Hydrogen-generating alloy, method for using hydrogen-generating alloy, negative electrode material for magnesium battery, hydrogen-generating agent for power generation, hydrogen storage alloy, and porous metallic material

Abstract

To provide a hydrogen-generating alloy, a method of using the hydrogen-generating alloy, a negative electrode material for a magnesium battery, a hydrogen-generating agent for power generation, a hydrogen storage alloy, and a porous metallic material that achieve a high reaction rate of hydrogen generation.SOLUTION: A chemical composition comprises, in mass%, 0.1 mass% or more of at least one metal selected from In and Li, 0.1 mass% or more of Ga, and the balance consisting of Mg and impurities; and a metal structure includes a lamellar structure composed of a matrix phase that is any of a Mg solid solution, a Mg-In solid solution, or a Li solid solution in which at least one metal selected from In and Li is dissolved, and a secondary phase Mg5Ga2 phase in which at least one metal selected from In and Li is dissolved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydrogen-generating alloy that generates hydrogen by a hydrolysis reaction, a method for using the hydrogen-generating alloy, a negative electrode material for magnesium batteries, a hydrogen generating agent for power generation, a hydrogen storage alloy, and a porous metal material. [Background technology]

[0002] In recent years, carbon dioxide emission regulations have required a reduction in the use of fossil fuels. Hydrogen, which does not emit carbon dioxide through oxidation or combustion, has been attracting attention as a next-generation fuel to replace fossil fuels.

[0003] The main methods for producing industrial hydrogen are water electrolysis, which requires a large amount of electricity, and steam reforming of fossil fuels, which involves the emission of carbon dioxide. However, research is being conducted into a metal hydrolysis method as a method for producing hydrogen that does not require electricity or carbon dioxide emissions.

[0004] The hydrogen-generating alloy described in Patent Document 1 has a metal structure including a lamellar structure consisting of an Mg phase mainly composed of Mg and an MgCa phase mainly composed of MgCa, and is capable of generating a large amount of hydrogen through a hydrolysis reaction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2023-125624 A (pages 6 to 11, Figures 2 to 6) [Patent Document 2] Chinese Patent No. 108118222 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the hydrogen generating alloy of Patent Document 1, the saturated calomel electrode potential of the MgCa phase in the galvanic corrosion that occurs between the Mg phase and the MgCa phase is −1.85 V, which is smaller than the saturated calomel electrode potential of pure Mg, which is −1.64 V. This causes a problem in that the reaction rate is slow, with the amount of hydrogen generated per minute being 0.36 ml / g.

[0007] Furthermore, the hydrogen-generating alloy described in Patent Document 2 is manufactured as a high-strength Mg-In-Ga-based alloy in which the crystal structure (crystal grains) is refined by mechanical vibration and application of a magnetic field during casting. However, since it does not have a lamellar structure that serves as the starting point for the hydrolysis reaction, there is a problem in that the reaction rate of hydrogen generation is slow.

[0008] The present invention has been made with a focus on these problems, and aims to provide a hydrogen-generating alloy with a high reaction rate for hydrogen generation, a method for using the hydrogen-generating alloy, a negative electrode material for magnesium batteries, a hydrogen generating agent for power generation, a hydrogen storage alloy, and a porous metal material. [Means for solving the problem]

[0009] The hydrogen generating alloy of the present invention, which solves the above problems, The chemical composition is, in mass%, 0.1 mass% or more of one or more metals selected from In and Li, 0.1 mass% or more of Ga, and the balance: Mg and impurities; The metal structure is characterized by including a lamellar structure consisting of a parent phase which is any one of an Mg solid solution, an Mg-In solid solution, and a Li solid solution in which one or more metals selected from the group consisting of In and Li are dissolved, and a second phase, an Mg5Ga2 phase in which one or more metals selected from the group consisting of In and Li are dissolved. According to this feature, one or more metals selected from In and Li are dissolved in the matrix phase and the second phase Mg5Ga2, thereby providing a hydrogen generating alloy with a large potential difference between the matrix phase and the second phase Mg5Ga2 and a high reaction rate for hydrogen generation through hydrolysis.

[0010] The second phase Mg5Ga2 is characterized in that it is in solid solution. According to this feature, the generation of the intermetallic compound Mg5Ga2 is controlled by heat treatment, i.e., the second phase Mg5Ga2 is solid-solutionized, thereby suppressing hydrogen generation due to hydrolysis reaction, thereby improving the storage stability of the hydrogen-generating alloy.

[0011] The composition is characterized in that it contains, in place of a portion of the Mg, one or more metals selected from the group consisting of Ni, Ca, Cu and Sn in a total amount of 0.01 to 1 mass %. According to this feature, the presence of an intermetallic compound with Mg can promote the hydrolysis reaction.

[0012] The thickness of the matrix phase and the second phase Mg5Ga2 phase in the lamellar structure is 50 nm or more and 5000 nm or less. According to this feature, the interface between the parent phase and the second phase Mg5Ga2 phase becomes the starting point of galvanic corrosion, which can further promote the hydrolysis reaction.

[0013] The metal structure is characterized in that it consists of only the lamellar structure. This feature makes it possible to increase the amount of hydrogen generated per unit time in the early stage of the hydrolysis reaction.

