JPS5841333B2 - Alloy for hydrogen storage - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydrogen storage alloy, and more specifically, the present invention relates to a hydrogen storage alloy that can store a large amount of hydrogen in the form of a hydride, and can easily and quickly release hydrogen with a small amount of heating. This invention relates to a new and practically useful hydrogen storage alloy that has an extremely small difference between storage pressure and release pressure, that is, hysteresis.

Hydrogen has no resource limitations and is clean, transportable,
Because it is easy to store, it is attracting attention as a new energy source to replace fossil fuels.

However, since hydrogen is a gas at room temperature and its liquefaction temperature is extremely low, it is important to develop storage technology for hydrogen.

A storage method that has attracted attention in recent years is a method in which hydrogen is absorbed into a metal and stored as a metal hydride.

In addition, the absorption/desorption reaction between metals and hydrogen is reversible, and a considerable amount of reaction heat is generated and absorbed during the reaction, and hydrogen absorption/desorption pressure depends on temperature. Research is being conducted to apply it to pressure (mechanical) energy conversion devices.

The properties required for such a hydrogen storage material are that it is inexpensive and abundant in terms of resources, that it is easy to activate and has a large hydrogen storage capacity, that it has an appropriate hydrogen storage and desorption equilibrium pressure near room temperature, and that it has an appropriate hydrogen storage and desorption equilibrium pressure. The hysteresis of hydrogen is small, the hydrogen absorption and release reaction is reversible, and its speed is high.

As a typical known hydrogen storage material, for example, LaNi
5. FeTi is known.

These alloys have a reversible hydrogen storage and release reaction and a large hydrogen storage capacity, but the hydrogen storage and release reaction is slow.
It cannot be said that activation is easy, and it has drawbacks such as large hysteresis, which poses a serious problem in practical use.

The inventors conducted research to eliminate the drawbacks of these conventional hydrogen storage alloys, and found that an alloy composed of rare earth metals, nickel, aluminum, and titanium or zirconium satisfies the above conditions and is superior to conventional alloys. They discovered that it was extremely useful and completed the invention.

That is, the present invention provides an RNi5-αAlα alloy with (
This was done by focusing on substituting a part of R (representing a rare earth metal) with titanium or zirconium (represented by Mt), or adding titanium or zirconium (Mt), and the hydrogen storage material of the present invention The alloy has the general formula R
It is represented by Ni5-XAlyMtz.

In the formula, X is a number in the range of 0.01 to 2.0, y is 0.01
A number in the range of ~2.0, 2 is a number in the range of 0-0.2 (excluding O), and 5.0≦5- x + y + z
The relationship ≦5.2 holds true.

In the present invention, the rare earth metal (R) includes not only a single metal but also a mixed metal (Mm).

Mitshu metal (Mm) is a mixed metal that generally contains 25 to 30% by weight of lanthanum and 40 to 50% by weight of cerium, praseodymium, neodymium, samarium, phosphorus, etc., and has trace amounts of impurities.

It is generally known that rare earth metals (R) and nickel form a metal compound called 1,RNis that forms a CaCu5 type hexagonal crystal, but metals other than LaNi5 have a high hydrogen storage and desorption pressure near room temperature.

For example, MmN i is 20 to 40 atmospheres, CeNi,
or S mN i 5, it is 40 to 80 atm.

Therefore, the hydrogen absorption and desorption pressure is reduced by substituting a portion of nickel with aluminum.

That is, in RNi5-αAlα, α is 0.01 to 2
．． Adjust within the range of 0.

The preferable range of the amount of aluminum (value of α) is 0.1 to
It is 1.0.

However, in these alloys, the difference between hydrogen storage pressure and hydrogen release pressure, ie, hysteresis, becomes large.

For example, MrTINi4.7AI.

, 3, the hydrogen storage pressure is about 13 atm at 30°C, the hydrogen release pressure is about 7 atm, and the hysteresis is about 6 atm.
There is also atmospheric pressure.

The large hysteresis means that in order to operate hydrogen storage and desorption, the hydrogen storage alloy or its metal hydride must be heated and cooled with a larger temperature difference, or hydrogen must be pressurized or depressurized with a larger pressure difference. However, hydrogen storage capacity and hydrogenation reaction heat cannot be effectively utilized.

