JP2006008441A - Material for storing hydrogen and method for production the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a material for storing hydrogen in which the hydrogen releasing temperature is lowered and to provide a method for producing the same. <P>SOLUTION: In the material for storing hydrogen which is obtained by finely dividing a mixture or a composite material of lithium hydride and lithium amide through a prescribed mechanically pulverizing treatment, the material for storing hydrogen has a specific surface area according to the BET method of 15 m<SP>2</SP>/g or higher. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydrogen storage material used as a fuel for fuel cells and the like, and a method for producing the same.

NO _X and development of fuel cells have been actively as a clean energy source that does not emit greenhouse gases such as toxic substances and CO ₂ in the SO _X or the like, and is already practiced in several areas. As an important technology that supports this fuel cell technology, there is a technology for storing hydrogen as fuel for the fuel cell. As storage forms of hydrogen, compression storage by high-pressure cylinders, cooling storage by liquid hydrogenation, and storage by hydrogen storage materials are known. Among these forms, storage by hydrogen storage materials is used for distributed storage and transportation. This is advantageous. Hydrogen storage materials include materials with high hydrogen storage efficiency, that is, materials with a high hydrogen storage amount per unit weight or volume of the hydrogen storage material, materials that absorb / release hydrogen at a low temperature, and good durability. A material having is desired.

Conventionally, as a hydrogen storage material, various materials such as metal materials such as rare earth, titanium, vanadium, and magnesium, lightweight inorganic compounds such as metal alanate (for example, NaAlH ₄ and LiAlH ₄ ), and carbon, etc. It has been known. In addition, for example, a hydrogen storage method using lithium nitride represented by the following formula (1) has also been reported (see, for example, Non-Patent Documents 1 and 2).
Li ₃ N + 2H ₂ ⇔Li ₂ NH + LiH + H ₂ ⇔LiNH ₂ + 2LiH (1)

Here, absorption of hydrogen by Li ₃ N started from about 100 ° C., and 9.3 mass% hydrogen absorption was confirmed at 255 ° C. for 30 minutes. In addition, it has been reported that the absorption characteristics of absorbed hydrogen pass through two steps: 6.3% by mass at less than 200 ° C. and 3.0% by mass at 320 ° C. or higher by slowly heating. . That is, the reaction of the following formula (2) corresponding to the right side portion of the above formula (1) starts to proceed at a little less than 200 ° C., and the reaction of the following formula (3) corresponding to the left side portion of the above formula (1) is about 320 It has been shown to begin to progress at ° C.
LiNH ₂ + 2LiH → Li ₂ NH + LiH + H ₂ ↑ (2)
Li ₂ NH + LiH → Li ₃ N + H ₂ ↑ (3)

However, the lithium nitride represented by the above formula (1) has a problem that the hydrogen release temperature is high.
Ruff, O., and Goerges, H., Berichte der Deutschen Chemischen Gesellschaft zu Berlin, Vol. 44, 502-6 (1911) Ping Chen et al., Interaction of hydrogen with metalnitrides andimides, NATURE Vol.420, 21 NOVEMBER 2002, p302〜304

In view of such circumstances, the inventors previously made a nanostructure of lithium amide (LiNH ₂ ) and lithium hydride (LiH) in Japanese Patent Application No. 2003-291672 to shift the hydrogen generation reaction temperature to the low temperature side. A hydrogen storage material has been disclosed. However, it is desired to further lower the hydrogen generation reaction temperature.
The present invention has been made in view of such circumstances, and an object thereof is to provide a hydrogen storage material in which the hydrogen generation temperature is lowered, and a method for producing the same.

That is, according to the first aspect of the present invention, there is provided a hydrogen storage material obtained by refining a mixture or composite of lithium hydride and lithium amide by a predetermined mechanical pulverization treatment, and having a specific surface area of 15 m by the BET method. A hydrogen storage material characterized by being ² / g or more is provided.
In the hydrogen storage material according to the first aspect, the specific surface area is preferably 30 m ² / g or more from the viewpoint of further increasing the hydrogen release rate.

According to a second aspect of the present invention, there is provided a hydrogen storage material obtained by refining a mixture or composite of lithium hydride and magnesium amide by a predetermined mechanical pulverization treatment, having a specific surface area of 7. A hydrogen storage material characterized by being 5 m ² / g or more is provided.
In the hydrogen storage material according to the ^second aspect, the specific surface area is preferably 15 m ² / g or more from the viewpoint of further increasing the hydrogen release rate. The mixing ratio of lithium hydride to 1 mol of magnesium amide is preferably 1.5 mol or more and 4 mol or less.

