Metal-supported two-dimensional borohydride sheet-containing substance, and method for producing metal-supported two-dimensional borohydride sheet-containing substance

Abstract

This method for producing a metal-supported two-dimensional borohydride sheet-containing substance comprises: a step for dispersing a two-dimensional borohydride sheet in water to prepare a first dispersion; a step for adding a hydroxide containing an alkali metal or a group 2 element to the first dispersion, to prepare a second dispersion having a pH of 4-9; and a step for concentrating and drying the second dispersion to obtain a product.

Description

Metal-supported two-dimensional borohydride sheet-containing material, and method for producing metal-supported two-dimensional borohydride sheet-containing material

[0001] The present invention relates to a metal-supported two-dimensional borohydride sheet-containing material and a method for producing the metal-supported two-dimensional borohydride sheet-containing material. This application claims priority to Japanese Patent Application No. 2024-006959, filed on January 19, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, new functional phenomena have been discovered in materials in which atoms form two-dimensional networks (hereinafter referred to as "atomic network materials"), and atomic network materials have attracted attention for their potential as functional materials.

[0003] Two-dimensional borohydride sheet-containing materials, a type of atomic network material, have been reported by theoretical calculations to exhibit excellent performance as battery electrodes when some of the hydrogen atoms are substituted with alkali metals (see, for example, Non-Patent Documents 1 to 4). Theoretical calculations show that two-dimensional borohydride sheet-containing materials are flat materials with no edges that extend to infinity.

[0004] Z. Wang, T. Zhao, J. Yao, Y. Kishikawa, M. Takei, Evaluation of the Electrochemical Characterizations of Lithium-Ion Battery (LIB) Slurry with 10 Electrical Equivalent Circuit (EEC), Journal of The Electrochemical Society, 164(2), 2017, A8-A17. Xiaoming Zhang, Jumping Hu, Yingchun Cheng, Hui Ying Yang, Yugui Yao, Shengyuan A. Yang, “Borophene as an extremely high capacity electron material for Li-ion and Na-ion “batteries”, Nanoscale, 2016, 8, 15340. Lele Li, Hong Zhang, Xinlu Cheng, “The high hydrogen storage capacities of Li-decorated borophene”, Computational Materials Science 137 (2017) 119-124. Sandip Haldar, Sankha Mukherjeea, Chandra Veer Singh, “Hydrogen storage in Li, Na and Ca decorated and defective Borophene: a first principles study”, RSC Adv. 2018, 8, 20748.

[0005] However, in the conventional technology, it is necessary to prepare an ion exchange resin containing the metal to be introduced into the two-dimensional borohydride sheet, and it is not possible to quantitatively control the amount of metal introduced.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a method for producing a metal-supported two-dimensional borohydride sheet-containing material, which allows quantitative control of the amount of metal introduced and easily produces a metal-supported two-dimensional borohydride sheet-containing material.

[0007] The present invention has the following aspects. [1] A method for producing a metal-loaded two-dimensional borohydride sheet-containing material, comprising the steps of: dispersing a two-dimensional borohydride sheet in water to prepare a first dispersion; adding a hydroxide containing an alkali metal or a Group 2 element to the first dispersion to prepare a second dispersion having a pH of 4 to 9; and concentrating and drying the second dispersion to obtain a product. [2] The method for producing a metal-loaded two-dimensional borohydride sheet-containing material according to [1], wherein the pH of the second dispersion is 6.5 to 7.5. [3] The product is a metal-loaded two-dimensional borohydride sheet-containing material comprising (M ｘ H １－ｘ B) ｎ (M is an alkali metal atom or a Group 2 element, H is a hydrogen atom, B is a boron atom, 0.01≦x<1, n≧6), wherein the B is arranged in a hexagonal ring, and the hexagons formed by the B have a mesh-like two-dimensional network formed by connecting the hexagons, and at least the M and the B are bonded by a three-center two-electron bond, a two-center two-electron bond, or an ionic bond. [1] The method for producing a metal-loaded two-dimensional borohydride sheet-containing material according to [2] or [3].

