu atom at the 6c position in space group R-3 m (166) is totally replaced by Mg and each Pu atom in the 3a position of PuNi3 structure is replaced by La to build the new AB2C9 type structure. This structure type can be visualized as built by stacking layers of AB5 (CaCu5) and AB2 (MgCu2, MgZn2 and MgNi2) structural sub units along the c-direction.

Vapor-liquid equilibria for the hydrobromic acid/sulfuric acid/water system were measured in an Othmer still at low hydrobromic acid concentration, i.e., below the azeotropic composition, for use in the development of thermochemical hydrogen production cycles involving the equilibrium reaction of bromine, sulfur dioxide, and water to sulfuric acid and hydrogen bromide.