Hydrogen storage material, hydrogen storage container, and hydrogen supply device

Abstract

Provided is a hydrogen storage material that has a TiFe-based alloy that exhibits an excellent durability, an excellent initial activation, and also a satisfactory hydrogen storage amount and satisfactory hydrogen storage / release characteristics. Also provided are: a hydrogen storage container provided with the hydrogen storage material; and a hydrogen supply device provided with the hydrogen storage container. The hydrogen storage material has an alloy with the prescribed element composition given by formula (1), wherein, in a 1000X COMP image of this alloy provided by EPMA of its cross section, an La-concentrated phase having a phase diameter of 0.1 μm to 10 μm is present at 10 to 3000 times in an 85 μm × 120 μm field of view in the COMP image. The hydrogen storage container is provided with this hydrogen storage material, and the hydrogen supply device is provided with this hydrogen storage container. (1): Ti(1-a-b)LaaM1bFecMndM2eCf

Description

Hydrogen storage material, hydrogen storage container and hydrogen supply device

[0001] The present invention relates to a hydrogen storage material, a hydrogen storage container, and a hydrogen supply device.

[0002] Hydrogen absorbing (storage) alloys are alloys that can reversibly absorb and release hydrogen, and are already used as negative electrode materials in nickel-metal hydride secondary batteries. In recent years, however, they have also been expected to be materials that can safely store hydrogen, which has attracted attention as an energy source, and efforts are being made to put them to practical use in hydrogen storage and supply systems. There are various types of hydrogen absorbing alloys, including AB5-based, AB2-based, TiFe-based, and BCC-based alloys such as TiVCr. Of these, TiFe-based alloys are the cheapest raw materials, and are the most promising materials for hydrogen storage applications, which require quantities far exceeding those used in batteries.

[0003] However, TiFe alloys are difficult to activate, requiring a temperature of 400°C or higher and a pressure of 3 MPa or higher for initial activation, making them difficult to use. It is known that various additive elements are effective in improving this, and the following patent documents, for example, disclose such techniques:

[0004] In Patent Document 1, the rational formula Ti １＋ｋ Fe １－ｌ Mn ｌ A ｍ (where 0≦k≦0.3, 0<l≦0.3, 0<m≦0.1, and A is at least one element selected from the group consisting of niobium and rare earth elements.) Furthermore, it is disclosed that by adding Mn and element A (at least one element selected from the group consisting of Nb and rare earth elements) to a TiFe alloy, an alloy that is easy to activate and has a sufficient hydrogen storage capacity can be obtained.

[0005] Patent Document 2 describes a compound of the general formula (T １－ａ Fe ａ ) １００－ｂ－ｃ－ｄ La ｂ M ｃ M' ｄ(wherein T is at least one element selected from Ti, Zr, and Hf; M is at least one element selected from V, Nb, Ta, Cr, Mo, and W; M' is at least one element selected from Mn, Co, Ni, Cu, Zn, B, Al, Ge, and Sn; a is an atomic ratio of 0.45≦a≦0.55; and b, c, and d are, in atomic percent, 0.01≦b≦10, 0≦c≦20, and 0≦d≦30, respectively), and characterized in that a fine crystalline phase with a grain size of 10 μm or less is precipitated in at least a part of the alloy structure. Furthermore, it is disclosed that a hydrogen storage alloy with excellent hydrogen storage properties and corrosion resistance can be obtained by appropriately setting the types of elements constituting the T component, Fe component, La component, M component, and M' component in the general formula and the composition ratio of each component, and then cooling and solidifying the alloy and then performing a heat treatment to precipitate a fine crystalline phase.

[0006] Patent Document 3 describes a compound of the general formula A ａ T ｂ M ｃ M' ｄ (wherein A is at least one element selected from Ti, Zr, Hf, and V; T is at least one element selected from Ni, Co, Fe, Cu, Mn, and Cr; M is at least one element selected from Al, Si, Ga, Ge, Zn, Sn, In, and Sb; M' is at least one element selected from B, C, N, and P; and a, b, c, and d are, in atomic %, 20≦a≦70, 30≦b≦60, 5≦c≦40, 0.1≦d≦10, and a+b+c+d=100, respectively), and characterized in that a fine crystalline phase with a grain size of 10 μm or less is precipitated in at least a part of the alloy structure. Furthermore, it is disclosed that a hydrogen storage alloy with excellent hydrogen storage properties and corrosion resistance can be obtained by appropriately setting the types of elements constituting the A component, T component, M component, and M' component in the general formula and the composition ratio of each component, and then cooling and solidifying the alloy and then performing a heat treatment to precipitate a fine crystalline phase.

