JP7680740B2 - Alloy, hydrogen extraction system, hydrogen storage material, and method for producing alloy - Google Patents

Description

The present invention relates to alloys that can be used for hydrogen storage.

Hydrogen has been attracting attention as a fuel that does not emit carbon dioxide. However, hydrogen has a low energy density per volume, so a hydrogen storage material is required to increase the density of hydrogen when it is transported or carried. For example, Patent Document 1 discloses a hydrogen storage material made of Al-Fe or Al-Mn.

JP 2019-199640 A

However, the hydrogen storage material disclosed in Patent Document 1 requires ultra-high pressure hydrogen of 70,000 atmospheres or more in order to store hydrogen, which poses the problem of high costs for storing hydrogen.

One aspect of the present invention aims to realize an alloy that can absorb hydrogen from the atmosphere at room temperature and pressure.

In order to solve the above problems, an alloy according to one embodiment of the present invention has a composition of Al _x Fe _1-x (x=0.7 to 0.9), Al _x Co _1-x (x=0.7 to 0.9) or Al _x Mn _1-x (x=0.7 to 0.9), the alloy has an amorphous structure and a plurality of first regions in which the density of the alloy is lower than that of other regions, and in a cross section of the alloy cut along a plane perpendicular to a surface of the alloy, the distance between adjacent first regions is 30 nm or less.

According to one aspect of the present invention, it is possible to realize an alloy that absorbs hydrogen from the atmosphere at room temperature and pressure.

FIG. 1 is a schematic diagram showing the structure of an alloy according to one embodiment of the present invention. 1 is a SEM photograph of the surface of the alloy opposite to the substrate side. 1 is a scanning TEM HAADF image of the alloy. 1 is a block diagram showing a configuration of a hydrogen extraction system in one embodiment of the present invention. FIG. 1 is a cross-sectional TEM image of an alloy according to Example 1 of the present invention. 1 is a cross-sectional TEM image of an alloy as Comparative Example 1 of the present invention. 1 is a SEM photograph of the alloy of Comparative Example 1, showing the surface opposite to the substrate side. 1 is an electron beam diffraction image of the alloy of Example 1 obtained using a TEM. 1 is an electron beam diffraction image of Comparative Example 1 obtained using a TEM. 1 is a graph showing the results of measuring the hydrogen distribution present inside the alloy of Example 1 and the alloy of Comparative Example 1 after exposing them to the atmosphere at room temperature and normal pressure. 1 is a graph showing the amount of hydrogen released from an alloy of a modification of Example 1 that has absorbed hydrogen. 1 is a cross-sectional TEM image of an alloy of Reference Example 1 of the present invention. 1 is a graph showing the results of measuring the hydrogen distribution present inside the alloy of Reference Example 1 after exposing the alloy to the atmosphere at room temperature and normal pressure. 1 is a HAADF image of the alloy of Reference Example 2 by a scanning TEM method. 15 is a graph created by calculating contrast intensities on lines L1 and L2 shown in FIG. 14. 1 is a cross-sectional TEM image of an alloy of Example 2 of the present invention. 1 is an electron beam diffraction image of the alloy of Example 2 obtained using a TEM. 13 is a graph showing the amount of hydrogen released from an alloy of a modified example of Example 2 that has absorbed hydrogen. 1 is a cross-sectional TEM image of an alloy of Example 3 of the present invention. 1 is a cross-sectional TEM image of an alloy of Comparative Example 2 of the present invention. 1 is a SEM photograph of the alloy of Example 3, showing the surface opposite to the substrate side. 1 is an SEM photograph of the alloy of Comparative Example 2, showing the surface opposite to the substrate side. 1 is an electron beam diffraction image of the alloy of Example 3 obtained using a TEM. 1 is an electron beam diffraction image of Comparative Example 2 obtained using a TEM. 1 is a graph showing the results of measuring the hydrogen distribution present inside the alloys of Example 3 and Comparative Example 2 after exposing the alloys to the atmosphere at room temperature and normal pressure. 13 is a graph showing the amount of hydrogen released from an alloy of a modified example of Example 3 that has absorbed hydrogen. 1 is a cross-sectional TEM image of an alloy of Comparative Example 3 of the present invention. 1 is an electron beam diffraction image of an alloy as Comparative Example 3 of the present invention, obtained using a TEM. 1 is a graph showing the results of measuring the hydrogen distribution present inside the alloy of Comparative Example 3 after exposing the alloy to the atmosphere at room temperature and normal pressure. 13 is a graph showing the amount of hydrogen released from an alloy of a modified example of Comparative Example 3 that has absorbed hydrogen. 1 is a cross-sectional TEM image of an alloy of Example 4 of the present invention. 1 is an electron beam diffraction image of the alloy of Example 4 obtained using a TEM. 1 is a graph showing the results of measuring the hydrogen distribution present inside the alloy of Example 4 after exposing the alloy to the atmosphere at room temperature and normal pressure. 1 is a cross-sectional TEM image of an alloy of Example 5 of the present invention. 1 is an electron beam diffraction image of the alloy of Example 5 obtained using a TEM. 1 is a graph showing the results of measuring the hydrogen distribution present inside the alloy of Example 5 after exposing the alloy to the atmosphere at room temperature and normal pressure. 13 is a graph showing the amount of hydrogen released from an alloy of a modified example of Example 5 that has absorbed hydrogen.

