Method for producing hydrogen boride-containing sheet, hydrogen boride-containing sheet, and use of the same

Abstract

To provide a method for producing a hydrogen boride-containing sheet capable of obtaining a hydrogen boride-containing sheet larger than the conventional one, and to provide the hydrogen boride-containing sheet.SOLUTION: The method for producing a hydrogen boride-containing sheet according to an embodiment includes obtaining hydrogen boride by bringing a metal boride into contact with an ion exchange material, and forming a hydrogen boride-containing sheet on a substrate by heating a mixed liquid containing the obtained hydrogen boride and a liquid medium on the substrate.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE The present invention relates to a method for producing a borohydride-containing sheet, a borohydride-containing sheet, and uses thereof. [Background technology]

[0002] Borohydride (HB) n is a material having a structure in which boron atoms form a two-dimensional network via hydrogen atoms, and has attracted attention because it is lightweight and available in abundance (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 074518 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the size of the hydrogen boride sheets synthesized so far has been on the order of 10 μm at most, and larger hydrogen boride sheets are needed for practical use.

[0005] An object of the present invention is to provide a method for producing a boron-containing sheet, which is capable of producing a larger boron-containing sheet than conventional ones, and a boron-containing sheet. [Means for solving the problem]

[0006] The present invention may include the following aspects. [1] A method for producing a borohydride-containing sheet, comprising: contacting a metal boride with an ion exchange material to obtain borohydride; and heating a mixture containing the obtained borohydride and a liquid medium on a substrate to form a borohydride-containing sheet on the substrate. [2] The method of [1], further comprising, prior to heating on the substrate, evaluating the borohydride by analysis of the obtained borohydride. [3] The method according to [2], wherein the evaluation includes determining whether the spectroscopic spectrum of the obtained borohydride includes a peak of sufficient magnitude at a predetermined position. [4] The method according to any one of [1] to [3], wherein the heating on the substrate is carried out at a temperature of the boiling point of the liquid medium (when the liquid medium is heated under a pressure different from atmospheric pressure, such as a reduced pressure, the heating means the boiling point under that pressure; the same applies below) or higher and 200°C or lower. [5] The method according to any one of [1] to [4], further comprising: drying the obtained borohydride after obtaining the borohydride and before heating on the substrate; and mixing the dried borohydride with the liquid medium. [6] The method of [5], wherein drying the obtained borohydride to a powder form comprises heating the obtained borohydride at a first temperature and heating the obtained borohydride at a second temperature greater than the first temperature. [7] A method for producing a borohydride-containing sheet having an increased size, the method comprising heating a mixture containing a raw material including the borohydride-containing sheet and a liquid medium on a substrate. [8] The method according to [7], wherein the heating step includes evaporating the liquid medium on the substrate and further heating the borohydride-containing sheet remaining after the liquid medium has evaporated. [9] A borohydride-containing sheet having a length in at least one direction of 100 μm or more.

[10] The borohydride-containing sheet according to [9], having a flat shape.

[11] The borohydride-containing sheet according to [9] or

[10] , wherein the borohydride content is 10 mass% or more.

[12] A hydrogen storage material, a catalyst, an electronic material, a communication material, an electrode material, or a fuel material, comprising the borohydride-containing sheet according to any one of [9] to

[11] . Effect of the Invention

[0007] According to the present invention, the size of the borohydride-containing sheet can be increased. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a borohydride-containing sheet 10 according to an embodiment. [Diagram 2] 4 is a flowchart showing a method for manufacturing a borohydride-containing sheet according to one embodiment. [Figure 3A] 5A to 5C are schematic diagrams illustrating a process for forming a borohydride-containing sheet according to an embodiment. [Figure 3B] 5A to 5C are schematic diagrams illustrating a process for forming a borohydride-containing sheet according to an embodiment. [Figure 3C] 5A to 5C are schematic diagrams illustrating a process for forming a borohydride-containing sheet according to an embodiment. [Figure 4] 3 is an infrared absorption spectrum of the borohydride produced in Example 1. [Diagram 5] Photograph of the borohydride-containing sheet produced in Example 1. [Figure 6] Photograph of the borohydride-containing sheet produced in Example 1. [Figure 7] 1 is an X-ray diffraction (XRD) pattern of the borohydride-containing sheet produced in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The manufacturing method of the boron-containing sheet and the boron-containing sheet of the embodiment will be described below. Note that the following embodiment shows one aspect of the present invention, does not limit the present invention, and can be arbitrarily changed within the scope of the technical idea of ​​the present invention. In addition, each configuration and each feature of the embodiment can be arbitrarily combined.

