Hydrogen storage body, method for manufacturing same, and hydrogen container

Abstract

A hydrogen storage body (1) includes: a metal porous body (2) having pores (21); and hydrogen storage alloy particles (3) comprising a hydrogen storage alloy and held in the pores (21) in the metal porous body (2). The pores (2) have accommodation spaces (211) in which the hydrogen storage alloy particles (3) are accommodated. The average value of the ratio Dopening / dMH of an opening diameter Dopening (unit: μm) of an accommodation space (211) in which the hydrogen storage alloy particles (3) are accommodated, the opening diameter being represented by the below-mentioned formula, to a circumscribed circle equivalent diameter dMH (unit: μm) of each hydrogen storage alloy particle (3) as obtained by the observation of the surface of the hydrogen storage body (1) is greater than or equal to a cube root of the expansion ratio of the volume when hydrogen is occluded in the hydrogen storage alloy particles (3).　Dopening = (Dmax+Dmin) / 2, wherein Dmax represents the diameter (unit: μm) of a smallest circle among the circumscribed circles of the openings in the accommodation spaces (211), and Dmin represents the diameter (unit: μm) of a largest circle among inscribed circles of the openings in the accommodation spaces (211).

Description

Hydrogen storage material, its manufacturing method and hydrogen container

[0001] The present invention relates to a hydrogen storage material, a method for producing the same, and a hydrogen container.

[0002] In recent years, there has been concern about the environmental impact of using fossil fuels, and the use of hydrogen, which has a lower environmental impact, as an energy source is expected. To use hydrogen as an energy source, devices including a hydrogen storage material that can reversibly store and release hydrogen are sometimes used. For example, Patent Document 1 describes a hydrogen tank that stores hydrogen using a hydrogen storage material. Also, for example, Patent Document 2 describes a hydrogen pressure boosting system that uses a hydrogen storage material to boost the pressure of hydrogen.

[0003] JP 2007-309457 A JP 2019-19884 A

[0004] Powdered hydrogen storage alloys are often used as hydrogen storage materials in hydrogen tanks and hydrogen boosting systems. However, hydrogen storage alloys have the property of expanding when they absorb hydrogen and contracting when they release hydrogen. Furthermore, when powdered hydrogen storage alloys are filled into a container such as a hydrogen tank or hydrogen boosting system, the hydrogen storage alloy is densely packed in the lower part of the container, while a void is created in the upper part of the container. If hydrogen is absorbed into the hydrogen storage alloy in this unevenly distributed state within the container, the expansion of the hydrogen storage alloy may cause high stress on the container.

[0005] To mitigate the problems caused by the expansion of hydrogen storage alloys, a technique has been proposed in which resin is interposed between the particles of the hydrogen storage alloy, and the resin is deformed when the hydrogen storage alloy expands, thereby alleviating the stress on the container. However, because resin has a relatively high thermal resistance, interposing resin between the particles of the hydrogen storage alloy makes it difficult for the temperature of the hydrogen storage alloy to change. Therefore, in this case, there is a problem in that it becomes difficult to quickly absorb and release hydrogen into and from the hydrogen storage alloy.

[0006] The present invention has been made in consideration of such problems, and aims to provide a hydrogen storage material that undergoes little volume change upon absorbing hydrogen and has excellent thermal conductivity, a method for manufacturing the same, and a hydrogen container equipped with the hydrogen storage material.

[0007] One aspect of the present invention is a hydrogen storage body comprising: a metal porous body having pores; and hydrogen storage alloy particles made of a hydrogen storage alloy and held in the pores of the metal porous body, wherein the pores have spaces in which the hydrogen storage alloy particles are held; and a circumscribed circle equivalent diameter d of the hydrogen storage alloy particles obtained by observing the surface of the hydrogen storage body. MH The opening diameter D of the space in which the hydrogen storage alloy particles are accommodated is expressed by the following formula (1) relative to the diameter (unit: μm) of the space. opening (unit: μm) ratio D opening / d MH is equal to or greater than the cube root of the volume expansion ratio when hydrogen is absorbed into the hydrogen storage alloy particles. opening = (D max +D min ) / 2 ... (1)

[0008] However, D in the formula (1) max is the diameter (unit: μm) of the smallest circle circumscribing the opening of the storage space on the surface of the hydrogen storage body, and D min is the diameter (unit: μm) of the largest circle inscribed in the opening of the storage space on the surface of the hydrogen storage body.

[0009] The hydrogen storage alloy particles in the hydrogen storage material are held in the storage spaces of the pores of the metal porous body. MH (unit: μm) to the opening diameter D of the storage space in which the hydrogen storage alloy particles are stored opening (unit: μm) ratio D opening / d MH The average value of the ratio D opening / d MHBy setting the average value of (a) to be within the specified range, it is possible to form sufficiently large voids around the hydrogen storage alloy particles contained in the storage space. Furthermore, by forming voids around the hydrogen storage alloy particles, it is possible to easily prevent the hydrogen storage alloy particles from pressing against the metal porous body even when the hydrogen storage alloy particles absorb hydrogen and expand within the storage space. Therefore, the hydrogen storage body can reduce the amount of volume change when hydrogen is absorbed.

[0010] Furthermore, the metal porous body has high thermal conductivity, so that when the temperature of the hydrogen absorbing body is changed, the temperature of the hydrogen storage alloy particles held in the storage space of the metal porous body can be quickly changed, thereby enabling hydrogen to be quickly absorbed into the hydrogen absorbing body and released from the hydrogen absorbing body.

[0011] As described above, according to the above-described embodiment, it is possible to provide a hydrogen absorbing material that undergoes little volume change upon absorbing hydrogen and has excellent thermal conductivity.

[0012] FIG. 1 is a partial cross-sectional view showing a main part of a hydrogen absorbing material in embodiment 1. FIG. 2 is a partial cross-sectional view showing a main part of a molded body of a mixture in the manufacturing method of a hydrogen absorbing material in embodiment 1. FIG. 3 is a partial cross-sectional view showing a main part of a hydrogen absorbing material in embodiment 2. FIG. 4 is a partial cross-sectional view showing a main part of a resin foam in the manufacturing method of a hydrogen absorbing material in embodiment 2. FIG. 5 is an SEM image of the surface of a hydrogen absorbing material in Experimental Example 1. FIG. 6 is an SEM image in which the opening of the pores in FIG. 5 is enlarged. FIG. 7 is an SEM image in which the pores on the surface of a hydrogen absorbing material in Experimental Example 2 are enlarged. FIG. 8 is a partial cross-sectional view showing a main part of a hydrogen container in embodiment 3.

