JPS5814361B2 - Method for manufacturing hydrogen storage materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydrogen storage material that plastically stores and generates hydrogen by receiving and receiving heat or increasing and decreasing hydrogen pressure, and in particular, the hydrogen storage characteristics deteriorate even after repeated use many times. The main objective is to provide a long-life and economical hydrogen storage material.

Some metals or alloys can reversibly absorb and release hydrogen by transferring heat or increasing or decreasing hydrogen pressure.

These substances have the property that when they repeatedly absorb and release hydrogen, they eventually turn into powder approximately several micrometers in size.

When it is pulverized in this way, the voids between each particle involved in hydrogen storage and release are reduced, and the pulverized material gradually solidifies, making it difficult to store and extract hydrogen.

Therefore, in order to solve this problem, conventionally, porous tubes or porous partitions were interposed in the granular hydrogen storage material, and hydrogen was supplied by passing through the porous material. When hydrogen was to be absorbed and released, hydrogen was extracted by passing it through this metal porous tube.

However, in this case, since the hydrogen storage container is filled with metal in a fine powder state, even if a porous wall is used, there will be local gaps in the filling state. Among the metal hydrides used for commercial use, this phenomenon was often observed in relatively active materials such as TiMn1, 5, TiFe, and LaNi, which can be used at room temperature, and was particularly noticeable the more hydrogen absorption/desorption cycles were used.

In addition to the pulverization caused by repeated storage and release cycles of hydrogen, the hydrogen storage material at the bottom of the container may also be damaged by vibration, impact, or pressurization of the container during transportation, movement, or filling with hydrogen gas. become extremely dense.

In this state, the diffusion rate of hydrogen is significantly slowed down, and the hydrogen storage efficiency (the actual amount of hydrogen stored relative to the amount of hydrogen that can be stored) and the hydrogen utilization efficiency (the actual amount of hydrogen released relative to the total amount of hydrogen stored) are The cost was low in practical terms, and the economic loss was large.

This will be explained next using a specific example.

Now, TiMn1,, hydride (TiMn1.5H2,
47) tTspe hydride (TiFeH1.65), L
FIG. 1 shows the relationship between the ambient temperature of aNi, a hydride (LaNi5Ha.7) (a substance in which a hydrogen storage material has occluded hydrogen is referred to as a hydride), and the equilibrium hydrogen pressure at that time.

In the figure, the right side of the two straight lines for each material showing hydrogen storage/release characteristics is the hydrogen storage region, and the left side is the hydrogen release region.

Examples of relatively good conventional containers include containers equipped with pipes for heating and cooling media consisting of water or organic chlorides, which are filled with metal hydrides through porous partition walls or porous hydrogen pipes. Then, pressurized hydrogen gas is supplied from the hydrogen supply pipe and stored, and hydrogen is stored by converting metal powder into metal hydride. When hydrogen is needed, hydrogen is released by opening the hydrogen release valve. It is released from a pipe.

Here, the heating and cooling medium pipe is used to prevent the reaction suppression effect due to the considerable amount of reaction heat that is generated during hydrogen storage and release by passing the heating and cooling medium and acts to hinder the hydrogen storage and release reaction. used for.

However, in the conventional container described above, despite these various improvements, as the hydrogen absorption/release cycle is repeated, the metal powder becomes finer, and the powder becomes more solid, especially toward the bottom of the container. The condensation phenomenon was significant, and the hydrogen storage efficiency and hydrogen utilization efficiency tended to deteriorate.

The present invention integrates a substance that hardly reacts with hydrogen between granular or lumpy metal materials that have a hydrogen storage effect, and separates the granular or lumpy metal materials for hydrogen storage from each other.
This method prevents as much as possible the coarsening and caking of the powder due to pulverization by separating it, and makes it extremely easy for individual granular or lump materials to come into contact with hydrogen, eliminating the above-mentioned drawbacks of the conventional method. be.

That is, the present invention heats both of the above-mentioned substances at a temperature below the melting point of the substance that absorbs and releases hydrogen and above the melting point of the substance that does not absorb and release hydrogen, so that the surface of the former substance is coated with the latter substance. This is a method for producing a hydrogen storage material, which is then crushed to obtain a granular or lumpy hydrogen storage material in which the former substance is partially exposed on the surface.

Hydrogen storage and release reactions for different metal materials are expressed as follows.

However, M is a single metal or an alloy, MH is a metal hydride, and Q is the reaction heat amount.

Typical metal hydrides that react as described above include:
TiMr1.5Hx, TiFeHx, LaNi, Hx,
LaCo5HxtMmNt! HxlNg2CuHxlM
g2NtH, tvHx, vNbHx (where Mm is Mitsushi metal, a mixture of rare elements, and X is the number of hydrogen atoms per mole of metal or alloy), and generally alkali metals and alkaline earths. Metal hydrides of alloys synthesized by combinations of metals, rare metals, transition metals, etc. can be used as the hydrogen storage/release material of the present invention.