[0007] JP-A No. 61-250136 JP-A No. 10-265875 JP-A No. 10-265888

[0008] The addition of rare earth elements, as described in Patent Documents 1 and 2, is effective in improving initial activation, increasing storage capacity, increasing equilibrium pressure during hydrogen absorption and desorption, and eliminating the two-stage plateau. However, excessive addition of rare earth elements increases the oxygen value of the alloy, which has the disadvantage of reducing durability. Therefore, the present invention aims to provide a hydrogen storage material containing a TiFe-based alloy that exhibits excellent durability, good initial activation, and sufficient hydrogen absorption and desorption capacity while reducing the amount of rare earth elements added. It is also an object of the present invention to provide a hydrogen storage container comprising the hydrogen storage material, and a hydrogen supply device comprising the hydrogen storage container.

[0009] As a result of extensive research to solve the above problems, the present inventors discovered an alloy having a specific element composition containing Ti, La, and Fe, and completed the present invention.

[0010] That is, according to the present invention, there is provided a hydrogen storage material comprising an alloy having an elemental composition represented by the following formula (1), wherein, in a COMP image of a cross section of the alloy taken by EPMA at 1000x magnification, there are 10 to 3000 phases in which a rare earth element (La in the alloy of the present invention) is concentrated and which have a phase diameter of 0.1 μm to 10 μm within a field of view of 85 μm × 120 μm in the COMP image. [In formula (1), M1 represents at least one element selected from the group consisting of V, Zr, Nb, and Ta, and M2 represents at least one element selected from transition metal elements (excluding rare earth elements, M1, Ti, Fe, and Mn), Al, B, Ga, Si, and Sn. Here, rare earth elements include Sc and Y. a represents 0.0011≦a≦0.016, b represents 0≦b≦0.20, c represents 0.40≦c≦1.15, d represents 0≦d≦0.40, e represents 0≦e≦0.20, f represents 0≦f≦0.07, and c+d+e represents 0.60≦c+d+e≦1.20.]

[0011] According to another aspect of the present invention, there are provided a hydrogen storage container including the above-mentioned hydrogen storage material, and a hydrogen supply device including the hydrogen storage container.

[0012] Since the hydrogen storage material of the present invention contains an alloy with the above-mentioned specific element composition, it has excellent durability, good initial activation, and exhibits sufficient hydrogen absorption capacity and hydrogen absorption / desorption characteristics, making it suitable for use in hydrogen storage.

[0013] Fig. 1 is a COMP image photograph of a cross section of a heat-treated alloy flake of Example 1. Fig. 2 is a COMP image photograph of a cross section of a heat-treated alloy flake of Comparative Example 1. Fig. 3 is a COMP image photograph of a cross section of a heat-treated alloy flake of Comparative Example 3. Fig. 4 is a hydrogen pressure-composition isotherm diagram (PCT curve) at 30°C for the alloy powder of Example 1 and the alloy powder of Comparative Example 1.

[0014] The present invention will be described in detail below. The hydrogen storage material of the present invention is a material having an alloy with an elemental composition represented by the following formula (1). Preferably, the material is made of the alloy. [In formula (1), M1 represents at least one element selected from the group consisting of V, Zr, Nb, and Ta, and M2 represents at least one element selected from transition metal elements (excluding rare earth elements, M1, Ti, Fe, and Mn), Al, B, Ga, Si, and Sn. Here, rare earth elements include Sc and Y. a represents 0.0011≦a≦0.016, b represents 0≦b≦0.20, c represents 0.40≦c≦1.15, d represents 0≦d≦0.40, e represents 0≦e≦0.20, f represents 0≦f≦0.07, and c+d+e represents 0.60≦c+d+e≦1.20.]

[0015] In formula (1), a, b, c, d, e, and f represent the content ratio of each element as a molar ratio, and the details are as follows. Hereinafter, the content ratio may be referred to as the "content" or "amount."

[0016] La in formula (1) is effective in improving initial activation, increasing the amount of hydrogen storage, increasing the equilibrium pressure during hydrogen storage and desorption, and eliminating the two-stage plateau in the PCT curve. In formula (1), the La content a is in the range of 0.0011≦a≦0.016, preferably 0.0015≦a≦0.014, and more preferably 0.0020≦a≦0.012.

