HYDROGEN STORAGE MATERIAL, HYDROGEN STORAGE CONTAINER, AND HYDROGEN SUPPLY APPARATUS

Abstract

Provided are hydrogen storage materials having hydrogen absorption (storage) desorption properties suitable for hydrogen storage in a temperature range of 0? C. or lower. Also provided are a hydrogen storage container containing the hydrogen storage materials, and a hydrogen supply apparatus including the hydrogen storage container. The hydrogen storage materials have an alloy with an elemental composition represented by Formula (1):

##STR00001##

in Formula (1), M is at least one kind selected from Mn, Co, and Al and essentially contains Mn, a satisfies 0.00?a?0.62, b satisfies 0.20?b?0.57, c satisfies 0.17?c?0.60, d satisfies 4.50?d?5.20, e satisfies 0.15?e?0.70, a+b+c=1, c+e satisfies 0.55?c+e?1.20, and d+e satisfies 5.13?d+e?5.40.

Claims

1. A hydrogen storage material, comprising: an alloy having a composition represented by the following Formula (1), ##STR00004## where M is at least one kind selected from Mn, Co, and Al and essentially contains Mn, a satisfies 0.00?a?0.62, b satisfies 0.20?b?0.57, c satisfies 0.17?c?0.60, d satisfies 4.50?d?5.20, e satisfies 0.15?e?0.70, a+b+c=1, c+e satisfies 0.55?c+e?1.20, and d+e satisfies 5.13?d+e?5.40.

2. The hydrogen storage material according to claim 1, wherein M is Mn or both of Mn and Co, a satisfies 0.00?a?0.40, and c satisfies 0.20?c?0.60 in Formula (1).

3. The hydrogen storage material according to claim 1, the alloy satisfying a relational expression of [{ln(P.sub.a1)?ln(P.sub.a2)}/0.2]?4.20: wherein, P.sub.a1 is desorption pressure at a hydrogen amount of 0.3 wt %, and P.sub.a2 is desorption pressure at a hydrogen amount of 0.1 wt % in a hydrogen pressure-composition isotherm for the alloy at ?20? C.

4. The hydrogen storage material according to claim 3, wherein the P.sub.a1 and the P.sub.a2 satisfy a relational expression of [{ln(P.sub.a1)?ln(P.sub.a2)}/0.2]?2.00.

5. A hydrogen storage container, containing: the hydrogen storage material according to claim 1.

6. A hydrogen supply apparatus, comprising: the hydrogen storage container according to claim 5.

7. The hydrogen storage material according to claim 2, the alloy satisfying a relational expression of [{ln(P.sub.a1)?ln(P.sub.a2)}/0.2]?4.20: wherein, P.sub.a1 is desorption pressure at a hydrogen amount of 0.3 wt %, and P.sub.a2 is desorption pressure at a hydrogen amount of 0.1 wt % in a hydrogen pressure-composition isotherm for the alloy at ?20? C.

8. The hydrogen storage material according to claim 7, wherein the P.sub.a1 and the P.sub.a2 satisfy a relational expression of [{ln(P.sub.a1)?ln(P.sub.a2)}/0.2]?2.00.

9. A hydrogen storage container, containing: the hydrogen storage material according to claim 2.

10. A hydrogen storage container, containing: the hydrogen storage material according to claim 3.

11. A hydrogen storage container, containing: the hydrogen storage material according to claim 4.

12. A hydrogen supply apparatus, comprising: the hydrogen storage container according to claim 9.

13. A hydrogen supply apparatus, comprising: the hydrogen storage container according to claim 10.

14. A hydrogen supply apparatus, comprising: the hydrogen storage container according to claim 11.

15. A hydrogen storage container, containing: the hydrogen storage material according to claim 8.

16. A hydrogen supply apparatus, comprising: the hydrogen storage container according to claim 15.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0014] FIG. 1 shows hydrogen pressure-composition isotherms (PCT curves) of the alloy powder in Example 1 and the alloy powder in Comparative Example 1, measured at ?20? C. The y-axis indicates the hydrogen absorption pressure during hydrogen absorption and the hydrogen desorption pressure during hydrogen desorption.