[Embodiment 1]
Hereinafter, one embodiment of the present invention will be described in detail.

[Hydrogen storage material]
As a result of intensive research, the present inventors have found that in hydrogen storage materials including alloys having a composition of Al _x Fe _1-x (x = 0.7 to 0.9), alloys having a composition of Al _x Co _1-x (x = 0.7 to 0.9), or alloys having a composition of Al _x Mn _1-x (x = 0.7 to 0.9), the alloys having the following configurations store hydrogen in the atmosphere at room temperature and normal pressure. Here, in this specification, "room temperature" refers to a temperature of 15°C to 30°C, and "normal pressure" refers to atmospheric pressure, that is, 1 atmosphere (1013 hPa). Note that, even though it is atmospheric pressure, there are differences in low pressure and high pressure depending on the weather, so here, "normal pressure" means a pressure near atmospheric pressure (970 hPa to 1030 hPa). First, the details of the structure of the hydrogen storage material will be described.

Figure 1 is a schematic diagram showing the structure of alloy 10 according to one embodiment of the present invention. Alloy 10 is formed as a thin film on substrate 1 by, for example, a sputtering method. Substrate 1 in this embodiment is made of Si (silicon).

Alloy 10 has a composition of Al _x Fe _1-x (x=0.7-0.9), Al _x Co _1-x (x=0.7-0.9), or Al _x Mn _1-x (x=0.7-0.9). Alloy 10 has a non-crystalline (amorphous) structure. However, alloy 10 may contain microcrystals with a crystal grain size of several nm or less. In other words, alloy 10 may have a structure including an amorphous structure region and a microcrystal region. Here, "microcrystals" refers to "tiny crystal grains having a crystalline structure."

Alloy 10 has regions that are less dense than other regions at intervals of 30 nm or less on any straight line in a plane parallel to the surface. This will be explained using Figures 2 and 3.

Figure 2 is a scanning electron microscope (SEM) photograph of the surface of alloy 10 opposite to the substrate 1 (i.e., the surface of alloy 10). Figure 3 is a high-angle annular dark field (HAADF) image of alloy 10 by a transmission electron microscope (TEM) method. The HAADF image shown in Figure 3 is an HAADF image of alloy 10 cut along a plane parallel to the direction in which alloy 10 is layered on substrate 1 (in other words, the thickness direction of alloy 10). Note that alloy 10 shown in Figures 2 and 3 was formed on substrate 1 at room temperature using a target having a composition of Al:Fe = 76:24 in atomic ratio. The manufacturing method of alloy 10 will be described in detail later.

2 and 3, the alloy 10 is composed of a collection of columnar structures 11 (first columnar structures) with a diameter of 30 nm or less that extend along the thickness direction of the alloy 10 (in other words, the direction perpendicular to the surface of the alloy 10). In the SEM photograph of FIG. 2, the region that appears to be approximately circular, including a perfect circle, corresponds to the longitudinal end of the columnar structure 11. Also, as shown in FIG. 3, the columnar structure 11 is composed of a collection of multiple tiny columnar structures 12 (second columnar structures). More specifically, the columnar structure 11 includes multiple columnar structures 12 adjacent to each other via a second region 14 in which the density of the alloy 10 is lower than that of other regions in the columnar structure 11.

The alloy 10 is mostly composed of a plurality of columnar structures 11. In the HAADF image shown in FIG. 3, the region between one columnar structure 11 and the columnar structure 11 adjacent to the columnar structure 11 (hereinafter also referred to as the first region 13) is darker than the columnar structure 11. In the alloy 10, the first region 13 is continuously formed from one surface to the other surface of the alloy 10 in a cross section when the alloy 10 is cut on a plane perpendicular to the surface of the alloy 10. In the HAADF image, when the composition is the same, the higher the density, the brighter it appears. Therefore, the first region 13 has a lower density than the columnar structure 11. That is, the distance between the adjacent first regions 13 in the alloy 10 is 30 nm or less. With the above configuration, the alloy 10 has a structure in which, on any straight line on a plane parallel to the surface of the alloy 10 inside the alloy 10, there are regions with a lower density than other regions at intervals of 30 nm or less. In other words, alloy 10 has a plurality of first regions 13 in which the density of alloy 10 is lower than other regions, and in a cross section of alloy 10 cut along a plane perpendicular to the surface of alloy 10, the distance between adjacent first regions 13 is 30 nm or less. In this specification, the distance between adjacent first regions 13 refers to the distance between the point of lowest density in first region 13 and the point of lowest density in the first region adjacent to said first region 13.

