Hydrogen storage powder

Abstract

The present invention relates to a hydrogen storage powder which comprises a particulate metal hydride that is capable of absorbing / releasing hydrogen, and a heat-generating substance that absorbs electromagnetic waves and generates heat, wherein the bulk density of the heat-generating substance is 0.57 g / cm3 or less.

Description

Hydrogen Storage Powder

[0001] The present invention relates to a hydrogen storage powder used for storing hydrogen.

[0002] It is known to use hydrogen storage alloys as a means for storing hydrogen. For example, Patent Document 1 below proposes that a cylinder (cartridge) containing a hydrogen storage alloy is configured to be detachable from a mobile body such as a vehicle and used as a hydrogen energy source for the mobile body. However, the hydrogen storage density per unit weight of standard hydrogen storage alloys is low, for example, LaNi ５ In the case of ethylenediaminetetraacetic acid (EEA), the hydrogen content is low, about 1.4 wt %. Therefore, it is difficult to store the amount of hydrogen required for mobile applications.

[0003] In contrast, Mg-based hydrides (MgH ２ ) has a hydrogen storage density per unit weight of 7.6 wt%, which is far greater than that of standard hydrogen storage alloys, and is capable of absorbing large amounts of hydrogen. However, as pointed out in Patent Document 2 and elsewhere, Mg-based hydrides require high temperatures of 250°C or higher to absorb and release hydrogen, and in order to extract the stored hydrogen, the Mg-based hydride must be heated to a temperature at which hydrogen can be released, which takes time.

[0004] Japanese Patent Publication No. 2024-10894 Japanese Patent Publication No. 2009-291705

[0005] SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a hydrogen storage powder that has excellent controllability over the absorption / release of hydrogen by heat.

[0006] In response to this, the inventors have found that the above-mentioned problems can be solved by using a hydrogen storage powder containing a particulate metal hydride capable of absorbing and releasing hydrogen together with a heat-generating substance. Furthermore, the inventors have found that by using a heat-generating substance that absorbs electromagnetic waves and generates heat and has a specific bulk density, the metal hydride can be rapidly heated to a temperature at which it releases hydrogen, thereby achieving the present invention.

[0007] The hydrogen storage powder according to the first aspect of this embodiment is defined as follows: It contains a particulate metal hydride capable of absorbing / desorbing hydrogen and a heat-generating substance that absorbs electromagnetic waves and generates heat, and the bulk density of the heat-generating substance is 0.57 g / cm ３ The bulk density here is loose bulk density, which is the value obtained by gently placing the object to be measured in a measuring cylinder and dividing the mass of the object to be measured by its volume.

[0008] According to the hydrogen storage powder of the first aspect defined as above, the powder contains a heat-generating substance that absorbs electromagnetic waves and generates heat, in addition to a metal hydride that is not normally heated by electromagnetic waves. As a result, by directly transferring energy to the heat-generating substance through electromagnetic wave irradiation, the entire hydrogen storage powder including the metal hydride can be heated more rapidly than with conventional external heating methods that use thermal conduction or radiation. According to the research of the present inventors, it has been found that reducing the bulk density of the heat-generating substance contained in the hydrogen storage powder is effective in increasing the temperature rise rate of the hydrogen storage powder, and the bulk density of the heat-generating substance can be reduced to 0.57 g / cm. ３ The following applies.

[0009] As a second aspect of this embodiment, in the first aspect, the metal hydride can be at least one of magnesium hydride and lithium hydride.

[0010] As a third aspect of the present embodiment, in the first or second aspect, the heat-generating material that absorbs electromagnetic waves and generates heat is selected from the group consisting of carbon, Ti, ZrH ２ , TiH ２ , LaHx (x=2 to 3), and VHx′ (x′=0.5 to 2).

[0011] As a fourth aspect of the present embodiment, in any one of the first to third aspects, in order to reduce the bulk density of the exothermic substance, the exothermic substance has a bulk density of 0.2 g / cm ３ and may be at least one selected from the group consisting of carbon black, carbon nanotubes, and carbon nanofibers.