[0008] According to the present invention, it is possible to provide a method for producing a metal-supported two-dimensional borohydride sheet-containing material, which allows quantitative control of the amount of metal introduced and easily produces a metal-supported two-dimensional borohydride sheet-containing material.

[0009] FIG. 1 is a schematic diagram showing the molecular structure of a metal-supported two-dimensional borohydride sheet-containing substance according to one embodiment of the present invention. FIG. 2 is a diagram showing the relationship between the amount of sodium hydroxide aqueous solution added and the pH of the dispersion in Example 1. FIG. 3 is a diagram showing the results of X-ray diffraction measurement of the product obtained in Example 1. FIG. 4 is a diagram showing the results of infrared spectroscopy of the product obtained in Example 1. FIG. 5 is a diagram showing the results of thermal desorption spectroscopy of the product obtained in Example 1. FIG. 6 is a diagram showing the results of thermal desorption spectroscopy of the two-dimensional borohydride sheet. FIG. 7 is a diagram showing the results of X-ray photoelectron spectroscopy of the product obtained in Example 1. FIG. 8 is a diagram showing the results of ultraviolet-visible absorption spectroscopy of the product and the two-dimensional borohydride sheet obtained in Example 1. FIG. 9 is a diagram showing the relationship between the amount of sodium hydroxide aqueous solution added and the pH of the dispersion in Example 2. FIG. 10 is a diagram showing the relationship between the amount of sodium hydroxide aqueous solution added and the pH of the dispersion in Example 3. FIG. 11 is a diagram showing the relationship between the amount of sodium hydroxide aqueous solution added and the pH of the dispersion in Example 4. FIG. 12 is a diagram showing the relationship between the amount of sodium hydroxide aqueous solution added and the pH of the dispersion in Example 5. FIG. 13 is a diagram showing the relationship between the amount of sodium hydroxide aqueous solution added and the pH of the dispersion in Example 5. 17 is a diagram showing the relationship between the amount of sodium hydroxide aqueous solution dropped and the pH of the dispersion in Example 6. FIG. 18 is a diagram showing the results of X-ray diffraction measurement of the product obtained in Example 6. FIG. 19 is a diagram showing the results of infrared spectroscopy of the product obtained in Example 6. FIG. 19 is a diagram showing the results of infrared spectroscopy of the product obtained in Example 6, illustrating the change in absorption peak depending on the amount of potassium doped. FIG. 19 is a diagram summarizing the results shown in FIG. 17. FIG. 19 is a diagram showing the results of X-ray photoelectron spectroscopy of the product obtained in Example 6. FIG. 20 is a diagram showing the results of X-ray photoelectron spectroscopy of a two-dimensional borohydride sheet. FIG. 21 is a diagram showing the results of thermal desorption spectroscopy of the product obtained in Example 6.

[0010] The following describes an embodiment of the method for producing a metal-supported two-dimensional boron-hydride sheet-containing material of the present invention. Note that this embodiment is specifically described to better understand the gist of the invention, and does not limit the present invention unless otherwise specified.

[0011] [Metal-supported two-dimensional borohydride sheet-containing material] The metal-supported two-dimensional borohydride sheet-containing material obtained by the method for producing a metal-supported two-dimensional borohydride sheet-containing material according to one embodiment of the present invention is ｘ H １－ｘ B) ｎ (where M is an alkali metal atom or a Group 2 element, H is a hydrogen atom, and B is a boron atom; 0.01≦x<1, n≧6). In the metal-supported two-dimensional borohydride sheet-containing material, the B is arranged in a hexagonal ring, and the hexagons formed by the B are connected to form a mesh-like two-dimensional network. In the metal-supported two-dimensional borohydride sheet-containing material, at least the M and the B are bonded by a three-center two-electron bond, a two-center two-electron bond, or an ionic bond. Hereinafter, the alkali metal atom or Group 2 element may also be referred to as a "metal atom (M)."

[0012] In the metal-supported two-dimensional boron hydrogen sheet-containing material of this embodiment, as shown in Figure 1, boron atoms (B) are arranged in a hexagonal ring like a benzene ring and are present at the vertices of the hexagon, and the hexagons formed by the boron atoms (B) are connected without gaps to form a mesh-like surface structure (two-dimensional network). In the metal-supported two-dimensional boron hydrogen sheet-containing material of this embodiment, the hexagonal mesh formed by the boron atoms (B) refers to, for example, a honeycomb structure.