[0015] FIG. 2 shows hydrogen pressure-composition isotherms (PCT curves) of the alloy powder in Example 1 and the alloy powder in Comparative Example 3, measured at ?20? C. The y-axis indicates the hydrogen absorption pressure during hydrogen absorption and the hydrogen desorption pressure during hydrogen desorption.

DESCRIPTION OF EMBODIMENTS

[0016] Hereinafter, the present invention will be described in detail. The hydrogen storage materials of the present invention are materials comprising alloys having elemental composition represented by the following Formula (1). The hydrogen storage materials are preferably materials consisting of the alloys of the present invention. Hereinafter, the alloy having elemental composition represented by Formula (1) may also be referred to as an alloy or alloys of the present invention.

##STR00003##

[in Formula (1), M is at least one kind selected from Mn, Co, and Al and essentially contains Mn, a satisfies 0.00?a?0.62, b satisfies 0.20?b?0.57, c satisfies 0.17?c?0.60, d satisfies 4.50?d?5.20, e satisfies 0.15?e?0.70, a+b+c=1, c+e satisfies 0.55?c+e?1.20, and dte satisfies 5.13?d+e?5.40.]

[0017] In Formula (1), a, b, c, d, and e, represent content of the respective elements by atomic ratio, and detailed description thereof is as follows. Hereinafter, the content ratio may be referred to as a content or an amount.

[0018] La is effective in increasing the hydrogen absorption amount of invented alloys, and a, which represents the content of La in Formula (1), satisfies 0.00?a?0.62. The lower limit of a is preferably 0.01?a, and more preferably 0.02?a. The upper limit of a is preferably a?0.40. In a case that a is larger than the upper limit, the hydrogen equilibrium pressure may be too reduced.

[0019] Ce is effective in raising the hydrogen equilibrium pressure of invented alloys, and b, which represents the content of Ce in Formula (1), satisfies 0.20?b?0.57. The lower limit of b is preferably 0.22?b. In a case that b is larger than the upper limit, the hysteresis of the PCT curve may be worsen.

[0020] Sm is effective in raising the hydrogen equilibrium pressure and is also effective in improving of squareness in the PCT curve of invented alloys. c, which represents the content of Sm in Formula (1), satisfies 0.17?c?0.60. The lower limit of c is preferably 0.20?c and more preferably 0.22?c and particularly preferably 0.24?c. The upper limit of c is preferably c?0.55. In a case that c is smaller than the lower limit, the effect of raising the hydrogen equilibrium pressure may not be enough and the effect of improvement of squareness in the PCT curve may not be attained, and in a case that c is larger than the upper limit, the hydrogen absorption amount may be reduced. In this regard, the squareness refers to the squareness between plateau region and steep pressure dropping region toward end of desorption for desorption PCT curve, thus, improvement of squareness of materials could be regarded as increasing their available hydrogen capacity. The index of this squareness in the present application will be described later.

[0021] Ni is effective in improving the durability of the hydrogen storage alloys according to the present invention and reducing the hysteresis, and d, which represents the content of Ni in Formula (1), satisfies 4.50?d?5.20. The lower limit of d is preferably 4.55?d, and the upper limit of d is preferably d?5.15. In a case that d is smaller than the lower limit, the effect of improving the durability and the effect of reducing the hysteresis may not be enough, and in a case that d is larger than the upper limit, the hydrogen absorption amount may be reduced.

[0022] M is at least one kind selected from Mn, Co, and Al and essentially contains Mn, and is effective in reducing the hysteresis of the PCT curve of invented alloys. e, which represents the content of M in Formula (1), satisfies 0.15? e? 0.70. The lower limit of e is preferably 0.17? e. In a case that e is smaller than the lower limit, the effect of reducing the hysteresis of the PCT curve may not be enough, and in a case that e is higher than the upper limit, the hydrogen equilibrium pressure may be too low, and the reaction speed of hydrogen absorption and desorption may be worsened.

