JP3406615B2 - Activation, initial activation and stabilization of hydrogen storage alloy - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for activating, initially activating or stabilizing a hydrogen storage alloy having hydrogen activated metal dispersed therein.

[0002]

2. Description of the Related Art Hydrogen storage alloys are materials used for storage and release of hydrogen by utilizing the property of reversibly reacting with hydrogen to form hydrides, such as titanium, rare earth elements, magnesium, calcium, Hydrogen-activating metals such as nickel, iron, and manganese are alloyed with base metals such as zirconium. In order to store hydrogen in the hydrogen storage alloy, it is necessary to repeat the hydrogen activation treatment a plurality of times in an atmosphere of high pressure, high vacuum, high temperature, or the like. For example, La-Ni-
In the case of an Al-based hydrogen storage alloy, vacuum deaeration is performed at 80 to 100 ° C., and hydrogen introduction / exhaust is repeated 10 times or more at 1 to 3 MPa. In the Mg-Ni-based hydrogen storage alloy, vacuum degassing is performed at 350 ° C., and hydrogen introduction / exhaust is repeated 10 times or more at 2 to 5 MPa.

Hydrogen activation treatment (initial activation) is a costly operation because it requires complicated steps. Moreover,
This is a very dangerous work because the activated hydrogen storage alloy easily ignites and ignites in the atmosphere. Therefore, it is necessary to open the container in water and poison the alloy surface with sulfides. The activated hydrogen storage alloy is in an unstable state in which it is deactivated by exposure to the atmosphere. The hydrogen storage alloy can be maintained in an active state by dipping and storing it in a lower saturated hydrocarbon liquid such as propane, butane, pentane, etc. However, the handling operation for that purpose is troublesome.

As described above, the practical use of the hydrogen storage alloy is as follows.
There are many problems to be solved such as workability of initial activation, high cost, instability of activated hydrogen storage alloy, and danger during handling. Moreover, most hydrogen storage alloys have a small hydrogen storage capacity of about 2% at maximum. The present invention solves such a problem, by using a supersaturated aqueous solution of a metal fluoride as a treatment chemical, the hydrogen storage alloy can be easily activated, and the activated hydrogen storage alloy in an air atmosphere. The purpose is to be able to maintain a stable state.

[0005]

In the present invention, activation treatment or stabilization treatment is performed by treating a hydrogen storage alloy with a supersaturated aqueous solution of metal fluoride. The hydrogen storage alloy is subjected to hydrogen activation treatment after the activation treatment, and the hydrogen activation treated hydrogen storage alloy is subjected to stabilization treatment as required. When a hydrogen storage alloy containing a hydrogen activated metal is treated with a supersaturated aqueous solution of a metal fluoride, at least the surface or surface layer of the hydrogen storage alloy is activated. After evacuation of the activated hydrogen storage alloy, hydrogen is introduced into the hydrogen storage alloy by introducing hydrogen gas. When the hydrogen storage alloy is treated with a supersaturated aqueous solution of hydrogen fluoride, the surface of the hydrogen storage alloy becomes inactive to toxic substances other than hydrogen.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The conventional activation treatment is effective only for hydrogen storage alloys whose component system is specified, and the treatment itself is complicated. Therefore, various investigations and investigations have been made on a method for easily activating hydrogen storage alloys of various component systems on a surface having high hydrogen activating ability only by chemical treatment. As a result, they have found that hydrogen activation treatment is extremely easy when a hydrogen storage alloy is treated with a specific aqueous metal fluoride solution. Furthermore, when the research on the influence of the metal fluoride aqueous solution on the hydrogen storage alloy was repeated, it was clarified that the hydrogen storage alloy was extremely stabilized when the initially activated hydrogen storage alloy was retreated with the same metal fluoride aqueous solution. did.

[Preparation of Aqueous Metal Fluoride Solution] The aqueous metal fluoride solution used in the present invention is a supersaturated aqueous solution of a metal fluoride such as a metal hexafluoride compound containing an alkali metal. A typical metal fluoride is aluminum hexafluoride potassium (K ₃ AlF ₆ ), but T is used instead of Al.
i, Zr, Si, etc. can also be used, and sodium aluminum hexafluoride containing Na as a component in place of K (Na ₃ A
Fluorides such as IF ₆ ) can also be used. The metal fluoride is selected according to the use and purpose, and it is also possible to mix two or more kinds of metal fluorides. Potassium hexafluoride potassium (K ₂ TiF ₆ ), potassium zirconium hexafluoride (K ₂
ZrF ₆ ), potassium silicofluoride (K ₂ SiF ₆ ), and other compounds containing a hydrogen storage alloy element can also be used. However, all of these fluorides have low solubility in water, and among them, K ₂ SiF ₆ reacts sensitively to a decrease in water temperature and crystals are significantly precipitated. Therefore, it is necessary to pay attention to the preparation of the chemical solution when using the fluoride.

