JP2008043927A - Method of manufacturing hydrogen storage material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a hydrogen storage material with a low hydrogen releasing temperature. <P>SOLUTION: Either one or both of MgH<SB>2</SB>and metal Mg, and LiNH<SB>2</SB>are weighed in a manner that the molar ratio of Mg and Li is adjusted to be Mg:Li=1:(1.2 to 2.4) and further LiH is weighed in a manner that the molar ratio of Mg and Li in the total when LiH is added is adjusted to be Mg:Li=1:(2.2 to 6) and they are pulverized and mixed. Next, the sample obtained by mixing and pulverizing treatment is heated at a prescribed temperature under hydrogen atmosphere and kept for a prescribed time to obtain a hydrogen storage material. Preferably, the sample obtained by the heating treatment is further pulverized and mixed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a hydrogen storage material for generating hydrogen gas used as fuel for a fuel cell or the like.

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 gas as fuel for the fuel cell. Known storage forms of hydrogen gas include compression storage using a high-pressure cylinder, cooling storage using liquid hydrogenation, storage using a hydrogen storage material, and the like.

  A storage method using a hydrogen storage material, which is one of these hydrogen storage forms, is advantageous in terms of distributed storage and transportation. 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.

Known hydrogen storage materials include metal materials centered on rare earth, titanium, vanadium, magnesium, etc., lightweight inorganic compounds such as metal alanade (for example, NaAlH ₄ and LiAlH ₄ ), carbon, and the like. In addition, for example, a hydrogen storage method using lithium nitride represented by the following formula (1) has been reported (for example, see 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 start temperature and the hydrogen release temperature are 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 and imides, NATURE Vol.420, 21 NOVEMBER 2002, p302 ~ 304

  The present invention has been made in view of such circumstances, and an object thereof is to provide a method for producing a hydrogen storage material having a low hydrogen release temperature.

In order to solve such problems, the inventors previously disclosed a method for producing a hydrogen storage material containing LiH and Mg (NH ₂ ) ₂ in Japanese Patent Application No. 2005-280178. However, even the hydrogen storage material disclosed in Japanese Patent Application No. 2005-280178 cannot be said to have a sufficiently low hydrogen release temperature, and further reduction in the hydrogen release temperature is required.

  Further, in the method for producing a hydrogen storage material disclosed in Japanese Patent Application No. 2005-280178, it takes a long time to make the components nanostructured and combined, and the productivity is not necessarily good. . Therefore, it is extremely preferable that a hydrogen storage material having a desired hydrogen release temperature can be produced easily and in a short time.

The present invention also solves such a new problem, and the method for producing a hydrogen storage material according to the first aspect of the present invention provides Mg (NH ₂ ) ₂ (magnesium amide) obtained by heat treatment. ) And LiH (lithium hydride) mixture.

In the method for producing a hydrogen storage material according to the second aspect of the present invention, first, MgH ₂ (magnesium hydride), one or both of metal Mg and LiNH ₂ (lithium amide) are mixed with Mg and Li. Weigh so that the molar ratio is Mg: Li = 1: 1.2 to 2.4, more preferably Mg: Li = 1: 1.5 to 2.2, and then add LiH (lithium hydride) to this. LiH is weighed so that the total molar ratio of Mg and Li when added is Mg: Li = 1: 2.2 to 6, and these are pulverized and mixed. Next, the sample obtained by the mixing and pulverizing process is heated to a predetermined temperature in a hydrogen atmosphere and held for a predetermined time, thereby obtaining a hydrogen storage material. Preferably, the sample obtained by this heat treatment is further pulverized and mixed.

In the method for producing a hydrogen storage material according to the third aspect of the present invention, first, MgH ₂ , one or both of metal Mg and LiNH ₂ are pulverized and mixed. Next, the sample obtained by the pulverization and mixing process is heated to a predetermined temperature in a hydrogen atmosphere and held for a predetermined time. Further, LiH is added to the sample obtained by this heat treatment and pulverized and mixed to obtain a hydrogen storage material. Preferably, the molar ratio of Mg to Li in either or both of MgH ₂ and metallic Mg and LiNH ₂ is Mg: Li = 1: 1.2 to 2.4, more preferably Mg: Li = 1: 1. The total molar ratio of Mg and Li when LiH is further added is Mg: Li = 1: 2.2-6.