[0013] (Embodiment 1) An embodiment of the hydrogen storage material will be described with reference to Figures 1 and 2. As shown in Figure 1, the hydrogen storage material 1 of this embodiment includes a metal porous body 2 having pores 21, and hydrogen storage alloy particles 3 made of a hydrogen storage alloy and held within the pores 21 of the metal porous body 2.

[0014] [Metal Porous Body 2] The metal porous body 2 is made of metal and has pores 21 that hold hydrogen storage alloy particles 3. As shown in FIG. 1 , the pores 21 of the metal porous body 2 have storage spaces 211 that accommodate the hydrogen storage alloy particles 3. The shape of the storage spaces 211 is not particularly limited and can take various shapes. When the hydrogen storage body 1 is produced using a pore-forming material, as described below, the storage spaces 211 may be formed as spherical spaces in the metal porous body 2. Note that the term "spherical" as mentioned above includes not only a geometrically defined spherical shape but also shapes that are generally recognized as spherical, such as shapes with irregularities on the inner surface of a sphere and shapes that are deformed from a sphere, such as a spheroid.

[0015] 6, the surface of the hydrogen absorbing material 1 is provided with an opening for a storage space 211 containing the hydrogen storage alloy particles 3. The circumscribed circle equivalent diameter d of each hydrogen storage alloy particle 3 obtained by observing the surface of the hydrogen absorbing material 1 is MH The opening diameter D of the accommodation space 211 in which the hydrogen storage alloy particles 3 are accommodated is expressed by the following formula (1) relative to the diameter (unit: μm) of the accommodation space 211. opening (unit: μm) ratio D opening / d MH is equal to or greater than the cube root of the volume expansion ratio when hydrogen is absorbed into the hydrogen storage alloy particles 3. opening = (D max +D min ) / 2 ... (1)

[0016] However, D in the formula (1) max is the diameter (unit: μm) of the smallest circle circumscribing the opening of the storage space 211 on the surface of the hydrogen storage material 1, and D min is the diameter (unit: μm) of the largest circle inscribed in the opening of the accommodation space 211 on the surface of the hydrogen absorbing material 1.

[0017] The circumscribed circle equivalent diameter d of the hydrogen storage alloy particle 3 MH(unit: μm) is the diameter (unit: μm) of the smallest circle circumscribing the hydrogen storage alloy particle 3 on the surface of the hydrogen storage material 1. The volume expansion ratio when hydrogen is absorbed into the hydrogen storage alloy particle 3 is specifically the ratio of the volume of the hydrogen storage alloy particle 3 in a fully hydrogenated state to the volume of the hydrogen storage alloy particle 3 in a state where no hydrogen is absorbed.

[0018] In the hydrogen storage material 1, when hydrogen is absorbed into the hydrogen storage alloy particles 3, the hydrogen storage alloy particles 3 expand as described above. The volume of the expanded hydrogen storage alloy particles 3 is calculated by multiplying the volume of the hydrogen storage alloy particles 3 in a state where no hydrogen is absorbed by the expansion ratio described above. Here, since the expansion of the hydrogen storage alloy particles 3 is considered to occur isotropically, the particle size of the hydrogen storage alloy particles 3 in a state where hydrogen is absorbed is considered to be approximately calculated by multiplying the particle size of the hydrogen storage alloy particles 3 in a state where no hydrogen is absorbed by the cube root of the expansion ratio of the hydrogen storage alloy particles 3.

[0019] On the other hand, the opening diameter D of the accommodation space 211 expressed by the above formula (1) opening represents the average size of the opening of the accommodation space 211 that opens to the surface of the hydrogen absorbing material 1. The inner size of the accommodation space 211 is always the opening diameter D of the accommodation space 211. opening The value is greater than or equal to this.

[0020] Therefore, in the hydrogen storage material 1, the ratio D opening / d MH By making the average value of the expansion ratio of the hydrogen storage alloy particles 3 equal to or greater than the cube root of the expansion ratio of the hydrogen storage alloy particles 3, it is possible to form sufficiently large voids around the hydrogen storage alloy particles 3 accommodated in the accommodation space 211. As a result, when the hydrogen storage alloy particles 3 expand in the accommodation space 211, the hydrogen storage alloy particles 3 can be easily prevented from pressing against the metal porous body 2, and the amount of change in volume of the hydrogen storage body 1 when hydrogen is absorbed can be reduced.

[0021] From the viewpoint of more reliably obtaining the above-mentioned effect, the ratio D opening / d MH The average value of is preferably 1.05 or more, and more preferably 1.10 or more.

[0022] In addition, the ratio Dopening / d MH The average value of is calculated, for example, by the following method: First, the surface of the hydrogen absorbing material 1 is observed using a scanning electron microscope (i.e., SEM) to obtain an enlarged photograph of the plurality of accommodation spaces 211. Next, based on the enlarged photograph of each accommodation space 211, the circumscribed circle equivalent diameter d of the hydrogen storage alloy particles 3 accommodated in the accommodation space 211 is calculated. MH (unit: μm), the diameter D of the smallest circle circumscribing the opening of the accommodation space 211 max (unit: μm) and the diameter D of the largest circle inscribed in the opening of the accommodation space 211 min Then, using these values, the ratio D opening / d MH Then, the ratio D obtained for the plurality of accommodation spaces 211 is calculated. opening / d MH The ratio D opening / d MH The average value of

[0023] The ratio D opening / d MH The number of the accommodation spaces 211 used to calculate the average value of the ratio D opening / d MH By increasing the number of the accommodation spaces 211 used to calculate the average value of opening / d MH The average value of the ratio D opening / d MH The number of accommodation spaces 211 used to calculate the average value may be, for example, five or more.