The present inventors have proposed that in the alloy represented by the general formula RNi5-αAlα, a portion of the alloy may be replaced with titanium or zirconium (Mt), or titanium or zirconium (Mt) may be substituted with titanium or zirconium (Mt).
It has been found that the addition of t) greatly reduces the hysteresis of hydrogen storage and release pressure.

The hydrogen storage alloy of the present invention has the general formula RNs=, xAlyM
It is expressed as tz.

In the formula, X is a number in the range of 0.01 to 2, and y is 0.01 to 2.
．． The number in the range of 0, Z is a number in the range of O to 0.2 (however, O is excluded), and the relationship 5.0≦5−x+y+z≦5.2 holds true.

When titanium or zirconium replaces a part of RNi5-αA1α, it becomes a metal compound that forms an RNi5-type hexagonal crystal with a rare earth metal, similar to aluminum.

That is, in RNi5-xAlyMtz,
The relationship 1-z and y≧2 holds true, and 5-X+ y +
z=5.

When titanium or zirconium is added to RNi5-αAlα, its structure is unknown, but basically R
It is a Nis type metal compound.

RNi... In AlyMtz, X2y and y≧2
The following relationship is established, 2 is a number in the range of O1 to 0.1 (however, O is excluded), and 5.0<5-x+y+z≦5.2.

In addition to the above-mentioned two typical examples, there is naturally a range of cases in which titanium or zirconium is substituted for a part of RNis-αAlα and cases in which titanium or zirconium is added.

Due to the presence of titanium or zirconium, the difference in hydrogen storage and release pressure at 300C and hysteresis are reduced! vhnNi4
．． s A1g4T io, 1 is approximately 1.5 atm, MmN
i4.7A'o-: +Tio, 15 was about 3 atmospheres, and the hysteresis was reduced to less than half that of the conventional alloy in which titanium was not substituted or added.

As in the latter example, titanium or zirconium is added to RNi5-αA1α, and the alloy is RNi-αAlα(
In the example above, MmNi4! IAI is particularly useful for reducing hysteresis by reducing only the hydrogen storage pressure, with almost no change in the hydrogen release pressure compared to IAI.

The details of the function of titanium or zirconium are unknown.

However, titanium or zirconium RNi5-α
In alloys in which part of Alα is replaced, the hydrogen storage and desorption pressure increases overall and S, whereas in alloys in which titanium or zirconium is added to RNi, -αAlα, the hydrogen storage and desorption pressure decreases in total and X. Therefore, it can be concluded that there is a slight difference in the function of titanium or zirconium due to the difference in the crystal structure of the metal compound.

Titanium or zirconium occludes hydrogen by itself, but the occluded hydrogen becomes a solid solution in titanium or zirconium to form an extremely stable compound, and the occluded hydrogen is not easily released.

Therefore, as the amount of titanium or zirconium increases, the hydrogen storage capacity of the alloy decreases, and furthermore, the plateau region of the hydrogen storage and release pressure curve tends to become two-step.
In Ni5-xAlyMtz, 2 is limited to a number in the range of 0 to 0.2 (excluding O), preferably y≧2, and when X=y, 2 is in the range of O to 0.1. The number of (
(excluding 0) and the amount of titanium or zirconium added is limited.

The hydrogen storage alloy of the present invention can be manufactured by taking predetermined amounts of each component metal, mixing them, and melting them.

When melting each component metal, the melting point range is 600°C to 1
, 700℃, so after first melting the components excluding titanium or zirconium, titanium or zirconium is added and melted again, or titanium or zirconium powder is added to the melt of the metal components excluding titanium or zirconium. Alternatively, a predetermined alloy can be produced by adding small lumps and a liquid-solid reaction.

Hydrogen storage alloys are usually used in powder form to increase surface area.

The hydrogen storage alloy produced by the above method is sealed in a sealed container, degassed, and then pressurized with hydrogen of around 10 atm at room temperature, so that it immediately starts to react with hydrogen, and the hydrogen storage reaction Activation can be completed in a very short time of several minutes, followed by vacuum degassing, with just one hydrogen storage and desorption operation.

As described above, the hydrogen storage alloy of the present invention is a new alloy developed for the first time and has all the properties required as a hydrogen storage material. The hydrogen storage capacity as a hydrogen storage alloy and the reaction heat accompanying the hydrogen storage and release reaction can be effectively utilized.