  According to the present invention, there is an advantage that a hydrogen storage material having a lowered hydrogen release temperature can be produced in a shorter process than in the prior art.

Hereinafter, embodiments of the present invention will be described. The hydrogen storage material obtained by the method for producing a hydrogen storage material according to the present invention is essentially composed of a composite mixture of Mg (NH ₂ ) ₂ (magnesium amide) and LiH (lithium hydride). Therefore, this mixture may contain unreacted raw material components.

The first method for producing a hydrogen storage material is a method in which “mixture of Mg (NH ₂ ) ₂ and LiH” obtained by heat treatment is pulverized and mixed. Conventionally, a mixture of Mg (NH ₂ ) ₂ and LiH obtained by heat treatment has been used as it is for absorption / release of hydrogen, but by subjecting this mixture to further pulverization treatment, it will be shown in the examples described later. As described above, the hydrogen release temperature can be lowered.

The “mixture of Mg (NH ₂ ) ₂ and LiH” obtained by heat treatment is a mixture of MgH ₂ and / or metal Mg and LiNH _2, and this is heat-treated in a hydrogen atmosphere. Or a mixture obtained by reacting with hydrogen at a predetermined temperature after heat treatment in a vacuum atmosphere, and a mixture obtained by the second and third production methods described later. Examples of the Mg raw material that can be used for pulverization and mixing of LiNH _{2 in place of} or together with MgH ₂ and metal Mg include magnesium compounds such as Mg ₃ N ₂ , MgNH, and LiMgN.

Note that the heat treatment in this vacuum atmosphere in the manufacturing method having the heat treatment step in the vacuum atmosphere promotes decomposition of LiNH _{2 as} a raw material to increase the reactivity, and the resulting Mg (NH ₂ ) _This is performed in order to improve the hydrogen storage performance of a mixture of ₂ and LiH.

  Various known grinding methods can be used as the grinding method. For example, a planetary ball mill can be used in the case of small-scale production, and in the case of mass production, as disclosed in Japanese Patent Application Laid-Open No. 2004-306016, the inventors previously described a roller mill, an inside and outside A cylinder rotating mill, an attritor, an inner piece mill, an airflow grinding mill, or the like can be used. Moreover, a rolling mill, a vibration mill, etc. are used suitably.

  Note that the pulverization atmosphere is an inert gas atmosphere such as argon gas or helium gas, a hydrogen gas atmosphere, or a mixed gas atmosphere thereof. Furthermore, it is more desirable that the atmospheric pressure is a positive pressure with respect to the atmospheric pressure in order to prevent air contamination.

A second method for producing a hydrogen storage material is as follows: (A1) MgH ₂ (magnesium hydride), one or both of metal Mg and LiNH ₂ (lithium amide), and the molar ratio of Mg and Li is Mg: Li = 1: 1.2 to 2.4, preferably Mg: Li = 1: 1.5 to 2.2, and the total molar ratio of Mg and Li when LiH is added thereto LiH is weighed so that Mg: Li = 1: 2.2 to 6, and these are pulverized and mixed. (A2) The sample obtained in step A1 is heated to a predetermined temperature in a hydrogen atmosphere. , And a step of holding for a predetermined time. Preferably, (A3) a step of pulverizing (re-grinding) the sample obtained in step A2 is further added.

By controlling the ratio of Mg and Li in LiNH ₂ and LiH as well as either or both of MgH ₂ and metal Mg used as raw materials as described above in the A1 step, hydrogen release as shown in the examples described later A hydrogen storage material having a low temperature can be obtained.

  The pulverization method in step A1 is in accordance with the pulverization method used in the first manufacturing method described above.

In step A1, when the amount of LiNH ₂ is less than the lower limit of the ratio, the amount of hydrogen released in the hydrogen storage material obtained by finishing step A2 or step A3 is reduced. On the other hand, when the amount of LiNH _{2 is} larger than the upper limit of the ratio, the hydrogen release temperature of the hydrogen storage material that is the final product becomes high.

  In step A1, when the amount of LiH is smaller than the lower limit value of the ratio, the hydrogen release temperature is increased, and when the amount of LiH is larger than the upper limit value of the ratio, the amount of released hydrogen is decreased.