[0014] A method for using a hydrogen generating alloy according to another aspect of the present invention includes: The chemical composition is, in mass%, 0.1 mass% or more of one or more metals selected from In and Li, 0.1 mass% or more of Ga, and the balance: Mg and impurities; A method for using a hydrogen generating alloy having a metal structure including a lamellar structure composed of a parent phase which is any one of an Mg solid solution, an Mg-In solid solution, and a Li solid solution in which one or more metals selected from In and Li are solid-solved, and a second phase Mg5Ga2 in which one or more metals selected from In and Li are solid-solved, a heat treatment step of heating the hydrogen generating alloy to form a solid solution of the second phase Mg5Ga2; The method is characterized by comprising a tempering step of heating the hydrogen generating alloy that has been subjected to the heat treatment step to regenerate the lamellar structure. According to this feature, the second phase Mg5Ga2 is converted into a solid solution by the heat treatment process, thereby suppressing hydrogen generation due to the hydrolysis reaction and improving the shelf life of the hydrogen-generating alloy. Furthermore, the second phase Mg5Ga2 is reprecipitated by the tempering process to regenerate the lamellar structure, thereby restoring the hydrolysis properties, resulting in excellent handleability of the hydrogen-generating alloy. [Brief explanation of the drawings]

[0015] [Figure 1] 1A and 1B are photographs showing backscattered electron images of the metal structures of hydrogen-generating alloys according to examples of the present invention, where (a) is a comparative Mg-Ga alloy (cast material), (b) and (d) are Mg-In-Ga alloys (cast materials) as hydrogen-generating alloys according to examples, and (c) is a heat-treated Mg-In-Ga alloy (heat-treated material) obtained by heat-treating (b). [Figure 2] (a) is a photograph showing a backscattered electron image of the metal structure of the Mg-Ga alloy (cast material) in Figure 1(a), (b) is the composition analysis result thereof, and (c) is a graph showing the X-ray diffraction pattern thereof. [Figure 3] (a) is a photograph showing a backscattered electron image of the metal structure of the Mg-In-Ga alloy (cast material) in Figure 1(d), (b) is the composition analysis result, and (c) is a graph showing the X-ray diffraction pattern. [Figure 4] 1(b) and 1(c) show backscattered electron images and the results of composition analysis of the Mg-In-Ga alloy (cast material) shown in FIG. 1(b) and the Mg-In-Ga alloy (heat-treated material) shown in FIG. 1(c). [Figure 5] (a) is a photograph showing a backscattered electron image of the metal structure of the Mg-In-Ga alloy (heat-treated material) shown in Figure 1(c) after tempering, and (b) is a diagram showing the results of its composition analysis. [Figure 6]FIG. 1(d) shows a comparison of the hydrogen generation curve of the hydrogen generation alloy (Mg-In-Ga alloy whose parent phase is Mg solid solution (α-Mg)) and that of a conventional hydrogen generation alloy (Mg-Ca alloy). [Figure 7] FIG. 1 is a graph showing the hydrogen generation curve of a hydrogen generating alloy according to the present invention (an Mg—In—Ga-based alloy whose parent phase is an Mg—In solid solution (Mg0.1In0.9)). DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the hydrogen generating alloy according to the embodiment of the present invention will be described in detail. However, the present invention can be embodied in many different forms and is not limited to the following embodiments and examples.

[0017] (Hydrogen generating alloy) A hydrogen generating alloy according to an embodiment of the present invention (hereinafter sometimes referred to as "the present hydrogen generating alloy") has a chemical composition, in mass %, of at least 0.1 mass % of one or more metals selected from In and Li, at least 0.1 mass % of Ga, and the balance being Mg and impurities. The metallographic structure includes a lamellar structure consisting of a matrix phase that is any one of an Mg solid solution, an Mg-In solid solution, and a Li solid solution in which at least one metal selected from In and Li is dissolved, and a second phase, Mg5Ga2, in which at least one metal selected from In and Li is dissolved. That is, the present hydrogen generating alloy is any one of a so-called Mg-In-Ga-based alloy, an Mg-Li-Ga-based alloy, and an Mg-In-Li-Ga-based alloy, and exhibits excellent hydrolysis characteristics (hydrogen release characteristics) by utilizing a local cell structure due to the lamellar structure formed by the matrix phase in which at least one metal selected from In and Li is dissolved and the second phase, Mg5Ga2.

[0018] In this hydrogen generating alloy, the parent phase of Mg solid solution is formed when Mg is 72 at.% or more, the parent phase of Mg-In solid solution is formed when In is 19 at.% or more, and the parent phase of Li solid solution is formed when Li is 17 at.% or more.

[0019] The second phase, Mg5Ga2, is produced by adding Ga to the matrix phase, which is any one of the above-mentioned Mg solid solution, Mg-In solid solution, and Li solid solution.

[0020] (chemical composition) In this hydrogen-generating alloy, Ga and Mg form the intermetallic compound Mg5Ga2. The Ga content in this hydrogen-generating alloy is 0.1 mass% or more, which increases the rate of the hydrolysis reaction originating from the lamellar structure consisting of the parent phase and the secondary phase Mg5Ga2, enabling a large amount of hydrogen to be generated in a short period of time.

[0021] In this hydrogen generating alloy, one or more metals selected from In and Li are dissolved in the matrix phase and the second phase Mg5Ga2. Note that, when the content of one or more metals selected from In and Li in this hydrogen generating alloy is 0.1 mass% or more, the potential difference (galvanic potential difference) between the matrix phase and the second phase Mg5Ga2 can be increased, and the hydrolysis reaction can be promoted.