[0012] In a fifth aspect of the present embodiment, in any one of the first to fourth aspects, carbon can be preferably used as the exothermic substance. In this case, the content of the carbon relative to the metal hydride is more preferably 3 to 15 mass %.

[0013] As a sixth aspect of the present embodiment, in any one of the first to fifth aspects, the hydrogen storage powder may further contain a catalyst that facilitates hydrogen absorption / desorption. ２ O ５ , Ti, Ti compounds, Ni, NiO, V and V ２ O ５ The polymerizable compound may be at least one selected from the group consisting of:

[0014] FIG. 1 is a graph showing the relationship between the bulk density of an exothermic substance and the rate of temperature rise.

[0015] Next, a hydrogen storage powder according to one embodiment of the present invention will be specifically described. In this specification, the term "to" indicating a range of values ​​is used to mean that the values ​​before and after the range are included as the lower and upper limits. In this specification, "mass %" and "weight % (wt %)" are synonymous.

[0016] The hydrogen storage powder according to this embodiment (hereinafter, sometimes simply referred to as "the present hydrogen storage powder") comprises a particulate metal hydride capable of absorbing and releasing hydrogen, a heat-generating material, and optionally a catalyst. The metal hydride functions as a hydrogen storage alloy.

[0017] <Metal hydride> As the metal hydride, particulate magnesium hydride (MgH ２ Magnesium hydride can absorb and release hydrogen under certain temperature and pressure conditions according to the following reaction formula: MgH ２ ⇔Mg + H ２

[0018] The purity of the magnesium hydride used as the raw material for the present hydrogen storage powder is not particularly limited, and commercially available magnesium hydride can be used.

[0019] It is also possible to use lithium hydride (LiH) as a metal hydride capable of absorbing / desorbing hydrogen.

[0020] That is, the present hydrogen storage powder can be configured to contain at least one of magnesium hydride and lithium hydride (LiH) as the metal hydride.

[0021] <Catalyst> The hydrogen storage powder according to this embodiment may further contain a catalyst in addition to the metal hydride and the exothermic substance. The catalyst in this embodiment has the effect of facilitating the absorption / desorption of metal. Specifically, the catalyst is composed of a metal or metal compound that has the effect of bringing the pressure and / or temperature at which the metal hydride absorbs / desorbs hydrogen closer to atmospheric pressure and / or ambient temperature.

[0022] Specific examples of the catalyst in this embodiment include Nb, Nb ２ O ５ , Ti, Ti compounds, Ni, NiO, V and V ２ O ５ Here, the Ti compound can be at least one selected from the group consisting of TiMn ２ , TiNb, TiFe, TiAl, TiNi, TiV, TiH ２ , TiO ２ Examples include:

[0023] The catalyst in this embodiment is preferably in the form of particles, and more preferably uniformly dispersed in the hydrogen storage powder.

[0024] The content of the catalyst relative to the metal hydride is preferably 2 to 15% by mass. From the viewpoint of fully exhibiting its catalytic function, the content is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more. Furthermore, from the viewpoint of suppressing a decrease in the hydrogen storage capacity (hydrogen release capacity) per unit weight of the hydrogen storage powder while fully obtaining the catalytic function, the content is preferably 15% by mass or less, more preferably 14% by mass or less, and even more preferably 13% by mass or less. When two or more types of metal hydrides are contained, the content of the catalyst relative to the metal hydrides refers to the ratio to the total content of the metal hydrides. When two or more types of catalysts are contained, the content of the catalyst relative to the metal hydrides refers to the total content of the catalyst relative to the metal hydrides.

[0025] <Heat-generating substance> The heat-generating substance in this embodiment is a substance that generates heat by absorbing electromagnetic waves. Microwaves are particularly preferable as the electromagnetic waves to be absorbed. Microwaves in this specification refer to electromagnetic waves in the frequency range of about 300 MHz to 300 GHz.

