JPS5848481B2 - Hydrogen storage materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydrogen storage material, particularly a practical hydrogen storage material that is made of a multi-component alloy based on Ti and Mn and can store hydrogen at high density and safely. .

The hydrogen storage material of the present invention is represented by the general formula ABa, and A
is 58 to 100 atoms (but does not include 100 atoms)
Ti, the balance is composed of at least one metal selected from the group consisting of Zr and Hf, and B is composed of Mn of 20 to 100 atoms (excluding 100 atoms φ), and the balance is Fe.
．． It is made of at least one metal selected from the group consisting of Co and Ni, and the atomic ratio a of B to A is 1.0 to 3.
It consists of an alloy of 0.

This alloy is a safe and practical material that can store large amounts of hydrogen very easily at room temperature and can reversibly release large amounts of stored hydrogen by changing the ambient hydrogen pressure, temperature conditions, or electrochemical conditions. Moreover, it is an economical metal material.

Conventionally, when storing or transporting hydrogen, it has been common practice to store or transport hydrogen after highly compressing it in a pressure-resistant container, or in rare cases, storing or transporting it as liquid hydrogen while keeping it at an extremely low temperature.

However, both require special containers, and in the former, even if highly compressed at over 100 atmospheres, the hydrogen density is still small, so the amount stored per unit volume of the container is small, and in the latter, the amount of hydrogen stored per unit volume of the container is small. In both cases, the storage equipment must be extremely large, making transportation difficult. It was inconvenient to carry, and it was not a force method that could be applied to the required storage device that was small and transportable.

Another known method is to absorb hydrogen into a certain metal or alloy, store it, and release it when used. In particular, since the amount of hydrogen absorbed per unit volume of metals or alloys is small, hydrogen storage methods are known. It is attracting attention as

This reaction is expressed as −l H f (Kca
l/mol! e H2) is a solid-gas reaction accompanied by an exothermic reaction.

22 -M (solid) + H2 (gas): -MHn (solid) -JH
fn
Metals or alloys that are H solids can absorb hydrogen under a hydrogen atmosphere at a specific temperature and pressure or under electrochemical conditions to form a metal hydride and hold hydrogen at high density. Further, by changing temperature or pressure conditions or electrochemical conditions, occluded hydrogen can be reversibly released.

Metal hydrides (MHn) are in a state in which hydrogen enters and bonds with the lattice of metal crystals, so it stores hydrogen at a density comparable to that of liquid hydrogen, and also retains hydrogen in a solid state. Therefore, if hydrogen extraction, storage speed, method, etc. have practically satisfactory characteristics, and the price is low from a practical point of view, then the current gas cylinder power method and liquid hydrogen method could be replaced. It can be replaced, and because it is solidified, it is extremely safe.

It is also advantageous in that unlike liquid hydrogen, there is no loss due to evaporation and it can be stored for a long time.

Among the metal materials for hydrogen storage that have been discovered so far, Mg. Mg-Ni system, Mg-Cu system, R-Ni
．． R-Co alloy (R: rare earth element), Ti-F
There are also e-based alloys.

However, these materials also have several drawbacks as practical hydrogen storage materials.

For example, Mg. Mg-Ni. Mg--Cu alloys have a relatively small amount of hydrogen storage per unit weight, and hydrogen storage and release must be carried out at high temperatures of 250 DEG C. or higher.

Also, on the contrary, R-Ni. R-Co alloy and T
i Fe-based alloys are capable of intercalation and desorption at room temperature, but R-Ni. R-Co alloys are expensive and have a low hydrogen storage capacity per unit weight of metal.

In addition, Ti-Fe alloys are exposed to high temperatures during initial hydrogenation.
It requires high pressure conditions and also absorbs hydrogen. The release reaction is relatively slow, and the hydrogen dissociation pressure-hydride combination isotherm curve during hydrogen storage and release becomes two steps.

Compared to the conventional hydrogen storage materials, the present invention significantly eases operating conditions such as absorption and release of hydrogen, increases the amount of hydrogen storage and release per unit weight, and has extremely various properties necessary for practical use. The purpose of the present invention is to provide excellent and low-cost materials for hydrogen storage, retention, and transportation.

The storage material of the present invention is the Ti-Mn binary alloy and ternary alloy for hydrogen storage previously proposed by the present inventors. Part of Ti is replaced with Zr or Hf, and part of Mn is replaced with Fe. Co. N
By replacing it with i, among various custom orders for hydrides, we aim to flatten and expand the horizontal region of the hydrogen dissociation equilibrium pressure region, the so-called plateau pressure region, in the hydrogen dissociation pressure - hydride composition isotherm. It has significantly improved the amount of hydrogen released at room temperature and atmospheric pressure, which is the most important requirement for a hydrogen storage material.
It has been completed to be even more practical.