[0022] Furthermore, In, when dissolved in the matrix, changes the crystal structure of the hydrogen generating alloy to FCC (face-centered cubic lattice), thereby improving the plastic workability.

[0023] Furthermore, Li, when dissolved in the matrix, changes the crystal structure of the hydrogen generating alloy to a BCC (body-centered cubic) structure, thereby improving the plastic workability.

[0024] The balance of this hydrogen generating alloy is Mg and impurities. Examples of impurities include elements such as Na, Al, Si, Cl, Ca, Mn, Fe, Co, Ni, Cu, Zn, Sr, Pb, Sn, and Ba. From the viewpoint of maintaining the amount of hydrogen generated, the impurity content is preferably 1% by mass or less, and more preferably 0.1% by mass or less.

[0025] Among the above impurities, Ni, Ca, Cu, and Sn are metals that form intermetallic compounds with Mg. The presence of these intermetallic compounds promotes the hydrolysis reaction of Mg, thereby increasing the amount of hydrogen generated per unit time. Therefore, when the present hydrogen-generating alloy is used in a situation where a large amount of hydrogen is required in a short period of time, the hydrogen-generating alloy preferably contains one or more metals selected from the group consisting of Ni, Ca, Cu, and Sn in place of a portion of the Mg. In this case, the content of the one or more metals selected from the group consisting of Ni, Ca, Cu, and Sn in the present hydrogen-generating alloy is preferably 0.01% by mass or more and 1% by mass or less, more preferably 0.25% by mass or more and 0.5% by mass or less.

[0026] The chemical composition of this hydrogen-generating alloy was measured by EDS (energy dispersive X-ray spectroscopy). Specifically, the spot size (SS) and bias were adjusted at a WD (working distance) of 10 mm, and measurements were taken at five or more arbitrary positions for each generated phase in the sample at 1000x magnification within the range of 2000-7000 cps using the SSM count rate monitor of the EDS analysis application Analyzer Manager. The average value was used as the chemical composition of the hydrogen-generating alloy as the composition analysis result.

[0027] (Metal structure) This hydrogen-generating alloy has a lamellar structure consisting of a parent phase and a secondary phase, Mg5Ga2 (see, for example, Figures 1(b) and (d)). Figure 1 shows backscattered electron images of the metal structure of the hydrogen-generating alloy taken with a scanning electron microscope (SEM). In Figures 1(b) and (d), the dark areas are the parent phase (α-Mg), and the bright areas are the secondary phase, Mg5Ga2.

[0028] Furthermore, the hydrogen-generating alloy in this embodiment is available in three states: a cast material having a parent phase and a second phase Mg5Ga2 phase; a heat-treated material in which the second phase Mg5Ga2 phase has been solid-solved in at least a part of the entire metal structure by heat treatment, and the lamellar structure has disappeared; and a tempered material in which the second phase Mg5Ga2 phase has been regenerated by tempering the heat-treated material, and the alloy has a parent phase and a second phase Mg5Ga2 phase.

[0029] (lamellar structure) The lamellar structure is a layered structure consisting of a matrix and a secondary Mg5Ga2 phase. In this hydrogen-generating alloy, the thicknesses of the matrix and secondary Mg5Ga2 phases in the lamellar structure are small, and the interface area between the matrix and secondary Mg5Ga2 phases per unit mass is large. This makes the interface between the matrix and secondary Mg5Ga2 phases in the lamellar structure the starting point for galvanic corrosion, making the hydrolysis reaction more likely to occur. Furthermore, during the hydrolysis of magnesium, the pH near the Mg surface generally increases as the reaction progresses, forming a passive Mg(OH)2 on the Mg surface and inhibiting the hydrolysis reaction. However, in this hydrogen-generating alloy, the lamellar structure is so fine that the Mg(OH)2 produced during the hydrolysis reaction is released outside the lamellar structure (outside the reaction system) by hydrogen bubbles (hydrogen bubbles) that are also produced. In this way, the hydrolysis reaction continues without being affected by Mg(OH)2, and most of the Mg constituting this hydrogen generating alloy contributes to the hydrolysis reaction, enabling a large amount of hydrogen to be generated.

[0030] As mentioned above, a fine lamellar structure is preferable, but if the thickness of the parent phase and the second phase Mg5Ga2 in the lamellar structure is too thin, Mg(OH)2 formed during the hydrolysis reaction may not be properly discharged to the outside of the lamellar structure and may remain in the lamellar structure. Therefore, the thickness of both the parent phase and the second phase Mg5Ga2 in the lamellar structure is preferably 50 nm or more and 5000 nm or less, more preferably 100 nm or more and 1000 nm or less, and even more preferably 100 nm or more and 250 nm or less.

[0031] Furthermore, it has been confirmed that in the liquid metal remaining after the hydrolysis reaction, not only the Mg(OH)2 expelled from the lamellar structure but also the pure substances In, Li, and Ga remain unreacted in the metal structure. This suggests that at least In and Ga can be reused in this hydrogen-generating alloy.

[0032] The thicknesses of the parent phase and the second phase Mg5Ga2 phase in the lamellar structure were determined by obtaining a backscattered electron image at 10,000x magnification using an SEM, measuring the thicknesses of the parent phase and the second phase Mg5Ga2 phase at any 10 points on the backscattered electron image, and averaging the respective thicknesses to determine the thicknesses of the parent phase and the second phase Mg5Ga2 phase.

