JPH11343524A - Production of hydrogen storage alloy and the alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a hydrogen storage alloy excellent in hysteresis characteristics in which cycle treatment of occluding hydrogen under the pressure higher than that in ordinary activating treatment in particular and reducing the pressure into a vacuum is executed as for the improvement of the hysteresis of a body-centered cubic structure series hydrogen storage alloy and to provide the alloy. SOLUTION: This is a method for producing a hydrogen storage alloy having a body-cented cubic structure, in which cycle treatment in which a stage of occluding hydrogen into a hydrogen storage alloy under the pressure higher than that in the condition of activating treatment and a stage of reducing the pressure into a vacuum are repeated many times is executed. After the cycle treatment, ordinary activating treatment is executed. The cycle treatment is executed after ordinary activating treatment. As for the cycle treatment, at the time of occluding hydrogen, the temp. is less than 20 deg.C, and the presure is 2 to 15 MPa, and at the time of releasing hydrogen, the temp. is >=50 deg.C, and the degree of vacuum is <=5 kPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in hysteresis of a body-centered cubic hydrogen storage alloy, and more particularly, to a cycle treatment of storing and depressurizing to a vacuum with a higher pressure of hydrogen than a normal activation treatment to improve the hysteresis characteristics. The present invention relates to a method for producing an excellent hydrogen storage alloy and an alloy thereof.

[0002]

2. Description of the Related Art As a means for storing and transporting hydrogen, a hydrogen storage alloy can store and store hydrogen gas of about 1000 times or more the volume of the alloy itself, and its volume density is liquid or solid hydrogen. It is almost the same or more. As this hydrogen storage material, V, Nb, Ta, Ti-
Metals having a body-centered cubic structure (hereinafter, referred to as a BCC structure) such as V alloys generate a larger amount of hydrogen than AB ₅ type alloys such as LaNi ₅ or AB ₂ type alloys such as TiMn ₂ which are already in practical use. Occlusion has been known for a long time. In this BCC structure, there are many hydrogen storage sites in the crystal lattice, and the calculated hydrogen storage amount is H / M = 2.0.
(For alloys such as Ti and V with an atomic weight of about 50, about 4.0 wt.
%), Which is extremely large.

[0003] On the other hand, when a hydrogen storage alloy is used, it is required that hysteresis is small in characteristics. If the hysteresis is large, the effective use amount of hydrogen under the use environment becomes significantly smaller than the characteristics of the alloy itself. In particular, since many BCC-based hydrogen storage alloys originally have a large hysteresis, some countermeasures are required. As a prior art in this field, for example,
As disclosed in, for example, Japanese Patent Application Laid-Open No. 954467 and Japanese Patent Application Laid-Open No. 57-101632, those in which alloy components are devised and those in which heat treatment such as annealing is performed are known. These techniques are not practical because the components are limited or heating is required. Pure vanadium alloy absorbs about 4.0 wt%, which is almost the same as the value calculated from the crystal structure, and releases about half of it at normal temperature and pressure. It is known that Nb and Ta of group 5A elements of the same periodic table also show a large amount of hydrogen storage and good hydrogen release characteristics.

[0004] Pure metals such as V, Nb, Ta and the like are very costly and are not practical in industrial applications requiring a certain amount of alloy, such as hydrogen tanks and Ni-MH batteries. Heretofore, the characteristics of alloys having a BCC structure such as Ti-V have been improved. However, there is a specific problem that the hysteresis characteristic as the evaluation of the effective use range with respect to the use environment is reduced due to a large hysteresis characteristic. Therefore, there has been a demand for a technique for improving the hysteresis characteristics of the above BCC structural alloy by a relatively simple and cost-effective treatment and expanding the effective use range.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to provide a BC
Investigating a method for reducing hysteresis in C-based alloys, bringing the effective amount of hydrogen closer to the inherent properties of the alloy itself,
It is an object of the present invention to provide a method for producing a hydrogen storage alloy which enables improvement in the hydrogen absorption / desorption characteristics of a system alloy, and an alloy thereof. Another object of the present invention is to consider a cycle process of absorption and release under a high pressure different from the conventional activation process, thereby improving the hysteresis by allowing hydrogen to easily pass between alloy atoms. It is an object of the present invention to provide a method of manufacturing a hydrogen storage alloy and an alloy thereof. Further, another object of the present invention is to examine the processing timing in order to prevent poisoning at the time of filling in a hydrogen storage container or forming a battery electrode, etc. It is an object of the present invention to provide a method for producing a hydrogen storage alloy in a state where no hydrogen is generated and an alloy thereof.

