Hydrogen storage powder

Abstract

To provide hydrogen storage powder that effectively absorbs electromagnetic waves and is rapidly heated to a temperature at which a metal hydride releases hydrogen.SOLUTION: Hydrogen storage powder includes particulate metal hydrides capable of absorbing and releasing hydrogen and a heat-generating material that absorbs electromagnetic waves and generates heat, wherein a bulk density of the heat-generating material is 0.57 g / cm3 or less. The metal hydride can be at least one selected from magnesium hydride and lithium hydride. The heat-generating material can be at least one selected from the group consisting of carbon, Ti, ZrH2, TiH2, LaHx, and VHx.SELECTED DRAWING: None

Description

[Technical Field]

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

[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 moving body such as a vehicle, and used as a hydrogen energy source for the moving body. However, standard hydrogen storage alloys have low hydrogen storage density per weight (about 1.4 wt% for LaNi5), making it difficult to store the amount of hydrogen required for mobile applications.

[0003] In contrast, Mg-based hydride (MgH2) has a hydrogen storage density per 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 other documents, 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 the hydrogen can be released, which takes time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-10894 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-291705 Summary of the Invention [Problem to be solved by the invention]

[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 absorbs electromagnetic waves well and can be rapidly heated to a temperature at which metal hydrides release hydrogen. [Means for solving the problem]

[0006] The hydrogen storage powder according to the first aspect of the present invention is defined as follows: The device comprises a particulate metal hydride capable of absorbing / releasing hydrogen and a heat-generating substance that generates heat by absorbing electromagnetic waves, and the heat-generating substance has a bulk density of 0.57 g / cm. 3 The following is the result. The bulk density here refers to 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.

[0007] According to the hydrogen storage powder of the first aspect defined in this manner, the hydrogen storage powder is composed of 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.By directly transferring energy to the heat-generating substance by irradiating it with electromagnetic waves, the entire hydrogen storage powder, including the metal hydride, can be heated more rapidly than conventional external heating methods using thermal conduction or radiation. According to the research of the present inventors, 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 contained in the hydrogen storage powder, and the bulk density of the exothermic substance is 0.57 g / cm 3 The following applies.

[0008] Here, the metal hydride can be at least one selected from magnesium hydride and lithium hydride (second aspect).

[0009] The exothermic substance that generates heat by absorbing electromagnetic waves can be at least one selected from carbon, Ti, ZrH2, TiH2, LaHx, and VHx (third aspect).

[0010] In order to reduce the bulk density of the exothermic substance, the exothermic substance has a bulk density of 0.2 g / cm 3The material may be at least one selected from the following carbon black, carbon nanotubes, and carbon nanofibers (fourth aspect).

[0011] The heat-generating substance is preferably carbon, which has high microwave absorption capacity. In this case, the carbon content can be 3 to 15 mass % relative to the mass of the metal hydride (fifth aspect).

[0012] This hydrogen storage powder can be configured to further contain a catalyst that facilitates hydrogen absorption / desorption. The catalyst can be at least one selected from Nb, Nb2O5, Ti, a Ti compound, Ni, NiO, V, and VO5 (sixth aspect). [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the relationship between the bulk density of a heat-generating substance and the rate of temperature rise. DETAILED DESCRIPTION OF THE INVENTION

[0014] Next, the hydrogen storage powder according to one embodiment of the present invention will be specifically described. The hydrogen storage powder comprises a metal hydride as a hydrogen storage alloy, an exothermic material, and a catalyst as its constituent elements.

[0015] An example of a metal hydride is particulate magnesium hydride (MgH2), which can absorb and release hydrogen under specific temperature and pressure conditions according to the following reaction formula: MgH2⇔Mg+H2 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. Lithium hydride (LiH) can also be used as the metal hydride capable of absorbing / desorbing hydrogen. That is, the present hydrogen storage powder can be configured to contain at least one metal hydride selected from magnesium hydride and lithium hydride (LiH).