[0033] The thicknesses of the parent phase and the second Mg5Ga2 phase in the lamellar structure can be controlled by the cooling rate during production of the hydrogen-generating alloy. Specifically, by decreasing the cooling rate, the parent phase and the second Mg5Ga2 phase in the lamellar structure can be made thicker, and by increasing the cooling rate, the parent phase and the second Mg5Ga2 phase can be made thinner.

[0034] The present hydrogen-generating alloy may have a metal structure consisting solely of a lamellar structure, in other words, the area ratio of the lamellar structure to the entire metal structure may be 100%. Accordingly, the larger the area ratio of the lamellar structure, which has many fine interfaces, the greater the amount of hydrogen generated per unit time in the initial stage of the hydrolysis reaction. The present hydrogen-generating alloy may also be configured to have a metal structure consisting solely of a lamellar structure by adjusting its chemical composition. For example, in the present hydrogen-generating alloy whose parent phase is a Mg solid solution (α-Mg), the Mg content is preferably 80 to 82 at.% in order to have a metal structure consisting solely of a lamellar structure.

[0035] (Method for producing hydrogen generating alloy) Next, an example of a method for producing the present hydrogen-generating alloy will be described. The present hydrogen-generating alloy is produced by placing raw materials, prepared so that 99.9% pure metal materials (Mg, Ga, In, or Li) have the above-mentioned chemical composition, in an iron crucible and melting them in an electric furnace at a temperature of about 700 to 800°C in an inert gas atmosphere such as carbon dioxide. To avoid uneven distribution of solute atoms, the raw materials are stirred with an iron rod, and the melted raw materials are placed in a water-cooled copper mold in the air and cooled. In this embodiment, the hydrogen-generating alloy produced by this production method is referred to as a cast material.

[0036] (How to use hydrogen generating alloy) Next, a method for using this hydrogen-generating alloy will be described. First, the hydrogen-generating method for this hydrogen-generating alloy involves contacting the alloy with a corrosive solution, which causes a hydrolysis reaction starting from a lamellar structure consisting of a parent phase and a secondary phase, Mg5Ga2, to generate hydrogen. This hydrogen-generating alloy is not limited to a specific type of corrosive solution, and the corrosive solution may be any acidic, neutral, or alkaline solution. It is also possible to continuously generate a large amount of hydrogen by using water (HO).

[0037] Furthermore, this hydrogen-generating alloy can be heat-treated to form a solid solution of the second phase Mg5Ga2 by, for example, placing the cast material in a glass tube, evacuating it, replacing the atmosphere with Ar, and heating it in a muffle furnace at a predetermined temperature for a predetermined time, followed by oil quenching, thereby suppressing hydrogen generation due to hydrolysis and improving the shelf life of the hydrogen-generating alloy. Note that, as described above, the heat treatment process differs from casting, in which metallic materials are melted at high temperatures, in that the alloy is heated to form a solid solution of the second phase Mg5Ga2 in the solid state, thereby eliminating the lamellar structure.

[0038] Furthermore, the present hydrogen generating alloy can be tempered by heating the heat-treated material at a predetermined temperature to reprecipitate the second phase Mg5Ga2 and regenerate the lamellar structure, thereby restoring its hydrolysis properties.

[0039] As described above, the hydrogen generating alloy according to this embodiment has a chemical composition, in mass %, of at least 0.1 mass % of one or more metals selected from In and Li, at least 0.1 mass % of Ga, and the remainder being Mg and impurities. The metal structure includes a lamellar structure consisting of a parent phase that is either an Mg solid solution, an Mg-In solid solution, or a Li solid solution in which at least one metal selected from In and Li is dissolved, and a second phase, Mg5Ga2, in which at least one metal selected from In and Li is dissolved. This increases the potential difference between the parent phase and the second phase, Mg5Ga2, and enables the provision of a hydrogen generating alloy with a high reaction rate for hydrogen generation by hydrolysis.

[0040] Furthermore, in the hydrogen-generating alloy according to this embodiment, one or more metals selected from In and Li are dissolved in the matrix, and an Mg-In solid solution (FCC) and an Li solid solution (BCC) are formed, thereby changing the crystal structure and providing a hydrogen-generating alloy with excellent plastic workability. The results of a room-temperature rolling test of the hydrogen-generating alloy according to this embodiment are shown in Table 1 below.

[0041] [Table 1]

[0042] As shown in Table 1, for example, the hydrogen generating alloy according to this embodiment, Mg—In—Ga based alloy (Mg 94 In4Ga2 and Mg 72 In 27 The as-cast material of MgGa1 is a comparative example of Mg-Ga alloy (Mg 90 Ga 10 ) has a larger LCR (rolling limit) value than the cast material, and has improved plastic workability.

[0043] In addition, Mg-In-Ga alloys (Mg 94 The heat-treated In4Ga2) material, which was heat-treated at 420°C for 50 hours, has an LCR value equivalent to that of the Mg-Al-Zn alloy (AZ31), a general-purpose wrought magnesium alloy, and its plastic workability has been further improved.

[0044] In addition, the matrix is a Mg-In solid solution (Mg 0.1 In 0.9 ) Mg-In-Ga alloy (Mg 72 In 27 The heat-treated material, which was heat-treated at 400°C for 50 hours, had an LCR value approximately 40% higher than that of the Mg-Al-Zn alloy (AZ31), and the plastic workability was further improved. 72 In 27 In the heat-treated material of Mg5Ga1), the second phase Mg5Ga2 is not completely solid-solutionized, but by changing the conditions of the heat treatment and composition, it is possible to completely solidify the second phase Mg5Ga2.