[0010] <1. Hydrogen borate-containing sheet> The borohydride-containing sheet according to one embodiment is a borohydride-containing sheet having a length in at least one direction of 100 μm or more.

[0011] The present inventors have found that the method described below can produce a boron-containing sheet having a larger size than the conventional one. The size of the conventionally known boron-containing sheet is at most on the order of 10 μm, and no method has been found for producing a boron-containing sheet having a size of 100 μm or more.

[0012] <1.1 Definition> In this specification, the term "borohydride" refers to a compound of hydrogen and boron. Specifically, borohydride represented by the chemical formula HB is known. Each boron atom (B) is connected to another via a hydrogen atom (H) to form a two-dimensional network. A borohydride that has formed a two-dimensional network can be represented by, for example, the chemical formula (HB) n (n: natural number). The boron hydride may have a two-dimensional network in which boron atoms form a six-membered ring structure to form a continuous honeycomb structure, or may have a two-dimensional network in which boron atoms form other ring structures such as a five-membered ring structure or a seven-membered ring structure.

[0013] In this specification, the term "borohydride-containing sheet" refers to a material that contains borohydride and has a two-dimensionally extending sheet shape. Note that the borohydride-containing sheet is not limited to one that contains only pure borohydride, and may contain borohydride doped with elements other than boron and hydrogen, or other materials.

[0014] The borohydride-containing sheet contains, for example, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more of borohydride. The borohydride-containing sheet may consist essentially of borohydride (it may contain unavoidable impurities).

[0015] <1.2 Shape of borohydride sheet> FIG. 1 is a schematic diagram showing an example of a borohydride-containing sheet 10 according to this embodiment. The borohydride-containing sheet 10 has two main surfaces 12a, 12b located opposite each other, and a side surface 14 connecting the peripheries of the two main surfaces 12a, 12b to each other. In this case, the main surfaces 12a, 12b are flat surfaces along the xy plane, and the side surface 14 is a surface along the z direction. One or both of the main surfaces 12a, 12b have the largest area on the surface of the borohydride-containing sheet 10. As shown in FIG. 1, the borohydride-containing sheet 10 is preferably substantially flat without having a twisted or wavy shape. However, the borohydride-containing sheet does not have to be completely flat, and may have, for example, a gently curved surface partially or entirely. The term "flat shape" as used herein means that the shape of the boron-containing sheet 10 is substantially flat overall, as shown in FIG. 1, and slight irregularities may be present on the main surface or side surfaces of the sheet, and slight warping or distortion may be present on the edges of the sheet.

[0016] The borohydride-containing sheet 10 has a length measured along at least one direction (e.g., length L1 in the x direction in FIG. 1) of 100 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, 300 μm or more, 350 μm or more, 400 μm or more, 450 μm or more, 500 μm or more, 550 μm or more, 600 μm or more, 650 μm or more, 700 μm or more, 750 μm or more, 800 μm or more, 850 μm or more, 900 μm or more, 950 μm or more, or 1 mm or more. Preferably, the boron-containing sheet 10 has lengths measured along two mutually perpendicular directions (e.g., length L1 in the x direction and length L2 in the y direction in FIG. 1 ) of 100 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, 300 μm or more, 350 μm or more, 400 μm or more, 450 μm or more, 500 μm or more, 550 μm or more, 600 μm or more, 650 μm or more, 700 μm or more, 750 μm or more, 800 μm or more, 850 μm or more, 900 μm or more, 950 μm or more, or 1 mm or more. Preferably, the borohydride-containing sheet 10 has a minimum length along major surfaces 12a, 12b of 100 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, 300 μm or more, 350 μm or more, 400 μm or more, 450 μm or more, 500 μm or more, 550 μm or more, 600 μm or more, 650 μm or more, 700 μm or more, 750 μm or more, 800 μm or more, 850 μm or more, 900 μm or more, 950 μm or more, or 1 mm or more.

[0017] By adjusting conditions such as the borohydride concentration in the solution and the size of the vessel in which the borohydride sheet is prepared, the size of the borohydride-containing sheet 10 can be made very large. There is no particular upper limit to the size of the borohydride-containing sheet 10, but for example, the maximum length of the borohydride-containing sheet 10 along the main surfaces 12a and 12b is 10 m.