Although the chemical reaction occurring in the A1 step is not clear, LiNH ₂ changes to LiH or Li ₂ NH (lithium imide) while releasing ammonia and hydrogen, so MgH ₂ and metal Mg used as the Mg source are It may be combined with the released ammonia or hydrogen.

The step A2 is a treatment for changing the sample obtained in the step A1 into a material system capable of releasing hydrogen (hereinafter referred to as “hydrogenation treatment”), whereby the sample obtained in the step A1 is substantially changed. In addition, it can be changed to a material structure composed of Mg (NH ₂ ) ₂ and LiH.

This hydrogenation treatment is performed in a state where the sample is heated to a constant temperature in a hydrogen atmosphere, and is preferably performed in the range of 140 ° C to 250 ° C. If the temperature is lower than 140 ° C., the reaction between the sample and hydrogen is difficult to proceed, so that a long time is required for the reaction, and the productivity is lowered. On the other hand, if it is 250 ° C. or higher, the hydrogen release temperature when hydrogen is released thereafter becomes high. According to the powder X-ray diffraction (XRD) chart of the sample heated to 250 ° C. or higher, the peak other than Mg (NH ₂ ) ₂ and LiH is the reason why the hydrogen release temperature increases when the treatment temperature in the A2 step is increased. Appears, it is considered that it has changed to a phase where it is difficult to release hydrogen at low temperatures.

  The pressure of the hydrogen atmosphere in step A2 is preferably a positive pressure. More preferably, the hydrogen partial pressure is 2 MPa or more. As a result, the reaction between the sample and hydrogen can be promoted. The hydrogen atmosphere is not limited to a pure hydrogen gas atmosphere, and may be a mixed gas atmosphere of hydrogen gas and inert gas. This hydrogenation treatment may be performed under conditions where the sample is mixed (stirred) or pulverized and mixed so that the reaction is further promoted.

Although the A3 step is not an essential step, the hydrogen release temperature can be further reduced by performing the A3 step as compared to the hydrogen storage material obtained after the end of the A2 step, as shown in the examples described later. it can. This A3 process is sufficient as long as the microstructure of Mg (NH ₂ ) ₂ and LiH can be constructed, and the pulverization time, temperature conditions, and pulverization method are appropriately set so as to obtain the performance desired for the hydrogen storage material. .

Next, the 3rd manufacturing method of a hydrogen storage material is demonstrated. In this third production method, (B1) a step of grinding and mixing one or both of MgH ₂ and metallic Mg and LiNH _2, and (B2) a sample obtained by the B1 step at a predetermined temperature in a hydrogen atmosphere. And a step of (B3) adding lithium hydride to the sample obtained by the step B2 and pulverizing and mixing (additional pulverization).

In the B1 step, the molar ratio of Mg and Li in either or both of MgH ₂ and metal Mg and LiNH ₂ is preferably Mg: Li = 1: 1.2 to 2.4, and more preferably Mg: Li = 1: 1.5 to 2.2. This is a molar ratio that is a composition in which a reaction of Mg + H ₂ + 2LiNH ₂ → Mg (NH ₂ ) ₂ + 2LiH or MgH ₂ + 2LiNH ₂ → Mg (NH ₂ ) ₂ + 2LiH occurs, and Mg: Li = 1: 2 is assumed to be ideal. However, the present inventors found that a Mg in MgH ₂ or metal Mg Li molar ratio and the hydrogen release amount or a result of the relationship of intensive studies of hydrogen release temperature for the, MgH ₂ and one or both LiNH ₂ Metropolitan metal Mg By increasing the molar ratio of Li to Mg: Li = 1: 1.2 to 2.4, and more preferably Mg: Li = 1: 1.5 to 2.2, the hydrogen release amount increases and the hydrogen release temperature. It was found that the temperature could be lowered. Thus, in the present invention, the molar ratio of Mg and Li can be appropriately set to a suitable composition in accordance with the desired performance of the hydrogen storage material.

In the B1 step, LiNH ₂ changes to LiH or Li ₂ NH (lithium imide) while releasing ammonia and hydrogen, similarly to the A1 step of the second manufacturing method. Therefore, the MgH ₂ used as the Mg source It is conceivable that the metal Mg combines with the released ammonia and hydrogen.

