Yasuaki Osumi

Hydrogen absorption-desorption characteristics of MmNiAlM and MmNiMnM alloys (Mm misch metal)

In order to reduce the large hysteresis effect in MmNi hydrides (Mm  misch metal) we studied the hydrogen absorption-desorption characteristics of multicomponent alloys such as MmNi5−xAl(Mn)y−zMz and MmNi5−xAl(Mn)yM2 (M = Co, Cr, Cu, Nb, Ti, V, Zr; x = 0.3 − 0.5; y = 0.3 − 0.5; z = 0.05 − 0.1). The substitution or addition of the element M eliminates the large hysteresis effect that occurs during an absorption-desorption cycle. The hysteresis factor (equal to In(PaPd)) for MmNi4.7Al0.3M0.1 hydrides decreased for additives M in the following order: Zr > Co > Cr > Ti,V > Cu. Investigations of the effects of cycling showed that spalling occurred more rapidly for MmNi4.5Mn0.5 than for MmNi4.5Mn0.5Zr0.005 and MmNi4.5Mn0.5Zr0.1.

Hydrogen absorption-desorption characteristics of mischmetal-nickel-aluminum alloys

Abstract The hydrogen absorption and desorption characteristics of mischmetal (Mm)-nickel-aluminum alloys were investigated. MmNi5−xAlx (x = 0.25 −0.5) have been found to have the same hexagonal structure as LaNi5 and MmNi5, and they reacted readily with hydrogen to form the hydrides MmNi4.75 Al0.25H5.4, MmNi4.65Al0.35H 5.3H5.3 and MmNi4.5Al0.5H4.9 (hydrogen content: 1.3,1.2 and 1.2 wt.%, respectively) under 60 atm hydrogen pressure at room temperature. The dissociation pressures of these hydrides were dependent on the aluminum content (aluminum partially substitutes for nickel) and the value of log Pbecame lower than the value for MmNi5 hydride as x increased. The enthalpy change on hydride formation as determined from the dissociation isotherms for the MmNi4.5Al0.5-H system was − 5.5 kcal (mol H2)−1; this value was smaller than those for LaNi5 and MmNi5. The dissociation pressure at 30 °C was 3 atm and was nearly the same as that of LaNi5. The desorption rate of hydrogen for MmNi4.5Al0.5 was larger than those for LaNi5 and MmNi5) and a value of 2.1 – 4.3 kcal mol−1 was obtained for the apparent activation energy of hydrogen desorption. For MmNi4.5Al0.5 the hydrogen absorption-desorption cycle was repeated 30 times, but no variation in the hydrogen absorption-desorption capacity was observed. The hydride of MmNi4.5A10.5 proved to be suitable for use as a stationary hydrogen storage material.

Development of mischmetal-nickel and titanium-cobalt hydrides for hydrogen storage☆

Abstract Fundamental studies were carried out to develop hydrides of mischmetal-nickel (Mm-Ni) and Ti-Co alloys with suitable properties for use as stationary hydrogen storage materials. In order to improve the properties of MmNi5 and TiCo hydrides we studied the hydrogen absorption-desorption characteristics of ternary alloys such as Mm1−x AxNi5 (A  Ca, Ti; x = 0.1−0.75), MmNi5−yBy (B  Al, Co, Cr, Mn; y = 0.1 − 4), Ti1−xAxCo and TiCO1−x Ax (A  Cr, Cu, Fe, La, Mn, Ni, V; x = 0.05− 0.5). The hydrides of MmNi4.5Al0.5, MmNi2.5Co2.5, MmNi4.5Cr0.5, MmNi4.5Mn0.5, TiCo0.5Mn0.5 and TiCo0.5Fe0.5, judged according to an appropriate set of criteria, rank higher than or equal to those of LaNi5, MmNi5, TiFe and TiCo and have properties suitable for a stationary hydrogen storage material.

Hydrogen absorption-desorption characteristics of misch metal-nickel-silicon alloys