The inventors' intensive research has revealed that due to this structure, alloy 10 can absorb hydrogen from the atmosphere at room temperature and pressure, although the detailed mechanism is not clear. Therefore, alloy 10 can be suitably used as a hydrogen storage material. It is believed that alloy 10 absorbs hydrogen from water molecules or hydrogen molecules contained in the atmosphere.

As described above, in the SEM photograph shown in FIG. 2, the regions that appear to be approximately circular, including perfect circles, correspond to the longitudinal ends of the columnar structures 11. In other words, in the cross section of alloy 10 when alloy 10 is cut along a plane parallel to the surface of alloy 10, the distance between adjacent first regions is 30 nm or less.

In the present embodiment, the alloy 10 is composed of a collection of columnar structures 11, and has a structure with regions that are spaced 30 nm or less apart and have a lower density than other regions, but the alloy of the present invention is not limited to this. The alloy of the present invention may have other configurations as long as it has a structure with regions that are spaced 30 nm or less apart and have a lower density than other regions, and may have a particulate or layered structure, for example.

As described above, alloy 10 has a composition of Al _x Fe _1-x (x=0.7-0.9), an alloy having a composition of Al _x Co _1-x (x=0.7-0.9), or an alloy having a composition of Al _x Mn _1-x (x=0.7-0.9). As a result, when alloy 10 is produced by the manufacturing method described below, alloy 10 having the above configuration can be obtained. When x is less than 0.7, the produced alloy has a crystalline structure, not an amorphous structure, and the hydrogen storage capacity is reduced. Also, when x exceeds 0.9, the alloy has a crystalline structure, and the hydrogen storage capacity is reduced.

In this embodiment, alloy 10 releases hydrogen by heating the absorbed hydrogen. Specifically, when alloy 10 in this embodiment is heated, it gradually releases hydrogen from about 100°C, and the amount of hydrogen released increases as the temperature rises to about 150°C. A heating rate of 10°C/min is preferred.

In this embodiment, the alloy 10 is composed only of Al and Fe, Co, or Mn. These substances are inexpensive metals and can be produced more cheaply than existing hydrogen storage alloys.

[Method of manufacturing hydrogen storage material]
The alloy 10 can be produced, for example, by a sputtering method. More specifically, the temperature of the base material 1 is kept below 200° C., preferably below 100° C., and more preferably at room temperature (specifically, 15° C. to 30° C.), and a sputtering process (alloy lamination process) is performed to produce the alloy 10 having the above-mentioned configuration.

The substrate 1 is not particularly limited, and may be, for example, metals such as Si, Al, and stainless steel, heat-resistant polymeric substances such as polyimide, and ceramics such as SiC and alumina. In the sputtering process, a sintered body of a mixed powder having the same composition as the alloy to be produced (i.e., a composition of Al _x Fe _1-x (x=0.7-0.9), Al _x Co _1-x (x=0.7-0.9), or Al _x Mn _1-x (x=0.7-0.9)) is used as a target. The sputtering process can be performed in an inert gas atmosphere (for example, an Ar atmosphere).

If the sputtering process is performed at a temperature of the substrate 1 higher than room temperature, the structure will not have regions with a lower density than other regions at intervals of 30 nm or less on any straight line on a plane parallel to the surface. For example, if the sputtering process is performed at a temperature of the substrate 1 of 200°C, the interval between regions with a lower density than other regions on any straight line on a plane parallel to the surface will be greater than 30 nm. Furthermore, if the sputtering process is performed at a temperature of the substrate 1 of 300°C or higher, the alloy will have a crystalline structure rather than an amorphous structure, and the hydrogen storage capacity will be reduced.

The above-mentioned method for producing the hydrogen storage material is one example of a method for producing alloy 10. Alloy 10 can be produced by forming a film while maintaining the temperature of substrate 1 at room temperature, for example, by physical vapor deposition methods such as vacuum deposition, thermal spraying, and laser deposition. Alloy 10 can also be produced by mechanical alloying using a ball milling device.

[Application example of Alloy 10]
As described above, the alloy 10 can absorb hydrogen from the atmosphere at room temperature and pressure. Therefore, the alloy 10 can be suitably applied to a hydrogen extraction system that extracts hydrogen from the atmosphere. Here, an example of the hydrogen extraction system will be described.

Figure 4 is a block diagram showing the configuration of the hydrogen extraction system 100 in this embodiment. As shown in Figure 4, the hydrogen extraction system 100 includes a hydrogen storage section 110 and a hydrogen release section 120.

The hydrogen absorbing unit 110 absorbs hydrogen using alloy 10 as a hydrogen absorbing material. The hydrogen absorbing unit 110 may be, for example, a container coated with alloy 10. Since the hydrogen absorbing unit 110 comprises alloy 10, hydrogen can be absorbed in the hydrogen absorbing unit 110 by exposing the hydrogen absorbing unit 110 to the atmosphere.