[0008] For example, the metal fluoride solution using K ₃ AlF _6, to dissolve the K ₃ AlF ₆ to 25 ° C. in distilled water at 0.03 W / V (weight to volume ratio), sufficiently mixed and stirred Is prepared by. The concentration of K ₃ AlF ₆ is determined in the range of 0.01 to 0.5 W / V depending on the purpose. Instead of distilled water, ion exchange water, tap water, well water, etc. can be used. The water temperature at the time of preparation should be 18 to 40 ° C, but 3
Best results are obtained with water temperatures between 0 and 35 ° C. The pH of the aqueous metal fluoride solution immediately after preparation is about 4.00 to 5.00.
Is in the range. The pH value rises to about 5.2 to 5.8 at the same time when the activation treatment is started, and changes to the neutral side depending on the treatment purpose and the treatment time. In some cases, the pH may exceed about 7.00 and shift to the alkaline side, and the pH may be around 12.

[Activation Treatment] When the hydrogen storage alloy is activated using the prepared metal fluoride aqueous solution, at least the surface or the surface layer of the hydrogen storage alloy is modified to have a high activation ability. Although there are no particular restrictions on the treatment conditions, the hydrogen storage alloy is activated in a normal temperature atmosphere at or near room temperature (preferably 18 to 40 ° C.). When the powder or fine powder hydrogen storage alloy is activated, the treatment effect is improved because the surface or surface layer area is large. In addition, when the mechanical alloying method, which mechanically alloys the powder that has been activated using a stirrer that gives high speed and high energy, is applied, the particles are highly activated up to the center of the particles. Activation becomes easier and the initial hydrogen storage amount increases. Similar treatment effects can be expected with alloys and composite materials in which activated powder is melted together with other alloy elements.

The activated hydrogen storage alloy is stable even in the atmosphere, and hydrogen can be quickly stored by the subsequent hydrogen activation treatment (initial activation). Moreover, the condensation property and heat transfer property of water on the surface of the hydrogen storage alloy are remarkably improved. The reason why the activation ability of the hydrogen storage alloy is increased by the activation treatment using the aqueous solution of metal fluoride is not always clear, but it is presumed that it is caused by changes in the properties, structure, structure, etc. of the surface or surface layer.
In fact, when observing the activated hydrogen storage alloy, a complex groove structure with fine irregularities and protrusions is detected on the surface, which shows that the specific surface area is large. Further, the result of the surface analysis shows that the compound of fluorine and metal is present on at least the surface or the surface layer portion of the hydrogen storage alloy.

[Hydrogen Storage: Initial Activation] By evacuating the activated hydrogen storage alloy at a low vacuum level without heating, the metal fluoride aqueous solution is removed from the hydrogen storage alloy. Next, when hydrogen is introduced in a normal temperature atmosphere at a low pressure of about 1 MPa as compared with conventional hydrogen storage, hydrogen is quickly stored in the hydrogen storage alloy.
The powdery hydrogen storage alloy can be easily controlled at the initial stage of the hydrogen activation treatment in which the hydrogen activation reaction and the dehydrogenation reaction are repeated. The hydrogen storage amount can be adjusted by temperature, pressure and the like. Since hydrogen absorption proceeds rapidly, complicated hydrogen activation treatments such as conventional high temperature high vacuum deaeration and initial activation treatment under high pressure and high temperature which are repeated 10 times or more are not required.

[Retreatment: Stabilization Treatment] When hydrogen-activated hydrogen storage alloy is retreated with a metal fluoride aqueous solution or a waste liquid of a metal fluoride aqueous solution, substances other than hydrogen molecules, such as air and water, are poisonous. The surface of the hydrogen storage alloy is protected from this. Therefore, the reprocessed hydrogen storage alloy can be easily handled such as storage, transfer and processing. For example, it becomes easy to develop a fine particle hydrogen storage alloy on a thin film or to layer fine particle hydrogen storage alloys having different compositions and characteristics in layers. As a result, when used as an electrode for a nickel / hydrogen secondary battery, improvements in characteristics such as corrosion resistance, life, and electric capacity can be expected. Even when discarding the hydrogen storage alloy subjected to the hydrogen activation treatment, phenomena such as ignition and ignition due to air oxidation in the air atmosphere can be prevented by the retreatment, so that the disposal treatment becomes safe and easy.