With the hydrogenation process in the B2 step, the Mg compound contained in the sample obtained in the B1 step can be changed to Mg (NH ₂ ) ₂ . The treatment temperature and atmosphere in the B2 step are the same as those in the A2 step of the second production method described above.

  By performing the B3 step of adding LiH to the sample and pulverizing and mixing after the completion of the B2 step, the hydrogen release temperature of the obtained hydrogen storage material can be lowered. In this B3 step, the amount of LiH added to the reaction product obtained in the B2 step is such that the overall molar ratio of Mg and Li is Mg: Li = 1: 2.2- Preferably, the hydrogen storage material satisfying such a condition has a lower hydrogen release temperature than a hydrogen storage material outside this range. In Step B3, LiH also shows the effect of capturing ammonia released simultaneously with hydrogen, but the characteristic of capturing LiH ammonia added to the reactant is that the molar ratio of Mg to Li as a whole is a hydrogen storage material. This is particularly true when Mg: Li = 1: 2.2-6.

  In these first to third methods for producing hydrogen storage materials, B, C, Mn, Fe, Co, Ni, Pt, Pd, Rh, Na, Mg, K, Ir, Nb, La, and Ca are used as catalysts. Adding metal, chloride, oxide of one or more elements selected from Ti, V, Cr, Cu, Zn, Al, Si, Ru, Mo, Ta, Zr, Hf, Ag Therefore, the hydrogen release temperature can be lowered as compared with the case where such a catalyst is not added.

  The timing for adding such a catalyst is preferably before the hydrotreatment, and the catalyst is preferably pulverized and mixed with an additive (sample). Specifically, in the second production method, the effect of lowering the hydrogen release temperature is reduced when a catalyst is further added to a weighed raw material and pulverized and mixed, rather than when a catalyst is added during the re-grinding process in step A3. Appears prominently. The third manufacturing method is the same as this. Rather than simultaneously adding the catalyst when adding LiH, the catalyst is added to the raw material, pulverized and mixed, hydrogenated, and further added with LiH for additional pulverization. It is preferable to carry out.

  In addition, the manufacturing method which combined the 2nd, 3rd manufacturing method mentioned above, ie, by giving B3 process of the 3rd manufacturing method to the sample obtained through the A1 process of the 2nd manufacturing method, and the A2 process. In addition, a hydrogen storage material having a reduced hydrogen release temperature can be obtained.

It is also true that the hydrogen storage material of this system can be produced by obtaining Mg (NH ₂ ) ₂ as a raw material and pulverizing and mixing it with LiH as a modification of the above-described production method. However, since Mg (NH ₂ ) ₂ is not industrially produced in large quantities, it is difficult to obtain it as a raw material. In addition, in the production of Mg (NH ₂ ) _{2 on} a reagent scale, it is necessary to treat the metal Mg, which has been finely pulverized, in an NH ₃ atmosphere of about 0.83 MPa and treat it at 300 ° C. for one day or more. Furthermore, in order to transfer this to industrial production, it is necessary to compress and cool the flow gas to separate the flow gas into NH ₃ and H ₂ because H ₂ is mixed into the flow gas. Thus, the production of Mg (NH ₂ ) ₂ requires a long reaction time and requires energy consumption for gas separation.

On the other hand, MgH ₂ , metal Mg, and LiNH ₂ can be easily obtained in large quantities as raw materials. In addition, Mg (NH ₂ ) ₂ can be produced even with a reaction time of about 2 hours, and it is not necessary to separate LiH from the viewpoint of use as a hydrogen storage material, and further, it is not necessary to separate gas components. Can be manufactured. According to the above-described method for producing a mixture of Mg (NH ₂ ) ₂ and LiH, stable production can be performed taking advantage of such merits.

  Hereinafter, examples will be described in detail.

For the production of hydrogen storage materials, magnesium hydride (MgH ₂ ; purity 95%, handled by Amax Co.), lithium hydride (LiH; purity 95%, Sigma-Aldrich), lithium amide (LiNH ₂ ; purity 95% Sigma-Aldrich) and magnesium metal (Mg; purity 99.9%, high purity chemical laboratory, particle size 180 μm or less) were used.