According to a third aspect of the present invention, there is provided a hydrogen storage material obtained by refining a mixture or composite of magnesium hydride and lithium amide by a predetermined mechanical pulverization treatment, having a specific surface area of 7.5 m by the BET method. A hydrogen storage material characterized by being ² / g or more is provided.

In the hydrogen storage material according to the third aspect, the specific surface area is preferably 15 m ² / g or more from the viewpoint of further increasing the hydrogen release rate. The mixing ratio of magnesium hydride to 1 mol of lithium amide is preferably 0.5 mol or more and 2 mol or less.

According to a fourth aspect of the present invention, there is provided a hydrogen storage material comprising hydrogenated lithium imide, wherein the specific surface area by the BET method is 10 m ² / g or more. The

In the hydrogen storage material according to the fourth aspect, the specific surface area is preferably 15 m ² / g or more from the viewpoint of further increasing the hydrogen release rate. As the lithium imide, a lithium imide synthesized by reacting lithium nitride with hydrogen or thermally decomposing lithium amide is preferably used.

According to a fifth aspect of the present invention, there is provided a hydrogen storage material obtained by hydrogenating a mixture and composite of magnesium nitride and lithium imide, wherein the specific surface area by the BET method is 5 m ² / g or more. A hydrogen storage material is provided.
In the hydrogen storage material according to the fifth aspect, the specific surface area is preferably 10 m ² / g or more from the viewpoint of further increasing the hydrogen release rate.

  Each of the above hydrogen storage materials preferably further contains a catalyst that enhances the ability to absorb and release hydrogen. Examples of this catalyst include B, C, Mn, Fe, Co, Ni, Pt, Pd, Rh, Li, Na, Mg, One or more selected from K, Ir, Nd, Nb, La, Ca, V, Ti, Cr, Cu, Zn, Al, Si, Ru, Mo, W, Ta, Zr, Hf and Ag A metal, a compound thereof, an alloy thereof, or a hydrogen storage alloy is preferably used.

According to a sixth aspect of the present invention, there is provided a method for producing a hydrogen storage material comprising hydrogenated lithium imide,
Mechanically pulverizing and mixing the lithium amide powder and the catalyst for enhancing hydrogen absorption and release;
Thermally decomposing the object to be processed obtained by the pulverization step, and changing lithium amide contained in the object to be processed into lithium imide;
Hydrogenating the lithium imide;
Have
By the series of steps, a method for producing a hydrogen storage material is provided, wherein a hydrogenated lithium imide having a specific surface area of 10 m ² / g or more by BET method is obtained.

According to a seventh aspect of the present invention, there is provided a method for producing a hydrogen storage material comprising hydrogenated lithium imide,
Mechanically grinding lithium amide powder;
After the pulverization step, a step of further adding a catalyst that enhances hydrogen absorption / release capability to the lithium amide powder, pulverizing and mixing, and supporting the catalyst on the lithium amide powder;
Pyrolyzing the object to be treated obtained by the catalyst supporting step, and changing lithium amide contained in the object to be treated to lithium imide;
Hydrogenating the lithium imide;
Have
By the series of steps, a method for producing a hydrogen storage material is provided, wherein a hydrogenated lithium imide having a specific surface area of 10 m ² / g or more by BET method is obtained.

  According to this invention, the hydrogen storage material manufactured by the manufacturing method of the hydrogen storage material which concerns on these 6th and 7th viewpoints is provided.

  According to the present invention, the hydrogen release temperature can be lowered as compared with the prior art. As a result, the energy required for heating to release hydrogen from the hydrogen storage material is reduced, and restrictions on the material and structure of the container and the like filled with the hydrogen storage material are relaxed.

  The hydrogen storage material according to the present invention is roughly divided into two material systems. The first material system includes a material made of a mixture or composite of a metal hydride and a metal amide compound and refined by a predetermined mechanical pulverization process. The second material system includes a material obtained by hydrogenating a material containing a metal imide compound. The material included in the second material system is also preferably refined by a predetermined mechanical pulverization process.

First, the first material system will be described. The combinations of metal hydride and metal amide compound in this system include lithium hydride (LiH) and lithium amide (LiNH ₂ ), lithium hydride and magnesium amide (Mg (NH ₂ ) ₂ ), magnesium hydride (MgH _2). ) And lithium amide. These have different hydrogen release temperatures as basic characteristics of the materials, and there are also differences in specific surface area values that lower the hydrogen release temperature.