Here, considering the practical aspect that hydrogen can be absorbed and released at around room temperature, TiMn1.5, TiF
e+LaNi5jMmNi5, CaNi5 is preferable,
Furthermore, Mg2Ni is a preferable material from the viewpoint of a large amount of absorbed hydrogen per unit weight.

On the other hand, as the inclusion that hardly absorbs hydrogen used in the present invention, metal materials having a low melting point such as Mg and At are preferable.

This is because these substances have a lower melting point than the above-mentioned practical hydrogen storage/release metal materials, so when the material of the present invention is manufactured by the melting method, the alloy composition of the hydrogen storage/release metal materials can be manufactured without any damage. This is because the hydrogen storage capacity does not deteriorate due to surface contamination such as oxidation or nitridation.

In addition, from the viewpoint of facilitating the movement of hydrogen, a material with a high self-diffusion rate of hydrogen is preferable.

However, the diffusion rate of hydrogen is generally about the same for most metals (diffusion coefficient: about 10-4 at room temperature).
~1.0-5 cr2/sec), so this need not be taken into consideration much.

Therefore, Mg, At, Ca, Zn focusing on low melting point
, In, Pb, Sn, etc., and alloys of these metals are preferably selected.

Below, TiMn1. , will be described below.

First, a TiMr1.5 alloy is formed by a high temperature melting method such as argon arc melting, and the resulting alloy ingot is
Mechanically crush into approximately 0 mm square pieces.

39 kg of crushed TiMn1.5 alloy granules and 1 At powder
Put Yug into the same magnesia crucible and bring it to a temperature of about 700℃.
High frequency dissolution was carried out for about 10 minutes.

The resulting metal grains have Ats on the grain boundary surface and TiMr inside.
It has a structure consisting of 1.5.

This is because the melting point of TiMn1.5 is about 1315°C, while the melting point of At is about 659°C. Therefore, at the set melting temperature of 700°C, TiNn1.5 does not undergo any compositional change, but rather undergoes homogenization heat treatment. Although the properties improved due to the effect, At dissolved and TiMn1. This is because the TiMn1.5 alloy flows almost uniformly onto the grain boundary surface of the alloy, adheres to the surface through the cooling process, and coats the TiMn1.5 alloy.

The metal lump of about 10 to 12 mL square thus formed is further crushed into pieces of about several mm square and filled into a hydrogen storage container.

Further, a hydrogen storage material was also formed using TiFe by coating It in exactly the same manner.

FIG. 2 shows an example of a hydrogen storage container filled with the hydrogen storage material of the present invention.

Here, 1 is a pressure-resistant hydrogen storage container made of aluminum with a wall thickness of 10 mm, 2 is an alloy of hydrogen storage/release material whose surface is covered with At3 as an inclusion, and 4 is a granular alloy that passes through a valve together with hydrogen. This is a filter made of porous material to prevent water from flowing out.

Reference numeral 5 denotes a space filled with hydrogen gas, which is secured in case the container 1 is distorted or destroyed due to expansion of the hydrogen storage material 2 due to hydrogenation, and occupies about 15 inches of the total internal volume.

6 is a gap between the granular hydrogen storage materials coated with At, which facilitates the flow of hydrogen gas.

7 is a hydrogen gas inlet/output pipe, and 8 is a valve for introducing and extracting hydrogen gas.

The hydrogen storage and release method involves evacuating the pressure vessel 1 with an internal volume of 10 liters containing a granular alloy coated with At at room temperature using a vacuum pump to remove air and other impurities.

Next, when hydrogen gas was supplied from the valve 8, the granular alloy began to absorb hydrogen and formed a metal hydride.The total amount of absorbed hydrogen at this time was 8-
Reached 3.

After the hydrogen storage reaction was completely completed, the valve 8 was closed to complete the hydrogen storage operation process.

Next, when valve 8 is opened at room temperature, hydrogen gas is generated steadily at several atmospheres, and a total amount of hydrogen gas of about 7-3 is released for both TiMnl,s and TiFe, which can be used. Ta.

At this time, the hydrogen storage material has a structure as shown in the enlarged view of Fig. 3, and the inner alloy 2 coated with At3 is
Although there were cracks, each grain agglomerate was coated with At, so even if the hydrogen storage/release cycle was repeated, further pulverization was extremely suppressed, and the grain shape was not damaged.
There was no deterioration in the hydrogen storage/release rate due to powder caking, and no distortion or expansion of the pressure vessel 1 occurred.

This is because At, which absorbs almost no hydrogen, acts as a binder between metal hydride particles and suppresses the pulverization of the granular hydrogen storage material, and At, which is a non-hydrogen storage material, This is because the shape does not change at all even after repeated hydrogen absorption/release cycles, and the effect as an inclusion continues indefinitely.

Note that even if the entire surface of the granular hydrogen storage material is covered with A/, which is a non-hydrogen storage material, the action of the hydrogen storage material is not impaired, although the hydrogen storage rate is slowed down.

This is because the size of hydrogen atoms is extremely small, so hydrogen easily penetrates into At, diffuses and permeates, and reaches the hydrogen storage material where it is stored.

However, this case is not practical because the hydrogen absorption rate is slow.