[0018] The thickness D of the borohydride-containing sheet 10 is not particularly limited as long as it is sufficiently small compared to the two-dimensional spread. For example, the borohydride-containing sheet 10 may be made of one layer of borohydride, or may have a shape in which two or more layers of borohydride are laminated. The upper limit of the number of layers is not particularly limited. For example, the thickness D of the borohydride-containing sheet 10 along a direction perpendicular to the main surfaces 12a and 12b is ¼ or less of the minimum length along the main surfaces 12a and 12b. For example, the thickness D of the borohydride-containing sheet 10 is 1 nm or more and 100 μm or less, 10 nm or more and 50 μm or less, 100 nm or more and 20 μm or less, 500 nm or more and 10 μm or less, or 1 μm or more and 5 μm or less.

[0019] The size of the borohydride-containing sheet 10 can be determined by observing a single piece of borohydride-containing sheet 10 formed as a continuous sheet with an optical microscope or the like and measuring the length of the borohydride-containing sheet 10 along any direction.

[0020] <1.3 Properties of borohydride sheet> The boron hydride constituting the boron hydride-containing sheet 10 according to this embodiment may be amorphous or polycrystalline, or a mixture of these. Therefore, the boron hydride-containing sheet 10 has low reflectance in the visible light region and is transparent to visible light. However, the boron hydride-containing sheet 10 does not completely transmit visible light, but rather absorbs light gradually from a wavelength of about 800 nm, and the absorbance increases sharply from a wavelength of about 500 nm, and absorbs light with a wavelength of 400 nm or less almost completely. As a result, the boron hydride-containing sheet 10 appears yellow in appearance.

[0021] <1.4 Uses of borohydride sheets> The borohydride-containing sheet 10 according to this embodiment can be used as a hydrogen storage material, a catalyst, an electronic material, a communication material, an electrode material, or a fuel material, or as a material constituting such functional materials. This is due to the characteristics of borohydride, such as the inclusion of hydrogen atoms in the structure, being lighter than graphene, and having electrical conductivity on the same order as graphene.

[0022] A hydrogen storage material, catalyst, electronic material, communication material, electrode material, or fuel material according to one embodiment includes the borohydride-containing sheet described above.

[0023] According to the above-mentioned hydrogen boride-containing sheet, the hydrogen boride sheet can be used in a larger area than before. In general, hydrogen boride has the following characteristics: (a) lightweight, (b) abundant resources, (c) no waste load, and (d) recyclable. Due to these characteristics, hydrogen boride has attracted attention as an energy material, and its practical use in hydrogen transportation and CO2 reduction reactions has been confirmed. It is also theoretically predicted that it will show high performance as a battery material and a communication material. The availability of hydrogen boride sheets with a large area makes it easier to implement them in society for multifaceted use. In particular, when the hydrogen boride-containing sheet has a size of 1 mm or more, it becomes easy to handle it by hand, which greatly expands the industrial applicability of the hydrogen boride sheet. In addition, since millimeter waves are used in the 5G and 6G communication bands, the production of hydrogen boride-containing sheets with a size of 1 mm or more as described above is expected to lead to practical use as a communication material for millimeter waves.

[0024] <2. Manufacturing method of borohydride-containing sheet> A method for producing a borohydride-containing sheet according to one embodiment includes the steps of: (1) contacting a metal boride with an ion exchange material to obtain a hydrogen boride; (2) forming a borohydride-containing sheet on a substrate by heating the mixture containing the obtained borohydride and a liquid medium on the substrate; The method includes:

[0025] <2.1 Definition> In this specification, the term "metal boride" refers to a compound of one or more metal elements and boron. For example, metal boride has a structure in which boron atoms form a two-dimensional network. For example, metal boride has a layered structure in which metal cations are inserted between boron layers formed by a two-dimensional network of boron atoms. One example of a metal boride is metal diboride represented by the composition formula MB2. Examples of metal borides include metal diborides such as magnesium diboride (MgB2), aluminum diboride (AlB2), tantalum diboride (TaB2), zirconium diboride (ZrB2), rhenium diboride (ReB2), chromium diboride (CrB2), titanium diboride (TiB2), vanadium diboride (VB2), and yttrium diboride (YB2); multi-metal borides such as yttrium chromium diboride (YCrB4); potassium diboride (K2B9, KB9, KB 18 Metal borides of other compositions include lithium diboride (Li2B5), lithium boride (Li2B5), etc. Most of the metal diborides have a structure in which the boron atoms form six-membered rings, while yttrium chromium diboride (YCrB4) has a structure in which the boron atoms form five- and seven-membered rings.

[0026] As used herein, "ion exchange material" refers to a material that has ion exchange capacity. For example, an ion exchange material contains ions that can be exchanged with metal cations. Preferably, an ion exchange material is capable of exchanging metal cations with protons (H + ) is a material capable of exchanging with the metal boride. Non-limiting examples of ion exchange materials include ion exchange resins. Any ion exchange resin capable of exchanging with the metal boride can be used.