[0023] d+e in Formula (1) represents the sum of the contents of Ni and M. The value of d+e affects the hysteresis of the PCT curve and the hydrogen storage amount of the materials of the present invention, and by adjusting the value of d+e to be within the following range, alloys, which have small hysteresis of the PCT curves while maintaining the sufficient hydrogen storage capacity, can be obtained. d+e satisfies 5.13? d+e? 5.40, and the lower limit of d+e is preferably 5.15? d+e.

[0024] As described above, both Sm and M in Formula (1) are elements effective in raising the equilibrium pressure during hydrogen absorption or desorption, improving the squareness in the PCT curve, and reducing the hysteresis of the PCT curve of invented alloys, in addition, these effects can be enhanced when both elements are applied simultaneously in Formula (1). In Formula (1), c+e satisfies 0.55? c+e? 1.20, and preferably 0.57? c+e? 1.17.

[0025] The elemental composition of the alloys of the present invention can be confirmed by quantitative analysis using an Inductively Coupled Plasma (ICP) analysis apparatus. In the present specification, unless specified otherwise, the alloys of the present invention refer to the alloys having the elemental composition in accordance with by Formula (1).

[0026] The alloys of the present invention may contain inevitable impurities derived from raw materials and the like. Examples of the inevitable impurities include, but are not limited to, Pr, and Nd. The acceptable amount of inevitable impurities in the alloys of the present invention is 0.5 mass % or less.

[0027] The alloys of the present invention can be obtained as alloy flakes or other shapes as described later. The average grain size of crystal in the alloy flake or slab is preferably 25 to 250 ?m and more preferably 40 to 230 ?m. The average grain size of crystal can be measured as follows. The alloy flake or slab is embedded in a normal temperature curable-type resin (for example, epoxy resin), the resin is cured, embedded alloy is subjected to being cut and precision polishing using a wet polishing machine, and finally the polished cross-section with mirror-like surface is obtained. Next, for example, the cross section of the alloy is etched with a 0.1 M nitric acid aqueous solution, then a polarization microscope is used to measure the lengths of the major axial diameter and the minor axial diameter of each grain, and the grain size of the crystal is defined as (length of the major axial diameter+length of the minor axial diameter)/2. The grain size is measured in this way, and the average of three grain size per alloy flake or slab is taken as the average grain size. The size of the alloy flake or slab for measuring the crystal grain size is not particularly limited. For example, an alloy slab of about 1 cm.sup.3 may be used. Further, the grain size may be measured by using an alloy flake of about 1 cm.sup.2, and even in that case, the average grain size is preferably 25 to 250 ?m.

[0028] It is preferable that, in the hydrogen pressure-composition isotherm (PCT curve) for the alloys of the present invention at ?20? C., a hydrogen desorption pressure P.sub.a1 at 0.3 wt % H.sub.2 and a hydrogen desorption pressure Paz at 0.1 wt % H.sub.2 satisfy a relational expression of [{ln(P.sub.a1)?ln(P.sub.a2)}/0.2]?4.20. Since the PCT curve has the above features, the squareness of the curve becomes clearer, which indicates that more hydrogen can be desorbed when hydrogen desorption is terminated at a predetermined pressure, and thus, these alloys are very suitable hydrogen storage materials that can be utilized without leaving stored hydrogen. It is more preferable that P.sub.a1 and P.sub.a2 satisfy the relationship of [{ln(P.sub.a1)?ln(P.sub.a2)}/0.2]?2.00. In addition, the results of the above expression are regarded as the index of squareness of PCT curves for hydrogen desorption. In order to obtain P.sub.a2, it is preferable to measure two or more hydrogen desorption pressures between 0.08 wt % H.sub.2 to 0.12 wt % H.sub.2.