[0006]

The object of the present invention is to provide a method for producing a hydrogen storage alloy having a body-centered cubic structure, comprising the steps of: causing the hydrogen storage alloy to store hydrogen at a higher pressure than the activation condition. And a step of repeating the step of reducing the pressure to a vacuum a plurality of times is achieved by a method for producing a hydrogen storage alloy. Further, the above object is also achieved by a method for producing a hydrogen storage alloy, wherein a normal activation treatment is performed after the cycle treatment. Further, the above object is also achieved by a method for producing a hydrogen storage alloy, wherein the cycle treatment is performed after a normal activation treatment.

Another object of the present invention is to provide a fuel cell system in which the above-mentioned cycle processing is performed at a pressure of 2 MPa (20 kgf
/ Cm ² ) or more and 15 MPa (150 kgf / cm ² ) or less, and a degree of vacuum of 5 kPa (0.
It is also achieved by a method for producing a hydrogen storage alloy, which is not more than 5 kgf / cm ² ). Further, the above object is a hydrogen storage alloy having a body-centered cubic structure as a main phase, and has a hysteresis factor defined by Hf = Pa / Pd of 1.0 to 5.0. This is also achieved by a hydrogen storage alloy having excellent hydrogen absorption and desorption characteristics. Here, as shown in FIG. 8, Pa is the storage equilibrium pressure average value, and Pd is the release equilibrium pressure average value, both of which are values obtained from the plateau portion of the pressure-composition isotherm.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a conventional hydrogen storage alloy, the amount of effective use of hydrogen is significantly smaller than the material characteristics because of the existence of hysteresis. The normal activation treatment of the BCC alloy is performed under a pressure lower than ² MPa (20 kgf / cm ² ), but in the present invention, hydrogen absorption and desorption are repeated under specific conditions separately from the normal activation treatment of the alloy. As a result, the hysteresis was reduced. This has made it possible to increase the effective usage of hydrogen. That is, the hydrogen absorption / desorption characteristics of the hydrogen storage alloy are measured by pressure composition isothermal measurement (PCT diagram)
As a result, as shown in FIG. 4, a use environment region and an effective hydrogen use amount specific to the alloy are obtained. At this time, if the hysteresis is large, there arises a problem that the effective use amount of hydrogen becomes small with respect to a certain use environment range and the hydrogen capacity becomes insufficient. In the study for solving this problem, as shown in FIG. 7, when the activation treatment of the hydrogen storage alloy is repeated under a certain condition, for example, after 5 or 10 cycles from the initial large hysteresis of the PCT diagram It was found that there was a phenomenon that gradually decreased in. The conditions at this time are activation conditions: 0 to 60 ° C., 0 to 1 MPa (0 to 10 MPa).
kgf / cm ² ), usage environment: 0-40 ° C, 0-1MP
a (0 to 10 kgf / cm ² ).