Furthermore, activation of the hydrogen storage and release reaction is extremely easy, and a large amount of hydrogen can be stored and released at a high density, and hydrogen can be stored and released at a temperature close to room temperature. There is no deterioration in the performance of the alloy, making it a practically extremely useful hydrogen storage material.

Example 1 Commercially available Mitsushi metal, nickel, aluminum, and titanium were mixed into Mm:Ni:Al:Ti=1:4.
5:0.45:0.05, and this was vacuum melted in a high purity aluminum crucible.

The dissolution operation was repeated several times to homogenize the composition.

Analysis of the obtained alloy revealed that the composition was Mr'rINi4.
．． 5Alo, 45Tio,.

, was confirmed.

Grind this alloy into 100 to 120 meshes, approximately 5g
r was accurately weighed and sealed in a sealed reaction vessel.

After degassing the sealed reaction vessel by vacuum suction, hydrogen with a purity of 99.999% was introduced into the sealed reaction vessel for 20 minutes.
kg/cr? When the pressure was increased to 1, the hydrogen storage reaction immediately started at room temperature.

After sufficiently absorbing hydrogen, vacuum suction was performed again.

Activation of the alloy was almost completely achieved with one hydrogen storage/release.

This sealed reaction vessel was immersed in a constant-temperature water bath maintained at a constant temperature, and the amount of hydrogen introduced and pressure changes were measured to create pressure composition isotherms.

FIG. 1 is a pressure-composition curve at 30° C., with the upper portion being during occlusion and the lower portion being during desorption.

As is clear from the figure, the hydrogen storage capacity of the alloy is large and shows a good plateau region.

This pressure-composition isotherm was created at various temperatures, and the relationship between pressure and temperature at the center of the plateau region is shown in FIG. 2 as the logarithm of pressure-the reciprocal of absolute temperature.

Again, the upper straight line represents the hydrogen storage reaction, and the lower straight line represents the hydrogen release reaction.

The dotted line is a pressure-temperature diagram of a hydrogen storage alloy having a composition of MmN i 4.5A Io,s.

As is clear from FIG. 2, the hydrogen storage alloy of the present invention has significantly improved hysteresis compared to the comparative example.

In the comparative example, a higher pressure of hydrogen was required for activation, and 2.3 hydrogen absorption and desorption operations were required for almost complete activation.

Example 2 A hydrogen storage alloy having the composition MmN i4.7AIo, 3Tio, o5 was produced and activated in the same manner as in Example 1.

The pressure-temperature relationship of this hydrogen storage alloy is shown in FIG.

A comparative example is a hydrogen storage alloy having the composition MmNi+, 7Al□, 3.

As is clear from FIG. 3, the hysteresis is significantly improved compared to the comparative example.

In addition, compared to the comparative example, the hydrogen release pressure is almost unchanged and the hydrogen storage pressure is reduced, so there is no significant deviation from the pressure characteristics of the comparative example, which is advantageous for the design of metal hydride reactors. It is.

Example 3 Composition IVrnN t4.7 A Ig, 3 Z ro
, 1 were produced and activated in the same manner as in Example 1.

The pressure-temperature relationship of this hydrogen storage alloy is shown in FIG.

A comparative example is a hydrogen storage alloy having the composition MmN i4.7A lo,s.

As is clear from FIG. 4, the hysteresis is significantly improved compared to the comparative example.

Further, as in Example 2, the hydrogen storage alloy of the present invention is advantageous in that the hydrogen release pressure is almost unchanged and the hydrogen storage pressure is reduced compared to the comparative example.

[Brief explanation of drawings]

Figure 1 is a pressure-composition isotherm diagram of Example 1 of the hydrogen storage alloy of the present invention, Figure 2 is a pressure-temperature diagram of Example 1 shown together with a comparative example, and Figures 3 and 4 are the same. The pressure-temperature diagram of Example 2 and Example 3 shown together with a comparative example.

Claims (1)

[Claims] 1 General formula BNi6. A hydrogen storage alloy represented by cAlyMt2. In the formula, R is a rare earth metal, Mt is titanium or zirconium, X is a number in the range of 0.01 to 2.0, and y is 0.01 to
A number in the range of 2.0, 2 is a number in the range of O to 0.2 (however, O
), and 5.0≦5− x + y +2≦5
．． Two relationships are established. 2. In claim 1, X=y+z and y
A hydrogen storage alloy that satisfies the relationship ≧2. 3 In claim 1, x−y and y≧2
and 2 is a number in the range of 0-0.1 (excluding O).