[0029] The alloys of the present invention satisfy preferably the relationship of [{ln(P.sub.a3)?ln(P.sub.a1)}/0.8]?0.50, and more preferably the relationship of [{ln(P.sub.a3)?ln(P.sub.a1)}/0.8]?0.28. In which, P.sub.a1 and Pas are hydrogen desorption pressure at 0.3 wt % H.sub.2 and hydrogen desorption pressure at 1.1 wt % H.sub.2 in the PCT curve at ?20? C., respectively. This is because when the above relationship is satisfied, the required hydrogen pressure is easily maintained, and the available amount of hydrogen can be secured as much as possible at the hydrogen supply destination, which are advantageous. In addition, the relationship of the above expression is used as the index of plateau flatness for hydrogen desorption curves.

[0030] Further, it is preferable that, invented alloys satisfy the relationship of ln(P.sub.b1)/ln(P.sub.b2)?0.60, in which, P.sub.b1 and P.sub.b2 are hydrogen absorption pressure and hydrogen desorption pressure at 0.8 wt % H.sub.2 in the PCT curves at ?20? C., respectively. Since the alloy satisfying the above expression exhibits a small hysteresis in the PCT curve, there is no need to generate a large pressure difference or temperature difference between absorption and desorption of hydrogen, and efficient operation is possible. In addition, the relationship of the above expression is used as the index of hysteresis of the PCT curve.

[0031] Further, in the PCT curves for the alloys of the present invention at ?20? C., the hydrogen desorption pressure P.sub.b2 at 0.8 wt % H.sub.2 is preferably 0.05 MPa or higher, and more preferably 0.10 MPa or higher. Such alloys possess more favorable hydrogen desorption properties in a temperature range of ?20 to 0? ? C. Though there is no particular upper limit in P.sub.b2, the upper limit is practically about 4.00 MPa at ?20? C.

[0032] It is particularly preferable that the invented alloys which form the invented hydrogen storage materials satisfy the above-mentioned relationships related with PCT curves, but it is also permissible that the invented alloys do not partially satisfy the above-mentioned relationships.

[0033] Next, a method for producing the hydrogen storage materials of the present invention will be described. First, examples of the method for preparing the alloys include strip casting methods such as a single roll method, a twin roll method, and a disk method, and a permanent mold casting method.

[0034] For example, in the strip casting method, raw materials blended so that the casted alloys will has a desired composition are prepared. The blended raw materials are then melted by heating in an inert gas atmosphere such as Ar to obtain a molten alloy, and the molten alloy is poured on a water-cooled copper roll, rapidly cooled and solidified, thereby alloy flakes are obtained. In the case of permanent mold casting method, a molten alloy is obtained in the same manner as mentioned above, and then the molten alloy is poured into a water-cooled copper mold to be cooled and solidified, whereby an ingot or slab is obtained. Usually, cooling rates are different between the strip casting method and the permanent mold casting method, so the strip casting method is generally more preferable than mold casting in order to obtaining alloy flakes with less segregation and uniform element distribution. Depression of segregation and uniformity of elemental distribution are very important for the invented alloys which form the invented hydrogen storage materials, therefore the strip casting method is a preferred method in the present invention as alloy production method.

[0035] Note that, in the case of strip casting methods, the preferrable cooling rate of the molten alloy for producing the alloy flakes, is as follows. The cooling rate from a temperature at which the cooling of the molten alloy begins (for example, a temperature at the time when the molten metal came in contact with the cooling roll) until the alloy temperature reaches 1000? C. is set to be 300? C./sec or higher. The cooling rate is preferably 700? C./sec or higher, more preferably 1000? C./sec or higher, and particularly preferably 4000? C./sec or higher. Though there is no particular upper limit for the cooling rate, the upper limit is practically about 20000? C./sec or lower. The beginning temperature of cooling of the molten alloy is usually within about 1300 to 1500? C., though the temperature varies depending on the composition of the alloy.

[0036] The cooling rate at less than 1000? C. is not particularly limited, and for example, in a case of the strip casting method, after being detached from the roll, the alloy flakes may be leaved to cool, and collected at a temperature of, for example, 100? C. or lower.