[0024] The expansion ratio of the hydrogen storage alloy particles 3 can be calculated based on the volume expansion coefficient of the hydrogen storage alloy during hydrogen absorption, as described in various documents. More specifically, when the volume expansion coefficient of the hydrogen storage alloy constituting the hydrogen storage alloy particles 3 is expressed as k (unit: %), the expansion ratio of the hydrogen storage alloy particles 3 is expressed by the following formula (2). The volume expansion coefficient of the hydrogen storage alloy during hydrogen absorption can be measured, for example, by comparing the volume of a unit cell obtained by X-ray diffraction. Expansion ratio = (k + 100) / 100 ... (2)

[0025] The size of the storage space 211 can be controlled, for example, in the manufacturing method described below, by adjusting the amount of pore-forming material or pore-forming aid attached to the hydrogen storage alloy particles 3. More specifically, to form a larger storage space 211, for example, a larger amount of pore-forming material and / or pore-forming aid may be attached to the hydrogen storage alloy particles 3, or a pore-forming material with a larger particle size may be attached.

[0026] As shown in FIG. 1 , the pores 21 of the metal porous body 2 may have, in addition to the storage spaces 211, connection spaces 212 that connect the storage spaces 211 to the storage spaces 211 adjacent to the storage spaces 211 and between the storage spaces 211 and the outside of the metal porous body 2. For example, the metal porous body 2 of this embodiment is made of a sintered product of metal powder 22, and the voids between the metal particles 221 that make up the metal powder 22 form the connection spaces 212 of the pores 21. By providing the connection spaces 212 in the metal porous body 2 in this manner, hydrogen supplied from outside the metal porous body 2 can be guided to the hydrogen storage alloy particles 3 via the connection spaces 212 of the pores 21 and the storage spaces 211, and can be absorbed by the hydrogen storage alloy particles 3. Furthermore, the hydrogen storage body 1 can guide hydrogen released from the hydrogen storage alloy particles 3 to the outside of the metal porous body 2 via the storage spaces 211 and connection spaces 212 of the pores 21.

[0027] On the surface of the hydrogen absorbing body 1, it is preferable that the diameter of the largest circle inscribed in the opening of the connection space 212 is smaller than the volumetric median diameter of the hydrogen storage alloy particles 3. In this case, it becomes difficult for the hydrogen storage alloy particles 3 to pass through the connection space 212, and therefore it is easier to prevent the hydrogen storage alloy particles 3 from falling out of the storage space 211.

[0028] When the metal porous body 2 is composed of a sintered product of metal powder 22, the volumetric median diameter of the metal particles 221 constituting the metal powder 22 is preferably smaller than the volumetric median diameter of the hydrogen storage alloy particles 3. In this case, the metal powder 22 can be sintered at a lower temperature during the manufacturing process of the hydrogen storage body 1. Therefore, the metal porous body 2 can be formed while suppressing deterioration of the hydrogen storage alloy particles 3 due to heating during sintering. From the viewpoint of more reliably achieving this effect, the average particle diameter of the metal particles 221 constituting the metal powder 22 is preferably ½ or less, more preferably ⅕ or less, and even more preferably ⅙ or less, of the average particle diameter of the hydrogen storage alloy particles 3.

[0029] The average particle size of the metal particles 221 and the volume-based median size of the hydrogen storage alloy particles 3 are cumulative 50% particle sizes determined based on the volume-based particle size distribution. The volume-based particle size distribution can be obtained using, for example, a laser diffraction / scattering particle size measuring device.

[0030] In the hydrogen absorbing material 1 of this embodiment, the average particle size of the metal particles 221 constituting the metal powder 22 can be appropriately set within the range of, for example, 0.1 μm or more and 20 μm or less.

[0031] The pores 21 of the metal porous body 2 preferably have an interconnected pore structure, that is, a structure in which each pore 21 is connected to other pores 21. In this case, hydrogen can more easily flow throughout the entire hydrogen storage body 1, thereby increasing the amount of hydrogen that can be stored in the hydrogen storage body 1.

[0032] The metal constituting the metal porous body 2 may be any metal other than a hydrogen storage alloy, that is, any metal that cannot reversibly absorb and release hydrogen. More specifically, the metal constituting the metal porous body 2 may be iron, iron alloy, copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, or the like.

[0033] The metal constituting the metal porous body 2 preferably has a melting point lower than that of the hydrogen storage alloy. In this case, when the hydrogen storage body 1 is produced, the metal porous body 2 can be formed while suppressing deterioration of the hydrogen storage alloy particles 3 due to heating.

[0034] [Hydrogen Storage Alloy Particles 3] The hydrogen storage alloy particles 3 are made of a hydrogen storage alloy and are held in the storage spaces 211 in the pores 21 of the metal porous body 2. It is preferable that a portion of the surface of the hydrogen storage alloy particles 3 is separated from the metal porous body 2. By providing a gap between the hydrogen storage alloy particles 3 and the metal porous body 2 in this manner, when the hydrogen storage alloy particles 3 absorb hydrogen, it is possible to more easily prevent the hydrogen storage alloy particles 3 from expanding beyond the storage spaces 211 of the metal porous body 2 and deforming the metal porous body 2. Therefore, in this case, it is possible to more easily prevent the expansion of the hydrogen storage material 1 when hydrogen is absorbed.

[0035] The hydrogen storage alloy particles 3 may be fixed to the inner surface of the metal porous body 2, or may be movably held within the pores 21 of the metal porous body 2. In either case, by accommodating the hydrogen storage alloy particles 3 in the accommodation space 211, it is possible to more easily prevent the hydrogen storage alloy particles 3 from expanding beyond the pores 21 of the metal porous body 2 when the hydrogen storage alloy particles 3 absorb hydrogen. As a result, it is possible to more easily suppress the expansion of the hydrogen storage body 1 when hydrogen is absorbed.

[0036] From the viewpoint of further reducing the thermal resistance between the hydrogen storage alloy particles 3 and the metal porous body 2 and further increasing the thermal conductivity of the hydrogen storage body 1, it is preferable that a portion of the surface of the hydrogen storage alloy particles 3 is bonded to the metal porous body 2.

[0037] There are no particular limitations on the composition of the hydrogen storage alloy that constitutes the hydrogen storage alloy particles 3. Examples of the hydrogen storage alloy that can be used to constitute the hydrogen storage alloy particles 3 include AB5-type rare earth alloys such as LaNi5 and mischmetal-nickel alloys, AB2-type Laves phase alloys such as MgZn2 and ZrNi2, AB-type titanium alloys such as TiFe and TiCo, A2B-type magnesium alloys such as Mg2Ni and Mg2Cu, and solid solution BCC alloys such as Ti-V alloys and Ti-Cr alloys.