[0016] The catalyst is composed of a metal or metal compound that has the effect of bringing the pressure or temperature at which the metal hydride absorbs / desorbs hydrogen closer to normal pressure or temperature. Specifically, at least one selected from Nb, Nb2O5, Ti, Ti compounds, Ni, NiO, V, and V2O5 can be used as the catalyst. Examples of Ti compounds include TiMn2, TiNb, TiFe, TiAl, TiNi, TiV, TiH2, and TiO2.

[0017] The catalyst is preferably in the form of particles and uniformly dispersed in the hydrogen storage powder, and is preferably contained in an amount of 2 to 15 mass% relative to the mass of the metal hydride. If the amount is less than 2 mass%, the catalyst function cannot be fully exerted, and if the amount is more than 15 mass%, the catalyst function is not improved and the amount of hydrogen stored (amount of hydrogen released) per unit weight of the hydrogen storage powder decreases.

[0018] The exothermic substance is a substance that generates heat by absorbing microwaves, and specifically is at least one selected from carbon (C), Ti, ZrH2, TiH2, LaHx (x = 2 to 3), and VHx (x = 0.5 to 2). Carbon and Ti have both a large relative permittivity and a large dielectric loss factor, and generate heat efficiently when exposed to microwaves. ZrH2, TiH2, LaHx, and VHx are metal hydrides that easily absorb microwaves and are difficult to decompose at high temperatures. Of these, it is particularly preferable to use carbon as the exothermic substance from the viewpoint of increasing the rate of temperature rise.

[0019] 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 used as a raw material. In this embodiment, the bulk density of the exothermic substance is set to 0.57 g / cm 3 The following applies. As a carbon material with low bulk density, the bulk density is 0.2 g / cm 3 The following carbon black, carbon nanotube, or carbon nanofiber can be used. Examples of carbon black that can be used include acetylene black and ketjen black.

[0020] The exothermic substance is preferably contained in an amount of 3 to 15 mass % relative to the mass of the metal hydride, because if it is less than 3 mass %, the effect of raising the temperature of the entire hydrogen storage powder is insufficient, and if it exceeds 15 mass %, the effect of further increasing the temperature rise rate is small and the amount of hydrogen stored (amount of hydrogen released) per unit weight of the hydrogen storage powder decreases.

[0021] The method for producing the hydrogen storage powder is as follows. The metal hydride, catalyst, and exothermic substance are weighed in predetermined proportions as raw materials and mixed and stirred in an inert gas or hydrogen atmosphere using a mixing and stirring means. This allows the production of a hydrogen storage powder as a mixed powder in which the catalyst and exothermic substance are uniformly dispersed. The mixing and stirring means can be a mortar or a stirrer, a ball mill, a planetary ball mill, an attritor, a bead mill, or the like.

[0022] In the hydrogen storage powder of this embodiment obtained as described above, the exothermic material absorbs the microwaves (2.45 GHz) emitted from the microwave heating device, generating heat, and the entire hydrogen storage powder, including the metal hydride, is heated more rapidly than in conventional external heating methods using 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. 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 in the range of 200 to 450° C. Furthermore, the hydrogen gas atmosphere is preferably a pressurized atmosphere. [Example]

[0023] Next, an embodiment of the present invention will be described. Here, in a glove box with an Ar atmosphere, catalyst and exothermic material were added to metal hydride in the amounts shown in Tables 1 to 8 below, and after lightly mixing in a mortar, the mixture was mixed in an Ar atmosphere using a planetary ball mill at 400 rpm for 15 minutes under a pressure of 0.5 MPa to produce hydrogen storage powder. The entire amount of hydrogen storage powder was then placed in a quartz test tube for microwave heating, and a heating test was conducted in an Ar atmosphere using a low microwave output of 500 W or less. The temperature reached 60 seconds after the start, starting from room temperature, was measured with a thermocouple. These results are shown in Tables 1 to 8 below.