[0037] Furthermore, in order to obtain alloys having a more uniform composition distribution, the alloy flakes obtained by the cooling may be subjected to a heat treatment. The heat treatment can be performed in a range of 700? C. or higher and 1200? C. or lower in an inert gas atmosphere such as Ar. The heat treatment temperature is preferably 950? C. or higher and 1150? C. or lower, and the heat treatment time is 1 hour or more and less than 24 hours and preferably 3 hours or more and less than 15 hours.

[0038] Next, the alloy flakes obtained by the casting is ground in order to obtain alloy powder. The grinding can be performed by using a known grinder. Average particle size of the alloy powder is preferably 1000 ?m or smaller, and more preferably 500 ?m or smaller. Though it is not necessary to specifically define the smaller limit of the particle size of the alloy powder, the smaller limit is practically about 0.1 ?m. Here, the particle size of the alloy powder refers to a diameter measured by a sieve shaker (Ro-Tap).

[0039] The hydrogen storage materials of the present invention may be such alloy powder itself, a composite obtained by mixing the alloy powder with a resin or the like and molding the mixture into an arbitrary form such as a granular form, or articles attached on temperature-controllable apparatus. In this case, the resin functions as a binder for the alloy powder. The mixing can be performed by a known method. For example, the mixing can be performed using a mortar, or using a rotary mixer such as a double cone rotary mixer or a V-type rotary mixer, a stirring mixer such as a blade-type stirring mixer or a screw-type stirring mixer, or the like. It is also possible to perform the mixing while grinding the alloy flakes and the binder using a grinder such as a ball mill or an attritor mill.

[0040] Hydrogen storage containers of the present invention contain the hydrogen storage materials disclosed above, and as for the materials and shapes of the containers, a known materials and a known shape can be used.

[0041] Hydrogen supply apparatuses of the present invention include the hydrogen storage container, and as for the configurations other than the container with the invented hydrogen storage materials, known configurations can be used.

EXAMPLES

[0042] Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the descriptions of Examples, the alloys of the present invention in Examples, and the alloys in Comparative Examples that are not the alloys of the present invention, are all referred to as an alloy or alloys. In addition, an alloy obtained in shape of flakes by the strip casting method is referred to as alloy flakes, and a product obtained by grinding the alloy flakes is referred to as alloy powder.

Example 1

[0043] Raw materials were weighed so that an elemental composition of an alloy to be finally obtained became the composition shown in Table 1 and melted in a high frequency melting furnace in an argon gas (Ar) atmosphere, thereby molten alloy was prepared. The molten alloy was rapidly cooled and solidified by a strip casting method. The molten alloy was poured at a temperature of 1500? C. on a water-cooled copper roll in strip-cast apparatus, and alloy flakes with an average thickness of about 0.3 mm were obtained. A temperature at which the cooling of the molten alloy began, that is, when the molten alloy came into contact with the water-cooled copper roll, was about 1450? C. A difference existed in the cooling rate of the molten alloy between the contact side and the non-contact side with the roll of the molten alloy, and the cooling rate at from 1450? C. to 1000? C. was between 6000? C./sec and 9000? C./sec.

[0044] The alloy flakes obtained above were subjected to heat treatment by being kept it in an Ar atmosphere at 1030? C. for 10 hours by using a heat treatment furnace. The heat-treated alloy flakes were embedded in an epoxy resin, the resin was cured and subjected to being cut and precision polishing using a wet polishing machine, and finally the polished surface was mirror finished, thereby forming a cross section of the alloy. Then the cross section of the alloy was etched with a 0.1 M nitric acid aqueous solution. The average grain size of crystal in the alloy was obtained by using a polarization microscope (manufactured by Olympus Corporation) with the above-described method. In this alloy, the average grain size was 93 ?m.

[0045] After the heat treatment, the heat-treated alloy flakes were ground by using a stainless-steel mortar, and then alloy powder with a particle size of under 500 ?m was obtained using a sieve having an opening size of 500 ?m.

