Hydrogen storage material and method for manufacturing the same

Abstract

To provide a hydrogen storage material with reduced cost for absorbing or releasing hydrogen.SOLUTION: A hydrogen storage material according to one aspect of the present invention contains a hydride represented by a composition formula AlxMn1-xHy where x is 0.1 or more and 0.5 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a hydrogen storage material and a method for producing the same. [Background technology]

[0002] Hydrogen is a secondary energy source that can be produced from a variety of primary energy sources using various methods. Energy systems using hydrogen are expected to offer benefits such as high energy efficiency and low environmental impact, and are therefore anticipated to be put into practical use (commercialized) in the future.

[0003] The energy density of hydrogen per unit volume is low, about one-third that of natural gas. Therefore, when transporting and storing hydrogen, high-density hydrogen storage is required. Hydrogen storage alloys can dissociate hydrogen molecules on the alloy surface and store hydrogen atomically within the alloy. For example, Patent Document 1 describes an alloy with the composition formula Al x Fe 1-x (x is between 0.70 and 0.80), or Al y Mn 1-y A hydrogen storage material is disclosed, represented by (y being between 0.60 and 0.70). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-199640 [Overview of the project] [Problems that the invention aims to solve]

[0005] In hydrogen storage materials, there is a need to lower the pressure required for hydrogen storage in order to reduce the cost of storing hydrogen. Furthermore, there is a need to lower the temperature at which the stored hydrogen is released in order to reduce the cost of releasing and recovering the stored hydrogen.

[0006] One aspect of the present invention aims to realize a hydrogen storage material capable of reducing the cost for hydrogen absorption or release and a method for manufacturing the same.

Means for Solving the Problems

[0007] In order to solve the above problems, a hydrogen storage material according to one aspect of the present invention contains a hydride represented by the compositional formula Al x Mn 1-x H y where x is 0.1 or more and 0.5 or less.

[0008] In order to solve the above problems, a method for manufacturing a hydrogen storage material according to one aspect of the present invention includes a mixture preparation step of weighing Al and Mn such that the amount of Mn is 1 to 9 times the amount of Al in terms of atomic ratio, and mixing the weighed Al and Mn to prepare a mixture; a solid-phase reaction step of subjecting the mixture to a solid-phase reaction at a pressure of 0.5 GPa to 2 GPa and a temperature of 1000°C to 1100°C to produce an Al-Mn alloy; and a hydrogenation step of hydrogenating the Al-Mn alloy under a pressure of 0.5 GPa to 10 GPa.

[0009] In order to solve the above problems, a method for manufacturing a hydrogen storage material according to one aspect of the present invention includes a mixture preparation step of weighing Al and Mn such that the amount of Mn is 1 to 9 times the amount of Al in terms of atomic ratio, and mixing the weighed Al and Mn to prepare a mixture; an arc melting step of subjecting the mixture to arc melting at a temperature of 2000°C to 3000°C to produce an Al-Mn alloy; and a hydrogenation step of hydrogenating the Al-Mn alloy under a pressure of 0.5 GPa to 10 GPa.

Effects of the Invention

[0010] According to one aspect of the present invention, the cost for hydrogen absorption or release can be reduced.

Brief Description of the Drawings

[0011] [Figure 1] This is a profile obtained by XRD measurement performed on the hydrogen storage material of Example 1 of the present invention. [Figure 2] This graph shows the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 1. [Figure 3] This is the profile obtained by XRD measurement performed on the hydrogen storage material of Example 2 of the present invention. [Figure 4] This graph shows the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 2. [Figure 5] This is the profile obtained by XRD measurement performed on the hydrogen storage material of Example 3 of the present invention. [Figure 6] This graph shows the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 3. [Figure 7] This is the profile obtained by XRD measurement performed on the hydrogen storage material of Example 4 of the present invention. [Figure 8] This graph shows the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 4. [Figure 9] This is the profile obtained by XRD measurement performed on the hydrogen storage material of Example 5 of the present invention. [Figure 10] This graph shows the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 5. [Figure 11] This is the profile obtained by XRD measurement performed on the hydrogen storage material of Example 6 of the present invention. [Figure 12] This graph shows the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 6. [Figure 13] This graph plots the hydrogen storage materials of Examples 1-6, Al2MnH3, and MnH, with the value of x on the horizontal axis (where Al:Mn=x:1-x is the atomic ratio of Al to Mn in the starting materials) and the hydrogen release temperature on the vertical axis. [Modes for carrying out the invention]

[0012] [Embodiment 1] Hereinafter, an embodiment of the present invention will be described in detail. The following description is for better understanding of the gist of the invention and does not limit the present invention unless otherwise specified. Also, unless otherwise specified in this specification, "A~B" representing a numerical range means "A or more and B or less".