[0045] Furthermore, the hydrogen-generating alloy according to this embodiment has excellent handleability because the second phase Mg5Ga2 is converted into a solid solution through a heat treatment process, thereby suppressing hydrogen generation due to a hydrolysis reaction and improving the shelf life of the hydrogen-generating alloy, and the second phase Mg5Ga2 is reprecipitated through a tempering process to regenerate a lamellar structure, thereby restoring the hydrolysis properties.

[0046] Furthermore, since the hydrogen generating alloy according to this embodiment has a high reaction rate for hydrogen generation, Mg-based hydroxides (such as Mg(OH)2) generated by the hydrolysis reaction are easily released into the corrosive solution together with the generated hydrogen, thereby preventing the formation of a hydroxide film.

[0047] Furthermore, with conventional Mg-Ca-based alloys (see Patent Document 1) and Mg-In-Ga-based alloys (see Patent Document 2), the etching solution had to be heated to about 20 to 60°C to improve the reaction rate of hydrogen generation by hydrolysis, but with the hydrogen generating alloy according to the present embodiment, the potential difference is large, and the heat of reaction in the hydrolysis reaction also increases, causing the etching solution to be heated. Therefore, the reaction rate of hydrogen generation by hydrolysis can be improved without external heating.

[0048] (Anode material for magnesium batteries) Next, a description will be given of an embodiment of a magnesium battery negative electrode material according to another aspect of the present invention. However, the present invention can be embodied in many different forms and is not limited to the following exemplary embodiment.

[0049] The negative electrode material for a magnesium battery according to the embodiment of the present invention has the same structure as the above-mentioned hydrogen generating alloy and can be used as a negative electrode active material for a magnesium battery. Specifically, for example, a magnesium-air battery can be constructed by using oxygen in air as a positive electrode active material and the negative electrode material for a magnesium battery according to the present embodiment as a negative electrode active material.

[0050] Furthermore, the magnesium battery negative electrode material according to this embodiment has a high reaction rate of hydrogen generation due to a hydrolysis reaction, and generates a large amount of hydrogen per unit mass and per unit volume; in other words, the amount of electricity per unit mass and per unit volume is large, and therefore a battery having a large discharge capacity can be constructed.

[0051] Furthermore, by controlling the metal structure of the magnesium battery negative electrode material (such as the thickness of the parent phase and the secondary phase Mg5Ga2 in the lamellar structure), the reaction rate of the hydrolysis reaction can be controlled, which makes it possible to adjust the output density of the battery.

[0052] (Hydrogen generating agent for power generation) Next, a hydrogen generating agent for power generation according to another embodiment of the present invention will be described. However, the present invention can be embodied in many different forms and is not limited to the exemplary embodiments shown below.

[0053] The hydrogen generating agent for power generation according to an embodiment of the present invention has the same configuration as the above-described hydrogen generating alloy, and can be used as a hydrogen generating agent for hydrogen power generation (steam power generation, gas turbine power generation) in which hydrogen is combusted to generate electricity. When the alloy is used as a hydrogen generating agent for power generation, it is preferable to process the alloy into a granular, thin plate, or other shape.

[0054] The hydrogen generating agent for power generation according to this embodiment has a high reaction rate for generating hydrogen through a hydrolysis reaction, and generates a large amount of hydrogen per unit mass and per unit volume. Therefore, when used for hydrogen power generation, a relatively large amount of energy can be obtained even with a small volume of hydrogen generating agent for power generation.

[0055] (hydrogen storage alloy) Next, a hydrogen storage alloy according to another embodiment of the present invention will be described. However, the present invention can be embodied in many different forms and is not limited to the following exemplary embodiment.

[0056] In the hydrogen storage alloy according to the embodiment of the present invention, hydrogen generated by the hydrolysis reaction of the hydrogen generating alloy described above is taken in and held as Mg-based hydrides inside the alloy.

[0057] Furthermore, when the hydrogen storage alloy according to this embodiment is heated, the Mg-based hydride held within the alloy is thermally decomposed, releasing hydrogen. Thus, the hydrogen storage alloy according to this embodiment has hydrogen absorption and release properties, and can be used as an energy conversion material for storing and transporting hydrogen.

[0058] (Porous metal materials) Next, a porous metal material according to another embodiment of the present invention will be described. However, the present invention can be embodied in many different forms and is not limited to the following exemplary embodiment.

[0059] The porous metal material according to the embodiment of the present invention can be produced by heating the above-mentioned hydrogen storage alloy, and has a large number of pores formed therein.

[0060] More specifically, the porous metal material is a sponge-like metal material with holes inside the alloy, which is formed when the Mg-based hydride held inside the hydrogen storage alloy is thermally decomposed and the hydrogen foams.

[0061] Furthermore, the porous metal material according to this embodiment is lighter in weight than ordinary metals due to the presence of pores within the alloy, and the pore shape and the resulting large surface area can be utilized to make shock absorbers, soundproofing materials, heat insulating materials, biomedical materials, and the like.

[0062] In addition, if the porous metal material according to this embodiment has not been subjected to the heat treatment described above, the metal base itself has a local battery structure with a lamellar structure consisting of a parent phase and a second phase Mg5Ga2 phase, which makes it possible to generate hydrogen through a hydrolysis reaction.

[0063] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications can be made. [Example]

[0064] Here, the hydrogen generating alloys according to the examples of the above-described embodiment were actually produced, and their hydrolysis characteristics were confirmed.