[0046] PCT curves of the alloy powder were obtained by using an automatic high pressure Sieverts apparatus for PCT measurement (manufactured by Fuse Technonet Co., LTD.). Prior to the measurement, the measurement tube with alloy powder was vacuumed at 80? C. for 1 hour, and then the hydrogen pressure was increased to about 2.5 MPa, and finally hydrogen was absorbed into the alloy powder until the hydrogen pressure was stabilized at ?20? C. Subsequently, vacuuming was performed at 80? C. for 0.5 hours, and then the hydrogen pressure was increased to about 2.5 MPa, and finally hydrogen was absorbed into the alloy powder until the hydrogen pressure was stabilized at ?20? C., and these series of operations were performed twice for activation. Next, after vacuuming at 80? C., the equilibrium pressures of hydrogen absorption and desorption (hydrogen absorption pressure and hydrogen desorption pressure) were measured by changing the hydrogen pressure between 0.01 MPa to 2.0 MPa at ?20? C. The obtained hydrogen pressure-composition isotherms (PCT curves) are shown in FIG. 1.

[0047] From the desorption curve of the obtained PCT curve, the available hydrogen amount, which is the difference between the hydrogen amount at 2.0 MPa and the hydrogen amount at 0.1 MPa, and the hydrogen desorption pressure at 0.8 wt % H.sub.2 were read. The results are shown in Table 1.

[0048] The squareness of the PCT curve of hydrogen desorption for the alloy powder was calculated by using equation {ln(P.sub.a1)?ln(P.sub.a2)}/0.2. Where P.sub.a1 is desorption pressure at 0.3 wt % H.sub.2 and Paz at 0.1 wt % H.sub.2, respectively, obtained from the PCT curve. The results are shown in Table 1.

[0049] The plateau flatness in the PCT curve of hydrogen desorption for the alloy powder was calculated by using equation {ln(P.sub.a3)?ln(P.sub.a1)}/0.8. Where P.sub.a1 is desorption pressure at 0.3 wt % H.sub.2 and P.sub.a3 at 1.1 wt % H.sub.2, respectively obtained from the PCT curve. The results are shown in Table 1.

[0050] The hysteresis of the PCT curves for the alloy powder was calculated by using equation ln (P.sub.b1/P.sub.b2). Where P.sub.b1 is absorption pressure at 0.8 wt % H.sub.2 for absorption curve, and P.sub.b2 is desorption pressure at 0.8 wt % H.sub.2 for desorption curve, respectively, obtained from the PCT curves. The results are shown in Table 1.

Examples 2 to 8, and 10 to 23

[0051] Alloy flakes and alloy powder of each Examples were prepared in the same manner as in Example 1, except that the elemental composition of the finally obtained alloy was changed to those shown in Table 1. Then the hydrogen absorption and desorption properties (squareness and the like) were measured. During alloys preparation pouring temperatures, temperatures at which the cooling began, and cooling rates of molten alloys of these Examples were 1500? C., 1450? C., and between 6000? C./sec and 9000? C./sec, respectively, all of which were approximately the same as those in Example 1. In this regard, the equilibrium pressures (hydrogen absorption pressure and hydrogen desorption pressure) were measured by changing the hydrogen pressure between 0.01 MPa to 3.0 MPa in Examples 11, 17 and 18 and between 0.01 MPa to 4.0 MPa in Example 12. As in Example 1, the available hydrogen amounts in Examples 2 to 8, 10, 13 to 16 and 23 were each taken as the difference between the hydrogen amount at hydrogen desorption pressure of 2.0 MPa and the hydrogen amount at hydrogen desorption pressure of 0.1 MPa. The available hydrogen amounts in Examples 11, 17 and 18 were each taken as the difference between the hydrogen amount at hydrogen desorption pressure of 3.0 MPa and the hydrogen amount at hydrogen desorption pressure of 0.1 MPa. The available hydrogen amount in Example 12 was taken as the difference between the hydrogen amount at hydrogen desorption pressure of 4.0 MPa and the hydrogen amount at hydrogen desorption pressure of 0.1 MPa. The available hydrogen amounts in Examples 19 to 22 were each taken as the difference between the hydrogen amount at hydrogen desorption pressure of 2.0 MPa and the hydrogen amount at hydrogen desorption pressure of 0.01 MPa. The results of various measured values are shown in Table 1.