[0027] Non-limiting examples of ion exchange resins include strong acid ion exchange resins and weak acid ion exchange resins. Strong acid ion exchange resins are polymers having sulfo groups (-SO3H) as ion exchange groups. Examples of base materials for such ion exchange resins include styrene polymers, divinylbenzene polymers, and styrene-divinylbenzene copolymers. Weak acid ion exchange resins are polymers having carboxylic acid groups (-COOH) as ion exchange groups. Examples of base materials for such ion exchange resins include acrylic acid (co)polymers and methacrylic acid (co)polymers.

[0028] <2.2 Details of manufacturing method> The present inventors have found that the above method makes it possible to obtain a borohydride-containing sheet having a larger size than conventionally available. Fig. 2 is a flow chart showing a method for producing a borohydride-containing sheet according to Example 1 described later. Fig. 2 includes not only essential steps but also optional steps. Hereinafter, the method will be described in detail with reference to Fig. 2.

[0029] <2.2.1 Step (1) of producing borohydride> First, the above item (1) will be explained. By contacting the metal boride with the ion exchange material, an ion exchange reaction occurs in which the metal cation of the metal boride is converted into a proton (H + ) to form borohydride (HB) n is generated (step S200 in FIG. 2).

[0030] The ion exchange reaction preferably proceeds in a liquid. For example, the ion exchange reaction occurs when the metal boride dissolved in the liquid medium comes into contact with the ion exchange material present in a solid state in the liquid medium at the solid-liquid interface. Any liquid medium can be used as long as the ion exchange reaction proceeds. For example, a liquid medium (such as a polar solvent) capable of dissolving the metal boride can be used. Examples of liquid media include inorganic solvents such as water, and organic solvents such as methanol, ethanol, acetonitrile, and N,N-dimethylformamide.

[0031] The concentration of the metal boride in the reaction solution is not particularly limited, but is preferably 0.01 g / L or more and 500 g / L or less. If the concentration of the metal boride is less than 0.01 g / L, a sufficient amount of hydrogen boride may not be obtained. If the concentration of the metal boride is more than 500 g / L, excessive aggregation of the product may occur, and a sheet-like product may not be obtained.

[0032] Preferably, during or after the ion exchange reaction, residues such as ion exchange resin and impurities such as reaction by-products (e.g., boric acid) are removed (step S202 in FIG. 2). The removal method is not particularly limited, and any method such as filtration, extraction, chromatography, recrystallization, and adsorption can be used. The removal of residues and impurities may be performed at any timing, and may be performed in multiple steps.

[0033] If the generated borohydride is dissolved or dispersed in a liquid medium (hereinafter, borohydride dissolved or dispersed in a liquid medium will be referred to simply as the "sample solution"), one may proceed to (2) without going through the step indicated by the dashed line in FIG. 2, or one may first remove the liquid medium to obtain solid borohydride. By removing the liquid medium by any method such as heating or reducing pressure, a dried powder of borohydride can be obtained (step S204 in FIG. 2). If a volatile liquid is used as the liquid medium, it may be left at room temperature.

[0034] When the liquid medium is removed by one-stage heating, the heating temperature is preferably equal to or higher than the boiling point of the liquid medium (e.g., 70°C or higher, 80°C or higher, 90°C or higher, or 100°C or higher) and equal to or lower than 200°C. If the heating temperature is lower than the boiling point of the liquid medium, the liquid medium may not be sufficiently vaporized. If the heating temperature exceeds 200°C, hydrogen in the borohydride may be desorbed.

[0035] In the heat treatment, only one heating step may be performed as described above, but multiple heating steps may be performed as shown in FIG. 2 and in Example 1 described later. Hereinafter, multiple heating steps as in Example 1 will be described. For example, as shown in FIG. 2, the heat treatment in step S204 includes step S204a in which the obtained borohydride is heated at a first temperature, and step S204b in which the obtained borohydride is heated at a second temperature higher than the first temperature. In step S204a, most of the liquid medium is vaporized, and in step S204b, the liquid medium remaining in the sample is further vaporized to dry the sample. By gradually increasing the temperature in multiple steps in this manner, impurities that precipitate during heating can be efficiently separated. The first temperature is not particularly limited as long as it can promote the vaporization of the liquid medium, and is, for example, 0° C. to 200° C., 20° C. to 150° C., or 70° C. to 100° C. The heating time at the first temperature is not particularly limited, and heating can be performed until most of the liquid medium is vaporized and there is no liquid component in appearance. In the first heating step S204b, since it is sufficient to dry the sample, natural evaporation without heating or a drying method such as decompression may be used. Heating and drying methods may be used in combination. The second temperature is preferably equal to or higher than the boiling point of the liquid medium and equal to or lower than 200°C. If the second temperature is lower than the boiling point of the liquid medium, the liquid medium may not evaporate sufficiently. If the second temperature exceeds 200°C, hydrogen in the borohydride may be desorbed. The heating time at the second temperature is not particularly limited, but is, for example, 1 to 2 hours.

