JPS583025B2 - Metal materials for hydrogen storage - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on the general formula Ti-Mn-M (where M is V, C
The present invention relates to a practical metal material for hydrogen storage, which is made of an alloy represented by at least one metal selected from the group consisting of: r, Fe, Co, Nt, Cu, and Mo, and is capable of storing hydrogen at high density and safely. It is something.

BACKGROUND ART It has been known that certain metals, such as transition metals in groups 1-2 of the periodic table, form metallic compounds with hydrogen.

These metal hydrides are, for example, LaH3 + CeH
It is shown as 3 + TtH2 t ZrH2VH2, NbH2, and a maximum of three hydrogen atoms are bonded to one metal atom in a solid metal.

Each of these single metal materials can absorb hydrogen and retain it at high density under a hydrogen atmosphere at a specific temperature and pressure, and can further absorb hydrogen by changing the temperature or pressure conditions or both. It has the property of being able to release hydrogen reversibly.

Metals forming metal hydrides can therefore be used as materials for storing and retaining hydrogen.

However, these single metal materials have several drawbacks compared to the gas cylinder method and liquid hydrogen method that are currently commonly used as hydrogen storage methods.

For example, many of the above-mentioned metal hydrides have a strong bond between the metal and hydrogen, so when absorbing or releasing hydrogen, they must be operated under harsh conditions, i.e., in the case of Ti, near normal pressure. To start hydrogen absorption at about 400
It has the disadvantage of requiring heating above ℃.

Later, Ti-based alloys were discovered, namely FeTi,
Ti (or Zr)-Cu alloy, Ti (or Zr)
Although the hydrogen absorption and release conditions for r)-Ni alloys and the like have been somewhat relaxed, they still require heating at several hundred degrees centigrade or higher for a relatively long period of time.

On the other hand, alloys of rare earth elements such as R-Ni5 and R-Co5 (R: rare earth element) have been found as hydrogen storage materials with easy operating conditions for hydrogen absorption and release.

However, these materials have a relatively small amount of hydrogen storage per unit weight compared to other hydrogen storage materials, and in order to demonstrate the hydrogen storage material properties of the alloys of the present invention,
In Figures 3 and 4, the vertical axis shows the hydrogen dissociation equilibrium pressure (Pat
m), and the horizontal axis shows the hydrogen absorption amount (x
A P-x-T relationship diagram is shown in which a material (alloy) temperature isotherm (T° C.) is drawn on a graph of ccH2/g).

In these figures, the sample temperature (T°C) is 25°C, and the samples are numbered A (M=V), A (M=V), D(M=Cr), E(M
= Fe), G (M = Co), and H (M = Ni) in Figure 4.
), I (M=Cu), and J (M=Mo), respectively.

From Table 1 and Figures 3 and 4, it can be seen that the alloy of the present invention has a relatively large amount of absorbed hydrogen and released hydrogen, and furthermore, the predetermined pressure at each temperature is almost horizontal to the amount of hydrogen absorbed (x). It can be seen that the pressure range, so-called plateau pressure, exists in the range of 4 to 20 atm at room temperature, and that it is very excellent as a metal material for hydrogen storage, as it does not require heating when releasing hydrogen.

Other advantages of the alloy of the present invention are (1) In an alloy whose lattice constant is adjusted to an optimal value, the M content of the Ti-Mn-M alloy is approximately 10 atomic % or less at most; Even though V, Mo, etc. are expensive, it is a material that is cheaper in cost compared to known hydrogen storage materials, (2) the speed at which hydrogen is absorbed and released is sufficiently high, and (3) the metal hydride The amount of heat generated in the reaction (-ΔHf) has a value around 6 to 8 Kcal/molH2, and because the amount of heat generated is small, the endothermic loss due to hydrogen release is small, making it suitable as an alloy for hydrogen storage. (4) Initial hydrogen For example, it is extremely easy to

In Table 1 and Figures 3 and 4 above, M in the Ti-Mn-M alloy is shown next when it consists of one type of metal. However, in the Ti-Mn-M alloy of the present invention, the same effect can be obtained even when M is not only one type of metal but two or more types of metals.

That is, M is V, Cr, Fe, Co, Ni, Cu, Mo
Even in the case of two or more metals selected from the seven elements, Ti
As a -Mn-M alloy, if the alloy phase forms a single MgZn2-type larvae phase and its crystal lattice constant is adjusted to fall within the above-mentioned optimum value, the above-mentioned Table 1, Figure 3, It was confirmed that characteristics almost equivalent to those shown in Figure 4 could be obtained.

As specific examples of these, Table 2 shows sample symbols K, L, M.
The characteristics are shown using three representative samples.

As described above, the alloy system of the present invention is sufficiently practical in terms of properties.