Example 9

[0052] Alloy flakes and alloy powder were prepared in the same manner as in Example 2, except that the heat treatment after alloy casting was not performed, and the hydrogen absorption and desorption properties (squareness and the like) were measured. During the alloy preparation pouring temperature, temperature at which the cooling began, and cooling rate of molten alloys in Example 9 were 1500? C., 1450? C., and between 6000? C./sec and 9000? C./sec, respectively, which were approximately the same as those in Example 1. The results of various measured values are shown in Table 1.

Comparative Examples 1 to 5

[0053] Alloy flakes and alloy powder of each Comparative Examples were prepared in the same manner as in Example 1, except that the elemental composition of the finally obtained alloy was changed to those shown in Table 1. Then the hydrogen absorption and desorption properties (squareness and the like) were measured. During alloys preparation pouring temperatures, temperatures at which the cooling began, and cooling rates of molten alloys of these Comparative Examples were 1500? C., 1450? C., and between 6000? C./sec and 9000? C./sec, respectively, all of which were approximately the same as those in Example 1. The results of various measured values are shown in Table 1. In Comparative Example 2, since the hydrogen absorption amount did not reach 1.1 wt % at the time of the PCT curve measurement, the plateau flatness could not be calculated. The hydrogen pressure-composition isotherms (PCT curves) of Comparative Example 1 are shown in FIG. 1. Further, the hydrogen pressure-composition isotherms (PCT curves) of Comparative Example 3 are shown in FIG. 2.