Abstract The hydrogen absorption and desorption characteristics of misch metal-nickel-silicon alloys were investigated. The alloys MmNis5−ySiy (Mm denotes misch metal and 0.4 ⩽ y ⩽ 0.8) were found to have the same hexagonal structure as LaNi5 and MmNi5, and they reacted readily with hydrogen to form the hydrides MmNi4.6 Si0.45H4.35, MmNi4.5 Si0.5H3.8, MmNi4.4Si0.6H2.1 and MmNi4.2Si0.8H3.1 (hydrogen contents of 1.0 wt.%, 0.9 wt.%, 0.5 wt.% and 0.7 wt.% respectively) under a hydrogen pressure of 60 atm at room temperature. The dissociation pressures of these hydrides were dependent on the silicon content (the silicon partially substitutes for nickel), and the value of log P became lower than that for MmNi5 hydride as y was increased. The enthalpy changes on hydride formation as determined from the dissociation isotherms for the MmNi4.5Si0.5-H and MmNi4.2Si0.8-H systems were −6.6 kcal (mol H2)−1 and −9.0 kcal (mol H2)−1 respectively; the value for the former was smaller than that for LaNi5, and the value for the latter was greater than those for LaNi5 and MmNi5. The dissociation pressures of these hydrides at 20 °C were 7.5 atm and 1.5 atm respectively. The desorption rate of hydrogen for MmNi4.2Si0.8 was larger than those for LaNi5 and MmNi5, and a value of 10.9–12.0 kcal mol−1 was obtained for the apparent activation energy of hydrogen desorption. The hydrides of MmNi4.6Si0.4, MmNi4.5Si0.5 and MmNi4.5Si0.8 have properties which make them suitable as stationary hydrogen storage materials.

Hydrogen storage properties of Ti1 + xCr2−yMny alloys

Abstract Fundamental studies were performed with the aim of developing hydrides of titanium-based alloys with suitable properties for hydrogen and energy storage applications. We investigated the hydrogen absorption-desorption characteristics of the alloy Ti1 + xCr2−yMny (0.1 ⩽ x ⩽ 0.3; 0 ⩽ y ⩽ 1). The rate of the initial activation process increased as x was increased, but the reversible hydrogen storage capacity decreased. Ti1 + xCr2−yMny reacted readily with hydrogen to form hydrides at a hydrogen pressure of 40 atm and −20 °C. The reversible hydrogen storage capacity of Ti1.2Cr2−yMny decreased with decreasing manganese content while the plateau pressure increased. The hysteresis in the absorption-desorption isotherms decreased markedly for titanium concentrations in the range 0.2 ⩽ x ⩽ 0.3 and for manganese concentrations in the range 0.5 ⩽ y ⩽ 0.8.

Hydrogen absorption-desorption characteristics of mischmetal-Ni-Cr-Mn alloys

Abstract The hydrogen absorption and desorption characteristics of mischmetal (Mm)-Ni-Cr-Mn alloys were investigated. The alloys MmNi5−yCry−zMnz (y = 0.5; z = 0-0.25) were found to have the same hexagonal structure as LaNi5 and MmNi5, and they reacted readily with hydrogen to form the hydrides MmNi4.5Cr0.5H6.3, MmNi4.5Cr0.46Mn0.04H6.3, MmNi4.5Cr0.45 Mn0.05H6.8 and MmNi4.5Cr0.25Mn0.25H6.9 (hydrogen contents (wt.%) of 1.4, 1.4, 1.5 and 1.6 respectively) under a hydrogen pressure of 25 atm at room temperature. The dissociation pressures of these hydrides were dependent on the manganese content (manganese partially substitutes for chromium) and the value of logP became lower than that for MmNi4.5Cr0.5 hydrides as z was increased. The enthalpy changes on hydride formation as determined from the dissociation isotherms for the MmNi4.5Cr0.5−zMnz-H (z = 0.04, 0.05 and 0.25) systems were − 6.7 kcal (mol H2)−1, −7.1 kcal (mol H2)−1 and −7.1 kcal (mol H2)−1 respectively; these values were smaller than that for LaNi5. The dissociation pressures of these hydrides at 20°C were 4.0 atm, 3.0 atm and 1.9 atm respectively. The desorption rate of hydrogen for MmNi4.5Cr0.46Mn0.04 was larger than those for LaNi5 and MmNi5, and a value of 7.3–7.9 kcal mol−1 was obtained for the apparent activation energy of hydrogen desorption. For MmNi4.5Cr0.46Mn0.04 and MmNi4.5Cr0.25Mn0.25 the hydrogen absorption-desorption cycles were repeated 30 times but no variation in the hydrogen absorption capacity was observed. The hydrides of MmNi4.5Cr0.46Mn0.04 MmNi4.5Cr0.45Mn0.05 and MmNi4.5Cr0.25Mn0.25 have properties which make them suitable as stationary hydrogen storage materials.

Hydrogen storage properties of TiFe1−xNiyMz alloys

The TiFe1−xNix-H system shows properties which make it suitable for heat pump or heat storage applications at temperatures from 100 to 200 °C. This system can be modified by substituting or adding a small amount of a fourth metal M. The hydrogen absorption properties of the modified system TiFe1−xNiyMz (M  V, Nb; 0 < x < 0.3; 0 < y < 0.3; 0 < z < 0.1) were investigated. The addition of vanadium has a marked effect on activation but produces little change in the dissociation pressure, the hydrogen storage capacity or the plateau slope and hysteresis of the hydrogen absorption-desorption isotherms. Similar observations were made when the additive was niobium.