[Form, Material, etc. of Hydrogen Storage Alloy] The hydrogen storage alloy has various forms such as a material, an intermediate product and a finished product. Examples thereof include powder, fine particles, thin films, sheets, capsules and laminated materials. As a material,
Titanium, rare earth elements, elements such as magnesium, calcium, zirconium and the like, and hydrogen activating elements such as nickel, iron and manganese, which are known as the base of hydrogen storage alloys, and alloys of these elements and the like are available. It can also be used as a non-metal material or a composite material in which a base element, a hydrogen activation element or an alloy is dispersed.

[0014]

Example 1 A lanthanum nickel alloy LaNi _4.7 Al _0.3 having a grain size of 0.2 to 0.1 mm was used as a powdery hydrogen storage alloy. The metal fluoride aqueous solution was prepared by dissolving potassium aluminum hexafluoride in 0.025 W / V in distilled water. 10 g of the hydrogen storage alloy was put into a beaker containing 400 ml of an aqueous metal fluoride solution, and after sufficiently stirring with a stirrer, the supernatant liquid was removed and the particles precipitated at the bottom of the beaker were collected. PH of aqueous metal fluoride solution
The value changed from 5.0 to around 8.0 during the treatment. The surface of the activated hydrogen storage alloy is ESCA (surface analysis), E
PMA (extreme surface composition analysis) and X-ray analysis showed that lanthanum and a compound containing fluorine, lanthanum fluoride (La
The production of F ₃ ) was confirmed.

The activated powdered hydrogen storage alloy was filled in the reaction cell of the measurement system, and the metal fluoride aqueous solution was removed from the hydrogen storage alloy by evacuation to about 0.1 Torr. Then, about 1 MPa of hydrogen gas was introduced. Simultaneously with the introduction of hydrogen gas, hydrogen storage by the hydrogen storage alloy started, and a rapid hydrogen activation phenomenon was observed. When the surface of the hydrogen storage alloy subjected to the hydrogen activation treatment was similarly analyzed, LaF ₃ was still detected, and lanthanum and fluorine were hardly released from the alloy surface even by the initial activation treatment.

After the hydrogen storage alloy is made into a metal hydride by sufficiently absorbing hydrogen gas, the reaction cell is opened in the waste liquid of the metal fluoride aqueous solution, and the metal hydride is taken out from the reaction cell and precipitated in the solution. Let Evaporate the precipitate
When the particle size was measured after drying to dryness, it was found to be in the form of fine particles centered at 40 μm. The results of analysis by ESCA are shown in FIGS. In the sample not treated with the aqueous metal fluoride solution, a peak of La shifted from the binding energy in the metallic state was measured on the surface of the sample (FIGS. 1 and 2).
Further, a peak of La ₂ O ₃ generated by natural oxidation appears, and a peak of La in a metallic state appeared by continuing etching. Ni (Figs. 3, 4) and Al (Fig. 5,
6) was scattered in a metallic state.

In the sample subjected to the activation treatment, La (FIGS. 7 to 10) and Ni shifted from the binding energy in the metallic state were used.
The peaks (Figs. 11-14) were measured. In the shifted peak, oxide disappeared from the sample surface, and La was observed on the outermost surface.
F ₃ indicates that a Ni-rich layer is formed immediately below the outermost surface. In fact, when the activated sample is etched, the fluoride on the sample surface is scraped off, and La and N in the metallic state are removed.
i appeared. Al did not exist on the sample surface, and gradually appeared as a metal state toward the lower layer as the etching continued (FIGS. 15 to 18). These results mean that the inside of the sample is maintained in the original alloy state without change in composition.

The pressure-composition-temperature characteristics and reaction characteristics of the hydrogen-activated hydrogen storage alloy were investigated. In FIG. 19, the pressure when hydrogen is stored at room temperature is plotted on the vertical axis, and the concentration of hydrogen stored in the hydrogen storage alloy is plotted on the horizontal axis, and the activated sample and the first and second initial activation treatments are shown. The pressure-composition-temperature characteristic of the applied sample is shown. When a hydrogen pressure of about 10 atm was applied to the sample that was lightly evacuated (first time), the hydrogen storage reaction immediately started and the hydrogen concentration reached about 0 to 0.8 (marked with ⊚). Above that, the maximum concentration was reached through almost the same process as the well-activated sample. In the second hydrogen activation treatment, the hydrogen absorption reaction was started very easily by the application of several atmospheric pressures, and exhibited the characteristics equivalent to those of the conventional sample in which the hydrogen activation treatment was repeated tens of times or more.