[Examples 1-3, Comparative Examples 1-3]
Table 1 shows the outline of the production conditions of Examples 1 to 3 and Comparative Examples 1 to 3. In an Ar-purified glove box (hereinafter referred to as “glove box”, the inside of which is referred to as 1 gm Ar) held in an argon (Ar) atmosphere at 1 atm. ₂ -LiNH ₂ , Mg—LiNH ₂ , MgH ₂ —Mg—LiNH ₂ were weighed to a total of 1.3 g, and high chromium steel was added to a high chromium steel valve-equipped mill container (hereinafter referred to as “mill container”). It was put together with a steel ball and sealed. A mill container was attached to a planetary ball mill apparatus (Prit type P5, manufactured by Fritsch) installed in an air atmosphere, and milled for 2 hours at a rotational speed of 250 rpm.

  Thereafter, the mixture obtained by milling in the glove box was transferred to a reaction vessel (hereinafter referred to as “reaction vessel”) having an internal volume of 30 ml. In Examples 1 and 3 and Comparative Examples 1 and 3, the inside of the reaction vessel was evacuated and the inside thereof was kept in a vacuum atmosphere and kept at 250 ° C. for 16 hours.

  Subsequently, hydrogenation treatment was performed. That is, the positive pressure was gradually increased so that the hydrogen pressure was increased by 1 MPa per minute in the reaction vessel, and a hydrogen gas atmosphere of 10 MPa (gauge pressure) was performed in Example 1 and Comparative Example 1 at 200 ° C. for 2 hours. Example 3 and Comparative Example 3 were held at 200 ° C. for 12 hours. The rate of temperature increase up to 200 ° C. was 2 ° C./min. For Example 2 and Comparative Example 2, the inside of the reaction vessel was maintained as a hydrogen gas atmosphere of 10 MPa (gauge pressure) at 200 ° C. for 12 hours without performing the vacuum heat treatment, and the hydrogenation treatment was performed.

  The sample thus obtained was taken out in the glove box, and for Examples 1 to 3, the taken sample was again transferred to the mill container and mounted on the planetary ball mill device, and milled at 120 rpm for 120 minutes. did. The sample thus obtained was taken out in the glove box. In Comparative Examples 1 to 3, such re-grinding treatment is not performed. That is, the presence or absence of this regrinding process is used as a reference for distinguishing between the first to third embodiments and the first to third comparative examples.

The hydrogen release temperature of the sample thus produced was measured by using a differential thermal balance apparatus (TG / DTA6200 manufactured by SII Nanotechnology) installed in the glove box and increasing the temperature at 5 ° C./min in a helium gas flow. The peak temperature of the endothermic peak of the DTA chart was taken as the hydrogen release temperature. Moreover, the amount of weight reduction (mass%) when heated from room temperature to 400 ° C. was defined as the hydrogen release amount.

  The results are also shown in Table 1. As is clear from the comparison between Example 1 and Comparative Example 1, the comparison between Example 2 and Comparative Example 2, and the comparison between Example 3 and Comparative Example 3, the hydrogen release temperature was changed from 34 ° C. to 34 ° C. It was confirmed that the temperature could be lowered by 37 ° C.

[Examples 4 to 16, 46 to 51, Comparative Examples 4 to 6, 13, and 14]
Table 2 shows the outline of the production conditions of Examples 4 to 16, 46 to 51, and Comparative Examples 4 to 6, 13, and 14. In a glove box as the composition shown in Table _{2, MgH 2 -LiNH 2 -LiH,} Mg-LiNH 2 -LiH, MgH 2 -Mg-LiNH 2 -LiH, MgH 2 -LiNH 2, Mg-LiNH 2, MgH ₂ —Mg—LiNH ₂ was weighed and milled in the same manner as in Example 1 described above.

  Next, for each sample, the milling sample was transferred to the reaction vessel in the glove box, the inside thereof was evacuated, and then filled with high-purity hydrogen gas so that the internal pressure was 10 MPa. Hydrogenation was carried out with a hydrogenation time.

  Subsequently, some of the samples shown in Table 2 were transferred again to the mill container, and milled for the regrinding time shown in Table 2 at a rotational speed of 250 rpm using a planetary ball mill apparatus. The sample thus obtained was taken out in the glove box.

Evaluation of each manufactured sample is in accordance with Example 1, and the results are also shown in Table 2.

