JP2005054243A - Hydrogen storage material, its production method, and hydrogen generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen storage material consisting essentially of Mg which has a high reaction rate and reduced hysteresis while making the most of high hydrogen storage capacity and excellent plateau flatness in a PCT (Pressure-Composition-Temperature) chart characteristic of Mg metal. <P>SOLUTION: The hydrogen storage material has a metallic structure comprising: (a) a simple substance phase of Mg; and (b) a solid solution phase in which Mg atoms are incorporated into the crystal structure of V or V atoms are incorporated into the crystal structure of Mg, and has a composition expressed by formula of Mg<SB>X</SB>V<SB>1-X</SB>(0.2≤X≤0.9). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydrogen storage material containing at least Mg and V, a method for producing the same, and a hydrogen generator incorporating the hydrogen storage material.

  In recent years, from the viewpoints of environmental problems and energy problems, technological development relating to fuel cells and other devices and systems using hydrogen as fuel has been actively promoted. In addition, the development of technology related to hydrogen production, which is indispensable for supplying hydrogen, and technology related to the transport and storage of hydrogen are being actively promoted.

  Hydrogen supply methods are roughly classified into a method using hydrogen generation means and a method using hydrogen storage means. Examples of the hydrogen generating means include water electrolysis and fossil fuel reforming. Examples of the hydrogen storage means include high-pressure hydrogen or liquid hydrogen storage containers, hydrogen storage materials that store hydrogen, and the like. Among them, the method for storing hydrogen in the hydrogen storage material is particularly excellent from the viewpoint of compactness and safety.

Among hydrogen storage materials, metal materials, chemical hydrides, carbon-based materials, and the like are promising (see, for example, Patent Documents 1 and 2). As metal hydrogen storage materials, V metal capable of storing 3.9% by weight of hydrogen, Mg metal capable of storing 7.6% by weight of hydrogen, and the like are known. Theoretically, NaAlH ₄ having a hydrogen storage capacity of 7.4% by weight is known as a chemical hydride, but there is a problem in the stability of the material. Regarding carbon-based materials, there are many aspects that have not been confirmed yet in terms of hydrogenation characteristics.
Japanese Patent Laid-Open No. 10-147827 JP 11-1117036 A

  As a hydrogen storage material excellent in compactness and safety, Mg having a high hydrogen storage capacity and stable is promising. Mg metal can be occluded and released by making its form particulate. However, there is a drawback that the reaction rate of hydrogenation / dehydrogenation is slow. As a result, there is a large hysteresis in the hydrogen equilibrium pressure-hydrogen storage amount isotherm (hereinafter referred to as PCT diagram). The PCT diagram is an important index for evaluating the practicality of hydrogen storage materials. The present invention has been made in view of these points.

  That is, the present invention is a hydrogen storage material that has a high reaction rate and a low hysteresis while taking advantage of the high hydrogen storage capacity that is characteristic of Mg metal and the excellent plateau flatness in the PCT diagram, for example, a single-stage plateau. Is to provide. The present invention also provides a hydrogen generator using such a hydrogen storage material.

The present invention provides a metal comprising (a) a single phase of Mg (magnesium) and (b) a solid solution phase in which Mg atoms are incorporated into the crystal structure of V or V atoms are incorporated into the crystal structure of Mg. The organization consists of a formula:
Mg _X V _1-X (0.2 ≦ X ≦ 0.9)
It is related with the hydrogen storage material (henceforth the hydrogen storage material X) which has the composition represented by these.

  The hydrogen storage material X can be obtained by a production method including a step of mixing particulate Mg metal and particulate V metal, and heating and dissolving the obtained mixture at 700 to 1000 ° C.

  The hydrogen storage material X is also obtained by a production method including a step of mixing particulate Mg metal and particulate V metal, and applying a mechanical shearing force to the obtained mixture by a mechanical alloying method. Can do.

The present invention also comprises a metal structure containing (a) a solid solution phase in which carbon atoms are incorporated into the Mg crystal structure, and (b) a solid solution phase in which carbon atoms are incorporated into the V crystal structure, formula:
(Mg _X V _1-X ) C _Y (0.2 ≦ X ≦ 0.9, 0 <Y ≦ 0.4)
Is related to a hydrogen storage material (hereinafter referred to as hydrogen storage material Y).