[0013] In the following description, prior to the description of the hydrogen storage material and the like in the embodiment of the present invention, the findings of the present invention will be outlined. The inventors of the present invention have newly discovered a hydride represented by the compositional formula Al x Mn 1-x H y where x is 0.1 or more and 0.5 or less. And the inventors of the present invention have completed the present invention by obtaining the finding that the hydride has a lower temperature for releasing hydrogen or can be hydrogenated at a lower pressure compared to the hydride represented by Al x Mn 1-x H y where x is greater than 0.5. Hereinafter, the hydrogen storage material of the present invention will be described in detail.

[0014] The hydrogen storage material in the present embodiment contains a hydride represented by the compositional formula Al x Mn 1-x H y where x is 0.1 or more and 0.5 or less (hereinafter referred to as Al-Mn hydride). Note that the hydrogen storage material of one aspect of the present invention may be composed only of the above Al-Mn hydride. The Al-Mn hydride of the present invention may have a hcp (hexagonal close packed) structure or a fcc (face centered cubic) structure as described below.

[0015] <hcp structure> The above Al-Mn hydride of one aspect of the present invention may have a hcp structure. In the following description, the Al-Mn hydride having a hcp structure will be described as a hcp structure hydride. The hcp structure hydride has a temperature at which hydrogen is released from the hcp structure hydride (hereinafter also referred to as the hydrogen release temperature) of 175 °C or lower. The hydrogen release temperature is lower than about 190 °C, which is the hydrogen release temperature of the hydrogen storage material disclosed in Patent Document 1, and can reduce the cost for releasing hydrogen. In this specification, the "hydrogen release temperature" is defined as the temperature at which the amount of hydrogen released peaks when the hydrogen storage material storing hydrogen is heated from room temperature at a predetermined heating rate.

[0016] In the hcp structure hydride of one aspect of the present invention, the above x may be 0.1 or more and 0.2 or less. In this case, since the hydrogen release temperature becomes 125 °C or lower, the cost for releasing hydrogen can be further reduced.

[0017] <fcc structure> The above Al-Mn hydride of one aspect of the present invention may have a fcc structure. In the following description, the Al-Mn hydride having a fcc structure will be described as a fcc structure hydride. The fcc structure hydride can have a pressure (hereinafter also referred to as the hydrogen storage pressure) for storing hydrogen in the Al-Mn alloy described below to produce an Al-Mn hydride of 0.5 to 3 GPa. The hydrogen storage pressure is lower than about 5 GPa, which is the hydrogen storage pressure in the hydrogen storage material disclosed in Patent Document 1, and can reduce the cost for storing hydrogen.

[0018] (Manufacturing method of Al-Mn hydride) Next, the manufacturing method of the Al-Mn hydride in the present embodiment will be described. The Al-Mn hydride in the present embodiment includes a mixture preparation step, an Al-Mn alloy preparation step, and a hydrogenation step.

[0019] In the mixture preparation process, first, Al and Mn are weighed so that the amount of Mn is 1 to 9 times the amount of Al in atomic ratio. Then, the weighed Al and Mn are mixed to prepare the mixture. The method of mixing Al and Mn is not particularly limited; for example, they may be mixed using a mortar and pestle.

[0020] The Al-Mn alloy manufacturing process is a process in which the mixture of Al and Mn prepared in the mixture manufacturing process is alloyed to produce an Al-Mn alloy (hereinafter referred to as the Al-Mn alloy). The alloying of the Al and Mn mixture can be carried out by either the high-pressure solid-phase reaction method (solid-phase reaction process) or the arc melting method (arc melting process).

[0021] The high-pressure solid-phase reaction method is a method of alloying a mixture by reacting it in solid phase under high temperature and high pressure conditions. In this embodiment, an Al-Mn alloy can be produced by reacting a mixture of Al and Mn in solid phase at a pressure of 0.5 GPa to 2 GPa and a temperature of 1000°C to 1100°C. The solid-phase reaction time can be 3 minutes to 1 hour. The solid-phase reaction is preferably carried out under an inert gas atmosphere.

[0022] The arc melting method is a method of alloying a mixture by heating it to a high temperature using an arc melting furnace, melting the mixture, and rapidly cooling the molten material. In this embodiment, an Al-Mn alloy can be produced by melting Al and Mn at a temperature of 2000°C to 3000°C and rapidly cooling the molten material. The above process may be repeated multiple times to ensure sufficient alloying of Al and Mn. Furthermore, arc melting is preferably performed under an argon gas atmosphere.