Furthermore, the cost is lower than that of the Ti-Mn alloy mentioned above.

The hydrogen storage material according to the present invention is made of TiMna (a = 1
．． 3 to 3.0) as the base alloy, and substantially Ti is O to 42
The number of atoms (however, not including O) is Zr. Fe. Co. It is formed by replacing Ni with at least one metal selected from Ni.

The above substitution ratio of Ti and Mn is T r Mn a
T i-Mn based on (a1.0 ~ 3.0)
In a multi-component alloy, it is determined from the composition range in which a homogeneous single phase of MgZn2 type (C14 type) Laves phase can exist and the results of hydrogenation characteristics described below.

The hydrogen storage material of the present invention is most easily produced by a direct melting method such as argon arc melting, which results in a homogeneous single phase alloy.

The resulting alloy ingot is relatively brittle and easily crushed mechanically.

If these pulverized alloy particles are kept in a sealed container made of stainless steel and brought into direct contact with gaseous hydrogen gas at room temperature at a pressure of several atmospheres or more, they will immediately begin to absorb hydrogen, and for a short period of time. Hydrogenation is completed within a while, for example at room temperature,
Ti, 6 Zr, 4 Mn, 7Nio. 3 H2
．． g7, and hydrogen gas is converted into a solid TiO. 6Zr. 4Mn1,7 Stored and maintained safely in large quantities and in Ni,3.

This hydrogenated alloy has become a fine powder with a particle size of several microns or less.

Conversely, if the alloy hydride is lowered again to a hydrogen pressure specific to each alloy or less, for example at room temperature, the absorbed hydrogen is reversibly released.

The following table shows examples of the hydrogen storage material of the present invention, its hydrogenation properties, and the crystal lattice constant of its hexagonal MgZn2 (C14) type crystal structure.

This table shows that the alloy of the present invention stores a large amount of hydrogen and reversibly releases a large amount of hydrogen.

Below, the range of the value of a of the present invention (a = 1.0 to 3.0)
and the range of the substitution ratio of Ti and Mn [each, O of Ti
42 atomic % (however, O is not included) and O to 80 atomic % of Mn (however, O is not included)] will be explained.

Although a complete phase diagram of the Ti-Mn binary alloy has not yet been obtained, it has been investigated in considerable detail, and among them, R. M. Waterstra
FIG. 1 shows a phase diagram of a Ti-Mn alloy according to T et al.

According to this phase diagram, as an intermetallic compound, T i M
n. M i Mn2 and TiMn3, φ phase, ρ phase and Rava phase are shown as intermediate phases.

The present inventors have previously discovered that some Ti-Mn binary alloys hydrogenate extremely easily even at room temperature, and the range of alloys that have excellent hydrogenation properties for hydrogen storage is as follows: The range in which the crystal structure forms a hexagonal MgZr2(C14) type ra/x phase, that is, the crystal lattice constants a and C of the MgZrz type are a=4.80 to 5.
It was confirmed that the alloy was a Ti-Mn alloy existing in the range of 10(A) and C=7.88 to 8.28(4).

Referring to the phase diagram of FIG. 1, the range of strength that forms the MgZrz type structure corresponds to one part of the larvous phase.

However, TiMnl. o-TiMn
3. .

It has been found that within the range of , the parent phase is substantially a MgZn2-type larvous phase, although some heterogeneity is present.

The present invention is directed to a Ti-Mn2 binary alloy in which the parent phase is substantially a MgZr2-type larvous phase, that is, a TiMn
1.0 to TiMn3.0, some of the Ti and Mn were added to the 3rd layer. It has been perfected by replacing it with a fourth element, and is a hydrogen storage material superior in characteristics to the TiMnZ element system and ternary system.

In the hydrogen storage alloy of the present invention, the larger the ratio of Ti to Zr (or Hf) substitution, the more
constant a. c increases, and as a result, the amount of absorbed hydrogen at a constant temperature increases.

However, when the substitution ratio exceeds 42 atoms, the dissociation equilibrium pressure decreases significantly, and the amount of hydrogen released at room temperature and atmospheric pressure decreases.

Therefore, in order to maintain a large amount of absorbed hydrogen and a large amount of released hydrogen, the Ti substitution ratio must be limited to a range of 0 to 42 atoms (excluding 0).

Furthermore, when the Ti substitution ratio increases beyond 42 atomic strips, the homogeneity, monophasicity, and crystallinity of the manufactured alloy deteriorate, and the plateau pressure region of the hydrogen dissociation pressure-composition isotherm becomes unclear. The characteristics of this product are also impaired.

Ti. Zr. Hf is a group 4A element in the periodic table, and these three elements are completely solid.

Therefore, when forming an alloy in which Ti is replaced with Zr or Hf, a sufficiently homogeneous alloy phase is formed, and since they are homogeneous, the effects for the purpose of the present invention are also the same.