[0065] In this example, a backscattered electron image of the hydrogen generating alloy prepared is shown in FIG. 1. Note that FIG. 1(a) shows a backscattered electron image of the Mg—Ga based alloy (Mg 90 Ga 10 ) is a backscattered electron image of the cast material of the hydrogen generating alloy of this example. 94 Figure 1(c) shows a backscattered electron image of the cast material of Mg-In-Ga alloy (Mg 94 Figure 1(d) shows a backscattered electron image of a Mg-In-Ga alloy (Mg) that was heat-treated at 420°C for 50 hours. 85 In5Ga 10 ) is a backscattered electron image of the cast material.

[0066] First, in order to confirm the change in the hydrogen generating alloy caused by the solid solution of In in the parent phase and the second phase Mg5Ga2, a Mg-In-Ga based alloy (Mg 85 In5Ga10 ) cast material (Fig. 1(d)) and a comparative Mg-Ga alloy (Mg 90 Ga 10 ) cast materials (see Figure 1(a)) are compared.

[0067] As shown in Fig. 2(a) and Fig. 3(a), the Mg-Ga alloy (Mg 90 Ga 10 ) and Mg-In-Ga alloys (Mg 85 In5Ga 10 ) is formed by adding Ga to Mg, forming a eutectic structure consisting of the parent phase (α-Mg) and the secondary phase Mg5Ga2 (Mg5Ga2), and the appearance of the metal structure is almost the same, so no differences can be recognized.

[0068] As shown in Figure 2(a), the Mg-Ga alloy (Mg 90 Ga 10 ), the composition analysis result for the part shown as the parent phase (α-Mg) was Mg-97.0, Ga-3.0 (at.%), and the composition analysis result for the part shown as the second phase Mg5Ga2 (Mg5Ga2) was Mg-81.2, Ga-18.8 (at.%) (see Figure 2(b)). On the other hand, as shown in Figure 3(a), the composition analysis result for the Mg-In-Ga based alloy (Mg 85 In5Ga 10 In this example, the composition analysis results for the portion designated as the parent phase (α-Mg) were Mg-92.7, In-4.9, and Ga-2.4 (at.%), and the composition analysis results for the portion designated as the second phase Mg5Ga2 (Mg5Ga2) were Mg-74.7, In-4.7, and Ga-20.6 (at.%) (see FIG. 3(b)). The composition analysis in this example was performed based on the peak intensity ratios shown in the X-ray diffraction (XRD) patterns (using a Bruker D8 ADVANCE) shown in FIGS. 2(c) and 3(c). Specifically, the composition analysis in this example was calculated from the two types of measurement results, the EDS analysis results (SEM), described above. The lattice constants and the diffraction peak angles in each case were calculated based on the composition ratios of each phase from the EDS analysis results, and the angle difference with the diffraction peaks obtained by XRD analysis was compared to quantitatively complement each other.

[0069] Thus, the Mg-In-Ga alloy (Mg 85 In5Ga 10 ) and a comparative Mg-Ga alloy (Mg 90 Ga 10 ) has almost the same metallic structure, but is different from Mg-In-Ga alloy (Mg 85 In5Ga 10 In the parent phase and the second phase Mg5Ga2 in the Mg-Ga alloy (Mg 90 Ga 10 ) and was found to have a clearly different composition.

[0070] Next, in order to confirm the change in the hydrogen generating alloy due to the heat treatment, the Mg-In-Ga alloy (Mg 94 In4Ga2) cast material (see Figure 1(b)) and Mg-In-Ga alloy (Mg 94 We compare the heat-treated In4Ga2 materials (see Figure 1(c)).

[0071] As shown in Figure 4, the Mg-In-Ga alloy (Mg 94 The cast material of Mg-In-Ga alloy (Mg In4Ga2) has a metal structure including a lamellar structure consisting of a parent phase and a secondary phase Mg5Ga2 phase, while the cast material is heat-treated to produce an Mg-In-Ga alloy (Mg 94 It was confirmed that the heat-treated In4Ga2 material lost the second phase Mg5Ga2 phase (Mg5Ga2) and was composed of the parent phase (α-Mg), as can be seen from the results of the composition analysis described below.

[0072] In addition, Mg-In-Ga alloys (Mg 94In the cast material of Mg-In-Ga alloy (In4Ga2), the composition analysis result of the part shown as the parent phase (α-Mg(A)) was Mg-97.6, In-2.4 (at.%), the composition analysis result of the part shown as the parent phase (α-Mg(B)) was Mg-93.4, In-4.7, Ga-1.9 (at.%), and the composition analysis result of the part shown as the second phase Mg5Ga2 phase (Mg5Ga2) was Mg-76.3, In-3.2, Ga-20.5 (at.%). 94 In the heat-treated In4Ga2 material, the composition analysis result for the part shown as the parent phase (α-Mg) was Mg-93.7, In-4.0, Ga-2.3 (at.%), which changed to approximately the same composition as the part shown as the parent phase (α-Mg(B)) in the cast material.

[0073] Thus, Mg-In-Ga alloys (Mg 94 Although the cast and heat-treated In4Ga2) alloys have the same composition, the heat treatment described above results in the heat-treated material containing In and Ga as a solid solution in the matrix, resulting in a solid solution of the metal structure. In other words, it was confirmed that the heat-treated material contains essentially only the matrix (α-Mg). Whether the metal structure is a solid solution can be confirmed by observing the atomic arrangement within the crystal in a TEM (transmission electron microscope) image. Furthermore, because the atomic radii of In, Ga, etc. are smaller than those of Mg, the lattice constant and the diffraction peak angle in this case can be calculated from the solid solubility, and the solid solution can be confirmed by comparing the angle difference with the diffraction peak obtained by XRD analysis.