Further, as a PCT characteristic of AB ₅ type MmNi ₅ shown in FIG. 2, as measured on a 40 ° C., hysteresis is confirmed that there is no, even after repeated activation treatment in this state in this system There was no change in hysteresis. Figure 3 ZrMn _0.6 is the AB ₂ type, which is another system
The PCT characteristics after the activation treatment of Cr _0.2 Ni _1.2 at 0 ° C. once and 10 times are shown. From this figure, it was found that in a system having a small hysteresis, no change was caused by repeated activation treatment. Therefore, large hysteresis is a problem unique to BCC type alloys. As described above, in the present invention, the hysteresis of the BCC type hydrogen storage alloy can be reduced in a short time by repeating the absorption and release of hydrogen under constant conditions different from normal use conditions. The condition at that time is preferably 0 ° C., 3.9 MPa during occlusion.
(40 kgf / cm ² ), 30 min, 60 at release
C. 5 kPa (0.05 kgf / cm ² ) or less, 5 cycles or more at 1 hr. If the pressure and temperature are outside these ranges, that is, if the pressure and temperature are outside these ranges, the effect of providing the hydrogen storage alloy with a path through which hydrogen can easily move cannot be sufficiently obtained.

In the present invention based on the above findings, hydrogen is forcibly penetrated between the elements of the alloy by storing hydrogen at a higher pressure than in the ordinary activation treatment. By repeating this, it is presumed that a path for hydrogen to move between atoms is formed, hydrogen easily enters, and the plateau pressure on the occlusion side decreases, resulting in a decrease in hysteresis. In addition, the pressure at the time of the activation treatment of the normal BCC type alloy and the pressure at the upper limit of the use environment are 1.1 MPa (11 kgf / cm ² ). Although it is considered that the hydrogen storage tank is activated in this cycle processing, if the hydrogen storage container is filled with an alloy or a battery electrode is formed after this cycle processing, there is a risk of poisoning during the handling. is there. Therefore, it is preferable to perform the activation processing after this cycle processing. In particular, it is desirable to perform the process after the product is completed, for example, after filling in a hydrogen storage container. Conversely, if the activation treatment is performed before filling, hydrogen can be easily absorbed during the next cycle treatment. Hereinafter, the present invention will be described in more detail based on examples.

[0011]

EXAMPLE In this example, a Ti-Cr-V alloy composition was used. A sample of the hydrogen storage alloy was prepared as follows. All of the samples of this example were arc-melted in argon using a water-cooled copper hearth in an ingot of about 20 g. In the data of the present example, the ingot as cast was pulverized in the air, and the ingot was not subjected to the activation treatment, and was subjected to the cycle treatment under the conditions shown in Table 1.

[0012]

[Table 1]

FIG. 1 shows the results of Table 1 in the form of a PCT characteristic diagram. The processing conditions are 0 ° C., 3.9 MPa (40 k
gf / cm ² ), 60 ° C VAC (5 kPa (0.05 k
gf / cm ² )). Table 1
A, b, c, d, and e correspond to each of the horizontal axes in FIG. Table 1 shows the rate of expansion of the range of use due to the decrease in hysteresis when the number of cycles increases from 1 cycle to 100 cycles. From this table,
After 100 cycles, an increase in hydrogen storage capacity of 0.88 H / M, 1.63 times, is obtained. Next, results of a test in which the cycle conditions are changed in the present embodiment will be described. Table 2 summarizes the results.

[0014]

[Table 2]

Table 2 shows that the conventional conditions are 0 ° C., 1.1M
The storage amount at 40 ° C. and 1 MPa (1 kgf / cm ² ) after 10 cycles of Pa (11 kgf / cm ² ) and 60 ° C. VAC is 0.58 H / M, and the effective usage amount is (40 ° C.,
Storage amount at 1.1 MPa (11 kgf / cm ² ))
(Amount released at 40 ° C. and 0.1 MPa (1 kgf / cm ² )), 4
The occlusion amount at 0 ° C. and 1 kgf / cm ² is 0.61-0.
At 82H / M, the effective use amount is 0.33-0.56H /
It turns out that it becomes a favorable value with M. Further, the relationship between the hysteresis reduction rate after 10 cycles and the pressurization during the cycle processing was determined by increasing the cycle processing conditions. The cycle processing conditions at that time are shown in Table 3, and FIG. 6 shows the measurement results of the characteristic values. The vertical axis represents the conventional activation condition of 10
This is a comparison in which Hf after repeating the cycle is set to 1.

