Yoshio Moriwaki

Life properties of TiMn alloy hydrides and their hydrogen purification effect

The effects of pressure-induced absorption-desorption cycling on the degradation properties and the hydrogen purification ability of TiMn alloy hydrides were studied. The lines in the characteristic X-ray diffraction pattern were much broader and weaker in the cycled alloys but the C14 hexagonal structure was maintained and no second phase was observed. The hydrogen capacity was reduced by 30% for TiMn binary alloy and by 20% for TiMn multicomponent alloys after about 10 000 cycles in contrast with the marked reduction observed for LaNi5. In some cases slight recovery could be produced by heating at 500 °C for 1 h in a vacuum after cycling. Gas chromatography measurements on hydrogen released from TiMn1.5 hydride showed that the hydrogen purity was better than 99.9999% (except for an H2O impurity) after a purge release of only a few per cent of hydrogen when the purity of the commercial grade hydrogen absorbed by the hydride was 99.99%. It can be concluded from the results of these measurements that hydrogen purification using TiMn alloy is related to two factors. The removal of N2, CO and CO2 proceeds by surface poisoning (i.e. oxidation, physisorption or chemisorption), whereas the removal of CH4, O2, H2O and Ar is controlled by surface poisoning and concentration. The hydrogen purification effect of TiMn alloy hydrides showed little degradation even after a large number of absorption-desorption cycles.

Control of hydrogen equilibrium pressure for C14-type laves phase alloys

Abstract It is very important to control continuously the hydrogen equilibrium pressure P -temperature T characteristics of hydrogen storage alloys to have them applicable in a wide range of temperatures. The relation between the alloy phases and the P-C-T characteristics was determined for C14 (MgZn 2 ) type Laves phase alloys based on Ti(Zr)Mn 2 by changing the alloy composition. The P-C-T characteristics, hysteresis and plateau pressure were changedsubstantially by suchtituting zirconium for titanium in the A site and other elements such as chromium, copper or nickel in the B site. In this case, the crystal lattice constants and hydrogen equilibrium pressure were changed more effectively by substituting zirconium for titanium in the A site. The range of equilibrium pressures covered was from 10 to 10 8 Pa at 20°C (this corresponds to the range from −50°C to +250°C at 1.013×10 5 Pa). The equilibrium pressure changes particularly markedly for lattice constants a =(4.84–5.05)×10 −10 m and c =(7.94–8.28)×10 −10 m. These results show that the C14-type Laves phase alloys with excellent flatnessof the plateau pressure and small hysteresis, are applicable in these ranges of temperatures and pressures for hydrogen storage. We have confirmed these results by fabricating a prototype heat pump with ahydrogen storage alloy that utilizes high temperature waste heat.

Electrode characteristics of C15-type laves phasealloys

Abstract Extensive studies on hydrogen storage alloys such as LaNi5, MmNi5, Ti(Zr)−Ni etc. have been actively carried out for the negative electrodes of Ni−H2 batteries. The present authors, on the contrary, have focused on C14-type and C15-typeLaves phase alloys of the AB2 type based on TiCr2, TiMn2 and ZrMn2, and have succeeded in optimizing them for electrode materials which can supply a high energy density by inspecting the relation between the composition of the alloys, the P−C−T characteristics and the electrode performance. The Mn:Cr ratio, A:B ratio and addition of vanadium to the C15-type Lavesphase ZrMn0.6Cr0.2Ni1.2 were examined to investigate the alloy phases, hydride characteristics (P−C−T) and electrode performance. As a result, electrodes composed of such alloys as ZrCr0.8Ni1.2 andZrMn0.5Cr0.2V0.1Ni1.2 were found to provide a large discharge capacity in a cell test with an abundant electrolytic solution.

Progress in materials applications for new-generation secondary batteries

The status of research and development on advanced batteries in Japan is reviewed. The three types of batteries attracting the most interest are: (1) nickel-metal hydride batteries, (2) secondary lithium batteries, and (3) secondary batteries using solid electrolytes. The advances made in the development of these batteries are described from the viewpoint of the application of new materials. The materials used for batteries come from multidisciplinary research. Hydrogen-storage alloys and conducting polymers are examples of materials with interdisciplinary origins. >