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The surface structure of Ti 0.31 Cr 0.33 V 0.36 , which is an excellent hydrogen absorbing alloy, was directly observed in the first absorption–desorption cycle of hydrogen by small-angle neutron scattering (SANS). In addition, characterizations by pressure–composition isotherm ( P – C – T ) measurements and X-ray diffraction (XRD) were also carried out. The results of these experiments revealed the relationship between the slope of a SANS profile ( α ) and the hydrogen content (H/M). We suggest that the variation of α with H/M can be understood by considering the volume expansion of the surface during hydrogenation, which may exercise a significant role in the change from rough to smooth surface.

Hydrogen absorbing alloys cause internal stress in reaction vessels due to the expansion that occurs when they absorb hydrogen. This stress is affected not only by the amount of reacting hydrogen but also by the ab/desorption cycles. In this paper, we analyze the reaction distribution in a reaction vessel through simulations and show that locally excess internal stress occurs near the heat media inlet. We also show that this excess stress is decreased by unifying the reaction ratio by exchanging heat between the heat media inlet and the outlet in the reaction vessel.

Hydrogen absorbing alloys have a number of useful functions, such as an energy conversion. As an application to refrigeration, a new MH-refrigeration system for a freezing compartment by using a hydrogen absorbing alloy has been developed. The MH-refrigeration system is able to attain the temperature of the freezing compartment below -30°C. And as an application to separation and purification of hydrogen, MH-hydrogen purification system for generator cooling has been developed. MH-hydrogen purification system is expected to decrease the generator's windage loss, resulting higher generator efficiency.

In order to apply hydrogen-absorbing alloys to new energy carrier uses, such as hydrogen storage tanks or Ni–MH batteries, a drastic increase in the hydrogen capacity of these alloys is required. For years, intermetallic compounds or single-phase alloys have been studied as hydrogen-absorbing materials. New approaches to alloy design, relating to multiphase alloys, are proposed and verified. These approaches help to identify a new structure on a multiphase alloy. As a result, a new hydrogen-absorbing alloy, consisting of a nano-structure having a large hydrogen capacity and good desorbing properties, was found.

The metal hydride (MH) actuator is based on a new concept using the reversible reaction between the heat energy and mechanical energy of a hydrogen absorbing alloy. As the MH actuator is driven by heat, the response speed depends on the heat conductivity of the alloy layer in the MH container. Changing the alloy layer thickness directly influences the hydrogen absorption speed, and the addition of Cu-powder to the alloy layer contributes to improve heat conductivity.The MH actuator is characterized by large output per weight of the unit, that is, compactness, noiseless operation and smooth action. As an actuator suitable for use in rehabilitation equiment, we have developed a large-output MH actuator that is driven by heat from eletric heaters and tapwater, and then applied it to a toilet seat lifter and investigated its adaptability.It is expected that such MH actuators will play important roles in the development of various types of rehabilitation equipment.

Sanyo is currently developing four types of fuel cell including phosphoric acid fuel cells (PAFCs), polymer electrolyte fuel cells (PEFCs), solid oxide fuel cells (SOFCs) and molten carbonate fuel cells (MCFCs). PAFC portable power units are fully developed. Such units are small, high performance, clean and quiet power sources which utilize a hydrogen absorbing alloy developed by Sanyo, as the fuel supplier. Their specific performance was maintained through 600 cycle tests. PEFC andSOFC RD the decay rate was 4.4%/1000 h over the 1800 h of operation. A 30 kW class direct internal reforming MCFC system with light petroleum fuels was developed jointly with Tonen Corporation and Toyo Engineering Corporation, with the support from the Petroleum Energy Center (PEC). This system produced an output power of 30.5 kW.

We have been developing a 250 W class portable fuel cell system with a hydrogen supplier utilizing a hydrogen-absorbing alloy to meet demand for a clean and silent power source. A Mm Y Ni Mn alloy with the CaCu5 structure was developed for the hydrogen supplier and characterized with regard to the amount of the effective hydrogen, Xeff under operating conditions of the fuel cell. Xeff values between two arbitrary temperature and pressure conditions were evaluated from parameters of a P-C isotherms model. The operating performance of the fuel cell unit was examined and the hydrogen supplier using this alloy was characterized. The hydrogen supplier and the fuel cell unit showed a successful operating performance. The calculated Xeff value under the operating conditions of the fuel cell well agreed with its actual operation result. It is concluded that the method of evaluating Xeff by using the P-C isotherms model could contribute to designing the fuel cell system.