  The hydrogen storage material Y is a mixture of particulate Mg metal, particulate V metal, and at least one selected from the group consisting of particulate carbon, particulate magnesium carbide, and particulate vanadium carbide, The obtained mixture can be obtained by a production method including a step of dissolving by heating at 700 to 1000 ° C.

  The hydrogen storage material Y is a mixture of particulate Mg metal, particulate V metal, and at least one selected from the group consisting of particulate carbon, particulate magnesium carbide, and particulate vanadium carbide. And it can obtain by the manufacturing method including the process of providing a mechanical shearing force to the obtained mixture by the mechanical alloying method.

The present invention also includes a metal structure containing (a) a solid solution phase in which boron atoms are incorporated into the crystal structure of Mg, and (b) a solid solution phase in which boron atoms are incorporated into the crystal structure of V. formula:
(Mg _X V _1-X ) B _Y (0.2 ≦ X ≦ 0.9, 0 <Y ≦ 0.4)
The hydrogen storage material (henceforth the hydrogen storage material Z) which has the composition represented by these.

  The hydrogen storage material Z is a mixture of particulate Mg metal, particulate V metal, and at least one selected from the group consisting of particulate boron, particulate magnesium boride, and particulate vanadium boride. In addition, the obtained mixture can be obtained by a production method including a step of heating and dissolving at 700 to 1000 ° C.

  The hydrogen storage material Z is also at least one selected from the group consisting of particulate Mg metal, particulate V metal, particulate boron, particulate magnesium borate, and particulate vanadium boride. Can be obtained by a production method including a step of applying mechanical shearing force to the obtained mixture by a mechanical alloying method.

In the above method for producing the hydrogen storage materials X, Y and Z, the average particle size of the particulate V metal is preferably 10 μm or less.
The present invention further relates to a hydrogen generation apparatus incorporating a hydrogen storage material X, Y or Z.

  According to the present invention, a hydrogen storage material mainly composed of Mg, having a high reaction rate and a small hysteresis, while taking advantage of the high hydrogen storage capability that is characteristic of Mg metal and the excellent plateau flatness in the PCT diagram. Can be provided.

Embodiment 1
The first hydrogen storage material X of the present invention is composed of a metal structure containing a single Mg phase and a solid solution phase of Mg and V. The hydrogen storage material X is preferably composed of a 100% solid solution phase, but usually contains a Mg simple substance phase and a V simple substance phase. The solid solution phase exists mainly near the boundary between the Mg single phase and the V single phase, and in the solid solution phase, Mg atoms are incorporated into the V crystal structure, or V atoms are incorporated into the Mg crystal structure. ing. The Mg single phase may contain a trace amount of V atoms as an inevitable impurity, and the V single phase may contain a trace amount of Mg atoms as an inevitable impurity.

  In the material containing the above three types of phases, the Mg single-phase and the V single-phase are in close contact with each other through the solid solution phase. In such a structure, at the time of hydrogenation, first, V metal immediately reacts with hydrogen and begins to occlude hydrogen. The occluded hydrogen moves to a single Mg phase through a solid solution phase in which V and Mg are mixed at an atomic level. Therefore, it becomes possible to quickly store hydrogen in the Mg single phase. On the other hand, when releasing hydrogen, hydrogen is easily released from the V metal through the solid solution phase from the Mg single phase. Accordingly, hydrogen is quickly released from the Mg single phase. As a result, the hydrogen storage material X is a hydrogen storage material having a high reaction rate related to the storage and release of hydrogen, although Mg is the main component.

The composition of the hydrogen storage material X has the formula:
Mg _X V _1-X (0.2 ≦ X ≦ 0.9)
It is represented by When X is less than 0.2, Mg is too little and hydrogen storage amount becomes insufficient. When X is more than 0.9, V is too little and a solid solution phase is not sufficiently formed, and the effect of the present invention is achieved. Cannot be obtained sufficiently. The higher the content of the solid solution phase in the hydrogen storage material X, the better.

