JP5356495B2 - High capacity hydrogen storage alloy - Google Patents

Description

  The present invention relates to a hydrogen storage material, a hydrogen absorption material for heat conversion, a hydrogen supply material for a fuel cell, a negative electrode material for a Ni-hydrogen battery, a hydrogen purification and recovery material, a hydrogen absorption material for a hydrogen gas actuator, etc. It relates to a storage alloy.

Conventionally, there are a cylinder method and a liquid hydrogen method for storing and transporting hydrogen, but a method using a hydrogen storage alloy is attracting attention instead of these methods. As is well known, hydrogen storage alloys have the property of reversibly reacting with hydrogen and absorbing and releasing hydrogen with the input and output of reaction heat. The technology for storing and transporting hydrogen using this chemical reaction has been put to practical use, and further, the development and practical application of the technology for configuring heat storage, heat transport system, etc. using reaction heat has been promoted. ing. As typical hydrogen storage alloys, LaNi ₅ , TiFe, TiMn _{1.5 and the} like are well known. Recently, attention has been focused on an alloy having a body-centered cubic structure (hereinafter referred to as a BCC alloy) that has a large effective hydrogen transfer amount near room temperature, and in particular, it is improved by adding additional elements to TiCrV alloy and TiCrV alloy There are alloys such as TiCr-based BCC alloys and TiMnV alloys as disclosed in Patent Document 1, and many BCC alloys whose characteristics have been improved by using special manufacturing methods and techniques have been proposed. For example, Patent Document 2 proposes an alloy in which TiCrV is replaced with Mo to increase the equilibrium dissociation pressure without greatly reducing the hydrogen release amount and to enable hydrogen release in a low temperature range.

Japanese Patent No. 3528599 JP 2006-188737 A

However, the BCC alloy forms a BCC alloy by adding an element having a BCC structure such as V and Mo in base over scan a Laves phase alloy such TiCr ₂ and TiMn _2, such as severe heat treatment depending on the composition There is a problem that a BCC single-phase structure cannot be obtained unless the production method is performed.
Moreover, in the practical application of various applications, it is necessary to further improve the characteristics of the hydrogen storage material.For example, increasing the amount of hydrogen storage, lowering the cost of raw materials, improving the plateau characteristics, improving the durability, etc. Are listed. Among them, it has been known for a long time that BCC alloys such as V, TiMnV-based and TiCrV-based alloys occlude a large amount of hydrogen compared to AB ₅ type alloys and AB ₂ type alloys that have already been put into practical use. However, the existing BCC-type hydrogen storage alloy has a problem in hydrogen release characteristics in a low temperature region such as below freezing point. In order to release hydrogen in a low temperature range, it is necessary to decrease the Ti / Cr ratio and increase the amount of Cr. However, this causes a problem that the amount of released hydrogen decreases. Therefore, there are many points that should be improved, such as further increase in the amount of effective hydrogen transfer and durability.

  The basic object of the present invention is to provide a hydrogen storage alloy that can effectively absorb and release hydrogen at room temperature, and has improved release characteristics in a low temperature range such as below freezing. It is the purpose.

The present invention of a high capacity hydrogen storage alloy has the general formula Ti _a Mo _b V _c (where a, b, c are at%, a + b + c = 100, 0 <b <25, c <70, a / b ≦ 2) And having a body-centered cubic structure.

  That is, the present invention is characterized in that Ti, Mo, and V are constituent elements and has a body-centered cubic structure, or Fe is used as a raw material for the hydrogen storage alloy. The constituent elements are basically a TiMoV ternary system or a TiMoVFe quaternary system, but the impurities inevitably mixed in the manufacturing are not limited to this. An alloy having this composition shows a BCC single-phase structure even when dissolved, so that no special heat treatment is required, but heat treatment may be performed depending on the application.

Note that the above-mentioned a, b, and c have a total amount of 100 and need to satisfy 0 <b <25.
Regarding the amount ratio a of Ti, when c ≧ 70, it is necessary to be less than 30 in order to prevent an extreme decrease in the equilibrium dissociation pressure. On the other hand, when c <70, a is 5 or more, satisfies a / b ≦ 2 in relation to the following b, and is in the range of a <50.
Further, the Mo amount ratio b is set to less than 25 as described above in order to prevent a significant decrease in mass storage density. Further, it is desirable that 0 <b <20.

  Further, in the relationship between the quantity ratios a and b, when c <70, it is necessary that a / b ≦ 2 as described above. By maintaining the relationship of the ratio, an extreme decrease in the equilibrium dissociation pressure can be prevented, and an alloy having an equilibrium dissociation pressure according to the application can be provided. There is an effect of reducing the amount of hydrogen (solid hydrogen) and increasing the amount of hydrogen that can be used effectively.

  Further, V is not an element that causes a significant change in the equilibrium dissociation pressure or the hydrogen storage amount, and therefore can be appropriately adjusted according to the contents of Ti and Mo, and the amount ratio c is 25 ≦ It can be selected within the range of c <100.