[0026] Specific examples of the heat-generating substance include carbon (C), Ti, and ZrH ２ , TiH ２ At least one selected from the group consisting of LaHx (x=2 to 3) and VHx' (x'=0.5 to 2) is preferred. Among these, carbon and Ti are preferred because they have a high relative permittivity and dielectric loss factor and generate heat efficiently with microwaves. In other words, they are preferred because they have a high microwave absorption capacity. ２ , TiH ２ , LaHx (x=2 to 3), and VHx' (x'=0.5 to 2) are preferred in that they are catalysts that easily absorb microwaves and are difficult to decompose at high temperatures. Among these, carbon is particularly preferred as the exothermic material from the viewpoint of increasing the rate of temperature rise.

[0027] As will be shown in the examples below, in order to increase the temperature rise rate of the hydrogen storage powder, it is effective to reduce the bulk density of the exothermic substance. In this embodiment, the bulk density of the exothermic substance is set to 0.57 g / cm ３ The bulk density is 0.5 g / cm or less. ３Preferably, 0.4 g / cm or less ３ More preferably, 0.3 g / cm ３ More preferably, 0.2 g / cm ３ The lower limit of the bulk density is not particularly limited, but is, for example, 0.01 g / cm ３ More than that is fine.

[0028] When carbon is used as the catalyst in this embodiment, a carbon material having a bulk density of 0.2 g / cm ３ It is more preferable to use the following: In addition to the above, it is even more preferable to use at least one type of carbon selected from the group consisting of carbon black, carbon nanotubes, and carbon nanofibers.

[0029] Examples of carbon black that can be used include acetylene black and ketjen black. Carbon nanotubes may be either single-walled carbon nanotubes (SWCNT) or multi-walled carbon nanotubes (MWCNT). Carbon nanofibers (CNF) may be either PAN-based or pitch-based.

[0030] The content of the exothermic substance relative to the metal hydride is preferably 3 to 15% by mass. From the viewpoint of sufficiently obtaining the effect of raising the temperature of the entire hydrogen storage powder, the content is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more. Furthermore, from the viewpoint of sufficiently increasing the temperature rise rate while suppressing a decrease in the hydrogen storage capacity (hydrogen release capacity) per unit weight of the hydrogen storage powder, the content is preferably 15% by mass or less, more preferably 14% by mass or less, and even more preferably 13% by mass or less.

[0031] When carbon is used as the exothermic material, the preferred carbon content relative to the metal hydride is also 3 to 15 mass % as described above.

[0032] <Production Method> The method for producing the present hydrogen storage powder is not particularly limited, but the hydrogen storage powder can be obtained, for example, by the following method. The above-mentioned metal hydride as raw materials, optionally a catalyst, and a heat-generating substance, weighed in a predetermined ratio, are mixed and stirred under an inert gas or hydrogen atmosphere using a mixing and stirring means. This allows the hydrogen storage powder to be produced as a mixed powder in which the optional catalyst and heat-generating substance are uniformly dispersed.

[0033] As the mixing and stirring means, a mortar or a stirrer, a ball mill, a planetary ball mill, an attritor, a bead mill, or the like can be used.

[0034] In the hydrogen storage powder according to the present embodiment obtained as described above, the exothermic substance absorbs electromagnetic waves, preferably microwaves (2.45 GHz) emitted from a microwave heating device, and generates heat, so that the entire hydrogen storage powder, including the metal hydride, is heated more rapidly than in conventional external heating methods that use thermal conduction or radiation. Then, the hydrogen storage powder (more specifically, the metal hydride) is heated to a temperature range of 200 to 350°C, and hydrogen is released.

[0035] After releasing hydrogen, the hydrogen storage powder can absorb hydrogen again by heating it in a hydrogen gas atmosphere. The heating temperature for hydrogen absorption may be, for example, in the range of 200 to 450° C. Furthermore, the hydrogen gas atmosphere is preferably a pressurized atmosphere.