The hydrogen release unit 120 heats the hydrogen storage unit 110 that has absorbed hydrogen, thereby releasing hydrogen from the hydrogen storage unit 110. Specifically, the hydrogen release unit 120 heats the hydrogen storage unit 110 to 150°C or higher, which is the temperature at which the alloy 10 releases the hydrogen stored therein.

In the hydrogen extraction system 100 having the above configuration, hydrogen can be absorbed in the hydrogen storage unit 110 at room temperature and pressure, and hydrogen can be extracted at the desired timing simply by heating the hydrogen storage unit 110 that has absorbed hydrogen.

First embodiment

One embodiment of the present invention will be described below. Figure 5 is a cross-sectional TEM image of an alloy serving as Example 1 of the present invention. Figure 6 is a cross-sectional TEM image of an alloy serving as Comparative Example 1 of the present invention. Figure 7 is an SEM photograph of the alloy of Comparative Example 1, taken from the side opposite the substrate. The SEM photograph of the alloy of Example 1, taken from the side opposite the substrate, is the SEM photograph shown in Figure 2.

The alloy of Example 1 was produced by magnetron sputtering using Si as the substrate. More specifically, the sputtering was carried out using a mixed powder sintered body having a molar ratio of Al:Fe = 76:24 as the target, with the Ar gas pressure set to 0.183 Pa and the substrate temperature held at 25°C. The alloy of Example 1 was deposited to a thickness of approximately 250 nm at a deposition rate of 5.4 nm/min.

The alloy of Comparative Example 1 was prepared in the same manner as in Example 1, except that the substrate was held at a temperature of 200°C during the sputtering process.

As shown in Figures 5 and 6, the alloy of Example 1 had more white lines extending along the thickness direction of the alloy than the alloy of Comparative Example 1. Specifically, in the alloy of Example 1, white lines were observed at intervals of 30 nm or less on any straight line on a plane parallel to the surface. On the other hand, in the alloy of Comparative Example 1, white lines were observed at intervals longer than 30 nm (for example, 50 nm) on any straight line on a plane parallel to the surface. As will be described later, the white lines are regions with a lower density than the black regions. Therefore, the alloy of Example 1 had a structure having regions with a lower density than other regions at intervals of 30 nm or less on any straight line on a plane parallel to the surface. The black regions in the photographs shown in Figures 5 and 6 are columnar structures. In the SEM photographs of Figures 2 and 7, the regions that appear approximately circular correspond to the longitudinal ends of the columnar structures.

Figure 8 is an electron beam diffraction image of the alloy of Example 1 using a TEM. Figure 9 is an electron beam diffraction image of Comparative Example 1 using a TEM. As shown in Figure 8, the electron beam diffraction image of the alloy of Example 1 has a structure close to a halo shape, and no spots due to the crystal structure were confirmed. Here, the halo shape means a halo. In other words, it can be seen that the alloy of Example 1 has a non-crystalline (amorphous) structure. However, as shown in Figure 8, the electron beam diffraction image of the alloy of Example 1 is not a complete halo shape, and a ring-shaped image is observed, so it is thought that it may contain microcrystals with a crystal grain size of less than a few nm (specifically, less than 5 nm). Note that, normally, when crystals with a grain size of several nm exist, they can be confirmed in a TEM image, but crystals with a grain size of several nm could not be observed in the TEM image of Example 1.

As shown in Figure 9, the alloy of Comparative Example 1 also had the same electron beam diffraction pattern as the alloy of Example 1, and had an amorphous structure.

10 is a graph showing the results of measuring the hydrogen distribution inside the alloy of Example 1 and the alloy of Comparative Example 1 after exposing them to the atmosphere at room temperature and pressure. The amount of hydrogen inside the alloy was measured by a recoil particle detection method using 2.8 MeV ^{4He +} as an analysis beam. In the graph shown in FIG. 10, the number of channels on the horizontal axis corresponds to the distance from the substrate, and the normalized yield on the vertical axis corresponds to the amount of hydrogen.

As shown in FIG. 10, the alloy of Example 1 contained more hydrogen than the alloy of Comparative Example 1. That is, it was shown that the alloy of Example 1 had a higher hydrogen storage capacity than the alloy of Comparative Example 1. Calculations based on the graph shown in FIG. 10 showed that the alloy of Example 1 absorbed 1.3 wt% of hydrogen relative to the weight of the alloy. This value is about the same as the hydrogen storage capacity when LaNi ₅ , TiFe, etc., which are conventionally known as hydrogen storage materials, are absorbed using high-concentration hydrogen gas. That is, the alloy of Example 1 absorbed hydrogen to the same extent as conventional hydrogen storage materials simply by exposing it to the atmosphere at room temperature and normal pressure.