[0023] The hydrogenation process is a process for producing the above-mentioned Al-Mn hydride by allowing hydrogen to be absorbed into the Al-Mn alloy produced in the Al-Mn alloy production process, thereby hydrogenating the Al-Mn alloy.

[0024] These researchers discovered that the structure of the resulting Al-Mn hydride changes depending on the pressure during the hydrogenation process. Specifically, when an Al-Mn alloy is hydrogenated at a pressure of 6 GPa to 10 GPa, an Al-Mn hydride with an hcp structure (i.e., an hcp structured hydride) is obtained, while when hydrogenated at a pressure of 0.5 GPa to 3 GPa, an Al-Mn hydride with an fcc structure (i.e., an fcc structured hydride) is obtained. The hydrogenation process is preferably carried out at a temperature of 650°C to 800°C. The duration of the hydrogenation process is not particularly limited, but can be, for example, 1 to 15 hours.

[0025] Furthermore, when the Al-Mn alloy with x = 0.5 is hydrogenated at a pressure of 9 GPa to 10 GPa, a hydride with an unknown structure is obtained, as will be explained in the examples described later. Hereafter, this hydride with an unknown structure will be referred to as an unknown structure hydride. The unknown structure hydride has peaks at at least one of the following positions in the profile obtained by XRD measurement using Mo as the X-ray source: 2θ = 14.4° to 14.6°, 16.9° to 17.1°, 20.5° to 20.7°, or 31.8° to 32.0°. The hydrogen release temperature of the unknown structure hydride is below approximately 190°C, which is the hydrogen release temperature of the hydrogen storage material disclosed in Patent Document 1, similar to the hcp structure hydride.

[0026] As described above, the hydrogen storage material of the present invention has the composition formula Al x Mn 1-x H y The present invention includes a hydride in which x is 0.1 or greater and 0.5 or less. As a result, the hydrogen release temperature is lower than that of the hydrogen storage material disclosed in Patent Document 1, or the hydrogen storage pressure is lower than that of the hydrogen storage material disclosed in Patent Document 1. Consequently, the hydrogen storage material of the present invention can reduce the cost of storing or releasing hydrogen. However, if x is less than 0.1, the hydrogen release temperature will be higher, which is undesirable.

[0027] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Examples]

[0028] An embodiment of the present invention is described below. In this embodiment, hydrogen storage materials according to Examples 1 to 6 shown below were prepared.

[0029] (Example 1) The hydrogen storage material of Example 1 was prepared as follows. First, Al and Mn powders were weighed in an atomic ratio of Al:Mn=3:7 and mixed using a mortar. The mixed mixture was subjected to a solid-phase reaction under conditions of a pressure of 1 GPa and 1050°C, and then removed to room temperature and atmospheric pressure to produce an Al-Mn alloy. The prepared Al-Mn alloy was set in a cubic anvil type high-pressure apparatus and hydrogenated under conditions of a pressure of 9 GPa and 750°C for about 2 hours, and then cooled to room temperature and reduced to atmospheric pressure to produce the hydrogen storage material of Example 1. The hydrogen storage material of Example 1 has the composition formula Al x Mn 1-x H y It is represented as such, and is a hydride with x = 0.3.

[0030] XRD measurements were performed on the hydrogen storage material of Example 1 using Mo as the X-ray source. The profile obtained by the XRD measurement is shown in Figure 1. As shown in Figure 1, the Bragg peak that appeared on the XRD profile of the hydrogen storage material of Example 1 was at the lattice volume v = 26.47 Å. 3 Indexing was possible using the hcp structure unit cells. That is, the hydrogen storage material of Example 1 contained an Al-Mn hydride with an hcp structure.

[0031] Next, a hydrogen release experiment was conducted to confirm the temperature at which hydrogen is released by heating the hydrogen storage material of Example 1 under atmospheric pressure. The hydrogen release experiment was performed using a thermobalance-mass spectrometer by heating the sample in a He flow atmosphere from room temperature at a heating rate of 10°C / min. The results of the hydrogen release experiment performed on the hydrogen storage material of Example 1 are shown in Figure 2. In Figure 2, H2 is represented as the vertical axis. + Ionic strength corresponds to the amount of hydrogen released from the hydrogen storage material. As shown in Figure 2, the hydrogen storage material of Example 1 had a hydrogen release temperature of approximately 171°C. Furthermore, the hydrogen storage capacity of the hydrogen storage material of Example 1 was calculated to be 1.09 wt% based on the weight loss measurement during hydrogen release using a thermobalance.