[0036] Prior to (2), the borohydride can be evaluated by analyzing the borohydride obtained (step S206 in FIG. 2). The inventors have found that the quality of the borohydride obtained in (1) can affect whether or not a borohydride sheet is formed in (2) or the size of the borohydride sheet formed. In order to obtain a large borohydride sheet, it is meaningful to evaluate the quality of the borohydride prior to (2). Examples of borohydride evaluation targets include the composition, structure, physical properties, purity, and size of borohydride. For example, it is presumed that the closer the obtained borohydride is to ideal borohydride in terms of composition, chemical structure, crystal structure, physical properties, purity, and the like, the higher the quality of the borohydride sheet obtained. As a result, it is presumed that the growth of the borohydride sheet in (2) is less likely to be inhibited, and a larger borohydride sheet is obtained. It is also presumed that the larger the obtained borohydride is, the larger the borohydride sheet is obtained. Note that samples that are evaluated as inappropriate can be reused as samples for resynthesis.

[0037] Here, as an example, the evaluation of borohydride by spectroscopic measurement, which will be described in Example 1 below, will be described in detail. For example, the evaluation of borohydride by spectroscopic measurement includes determining whether or not the spectroscopic spectrum of the obtained borohydride contains a peak at a predetermined position. Specifically, in Example 1, the infrared absorption spectrum of the obtained borohydride contains a peak at 1380 cm -1 In addition to the nearby peak, there is a peak at 1280 cm -1 This peak is attributed to the BHB bond, and the peak position depends on the boron-boron distance. -1 It has been discovered that if even a small amount of nearby absorption peak appears, a larger borohydride-containing sheet than before can be obtained. However, the spectroscopic measurement is not limited to infrared absorption spectrum measurement, and the peaks for confirmation are not limited to the above peaks. Any spectroscopic feature characteristic of borohydride can be used to evaluate borohydride.

[0038] One of the reasons for drying the borohydride before step (2) is to facilitate analysis and evaluation of the borohydride. Another reason is to facilitate the removal of impurities. That is, if impurities are still mixed in the dried borohydride, they can be easily separated from the borohydride by separating them during re-dissolution using differences in solubility, or by classifying them in the dry state.

[0039] As described above, when the obtained borohydride is dried, after performing necessary operations such as the above analysis, the dried borohydride is mixed with a liquid medium to obtain a sample solution in which the borohydride is dissolved or dispersed in the liquid medium, and the process proceeds to (2) (step S208 in FIG. 2). Here, the liquid medium used may be the same liquid medium as that used in the previous step, or may be a different liquid medium. In addition, the amount of borohydride in the sample solution after redissolution or redispersion is not particularly limited, but is preferably 1 mg or more and 10 g or less. If the amount of borohydride is less than 1 mg, a borohydride-containing sheet of sufficient size may not be obtained. If the amount of borohydride is more than 10 g, excessive aggregation of the borohydride may occur, and a clean borohydride-containing sheet may not be obtained.

[0040] <2.2.2 Step (2) of forming a borohydride sheet on a substrate> Next, the above item (2) will be explained. In (2), in order to form a borohydride-containing sheet on a substrate, a sample solution is filled onto the substrate (step S210 in FIG. 2), and then the liquid solvent is evaporated to form a borohydride-containing sheet on the substrate (step S212 in FIG. 2).

[0041] The type of substrate is not particularly limited. Substrates of any shape, material, and size can be used as long as they have a flat surface for forming a borohydride-containing sheet. Non-limiting examples of substrates include glass substrates, silicon substrates, mica substrates, HOPG (highly oriented pyrolytic graphite) substrates, SiC substrates, SiO2 substrates, meshes made of stainless steel or nickel (preferably meshes with a mesh hole size smaller than the size of the desired borohydride-containing sheet. For example, meshes on the order of 1 mm or smaller may be used). Note that any of the substrates may or may not have a coating such as an oxide film. In addition, the "substrate" in this specification is not limited to an independent plate-like member, but may be a flat portion that constitutes a part of a member having a predetermined shape such as a container.