[0074] In addition, Mg-In-Ga alloys (Mg 94 In the case of heat-treated Mg-In-Ga alloys, the metal structure is solid-solutionized, and the second phase Mg5Ga2 is lost, i.e., the lamellar structure is lost, resulting in weak or no hydrolysis properties. 94By tempering the heat-treated Mg-In-Ga alloy (Mg4Ga2) at 100-200°C, the secondary phase Mg5Ga2 is reprecipitated, i.e., the lamellar structure is regenerated, and the hydrolysis properties can be restored. For example, as shown in Figure 5, the hydrolysis properties of the Mg-In-Ga alloy (Mg 94 When the heat-treated alloy (In4Ga2) was tempered at 200°C for 50 hours, it was confirmed that the secondary phase Mg5Ga2 was reprecipitated from the grain boundaries and inside the grains (see the area enclosed by dotted lines, for example), and the lamellar structure was regenerated. Note that the hydrogen-generating alloy of the present invention can be repeatedly subjected to the heat treatment and tempering processes.

[0075] Furthermore, in this embodiment, the heat treatment temperature is set to 420°C, which is the optimum temperature for obtaining a parent phase (α-Mg) in which In and Ga are solid-dissolved, because the solid solubility limit of Ga in Mg is maximum at 420°C according to the Mg-Ga binary phase diagram (not shown), and the solid solubility limit of In in Mg is approximately 20 at.% at 420°C in the Mg-rich region according to the Mg-In binary phase diagram (not shown). However, it goes without saying that the heat treatment temperature is not limited to this and may be changed as appropriate depending on conditions such as the composition of the hydrogen-generating alloy.

[0076] Furthermore, the heat treatment time in this example was set to 50 hours, at which time it was confirmed that there was no change in the solution concentration during the heat treatment and that the second phase Mg5Ga2, which is the cast structure, was not observed. However, it goes without saying that the heat treatment time is not limited to this and may be changed as appropriate depending on conditions such as the composition of the hydrogen-generating alloy and the heat treatment temperature.

[0077] Next, as a comparative example, an Mg-Ca alloy (Mg 89.5 Ca 10.5 ) was produced as a cast material, and the Mg-In-Ga alloy (Mg 85 In5Ga 10 The difference in hydrolysis characteristics between the cast material (see Fig. 1(d)) and the Mg-In-Ga alloy (Mg 85 In5Ga 10 ) has a matrix of Mg solid solution (α-Mg).

[0078] Mg-Ca alloy (Mg 89.5 Ca 10.5 ) was used as the etchant, and reacted at room temperature (around 20°C) for 120 minutes, resulting in a hydrogen production of 43.0 ml / g. 89.5 Ca 10.5 ) produced 0.36 ml / g of hydrogen per minute.

[0079] Mg-In-Ga alloy (Mg 85 In5Ga 10 ) was used as the etchant, and reacted at room temperature (around 20°C) for 6.3 minutes, resulting in a hydrogen production of 644.0 ml / g. 85 In5Ga 10 ) produced 102.2 ml / g of hydrogen per minute.

[0080] As shown in the hydrogen generation curve in Figure 6, the Mg-In-Ga alloy (Mg 85 In5Ga 10 ) is a Mg-Ca alloy (Mg 89.5 Ca 10.5 It was confirmed that hydrogen generation was possible at a reaction rate 283.9 times faster than that of conventional hydrogen generation.

[0081] In addition, Mg-Ga alloys (Mg 90 Ga 10 ) has been confirmed to generate almost no hydrogen when bulk samples are reacted with a corrosive solution, and the addition of In to Mg-In-Ga alloys improves their hydrolysis characteristics (hydrogen release characteristics).

[0082] Furthermore, it was confirmed that the hydrogen-generating alloy of the present invention, due to its high reaction rate, releases Mg-based hydroxides generated by hydrolysis into the solution simultaneously with the generated hydrogen. Conventionally, Mg-based hydrogen-generating alloys have had the problem of the inhibition of the hydrolysis reaction due to passivation of a hydroxide film, but the hydrogen-generating alloy of the present invention can prevent the formation of a hydroxide film by releasing Mg-based hydroxides into the solution.

[0083] It was also confirmed that the hydrogen generating alloy of the present invention can continuously generate a large amount of hydrogen even when using distilled water (H2O) without being limited to a specific corrosive solution.

[0084] Furthermore, it was confirmed that the hydrogen generating alloy of the present invention has a large potential difference, and therefore the corrosion solution is heated due to an increase in the heat of reaction in the hydrolysis reaction, thereby making it possible to improve the reaction rate without external heating.

[0085] It was also confirmed that the hydrogen generating alloy of the present invention takes in the generated hydrogen as Mg-based hydrides inside the alloy.

[0086] As described above, these embodiments and examples can provide a hydrogen generating alloy with a high reaction rate for hydrogen generation.