In addition, this Ti-Mn-M alloy has simplified alloy manufacturing conditions as well as properties compared to the Ti-Mn binary alloy previously proposed by the present inventors. That is, the effective alloy phase as a hydrogen storage material in the Ti-Mn binary system and the Ti-Mn-M system alloy is both the MgZn2 type larvous phase, but as in the present invention, M as M in the Ti-Mn binary system is used. Newly added V, Cr, Fe, Co, Ni, Cu,
The crystallinity and homogeneity of the alloy could be improved by creating a multi-component alloy containing at least one metal such as Mo.

This is because the alloy obtained by arc melting etc.
As a result of examining the crystallinity and homogeneity of the Mn binary alloy and the Ti-Mn-M alloy by X-ray diffraction, it was clear that the crystallinity of the MgZn 2-type larvous phase alloy was improved by using the Ti-Mn-M alloy. It was observed that the quality and homogeneity were improved.

Therefore, in the process of homogenizing the alloy obtained by arc melting through heat treatment, etc., the conditions for homogenization heat treatment are significantly relaxed because Ti-Mn-M alloys originally have excellent alloy crystallinity and homogeneity. This makes the manufacturing process easier.

An example of manufacturing the metal material for hydrogen storage of the present invention has a purity of 99%.
% of Ti, Mn, and M are placed in a copper crucible and directly melted in an argon arc furnace. A fairly homogeneous button-shaped Ti--Mn--M alloy can be obtained by melting the front and back surfaces several times.

A homogeneous alloy can be obtained by subjecting this to homogenization heat treatment at 1100° C. for about 10 hours in an argon atmosphere, for example.

This alloy lump is relatively brittle and easily crushed mechanically.

Regarding the hydrogenation of this alloy, the obtained alloy is crushed into several pieces, placed in a reaction vessel made of stainless steel, for example, and the inside of the vessel is evacuated for several minutes using an oil rotary pump or the like. Then purity 9
If 9.9% hydrogen gas is added to the reaction vessel at a pressure of about 20 atm, hydrogen will begin to be absorbed immediately. For example, with an alloy weighing about 100 g, hydrogen absorption will be completed within a few minutes even at room temperature, and the particle size will be several microns. A hydride of a Ti-Mn-M alloy is produced.

Note that among the Ti-Mn-M alloys of the present invention, M=Co
The Ti-Mn-Co alloy in this case is related to the alloy previously proposed by the present inventors, but the Ti-Mn-Co alloy of the present invention
As is clear from the comparison in Table 1, the i-Mn-Co alloy has a greatly improved amount of released hydrogen at room temperature by adjusting the alloy phase and crystal lattice constant.

From the above, it is clear that the alloy represented by Ti-Mn-M (where M is at least one metal selected from V, Cr, Fe, Co, Ni, Cu, and Mo), and that the alloy is Mg
It consists of a Zn2 type larvae phase, and its crystal lattice constants a and c are a=4.86 to 4.90 Å, c=7.9, respectively.
The metal material for hydrogen storage, which has a thickness of 5 to 8.02 Å, has the characteristics of a large amount of absorbed hydrogen and a large amount of hydrogen released, as well as an appropriate plateau pressure, as well as low alloy cost, high reaction speed, and high reaction speed. It has many advantages such as low heat of formation and easy initial hydrogenation.

This Ti-Mn-M alloy has improved crystallinity and homogeneity than the Ti-Mn binary alloy, so it has the advantage of simplifying the manufacturing process.

Furthermore, from a practical standpoint, this Ti-Mn-M alloy is
By changing the composition (changing the element as M and changing the lattice constant), the plateau pressure can be reduced to approximately 1 at room temperature.
It has the feature that it can be adjusted continuously up to 20 ATM.

As described above, the Ti-Mn-M alloy of the present invention is an extremely useful material as a metal material for hydrogen storage.

[Brief explanation of drawings]

Figure 1 shows the relationship between the MgZn2 type crystal lattice constant a of a Ti-Mn-M alloy and the amount of hydrogen absorbed and released at 25°C, and Figure 2 shows the relationship between the crystal lattice constant c and the amount of hydrogen absorbed and released at 25°C. Figures 3 and 4, which show the relationship between the amount of absorbed and released hydrogen, show the relationship between the hydrogen dissociation equilibrium pressure and the amount of hydrogen absorbed at 25°C.

Claims (1)

[Claims] 1 General formula Ti-Mn-M (where M is V, Cr, F
At least one metal selected from the group consisting of Co, Co, Ni, Cu, and Mo), whose alloy phase consists of a MgZn2-type larvae phase, and whose crystal lattice constant a
and c are respectively a=4.86 to 4.90 Å, c=7.95
A metal material for hydrogen storage with a thickness of ~8.02 Å.