That is, the high-capacity hydrogen storage alloy of the present invention has a general formula Ti _a Mo _b V _c (where a, b, c are at%, a + b + c = 100, 0 <b <25, c <70, a / b ≦ 2) and has a body-centered cubic structure, it can absorb and release hydrogen effectively at room temperature, and has excellent emission characteristics at low temperatures such as below freezing.
In addition, for existing BCC-type hydrogen storage alloys, depending on the composition, a process such as severe heat treatment is required, but the alloys provided by the present invention exhibit a BCC structure even when dissolved in the entire composition range. Therefore, a post-treatment such as a special heat treatment is unnecessary, the manufacturing burden is reduced, and inclusion of unnecessary impurity elements accompanying the post-treatment can be eliminated.

It is a PCT line diagram of Ti ₄ Mo ₆ V _90. It is a graph showing the relationship between the Mo content and the equilibrium dissociation pressure of _{V 90 Ti 10-x Mo x} . It is a PCT line diagram of Ti ₂₀ Mo ₇ V _73. It is a graph showing the relationship between the Mo content and the hydrogen amount of movement _{Ti 33 Mo x V 67-x} . Is a diagram showing the relationship between the Ti / Mo and the equilibrium pressure in the Ti _30-x Mo _{x V 70} and _{Ti 10-x Mo x V 90} . Is a diagram showing the relationship between the Ti / Mo and the equilibrium pressure in the Ti ₃₃ Mo _x V _67-x and _{Ti 50 Mo x V 50-x} . It is the figure which plotted the composition range of the Ti-Mo-V ternary system alloy of this invention, and an Example test material.

Hereinafter, embodiments of the present invention will be described.
The high-capacity hydrogen storage alloy of the present invention can be obtained by preparing components so as to be within the composition range of the present invention, and by melting and solidifying. The dissolution and coagulation methods are not particularly limited in the present invention, and known methods can be employed.
The alloy obtained by melting and solidification has a BCC structure as melted, and does not require post-treatment such as heat treatment to obtain the BCC structure as in the prior art. However, the present invention does not exclude post-processing, and post-processing such as appropriate heat treatment can be performed as necessary.
The obtained high-capacity hydrogen storage alloy can absorb and release hydrogen effectively at room temperature, and also has excellent release characteristics in a low temperature range such as below freezing point.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a PCT diagram of Ti ₄ Mo ₆ V ₉₀ as melted. As is apparent from the figure, it shows a characteristic that shows a wide plateau region even at 0 ° C., and has excellent emission characteristics in a low temperature region. Furthermore, FIG. 2 shows the change in the equilibrium dissociation pressure with respect to the Mo content in a composition containing 90 at% V. As shown in the figure, the equilibrium dissociation pressure can be greatly changed by changing the content ratio of Ti and Mo, and a wide plateau in a low temperature region can be achieved under the required conditions.

In addition, this alloy can effectively absorb and release hydrogen even in the normal temperature range by adjusting the composition. FIG. 3 shows a PCT diagram of Ti ₂₀ Mo ₇ V ₇₃ . As is clear from the figure, the effective hydrogen transfer amount in the normal temperature region is also large.

  Furthermore, the effective hydrogen storage amount of the hydrogen storage alloy of the present invention greatly depends on the Mo amount, and an example is shown in FIG. It can be seen that the amount of Mo that secures an effective hydrogen storage amount of 300 cc / g and prevents a significant decrease in mass storage density is less than 25 at%. This tendency is the same for alloys having different Ti and V contents. Therefore, in the above reference example, the Mo content ratio is less than 25 at%.

Further, FIG. 5 shows the change in the equilibrium pressure with respect to the change in the Ti / Mo (a / b) ratio in each alloy in which the amount ratio of V is 70 and 90. Since an equilibrium pressure of 0.01 or more is required, when the amount ratio of V is 70, the equilibrium pressure may not be satisfied depending on the ratio of Ti / Mo, but the amount ratio of V is When it reaches 90, the equilibrium pressure is high, and an equilibrium pressure of 0.01 or more is secured regardless of the ratio of the above-mentioned quantitative ratios. For this reason, it is necessary to regulate the Ti / Mo ratio in accordance with the amount ratio c of V. That is, when c ≧ 70, the above ratio is not particularly required, and when c <70, the ratio a / b is regulated.
FIG. 6 is a diagram showing changes in the equilibrium pressure when a / b is changed in two types of hydrogen storage alloys. As is apparent from this figure, an equilibrium pressure of 0.01 is secured by setting a / b to 2.0 or less. Therefore, in the present invention, a / b ≦ 2 is an essential condition under the condition of c <70.

Further, for the alloys shown in Table 1, the effective hydrogen transfer amount was measured by calculating the plateau width excluding the solid solution hydrogen amount (meaning dead hydrogen) of 0.01 MPa or less. The results are shown in Table 1. Further, the composition of each alloy is plotted in the composition diagram shown in FIG.
As is apparent from the table and FIG. 7, the alloy within the scope of the present invention is excellent in the effective hydrogen transfer amount, and the alloy outside the range of the present invention and the reference example has a small effective hydrogen transfer amount. was gotten.

Claims (1)

It has a composition represented by the general formula Ti _a Mo _b V _c (where a, b, c are at%, a + b + c = 100, 0 <b <25, c <70, a / b ≦ 2), A high capacity hydrogen storage alloy characterized by having a centered cubic structure.

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