  In the hydrogen storage material X, the maximum hydrogen storage amount varies depending on the V content. The maximum hydrogen storage amount is 7.0% by weight when the atomic ratio of Mg to V is 9: 1. Further, when the atomic ratio of Mg and V is 2 to 8, the maximum hydrogen storage amount is 4.6% by weight.

  Conventionally, it was thought that the Mg element and the V element hardly dissolve each other and do not form a solid solution. However, as a result of the present inventors' investigation through repeated experiments, the Mg element and the V element become a solid solution. The hydrogen storage material X was found to be formed. The melting point of Mg alone is 650 ° C., the melting point of V simple substance is 1910 ° C., and they are greatly different, so that it is difficult to produce an alloy. This is presumed to be the reason why Mg element and V element were thought not to form a solid solution.

  The hydrogen storage material X is obtained by a production method including a step of mixing bulk or particulate Mg metal and particulate V metal, and heating and dissolving the obtained mixture. The temperature for heating and melting is preferably not less than the melting point of Mg alone and not more than the melting point of V alone, specifically 700 to 1000 ° C. In addition, it is preferable that the Mg metal is in the form of particles rather than the bulk in terms of homogenization of the alloy.

The hydrogen storage material X can also be obtained by a production method including a step of mixing particulate Mg metal and particulate V metal and applying a mechanical shearing force to the obtained mixture by a mechanical alloying method. .
In any method, the raw material charge ratio may be adjusted to the composition of the hydrogen storage material X.

  In any method, the average particle diameter of the particulate Mg metal is preferably 100 μm to 1 mm. The average particle size of the particulate V metal is preferably 10 μm or less. By making the average particle size of the particulate V metal 10 μm or less, dissolution of V atoms into the Mg crystal structure is promoted, and the content of the solid solution phase of Mg and V in the hydrogen storage material X can be increased. It is.

  If the V single phase is present in the hydrogen storage material, the rise at the time of hydrogenation in the PCT diagram becomes gradual, and a large hysteresis appears in the vicinity of the Y axis (hydrogen equilibrium pressure axis) when hydrogen is released. On the other hand, by setting the average particle size of V metal to 10 μm or less, a tendency peculiar to the V single phase is less likely to appear, and the PCT diagram has a sharp rise and a small hysteresis. Even if the characteristics of the V single phase are reduced, the reaction rate remains high because there are many phases in which V atoms are incorporated in the crystal structure of Mg.

Embodiment 2
The second hydrogen storage material Y of the present invention includes an Mg-based solid solution phase in which carbon atoms are incorporated into the Mg crystal structure, and a V-based solid solution phase in which carbon atoms are incorporated into the V crystal structure. It consists of a metal structure. The C content in the Mg-based solid solution phase is preferably 5 atomic% or more, and the C content in the V-based solid solution phase is preferably smaller. If the content of C in the solid solution phase mainly composed of Mg is too small, the effect of increasing the reaction rate is reduced, and the hydrogen storage amount decreases as the content increases. Further, the C content in the V-based solid solution phase does not particularly affect the hydrogen storage characteristics. Note that the Mg-based solid solution phase may contain a small amount of V atoms as an unavoidable impurity, and the V-based solid solution phase may include a small amount of Mg atoms as an unavoidable impurity.

  Conventionally, it was thought that carbon atoms hardly dissolve in Mg, but as a result of the present inventors' investigation through repeated experiments, it was found that a considerable amount of carbon atoms can be incorporated into the crystal structure of Mg. As a result, the hydrogen storage material Y was obtained.

  In the material containing the above two types of phases, the hydrogenation / dehydrogenation reaction proceeds rapidly, and the hysteresis in the PCT diagram becomes almost zero. At the time of hydrogenation, it is considered that the V-based solid solution phase containing carbon is difficult to hydrogenate, but the Mg phase containing carbon easily reacts with hydrogen. Therefore, although the hydrogen storage material Y has Mg as a main component, a hydrogen storage material having a high reaction rate related to hydrogen storage can be obtained.