[0038] The average particle size of the hydrogen storage alloy particles 3 can be appropriately set within the range of, for example, 1 μm or more and 200 μm or less.

[0039] [Method for manufacturing hydrogen absorbing material 1] In manufacturing the hydrogen absorbing material 1 of this embodiment, for example, a pore-forming material 213 is attached to the surface of hydrogen storage alloy particles 3, and then the hydrogen storage alloy particles 3 and metal powder 22 that will become the metal porous body 2 are mixed to prepare a mixture, and the mixture is molded to prepare the molded body 10 shown in Figure 2, and the molded body 10 is heated to remove the pore-forming material 213 and sinter the metal powder 22 to form the metal porous body 2.

[0040] In this way, by heating the hydrogen storage alloy particles 3, to which the pore-forming material 213 has been previously attached, together with the metal powder 22 and removing the pore-forming material 213, it is possible to form storage spaces 211 around the hydrogen storage alloy particles 3, while also forming connecting spaces 211 between the storage spaces 211, each of which has a narrower gap than the storage spaces 211. The storage spaces 211 thus formed have a cage-like shape that accommodates the hydrogen storage alloy particles 3. Therefore, according to the above-described manufacturing method, the hydrogen storage alloy particles 3 can be held within the storage spaces 211 in the pores 21 of the metal porous body 2.

[0041] In the manufacturing method of this embodiment, first, a pore-forming material 213 is attached to the surface of the hydrogen storage alloy particles 3. As the pore-forming material 213, a substance that can be thermally decomposed at a temperature lower than the melting point of the hydrogen storage alloy particles 3 can be used. More specifically, as the pore-forming material 213, an organic polymer such as an acrylic resin, a styrene-based resin, or a urethane resin can be used. From the viewpoint of more reliably forming voids around the hydrogen storage alloy particles 3, it is preferable that the thermal decomposition temperature of the pore-forming material 213 be lower than the sintering temperature of the metal powder 22.

[0042] The form of the pore-forming material 213 is not particularly limited. For example, the pore-forming material 213 may be in the form of a film or particles. The pore-forming material 213 may also be adhered to the surface of the hydrogen storage alloy particles 3 via a pore-forming assistant made of an organic substance. As the pore-forming assistant, for example, an organic polymer having adhesive properties such as polyvinyl acetate can be used. The thermal decomposition temperature of the pore-forming assistant is preferably lower than the sintering temperature of the metal powder 22.

[0043] The amount of pore-forming material 213 attached is preferably 1 part by mass or more and 50 parts by mass or less per 100 parts by mass of hydrogen storage alloy particles 3, more preferably 3 parts by mass or more and 40 parts by mass or less, even more preferably 5 parts by mass or more and 30 parts by mass or less, and particularly preferably 7 parts by mass or more and 20 parts by mass or less.

[0044] By setting the amount of the pore-forming material 213 to be preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more per 100 parts by mass of the hydrogen storage alloy particles 3, it is possible to appropriately widen the voids formed around the hydrogen storage alloy particles 3. Furthermore, by setting the amount of the pore-forming material 213 to be preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less per 100 parts by mass of the hydrogen storage alloy particles 3, it is possible to increase the amount of hydrogen storage alloy particles 3 held in the hydrogen storage material 1 and increase the amount of hydrogen that can be storable by the hydrogen storage material 1. Furthermore, in this case, it is possible to easily prevent the volume ratio of the pores 21 in the metal porous body 2 from becoming excessively high. As a result, it is possible to more easily prevent a decrease in the strength of the metal porous body 2.

[0045] Next, the hydrogen storage alloy particles 3 with the pore-forming material 213 attached thereto are mixed with the metal powder 22 that will become the metal porous body 2 to prepare a mixture. The content of the hydrogen storage alloy particles 3 in the mixture is preferably 40% by mass or more and 90% by mass or less, more preferably 45% by mass or more and 85% by mass or less, even more preferably 50% by mass or more and 80% by mass or less, and particularly preferably 55% by mass or more and 75% by mass or less, based on the total mass of the hydrogen storage alloy particles 3 and the metal powder 22.

[0046] By setting the content of hydrogen storage alloy particles 3 in the mixture to preferably 40 mass% or more, more preferably 45 mass% or more, even more preferably 50 mass% or more, and particularly preferably 55 mass% or more, relative to the total mass of the hydrogen storage alloy particles 3 and the mass of the metal powder 22, the amount of hydrogen storage alloy particles 3 held in the hydrogen storage material 1 can be increased, and the amount of hydrogen that can be absorbed by the hydrogen storage material 1 can be increased.

[0047] Furthermore, by setting the content of the hydrogen storage alloy particles 3 in the mixture to preferably 90 mass % or less, more preferably 85 mass % or less, even more preferably 80 mass % or less, and particularly preferably 75 mass % or less, based on the total mass of the hydrogen storage alloy particles 3 and the metal powder 22, it is possible to easily prevent the volume ratio of the pores 21 in the metal porous body 2 from becoming excessively high. As a result, it is possible to more easily prevent a decrease in the strength of the metal porous body 2.

[0048] If necessary, a liquid dispersion medium may be added to the mixture to disperse the hydrogen storage alloy particles 3 and the metal powder 22. By dispersing the hydrogen storage alloy particles 3 and the metal powder 22 in the liquid dispersion medium and liquefying the mixture, the mixture can be more easily formed into a desired shape. As a result, a hydrogen storage material 1 having the desired shape can be obtained.

[0049] As the liquid dispersion medium, for example, a liquid organic polymer such as polyalkylene oxide or polyvinyl alcohol, or a solution containing such an organic polymer, can be used.

[0050] After preparing the mixture, the mixture is molded into a desired shape to obtain a molded body 10. As shown in Fig. 2, the molded body 10 thus obtained has a structure in which hydrogen storage alloy particles 3 to which pore-forming material 213 is attached are embedded in metal powder 22. There are no particular limitations on the method for molding the mixture, and an appropriate method may be selected from known methods such as press molding, injection molding, powder rolling, and gelation freezing depending on the properties of the mixture.