[0024] The microwave heating device used here (μReactorEx, manufactured by Shikoku Keisoku Kogyo) has a wavelength of 2.45 GHz and a maximum output of 1 kW. The metal hydrides, catalysts, and exothermic substances used here are as follows: Metal hydrides: MgH2 (Bio-Coke Giken), LiH (Sigma-Aldrich) Catalyst: Nb2O5 (Kishida Chemical) Heat-generating materials: (Indicate the bulk density of carbon materials and other metals) Carbon black (bulk density 0.02 to 0.52 g / cm 3 ) Acetylene black and Ketjen black (0.02 to 0.20) Carbon nanotubes (0.02~0.15) Carbon nanofiber (0.15~0.30) Pure Cu fine powder (0.8~2.0) Ti nanoparticles (0.1-0.2) TiH2(0.2~0.6)

[0025] The evaluation results in Tables 1 to 8 reveal the following.

[0026] [Table 1]

[0027] Nos. 1 to 7 shown in Table 1 are samples of carbon (specifically, acetylene black, bulk density 0.12 g / cm) added as a heat-generating material. 3 In Nos. 1 to 4, the powder temperature barely rose even after 1 minute of microwave irradiation, but when 5% or more carbon was added, the temperature rose sharply (Nos. 5 and 6), and when 9% or more carbon was added, a temperature rise rate of 142°C / min was obtained (No. 7).

[0028] [Table 2]

[0029] Nos. 7 to 10 in Table 2 are examples in which the same hydrogen storage powder was used and 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 300W and 500W, it was found that rapid heating was possible even at an output of 300W.

[0030] [Table 3]

[0031] 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 densities of the exothermic materials used here were 0.2g / cm for TiH2, 0.8g / cm for Cu, and 0.2g / cm for Ti nanoparticles. 3 No. 15 is carbon (acetylene black: bulk density 0.12 g / cm 3 This is an example of a heating test in which only copper particles (Cu) were heated. As a result, the temperature of copper particles (Cu) barely rose. On the other hand, titanium nanoparticles (Ti) and titanium hydride (TiH2) rose in temperature even at an output of 300W, although not as much as carbon.

[0032] [Table 4]

[0033] No. 16 shown in Table 4 is an example in which part of the metal hydride (equivalent to 10 mass%) in the hydrogen storage powder of No. 10 was replaced with lithium hydride (LiH). No. 16 achieved a higher temperature rise rate than No. 10, which used only MgH2 as the metal hydride, but the temperature rise rate was still lower than No. 15, which was made of 100% carbon.

[0034] [Table 5]

[0035] Nos. 17 to 20 shown in Table 5 are carbon (acetylene black: bulk density 0.12 g / cm) 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 increases as the bulk density decreases. As shown in No. 20, the heating rate of the powder increases at a bulk density of 0.04 g / cm. 3 When using this material, even with a carbon content of 9 mass % (0.27 g), the temperature rise rate was equal to or greater than that of 100% carbon material.

[0036] Figure 1 shows the relationship between the bulk density of the exothermic substance and the heating rate obtained in a heating test. This figure shows the results of heating six types of carbon (containing no MgH2 or other additives) with different bulk densities shown in Table 6 below at 300 W for one minute. In Table 6, CB stands for carbon black, and Gr stands for graphite.

[0037] [Table 6]

[0038] 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 By setting the temperature to the value below, it is possible to obtain a temperature rise rate of 50°C / min or more even at a low output of 300W.

[0039] [Table 7]

[0040] 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 where the amount of SiO2 added was varied. As the amount added increased, the rate of temperature rise increased, and it can be seen that a temperature rise rate of over 250°C / min was achieved with an added amount of 0.27g (3 mass%).

[0041] [Table 8]

[0042] Nos. 20, 22 to 25 shown in Table 8 are examples of samples that underwent rapid heating for 100 seconds, and the maximum temperature reached and the amount of hydrogen before and after heating were analyzed. No. 25 is the same as No. 1, containing only MgH2, and No. 24 is the same as No. 2, containing MgH2 with Nb2O5 added. In both cases, the temperature barely rose in the 100 seconds after irradiation began, and no dehydrogenation reaction occurred. Nos. 20, 22, and 23 are made of even lower 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.

[0043] 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.

Claims

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

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

3. The heat-generating 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 and VHx.

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

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

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

Images