[0017] In formula (1), M1 is at least one element selected from the group consisting of V, Zr, Nb, and Ta. M1 is not necessarily required, but is an element that mainly contributes to adjusting various properties. For example, the M1 element forms an intermetallic compound with the main constituent elements Ti, Mn, Fe, etc., which has the effect of improving initial activation, and can be added when fine adjustment of properties is required depending on the usage conditions during hydrogen storage. In formula (1), b, which represents the content of M1, is 0≦b≦0.20, preferably 0≦b≦0.05.

[0018] In formula (1), c represents the Fe content. c is 0.40≦c≦1.15, preferably 0.50≦c≦0.95, and more preferably 0.65≦c≦0.95. If the Fe content in the TiFe-based alloy is high and c exceeds 1.15, initial activation becomes difficult, and there is a risk that a sufficient hydrogen storage capacity cannot be obtained when used as a hydrogen storage material. If the Fe content in the TiFe-based alloy is low and c is less than 0.40, the hydrogen storage capacity decreases, and the equilibrium pressure for hydrogen absorption and desorption becomes too low, and there is a risk that the alloy will not function effectively when used as a hydrogen storage material.

[0019] In formula (1), d represents the Mn content. d is 0≦d≦0.40, preferably 0.02≦d≦0.40, more preferably 0.04≦d<0.40, and particularly preferably 0.07≦d≦0.40. When the Mn content in the TiFe-based alloy is high and d exceeds 0.40, the equilibrium pressure for hydrogen absorption and desorption becomes too low, and hydrogen may not be effectively utilized when used as a hydrogen storage material. Conventionally, when the Mn content in the TiFe-based alloy is low, initial activation is difficult, and when used as a hydrogen storage material, a sufficient hydrogen storage capacity cannot be obtained, or the initial activation may require a great deal of effort and time, making it impractical. However, in the present application, even if d is 0, initial activation and hydrogen storage capacity sufficient for practical use can be obtained.

[0020] In formula (1), M2 represents at least one element selected from transition metal elements (excluding rare earth elements, M1, Ti, Fe, and Mn), Al, B, Ga, Si, and Sn. M2 is preferably at least one element selected from Co, Ni, Cu, Cr, Al, B, Ga, Si, and Sn. M2 is not necessarily required, but is an element that mainly contributes to adjusting various properties. For example, it can be contained when fine adjustment of properties is required depending on the usage conditions during hydrogen storage. In formula (1), e, which represents the content of M2, is 0≦e≦0.20, preferably 0≦e≦0.10.

[0021] In formula (1), f represents the content of C (carbon). f is in the range of 0≦f≦0.07, preferably 0.001≦f≦0.05, and more preferably 0.001≦f≦0.04. C is effective in increasing the equilibrium pressure during hydrogen absorption and desorption and in eliminating the two-stage plateau in the PCT curve.

[0022] In addition, La and C in formula (1) are both elements that are effective in increasing the equilibrium pressure during hydrogen absorption and desorption and in eliminating the two-stage plateau in the PCT curve, as described above, but a combination of the two elements can provide even greater effects. In formula (1), it is preferable that f is 0.001≦f and a+f is 0.002≦a+f≦0.05.

[0023] In formula (1), c+d+e represents the total content of Fe, Mn, and M2. This value affects the activation and equilibrium pressure of the hydrogen storage material of the present invention, and by adjusting it within the following range, an alloy can be obtained that is easy to initially activate while maintaining the equilibrium pressure necessary for hydrogen storage. c+d+e is 0.60≦c+d+e≦1.20, preferably 0.65≦c+d+e≦1.15, and more preferably 0.70≦c+d+e≦1.10.

[0024] The elemental composition of the alloy of the present invention represented by the above formula (1) can be confirmed by quantitative analysis using an ICP (Inductively Coupled Plasma) analyzer. In this specification, when referring to the alloy of the present invention, unless otherwise specified, it refers to the alloy having the elemental composition represented by formula (1).

[0025] The alloy of the present invention has the following structural characteristics. Specifically, in a COMP image of a cross section of the alloy taken by an EPMA (Electron Probe Micro Analyzer) at 1000x magnification, a phase enriched in a rare earth element (La in the alloy of the present invention) (hereinafter sometimes referred to as an R-enriched phase) is within a specific size range, and has the following characteristics: That is, the alloy is characterized in that 10 to 3000 R-enriched phases with a phase diameter of 0.1 μm to 10 μm are present within a field of view of 85 μm × 120 μm in the COMP image. Here, a COMP image is an image expressed with a contrast dependent on atomic number, and is also called a backscattered electron composition image.