[0087] It has also been confirmed that the reaction rate of hydrogen generation is similarly increased for hydrogen generating alloys made of Mg-In-Ga based alloys, Mg-Li-Ga based alloys, and Mg-In-Li-Ga based alloys, which have compositions different from those of the above-mentioned examples. For example, the Mg-In-Ga based alloy (Mg 72 In 27 As shown in the hydrogen evolution curve of Mg-Ca alloy (Mg), distilled water (H2O) was used as the corrosion solution and the reaction was carried out at room temperature (around 20°C) for 9.2 minutes. As a result, the hydrogen generation rate was 363.7 ml / g, that is, the hydrogen generation rate per minute was 39.5 ml / g. 89.5 Ca 10.5 It has been confirmed that the reaction rate of hydrogen generation is faster than that of Mg-In-Ga alloys (Mg72 In 27 Ga1) is a material whose parent phase is a Mg-In solid solution (Mg 0.1 In 0.9 ) [Industrial Applicability]

[0088] The present invention provides a hydrogen-generating alloy with industrial applicability, characterized by a high reaction rate for hydrogen generation via hydrolysis, due to the incorporation of one or more metals selected from In and Li into a parent phase (Mg solid solution, Mg-In solid solution, or Li solid solution) and a secondary phase (Mg5Ga2). This increases the galvanic potential difference between the parent phase and the secondary phase (Mg5Ga2). Furthermore, the hydrogen-generating alloy of the present invention can be used in a variety of ways, including by converting the secondary phase (Mg5Ga2) into a solid solution through a heat treatment process, thereby suppressing hydrogen generation via hydrolysis and improving the shelf life of the hydrogen-generating alloy. Furthermore, the hydrogen-generating alloy of the present invention can be used in a wide range of applications, including as anode materials for magnesium batteries, hydrogen generators for power generation, hydrogen storage alloys, and porous metal materials, all of which have the same composition.

Claims

1. The chemical composition is, in mass %, 0.1 mass % or more of one or more metals selected from In and Li, 0.1 mass % or more of Ga, and the balance: Mg and impurities; The metal structure is composed of a mother phase which is any one of an Mg solid solution, an Mg-In solid solution, and an Li solid solution in which one or more metals selected from the group consisting of In and Li are dissolved, and a second phase Mg ５ Ga ２ A hydrogen generating alloy comprising a lamellar structure consisting of a Fe phase and a Cu phase.

2. The second phase Mg ５ Ga ２ 2. The hydrogen generating alloy of claim 1, wherein the phases are in solid solution.

3. The hydrogen generating alloy according to claim 1 or 2, characterized in that it contains a total of 0.01 to 1 mass% of one or more metals selected from the group consisting of Ni, Ca, Cu and Sn in place of a portion of the Mg.

4. The parent phase and the second phase Mg ５ Ga ２ 3. The hydrogen generating alloy according to claim 1, wherein the thickness of each of the phases is 50 nm or more and 5000 nm or less.

5. 3. The hydrogen generating alloy according to claim 1, wherein the metal structure is composed solely of the lamellar structure.

6. The chemical composition is, in mass %, 0.1 mass % or more of one or more metals selected from In and Li, 0.1 mass % or more of Ga, and the balance: Mg and impurities; The metal structure is composed of a mother phase which is any one of an Mg solid solution, an Mg-In solid solution, and an Li solid solution in which one or more metals selected from the group consisting of In and Li are dissolved, and a second phase Mg ５ Ga ２ A method of using a hydrogen generating alloy comprising a lamellar structure consisting of a phase, the method comprising: By heating the hydrogen generating alloy, the second phase Mg ５ Ga ２ a heat treatment step for solid-solving the phases; A method for using a hydrogen-generating alloy, comprising a tempering step of heating the hydrogen-generating alloy that has been subjected to the heat treatment step to regenerate the lamellar structure.

7. The chemical composition is, in mass %, 0.1 mass % or more of one or more metals selected from In and Li, 0.1 mass % or more of Ga, and the balance: Mg and impurities; The metal structure is composed of a mother phase which is any one of an Mg solid solution, an Mg-In solid solution, and an Li solid solution in which one or more metals selected from the group consisting of In and Li are dissolved, and a second phase Mg ５ Ga ２ A magnesium battery negative electrode material comprising a lamellar structure consisting of a magnesium phase.

8. The chemical composition is, in mass %, 0.1 mass % or more of one or more metals selected from In and Li, 0.1 mass % or more of Ga, and the balance: Mg and impurities; The metal structure is composed of a mother phase which is any one of an Mg solid solution, an Mg-In solid solution, and an Li solid solution in which one or more metals selected from the group consisting of In and Li are dissolved, and a second phase Mg ５ Ga ２ A hydrogen generating agent for power generation, comprising a lamellar structure consisting of a phase.

9. The chemical composition is, in mass %, 0.1 mass % or more of one or more metals selected from In and Li, 0.1 mass % or more of Ga, and the balance: Mg and impurities; The metal structure is composed of a mother phase which is any one of an Mg solid solution, an Mg-In solid solution, and an Li solid solution in which one or more metals selected from the group consisting of In and Li are dissolved, and a second phase Mg ５ Ga ２ A hydrogen storage alloy characterized by comprising a lamellar structure consisting of a phase.

10. The chemical composition is, in mass %, 0.1 mass % or more of one or more metals selected from In and Li, 0.1 mass % or more of Ga, and the balance: Mg and impurities; The metal structure is composed of a mother phase which is any one of an Mg solid solution, an Mg-In solid solution, and an Li solid solution in which one or more metals selected from the group consisting of In and Li are dissolved, and a second phase Mg ５ Ga ２ A porous metal material characterized by having a lamellar structure consisting of a phase.

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