The composition of the hydrogen storage material Y has the formula:
(Mg _X V _1-X ) C _Y (0.2 ≦ X ≦ 0.9, 0 <Y ≦ 0.4)
It is represented by If X is less than 0.2, the amount of Mg is too small and the hydrogen storage amount becomes insufficient, and if X exceeds 0.9, V is too small and it becomes difficult to dissolve carbon in Mg. On the other hand, if Y exceeds 0.4, the hydrogen storage amount is greatly reduced. On the other hand, if Y is too small, an Mg-based solid solution phase and a V-based solid solution phase are hardly formed. Therefore, Y is preferably 0.05 or more.

  In the hydrogen storage material Y, the maximum hydrogen storage amount varies depending on V and carbon content. The maximum hydrogen occlusion amount increases from 7.0% by weight to 3.0% by weight as the carbon content Y is changed from 0 to 0.4 when the atomic ratio of Mg and V is 9: 1. Change. When the atomic ratio of Mg and V is 2 to 8, the maximum hydrogen storage amount is 4.6 wt% to 2.0 wt% as the carbon content Y is changed from 0 to 0.4. And change.

  The hydrogen storage material Y is a mixture of bulk or particulate Mg metal, particulate V metal, and at least one selected from the group consisting of particulate carbon, particulate magnesium carbide, and particulate vanadium carbide. And it can obtain by the manufacturing method including the process of heat-dissolving the obtained mixture. The temperature for heating and melting is preferably 700 to 1000 ° C. from the viewpoint that Mg metal dissolves and evaporation is small. In addition, it is preferable that the Mg metal is in the form of particles rather than the bulk in terms of homogenization of the alloy.

The hydrogen storage material Y is a mixture of particulate Mg metal, particulate V metal, and at least one selected from the group consisting of particulate carbon, particulate magnesium carbide, and particulate vanadium carbide, It can also be obtained by a production method including a step of applying a mechanical shearing force to the obtained mixture by a mechanical alloying method.
In any method, the charging ratio of the raw materials may be matched to the composition of the hydrogen storage material Y. As the particulate carbon, for example, amorphous carbon or graphite can be used.

  In any method, the average particle diameter of the particulate Mg metal is preferably 100 μm to 1 mm. The average particle size of the particulate carbon, magnesium carbide and vanadium carbide is preferably 10 to 100 μm. Further, the average particle diameter of the particulate V metal is preferably 10 μm or less. By making the average particle size of V metal 10 μm or less, as described above, a tendency peculiar to the V single phase is less likely to appear, and the PCT diagram has a sharp rise and has a small hysteresis. Because it becomes.

Embodiment 3
The third hydrogen storage material Z of the present invention includes an Mg-based solid solution phase in which boron atoms are incorporated into the Mg crystal structure, and a V-based solid solution phase in which boron atoms are incorporated into the V crystal structure. It consists of a metal structure. The B content in the Mg-based solid solution phase is preferably 5 atomic% or more, and the B content in the V-based solid solution phase is preferably smaller. If the B content in the solid solution phase mainly composed of Mg is too small, the effect of increasing the reaction rate is reduced, and the hydrogen storage amount decreases as the content increases. Further, the inclusion of B in the V-based solid solution phase does not particularly affect the hydrogen storage characteristics. Note that the Mg-based solid solution phase may contain a small amount of V atoms as an unavoidable impurity, and the V-based solid solution phase may include a small amount of Mg atoms as an unavoidable impurity.

  Conventionally, it was thought that boron atoms hardly dissolve in Mg. However, as a result of inventor's repeated experiments, it was found that a considerable amount of boron atoms can be incorporated into the crystal structure of Mg. Thus, the hydrogen storage material Z has been obtained.

  In the material containing the above two types of phases, the hydrogenation / dehydrogenation reaction proceeds rapidly, and the hysteresis in the PCT diagram becomes almost zero. During hydrogenation, the V-based solid solution phase containing boron hardly reacts with hydrogen. This is presumably because the Mg phase easily reacts with hydrogen by containing boron. Therefore, although the hydrogen storage material Z has Mg as a main component, a hydrogen storage material having a high reaction rate related to hydrogen storage can be obtained.