[0042] The method of filling the substrate with the sample solution is not particularly limited. For example, the substrate may be placed on a horizontal table and the sample solution may be pipetted onto the substrate. Any coating method such as spin coating, dip coating, bar coating, spray coating, etc. may be used. Here, the method adopted in Example 1 described later will be described in detail with reference to FIG. 3.

[0043] First, as shown in FIG. 3A, the substrate 32 is placed on the bottom surface of the container 30. Next, the internal space of the container 30 is filled with the sample solution S. As a result, the substrate 32 is immersed in the sample solution S, and the upper surface of the substrate 32 is filled with the sample solution S. Next, as shown in FIG. 3B, the container 30 is heated to evaporate the liquid medium of the sample solution S. When the heating is continued, eventually, as shown in FIG. 3C, the borohydride in the sample solution S remains on the upper surface of the substrate 32, and a large-area borohydride-containing sheet is formed on the substrate 32. According to this method, compared to pipetting, it is possible to suppress the bias of the borohydride on the substrate 32, and the uniformity of the borohydride-containing sheet formed can be improved. In addition, compared to the above-mentioned coating method, it is possible to fill the upper surface of the substrate 32 with a sufficient amount of borohydride, so that a large borohydride-containing sheet can be formed.

[0044] The heating temperature is preferably equal to or higher than the boiling point of the liquid medium (for example, 70°C or higher, 80°C or higher, 90°C or higher, or 100°C or higher) and equal to or lower than 200°C. If the heating temperature is lower than the boiling point of the liquid medium, the liquid medium may not evaporate sufficiently. If the heating temperature exceeds 200°C, hydrogen in the borohydride may be desorbed. It is preferable to continue heating after the liquid medium has completely evaporated. The heating time is not particularly limited, but may be, for example, 1 to 2 hours after the liquid medium has completely evaporated.

[0045] Finally, the borohydride-containing sheet 10 formed on the substrate 32 is collected. The collection method is not particularly limited. For example, the borohydride-containing sheet 10 may be physically peeled off from the substrate 32. A coating of a material to which the borohydride-containing sheet 10 does not easily adhere may be provided on the substrate 32 in advance. A peeling film that is easy to peel off may be provided on the substrate 32 in advance, and the borohydride-containing sheet 10 may be collected from the substrate 32 by peeling off the film. Alternatively, the borohydride-containing sheet 10 may be used in a state where it is adhered to the substrate 32. The borohydride-containing sheet 10 can be collected from the substrate 32 by any other method. Instead of using a substrate 32 separate from the container 30, the flat surface (bottom surface, side surface, etc.) of the container 30 may be used as the substrate 32.

[0046] As described above, by heating the mixture containing borohydride and a liquid medium on a substrate, a borohydride-containing sheet having a larger area than the conventional one can be formed on the substrate. The following is a speculation mechanism by which such a large area is realized. However, the following is merely speculation, and the present invention is not limited by theory. Hydrogen boride produced by the ion exchange reaction of metal boride has a nanosheet shape with a thickness of about several atomic layers. In the sample solution, it is assumed that the hydrogen boride nanosheets exist separately in a solvated state. Here, hydrogen boride (HB) is generally referred to as nIn the case of , all the outermost electrons of the boron atom and the hydrogen atom are used for covalent bonds, so there is no intermolecular interaction via a non-shared electron pair. For this reason, it is speculated that in the vicinity of the substrate, the interaction between the hydrogen boride nanosheet and the substrate surface is more dominant than the interaction between the hydrogen boride nanosheets themselves. In addition, in the interaction between the hydrogen boride nanosheet and the substrate surface, since the hydrogen boride nanosheet itself has a two-dimensional sheet shape, it is considered that the interaction between the sheet surface of the hydrogen boride nanosheet and the substrate surface is greater than the interaction between the end of the hydrogen boride nanosheet and the substrate surface. For this reason, it is speculated that in the vicinity of the substrate, the hydrogen boride nanosheet tends to stick to the substrate surface so that the sheet surface and the substrate surface are approximately parallel. In fact, according to the study by the present inventors, it was confirmed that a hydrogen boride-containing sheet along the substrate surface was formed not only when the substrate was placed horizontally, but also when the substrate was placed vertically. After the substrate surface is covered with hydrogen boride nanosheets, the direct interaction between the hydrogen boride nanosheets in the sample solution and the substrate surface is thought to be reduced, but in this case, it is presumed that the next dominant interaction is the interaction between the hydrogen boride nanosheets themselves. For this reason, it is thought that other hydrogen boride nanosheets will pile up on top of the hydrogen boride nanosheets attached to the substrate.