[0016]

[Table 3]

As shown in Table 3, the conditions are as follows: the pressurizing temperature is 0,15 ° C. within the range of the present invention, the comparative example is 25 ° C. and −20 ° C., and the pressure is 1.5, 2.5, 3.9 in the embodiment. , 9.8
Comparative examples were 3.9 and 2.5 MPa (40, 25 kg) as MPa (15, 25, 40, 100 kgf / cm ² ).
f / cm ² ). The VAC condition is a temperature of 60 ° C., and the upper limit of this temperature is limited to a temperature at which the BCC structure does not change. Also, from FIG. ,, And in particular, the hysteresis reduction rate is remarkably good. Other than that, it is close to the conventional level, but it can be seen that it is slightly improved. That is, as shown in FIG. 5, the results of the present embodiment can be summarized as follows. As shown in FIG.
As a result, it was confirmed that by performing the treatment in a temperature range higher than the conventional activation condition, the hysteresis of the hydrogen storage alloy can be remarkably narrowed and the absorption / desorption characteristics are improved.

[0018]

According to the present invention, the hysteresis of the BCC hydrogen storage alloy can be reduced, and the hydrogen storage / release characteristics can be improved. In the cycle treatment of the present invention, since the temperature and the pressure range are different from those of the conventional activation treatment, the conventional activation treatment becomes possible even after filling the hydrogen storage alloy, and the poisoning due to oxidation or the like in industrial practice is possible. Is solved, and the simplicity of the processing itself is advantageous in terms of cost.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a relationship between hysteresis of a PCT line and the number of cycles of a cycle process according to an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional alloy in which the hysteresis of a PCT line is unchanged by a cycle process.

FIG. 3 is a view showing a case in which the hysteresis of a PCT line of another conventional alloy is unchanged by a cycle process.

FIG. 4 is a diagram showing a relationship between a usage environment of hysteresis of a PCT line and an effective hydrogen usage amount of a conventional alloy.

FIG. 5 is a diagram showing the relationship between the use environment and the pressurizing condition, the activation process and the cycle process according to the present invention and the conventional alloy.

FIG. 6 is a diagram illustrating a relationship between a hysteresis reduction rate and a pressurizing condition according to the example of the present invention.

FIG. 7 shows a cycle of activation processing and PC of a conventional alloy.
It is a figure showing the situation where hysteresis of a T line changes with a cycle.

FIG. 8 shows a hysteresis factor (Hf =
It is an explanatory view showing the definition of (Pa / Pd).

Claims (5)

[Claims] 1. A method for producing a hydrogen storage alloy having a body-centered cubic structure, comprising the steps of: causing the hydrogen storage alloy to store hydrogen at a higher pressure than the activation treatment conditions; And a cycle process in which the above is repeated a plurality of times. 2. A method for producing a hydrogen storage alloy, wherein a normal activation treatment is performed after the cycle treatment of claim 1. 3. A method for producing a hydrogen storage alloy, wherein the cycle treatment according to claim 1 is performed after a normal activation treatment. 4. The cycle treatment according to claim 1, wherein the hydrogen is occluded at a temperature of less than 20 ° C., the pressure is 2 MPa (20 kgf / cm ² ) or more and 15 MPa (150 kgf / cm ² ) or less, and the hydrogen is released at a temperature of 50 ° C. or more and a degree of vacuum of 5 kPa ( 0.05kgf / c
m ² ) A method for producing a hydrogen storage alloy, characterized in that: 5. A hydrogen storage alloy having a body-centered cubic structure as a main phase, wherein Hf = Pa / Pd, Pa: average value of storage equilibrium pressure, Pd: average value of release equilibrium pressure (both are pressure-
A hydrogen storage alloy excellent in hydrogen absorption / desorption characteristics, characterized by having a hysteresis factor defined by a plateau portion of a composition isotherm) of 1.0 to 5.0.