Figure 11 is a graph showing the amount of hydrogen released from a modified alloy in which hydrogen was absorbed from the alloy of Example 1, in which the base material was changed to Al and the film thickness of the alloy was changed to about 1 μm. In Figure 11, the ion current on the left vertical axis corresponds to the amount of hydrogen released from the alloy. The graph shown in Figure 11 was created based on the results of measurements using a thermobalance-mass spectrometer. Specifically, the sample was heated from room temperature to 350°C at a heating rate of 10°C/min under He flow conditions, and the weight change and the amount of hydrogen released from the sample were measured.

As shown in FIG. 11, when the temperature of the alloy of the modified example of Example 1 was increased, hydrogen was gradually released from about 100°C, and the amount of hydrogen released increased as the temperature increased to about 150°C. Also, as shown in FIG. 11, the weight of the alloy decreased as the amount of hydrogen released increased. Hydrogen release was observed up to about 250°C. From these results, it can be seen that the alloy of the modified example of Example 1 can be sufficiently released of the absorbed hydrogen by heating it to 250°C at a heating rate of 10°C/min.

Second embodiment

Next, an alloy as Reference Example 1 of the present invention will be described. The alloy of Reference Example 1 was produced in the same manner as in Example 1, except that an Al ₇₆ Fe ₂₄ alloy, Al, and an Al ₇₆ Fe ₂₄ alloy were laminated in this order on a Si substrate. Figure 12 is a cross-sectional TEM image of the alloy of Reference Example 1. Figure 13 is a graph showing the results of measuring the hydrogen distribution present inside the alloy after exposing the alloy of Reference Example 1 to the atmosphere at room temperature and pressure.

As shown in Fig. 13, in the alloy of Reference Example 1, the amount of hydrogen present in the Al ₇₆ Fe ₂₄ layer present near the surface was greater than the amount of hydrogen present in the Al ₇₆ Fe ₂₄ layer present near the substrate. The Al film does not absorb hydrogen. This shows that the hydrogen absorbed in the alloy of Reference Example 1 is not hydrogen absorbed in the alloy during the sputtering process, but hydrogen absorbed in the alloy by exposure to the atmosphere after film formation.

Third embodiment

Next, an alloy as Reference Example 2 of the present invention will be described. The alloy of Reference Example 2 was produced in the same manner as in Example 1, except that the first Al ₇₆ Fe ₂₄ alloy layer 10a was formed on a Si substrate at a substrate holding temperature of 200°C, and then the second Al ₇₆ Fe ₂₄ alloy layer 10b was formed at a substrate holding temperature of 25°C. Figure 14 is a HAADF image of the alloy of Reference Example 2 by a scanning TEM method. Figure 15 is a graph produced by calculating the contrast intensity on the lines L1 and L2 shown in Figure 14.

As shown in Fig. 14, dark lines indicating relatively low density are more frequently seen in the second Al ₇₆ Fe ₂₄ alloy layer 10 b than in the first Al ₇₆ Fe ₂₄ alloy layer 10 a. More specifically, as shown in Fig. 15, it can be seen that in the second Al ₇₆ Fe ₂₄ alloy layer 10 b, regions with relatively low density exist at intervals of 30 nm or less, whereas in the first Al ₇₆ Fe ₂₄ alloy layer 10 a, regions with relatively low density exist at intervals longer than 30 nm.

Fourth embodiment

Next, an alloy according to Example 2 of the present invention will be described. The alloy according to Example 2 was produced in the same manner as the alloy according to Example 1, except that a mixed powder sintered body having a molar ratio of Al:Fe = 80:20 was used as the target.

Figure 16 is a cross-sectional TEM image of the alloy of Example 2. As shown in Figure 16, the alloy of Example 2, like the alloy of Example 1, had white lines at intervals of 30 nm or less on any straight line on a plane parallel to the surface. In other words, the alloy of Example 2 had a structure with regions that had a lower density than other regions at intervals of 30 nm or less on any straight line on a plane parallel to the surface.

Figure 17 is an electron beam diffraction image of the alloy of Example 2 using a TEM. As shown in Figure 17, the alloy of Example 2, like the alloy of Example 1, has a structure close to a halo shape, and no spots due to a crystal structure were confirmed. In other words, it can be seen that the alloy of Example 2 has a non-crystalline (amorphous) structure. However, as shown in Figure 17, the electron beam diffraction image of the alloy of Example 2 does not have a complete halo shape, and a ring-shaped image is observed, so it is thought that it may contain microcrystals with a crystal grain size of less than a few nm (specifically, less than 5 nm).