[0047] Because the size of the substrate is larger than the size of each hydrogen boride nanosheet, a hydrogen boride sheet larger than the original hydrogen boride nanosheet is formed on the substrate surface. Here, it is believed that the heating of the sample solution and substrate causes chemical bonds to form between the hydrogen boride nanosheets stacked on the substrate (both in the direction along the substrate and in the stacking direction perpendicular to the substrate surface). In this way, it is presumed that the hydrogen boride nanosheets bond to each other along the substrate surface to form a hydrogen boride sheet, resulting in the formation of a large-area hydrogen boride-containing sheet that cannot be achieved by simple growth in solution alone.

[0048] The size of the borohydride-containing sheet can also be adjusted by varying the size of the substrate used.

[0049] According to the above-mentioned method for producing a hydrogen boride-containing sheet, a hydrogen boride-containing sheet having a larger area than the conventional one can be produced. The size of the conventional hydrogen boride sheet was at most 10 μm×10 μm, but according to the present method, a hydrogen boride sheet of the order of 100 μm×100 μm, 1 mm×1 mm, or even larger can be formed. In other words, the area of ​​the hydrogen boride sheet that can be produced by the present method has increased by more than 100 times.

[0050] Furthermore, when boron is evaluated by analysis, it is possible to predict whether or not a large-area boron-containing sheet can be formed based on objective criteria, and therefore large-area boron-containing sheets can be produced with good reproducibility.

[0051] <3. Manufacturing method of borohydride-containing sheet with increased size> In one embodiment, a method for producing an increased size borohydride-containing sheet is a method that includes heating a mixture containing a raw material including a borohydride-containing sheet and a liquid medium on a substrate.

[0052] The method of 2 above is carried out by synthesis of borohydride by ion exchange reaction, but the method of producing a borohydride-containing sheet with an increased size according to the present embodiment is a method of producing a borohydride-containing sheet with an increased size compared to the borohydride-containing sheet of the raw material starting from a borohydride-containing sheet. For example, the borohydride-containing sheet obtained by this method has a larger sheet surface area compared to the borohydride-containing sheet of the raw material. In this method, the raw material containing the borohydride-containing sheet is dissolved or dispersed in a liquid medium, and then steps S210 and S212 in FIG. 2 are performed. As a result, the borohydride-containing sheets of the raw material are stacked on the substrate and bonded to each other, similar to the method of 2 above. As a result, a borohydride-containing sheet of a size larger than the raw material is formed on the substrate.

[0053] Heating the sample solution includes evaporating the liquid medium on the substrate and further heating the borohydride-containing sheet remaining after the liquid medium has evaporated. The heat treatment has the significance of both evaporating the liquid medium to dry the borohydride-containing sheet and bonding the borohydride nanosheets together to form a large-area borohydride-containing sheet. EXAMPLES

[0054] The present invention will be described below with reference to experimental examples, but the present invention is not limited to the following experimental examples.

[0055] <Example 1> Under an inert gas atmosphere, 1 g of magnesium boride MgB2 crystals (manufactured by Rare Metallic Co., Ltd.) was added to 200 mL of acetonitrile (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and dissolved. Next, 30 mL of ion exchange resin (product name Amberlite IR120B H HG, manufactured by Organo Co., Ltd.) was added to the above acetonitrile solution. After stirring this magnesium boride solution at room temperature for 72 hours, the residue in the reaction solution was filtered to obtain a yellow filtrate. The filtrate was heated at 70°C for 2 hours to evaporate the acetonitrile and obtain a yellow candy-like sample. Note that impurities precipitated during heating were appropriately removed. Next, the obtained sample was further heated at 120°C for 2 hours to obtain a yellow dry powder sample.

[0056] Infrared spectroscopy was performed on a portion of the powder sample. The infrared absorption spectrum is shown in Figure 4. -1 An absorption peak was confirmed near 1380 cm. This absorption peak corresponds to the boron-hydrogen bond. -1 Since a sufficiently large absorption peak was confirmed based on the absorption peak of the borohydride, it was determined that a suitable borohydride sample had been obtained.

[0057] 100 mg of the powder sample was dissolved again in 4 mL of acetonitrile to prepare a sample solution S. As shown in FIG. 3A, a flat glass substrate 32 was placed on the bottom of a container 30, and the sample solution S was poured into the container 30. The sample solution S was heated at 70° C. to completely evaporate the acetonitrile. Then, the sample solution S was heated at 120° C. for 2 hours, forming a borohydride-containing sheet 10 on the substrate 32 as shown in FIG. 3C. The borohydride-containing sheet 10 was then peeled off from the substrate 32 with a micro spatula to obtain a target sample. Note that the target sample was not formed continuously over the entire size of the substrate 32, but was divided into small segments by cracks. Each of these segments was a single borohydride-containing sheet 10. FIG. 5 is a photograph of the obtained sample, and FIG. 6 is a photograph of one of the samples shown in FIG. 5 taken.