[0051] The compact 10 thus obtained is heated at a temperature higher than the thermal decomposition temperature of the pore-forming material 213 and the sintering temperature of the metal powder 22, but lower than the melting point of the hydrogen storage alloy particles 3. When the compact 10 is heated at such a temperature, the pore-forming material 213 attached to the periphery of the hydrogen storage alloy particles 3 disappears due to thermal decomposition, and storage spaces 211 are formed around the hydrogen storage alloy particles 3. In addition, the metal powder 22 present around the hydrogen storage alloy particles 3 is integrated to form a metal porous body 2. Therefore, by heating the compact 10 at the aforementioned temperature, a hydrogen storage body 1 can be obtained.

[0052] As shown in FIG. 1, the hydrogen storage alloy particles 3 in the hydrogen storage material 1 of this embodiment are held in the storage spaces 211 in the pores 21 of the metal porous body 2. The circumscribed circle equivalent diameter d MH (unit: μm) relative to the opening diameter D of the accommodation space 211 in which the hydrogen storage alloy particles 3 are accommodated. opening (unit: μm) ratio D opening / d MH is equal to or greater than the cube root of the volume expansion ratio when hydrogen is absorbed into the hydrogen storage alloy particles. Therefore, even when hydrogen is absorbed into the hydrogen storage alloy particles 3 and the hydrogen storage alloy particles 3 expand within the accommodation space 211, the hydrogen storage alloy particles can be easily prevented from pressing against the metal porous body 2. Therefore, the hydrogen storage material 1 can reduce the amount of change in volume when hydrogen is absorbed.

[0053] Furthermore, the metal porous body 2 of this embodiment has high thermal conductivity. Therefore, when the temperature of the hydrogen absorbing body 1 is changed, the temperature of the hydrogen storage alloy particles 3 held in the accommodation space 211 of the metal porous body 2 can be quickly changed. This allows hydrogen to be quickly absorbed into the hydrogen absorbing body 1 and released from the hydrogen absorbing body 1.

[0054] Therefore, the hydrogen absorbing material 1 of this embodiment undergoes little volume change due to hydrogen absorption and has excellent thermal conductivity.

[0055] (Embodiment 2) In this embodiment, another example of a hydrogen storage material will be described. Note that, among the symbols used in this embodiment and subsequent embodiments, the same symbols as those used in the previous embodiments represent the same components as those in the previous embodiments, unless otherwise specified.

[0056] As shown in Fig. 3 as an example, the porous metal body 202 in the hydrogen absorbing body 102 of this embodiment has a three-dimensional network structure including columnar struts 23 and a hub 24 where a plurality of struts 23 are gathered together, and the voids around the struts 23 and the hub 24 form pores 21. The pores 21 in the porous metal body 202 are interconnected in portions not shown in Fig. 3. In other words, the porous metal body 202 has a continuous pore structure.

[0057] The hydrogen storage alloy particles 3 are held in the three-dimensional network structure of the metal porous body 202. Voids are formed between the metal porous body 202 and the hydrogen storage alloy particles 3, and the voids around the hydrogen storage alloy particles 3 in the pores 21 form storage spaces 211. The portions of the pores 21 excluding the storage spaces 211 form connection spaces 212.

[0058] To produce the hydrogen storage material 102 of this embodiment, a pore-forming material 213 is attached to the surface of the hydrogen storage alloy particles 3; then, as shown in Figure 4, a resin foam 4 containing the hydrogen storage alloy particles 3 and having an open pore structure is produced; a metal film that will become the metal porous material 202 is formed on the surface of the cell walls 42 of the resin foam 4; and then, by heating the resin foam 4, the pore-forming material 213 and the cell walls 42 are removed, thereby forming the metal porous material 202.

[0059] In the manufacturing method of this embodiment, first, a pore-forming material 213 is attached to the surface of the hydrogen storage alloy particle 3. The configuration of the hydrogen storage alloy particle 3, the configuration of the pore-forming material 213, and the amount of the pore-forming material 213 attached used in the manufacturing method of this embodiment are the same as those of the hydrogen storage alloy particle 3 and the pore-forming material 213 in the first embodiment.

[0060] Next, the hydrogen storage alloy particles 3 with the pore-forming material 213 attached thereto are mixed with an expandable resin, and the expandable resin is then expanded to produce a resin foam 4 containing the hydrogen storage alloy particles 3. The cells 41 of the resin foam 4 obtained in this manner have an open pore structure, i.e., a structure in which multiple cells are interconnected. Furthermore, the cell walls 42 of the resin foam 4 have a three-dimensional network structure having columnar struts 421 and hubs 422 where multiple struts 421 are aggregated, as shown in FIG. 4 . The hydrogen storage alloy particles 3 are held within the cell walls 42 of the resin foam 4.

[0061] There are no particular limitations on the foamable resin used to produce the resin foam 4, and any known foamable resin capable of forming an open pore structure can be used. For example, the resin constituting the resin foam 4 may be polyurethane, polyethylene, polystyrene, etc. Furthermore, there are no particular limitations on the method for foaming the foamable resin, and any known foaming method can be used.

[0062] It is preferable that the content of hydrogen storage alloy particles 3 in the resin foam 4 is, for example, in the range of 1 volume % or more and 55 volume % or less relative to the apparent volume of the resin foam 4, i.e., the volume of the resin foam 4 including the volume of the air bubbles 41.

[0063] By setting the content of hydrogen storage alloy particles 3 in the resin foam 4 to preferably 10 volume % or more, more preferably 20 volume % or more, and even more preferably 30 volume % or more of the apparent volume of the resin foam 4, the amount of hydrogen storage alloy particles 3 held in the hydrogen storage material 102 can be increased, and the amount of hydrogen that can be absorbed by the hydrogen storage material 102 can be increased.

[0064] The content of the hydrogen storage alloy particles 3 in the resin foam 4 can be adjusted by the mixing ratio of the expandable resin to the hydrogen storage alloy particles 3 and the expansion ratio of the expandable resin.

[0065] After obtaining a resin foam 4 containing hydrogen storage alloy particles 3 and having an open pore structure as described above, a metal film is formed on the surfaces of the cell walls 42 of the resin foam 4. While the method for forming the metal film on the surfaces of the cell walls 42 is not particularly limited, from the viewpoint of forming a metal film evenly over the entire resin foam 4, it is preferable to form the metal film on the surfaces of the cell walls 42 by a plating method. The metal constituting the metal film may be any metal other than a hydrogen storage alloy, i.e., any metal that cannot reversibly absorb and release hydrogen and that can be used to form a metal film by a plating method. Examples of metals that can be used to form the metal film include iron alloys, copper, copper alloys, chromium, chromium alloys, nickel, and nickel alloys.