The composition of the hydrogen storage material Z has the formula:
(Mg _X V _1-X ) B _Y (0.2 ≦ X ≦ 0.9, 0 <Y ≦ 0.4)
It is represented by When X is less than 0.2, the amount of Mg stored is too small, and the hydrogen storage amount becomes insufficient. When X exceeds 0.9, V is too small and it is difficult to dissolve boron in Mg. On the other hand, if Y exceeds 0.4, the hydrogen storage amount is greatly reduced. On the other hand, if Y is too small, an Mg-based solid solution phase and a V-based solid solution phase are hardly formed. Therefore, Y is preferably 0.05 or more.

  In the hydrogen storage material Z, the maximum hydrogen storage amount varies depending on the V and boron contents. The maximum hydrogen occlusion amount is 7.0 wt% to 3.0 wt% as the boron content Y is changed from 0 to 0.4 in the case of an atomic ratio of 9 to 1 between Mg and V. Change. In the case where the atomic ratio of Mg and V is 2 to 8, the maximum hydrogen storage amount is 4.6 wt% to 2.0 wt% as the boron content Y is changed from 0 to 0.4. To change.

  The hydrogen storage material Z is at least one selected from the group consisting of bulk or particulate Mg metal, particulate V metal, particulate boron, particulate magnesium borate, and particulate vanadium boride. Can be obtained by a production method including a step of heating and dissolving the obtained mixture. The temperature for heating and melting is preferably 700 to 1000 ° C. from the viewpoint that Mg metal dissolves and evaporation is small. In addition, it is preferable that the Mg metal is in the form of particles rather than the bulk in terms of homogenization of the alloy.

The hydrogen storage material Z is a mixture of particulate Mg metal, particulate V metal, and at least one selected from the group consisting of particulate boron, particulate magnesium boride, and particulate vanadium boride. And it can also obtain by the manufacturing method including the process of providing a mechanical shearing force with the mechanical alloying method to the obtained mixture.
In any method, the raw material charge ratio may be matched to the composition of the hydrogen storage material Z.

In any method, the average particle diameter of the particulate Mg metal is preferably 100 μm to 1 mm. The average particle size of particulate boron, magnesium boride, and vanadium boride is preferably 10 to 100 μm. Further, the average particle diameter of the particulate V metal is preferably 10 μm or less. By making the average particle size of V metal 10 μm or less, as described above, a tendency peculiar to the V single phase is less likely to appear, and the PCT diagram has a sharp rise and has a small hysteresis. Because it becomes.
EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these.

Bulk Mg and particulate V (average particle size 60 μm) at an atomic ratio of 1: 1 were mixed as a total weight of 20 g, and high-frequency dissolution was performed using a carbon crucible to obtain an ingot having a composition of Mg _0.5 V _0.5 . The high-frequency dissolution was performed in an argon atmosphere at an output of 2 kW for 1 hour at a melting point of Mg and below a melting point of V (900 ° C.).

  As a result of observing the metal structure of the cross-section of the obtained ingot, as shown in the schematic diagram of FIG. 1, the metal is composed of three kinds of Mg single phase 1, V single phase 2 and solid solution phase 3 of Mg and V element. It consisted of an organization. Here, since the melting temperature is set to be equal to or higher than the melting point of Mg alone and equal to or lower than the melting point of V simple substance, Mg is mainly dissolved to cover the V particles. Therefore, the solid solution phase 3 is formed at the boundary between the Mg single phase 1 and the V single phase 2.

Table 1 shows the results of composition analysis of the region of the solid solution phase 3 using an X-ray microanalyzer. From Table 1, it was confirmed that V atoms were incorporated into the crystal structure of Mg for a range of about 20 atom% to 90 atom%.

The ingot was mechanically pulverized until the average particle size became 50 μm, and PCT measurement was performed. FIG. 3 shows a PCT diagram (relationship between the hydrogen equilibrium pressure and the weight ratio of hydrogen occluded in the material) measured at 400 ° C.
For comparison, 20 g of pure Mg was weighed, and a Mg ingot was prepared by high-frequency dissolution under the same dissolution conditions using a carbon crucible. The obtained ingot was mechanically pulverized until the average particle diameter was the same as described above, and PCT measurement was performed. FIG. 4 shows a PCT diagram measured at 400 ° C.