Generally, once hydrogen absorption by permeation starts, the alloy mass becomes distorted due to hydrogenation reaction heat and powderization, hydrogen movement and diffusion occur in an avalanche manner, and the hydrogen absorption action rapidly occurs and is completed.

FIG. 4 shows an example of another hydrogen storage container using the hydrogen storage material of the present invention.

Similar to FIG. 2, the A4 according to the present invention is placed in the aluminum container
As shown in the figure, there is a heating pipe to prevent the amount of released hydrogen from decreasing due to the heat absorption effect during hydrogen extraction, and a heating pipe to prevent the amount of released hydrogen from decreasing due to the heat absorption effect during hydrogen absorption, as shown in the figure. A cooling pipe 9 is provided in the hydrogen storage container 1 to prevent a decrease in the amount of stored hydrogen.

10 is a heating/cooling water inlet valve, and 11 is a heating/cooling water discharge valve.

Reference numeral 12 denotes a stored hydrogen gas introduction pipe having a hydrogen gas introduction valve 13, and 14 a hydrogen extraction pipe having a hydrogen gas extraction valve 15.The purpose of 4, 5.6 is the same as in FIG. 2.

This container is particularly effective for TiFe-based alloys, etc., which have a slow hydrogen storage and release rate.

When the hydrogen storage container incorporating the hydrogen storage material of the present invention shown in FIGS. 2 and 4 was used, the hydrogen release characteristics were measured, and the results were as shown in FIGS. 5 and 6.

In the figure, curve A is the one shown in Figure 2, and curve B is the one shown in Figure 2.
In the case shown in the figure, curve C is a case in which a conventional hydrogen storage/release material not coated with At is used and the container is provided with a porous partition as shown in FIG. The case where granular At (average particle size: 1 m1) was simply mixed into the sample and the other conditions were the same as C was designated as D.

The characteristics were measured after 100 hydrogen absorption/release cycles.
After repeating the hydrogen storage/release material several times, the hydrogen storage container 1 is placed in a constant temperature bath at 20°C, and the surrounding temperature is kept at a constant temperature (20°C).
℃), and the rate of hydrogen released to atmospheric pressure due to diffusion and movement of hydrogen in the container 1 was measured.

In addition, in the case of the embodiment shown in Fig. 4 (curve B in the figure) and C,
In the case of D, the measurement was performed by flowing hot water at 60°C through the pipe 9.

In this measurement, hydrogen was stored over a long period of time until the amount of hydrogen stored reached 100% (calculated value), and then hydrogen was released.

As a result, in a container using the hydrogen storage material of the present invention, in order to release 100% hydrogen, TiMn1. ,H2
, 47, as shown in Figure 5, curves A and H, 10
Compared to the conventional container (with pipes for heating and cooling water) that uses porous partition walls and tubes without being coated with At, it takes 150 minutes as shown in curve C. However, only 90% could be released, and even when inclusions were simply mixed, the result was only slightly better.

In addition, in the case of TiFeH1.65, as shown in Figure 6, a container filled with the material of the present invention releases 100 Ti in 30 to 60 minutes, as shown by curves A and H, compared to the conventional one. As shown in curve C, only 80% of the material could be released even after 150 minutes.

Also, D was slightly better than that.

Furthermore, the time required to absorb 100% of hydrogen was more than three times shorter with the material of the present invention than with conventional materials.

This is because in the case of conventional containers, hydrogen diffuses and moves while passing through solidified metal fine powder, so the speed of diffusion and movement is slow, whereas in the case of the hydrogen storage material of the present invention, In this case, each particle of the hydrogen storage/release material does not simply exist with inclusions, but is coated and isolated, which suppresses pulverization and prevents caking, so the voids between each particle are filled with hydrogen. It remains intact even after repeated storage and release cycles,
This is because hydrogen diffusion and movement occur quickly and smoothly.

As described above, the hydrogen storage material obtained by the present invention is a granular or lumpy material in which the hydrogen storage/release material is partially covered with a material that hardly absorbs hydrogen. It can be built into a container, and the time required for storing and releasing hydrogen can be significantly shortened.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between ambient temperature and equilibrium hydrogen pressure of a typical metal hydride, FIG. 3 is a partially enlarged view of the hydrogen storage material, FIG. 4 is a vertical sectional view of another embodiment of a hydrogen storage container incorporating the hydrogen storage material of the present invention, and FIGS. 5 and 6 are hydrogen storage containers. - TiMn1. each as release material. , , is a diagram showing hydrogen release rate characteristics when using TiFe. 1...Hydrogen storage container, 2...Hydrogen storage/release material, 3...Non-hydrogen storage material as an inclusion.

Claims (1)

[Claims] 1 Heating both of the above-mentioned substances at a temperature below the melting point of the substance that absorbs and releases hydrogen and above the melting point of the substance that does not absorb and release hydrogen, coating the surface of the former substance with the latter substance, and then pulverizing it. A method for producing a hydrogen storage material, the method comprising: obtaining a granular or lumpy hydrogen storage material in which the former substance is partially exposed on the surface.