[0066] The molded body is then heated at a temperature higher than the thermal decomposition temperature of the pore-forming material 213 and the thermal decomposition temperature of the cell walls 42 in the resin foam 4 (i.e., the thermal decomposition temperature of the resin that constitutes the resin foam 4), but lower than the melting point of the hydrogen storage alloy particles 3. When the molded body is heated at such a temperature, the pore-forming material 213 attached to the periphery of the hydrogen storage alloy particles 3 disappears due to thermal decomposition, and storage spaces 211 are formed around the hydrogen storage alloy particles 3. Furthermore, the cell walls 42 in the resin foam 4 disappear due to thermal decomposition, leaving behind metal films, and a metal porous body 202 is formed that has a three-dimensional network structure that reflects the shape of the cell walls 42 in the resin foam 4.

[0067] As described above, a hydrogen storage material 102 having the above-described structure can also be obtained by heating a resin foam 4 containing hydrogen storage alloy particles 3 and removing the pore-forming material 213 and the cell walls 42 of the resin foam 4.

[0068] (Experimental Example 1) In this example, an example is described in which a hydrogen storage material in embodiment 1 was produced using hydrogen storage alloy particles made of LaNi5 and having a particle diameter of 100 μm and metal powder made of stainless steel and having an average particle diameter of 3 μm.

[0069] In this example, polyvinyl acetate was dissolved in acetone to prepare a 5% by mass solution of the pore-forming aid. Next, 50 parts by mass of the pore-forming aid solution was added to 100 parts by mass of the hydrogen storage alloy particles, and the mixture was thoroughly mixed and dried to adhere the pore-forming aid to the surfaces of the hydrogen storage alloy particles.

[0070] Next, a pore-forming agent was added to the hydrogen storage alloy particles and thoroughly mixed to adhere the pore-forming agent to the surfaces of the hydrogen storage alloy particles. The pore-forming agent used was spherical resin particles made of polymethyl methacrylate and having an average particle size of 10 μm ("Ganzpearl (registered trademark) GM-1001" manufactured by Aica Kogyo Co., Ltd.). The amount of pore-forming agent added was 10 parts by mass per 100 parts by mass of the hydrogen storage alloy particles before the pore-forming aid was attached.

[0071] Separately from the preparation of the hydrogen storage alloy particles, polyvinyl alcohol was dissolved in distilled water to prepare a dispersion medium with a polyvinyl alcohol concentration of 10 mass %.

[0072] The hydrogen storage alloy particles thus obtained were mixed with a metal powder and a dispersion medium to prepare a slurry mixture. The amount of metal powder in the mixture was 66 parts by mass per 100 parts by mass of the hydrogen storage alloy particles before the pore-forming material was attached. The amount of binder solution in the mixture was 59 parts by mass per 100 parts by mass of the hydrogen storage alloy particles before the pore-forming material was attached.

[0073] The mixture obtained as described above was poured into a rectangular parallelepiped mold having a length of 50 mm, a width of 10 mm, and a thickness of 5 mm, and then cooled to a temperature of -18°C or lower. This caused the mixture in the container to gel, resulting in a molded body. This molded body was dried to remove the distilled water, and then heated at 500°C for 2 hours in an inert gas atmosphere to thermally decompose the pore-forming material, pore-forming aid, and polyvinyl alcohol in the molded body. The molded body was then heated at 750°C for 3 hours to sinter the metal powder and form a metal porous body. In this manner, a hydrogen storage body was obtained.

[0074] 5 and 6 show examples of SEM images of the surface of a hydrogen storage material 103 obtained by observing the surface of the hydrogen storage material using a scanning electron microscope. As shown in Fig. 5, the hydrogen storage material 103 has a metal porous body 2 with a large number of pores 21, and it can be seen that the pores 21 are open on the surface of the metal porous body 2. It can also be seen that the metal porous body 2 contains hydrogen storage alloy particles 3, which are shown in a lighter color tone than the metal powder 22 that constitutes the metal porous body 2.

[0075] 6, it can be seen that the pores 21 have a storage space 211 and a connection space 212. It can also be seen that hydrogen storage alloy particles 3 are held within the storage space 211, and that voids are formed between the hydrogen storage alloy particles 3 and the metal porous body 2. It can also be seen that the metal porous body 2 is made of a sintered body of metal powder 22, and that connection spaces 212 are formed between the metal particles that make up the metal powder 22.

[0076] The circumscribed circle equivalent diameter d of the hydrogen storage alloy particle 3 accommodated in the accommodation space 211 measured based on FIG. MH is 102 μm, and the diameter D of the smallest circle circumscribing the opening of the accommodation space 211 is max is 223 μm, and the diameter D of the largest circle inscribed in the opening of the accommodation space 211 is min Therefore, the circumscribed circle equivalent diameter d of the hydrogen storage alloy particle 3 calculated from these values ​​is MH The opening diameter D of the accommodation space 211 in which the hydrogen storage alloy particles 3 are accommodated is opening Ratio D opening / d MH The value of is 1.68.

[0077] Table 1 shows the results of the above-mentioned d for five openings, including the opening shown in FIG. 6, among the openings present on the surface of the hydrogen absorbing material 103 of this example. MH , D max and D min The results of measuring the values ​​of D are shown in Table 1. The ratio D is calculated based on these values. opening / d MH The arithmetic mean value of the values ​​was 1.69. Meanwhile, it is known that the volume expansion ratio when hydrogen is absorbed into LaNi5 constituting the hydrogen storage alloy particles 3 of this example is about 27% (for example, Yasuaki Osumi, "Hydrogen Storage Alloys - Their Properties and Applications," Agne Technology Center, New Edition, Third Printing, 2008, pp. 65-67). Therefore, the volume expansion ratio when hydrogen is absorbed into the hydrogen storage alloy particles 3 is about 1.27, and the cube root of this is about 1.08.