[0032] (Example 2) The hydrogen storage material of Example 2 was prepared in the same manner as the hydrogen storage material of Example 1, except that the atomic ratio of Al to Mn in the starting materials was Al:Mn=2:8. The hydrogen storage material of Example 2 has the composition formula Al x Mn 1-x H y It is represented as such, and is a hydride with x = 0.2.

[0033] Figure 3 shows the profile obtained by XRD measurement performed on the hydrogen storage material of Example 2 using the same method as in Example 1. As shown in Figure 3, the Bragg peak that appeared on the XRD profile of the hydrogen storage material of Example 2 corresponds to the lattice volume v = 27.27 Å. 3 Indexing was possible using the hcp structure unit cells. That is, the hydrogen storage material of Example 2 contained an Al-Mn hydride with an hcp structure.

[0034] Figure 4 is a graph showing the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 2 using the same method as in Example 1. As shown in Figure 4, the hydrogen release temperature of the hydrogen storage material of Example 2 was 125°C. Furthermore, the hydrogen storage capacity of the hydrogen storage material of Example 2 was calculated to be 0.76 wt% based on the weight loss measurement during hydrogen release using a thermobalance.

[0035] (Example 3) The hydrogen storage material of Example 3 was prepared in the same manner as the hydrogen storage material of Example 1, except that the atomic ratio of Al to Mn in the starting materials was Al:Mn=1:9. The hydrogen storage material of Example 3 has the composition formula Al x Mn 1-x H y It is represented as such, and is a hydride where x is 0.1.

[0036] Figure 5 shows the profile obtained by XRD measurement performed on the hydrogen storage material of Example 3 using the same method as in Example 1. As shown in Figure 5, the Bragg peak that appeared on the XRD profile of the hydrogen storage material of Example 3 corresponds to the lattice volume v = 26.56 Å. 3 Indexing was possible using the hcp structure unit cells. That is, the hydrogen storage material of Example 3 contained an Al-Mn hydride with an hcp structure.

[0037] Figure 6 is a graph showing the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 3 using the same method as in Example 1. As shown in Figure 6, the hydrogen release temperature of the hydrogen storage material of Example 3 was 95°C. Furthermore, the hydrogen storage capacity of the hydrogen storage material of Example 3 was calculated to be 0.98 wt% based on the weight loss measurement during hydrogen release using a thermobalance.

[0038] (Example 4) The hydrogen storage material of Example 4 was prepared in the same manner as the hydrogen storage material of Example 1, except that the atomic ratio of Al to Mn in the starting materials was Al:Mn=4:6. The hydrogen storage material of Example 4 has the composition formula Al x Mn 1-x H y It is represented as such, and is a hydride with x = 0.4.

[0039] Figure 7 shows the profile obtained by XRD measurement performed on the hydrogen storage material of Example 4 using the same method as in Example 1. As shown in Figure 7, the Bragg peak that appeared on the XRD profile of the hydrogen storage material of Example 4 corresponds to the lattice volume v = 27.39 Å. 3 Indexing was possible using the hcp structure unit cells. That is, the hydrogen storage material of Example 4 contained an Al-Mn hydride with an hcp structure.

[0040] Figure 8 is a graph showing the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 4 using the same method as in Example 1. As shown in Figure 8, the hydrogen release temperature of the hydrogen storage material of Example 4 was 157°C.

[0041] (Example 5) The hydrogen storage material of Example 5 was prepared as follows. First, small pieces of Al and Mn were weighed and mixed in an atomic ratio of 3:7. The mixed mixture was heated to over 2000°C in an arc melting furnace to produce a molten body, and then the molten body was rapidly cooled. By repeating the series of melting and rapidly cooling operations four times, an Al-Mn alloy ingot was prepared. The prepared ingot was ground into powder in an agate mortar, and the resulting powder was shaped into pellets with a diameter of 1 mm and a height of 0.4 mm. Then, the prepared pellets were set in a cubic anvil type high-pressure device and hydrogenated for about 1 hour under conditions of a pressure of 1 GPa and a temperature of 750°C, and after cooling to room temperature, the pressure was reduced to atmospheric pressure to prepare the hydrogen storage material of Example 5. The hydrogen storage material of Example 5 has the composition formula Al x Mn 1-x H y It is represented as such, and is a hydride with x = 0.3.