[0036] Next, examples of the present invention will be described. <<Production of Hydrogen Storage Powder>> First, in a glove box with an Ar atmosphere, a catalyst and a heat-generating substance were added to a metal hydride in the types and amounts shown in Tables 1 to 8 below, and the mixture was lightly mixed in a mortar. After that, a planetary ball mill was used to mix the mixture in an Ar atmosphere at 400 rpm for 15 minutes under a pressure of 0.5 MPa to produce a hydrogen storage powder.

[0037] Evaluation: Heating Rate All of the hydrogen storage powders Nos. 1 to 13 and 15 to 25 obtained above were placed in a quartz test tube for microwave heating, and a heating test was performed in an Ar atmosphere with a low microwave output of 500 W or less. The heating test started from room temperature, and the temperature before the start (before initiation), the temperature reached 1 minute after initiation, and the temperature reached 100 seconds after initiation were measured with a thermocouple. These results are shown in Tables 1 to 8 below.

[0038] The microwave heating device used here (μReactorEx, manufactured by Shikoku Keisoku Kogyo) had a frequency of 2.45 GHz and a maximum output of 1 kW. The metal hydride, catalyst, and exothermic substance used here were as follows: Metal hydride: MgH ２ (manufactured by Biocoke Giken), LiH (manufactured by Sigma-Aldrich) Catalyst: Nb ２ O ５ (Kishida Chemical) Heat-generating material: (The bulk density of carbon materials and other metals is also listed) Carbon black (bulk density 0.02 to 0.52 g / cm ３ ) Acetylene black and Ketjen black (0.02-0.20) Carbon nanotubes (0.02-0.15) Carbon nanofibers (0.15-0.30) Pure Cu fine powder (0.8-2.0) Ti nanoparticles (0.1-0.2) TiH ２ (0.2 to 0.6)

[0039] The evaluation results in Tables 1 to 8 reveal the following.

[0040]

[0041] The hydrogen storage powders Nos. 1 to 7 shown in Table 1 contain carbon (specifically, acetylene black, bulk density 0.12 g / cm) added as a heat-generating material. ３ In Nos. 1 to 3, the powder temperature hardly increased even after 1 minute of microwave irradiation, but when 5 mass% or more of carbon was added, the temperature rose sharply (Nos. 4 to 6), and when 9 mass% of carbon was added, a temperature rise rate of 142°C / min was obtained (No. 7).

[0042]

[0043] Nos. 7 to 10 shown in Table 2 are examples in which the same hydrogen storage powder was used but the microwave output was changed. As the microwave output increased, the temperature rise rate of the hydrogen storage powder also increased, but since almost the same temperature rise rate was obtained at outputs of 300 W and 500 W, it was found that even at an output of 300 W, rapid heating was possible.

[0044]

[0045] Nos. 11 to 13 shown in Table 3 are examples of hydrogen storage powders in which the exothermic material was changed to something other than carbon compared to powder No. 10, and heating tests were conducted at an output of 300 W. The bulk density of the exothermic material used here was TiH ２ is 0.2 g / cm ３ , pure Cu fine powder is 0.8 g / cm ３ , Ti nanoparticles 0.2 g / cm ３ No. 15 is carbon (acetylene black: bulk density 0.12 g / cm ３ This is an example in which only the hydrogen storage powder No. 12, which used copper particles (Cu) as the exothermic material, showed almost no temperature rise. On the other hand, the hydrogen storage powder No. 12, which used titanium nanoparticles (Ti) and titanium hydride (TiH ２ The hydrogen storage powders Nos. 11 and 13, which used SiO2 as the exothermic material, were heated sufficiently even at an output of 300 W, although not as much as carbon.

[0046]

[0047] No. 16 shown in Table 4 is a powder in which a part (equivalent to 10 mass%) of the metal hydride in the hydrogen storage powder of No. 10 is replaced with magnesium hydride (MgH ２ In this example, the metal hydride was changed from MgH to lithium hydride (LiH). ２ Although a higher temperature rise rate was obtained than No. 10, which was made of only carbon, the temperature rise rate was still lower than No. 15, which was made of 100% carbon material.