[0019]

Example 2 The sample that was initially activated in Example 1 was charged again into the metal fluoride aqueous solution and stirred with a stirrer. The pH value of the aqueous metal fluoride solution is about 4.90 to 7.7 during stirring.
It changed between 0. After removing the metal fluoride aqueous solution,
The reprocessed sample was placed in a watch glass and dried in a dryer.
When the dried sample was exposed to the air, not only ignition and ignition phenomena but also rapid air oxidation phenomenon were not observed, although it was in an active state. The dried sample was exposed to the open air for 2 weeks or longer, and then put into the reaction vessel again and evacuated. Then, when 1 MPa of hydrogen gas was introduced, it was found that the hydrogen storage reaction immediately started and was not deactivated. That is, despite the fact that it was exposed to the atmosphere for a long time at room temperature, normal activation characteristics were exhibited by the activation treatment twice (FIG. 20).
A normal sample that has not been treated with an aqueous metal fluoride solution develops certain reaction characteristics by the application of high-pressure hydrogen, and therefore requires repeated occluding and releasing several tens of times and degassing at high temperature. It is noteworthy that the effect of the treatment with the aqueous solution of metal fluoride affects the recovery of the reaction characteristics.

[0020]

EXAMPLE 3 The particle size 0.075mm following Mg ₂ Ni alloy as the hydrogen storage alloy, Mg ₂ Ni alloy having a particle size 0.106～0.075Mm, particle size 0.250～0.106Mm Mm
A Ni _0.35 Mn _0.4 Al _0.3 Co _0.75 alloy (Mm: misch metal) was prepared. Aqueous metal fluoride solution 400 to which 0.025 W / V potassium hexafluoroaluminum has been added
20 g of each hydrogen storage alloy was put into a beaker containing ml, and after sufficiently stirring with a stirrer, the supernatant was removed and the particles precipitated at the bottom of the beaker were recovered. The recovered particles were filled in a reaction cell of the measurement system, and hydrogen activation was investigated by introducing hydrogen gas under the conditions shown in Table 1. As a result, as shown in FIGS. 21 to 23 and Table 1, the hydrogen storage reaction started at the same time as the introduction of the hydrogen gas, and the rapid activation occurred. Even after using the large-sized hydrogen reservoir, the pressure changed little, but it occluded hydrogen efficiently at room temperature in a short time.

[0021]

With respect to Samples Nos. 1 and 2, changes over time in the hydrogen storage reaction are shown in FIGS. 21 and 22
From the above, even if the Mg ₂ Ni alloy, which has not conventionally caused a hydrogen storage reaction at a high temperature of 350 ° C. or higher, it is changed to an active state in which hydrogen can be sufficiently stored at room temperature by activation treatment using an aqueous solution of metal fluoride. You can see that it is quality. When hydrogen gas was applied for the first time to sample No. 3, FIG.
As shown in, the hydrogen storage reaction was started. At room temperature, about 10 atm was first applied, and then it was changed to 15 atm and 20 atm, and the pressure change at each stage was observed over time. It is a typical example as an electrode of a nickel / hydrogen storage alloy secondary battery. Since the gas container having a large volume was used in this example, the pressure of the hydrogen gas was increased so that the pressure change could be easily observed. However, it is found that the actual applied pressure is about 10 atm at room temperature. .

[0023]

As described above, when the hydrogen storage alloy is activated by using the aqueous solution of metal fluoride, the degassing treatment under the high temperature and high vacuum atmosphere and the activation treatment for many times become unnecessary, and the activation The chemical treatment process and the treatment apparatus are simplified, and a hydrogen storage alloy suitable for mass production can be obtained. As a result, it becomes extremely easy to fill a fuel tank for automobiles, a storage container for heat storage, a heat pump, a refrigerator, a large-capacity hydrogen storage / transport container, a hydrogen storage container for a fuel cell, or the like, and to activate after filling. Moreover, according to the activation treatment using the aqueous solution of metal fluoride, the surface of the metal hydride is protected, so that the treatment in the atmosphere can be performed while maintaining the active state. Therefore, it is possible to use a plastic container or a plastic-coated paper container instead of using a high-pressure container. Furthermore, since the hydrogen-absorbing alloy particles dried in the air are active only against hydrogen gas and do not react with other gases such as oxygen in the air and moisture, a selective separating agent for hydrogen It can also be used as