As will be described in detail in the examples described later, in the case of a combination of lithium hydride and lithium amide, when the specific surface area by the BET method is 15 m ² / g or more, the hydrogen release temperature rapidly decreases. In other words, the hydrogen release temperature can be greatly lowered by setting the specific surface area to 15 m ² / g or more. Further, from the viewpoint of increasing the hydrogen release rate, the specific surface area is more preferably 30 m ² / g or more. Here, the hydrogen release rate is set to be 3 mass% (mass%) or more.

In the case of a combination of lithium hydride and magnesium amide, the specific surface area by the BET method is set to 7.5 m ² / g or more in order to lower the hydrogen release temperature. Further, from the viewpoint of increasing the hydrogen release rate, the specific surface area is preferably 15 m ² / g or more.

The hydrogen releasing reaction between lithium hydride and magnesium amide is represented by the following formula (4) and the following formula (5).
2LiH + Mg (NH ₂ ) ₂ ⇔Li ₂ NH + MgNH + 2H ₂ (4)
8LiH + 3Mg (NH ₂ ) ₂ ⇔4Li ₂ NH + Mg ₃ N ₂ + 8H ₂ (5)

  Considering the above formulas (4) and (5), in the above formula (4), 2 mol of lithium hydride is equivalent to 1 mol of magnesium amide, and the theoretical hydrogen storage rate is 5.48. It becomes mass%. On the other hand, in the above formula (5), 2.67 mol of lithium hydride is a chemical equivalent with respect to 1 mol of magnesium amide, and the theoretical hydrogen storage rate is 6.85 mass%. Therefore, the reaction that occurs predominantly changes as the composition ratio of magnesium amide and lithium hydride changes, and the hydrogen storage rate also changes.

Here, the above equation (5) is divided into the following equations (6a) and (6b).
6LiH + 3Mg (NH ₂ ) ₂ ⇔3Li ₂ NH + 3MgNH + 6H ₂ (6a)
_{3MgNH + 2LiH⇔Li 2 NH + Mg 3} N 2 + 2H 2 ... (6b)
Then, the above equation (6a) is obtained by multiplying the coefficient of each substance in the above equation (4) by three, and is substantially the same as the above equation (4). The above formula (6b) is a reaction between magnesium imide (MgNH) produced by the above formula (6a) and lithium hydride.

  In other words, the above formula (5) shows that when lithium hydride is made to exceed the stoichiometric ratio with respect to magnesium amide in order to cause the reaction of the above formula (4), a part of the produced magnesium imide is obtained. Shows that the reaction proceeds to the point where magnesium nitride is formed by reacting with excessively added lithium hydride.

  From these facts, when the mixing ratio of lithium hydride to 1 mol of magnesium amide is less than 2, magnesium amide is excessive with respect to lithium hydride. To do. In addition, when the mixing ratio of lithium hydride to 1 mol of magnesium amide is 2 which is a stoichiometric ratio, the above formula (4) proceeds predominantly. However, even if the mixing ratio of lithium hydride to magnesium amide is adjusted to the above formula (4), the generated magnesium imide actually depends on the mixed state (dispersed state) of magnesium imide and lithium hydride. It is considered that the reaction of the above formula (5) proceeds with the reaction of lithium hydride with some magnesium amide remaining without reacting.

  On the other hand, when the mixing ratio of lithium hydride to 1 mol of magnesium amide is more than 2 and less than 2.67, lithium hydride is excessive with respect to magnesium amide according to the above formula (4). From the above formula (5), lithium hydride is insufficient with respect to magnesium amide. In this case, when the mixing ratio is close to 2, the above formula (4) proceeds predominantly, and part of the generated magnesium imide changes to magnesium nitride, and as the mixing ratio increases to 2.67. The above formula (5) proceeds dominantly. When the mixing ratio of lithium hydride to 1 mol of magnesium amide is a stoichiometric ratio of 2.67 and when the mixing ratio is more than 2.67, the above formula (5) proceeds predominantly. .

  Which of these formulas (4) and (5) is mainly used depends on, for example, the hydrogen storage rate and the cycle characteristics of the reaction in which hydrogen is again stored in the product after hydrogen release (that is, the above-described formula). This can be determined in consideration of the equation (4) and the ease of reaction from the right side to the left side of the above equation (5). Moreover, it is thought that hydrogen release can be promoted by increasing the reaction probability of the other substance by making one of lithium hydride and magnesium amide excessive with respect to the other. However, if one of the substances is too much, there is a problem that the hydrogen storage rate with respect to the total amount is lowered.