[0013] As shown in FIG. 1, the metal-supported two-dimensional boron hydrogen sheet-containing material of this embodiment has a site where at least two adjacent boron atoms (B) are bonded to the same metal atom (M). In other words, at least the metal atom (M) and the boron atom (B) are bonded by a three-center two-electron bond. It is preferable that at least the metal atom (M) and the boron atom (B) are randomly bonded by a three-center two-electron bond. Furthermore, as shown in FIG. 1, the metal-supported two-dimensional boron hydrogen sheet-containing material of this embodiment has a site where at least one of the boron atoms (B) is bonded to the metal atom (M). In other words, at least the metal atom (M) and the boron atom (B) are bonded by a two-center two-electron bond. It is preferable that at least the metal atom (M) and the boron atom (B) are randomly bonded by a two-center two-electron bond. The bond between these metal atoms (M) and boron atoms (B) is classified as a bond called an ionic bond when the interaction between ions is dominant, but even in this case, it is preferable that the bond is random.

[0014] In addition, the metal-supported two-dimensional boron hydrogen sheet-containing material of this embodiment may have a site where two adjacent boron atoms (B) are bonded to the same hydrogen atom (H), as shown in FIG. 1 . In other words, the hydrogen atom (H) and the boron atom (B) may be bonded by a three-center two-electron bond. The hydrogen atom (H) and the boron atom (B) may be randomly bonded by a three-center two-electron bond. In addition, the metal-supported two-dimensional boron hydrogen sheet-containing material of this embodiment may have a site where one of the boron atoms (B) is bonded to a hydrogen atom (H), as shown in FIG. 1 . In other words, the hydrogen atom (H) and the boron atom (B) may be bonded by a two-center two-electron bond. The hydrogen atom (H) and the boron atom (B) may be randomly bonded by a two-center two-electron bond.

[0015] The metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment is a thin-film material having a two-dimensional network consisting of boron atoms (B), metal atoms (M), and hydrogen atoms (H). Furthermore, the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment contains almost no metal atoms derived from the metal diboride used in the manufacturing method of the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment described later, or other metal atoms. In the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment, the total number of boron atoms (B), metal atoms (M), and hydrogen atoms (H) forming the above-mentioned mesh-like surface structure is 1,000 or more.

[0016] The bond distance d1 between two adjacent boron atoms (B) shown in Fig. 1 is 0.15 nm to 0.19 nm. Also, the bond distance d2 between two adjacent boron atoms (B) connected via one metal atom (M) (or one hydrogen atom (H)) shown in Fig. 1 is 0.15 nm to 0.19 nm. Also, the bond distance d3 between adjacent boron atoms (B) and hydrogen atoms (H) (or metal atoms (M)) shown in Fig. 1 is 0.12 nm to 0.15 nm.

[0017] The thickness of the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment is 0.1 nm to 1.0 nm. In the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment, the length in at least one direction (e.g., the length in the X or Y direction in FIG. 1) is preferably 100 nm or more. Furthermore, the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment preferably includes a crystalline or amorphous body having a length in at least one direction of 100 nm or more. In the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment, if the length in at least one direction is 100 nm or more, the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment can be effectively used as a hydrogen storage material, a battery electrode material, and the like. The size (area) of the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment is not particularly limited, and can be formed to any size by the manufacturing method of the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment described below.

[0018] The metal-supported two-dimensional borohydride sheet-containing material of this embodiment is a two-dimensional material that has edges and wrinkles that can be seen with a transmission electron microscope.

[0019] Among the metal atoms (M), alkali metal atoms include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Among the metal atoms (M), Group 2 elements include magnesium (Mg), beryllium (Be), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[0020] The metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment is a material having a crystalline structure. Furthermore, in the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment, the bonding strength between the boron atoms (B) forming the hexagonal rings and between the boron atoms (B) and the metal atoms (M) or hydrogen atoms (H) is strong. Therefore, even if the metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment forms a crystal (aggregate) consisting of multiple layers during production, it can be easily cleaved along the crystal plane, similar to graphite, and separated (recovered) as a single layer of two-dimensional sheet.