[Brief description of drawings]

FIG. 1 LaN not treated with an aqueous metal fluoride solution
Graph showing La peaks obtained by ESCA analysis of i _4.7 Al _0.3 sample

FIG. 2: Same LaNi _4.7 Al _0.3 analyzed by ESCA.
Graph showing the peak of La obtained by ESCA analysis again after etching the sample

FIG. 3 LaN not treated with an aqueous metal fluoride solution
Graph showing Ni peaks obtained by ESCA analysis of i _4.7 Al _0.3 sample

Figure 4 Same LaNi _4.7 Al _0.3 analyzed by ESCA.
Graph showing the peak of Ni obtained by ESCA analysis again after etching the sample

FIG. 5: LaN not treated with aqueous metal fluoride solution
Graph showing Al peaks obtained by ESCA analysis of i _4.7 Al _0.3 sample

FIG. 6: Same LaNi _4.7 Al _0.3 analyzed by ESCA.
Graph showing Al peaks obtained by ESCA analysis again after etching the sample

FIG. 7: LaNi _4.7 treated with metal fluoride aqueous solution
L obtained by ESCA analysis of Al _0.3 sample
Graph showing peak of a

FIG. 8: The same LaNi _4.7 Al _0.3 ESCA analyzed.
Graph showing the peak of La obtained by ESCA analysis again after etching the sample

FIG. 9 is a graph showing La peaks obtained by ESCA analysis again after the same LaNi _4.7 Al _0.3 sample was further etched.

FIG. 10: La obtained by ESCA analysis again after continuing the etching of the same LaNi _4.7 Al _0.3 sample.
Graph showing the peak of

FIG. 11: LaNi treated with an aqueous metal fluoride solution
_4.7 Graph showing Ni peak obtained by ESCA analysis of _0.3 Al sample

FIG. 12 Same LaNi _4.7 Al analyzed by ESCA
Graph showing Ni peaks obtained by ESCA analysis again after etching _0.3 samples

FIG. 13 is a graph showing Ni peaks obtained by ESCA analysis again after further etching the same LaNi _4.7 Al _0.3 sample.

FIG. 14: Ni obtained by ESCA analysis again after the same LaNi _4.7 Al _0.3 sample was further etched.
Graph showing the peak of

FIG. 15: LaNi treated with an aqueous metal fluoride solution
_4.7 Graph showing Al peaks obtained by ESCA analysis of _0.3 Al samples

FIG. 16: Same LaNi _4.7 Al analyzed by ESCA
Graph showing Al peaks obtained by ESCA analysis again after etching _0.3 samples

FIG. 17 is a graph showing Al peaks obtained by ESCA analysis again after further etching the same LaNi _4.7 Al _0.3 sample.

FIG. 18: Al obtained by ESCA analysis again after the same LaNi _4.7 Al _0.3 sample was further etched.
Graph showing the peak of

FIG. 19: Pressure of hydrogen storage alloy used in Example 1-
Graph showing composition-temperature characteristics

FIG. 20 is a graph showing that the hydrogen storage alloy of Example 2 does not deactivate even after being exposed to the atmosphere for a long period of time.

FIG. 21 is a graph showing a state of initial activation of a Mg ₂ Ni alloy having a particle size of 0.075 mm or less (Example 3).

FIG. 22: Mg with a grain size of 0.106 to 0.075 mm or less
₂ Graph showing initial activation status of Ni alloy (Example 3)

FIG. 23 is a graph showing the initial activation status of MmNi _0.35 Mn _0.4 Al _0.3 Co _0.75 alloy (Example 3).

Claims (3)

(57) [Claims] 1. A hydrogen storage alloy is used as a supersaturated water of a metal fluoride.
Treated with a solution, at least the surface or surface layer of the hydrogen storage alloy
Activation of hydrogen storage alloys characterized by activating parts
Processing method. 2. A hydrogen storage alloy activated according to claim 1.
After vacuuming, hydrogen gas is introduced to absorb hydrogen.
Hydrogen storage alloy characterized by storing hydrogen in a storage alloy
Initial activation treatment method of gold. 3. A hydrogen storage mixture in which hydrogen is stored according to claim 2.
Treating gold with a supersaturated aqueous solution of metal fluoride to make it a toxic substance
In contrast, the surface of the hydrogen storage alloy is made inert.
Method for stabilizing hydrogen storage alloy.