  The lowest temperature (= 228 ° C.) among the hydrogen release temperatures of Comparative Examples 4 to 6 that did not use LiH as a raw material was used as a reference for distinguishing between the comparative example and the example. Moreover, it was judged that practical hydrogen storage amount was not obtained about the sample whose hydrogen discharge | release amount is less than 5 mass%, and such a sample was also used as the comparative example.

As is clear from comparison between Example 4 and Comparative Example 4, Example 11 and Comparative Example 5, Example 14 and Comparative Example 6, respectively, the hydrogen release temperature is reduced by 3 to 5 ° C. by adding LiH to the pulverized raw material. It was confirmed that it can be made. Further, it can be seen that either Mg or MgH ₂ may be used as the Mg source.

  Example 4, Example 5, 6, Example 11, Example 12, 13, Example 14, Example 15, 16, Example 7, Example 8, Example 9, Example 10, Example 46 As is clear from the comparison between Example 47, Example 48 and Example 49, Example 50 and Example 51, the hydrogen release temperature can be further lowered by performing re-grinding after hydrogenation. That was confirmed.

In the compositions of Examples 4 to 16 and 46 to 51 shown in Table 2, the molar ratio of Mg: Li in MgH ₂ and / or metal Mg and LiNH ₂ is Mg: Li = 1: 2. The total molar ratio of Mg and Li when LiH is added to Mg: Li = 1: 2.67-6. As shown in Table 2, when the amount of LiH added is increased, the hydrogen release temperature is preferably lowered, but on the contrary, an undesirable characteristic that the hydrogen release amount is decreased appears. In Comparative Examples 13 and 14, the hydrogen release amount was smaller than 5 mass%. From these results, the upper limit of Li in the molar ratio of Mg to Li as a whole when LiH was added was determined to be Mg: Li = 1: 6.

[Examples 17 to 25, 52 to 55]
Table 3 shows an outline of the production conditions of Examples 17 to 25, 52, and 53. According to the composition shown in Table 3, MgH ₂ —LiNH ₂ , Mg—LiNH ₂ , MgH ₂ —Mg—LiNH ₂ were weighed and milled in the same manner as in Example 1 described above. .

  The obtained sample was hydrogenated under the conditions shown in Table 3 in the same manner as in Example 4 described above. The sample after the hydrogenation treatment was transferred again to the mill container in the glove box, LiH (additional LiH) was weighed and added according to the composition shown in Table 3, and rotated at 250 rpm using a planetary ball mill device. Milling (additional grinding) was performed for 15 minutes or 120 minutes.

  In Examples 54 and 55, LiH was weighed and added to the samples of Examples 4 and 11 as shown in Table 3, and milled for 120 minutes at a rotation speed of 250 rpm using a planetary ball mill device. This is a sample that has been processed (additionally ground).

The evaluation of each sample manufactured in this manner is in accordance with Example 1, and the results are also shown in Table 3.

  Table 3 republishes the results of Examples 4, 11, and 14 for comparison. When Example 4 and Example 17, Example 11 and Example 21, and Example 14 and Example 25 are compared, respectively, LiH is not contained rather than the manufacturing method which grind | pulverizes the raw material containing LiH and hydrogenates after that. By adopting a production method in which the raw material is pulverized and then hydrogenated, followed by additional pulverization by adding LiH, the hydrogen release temperature is reduced by about 20 ° C., with only a slight increase in production time. It was confirmed that Further, as shown in Examples 18, 20, 22, and 24, it was confirmed that the hydrogen release temperature could be further reduced by about 15 ° C. by increasing the time for additional grinding.

  When Examples 17 and 18 are compared with Examples 19 and 20, and Examples 21 and 22 are compared with Examples 23 and 24, when the amount of LiH added increases, the hydrogen release temperature decreases even during the same additional grinding time. However, as shown in the characteristics of Examples 52 and 53, it can be understood that excessive addition of LiH is not preferable because the amount of released hydrogen decreases as the amount of LiH increases.

  As shown in the characteristics of Examples 54 and 55, even in the production method in which a pulverized product containing LiH is subjected to hydrogenation treatment and further pulverization is performed by adding LiH, the hydrogen storage temperature is 182-183 ° C. It was confirmed that the material was obtained.