[0021] The metal-supported two-dimensional borohydride sheet-containing material of this embodiment can provide a hydrogen storage material composed of light elements, unlike conventional hydrogen storage materials that use heavy metals.The metal-supported two-dimensional borohydride sheet-containing material of this embodiment can provide a battery material with excellent performance, different from carbon.

[0022] It has been reported that modifying a boron monoatomic layer with lithium ions can store 13.7% by mass of hydrogen relative to 100% by mass of the total mass of the boron monoatomic layer (see Lele Li, Hong Zhang, Xinlu Cheng, "The high hydrogen storage capacities of Li-decorated borophene", Computational Materials Science 137 (2017) 119-124). Therefore, the metal-supported two-dimensional borohydride sheet-containing material of this embodiment is expected to be used as a new hydrogen storage material that exceeds this. In addition, it is expected to be used as a solid acid catalyst material, a reducing agent functional material, etc.

[0023] It has been reported that modifying a boron monoatomic layer with sodium allows for the storage of 9.0 mass% of hydrogen per 100 mass% of the total mass of the boron monoatomic layer. It has also been reported that modifying a boron monoatomic layer with lithium allows for the storage of 6.8 mass% of hydrogen per 100 mass% of the total mass of the boron monoatomic layer. It has also been reported that modifying a boron monoatomic layer with calcium allows for the storage of 7.6 mass% of hydrogen per 100 mass% of the total mass of the boron monoatomic layer. (See Sandip Haldar, Sankha Mukherjeeea, and Chandra Veer Singh, "Hydrogen storage in Li, Na, and Ca decorated and defective borophene: a first principles study," RSC Adv. 2018, 8, 20748.) Based on the above report, the metal-supported two-dimensional borohydride sheet-containing material of this embodiment is expected to be used as a new hydrogen storage material that surpasses sodium-modified boron monolayers, lithium-modified boron monolayers, and calcium-modified boron monolayers.

[0024] Theoretical research has shown that when borohydride is modified with lithium, 11.57 mass% of hydrogen can be stored relative to 100 mass% of the total mass of the borohydride (see Phys. Chem. Chem. Phys., 2018, 20, 30304-30311). Therefore, the metal-supported two-dimensional boron sheet-containing material of this embodiment is expected to be used as a new hydrogen storage material that surpasses borohydride modified with lithium.

[0025] A monolayer of boron with a honeycomb atomic arrangement provides 5268mAhg of charge to lithium ions. －１ , 1860mAhg for sodium ions －１ It has been reported that lithium has a battery capacity of 372mAhg. －１ (Jingzhen Li, Georges A. Tritsaris, Xiuying Zhang, Bowen Shi, Chen Yang, Shiqi Liu, Jie Yang, Linqiang) Xu, Jinbo Yang, Feng Pan, Efthimios Kaxiras, Jing Lu, “Monolayer Honeycomb Borophene: A Promising Anode Material with a Record Capacity for Lithium-Ion and Sodium-Ion Batteries”, Journal of The Electrochemical Society, 2020 167 090527. The metal-supported two-dimensional boron hydride sheet-containing material of this embodiment is expected to be used as a new electrode material that surpasses boron monolayers and graphite with honeycomb-structured atomic arrangements.

[0026] Boron monolayers with a structure called β12 and X ３ The boron monolayer structure, called －１ The battery capacity is 19841240mAhg for sodium ions. －１(See Xiaoming Zhang, Junping Hu, Yingchun Cheng, Hui Ying Yang, Yugui Yao, Shengyuan A. Yang, "Borophene as an extremely high capacity electrode material for Li-ion and Na-ion batteries", Nanoscale, 2016, 8, 15340.) Therefore, the metal-supported two-dimensional borohydride sheet-containing material of this embodiment is expected to exhibit a battery capacity of 1000 kJ / cm² (see, for example, Xiaoming Zhang, Junping Hu, Yingchun Cheng, Hui Ying Yang, Yugui Yao, Shengyuan A. Yang, "Borophene as an extremely high capacity electrode material for Li-ion and Na-ion batteries", Nanoscale, 2016, 8, 15340). ３ It is expected that this material will be used as a new electrode material that surpasses the boron monolayer structure known as a "layer structure."