Hydrogen absorption-desorption characteristics of Ti-Co-Fe Alloys

Abstract The hydrogen absorption and desorption characteristics of Ti-Co-Fe alloys were investigated. Alloys of composition TiCo 1− x Fe x ( x = 0.05 − 0.5) were found to have the same cubic structure as TiCo and they reacted readily with hydrogen to form the hydrides TiCo 0.95 Fe 0.05 H 1.2 , TiCo 0.7 Fe 0.3 H 1.2 and TiCo 0.5 Fe 0.5 H 1.2 (hydrogen contents, 1.1 wt.%) under a hydrogen pressure of 30 atm at room temperature. The dissociation pressures of these hydrides are dependent on the iron content x (the iron partially substitutes for the cobalt) and the value of log P H 2 increases gradually with increasing x . The enthalpy change on hydride formation, determined from the dissociation isotherms for the TiCo 0.5 Fe 0.5 -H system, is −10.1 kcal (mol H 2 ) −1 ; this value is smaller than those (−13.8 kcal (mol H 2 ) −1 and −11.2 kcal (mol H 2 ) −1 respectively) of the TiCo-H and TiCo 0.5 Mn 0.5 -H systems. The temperature required to produce a dissociation pressure of 1 atm is 70 °C, which is lower than the temperatures required for TiCo (130 °C) or TiCo 0.5 Mn 0.5 (90 °C). A value of 6.2 kcal mol −1 was obtained for the apparent activation energy of hydrogen desorption. For TiCo 0.5 Fe 0.5 , only two cycles under mild conditions are needed for the activation treatment so the alloy can easily be activated. The hydrogen absorption-desorption cycles were repeated 30 times but no variation in the hydrogen absorption-desorption capacity was observed. The hydride of TiCo 0.5 Fe 0.5 proved to be suitable for use as a hydrogen storage material.

Hydrogen absorption-desorption characteristics of titanium-cobalt-manganese alloys

Abstract The hydrogen absorption and desorption characteristics of Ti-Co-Mn alloys were investigated. Alloys of composition TiCo 1− x Mn x ( x = 0.05 – 0.5) were found to have the same cubic structure as TiCo and they reacted readily with hydrogen to form the hydrides TiCo 0.95 Mn 0.05 H 1.4 , TiCo 0.9 Mn 0.1 H 1.4 , TiCo 0.8 Mn 0.2 H 1.6 and TiCo 0.5 Mn 0.5 H 1.7 (hydrogen content 1.3, 1.3, 1.4 and 1.6 wt.% respectively) under a hydrogen pressure of 30 atm at room temperature. The dissociation pressures of these hydrides are dependent on the manganese content x (the manganese partially substitutes for the cobalt) and the value of log P increases gradually with increasing x . In addition, with increasing x , the width of the plateau in the isotherms becomes greater than that of TiCo hydride and the hydrogen content increases. The enthalpy change on hydride formation determined from the dissociation isotherms for the TiCo 0.5 Mn 0.5 −H system is −11.2 kcal (mol H 2 ) −1 ; this value is smaller than that of the TiCo-H system. The temperature required to produce a dissociation pressure of 1 atm is 90 °C, which is lower than the temperature required for TiCo (130 °C). The desorption rate of hydrogen for TiCo 0.5 Mn 0.5 is greater than that for TiCo, and a value of 9.9–11.4 kcal mol −1 was obtained for the apparent activation energy of hydrogen desorption. For TiCo 0.5 Mn 0.5 , only two cycles under mild conditions are needed for the activation treatment so the alloy can be easily activated. The hydrogen absorption-desorption cycles were repeated 30 times but no variation in the hydrogen absorption-desorption capacity was observed. The hydride of TiCo 0.5 Mn 0.5 proved to be suitable for use as a hydrogen storage material.

Development of a hydrogen storage system using metal hydrides

Abstract Fundamental research has been carried out on the development of the basic technology for a stationary hydrogen storage system using metal hydrides. We have built and tested a misch metal-nickel-manganese hydride storage reservoir (a unit cell), with an effective storage capacity of 1.6 m 3 of hydrogen. On the basis of the experiments, we have built and tested a stationary hydride reservoir for hydrogen storage constructed from many layers of the unit cells; this has a possible storage capacity of 16 m 3 of hydrogen.