[0042] Figure 9 shows the profile of the hydrogen storage material of Example 5, obtained by energy dispersion using white X-rays at the large synchrotron radiation facility SPring-8 BL14B1, with the X-axis converted to the diffraction angle 2θ when measured using a Mo source. As shown in Figure 9, the hydrogen storage material of Example 5 had an fcc structure.

[0043] Figure 10 is a graph showing the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 5 using the same method as in Example 1. As shown in Figure 10, the hydrogen storage material of Example 5 showed peaks in hydrogen release at 241°C and 285°C.

[0044] (Example 6) The hydrogen storage material of Example 6 was prepared in the same manner as the hydrogen storage material of Example 5, except that the atomic ratio of Al to Mn in the starting materials was Al:Mn=1:1, and that it was hydrogenated for about 14 hours under conditions of a pressure of 9 GPa and a temperature of 750°C. The hydrogen storage material of Example 1 has the composition formula Al x Mn 1-x H y It is represented as such, and is a hydride with x = 0.5.

[0045] Figure 11 shows the profile obtained by XRD measurement performed on the hydrogen storage material of Example 6 using the same method as in Example 5. Figure 11 also shows the results of XRD measurement performed on the pellet-shaped hydrogen storage material of Example 6 at different measurement positions. Specifically, the profiles shown as (a) to (e) in Figure 11 are the profiles obtained by performing XRD measurement at measurement positions at distances of 0 mm, 0.15 mm, 0.20 mm, 0.25 mm, and 0.35 mm, respectively, from one of the bottom surfaces of the pellet shape.

[0046] As shown in Figure 11, the hydrogen storage material of Example 6 shows a Bragg peak derived from Al2MnH3, a known Al-Mn hydride, and an alloy phase that does not contain hydrogen. 0.45 Mn 0.55 In addition to the Bragg peak originating from the substance, Bragg peaks originating from a substance with an unknown structure were observed at the positions indicated by circles in Figure 11. In particular, in all profiles shown as (a) to (e) in Figure 11, Bragg peaks originating from a substance with an unknown structure were observed at the position 2θ = 14.4° to 14.6°.

[0047] Figure 12 is a graph showing the results of a hydrogen release experiment conducted on the hydrogen storage material of Example 6 using the same method as in Example 1. As shown in Figure 12, the hydrogen storage material of Example 6 showed a peak in hydrogen release at approximately 180°C.

[0048] Figure 13 is a graph plotting the hydrogen storage materials of Examples 1-6, the conventionally known hydrogen storage material Al2MnH3, and manganese hydride MnH, with the value of x (where Al:Mn=x:1-x) as the atomic ratio of Al to Mn in the starting materials on the horizontal axis and the hydrogen release temperature on the vertical axis. In Figure 13, the hydrogen release temperature of the hydrogen storage material of Example 5 is plotted as 241°C. As shown in Figure 13, the hydrogen storage materials of Examples 1-4 and 6, which were hydrogenated at a pressure of 9 GPa, had lower hydrogen release temperatures compared to the conventionally known Al2MnH3. In particular, the hydrogen storage material of Example 2, where the value of x is 0.2, and the hydrogen storage material of Example 3, where the value of x is 0.1, had hydrogen release temperatures of 130°C or lower.

Claims

1. Al ｘ Mn １－ｘ H ｙ It is represented as and includes a hydride in which x is 0.1 or more and 0.5 or less, The aforementioned hydride is a hydrogen storage material having an HCP structure.

2. The hydrogen storage material according to claim 1, wherein x is 0.1 or more and 0.2 or less.

3. A mixture preparation step involves weighing Al and Mn such that the amount of Mn is 1 to 9 times the amount of Al in atomic ratio, and then mixing the weighed Al and Mn to produce a mixture. A solid-phase reaction step is performed to produce an Al-Mn alloy by reacting the aforementioned mixture in a solid-phase state at a pressure of 0.5 GPa to 2 GPa and a temperature of 1000°C to 1100°C. A method for producing a hydrogen storage material, comprising a hydrogenation step of hydrogenating the Al-Mn alloy under a pressure of 6 GPa to 10 GPa.

4. A mixture preparation step involves weighing Al and Mn such that the amount of Mn is 1 to 9 times the amount of Al in atomic ratio, and then mixing the weighed Al and Mn to produce a mixture. An arc melting step in which the above mixture is arc-melted at a temperature of 2000°C to 3000°C to produce an Al-Mn alloy, A method for producing a hydrogen storage material, comprising a hydrogenation step of hydrogenating the Al-Mn alloy under a pressure of 6 GPa to 10 GPa.

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