[0058] <Evaluation Example 1: Evaluation of sample size> The obtained samples were flat sheet-like samples of various sizes. The obtained samples were observed under an optical microscope to evaluate the size of the samples. Most of the obtained samples were 100 μm or more in all directions along the main surface of the sheet. As shown in FIG. 6, the largest of the obtained samples had a length of 1 mm or more (approximately 2 mm) in multiple directions along the main surface. The thickness along the direction perpendicular to the main surface was approximately 50 μm. When the surfaces of the obtained samples were observed under a scanning electron microscope (SEM), no cracks were observed and a very clean surface was observed.

[0059] <Evaluation Example 2: Measurement of X-ray diffraction (XRD) pattern> Figure 7 shows the XRD pattern of the obtained sample. A known borohydride-like pattern was confirmed. However, the peaks in the XRD pattern were very broad, suggesting that the sample was polycrystalline with very small crystallite sizes, or substantially amorphous (e.g., fine crystallites randomly scattered in an amorphous structure).

[0060] <Example 2> In Example 1, the sample was completely dried once after the reaction and then redissolved in a solvent, but in Example 2, it was confirmed that the borohydride-containing sheet 10 could be obtained even if the drying and redissolving steps were omitted. Specifically, magnesium boride MgB2 and ion exchange resin were reacted in acetonitrile in the same manner as in Example 1, and then residues and impurities were appropriately removed to obtain a reaction liquid containing acetonitrile as a solvent. Next, the obtained reaction liquid was heated at 70°C to completely vaporize acetonitrile. After that, the sample was further heated at 120°C for 2 hours, and the borohydride-containing sheet 10 was obtained without going through the drying and redissolving steps.

[0061] <Comparative Example 1> 1280 cm in the above infrared spectrum -1 It was confirmed that the absorption peak in the vicinity changes depending on the experimental conditions, the amount of impurities, and other accidental conditions. -1 When the nearby absorption peak was small or when the peak was not observed, the boron-containing sheet 10 exceeding 1 mm was not obtained. Therefore, the above-mentioned evaluation by infrared spectrum can be an index for obtaining a boron-containing sheet 10 having a large size. [Explanation of symbols]

[0062] 10... borohydride-containing sheet, 12... main surface, 14... side surface, 30... container, 32... substrate, S... sample solution

Claims

1. A method for producing a borohydride-containing sheet, comprising: contacting a metal boride with an ion exchange material to obtain a borohydride; forming a borohydride-containing sheet on a substrate by heating the mixture containing the borohydride and a liquid medium on the substrate; A method comprising:

2. and evaluating the borohydride by analysis of the resulting borohydride prior to heating on the substrate. The method of claim 1.

3. The evaluation includes determining whether the obtained spectroscopic spectrum of the borohydride includes a peak of sufficient magnitude at a predetermined position. The method of claim 2.

4. The heating on the substrate is performed at a temperature equal to or higher than the boiling point of the liquid medium and equal to or lower than 200° C. The method according to any one of claims 1 to 3.

5. After obtaining the borohydride and before heating on the substrate, drying the resulting borohydride; and mixing the dried borohydride with the liquid medium; The method of any one of claims 1 to 3, further comprising:

6. Drying the obtained borohydride into a powder form includes: heating the resulting borohydride at a first temperature; heating the resulting borohydride at a second temperature greater than the first temperature; The method of claim 5 , comprising:

7. 1. A method for producing a borohydride-containing sheet of increased size, comprising: A method comprising heating a mixture comprising a liquid medium and a feedstock comprising a borohydride-containing sheet on a substrate.

8. The heating is allowing the liquid medium to evaporate on the substrate; Further heating the borohydride-containing sheet remaining after the liquid medium has evaporated; The method of claim 7, comprising:

9. A borohydride-containing sheet having a length in at least one direction of 100 μm or more.

10. 10. The borohydride-containing sheet of claim 9 having a flat shape.

11. The borohydride-containing sheet according to claim 9 or 10, wherein the borohydride content is 10 mass% or more.

12. A hydrogen storage material, a catalyst, an electronic material, a communication material, an electrode material, or a fuel material, comprising the borohydride-containing sheet according to claim 9 or 10.

Images