[0026] Here, the cross section of the alloy refers to a cross section formed by embedding the alloy in a room temperature setting type resin (e.g., epoxy resin), hardening it, and then roughly polishing and precision polishing it with a wet polishing machine, and finally finishing the polished surface to a mirror finish. There is no particular limitation on the size of the alloy when forming the cross section, but for example, an alloy thin piece of about 1 cm square or a 1 cm ３ It is sufficient to use alloy flakes of this order.

[0027] When the cross section of the alloy of the present invention is observed, a sea-island structure is formed in which a plurality of R-enriched phases are present in the main phase of the TiFe-based alloy. The R-enriched phases, which are islands, are dispersed in the main phase of the TiFe-based alloy, which is the sea, as described above. Although the detailed mechanism is unclear, the alloy exhibits good initial activation as a hydrogen storage material and can efficiently and effectively absorb and release hydrogen repeatedly. The elements in the main phase and the R-enriched phases can be confirmed by mapping images of the contained elements obtained by area analysis using EPMA.

[0028] The alloy of the present invention, when crushed and sized to 300 μm to 500 μm, preferably has an oxygen value of 500 ppm or less, more preferably 400 ppm or less, in the powder state. Here, the oxygen value refers to the O value, and hereinafter, all oxygen values ​​refer to the O value. The "O value" is the total amount of oxygen contained in oxygen and oxygen compounds in the alloy powder, expressed as the amount of oxygen atoms. A low oxygen value of an alloy means that the amount of surrounding impurities (O ２It is believed that the lower the oxygen value, the less likely the alloy is to deteriorate when hydrogen is repeatedly absorbed and released, and the more durable the alloy is.

[0029] The alloy of the present invention is preferably sized to 300 μm to 500 μm and subjected to an initial activation process. After this process, the oxygen value of the alloy powder of 150 μm or less resulting from the pulverization of the alloy is preferably 6000 ppm or less, and more preferably 5500 ppm or less. The initial activation process involves pulverizing the alloy to an appropriate degree by absorbing and releasing hydrogen, creating an active surface for the alloy to react with hydrogen. However, pulverization of the alloy also increases the oxygen value, potentially leading to alloy degradation. Therefore, the lower the oxygen value of an alloy pulverized after the initial activation process, the more durable it is and the more suitable it is for use as a hydrogen storage material. The proportion of alloy powder of 150 μm or less after the initial activation process is preferably 5 wt% or more relative to the amount of alloy used in the initial activation process. At this point, the alloy is in a state where it can absorb and release hydrogen sufficiently to function as a hydrogen storage material, meaning that the initial activation is satisfactory.

[0030] The alloy of the present invention has a hydrogen absorption pressure P ａ１ and hydrogen absorption pressure P at 1.3 wt% hydrogen ａ２ where 0≦log １０ (P ａ２ ) -log １０ (P ａ１ )≦0.65, and the hydrogen release pressure P ｂ１ and hydrogen release pressure P at 1.3 wt% hydrogen ｂ２ where 0≦log １０ (P ｂ２ ) -log １０ (P ｂ１)≦0.80. This is because the PCT curve having the above characteristics makes it easier to absorb and release hydrogen, making it a very suitable hydrogen storage material. The relationship between the above two equations is used as an index of "plateau flatness", with the former being an index of "plateau flatness during hydrogen absorption" and the latter being an index of "plateau flatness during hydrogen release". In the PCT curve, when the relationship between the hydrogen absorption pressure and the pressure satisfies the above equation, it has the advantage of making it easier to reach the desired hydrogen absorption capacity in a relatively short time. In addition, in the PCT curve, when the relationship between the hydrogen release pressure and the pressure satisfies the above equation, it has the advantage of making it easier to maintain the required hydrogen pressure at the hydrogen supply destination, thereby ensuring as much usable hydrogen as possible.

[0031] The P ｂ１ is preferably 0.01 MPa or more, more preferably 0.03 MPa or more, and particularly preferably 0.05 MPa or more. This is because hydrogen release becomes better in the temperature range from room temperature to 95°C. ｂ１ There is no particular upper limit to the pressure, but it is substantially about 1.00 MPa.