Figure 18 is a graph showing the amount of hydrogen released from the alloy of Example 2, which is a modified example in which the alloy substrate is changed to Al and the alloy film thickness is changed to about 1 μm, in which hydrogen is absorbed. Here, the sample was heated from room temperature to 200°C at a heating rate of 10°C/min, and then held at 200°C for 5 minutes. As shown in Figure 18, when the temperature of the alloy of the modified example of Example 2 is increased, hydrogen is gradually released from about 100°C, and the amount of hydrogen released increases as the temperature increases to about 150°C. Also, as shown in Figure 18, the weight of the alloy decreases as the amount of hydrogen released increases. From this result, it can be seen that the alloy of the modified example of Example 2 can be sufficiently released by heating it to 200°C at a heating rate of 10°C/min and holding it at 200°C for 5 minutes.

Fifth embodiment

Next, we will explain the alloy as Example 3 of the present invention and the alloy as Comparative Example 2.

The alloy of Example 3 was prepared in the same manner as the alloy of Example 1, except that an alloy consisting of a mixed powder sintered body having a molar ratio of Al:Mn = 76:24 was used as a target. The alloy of Comparative Example 2 was prepared in the same manner as the alloy of Comparative Example 1, except that an alloy consisting of a mixed powder sintered body having a molar ratio of Al:Mn = 76:24 was used as a target.

Figure 19 is a cross-sectional TEM image of the alloy of Example 3. Figure 20 is a cross-sectional TEM image of the alloy of Comparative Example 2. Figure 21 is an SEM photograph of the alloy of Example 3, observed from the side opposite the substrate. Figure 22 is an SEM photograph of the alloy of Comparative Example 2, observed from the side opposite the substrate.

As shown in Figures 19 and 20, the alloy of Example 3 had more white lines extending along the thickness direction of the alloy than the alloy of Comparative Example 2. Specifically, in the alloy of Example 3, white lines were observed at intervals of 30 nm or less on any straight line on a plane parallel to the surface. On the other hand, in the alloy of Comparative Example 2, white lines were observed at intervals longer than 30 nm (e.g., 50 nm) on any straight line on a plane parallel to the surface. That is, the alloy of Example 3 had a structure having regions with a lower density than other regions at intervals of 30 nm or less on any straight line on a plane parallel to the surface. The black regions in the photographs shown in Figures 19 and 20 are columnar structures. In the SEM photographs of Figures 21 and 22, the regions that appear to be approximately circular correspond to the longitudinal ends of the columnar structures.

Figure 23 is an electron beam diffraction image of the alloy of Example 3 using a TEM. Figure 24 is an electron beam diffraction image of Comparative Example 2 using a TEM. As shown in Figure 23, the electron beam diffraction image of the alloy of Example 3 has a structure close to a halo shape, and no spots due to a crystal structure were confirmed. In other words, it can be seen that the alloy of Example 3 has a non-crystalline (amorphous) structure. However, as shown in Figure 23, the electron beam diffraction image of the alloy of Example 3 is not a complete halo shape, and a ring-shaped image is observed, so it is thought that it may contain microcrystals with a crystal grain size of less than a few nm (specifically, less than 5 nm). In addition, as shown in Figure 24, the alloy of Comparative Example 2 also has the same electron beam diffraction image as the alloy of Example 3, and has an amorphous structure.

Figure 25 is a graph showing the results of measuring the hydrogen distribution inside the alloy of Example 3 and the alloy of Comparative Example 2 after exposing them to the atmosphere at room temperature and pressure. As shown in Figure 25, the alloy of Example 3 contained more hydrogen than the alloy of Comparative Example 2. In other words, it was shown that the alloy of Example 3 has a higher hydrogen absorption capacity than the alloy of Comparative Example 2. Calculations made from the graph shown in Figure 25 showed that the alloy of Example 3 absorbed 0.5 wt% hydrogen relative to the weight of the alloy.

Figure 26 is a graph showing the amount of hydrogen released from the alloy of Example 3, which is a modified example in which the substrate of the alloy is changed to Al and the thickness of the alloy is changed to about 1 μm. Here, the sample was heated from room temperature to 200°C at a heating rate of 10°C/min, and then held at 200°C for 5 minutes. As shown in Figure 26, when the temperature of the alloy of the modified example of Example 3 is increased, hydrogen is gradually released from about 100°C, and the amount of hydrogen released increases as the temperature increases to about 150°C. Also, as shown in Figure 26, the weight of the alloy decreases as the amount of hydrogen released increases. From this result, it can be seen that the alloy of the modified example of Example 3 can be sufficiently released by heating the alloy to 200°C at a heating rate of 10°C/min and then holding it at 200°C for 5 minutes.

Sixth embodiment

Next, an alloy as Comparative Example 3 of the present invention will be described. The alloy of Comparative Example 3 was produced by magnetron sputtering using Si as the substrate. More specifically, the sputtering was carried out using a mixed powder sintered body having a molar ratio of Al:Fe = 76:24 as the target, with the Ar gas pressure set to 0.183 Pa and the substrate temperature held at 25°C. The alloy of Comparative Example 3 was deposited to a thickness of approximately 250 nm at a deposition rate of 49 nm/min.