CaNi5-H2系, LaNi5-H2系, Ca1-xLaxNi5-H2系の反応熱量の測定を, 水素高圧下の示差走査熱量測定 (DSC) を用いて試みた.その結果, DSCで得られた実測値と, van't Hoffプロットの傾きおよび熱重量分析より得られる重量変化からの計算値とを比較することにより, DSCで得られた反応熱量の値が妥当であることを確認した.さらにDSC測定から得られた反応熱量は, 圧力-組成等温線の有効水素吸収量と関係しており, 有効水素吸収量が大きくなるほど水素化・脱水素化の反応熱量は大きくなることがわかった.

The effective hydrogen capacity of TixCr2-yMny [≫X λ1.1 (1.08≤0x≤1.16), y λ1.0 (0.96≤y≤1.08)rsqb; exhibited the maximum value of 1.8 wt% in the pressure range of 33 MPa and 0.1 MPa at 296K (dissociation pressure: 5-11 MPa), and the alloy provided over 10% more capacity than conventional Ti-Cr-Mn (Ti1.2CrMn: 1.6 wt%, Ti1.2Cr1.9Mn0.1: 1.3 wt%). At the low temperature of 233 K, the alloy absorbed 2.0 wt% of hydrogen and the hydrogen desorption capacity at 0.1 MPa was 1.6 wt%. The dissociation pressure decreased with the Ti and the Mn contents and was explained by the function of the bulk modulus and the cell volume. According to the van't Hoff plots, the standard enthalpy differences (heat of formation) of the Ti1.16Cr0.92Mn1.08 and Ti1.08Cr1.04Mn0.96 hydrides were -21 and -22 kJ/molH2, respectively. These absolute values were about 10 kJ/molH2 smaller than those of LaNi5 and Ti-Cr-V. The alloy had sufficient hydriding and dehydriding kinetics. In the pressure range of 33 MPa and 0.1 MPa at 296 K, the alloy absorbed and desorbed 1.8 wt% of hydrogen in 60 sec and 300 sec, respectively. The hydrogen capacity changed gradually over many cycles and that after 1000 cycles was 94 % of the initial capacity. Thus Ti1.1CrMn can be utilized for a high- pressure MH tank which contains a hydrogen absorbing alloy with high dissociation pressure and compressed hydrogen.

The crystal structure of Zr-Ti-V-Ni-Mn alloys with pseudobinary Laves phases was determined by X-ray diffraction analysis. The structure of these alloys was a single phase of cubic-C15 or hexagonal-C14 or a mixture of these phases. It was found that the ratio of C15 type in alloy was dependent on the ratio(rA/rB) of average radii of A and B atoms in the formula AB2, and the mixture ratio of C15 type in alloys increased with the increase of the ratio (rA/rB). For example, as Zr atom in alloys is partially substituted by Ti atom or V atom is partially substituted by Ni or Mn atom, the mixture ratio of C15 type decreases on account of the decrease of radius ratio (rA/rB). This ratio (rA/rB) is available as an estimate factor of crystal structure for these alloys with pseudobinary Laves phases.

As environment conscious materials, hydrogen-absorbing alloys have several potential applications. We are now developing new applications, which are cadmium free secondary battery, CO2 emission free portable fuel cell and chloro-fluorocarbon free refrigeration system. This paper introduces these new applications and presents new hydrogen-absorbing alloys which are suitable for these applications.

CaNi5, a hydrogen absorbing alloy, has been applied for the complete decomposition and regerneration of methane. The complete decomposition of methane was realized at 773∼873K over CaNi5 when the amount of methane introduced had been less than 800 μmol·g-CaNi5−1. The complete recovery of methane was observed by adding excess hydrogen at 773K if the amount of carbon deposit had been controlled less than 100 μmol·g-CaNi5−1.

It was found that the charge/discharge capacities and charging efficiency for pseudobinary Laves phase alloy electrodes increase with increasing molding pressure. A molding pressure of 9-10ton/cm2 was necessary to reach the largest discharge capacity (398mAh/g) for Zr0.5Ti0.5 (V0.375Ni0.625)2 electrode. The increase of the contact surface area of alloys and Ni yields increasing capacity.

This invention relates to a hydrogen-absorbing alloy, and particularly provides a hydrogen-absorbing alloy having a body-centered cubic structure which has a periodical structure formed by spinodal decomposition, has a large hydrogen storage amount, has excellent hydrogen desorption characteristics and can mitigate activation conditions, the alloy comprises at least two elements of alloy components, wherein the relational curve between chemical free energy of solid solutions and an alloy composition has a shape describing an upwardly convexed curve, or said alloy comprises two solid solutions having a regular periodical structure formed by spinodal decomposition within a region satisfying the relation d2G/dXB2 < 0 (where G is chemical free energy and XB is a solute alloy concentration) as the principal phase.