[0027] [Method for producing a metal-loaded two-dimensional borohydride sheet-containing material] A method for producing a metal-loaded two-dimensional borohydride sheet-containing material according to one embodiment of the present invention comprises the steps of dispersing a two-dimensional borohydride sheet in water to prepare a first dispersion (hereinafter referred to as the "first step"), adding a hydroxide containing an alkali metal or a Group 2 element to the first dispersion to prepare a second dispersion having a pH of 4 or more and 9 or less (hereinafter referred to as the "second step"), and concentrating and drying the second dispersion to obtain a product (hereinafter referred to as the "third step").

[0028] "First Step" In the first step, a two-dimensional boron hydride sheet is added to water, and the water and the two-dimensional boron hydride sheet are stirred and mixed to disperse the two-dimensional boron hydride sheet in water, thereby preparing a first dispersion.

[0029] As the water, it is preferable to use distilled water.

[0030] The content of the two-dimensional borohydride sheet in the first dispersion is preferably 0.001 g / L to 2 g / L, more preferably 0.01 g / L to 1.5 g / L, and even more preferably 0.1 g / L to 1.2 g / L. If the content of the two-dimensional borohydride sheet is less than the lower limit, it takes a long time to dry in the subsequent process. If the content of the two-dimensional borohydride sheet exceeds the upper limit, it becomes difficult to stir.

[0031] When dispersing the two-dimensional borohydride sheet in water, the temperature of the water is preferably 10° C. or more and 50° C. or less. The time for stirring the water and the two-dimensional borohydride sheet is not particularly limited.

[0032] The first step is to remove nitrogen (N ２ It is preferable to carry out the reaction in an inert atmosphere of an inert gas such as nitrogen (N) or argon (Ar).

[0033] Here, a method for producing a two-dimensional borohydride sheet will be described.

[0034] "Method for manufacturing two-dimensional borohydride sheet" The method for manufacturing two-dimensional borohydride sheet is MB ２ The method includes a step (hereinafter referred to as "Step A") of mixing, in a polar organic solvent, a metal diboride having a tetrahydrofuran structure and an ion exchange resin in which metal ions constituting the metal diboride are coordinated with exchangeable ions.

[0035] MB ２ As the metal diboride having the hexagonal ring structure, one having a hexagonal ring structure is used, for example, aluminum diboride (AlB ２ ), magnesium diboride (MgB ２ ), tantalum diboride (TaB ２ ), zirconium diboride (ZrB ２ ), rhenium diboride (ReB ２ ), chromium diboride (CrB ２ ), titanium diboride (TiB ２ ), vanadium diboride (VB ２ Magnesium diboride is preferably used because it can easily undergo ion exchange with an ion exchange resin in a polar organic solvent.

[0036] The ion exchange resin in which ion-exchangeable ions are coordinated with metal ions constituting the metal diboride is not particularly limited, but examples thereof include a styrene polymer having a functional group (hereinafter referred to as "functional group α") in which ion-exchangeable ions are coordinated with metal ions constituting the metal diboride, a divinylbenzene polymer having the functional group α, and a copolymer of styrene having the functional group α and divinylbenzene having the functional group α. Examples of the functional group α include a sulfo group and a carboxyl group. Among these, a sulfo group is preferred because it can easily perform ion exchange with the metal ions constituting the metal diboride in a polar organic solvent.

[0037] The polar organic solvent is not particularly limited, and examples thereof include acetonitrile, N,N-dimethylformamide, etc. Among these, acetonitrile is preferred because it does not contain oxygen.

[0038] In step A, a metal diboride and an ion exchange resin are introduced into a polar organic solvent, and the mixed solution containing the polar organic solvent, the metal diboride, and the ion exchange resin is stirred to bring the metal diboride and the ion exchange resin into sufficient contact with each other. This causes ion exchange between the metal ions constituting the metal diboride and the ions of the functional group α of the ion exchange resin, resulting in the production of a two-dimensional hydrogen boride sheet having a two-dimensional network formed by boron atoms and atoms derived from the functional group α of the ion exchange resin.