  In FIG. 4, the return of the release curve (white dot plot) was hindered and a large hysteresis occurred, but in FIG. 3, the return of the release curve was greatly improved compared to the case of pure Mg, and the hysteresis was reduced. In the case of FIG. 4, it is considered that the Mg single phase and the V single phase are in close contact with each other via a solid solution phase in which Mg and V are dissolved at the atomic level. That is, during hydrogenation, the V metal immediately reacts with hydrogen and begins to occlude, and hydrogen can move into the Mg single-phase through the solid solution phase. On the other hand, when hydrogen is released, hydrogen is easily released from the V metal through the solid solution phase from the Mg single phase.

  Next, when the above hydrogen storage material was used to assemble a hydrogen generator using a storage container, a pressure regulator, and various pipes, when the storage container was set to 400 ° C., hydrogen with a discharge pressure of 0.1 MPa was stably stabilized. Could be generated.

At a 1: 1 atomic ratio, particulate Mg (20 mesh, average particle size 1 mm) and particulate V (300 mesh, average particle size 60 μm) are mixed in a total weight of 10 g, using a stainless steel container. Mechanical alloying was performed to obtain a powder material having a composition of Mg _0.5 V _0.5 . Mechanical alloying was performed in an argon atmosphere at 400 ° C. for 168 hours. As a result of observing the metal structure of the obtained powder material, it was composed of three kinds of metal structures as schematically shown in FIG.

  When PCT measurement was performed using the above powder material, the PCT diagram measured at 400 ° C. was the same as FIG. 3, and the return of the release curve was greatly improved and the hysteresis was small compared to pure Mg. It was.

At an atomic ratio of 8: 2: 1, bulk Mg, particulate V (average particle size 60 μm), and particulate amorphous carbon are mixed in a total weight of 20 g, and high-frequency dissolved using a carbon crucible. An ingot having a composition of Mg _0.8 V _0.2 C _0.1 was obtained. The high-frequency dissolution was performed in an argon atmosphere at an output of 2 kW for 1 hour at a melting point of Mg and below a melting point of V (900 ° C.).

  As a result of observing the metal structure of the cross section of the obtained ingot, as shown in the schematic diagram of FIG. 2, the Mg-based solid solution phase 4 in which carbon atoms are incorporated into the Mg crystal structure, and the crystal structure of V carbon atoms There were two types, V and a solid solution phase 5 mainly composed of V. Further, there was no V single phase, Mg single phase, or C single phase. Here, since the melting temperature is set to be equal to or higher than the melting point of Mg alone and to the melting points of V and C alone, it is considered that only Mg is dissolved.

Table 2 shows the results of composition analysis of the regions of the Mg-based solid solution phase 4 and the V-based solid solution phase 5 using an X-ray microanalyzer. From Table 2, it was confirmed that about 5 atomic% of carbon was incorporated in the solid solution phase mainly composed of Mg, and about 33 atomic% of carbon was incorporated into the solid solution phase mainly composed of V.

  The ingot was mechanically pulverized until the average particle size became 50 μm, and PCT measurement was performed. FIG. 5 shows a PCT diagram (relationship between hydrogen equilibrium pressure and weight ratio of hydrogen occluded in the material) measured at 400 ° C.

  In FIG. 5, compared to the case of pure Mg (FIG. 4), the return of the release curve is greatly improved, the hysteresis is very small, and the squareness is excellent. In the case of FIG. 5, this is probably because the V-based solid solution phase containing carbon hardly reacts with hydrogen during hydrogenation, and the Mg-based solid solution phase containing carbon easily reacts with hydrogen.

  Next, when the above hydrogen storage material was used to assemble a hydrogen generator using a storage container, a pressure regulator, and various pipes, when the storage container was set to 400 ° C., hydrogen with a discharge pressure of 0.1 MPa was stably stabilized. Could be generated.