  Therefore, it is preferable to determine the respective amounts of lithium hydride and magnesium amide in consideration of such hydrogen storage rate, utilization rate of reactants, cycle characteristics of hydrogen absorption / release reaction, and the like. Specifically, the mixing ratio of lithium hydride to 1 mol of magnesium amide is preferably 1.5 mol or more and 4 mol or less, and more preferably 2.5 mol so that the above formula (5) proceeds mainly. By setting it as 3.5 mol or less above, a hydrogen storage rate can be maintained higher than the other range.

In the case of a combination of magnesium hydride and lithium amide, the specific surface area by the BET method is set to 7.5 m ² / g or more in order to lower the hydrogen release temperature. Further, from the viewpoint of increasing the hydrogen release rate, the specific surface area is preferably 15 m ² / g or more.

The reaction between magnesium hydride and lithium amide is represented by the following formula (7) and the following formula (8).
MgH ₂ + 2LiNH ₂ ⇔Li ₂ NH + MgNH + 2H ₂ (7)
3MgH ₂ + 4LiNH ₂ ⇔Mg ₃ N ₂ + 2Li ₂ NH + 6H ₂ (8)

  Considering the above formulas (7) and (8), in the above formula (7), 0.5 mol of magnesium hydride is equivalent to 1 mol of lithium amide, and the theoretical hydrogen storage rate is 5 48 mass%. On the other hand, in the above formula (8), 0.75 mol of lithium hydride is a chemical equivalent with respect to 1 mol of lithium amide, and the theoretical hydrogen storage rate is 7.08 mass%. Therefore, the reaction that occurs predominantly changes as the composition ratio of magnesium hydride and lithium amide changes, and the hydrogen storage rate also changes.

  In other words, in the case of the combination of magnesium hydride and lithium amide, as in the case of the combination of lithium hydride and magnesium amide described above, the hydrogen storage rate, the utilization rate of the reactants, the cycle characteristics of the hydrogen absorption / release reaction, etc. In consideration, it is preferable to determine the amounts of magnesium hydride and lithium amide. Specifically, the magnesium hydride is preferably excessive, and the mixing ratio of lithium hydride to 1 mol of magnesium amide is preferably 0.5 mol or more and 2 mol or less. Furthermore, the hydrogen storage rate can be maintained higher than the other ranges by setting the amount to 0.5 mol or more and 1 mol or less so that the formula (8) proceeds mainly.

Next, the second material system will be described. As a material obtained by hydrogenating a material containing a metal imide compound, a material obtained by hydrogenating lithium imide (Li ₂ NH), a mixture of magnesium nitride (Mg ₃ N ₂ ) and lithium imide, and a composite are hydrogenated. Material. Here, in this specification, “hydrogenation of a substance” means that the substance is changed to a state in which hydrogen is taken in by reacting the substance with hydrogen. For example, hydrogenated lithium imide is obtained by reacting lithium imide with hydrogen, and its structure is not clear, but it does not change to lithium amide or ammonia, but reacts with hydrogen and incorporates hydrogen in some form. It refers to a material that, when heated to a predetermined temperature later, the incorporated hydrogen is released and returns to the original lithium imide.

Hydrogenated lithium imide has a specific surface area of 10 m ² / g or more by the BET method in order to lower the hydrogen release temperature. Further, from the viewpoint of increasing the hydrogen release rate, the specific surface area is preferably 15 m ² / g or more.

As the lithium imide, those synthesized by imidization by reacting lithium nitride (Li ₃ N) with hydrogen or thermal decomposition of lithium amide are preferably used. This is because when lithium imide is synthesized by reacting lithium hydride and lithium amide as in the past, this reaction is a solid-phase reaction, so that lithium hydride and lithium amide are homogeneous in a microscopic state. While large mechanical energy is required to make contact with the material, such treatment is actually difficult. On the other hand, the thermal decomposition or the like can synthesize lithium imide having a large specific surface area and promote hydrogenation. Because it can.

A material obtained by hydrogenating a mixture and composite of magnesium nitride and lithium imide has a specific surface area of 5 m ² / g or more by the BET method in order to lower the hydrogen release temperature. Further, from the viewpoint of increasing the hydrogen release rate, the specific surface area is preferably 10 m ² / g or more.

  The various hydrogen storage materials described above preferably further include a catalyst that enhances the ability to absorb and release hydrogen. Examples of the catalyst include B, C, Mn, Fe, Co, Ni, Pt, Pd, Rh, Li, Na, One or two selected from Mg, K, Ir, Nd, Nb, La, Ca, V, Ti, Cr, Cu, Zn, Al, Si, Ru, Mo, W, Ta, Zr, Hf and Ag The above metals or their compounds or their alloys, or hydrogen storage alloys are preferably used.