[0032] In addition, in the PCT desorption curve at 30°C, the hydrogen desorption pressure P ｂ３ and the hydrogen release pressure P at the hydrogen absorption amount +0.30 wt% from the starting point ｂ４ However, 1.2≦[0.2 / {log １０ (P ｂ４ ) -log １０ (P ｂ３ )}] is satisfied. When the PCT curve has the above characteristics, a large amount of hydrogen can be released when hydrogen release is completed at a predetermined pressure, and therefore the hydrogen storage material can be very suitable, as it can effectively utilize the stored hydrogen without leaving it in the alloy. １０ (P ｂ４ ) -log １０ (P ｂ３)} is used as an index showing the quality of the hydrogen release capacity, and for convenience, this value is referred to as the hydrogen release capacity index.

[0033] It is particularly preferable that the entire alloy of the present invention constituting the hydrogen storage material of the present invention satisfies the above relationship in the PCT curve, but it is also acceptable for only a part of the alloy to satisfy the above relationship.

[0034] The main phase of a TiFe-based alloy is a phase primarily containing a TiFe phase (which may contain substitution elements such as Mn). Hereinafter, this may be referred to simply as the main phase. The phase diameter of the main phase is preferably 200 μm or less, more preferably 150 μm or less. The phase diameter of the main phase is preferably 2 μm or more. The rare earth element-enriched phase (R-enriched phase) is a phase formed mostly of rare earth elements, which may also contain C (carbon) (although it may contain small amounts of other additive elements). When observed in the field of view of the cross section, the R-enriched phase is dispersed in the main phase as fine islands with a shape as shown in FIG. 1, and the phase diameter is in the range of 0.1 μm to 10 μm. Here, the phase diameter is the value obtained by measuring the major axis and minor axis of each phase and calculating "(major axis + minor axis) / 2".

[0035] When the alloy of the present invention contains C (carbon), the R-enriched phase contains a relatively large amount of C. Although the detailed mechanism is not clear, it is believed that the inclusion of C in the dispersed R-enriched phase as described above is more effective in increasing the equilibrium pressure during hydrogen absorption / desorption and in eliminating the two-stage plateau in the PCT curve.

[0036] Next, a method for producing the hydrogen storage material of the present invention will be described. First, examples of the method for preparing the alloy include strip casting methods such as a single roll method, a twin roll method, and a disk method, and die casting methods.

[0037] For example, in strip casting, raw materials are prepared that are blended to achieve the desired alloy composition. Next, the blended raw materials are heated and melted under an inert gas atmosphere such as Ar to form a molten alloy. The molten alloy is then poured onto a water-cooled copper roll and rapidly cooled and solidified to obtain an alloy flake. The water-cooled copper roll may also be one with a coating layer containing Ni, Cr, or other elements on its surface. The coating layer may be formed of, for example, a metal, alloy, or ceramic. In metal mold casting, a molten alloy is obtained in a similar manner, and then poured into a water-cooled copper mold, where it is cooled and solidified to obtain an ingot. Strip casting and metal mold casting have different cooling rates. Generally, strip casting is preferred for obtaining an alloy with minimal segregation and a uniform composition distribution. The alloy of the present invention is an alloy in which a fine R-enriched phase is dispersed separately from the main TiFe-based alloy phase. However, since it is preferable that the TiFe-based alloy main phase portion other than the R-enriched phase has a uniform composition distribution, strip casting is also preferred in the present invention. Furthermore, TiFe alloys are very hard and not easy to crush, so strip casting is also preferable in this respect.

[0038] In order to control the number of R-enriched phases with a diameter of 0.1 μm to 10 μm within the range of the present invention, the cooling rate of the molten alloy during the production of alloy flakes is controlled as follows. That is, the cooling rate from the cooling start temperature of the molten alloy (e.g., the temperature at which the molten alloy contacts the roll) until the alloy temperature reaches 950°C is set to 300°C / sec or higher. It is preferably 700°C / sec or higher, more preferably 1000°C / sec or higher, and particularly preferably 1500°C / sec or higher. There is no particular upper limit to this cooling rate, but in practice it is approximately 50,000°C / sec or lower. The cooling start temperature of the molten alloy varies depending on the alloy composition, but is generally in the range of approximately 1300 to 1500°C. There is no particular limit to the cooling rate below 950°C. For example, in the case of a strip casting method, the alloy may be separated from the roll and then cooled to, for example, 100°C or lower by natural cooling.

[0039] Furthermore, in order to obtain an alloy with a more uniform composition distribution in the TiFe-based alloy main phase, it is preferable to heat-treat the alloy flakes obtained by the above cooling. The heat treatment can be carried out in an inert gas atmosphere such as Ar at a temperature range of 700°C to 1250°C. The heat treatment temperature is preferably 900°C to 1150°C, and the heat treatment time is 0.35 hours to less than 48 hours, preferably 2 hours to less than 24 hours. This heat treatment can be carried out in a known heat treatment furnace capable of atmosphere control. For example, a chamber-type batch furnace, a continuous furnace, or a rotary furnace such as a rotary kiln furnace may be used.