[Examples 26 to 33, Comparative Examples 7 and 8]
Table 4 shows an outline of the production conditions of Examples 26 to 33 and Comparative Examples 7 and 8. The manufacturing method of these samples is the same as the manufacturing method of Example 4 except that the hydrogenation temperature in the manufacturing method of Example 4 described above is variously changed. Table 4 shows the evaluation results of the manufactured samples.

  As shown in the results of Examples 26 to 29 and Example 4, it is confirmed that the hydrogen release temperature tends to increase as the hydrogenation temperature increases. If the hydrogenation temperature is low, the hydrogen release temperature also becomes low. However, if the hydrogenation temperature is less than 140 ° C., there is a demerit that a long time is required for the hydrogenation treatment. In Comparative Examples 7 and 8 where the hydrogenation temperature exceeds 240 ° C., the hydrogen release temperature exceeded 228 ° C. (= hydrogen release temperature of Comparative Example 1). About Examples 30-33, it turns out that it is in the same tendency although the hydrogenation temperature dependence of hydrogen release temperature is small.

[Examples 34 to 38, Comparative Examples 9 to 12]
Table 5 shows an outline of the production conditions of Examples 34 to 38 and Comparative Examples 9 to 12. The production of these samples is the same as the production method of Example 4 except that the number of moles of LiNH ₂ and LiH used in the sample production method of Example 4 described above is variously changed. Table 5 shows the evaluation results of the manufactured samples. In all the samples shown in Table 5, the overall molar ratio of Mg and Li is Mg: Li = 1: 2.67.

From the results of Examples 4, 34 to 37, 59, 60 and Comparative Examples 9 and 10, the ratio of Mg to Li in MgH ₂ and LiNH ₂ is constant when the overall ratio of Mg and Li to which LiH is added is constant. It was confirmed that the hydrogen release temperature can be controlled by controlling. It was confirmed that the same was true when Mg was used as the raw material (Examples 32 and 38, Comparative Examples 11 and 12). Table 5, although the hydrogen release temperature when the number of moles of LiNH ₂ decreases tends to be low, because the hydrogen release amount when the number of moles of LiNH ₂ is reduced is reduced, it is possible to take out a sufficient amount of hydrogen I understand that it will disappear. On the other hand, when the amount of LiNH ₂ is large, the hydrogen release temperature becomes high. From the results shown in Table 5, the molar ratio of Mg: Li = 1: 1.2 to 2.4 in one or both of MgH ₂ and metal Mg and LiNH ₂ is Mg: Li = It can be judged that it is preferable to set it as 1: 1.5-2.2.

[Examples 39 to 42]
Table 6 shows an outline of the production conditions of Examples 39 to 42. These samples were produced by changing the hydrogenation temperature in the production methods of Examples 36 and 38 described above, and, for some samples, regrind the samples after the hydrogenation treatment for the time shown in Table 6 It is the same as that of the manufacturing method of Example 36,38 except the point which performed the process (For example, the regrinding process applied to manufacture of Example 5). Table 6 shows the evaluation results of the manufactured samples. In all the samples shown in Table 6, the overall molar ratio of Mg and Li is Mg: Li = 1: 2.67.

  As is clear from comparison between Example 36 and Example 39, the hydrogen release temperature can be lowered from 215 ° C. to 191 ° C. by lowering the hydrogenation temperature, and in addition to this, re-pulverization treatment is performed after the hydrogenation treatment. As shown in the evaluation results of Examples 40 and 41, it was confirmed that the hydrogen release temperature can be lowered to 187 ° C to 189 ° C. From the comparison between Example 38 and Example 42, it can be confirmed that the hydrogen release temperature can be lowered by lowering the hydrogenation temperature.

[Examples 43 to 45]
Table 7 shows an outline of the production conditions of Examples 43 to 45. The production method of Example 43 is the same as the production method of Example 6, but differs in that VCl ₂ as a catalyst is added to the sample after the hydrogenation treatment and then re-grinding treatment is performed. The addition rate of VCl ₂ is an internal split values (internal ratio) to the total molar amount of MgH ₂ and LiNH _2, it is the same for Examples 44 and 45 and examples described below 56-58.