  As a method for supporting such a catalyst on the hydrogen storage material, it is added to the raw material powder of various hydrogen storage materials and pulverized and mixed, or after the raw material powder is pulverized and mixed, it is further mixed (or pulverized and mixed). The method can be used.

  For example, a hydrogen storage material comprising a mixture or composite of a metal hydride and a metal amide compound is obtained by simultaneously grinding and mixing a predetermined amount of metal hydride powder, metal amide compound powder and catalyst, or a predetermined amount of metal hydride. The powder and the metal amide compound powder are pulverized and mixed, and a catalyst is added to and mixed with the obtained object to be processed. Then, the pulverizing and mixing conditions at that time are set so as to have a predetermined specific surface area after the pulverizing and mixing process.

  In addition, for example, a hydrogen storage material made of hydrogenated lithium imide is obtained by first mechanically pulverizing and mixing lithium amide powder and a catalyst that enhances hydrogen absorption and desorption ability, and then the object to be processed obtained by the previous pulverization step. Can be produced by changing the lithium amide contained in the material to be treated into lithium imide, and then hydrogenating the obtained lithium imide.

  Alternatively, the lithium amide powder is first mechanically pulverized, then a catalyst that enhances hydrogen absorption / release capacity is added to the lithium amide powder obtained by the previous pulverization treatment and pulverized and mixed to support the catalyst on the lithium amide powder. Subsequently, the object to be treated carrying the catalyst may be thermally decomposed to change lithium amide contained in the object to be treated to lithium imide, and then the obtained lithium imide may be hydrogenated. In the process for producing a hydrogen storage material made of hydrogenated lithium imide, the conditions for pulverizing lithium amide are set so as to have a predetermined specific surface area after pulverizing.

  A material obtained by hydrogenating a mixture and composite of magnesium nitride and lithium imide can be produced by pulverizing and mixing lithium amide powder and magnesium nitride, followed by imidization and hydrogenation. It can also be produced by a method in which lithium amide powder is pulverized and then imidized, and the resulting lithium imide and magnesium hydride are pulverized and mixed, followed by hydrogenation.

  The mechanical pulverization treatment of the hydrogen storage material belonging to each of the above-mentioned material systems is performed using known raw material powders such as a ball mill apparatus, a roller mill, an inner / outer cylinder rotating mill, an attritor, an inner piece mill, an airflow mill Various pulverization means can be used.

(1) Preparation of Lithium Hydride + Lithium Amide Sample Lithium hydride, lithium amide and titanium trichloride (TiCl ₃ ) (all manufactured by Aldrich, purity 95%) were used at a molar ratio of 1: 1: 0.02. These were weighed in a high-purity argon glove box so that the total amount was 1.3 g, and put into a mill vessel with a valve (250 ml) made of high chromium steel. Subsequently, after evacuating the inside of the mill vessel, high-purity argon gas was introduced at 1 MPa, and milling was performed at room temperature at 60 to 250 rpm for 3 to 360 minutes using a planetary ball mill apparatus (P-5, manufactured by Fritsch). A plurality of samples having different specific surface areas were processed. After the inside of the mill container was evacuated and filled with argon gas, the mill container was opened in a high purity argon glove box, and a sample was taken out.

(2) Preparation of lithium hydride + magnesium amide-based sample (a) Preparation of magnesium amide ₂ g of magnesium hydride (Azmax, purity 95%, MgH ₂ ) in a high purity argon glove box made of high chromium steel After charging into the container (internal volume: 250 ml), the inside of the mill container is evacuated, and subsequently the reaction of the following formula (9) is caused, so that the amount becomes 2 mol or more with respect to 1 mol of magnesium hydride. After the ammonia gas was introduced into the mill container, the mill container was sealed, and then this was milled for a predetermined time using a planetary ball mill apparatus at a rotation speed of 250 rpm at room temperature and in an air atmosphere. Thereafter, the amount of hydrogen in the reaction gas was measured from the mill vessel, and the pulverized product was measured by XRD, thereby confirming the formation of magnesium amide.
MgH ₂ + 2NH ₃ (g) → Mg (NH ₂ ) ₂ + 2H ₂ (g) (9)

(B) Mixed pulverization of magnesium amide and lithium hydride Lithium hydride (manufactured by Aldrich, purity 95%) and magnesium amide prepared as described above at a molar ratio of 8: 3, the total amount of which is 1.3 g Were weighed in a high-purity argon glove box and put into a high-chromium steel valve vessel (250 ml). Subsequently, after the inside of the mill container was evacuated, 1 MPa of high-purity argon gas was introduced, and milling was performed using a planetary ball mill apparatus at room temperature and 250 rpm for 3 to 360 minutes to obtain a plurality of samples having different specific surface areas. Produced. Subsequently, after the inside of the mill container was evacuated and filled with argon gas, the mill container was opened in a high purity argon glove box, and a sample was taken out.