Therefore, the substitution ratio of Hf to Ti is O~
A suitable content is 42 atomic % (not including O).

Regarding the substitution ratio of Mn, similarly, when the amount of Mn increases, the amount of absorbed hydrogen at a constant temperature increases, as in the case of replacing Ti with Zr (or }{f).

However, when it exceeds 80 atoms φ, the dissociation equilibrium pressure decreases significantly, and therefore the amount of hydrogen released at room temperature and atmospheric pressure decreases.

Therefore, in order to maintain a large amount of absorbed hydrogen and a large amount of released hydrogen, the Mn substitution ratio should be 0 to 80 atoms (
However, it does not include 0.

) must be limited to the range of

Furthermore, when the Mn substitution ratio increases beyond 80 atoms (the amount of Mn decreases), the initial hydrogen activation rate at room temperature also slows down, impairing the characteristics of the Ti--Mn-based hydrogen storage material.

There are a variety of methods for evaluating metal hydrides as hydrogen storage, retention and transport media.

For example, ease of initial hydrogenation, hydrogen storage and desorption rates, storage and desorption temperatures, hydrogen pressure during storage and desorption,
These include the amount of absorbed hydrogen per unit weight and volume, the amount of hydrogen released per unit weight and volume, the vastness and flatness of the plateau region of the hydrogen dissociation equilibrium pressure-composition isotherm, and the price of raw materials.

The various Ti-Mn-based alloy hydrides previously proposed by the present inventors were relatively excellent in all these respects.

From the perspective of practicality as a material for storing and transporting large amounts of hydrogen, among the various factors for the above evaluation, the amount of hydrogen released per unit weight at room temperature, the large plateau region, and the average level are important. Possibility is considered to be the most important factor.

The present invention is particularly advantageous in comparison with the previous Ti-Mn alloy.
These points are extremely excellent.

For each of the above hydrogen storage materials, the vertical axis is the logarithm of the hydrogen dissociation equilibrium pressure (P), and the amount of hydrogen storage in the alloy (X-?t o
An isothermal line (temperature T) can be drawn on a graph with m H/mol e alloy) on the horizontal axis.

This P-X-T characteristic is useful for comparing the performance of hydrides.

As an example, Tio, 7Zr0.3Mn1. 6Nio
．． The P-X-T characteristics of 4-HX are shown in Figure 2, and 'rlO
JlzrO. 4Mn. 7Nio. 3-Hx P-X-T
The characteristics are shown in FIG. 3. 6Zro. 9Mn1-Feo
．． The P-X-T characteristics of 1-Hx are shown in FIG. 4, and the P-X-T characteristics of Tio. 6
Z rO,4 Mnl. 5 Fe. 5Hx P-
The X-T characteristics are shown in FIG. 5.

Each isotherm shows a so-called "plateau region" in which a given pressure is approximately flat over a temperature range specific to the alloy. Around such a plateau pressure, the material absorbs a relatively large amount of hydrogen gas with a small pressure change. or the reverse process is possible.

Therefore, the longer the plateau region is, the larger the amount of released hydrogen is, and the better it is for practical use.

The alloy of the present invention rarely forms an oxide layer or nitride layer at room temperature, is hardly affected by impurities in hydrogen gas, absorbs hydrogen quickly and easily, and has high purity. Since it is possible to release a large amount of hydrogen, hydrogen can also be purified.

[Brief explanation of drawings]

Fig. 1 is a phase diagram of the Ti-Mn binary alloy that is the basis of the present invention, and Fig. 2 is a typical characteristic of Ti (37Zro.3Mnl.6NioJ) shown as an example of the present invention. Figure 3 is a hydrogen dissociation equilibrium pressure-hydride composition isotherm diagram, and similarly 'rlO.6zr0.4Mn1
．． 7Nio. The hydrogen dissociation equilibrium pressure-hydride composition isotherm diagram of trihydride, FIG. 4, similarly shows T I0. 6 Z
r0.4Mn1. g FeO. (Hydrogen dissociation equilibrium pressure - hydride composition isotherm diagram of hydride, Figure 5 is similarly 'r
io, 6zrO, 4M n 1 . 5 F e o.
It is a hydrogen dissociation equilibrium pressure-hydride isotherm diagram of pentahydride.

Claims (1)

[Claims] 1 Represented by the general formula ABa, A has 58 to 100 atoms (
However, it consists of Ti of 20 to 100 atoms φ (but does not contain 100 atoms), the balance is at least one metal selected from the group consisting of Zr and Hf, and , remainder or Fe. A hydrogen storage material comprising at least one metal selected from the group consisting of Co and Ni, and characterized in that the atomic ratio a of B to A is 1.0 to 3.0.