[0078]

[0079] Experimental Example 2 In this example, a hydrogen storage material 104 was fabricated in the same manner as in Experimental Example 1, except that spherical resin particles made of polymethyl methacrylate and having an average particle diameter of 3 μm ("Ganzpearl GM-0205S" manufactured by Aica Kogyo Co., Ltd.) were used as the pore-forming material. FIG. 7 shows an enlarged photograph of an opening on the surface of the hydrogen storage material 104. As shown in FIG. 7, the metal porous body 2 in this example has pores 21 each having a storage space 211 and a connection space 212, similar to the hydrogen storage material 103 in Experimental Example 1. Furthermore, hydrogen storage alloy particles 3 are held within the storage space 211, and voids are formed between the hydrogen storage alloy particles 3 and the metal porous body 2. Furthermore, the metal porous body 2 is composed of a sintered body of metal powder 22, and connection spaces 212 are formed between the metal particles constituting the metal powder 22.

[0080] The circumscribed circle equivalent diameter d of the hydrogen storage alloy particle 3 accommodated in the accommodation space 211 measured based on FIG. MH is 124 μm, and the diameter D of the smallest circle circumscribing the opening of the accommodation space 211 is max is 306 μm, and the diameter D of the largest circle inscribed in the opening of the accommodation space 211 is min Therefore, the circumscribed circle equivalent diameter d of the hydrogen storage alloy particle 3 calculated from these values ​​is MH The opening diameter D of the accommodation space 211 in which the hydrogen storage alloy particles 3 are accommodated is opening Ratio D opening / d MH The value of is 1.89.

[0081] Table 2 shows the results of the above-mentioned d for six openings, including the opening shown in FIG. 7, among the openings present on the surface of the hydrogen absorbing material 104 of this example. MH , D max and D min The results of measuring the values ​​of D are shown in Table 1. The ratio D is calculated based on these values. opening / d MHThe arithmetic mean value of the values ​​was 2.75. On the other hand, since the hydrogen storage alloy particles 3 of this example were composed of LaNi5 like the hydrogen storage alloy particles 3 of Experimental Example 1, the volume expansion ratio when hydrogen was absorbed into the hydrogen storage alloy particles 3 was about 1.25, and the cube root of this was about 1.08.

[0082]

[0083] As described above, according to the methods of Experimental Examples 1 and 2, a metal porous body having pores and hydrogen storage alloy particles made of a hydrogen storage alloy and held in the storage spaces of the pores are provided, and the circumscribed circle equivalent diameter d of the hydrogen storage alloy particles is MH The opening diameter D of the storage space in which the hydrogen storage alloy particles are stored opening Ratio D opening / d MH It was possible to obtain a hydrogen storage material in which the average value of is equal to or greater than the cube root of the volume expansion ratio when hydrogen is absorbed into the hydrogen storage alloy particles.

[0084] (Embodiment 3) In this embodiment, an example of the use of the hydrogen absorbing material 1 will be described. The hydrogen absorbing material 1 may be applied to hydrogen-related equipment configured to be able to reversibly absorb and release hydrogen. For example, the hydrogen absorbing material 1 of this embodiment is used in a hydrogen container 5 configured to be able to reversibly absorb and release hydrogen, as shown in FIG. 8.

[0085] The hydrogen container 5 has a container body 51 with a storage space 511 for storing hydrogen gas, a hydrogen storage material 1 arranged in the storage space 511, and a temperature adjustment means 52 configured to change the temperature of the hydrogen storage material 1.

[0086] The container body 51 of the hydrogen container 5 is configured to be able to retain hydrogen supplied from outside the hydrogen container 5 and hydrogen released from the hydrogen absorbing material 1 in the storage space 511. The container body 51 has at least one hydrogen port 53 configured to connect the outside of the hydrogen container 5 to the storage space 511. The hydrogen port 53 is configured to connect the external space to the storage space 511, thereby allowing hydrogen to be supplied from outside the hydrogen container 5 to the storage space 511 and / or hydrogen to be released from the hydrogen container 5 to the outside. The number of hydrogen ports 53 provided on the container body 51 may be one or two or more. For example, as shown in FIG. 8 , the container body 51 of this embodiment has one hydrogen port 53, and is configured so that the hydrogen port 53 can be used both to supply hydrogen from outside the hydrogen container 5 to the storage space 511 and to release hydrogen from the hydrogen container 5 to the outside.

[0087] The shape of the container body 51 is not particularly limited, and various shapes such as a cylindrical shape, a spherical shape, a box shape, etc. For example, the container body 51 of this embodiment has a cylindrical shape as shown in FIG.

[0088] The volume of the container body 51 is 300 m ３ The pressure fluctuation when releasing hydrogen from the hydrogen container 5 tends to increase as the volume of the container body 51 decreases. ３ By setting the volume of the vessel body 51 to 300 m or less, the effect of suppressing the pressure fluctuation during hydrogen release can be more effectively achieved. ３ By adopting the following configuration, the hydrogen container 5 can be easily made smaller, and restrictions on installation location can be reduced.

[0089] The maximum value of the internal pressure of the container body 51 is preferably 1 MPa (G) or less in terms of gauge pressure. ３ In addition to keeping the maximum internal pressure of the container body 51 at 1 MPa (G) or less, the safety of the container body 51 can be improved and maintenance of the container body 51 can be made easier.

[0090] The hydrogen absorbing material 1 is provided in the storage space 511 of the container body 51. The number, shape, arrangement, etc. of the hydrogen absorbing materials 1 provided in the container body 51 are not particularly limited, and can be set appropriately depending on the desired maximum hydrogen storage amount, the pressure when releasing hydrogen from the hydrogen container 5, etc.

[0091] The temperature adjustment means 52 changes the temperature of the hydrogen absorbing body 1, thereby releasing hydrogen absorbed in the hydrogen absorbing body 1 from the hydrogen absorbing body 1 to the storage space 511, or absorbing hydrogen in the storage space 511 into the hydrogen absorbing body 1. The method by which the temperature adjustment means 52 changes the temperature of the hydrogen absorbing body 1 is not particularly limited and various embodiments are possible. For example, the temperature adjustment means 52 in this embodiment is configured to change the temperature of the hydrogen absorbing body 1 by heating or cooling the entire container body 51. Therefore, for example, by increasing the temperature of the hydrogen absorbing body 1 with the temperature adjustment means 52, hydrogen can be released from the hydrogen absorbing body 1 to the storage space 511. Also, for example, by lowering the temperature of the hydrogen absorbing body 1, hydrogen in the storage space 511 can be absorbed into the hydrogen absorbing body 1.