(3) Preparation of magnesium hydride + lithium amide-based sample Magnesium hydride (manufactured by Amax Co., purity 95%) and lithium amide (manufactured by Aldrich, purity 95%) at a molar ratio of 3: 4, and their total amount Was weighed in a high-purity argon glove box so as to be 1.3 g, and placed in a high-chromium steel valve-equipped mill container (250 ml). Subsequently, after the inside of the mill container was evacuated, 1 MPa of high-purity argon gas was introduced, and milling was performed using a planetary ball mill apparatus at room temperature and 250 rpm for 3 to 360 minutes to obtain a plurality of samples having different specific surface areas. Produced. Subsequently, after the inside of the mill container was evacuated and filled with argon gas, the mill container was opened in a high purity argon glove box, and a sample was taken out.

(4) Production of lithium imide and its hydrogenation Lithium amide and titanium trichloride (both made by Aldrich, purity 95%) are in a molar ratio of 1: 0.01, so that their total amount is 1.3 g. Weighed in a high purity argon glove box and put into a mill vessel with a valve (250 ml) made of high chromium steel. Subsequently, after the inside of the mill container was evacuated, 1 MPa of high-purity argon gas was introduced, and milling was performed using a planetary ball mill apparatus at room temperature and 250 rpm for 3 to 720 minutes. Produced. Subsequently, after the inside of the mill container was evacuated and filled with argon gas, the mill container was opened in a high purity argon glove box, and each sample was transferred to a stainless steel reaction container (50 ml). The inside of this stainless steel container was evacuated and heat-treated at 350 ° C. for 6 hours to thermally decompose lithium amide and synthesize lithium imide. Further, the obtained lithium imide was treated in hydrogen gas at 3 MPa and 180 ° C. for 12 hours to be hydrogenated.

(5) Preparation of magnesium nitride + lithium imide sample and hydrogenation thereof Lithium imide prepared by the same method as in (4) above and magnesium nitride (Aldrich, purity 95%) were used at a molar ratio of 4: 1. Were weighed in a high-purity argon glove box so that the total amount was 1.3 g, and placed in a high-chromium steel valve vessel (250 ml). Subsequently, after the inside of the mill container was evacuated, 1 MPa of high-purity argon gas was introduced, and milling was performed using a planetary ball mill device at room temperature and 250 rpm for 3 to 360 minutes. Produced. Subsequently, after the inside of the mill container was evacuated and filled with argon gas, the mill container was opened in a high purity argon glove box, and a sample was taken out. Next, the sample after milling in a high-purity glove box is transferred to a stainless steel reaction vessel (50 ml), evacuated, and then introduced with high-purity hydrogen gas and maintained at 220 ° C., 3 MPa for 12 hours for hydrogenation. It was.

(6) Method for measuring BET specific surface area The BET specific surface area of the samples prepared according to the above (1) to (5) was measured using multipoint BET measurement with nitrogen gas (ASAP2400, manufactured by Micromeritics).

(7) Measurement of DTA endothermic peak temperature by hydrogen release 10 mg of each sample prepared by the above (1) to (5) was weighed, and the temperature rising rate was 5 ° C./min. A DTA curve was measured using a / DTA apparatus (TG / DTA300, manufactured by Seiko Instruments Inc.). And the endothermic peak temperature by hydrogen release was measured from the obtained DTA curve, and the temperature was made into the hydrogen release temperature.

(8) Measurement of hydrogen release amount The mass reduction rate from 30 ° C to 250 ° C of the TG curve obtained from the TG / DTA measurement from room temperature to 400 ° C in (7) above is obtained from the TG curve, and this is the hydrogen release rate. It was.