[0040] Next, the alloy flakes obtained by casting are pulverized to obtain alloy powder. The pulverization can be carried out using a known pulverizer. The particle size of the alloy powder is preferably 800 μm or less, and more preferably 500 μm or less. There is no particular need to specify a lower limit for the particle size of the alloy powder, but it is substantially about 0.1 μm. Here, the particle size of the alloy powder refers to the diameter measured using a sieve shaker (low tap type).

[0041] The alloy flakes or powders may be subjected to a mechanical alloying treatment using a ball mill or the like to further control the alloy structure. This treatment can improve the initial activation and hydrogen absorption / desorption properties.

[0042] The hydrogen storage material of the present invention may be the powdered alloy itself, or may be a composite obtained by mixing the alloy powder with a resin or the like and molding it into any shape, such as granules, or a composite immobilized in a temperature-controllable material. In this case, the resin functions as a binder for the alloy powder. Mixing can be performed by a known method. For example, mixing can be performed using a mortar, or a rotary mixer such as a double-cone or V-type mixer, or an agitator mixer such as a blade or screw type mixer. It is also possible to mix the alloy flakes and binder while pulverizing them using a pulverizer such as a ball mill or an attritor mill.

[0043] The hydrogen storage container of the present invention is provided with the hydrogen storage material produced as described above, and the container may be made of any known material and shape.

[0044] The hydrogen supply device of the present invention is provided with the hydrogen storage container, and other components may be publicly known.

[0045] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited thereto. In the description of these examples, both the alloys of the present invention in the examples and the alloys outside the present invention in the comparative examples will be referred to as "alloys." Furthermore, alloys obtained in the form of flakes by strip casting will be referred to as alloy flakes, and the alloy flakes crushed will be referred to as alloy powder.

[0046] Example 1: Raw material metals were weighed so that the elemental composition of the final alloy would be as shown in Table 1, and the materials were melted in an argon gas (Ar) atmosphere in a high-frequency melting furnace to produce a molten alloy. The molten alloy was then poured at a temperature of 1450°C and rapidly cooled and solidified by strip casting using a single-roll casting machine with a water-cooled copper roll, yielding alloy flakes with a thickness variation of approximately 0.1 to 0.4 mm and an average thickness of 0.25 mm. The cooling start temperature of the molten alloy, i.e., the temperature at the time of contact with the water-cooled copper roll, was approximately 1400°C. There was a difference in cooling rate between the roll contact side and the non-contact side of the molten alloy, with the cooling rate from 1400°C to 950°C ranging from 2000°C / s to 3000°C / s.

[0047] The alloy flakes obtained above were heat-treated in a heat treatment furnace in an Ar atmosphere at 1050°C for 6 hours. After the heat treatment, the alloy flakes were embedded in epoxy resin and hardened, then roughly polished and precisely polished with a wet polisher, and finally the polished surface was finished to a mirror finish to form an alloy cross section. The cross section was then examined using a FE (Field Emission) type EPMA (manufactured by JEOL Ltd., product name: JXA-8530F) at a magnification of 1000x, an accelerating voltage of 15 kV, and a current of 1 x 10 -7 A, area analysis (COMP image, mapping image of each element) was performed under the condition of a beam diameter of 1 μm. The number of R-enriched phases with a phase diameter of 0.1 to 10 μm was counted visually within a field of view of 85 μm x 120 μm in the COMP image. This count will be referred to as the "number of R-enriched phases." The results are shown in Table 1. A copy of the COMP image of the alloy cross section is also shown in Figure 1.

[0048] In addition, the alloy flakes after the heat treatment were crushed in a stainless steel mortar and sieved using sieves with 300 μm and 500 μm openings to obtain alloy powders of 300 μm to 500 μm for alloy oxygen value measurement and pulverization tests, and alloy powders of 500 μm or less for PCT curve measurement.

[0049] [Measurement of Alloy Oxygen Value] The oxygen values ​​of the obtained alloy powders of 300 μm to 500 μm were measured using an oxygen and nitrogen analyzer (ON836 manufactured by LECO Corporation). The results are shown in Table 1.