[0092] As described above, the hydrogen storage alloy particles 3 in the hydrogen storage material 1 are held within the pores 21 of the metal porous body 2. Therefore, the hydrogen storage material 1 can reduce the amount of change in volume when hydrogen is absorbed. Therefore, by applying the hydrogen storage material 1 to the hydrogen container 5 as in this embodiment, the load applied to the container body 51 when hydrogen is absorbed into the hydrogen storage material 1 can be more easily reduced, making it less likely that distortion will occur in the container body 51. Furthermore, in this case, hydrogen can be stored more efficiently in the hydrogen container 5.

[0093] The hydrogen absorbing material 1 used in the hydrogen container 5 preferably has hydrogen storage alloy particles made of a TiFe-based hydrogen storage alloy. Because TiFe-based hydrogen storage alloys are easy to handle, applying hydrogen storage alloy particles made of a TiFe-based hydrogen storage alloy to the hydrogen absorbing material 1 of the hydrogen container 5 can further improve the safety of the hydrogen container 5. In addition, because TiFe-based hydrogen storage alloys are relatively inexpensive among hydrogen storage alloys, further cost reductions in the hydrogen container 5 can be expected.

[0094] The TiFe-based alloys described above include TiFe binary alloys and TiFe-based multi-component alloys in which part of the Ti and / or Fe in the TiFe binary alloy is replaced with another element. The TiFe-based alloy may be, for example, a TiFeMn ternary alloy in which part of the Fe in the TiFe binary alloy is replaced with Mn. The TiFe-based alloy may also be a multi-component alloy obtained by further adding another metal element to the TiFeMn ternary alloy.

[0095] The above describes aspects of the hydrogen storage material and its manufacturing method based on embodiments and experimental examples, but the specific aspects of the hydrogen storage material and its manufacturing method according to the present invention are not limited to the above embodiments and experimental examples, and the configuration can be changed as appropriate within the scope that does not deviate from the gist of the present invention.

Claims

1. A porous metal body having pores, A hydrogen storage body comprising hydrogen storage alloy particles held within the pores of the porous metal body, A portion of the surface of the hydrogen storage alloy particles is bonded to the porous metal body, thereby fixing it to the inner surface of the porous metal body. The aforementioned pores have a containment space in which the hydrogen storage alloy particles are contained, The circumscribed diameter d of each hydrogen storage alloy particle obtained by observing the surface of the hydrogen storage material ＭＨ The opening diameter D of the containment space containing the hydrogen storage alloy particles, as shown in formula (1) below, relative to (unit: μm). ｏｐｅｎｉｎｇ Ratio D (unit: μm) ｏｐｅｎｉｎｇ / d ＭＨ A hydrogen storage material in which the average value of is greater than or equal to the cube root of the volume expansion ratio when hydrogen is absorbed into the hydrogen storage alloy particles. D ｏｐｅｎｉｎｇ =(D ｍａｘ +D ｍｉｎ ) / 2 ・・・(1) (However, D in the formula (1)) ｍａｘ is the diameter (unit: μm) of the smallest circle among the circles circumscribing the opening of the accommodation space on the surface of the hydrogen storage body, and D ｍｉｎ is the diameter (unit: μm) of the largest circle among the circles inscribed in the opening of the accommodation space on the surface of the hydrogen storage body.)

2. The hydrogen storage body according to claim 1, wherein the pores have connecting spaces that connect the storage space with an adjacent storage space, and the storage space with the outside of the porous metal body.

3. The hydrogen storage material according to claim 2, wherein the diameter of the largest circle inscribed in the opening of the connection space on the surface of the hydrogen storage material is smaller than the median diameter of the hydrogen storage alloy particles on a volume basis.

4. The hydrogen storage body according to any one of claims 1 to 3, wherein the metal porous body is a sintered product of metal powder.

5. The hydrogen storage material according to claim 4, wherein the median diameter on a volume basis of the metal powder constituting the metal powder is smaller than the median diameter on a volume basis of the hydrogen storage alloy particles.

6. The hydrogen storage body according to any one of claims 1 to 3, wherein the porous metal body has a three-dimensional network structure consisting of columnar struts and hubs formed by the aggregation of a plurality of the struts.

7. A method for producing a hydrogen storage body according to claim 4, A pore-forming material is attached to the surface of the hydrogen storage alloy particles. Subsequently, the hydrogen storage alloy particles and the metal powder that forms the porous metal body are mixed to produce a mixture. The mixture is molded to produce a molded body, A method for manufacturing a hydrogen storage body, comprising heating the molded body to remove the pore-forming material and sinter the metal powder to form the metal porous body.

8. The method for producing a hydrogen storage body according to claim 7, wherein the median diameter of the metal powder on a volume basis is smaller than the median diameter of the hydrogen storage alloy particles on a volume basis.

9. The method for producing a hydrogen storage body according to claim 7, wherein in forming the metal porous body, the heating is performed at a temperature higher than the thermal decomposition temperature of the pore-forming material and the sintering temperature of the metal powder, and lower than the melting point of the hydrogen storage alloy particles.

10. A method for producing a hydrogen storage body according to claim 6, A pore-forming material is attached to the surface of the hydrogen storage alloy particles. Subsequently, a resin foam containing the hydrogen storage alloy particles and having a continuous porous structure is prepared. A metal film that forms the metal porous body is formed on the surface of the cell wall of the resin foam. A method for producing a hydrogen storage body, comprising subsequently heating the resin foam to remove the pore-forming material and the bubble walls to form the metal porous body.

11. The method for producing a hydrogen storage body according to claim 10, wherein in forming the metal porous body, the heating is performed at a temperature higher than the thermal decomposition temperature of the pore-forming material and the thermal decomposition temperature of the bubble walls in the resin foam, and lower than the melting point of the hydrogen storage alloy particles.

12. A hydrogen container equipped with a hydrogen storage body according to any one of claims 1 to 3.

13. The hydrogen container according to claim 12, wherein the hydrogen storage alloy particles in the hydrogen storage body are composed of a TiFe-based hydrogen storage alloy.