(9) Test results of lithium hydride + lithium amide samples FIG. 1 shows DTA curves of four samples A to D selected from the samples prepared. Sample A was ground at 250 rpm for 3 minutes, Sample B was ground at 250 rpm for 10 minutes, Sample C was ground at 250 rpm for 30 minutes, Sample D was ground at 250 rpm for 120 minutes, each of the specific surface area of the sample A~D ^{is 11.6m 2 /g,19.9m 2 /g,34.8m 2 /g,40.5m 2} / g,. As shown in FIG. 1, as the pulverization time becomes longer, the pulverization progresses and the specific surface area increases, and when the specific surface area increases, the hydrogen release temperature (the position of the endothermic reaction valley indicated by the black dot in FIG. 1). It can be seen that (temperature) has shifted to the low temperature side. Sample A is outside the scope of the present invention, and samples B to D are within the scope of the present invention.

FIG. 2 is a graph showing the relationship between the specific surface area of each sample, the hydrogen release temperature, and the hydrogen release rate. From FIG. 2, in the hydrogen hydride + lithium amide type hydrogen storage material, the hydrogen release temperature is about 270 ° C. from about 320 ° C. compared with the case where the BET specific surface area is 15 m ² / g or more and less than 15 m ² / g. It was confirmed that the temperature was rapidly lowered to below ℃ and the hydrogen release rate was also 2 mass% or more. The hydrogen release temperature was 260 ° C. or less when the BET specific surface area was 30 m ² / g or more, and it was confirmed that the temperature was further lowered and the hydrogen release rate exceeded 3 mass%.

(10) Test results of lithium hydride + magnesium amide samples FIG. 3 is a graph showing the relationship between the specific surface area, hydrogen release temperature, and hydrogen release rate of each sample. In the hydrogen storage material of lithium hydride + magnesium amide, the hydrogen release temperature exceeds 230 ° C. when the BET specific surface area is 7.5 m ² / g or more, compared with the case where it is less than 7.5 m ² / g. It was confirmed that the temperature was lowered to 230 ° C. or lower, and the hydrogen release rate was 2% by mass or more. The hydrogen release temperature was 220 ° C. or less when the BET specific surface area was 15 m ² / g or more, and it was confirmed that the temperature was further lowered and the hydrogen release rate exceeded 3 mass%.

(11) Test Results of Magnesium Hydride + Lithium Amide Sample FIG. 4 is a graph showing the relationship between the specific surface area, hydrogen release temperature, and hydrogen release rate of each sample. Among the magnesium hydride + lithium amide samples, the hydrogen release temperature exceeded 230 ° C. when the BET specific surface area was 7.5 m ² / g or more, compared to the case where the BET specific surface area was less than 7.5 m ² / g. It was confirmed that the temperature was lowered to 230 ° C. or lower, and the hydrogen release rate was 2% by mass or more. The hydrogen release temperature was 220 ° C. or less when the BET specific surface area was 15 m ² / g or more, and it was confirmed that the temperature was further lowered and the hydrogen release rate exceeded 3 mass%.

(12) Test results of hydrogenated lithium imide FIG. 5 is a graph showing the relationship between the specific surface area of each sample, the hydrogen release temperature, and the hydrogen release rate. In the case of hydrogenated lithium imide, it is confirmed that the hydrogen release temperature is lowered from about 300 ° C. to 290 ° C. or less when the BET specific surface area is 10 m ² / g or more, compared to the case of less than 10 m ² / g. As a result, the hydrogen release rate was 2% by mass or more. The hydrogen release temperature was 280 ° C. or less when the BET specific surface area was 15 m ² / g or more, and it was confirmed that the temperature was further lowered and the hydrogen release rate exceeded 3 mass%.

(13) Test Results of Magnesium Nitride + Lithium Imide Sample FIG. 6 is a graph showing the relationship between the specific surface area, hydrogen release temperature, and hydrogen release rate of each sample. In a hydrogen storage material obtained by hydrogenating a pulverized mixture of magnesium nitride and lithium imide, the hydrogen release temperature exceeds 240 ° C. when the BET specific surface area is 5 m ² / g or more, compared to the case where it is less than 5 m ² / g. It was confirmed that the temperature was lowered to 240 ° C. or lower, and the hydrogen release rate was 2% by mass or more. The hydrogen release temperature was 230 ° C. or less when the BET specific surface area was 10 m ² / g or more, and it was confirmed that the temperature was further lowered and the hydrogen release rate exceeded 3 mass%.

  The hydrogen storage material according to the present invention is suitable as a hydrogen source of a fuel cell that generates power using hydrogen and oxygen as fuel.