[0050] [Pulverization Test] A pulverization test of the obtained 300 μm to 500 μm alloy powder was performed using an automatic PCT measurement high-pressure Sieverts device (manufactured by Hughes Technonet Co., Ltd.). Approximately 5 g of alloy powder was loaded into a sample chamber with a pressure accumulator, piping, and sample loading section, with a total volume of approximately 138 ml, and the following procedures (1) to (3) were performed. (1) Vacuuming was performed at 85°C for approximately 2 hours. (2) After pressurizing with a hydrogen pressure of approximately 2.7 MPa, the temperature was changed to -20°C and hydrogen was absorbed until the hydrogen pressure stabilized. (3) Steps (1) and (2) were repeated three times, followed by vacuuming at 85°C for approximately 5 hours to dehydrogenate. The processed alloy powder was classified using a sieve with 150 μm openings, and the oxygen value of alloy powder of 150 μm or less was measured. The ratio (wt %) of the weight of the alloy powder of 150 μm or less to the weight of the alloy powder before the test was taken as the pulverization rate. The results are shown in Table 1.

[0051] [Hydrogen Pressure-Composition Isotherm (PCT Curve) Measurement] The hydrogen absorption / desorption characteristics of the resulting alloy powders (500 μm or less) were measured using an automatic high-pressure PCT measurement system (manufactured by Hughes Technonet Co., Ltd.), and PCT curves were obtained. Prior to the measurement, a sample chamber filled with approximately 5 g of alloy powder was first evacuated at 85°C for approximately 2 hours, then pressurized to a hydrogen pressure of approximately 2.7 MPa. Finally, hydrogen was absorbed at 0°C until the hydrogen pressure stabilized. This series of operations was repeated three times to perform initial activation. After evacuating the sample for two hours at 85°C (vacuum level: approximately 0.5 to 2.5 Pa), the hydrogen pressure was varied between 0.01 MPa and approximately 2 MPa at a measurement temperature of 30°C, and the equilibrium pressure for hydrogen absorption and desorption was measured. Figure 4 shows the hydrogen pressure-composition isotherm (PCT curve) at 30°C. The hydrogen absorption capacity at a storage pressure of 1.0 MPa was also determined from the PCT curve during hydrogen absorption. The results are shown in Table 2.

[0052] [Plateau Flatness] Based on the obtained PCT curve, the plateau flatness values ​​for both hydrogen absorption and hydrogen desorption were obtained. For the absorption side, the plateau flatness values ​​for the absorption pressure P ａ１ and the absorption pressure P at 1.3 wt% hydrogen ａ２ Read the value of １０ (P ａ２ ) -log １０ (P ａ１ ) was used. For the release side, the value obtained by calculating the release pressure P ｂ１ and the release pressure P at 1.3 wt% hydrogen ｂ２ Read the value of １０ (P ｂ２ ) -log １０ (P ｂ１ The results are shown in Table 2.

[0053] [Hydrogen Release Capacity Index] From the obtained PCT curve, the intersection point between the equilibrium pressure of 0.01 MPa and the release curve is taken as the starting point, and the hydrogen release pressure P ｂ３ and the hydrogen release pressure P at the hydrogen storage amount +0.30 wt% from the starting point ｂ４ is read and [0.2 / {log １０ (Pｂ４ ) -log １０ (P ｂ３ The results are shown in Table 2.

[0054] (Examples 2 to 12) Alloy flakes and alloy powders for each example were prepared in the same manner as in Example 1, except that the elemental composition of the final alloy and the heat treatment conditions were changed as shown in Table 1. Area analysis of the alloy cross section, counting of R-enriched phases, measurement of alloy oxygen value, pulverization test, and PCT curve measurement were performed. Furthermore, the plateau flatness and hydrogen desorption capacity index during hydrogen absorption and hydrogen desorption were calculated from the PCT curve. The pouring temperature, cooling start temperature, and cooling rate of the alloy melt in these examples were approximately the same as in Example 1, at 1450°C, 1400°C, and between 2000°C / sec and 3000°C / sec. The results are shown in Tables 1 and 2.