Figure 27 is a cross-sectional TEM image of the alloy of Comparative Example 3. Figure 28 is an electron beam diffraction image of the alloy of Comparative Example 3 using a TEM. As shown in Figure 28, the electron beam diffraction image of the alloy of Comparative Example 3 has a structure close to a halo shape, and no spots due to a crystalline structure were confirmed. In other words, it can be seen that the alloy of Comparative Example 3 has a non-crystalline (amorphous) structure. Furthermore, as shown in Figure 27, the columnar structure seen in the alloy of Example 1 shown in Figure 5 could not be confirmed in the alloy of Comparative Example 3.

Figure 29 is a graph showing the results of measuring the hydrogen distribution inside the alloy of Comparative Example 3 after exposing the alloy to the atmosphere at room temperature and pressure. As shown in Figure 29, the alloy of Comparative Example 3 had a smaller amount of hydrogen stored inside than the alloy of Example 1 shown in Figure 10.

Figure 30 is a graph showing the amount of hydrogen released from a modified alloy in which hydrogen was absorbed, in which the base material of the alloy of Comparative Example 3 was changed to Al and the film thickness of the alloy was changed to about 1 μm. In Figure 30, the ion current on the vertical axis corresponds to the amount of hydrogen released from the alloy. The graph shown in Figure 30 shows the measurement results obtained by heating the sample from room temperature to 450°C at a heating rate of 10°C/min under He flow conditions. As shown in Figure 30, in the test using the above modified alloy of the alloy of Comparative Example 3, no hydrogen was released, or even if hydrogen was released, it was below the detection limit.

These results show that alloys that have an amorphous structure but do not form columnar structures, such as the alloy in Comparative Example 3, absorb a small amount of hydrogen at room temperature and pressure, and do not release hydrogen or release very little hydrogen.

Seventh embodiment

Next, an alloy according to Example 4 of the present invention will be described. The alloy according to Example 4 was produced in the same manner as the alloy according to Example 1, except that an alloy consisting of a mixed powder sintered body having a molar ratio of Al:Fe = 90:10 was used as the target.

Figure 31 is a cross-sectional TEM image of the alloy of Example 4. As shown in Figure 31, the alloy of Example 4, like the alloy of Example 1, had white lines at intervals of 30 nm or less on any straight line on a plane parallel to the surface. In other words, the alloy of Example 4 had a structure having regions with a lower density than other regions at intervals of 30 nm or less on any straight line on a plane parallel to the surface. The black regions in the photograph shown in Figure 31 are columnar structures.

Figure 32 is an electron beam diffraction image of the alloy of Example 4 using a TEM. As shown in Figure 32, the alloy of Example 4, like the alloy of Example 1, has a structure close to a halo shape, and no spots due to a crystal structure were confirmed. In other words, it can be seen that the alloy of Example 4 has a non-crystalline (amorphous) structure. However, as shown in Figure 32, the electron beam diffraction image of the alloy of Example 4 does not have a complete halo shape, and a ring-shaped image is observed, so it is thought that it may contain microcrystals with a crystal grain size of less than a few nm (specifically, less than 5 nm).

Figure 33 is a graph showing the results of measuring the hydrogen distribution inside the alloy of Example 4 after exposing it to the atmosphere at room temperature and pressure. As shown in Figure 33, the alloy of Example 4 is similar to the data for the alloy of Example 1 in the graph shown in Figure 10, and it can be seen that it absorbs a large amount of hydrogen like the alloy of Example 1. Since the manner in which hydrogen is absorbed is similar to that of the alloy of Example 1, it is thought that the alloy of Example 4 also releases the absorbed hydrogen when heated.

Eighth embodiment

Next, an alloy as Example 5 of the present invention will be described. The alloy of Example 5 was produced in the same manner as the alloy of Example 1, except that an alloy consisting of a mixed powder sintered body having a molar ratio of Al:Co = 76:24 was used as a target.

Figure 34 is a cross-sectional TEM image of the alloy of Example 5. As shown in Figure 34, the alloy of Example 5, like the alloy of Example 1, had white lines at intervals of 30 nm or less on any straight line on a plane parallel to the surface. In other words, the alloy of Example 5 had a structure having regions with a lower density than other regions at intervals of 30 nm or less on any straight line on a plane parallel to the surface. The black regions in the photograph shown in Figure 34 are columnar structures.

Figure 35 is an electron beam diffraction image of the alloy of Example 5 using a TEM. As shown in Figure 35, the alloy of Example 5, like the alloy of Example 1, has a structure close to a halo shape, and no spots due to a crystal structure were confirmed. In other words, it can be seen that the alloy of Example 5 has a non-crystalline (amorphous) structure. However, as shown in Figure 35, the electron beam diffraction image of the alloy of Example 5 does not have a complete halo shape, and a ring-shaped image is observed, so it is thought that it may contain microcrystals with a crystal grain size of less than a few nm (specifically, less than 5 nm).