Explanatory drawing which shows an example of the DTA curve of the hydrogen storage material which consists of lithium hydride and lithium amide. Explanatory drawing which shows the relationship between the specific surface area of the hydrogen storage material which consists of lithium hydride and lithium amide, hydrogen release temperature, and hydrogen release rate. Explanatory drawing which shows the relationship between the specific surface area of the hydrogen storage material which consists of lithium hydride and magnesium amide, hydrogen release temperature, and hydrogen release rate. Explanatory drawing which shows the relationship between the specific surface area of the hydrogen storage material which consists of magnesium hydride and lithium amide, hydrogen release temperature, and hydrogen release rate. Explanatory drawing which shows the relationship between the specific surface area of the hydrogen storage material which consists of hydrogenated lithium imide, hydrogen release temperature, and hydrogen release rate. Explanatory drawing which shows the relationship between the specific surface area of the hydrogen storage material which hydrogenated the grinding | pulverization mixture of magnesium nitride and lithium imide, hydrogen release temperature, and a hydrogen release rate.

Claims (18)

A hydrogen storage material obtained by refining a mixture or composite of lithium hydride and lithium amide by a predetermined mechanical grinding process,
A hydrogen storage material having a specific surface area of 15 m ² / g or more by BET method. The hydrogen storage material according to claim 1, wherein the specific surface area is 30 m ² / g or more. A hydrogen storage material obtained by refining a mixture or composite of lithium hydride and magnesium amide by a predetermined mechanical grinding process,
A hydrogen storage material having a specific surface area of 7.5 m ² / g or more by BET method. The hydrogen storage material according to claim 3, wherein the specific surface area is 15 m ² / g or more.   The hydrogen storage material according to claim 3 or 4, wherein a mixing ratio of lithium hydride to 1 mol of magnesium amide is 1.5 mol or more and 4 mol or less. A hydrogen storage material obtained by refining a mixture or composite of magnesium hydride and lithium amide by a predetermined mechanical grinding process,
A hydrogen storage material having a specific surface area of 7.5 m ² / g or more by BET method. The hydrogen storage material according to claim 6, wherein the specific surface area is 15 m ² / g or more.   The hydrogen storage material according to claim 6 or 7, wherein a mixing ratio of magnesium hydride to 1 mol of lithium amide is 0.5 mol or more and 2 mol or less. A hydrogen storage material comprising hydrogenated lithium imide,
A hydrogen storage material having a specific surface area of 10 m ² / g or more by BET method. The hydrogen storage material according to claim 9, wherein the specific surface area is 15 m ² / g or more.   The hydrogen storage material according to claim 9 or 10, wherein the lithium imide is synthesized by reacting lithium nitride with hydrogen or by thermally decomposing lithium amide. A hydrogen storage material obtained by hydrogenating a mixture and composite of magnesium nitride and lithium imide,
A hydrogen storage material having a specific surface area of 5 m ² / g or more by BET method. The hydrogen storage material according to claim 12, wherein the specific surface area is 10 m ² / g or more.   The hydrogen storage material according to any one of claims 1 to 13, further comprising a catalyst that enhances the ability to absorb and release hydrogen.   The catalyst includes B, C, Mn, Fe, Co, Ni, Pt, Pd, Rh, Li, Na, Mg, K, Ir, Nd, Nb, La, Ca, V, Ti, Cr, Cu, Zn, 15. One or more metals selected from Al, Si, Ru, Mo, W, Ta, Zr, Hf, and Ag, a compound thereof, an alloy thereof, or a hydrogen storage alloy. 2. A hydrogen storage material according to 1. A method for producing a hydrogen storage material comprising hydrogenated lithium imide,
Mechanically pulverizing and mixing the lithium amide powder and the catalyst for enhancing hydrogen absorption and release;
Thermally decomposing the object to be processed obtained by the pulverization step, and changing lithium amide contained in the object to be processed into lithium imide;
Hydrogenating the lithium imide;
Have
A method for producing a hydrogen storage material, wherein hydrogenated lithium imide having a specific surface area of 10 m ² / g or more by BET method is obtained by the series of steps. A method for producing a hydrogen storage material comprising hydrogenated lithium imide,
Mechanically grinding lithium amide powder;
After the pulverization step, a step of further adding a catalyst that enhances hydrogen absorption / release capability to the lithium amide powder, pulverizing and mixing, and supporting the catalyst on the lithium amide powder;
Pyrolyzing the object to be treated obtained by the catalyst supporting step, and changing lithium amide contained in the object to be treated to lithium imide;
Hydrogenating the lithium imide;
Have
A method for producing a hydrogen storage material, wherein hydrogenated lithium imide having a specific surface area of 10 m ² / g or more by BET method is obtained by the series of steps.   A hydrogen storage material produced by the method for producing a hydrogen storage material according to claim 16 or 17.

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