The manufacturing method of Example 44 is the same as the manufacturing method of Example 6, but differs in that VCl ₂ is added to the raw material (that is, VCl ₂ is added before the hydrogenation treatment). The manufacturing method of Example 45 is the same as the manufacturing method of Example 4, but differs in that VCl ₂ is added to the raw material. Example 44 is also a sample obtained by regrinding Example 45 for 120 minutes. Table 7 shows the evaluation results of the manufactured samples.

Comparing Example 6 and Example 43, it was found that the hydrogen release temperature can be lowered slightly by adding VCl ₂ during the regrinding treatment. Further, when Example 4 and Example 45 were compared, it was confirmed that the hydrogen release temperature could be lowered by 20 ° C. by adding VCl ₂ . In Example 44 obtained by regrinding Example 45, the hydrogen release temperature can be further lowered by 20 ° C., and the hydrogen release temperature can be lowered by 4 ° C. compared to Example 43 in which repulverization treatment is performed at the same time. It was confirmed that From these facts, in order to enhance the effect of the catalyst, it is judged that it is preferable to perform the addition before the hydrogenation treatment, such as adding the catalyst to the raw material and performing the pulverization and mixing treatment.

[Examples 56 to 58]
Table 8 shows an outline of the production conditions of Examples 56 to 58. The manufacturing method of Example 56 is the same as the manufacturing method of Example 17, except that VCl ₂ as a catalyst is added to the raw material (MgH ₂ + LiNH ₂ ). The manufacturing method of Example 57 is the same as the manufacturing method of Example 18, except that VCl ₂ is added to the raw material. Further, the production method of Example 58 is the same as the production method of Example 18, but differs in that VCl ₂ is added to the sample after the hydrogenation treatment and then additional grinding is performed. Table 8 shows the evaluation results of the manufactured samples.

  As is clear from the comparison between Example 17 and Example 56 and the comparison between Example 18 and Examples 57 and 58, it was confirmed that the hydrogen release temperature can be lowered by the addition of a catalyst. Further, when Example 57 and Example 58 are compared, it is found that the catalyst is preferably added to the raw material in order to lower the hydrogen release temperature.

  The present invention is suitable for producing a hydrogen storage material for supplying hydrogen gas, for example, in a fuel cell system that generates power using hydrogen and oxygen as fuel.

Claims (8)

A method for producing a hydrogen storage material, comprising pulverizing and mixing a mixture of Mg (NH ₂ ) ₂ and LiH obtained by heat treatment. One or both of MgH ₂ and metal Mg and LiNH ₂ are weighed so that the molar ratio of Mg to Li is Mg: Li = 1: 1.2 to 2.4, and LiH is added thereto. A step of weighing LiH so that the molar ratio of Mg to Li is 1: 2.2 to 6, and then crushing and mixing them;
A method for producing a hydrogen storage material, comprising: heating a sample obtained by the mixing and pulverizing process to a predetermined temperature in a hydrogen atmosphere and holding the sample for a predetermined time.   The method for producing a hydrogen storage material according to claim 2, further comprising a step of pulverizing and mixing the sample obtained by the heat treatment. Crushing and mixing one or both of MgH ₂ and metal Mg and LiNH ₂ ;
Heating the sample obtained by the pulverization and mixing process to a predetermined temperature in a hydrogen atmosphere and holding the sample for a predetermined time;
And a step of adding LiH to the sample obtained by the heat treatment and pulverizing and mixing the sample. The molar ratio of Mg: Li in MgH ₂ and / or metal Mg and LiNH ₂ is Mg: Li = 1: 1.2 to 2.4, and the total Mg when LiH is further added thereto. The method for producing a hydrogen storage material according to claim 4, wherein the molar ratio of Li to Li is Mg: Li = 1: 2.2-6.   As catalysts, B, C, Mn, Fe, Co, Ni, Pt, Pd, Rh, Na, Mg, K, Ir, Nb, La, Ca, Ti, V, Cr, Cu, Zn, Al, Si, Ru 6. A metal, chloride or oxide of one or more elements selected from Mo, Ta, Zr, Hf, and Ag is added. The manufacturing method of hydrogen storage material as described in any one of.   The method for producing a hydrogen storage material according to claim 6, wherein the catalyst is added before heat treatment in a hydrogen atmosphere, and is mixed and ground with an additive.   The method for producing a hydrogen storage material according to any one of claims 2 to 7, wherein the heat treatment in a hydrogen atmosphere is performed at 140 ° C to 250 ° C.