Total amount of particulate Mg (20 mesh, average particle size 1 mm), particulate V (300 mesh, average particle size 60 μm) and amorphous carbon having an average particle size of 10 μm in an atomic ratio of 8: 2: 1. The mixture was mixed at a weight of 10 g and subjected to mechanical alloying using a stainless steel container to obtain a powder material having a composition of Mg _0.8 V _0.2 C _0.1 . Mechanical alloying was performed in an argon atmosphere at 400 ° C. for 168 hours. As a result of observing the metal structure of the obtained powder material, it was found that an Mg-based solid solution phase in which carbon atoms were incorporated into the Mg crystal structure and a V-based solid solution phase in which carbon atoms were incorporated into the V crystal structure. There were two types, and there was no V single phase or the like.

  When the PCT measurement was performed using the above powder material, the PCT diagram measured at 400 ° C. was the same as FIG. 5, and the return of the release curve was greatly improved compared to pure Mg, and the hysteresis characteristics were improved. It was very good.

At a ratio of 8: 2: 1, bulk Mg, particulate V (average particle size 60 μm), and particulate boron are mixed in a total weight of 20 g, and high-frequency dissolved using a carbon crucible. Obtained an ingot of Mg _0.8 V _0.2 B _0.1 . The high-frequency dissolution was performed in an argon atmosphere at an output of 2 kW for 1 hour at a melting point of Mg and below a melting point of V (900 ° C.).

  As a result of observing the metal structure of the cross section of the obtained ingot, it was found that there was a Mg-based solid solution phase in which boron atoms were incorporated into the Mg crystal structure and a V-based solid solution phase in which boron atoms were incorporated into the V crystal structure. There were two types. Further, there was no V single phase. Here, since the melting temperature is set to be equal to or higher than the melting point of Mg alone and to the melting point of V alone, it is considered that only Mg is dissolved.

  Composition analysis of the Mg-based solid solution phase and the V-based solid solution phase with an X-ray microanalyzer revealed that about 5 atomic percent of boron was incorporated into the Mg-based solid solution phase, It was confirmed that about 40 atomic% of boron was incorporated into the phase.

  The ingot was mechanically pulverized until the average particle size became 50 μm, and PCT measurement was performed. FIG. 6 shows a PCT diagram (relationship between the hydrogen equilibrium pressure and the weight ratio of hydrogen occluded in the material) measured at 400 ° C.

  In FIG. 6, compared to the case of pure Mg (FIG. 4), the return of the release curve is greatly improved, the hysteresis is very small, and the squareness is excellent. This is probably because in the case of FIG. 6, the V-based solid solution phase containing boron hardly reacts with hydrogen during hydrogenation, and the Mg-based solid solution phase containing boron easily reacts with hydrogen.

  Next, when the above hydrogen storage material was used to assemble a hydrogen generator using a storage container, a pressure regulator, and various pipes, when the storage container was set to 400 ° C., hydrogen with a discharge pressure of 0.1 MPa was stably stabilized. Could be generated.

Particulate Mg (20 mesh, average particle size 1 mm) with an atomic ratio of 8: 2: 1, particulate V (300 mesh, average particle size 60 μm), and particulate boron (300 mesh, average particle size 60 μm) And a total weight of 10 g, and mechanical alloying was performed using a stainless steel container to obtain a powder material having a composition of Mg _0.8 V _0.2 B _0.1 . Mechanical alloying was performed in an argon atmosphere at 400 ° C. for 168 hours. As a result of observing the metallographic structure of the obtained powder material, it was found that an Mg-based solid solution phase in which boron atoms were incorporated into the Mg crystal structure and a V-based solid solution phase in which boron atoms were incorporated into the V crystal structure. There were two types and no V single phase.

  When PCT measurement was performed using the above powder material, the PCT diagram measured at 400 ° C. was the same as FIG. 6, and the return of the release curve was greatly improved compared to pure Mg, and the hysteresis characteristics were improved. It was very good.

  A hydrogen storage material was produced in the same manner as in Example 1 except that the average particle size of the particulate V was 8 μm. And the PCT diagram was calculated | required similarly to Example 1. FIG. As a result, the rise of the PCT diagram was further sharpened, and the hysteresis also tended to be smaller.

  In the case of the Mg—V—C system according to Examples 3 and 4 and the Mg—V—B system alloy according to Examples 5 and 6, the average particle size of the particulate V is set to 10 μm or less. It is considered that the dissolution of V in Mg is promoted to promote homogenization, and the effect of sharpening the rise of the release curve in the PCT diagram can be seen.