Figure 36 is a graph showing the results of measuring the hydrogen distribution inside the alloy of Example 5 after exposing it to the atmosphere at room temperature and pressure. As shown in Figure 36, the alloy of Example 5 is similar to the data for the alloy of Example 1 in the graph shown in Figure 10, and it can be seen that the alloy of Example 5 absorbs a large amount of hydrogen, just like the alloy of Example 1.

Figure 37 is a graph showing the amount of hydrogen released from a modified alloy of Example 5, in which hydrogen was absorbed and the base material was changed to Al and the film thickness of the alloy was changed to about 1 μm. In Figure 37, the ion current on the vertical axis corresponds to the amount of hydrogen released from the alloy. The graph shown in Figure 37 shows the results of measurements taken when the sample was heated from room temperature to 450°C at a heating rate of 10°C/min under He flow conditions. As shown in Figure 37, when the temperature of the alloy of the modified example of Example 5 was increased, hydrogen was gradually released from about 100°C, and the amount of hydrogen released increased as the temperature increased to about 150°C.

<Additional Note: At the time of filing this application, it is impossible or almost impractical to directly identify the "product" according to the present invention by its structure or characteristics>
Because there is a limit to the ability of current science and technology to evaluate the amorphous state and hydrogen storage state of a microscopic region of a hydrogen storage material, it was technically impossible to analyze the structure or characteristics of the "substance" to the extent described in the current claims at the time of filing this application. In addition, in light of the need for speed, etc., due to the nature of patent applications, it would require significantly excessive economic expenditure or time to carry out the work of identifying the structure or characteristics of the substance.

1 Base material 10 Alloy 11 Columnar structure (first columnar body)
12 Columnar structure (second columnar body)
13 First region 14 Second region 100 Hydrogen extraction system 110 Hydrogen storage section 120 Hydrogen release section

Claims (10)

An alloy having a composition of Al _x Fe _1-x (x=0.7 to 0.9), Al _x Co _1-x (x=0.7 to 0.9) or Al _x Mn _1-x (x=0.7 to 0.9),
The alloy is
It is a thin film,
Contains an amorphous structure,
a plurality of first regions in which the alloy has a lower density than other regions;
An alloy, wherein the distance between adjacent first regions is 30 nm or less in a cross section of the alloy cut along a plane perpendicular to a surface of the alloy. The alloy of claim 1, wherein in the cross section, the first region is formed continuously from one surface of the alloy to the other surface. The alloy according to claim 1 or 2, wherein the distance between adjacent first regions is 30 nm or less in a cross section of the alloy cut along a plane parallel to the surface of the alloy. the amorphous structure has a plurality of first columns adjacent to each other with the first region interposed therebetween,
The alloy according to any one of claims 1 to 3, wherein the first columnar body includes a plurality of second columnar bodies adjacent to each other via a second region in which the density of the alloy is lower than that of other regions in the first columnar body. A hydrogen storage part using the alloy according to claim 1 or 2 as a hydrogen storage material;
a hydrogen release section that releases hydrogen from the hydrogen storage section by heating the hydrogen storage section in which hydrogen has been stored. A hydrogen storage material for storing hydrogen,
The alloy includes an alloy having a composition of Al _x Fe _1-x (x=0.7 to 0.9), Al _x Co _1-x (x=0.7 to 0.9), or Al _x Mn _1-x (x=0.7 to 0.9),
The alloy is
It is a thin film,
Contains an amorphous structure,
a plurality of first regions in which the alloy has a lower density than other regions;
A hydrogen storage material, wherein the distance between adjacent first regions is 30 nm or less in a cross section of the alloy cut along a plane perpendicular to a surface of the alloy. The hydrogen storage material according to claim 6, wherein the distance between adjacent first regions is 30 nm or less in a cross section of the alloy cut along a plane parallel to the surface of the alloy. the amorphous structure has a plurality of first columns adjacent to each other with the first region interposed therebetween,
8. The hydrogen storage material according to claim 6, wherein the first columnar body includes a plurality of second columnar bodies adjacent to each other via a second region in which the density of the alloy is lower than that of other regions of the first columnar body. 1. A method for producing an alloy on a substrate, comprising the steps of:
The method for producing an alloy includes an alloy laminating step of laminating an alloy on the base material held at a temperature of 15° C. or higher and lower than 200° C., using a target having a composition of Al:Fe=x:1-x (x=0.7 to 0.9) in a molar ratio, Al:Co=x:1-x (x=0.7 to 0.9) in a molar ratio, or Al:Mn=x:1-x (x=0.7 to 0.9) in a molar ratio. An alloy manufactured by layering a target having a molar ratio of Al:Fe=x:1-x (x=0.7-0.9), Al:Co=x:1-x (x=0.7-0.9), or Al:Mn=x:1-x (x=0.7-0.9) on a substrate maintained at a temperature of 15°C or higher but lower than 200°C.

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