[0055] Comparative Examples 1 to 4 Alloy flakes and alloy powders for each comparative example were prepared in the same manner as in Example 1, except that the elemental composition of the final alloy and the heat treatment conditions were changed as shown in Table 1. Area analysis of the alloy cross section, counting of R-enriched phases, alloy oxygen value measurement, pulverization test, and PCT curve measurement were performed. Furthermore, the plateau flatness and hydrogen desorption capacity index during hydrogen absorption and hydrogen desorption were calculated from the PCT curve. The pouring temperature, cooling start temperature, and cooling rate of the alloy melt for these comparative examples were 1450°C, 1400°C, and between 2000°C / sec and 3000°C / sec, which were almost the same as those for Example 1. The results are shown in Tables 1 and 2. A copy of the COMP image of the alloy cross section for Comparative Example 1 is shown in Figure 2, and a copy of the COMP image of the alloy cross section for Comparative Example 3 is shown in Figure 3.

[0056]

[0057]

[0058] As is clear from the table, the alloys of each example have lower alloy oxygen values ​​and alloy oxygen values ​​after the pulverization test than the alloys of each comparative example, and therefore have excellent durability.The pulverization rate after the initial activation treatment is also sufficient, so the initial activation is good, and the alloys have sufficient hydrogen storage capacity and hydrogen absorption / desorption characteristics.

Claims

1. A hydrogen storage material comprising an alloy having an elemental composition represented by the following formula (1), wherein in a COMP image of a cross section of the alloy taken by EPMA at 1000 times, there are 10 to 3000 La-enriched phases having a phase diameter of 0.1 μm to 10 μm within a visual field of 85 μm x 120 μm in the COMP image. [In formula (1), M1 is at least one selected from the group consisting of V, Zr, Nb and Ta, and M2 is at least one selected from transition metal elements (excluding rare earth elements, M1, Ti, Fe and Mn), Al, B, Ga, Si and Sn. Here, the rare earth elements include Sc and Y. a is 0.0011≦a≦0.016, b is 0≦b≦0.20, c is 0.40≦c≦1.15, d is 0≦d≦0.40, e is 0≦e≦0.20, f is 0≦f≦0.07, and c+d+e is 0.60≦c+d+e≦1.20.] 2. The hydrogen storage material according to claim 1, wherein the alloy is crushed and sized to 300 to 500 μm to produce an alloy powder having an oxygen value of 500 ppm or less.

3. The hydrogen storage material according to claim 1, in which the alloy is crushed, the alloy powder is sized to 300-500 μm, and the alloy powder having an oxygen value of 150 μm or less is 6000 ppm or less after the following processes (1) to (3) are carried out. (1) Vacuuming is carried out at 85°C for about 2 hours. (2) After pressurizing with a hydrogen pressure of about 2.7 MPa, the temperature is changed to -20°C and hydrogen is absorbed until the hydrogen pressure stabilizes. (3) The operations (1) to (2) are repeated three times, and then the material is vacuumed at 85°C for about 5 hours to dehydrogenate.

4. The alloy has a PCT absorption curve, which is a hydrogen pressure-composition isotherm diagram at 30°C, of ​​0≦log １０ (P ａ２ ) -log １０ (P ａ１ The hydrogen storage material according to claim 1, which satisfies the relationship: ａ１ is the hydrogen absorption pressure at a hydrogen absorption capacity of 0.3 wt%, and P ａ２ is the hydrogen absorption pressure at a hydrogen absorption capacity of 1.3 wt %.

5. The alloy has a PCT release curve, which is a hydrogen pressure-composition isotherm at 30°C, of ​​0≦log １０ (P ｂ２ ) -log １０ (P ｂ１ The hydrogen storage material according to claim 1, which satisfies the relationship: ｂ１ is the hydrogen release pressure when the hydrogen storage amount is 0.3 wt%, and P ｂ２ is the hydrogen release pressure when the hydrogen storage capacity is 1.3 wt %.

6. The alloy has a PCT release curve, which is a hydrogen pressure-composition isotherm diagram at 30°C, of ​​1.2≦[0.2 / {log １０ (P ｂ４ ) -log １０ (P ｂ３ 2. The hydrogen storage material according to claim 1, which satisfies the relationship: ｂ３ is the hydrogen release pressure at a hydrogen storage amount of +0.10 wt % from the starting point, which is the intersection point between the equilibrium pressure of 0.01 MPa and the PCT release curve. ｂ４ is the hydrogen release pressure at a hydrogen storage amount of +0.30 wt % from the starting point.

7. The hydrogen storage material according to any one of claims 1 to 6, wherein the alloy is subjected to a mechanical alloying treatment.

8. The hydrogen storage material according to any one of claims 1 to 6, which is made of a composite material in which the alloy is mixed with a resin.

9. A hydrogen storage container comprising the hydrogen storage material according to any one of claims 1 to 6.

10. A hydrogen supply device comprising the hydrogen storage container according to claim 9.

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