  According to the hydrogen storage material of the present invention, it is possible to provide a hydrogen generator that is compact and highly safe, has a high hydrogen storage capacity, and can supply hydrogen quickly.

It is a schematic diagram of the metal structure of the hydrogen storage material whose composition is Mg _0.5 V _0.5 . It is a schematic diagram of the metal structure of the hydrogen storage material whose composition is Mg _0.8 V _0.2 C _0.1 . It is a PCT diagram of the hydrogen storage material whose composition is Mg _0.5 V _0.5 . It is a PCT diagram of pure Mg. It is a PCT diagram of a hydrogen storage material having a composition of Mg _0.8 V _0.2 C _0.1 . It is a PCT diagram of the hydrogen storage material whose composition is Mg _0.8 V _0.2 B _0.1

Explanation of symbols

1 Mg single phase 2 V single phase 3 Mg and V solid solution phase 4 Solid solution phase mainly composed of Mg 5 Solid solution phase mainly composed of V

Claims (11)

A hydrogen storage material,
(A) a single phase of Mg;
And (b) a metal structure including a solid solution phase in which Mg atoms are incorporated into the crystal structure of V or V atoms are incorporated into the crystal structure of Mg, and the formula:
Mg _X V _1-X (0.2 ≦ X ≦ 0.9)
A hydrogen storage material having a composition represented by:   The method for producing a hydrogen storage material according to claim 1, further comprising a step of mixing particulate Mg metal and particulate V metal, and heating and dissolving the obtained mixture at 700 to 1000 ° C.   The method for producing a hydrogen storage material according to claim 1, further comprising a step of mixing particulate Mg metal and particulate V metal, and applying mechanical shearing force to the obtained mixture by a mechanical alloying method. A hydrogen storage material,
(A) a solid solution phase in which carbon atoms are incorporated into the crystal structure of Mg;
(B) a metal structure containing a solid solution phase in which carbon atoms are incorporated into the crystal structure of V, and the formula:
(Mg _X V _1-X ) C _Y (0.2 ≦ X ≦ 0.9, 0 <Y ≦ 0.4)
A hydrogen storage material having a composition represented by:   Particulate Mg metal, particulate V metal, and at least one selected from the group consisting of particulate carbon, particulate magnesium carbide and particulate vanadium carbide are mixed, and the resulting mixture is 700. The method for producing a hydrogen storage material according to claim 4, comprising a step of heating and dissolving at ˜1000 ° C.   Particulate Mg metal, particulate V metal, and at least one selected from the group consisting of particulate carbon, particulate magnesium carbide, and particulate vanadium carbide are mixed, and the resulting mixture is mechanically mixed. The method for producing a hydrogen storage material according to claim 4, further comprising a step of applying a mechanical shearing force by an alloying method. A hydrogen storage material,
(A) a solid solution phase in which boron atoms are incorporated into the crystal structure of Mg;
(B) a metal structure containing a solid solution phase in which boron atoms are incorporated into the crystal structure of V, and the formula:
(Mg _X V _1-X ) B _Y (0.2 ≦ X ≦ 0.9, 0 <Y ≦ 0.4)
A hydrogen storage material having a composition represented by:   A mixture obtained by mixing particulate Mg metal, particulate V metal, and at least one selected from the group consisting of particulate boron, particulate magnesium borate, and particulate vanadium boride. The method for producing a hydrogen storage material according to claim 7, further comprising a step of heating and melting at 700 to 1000 ° C.   A mixture obtained by mixing particulate Mg metal, particulate V metal, and at least one selected from the group consisting of particulate boron, particulate magnesium borate, and particulate vanadium boride. The method for producing a hydrogen storage material according to claim 7, further comprising a step of applying a mechanical shearing force by mechanical alloying.   The method for producing a hydrogen storage material according to claim 2, 3, 5, 6, 8, or 9, wherein the average particle diameter of the particulate V metal is 10 µm or less.   A hydrogen generator incorporating the hydrogen storage material according to claim 1, 4 or 7.

Images