[0048]

[0049] Nos. 17 to 20 shown in Table 5 are carbon (acetylene black: bulk density 0.12 g / cm3) in the hydrogen storage powder of No. 10. ３ In No. 17, graphite was used as the high bulk density carbon. According to Table 5, the heating rate of the powder increased as the bulk density decreased, and as shown in No. 20, the heating rate increased at a bulk density of 0.04 g / cm. ３ When carbon of this type was used, even when the amount of carbon added to the metal hydride was 9 mass % (0.27 g), a temperature rise rate equal to or greater than that of a 100% carbon material was observed.

[0050] FIG. 1 is a graph showing the relationship between the bulk density of the exothermic substance and the temperature rise rate obtained in the heating test. This graph shows the relationship between the bulk density of the exothermic substance and the temperature rise rate obtained in the heating test. ２ The results are from heating each of the samples (containing no carbon black, etc.) at 300 W for 1 minute. In Table 6, CB represents carbon black and Gr represents graphite.

[0051]

[0052] As shown in the figure, there is a strong negative correlation between the bulk density and the rate of temperature rise, and the regression equation shows that the bulk density of the exothermic substance is 0.57 g / cm ３ It can be seen that by setting the temperature to the value below, a temperature rise rate of 50° C. / min or more can be obtained even with a low output of 300 W.

[0053]

[0054] Nos. 20 to 23 shown in Table 7 contain low bulk density carbon (0.04 g / cm3) as the exothermic material. ３ This is an example in which the amount of the additive used was varied. As the amount added increased, the rate of temperature rise increased, and it was found that a temperature rise rate of 250°C / min or more was obtained when the amount added was 0.27g (3 mass%).

[0055]

[0056] Nos. 20, 22 to 25 shown in Table 8 are examples in which rapid heating was carried out for 100 seconds, and the maximum temperature reached and the amount of hydrogen before and after heating were analyzed. No. 25 is the same MgH as No. 1. ２Only No. 24 is the same as No. 2, MgH ２ Nb ２ O ５ In all cases, the temperature barely rose within 100 seconds after the start of irradiation, and no dehydrogenation reaction occurred. Nos. 20, 22, and 23 were also prepared by adding a low bulk density carbon (0.04 g / cm ３ In all cases, the temperature reached 250°C or higher 100 seconds after the start of irradiation, indicating that a dehydrogenation reaction had occurred and hydrogen was being released. In particular, in Nos. 22 and 20, which were heated to a temperature of 350°C or higher, almost all of the hydrogen was released.

[0057] Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiments and examples, and various modifications are possible within the scope of the invention.

[0058] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2024-086619) filed on May 28, 2024, the contents of which are incorporated herein by reference.

Claims

1. A device comprising a particulate metal hydride capable of absorbing / releasing hydrogen and a heat-generating substance that generates heat by absorbing electromagnetic waves, wherein the bulk density of the heat-generating substance is 0.57 g / cm ３ The following is a hydrogen storage powder.

2. The hydrogen storage powder of claim 1, wherein the metal hydride is at least one of magnesium hydride and lithium hydride.

3. The exothermic material is carbon, Ti, ZrH ２ , TiH ２ 3. The hydrogen storage powder according to claim 1, wherein the powder is at least one selected from the group consisting of LaHx (x=2 to 3), and VHx' (x'=0.5 to 2).

4. The exothermic substance has a bulk density of 0.2 g / cm ３ The hydrogen storage powder according to claim 1 or 2, wherein the heat-generating substance is at least one selected from the group consisting of carbon black, carbon nanotubes, and carbon nanofibers.

5. The hydrogen storage powder according to claim 1 or 2, wherein the exothermic substance is carbon, and the content of the carbon relative to the metal hydride is 3 to 15 mass %.

6. The catalyst further comprises a catalyst that facilitates hydrogen absorption / desorption, and the catalyst is selected from Nb, Nb ２ O ５ , Ti, Ti compounds, Ni, NiO, V and V ２ O ５ 3. The hydrogen storage powder according to claim 1, wherein the powder is at least one selected from the group consisting of:

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