TABLE-US-00001 TABLE 1 Composition (atomic ratio) a b c d e Heat La Ce Sm Ni Mn Co Al c + e d + e treatment Example 1 0.35 0.35 0.30 4.72 0.16 0.36 0.82 5.24 1030? C. ? 10 h Example 2 0.30 0.38 0.32 4.72 0.16 0.36 0.84 5.24 1030? C. ? 10 h Example 3 0.25 0.40 0.35 4.72 0.16 0.36 0.87 5.24 1030? C. ? 10 h Example 4 0.35 0.35 0.30 4.82 0.06 0.36 0.72 5.24 1030? C. ? 10 h Example 5 0.35 0.35 0.30 4.92 0.06 0.36 0.72 5.34 1030? C. ? 10 h Example 6 0.35 0.25 0.40 5.12 0.21 0.00 0.61 5.33 1030? C. ? 10 h Example 7 0.25 0.22 0.53 5.02 0.21 0.00 0.74 5.23 1030? C. ? 10 h Example 8 0.35 0.25 0.40 5.02 0.21 0.00 0.61 5.23 1030? C. ? 10 h Example 9 0.30 0.38 0.32 4.72 0.16 0.36 0.84 5.24 None Example 10 0.15 0.46 0.39 4.72 0.16 0.36 0.91 5.24 1030? C. ? 10 h Example 11 0.05 0.51 0.44 4.72 0.16 0.36 0.96 5.24 1030? C. ? 10 h Example 12 0.00 0.54 0.46 4.57 0.16 0.51 1.13 5.24 1030? C. ? 10 h Example 13 0.35 0.35 0.30 4.59 0.11 0.54 0.95 5.24 1030? C. ? 10 h Example 14 0.35 0.35 0.30 4.74 0.19 0.36 0.85 5.29 1030? C. ? 10 h Example 15 0.35 0.35 0.30 4.71 0.22 0.36 0.88 5.29 1030? C. ? 10 h Example 16 0.35 0.35 0.30 4.72 0.20 0.36 0.86 5.28 1030? C. ? 10 h Example 17 0.10 0.38 0.52 4.69 0.19 0.36 1.07 5.24 1030? C. ? 10 h Example 18 0.10 0.38 0.52 4.67 0.21 0.36 1.09 5.24 1030? C. ? 10 h Example 19 0.50 0.27 0.23 4.72 0.16 0.36 0.75 5.24 1030? C. ? 10 h Example 20 0.50 0.27 0.23 4.70 0.18 0.36 0.77 5.24 1030? C. ? 10 h Example 21 0.60 0.22 0.18 4.72 0.16 0.36 0.70 5.24 1030? C. ? 10 h Example 22 0.60 0.22 0.18 4.67 0.21 0.36 0.75 5.24 1030? C. ? 10 h Example 23 0.35 0.35 0.30 4.72 0.11 0.36 0.05 0.82 5.24 1030? C. ? 10 h Comparative 0.35 0.35 0.30 5.02 0.21 0.00 0.51 5.23 1030? C. ? 10 h Example 1 Comparative 0.35 0.35 0.30 5.17 0.06 0.00 0.36 5.23 1030? C. ? 10 h Example 2 Comparative 0.35 0.35 0.30 4.92 0.16 0.36 0.82 5.44 1030? C. ? 10 h Example 3 Comparative 0.35 0.35 0.30 5.02 0.06 0.36 0.72 5.44 1030? C. ? 10 h Example 4 Comparative 0.35 0.35 0.30 4.57 0.16 0.71 1.17 5.44 1030? C. ? 10 h Example 5 Available Crystal hydrogen Hydrogen grain amount desorption pressure Plateau size (wt %) (MPa) at 0.8 wt % Squareness flatness Hysteresis (?m) Example 1 1.45 0.30 1.50 0.04 0.18 93 Example 2 1.45 0.36 1.03 0.07 0.20 89 Example 3 1.46 0.47 1.17 0.07 0.24 104 Example 4 1.47 0.48 0.45 0.07 0.35 95 Example 5 1.40 0.71 1.28 0.09 0.23 90 Example 6 1.41 0.30 0.98 0.13 0.26 85 Example 7 1.41 0.29 0.57 0.07 0.35 96 Example 8 1.44 0.20 0.42 0.10 0.43 102 Example 9 1.43 0.33 1.41 0.15 0.23 49 Example 10 1.43 0.62 1.72 0.13 0.38 62 Example 11 1.41 1.00 1.32 0.11 0.51 56 Example 12 1.34 1.35 1.72 0.19 0.55 51 Example 13 1.46 0.35 1.26 0.42 0.20 85 Example 14 1.42 0.31 2.70 0.08 0.15 94 Example 15 1.42 0.22 3.83 0.08 0.15 80 Example 16 1.44 0.25 2.96 0.10 0.15 84 Example 17 1.43 0.71 1.52 0.21 0.19 87 Example 18 1.43 0.58 1.50 0.18 0.19 87 Example 19 1.50 0.12 1.00 0.04 0.22 84 Example 20 1.52 0.10 0.37 0.06 0.26 98 Example 21 1.52 0.07 0.39 0.07 0.27 103 Example 22 1.50 0.05 0.99 0.07 0.26 106 Example 23 1.42 0.33 3.38 0.15 0.13 97 Comparative 1.45 0.15 0.57 0.13 0.79 95 Example 1 Comparative 0.82 0.50 0.50 0.88 97 Example 2 Comparative 1.31 0.51 6.12 1.19 0.03 82 Example 3 Comparative 1.38 0.56 4.48 0.29 0.13 85 Example 4 Comparative 1.28 0.80 2.91 0.09 0.56 78 Example 5

[0054] As is clear from the table, the alloy of each Example has favorable squareness of the PCT curve and shows a sufficient available hydrogen amount, compared to the alloy of each Comparative Example. Further, since the hydrogen desorption pressures at 0.8 wt % H.sub.2 are all 0.05 MPa or higher, hydrogen can be sufficiently absorbed and desorbed in a temperature range of 0? C. or lower. Moreover, hydrogen storage materials with small hysteresis in PCT curves are presented.