[0039] For example, if magnesium diboride is used as the metal diboride and an ion exchange resin having a sulfo group is used as the ion exchange resin, the magnesium ions (Mg ＋ ) and hydrogen ions (H ＋ ) to form two-dimensional borohydride-containing sheets having a two-dimensional network of boron atoms (B) and hydrogen atoms (H) as described above.

[0040] In step A, it is preferable to gently proceed with the ion exchange reaction between the metal ions constituting the metal diboride and the ions of the functional group α of the ion exchange resin without applying ultrasound or the like to the mixed solution.

[0041] When the mixed solution is stirred, the temperature of the mixed solution is preferably 15° C. to 35° C. The time for stirring the mixed solution is not particularly limited, but is, for example, 700 to 7000 minutes.

[0042] Step A is nitrogen (N ２ It is preferable to carry out the reaction in an inert atmosphere of an inert gas such as nitrogen (N) or argon (Ar).

[0043] Next, the mixed solution after stirring is filtered (step B). The method for filtering the mixed solution is not particularly limited, and for example, natural filtration, reduced pressure filtration, pressure filtration, centrifugal filtration, etc. are used. In addition, as the filter material, for example, filter paper based on cellulose, membrane filter, filter plate made by compression molding cellulose or glass fiber, etc., etc. are used.

[0044] The solution containing the product, which is separated from the precipitate by filtration, is then dried naturally or by heating to finally obtain the product alone, which is a two-dimensional borohydride sheet having a two-dimensional network formed by boron atoms and atoms derived from the functional group α of the ion exchange resin.

[0045] "Second Step" In the second step, a hydroxide containing an alkali metal or a Group 2 element is added to the first dispersion obtained in the first step to prepare a second dispersion having a pH of 4 or more and 9 or less. The pH of the second dispersion is preferably 4 or more and 7 or less. To prepare the second dispersion, an aqueous solution in which the hydroxide is dispersed in water is added dropwise to the first dispersion.

[0046] Examples of hydroxides containing alkali metals include sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), rubidium hydroxide (RbOH), and cesium hydroxide (CsOH). Examples of salts containing Group 2 elements include calcium hydroxide (Ca(OH) ２ ), magnesium hydroxide (Mg(OH) ２ ), barium hydroxide (Ba(OH) ２ ), strontium hydroxide (Sr(OH) ２ ), beryllium hydroxide (Be(OH)２ ) etc.

[0047] The concentration of the hydroxide containing an alkali metal or a Group 2 element in the second dispersion is preferably 0.01 mol / L to 2.0 mol / L, more preferably 0.1 mol / L to 1.5 mol / L, and even more preferably 0.5 mol / L to 1.2 mol / L. If the concentration of the hydroxide containing an alkali metal or a Group 2 element is less than the lower limit, the amount of solvent used will increase. If the concentration of the hydroxide containing an alkali metal or a Group 2 element exceeds the upper limit, it will be difficult to precisely control the pH.

[0048] While measuring the pH of the second dispersion with a pH test paper or a pH meter, the amount of the aqueous solution dropped onto the dispersion is adjusted so that the pH of the second dispersion becomes a predetermined value.

[0049] The temperature when preparing the second dispersion is preferably 10°C or higher and 50°C or lower.

[0050] The second step is to add nitrogen (N ２ It is preferable to carry out the reaction in an inert atmosphere of an inert gas such as nitrogen (N) or argon (Ar).

[0051] "Third Step" In the third step, the second dispersion obtained in the second step is concentrated and dried to obtain a product. The obtained product is the above-mentioned metal-supported two-dimensional borohydride sheet-containing material.

[0052] Examples of methods for concentrating and drying the second dispersion include vacuum drying and reduced pressure drying.

[0053] "Fourth Step" The method for producing a metal-supported two-dimensional borohydride sheet-containing material of this embodiment may include a fourth step. In the fourth step, the second dispersion obtained in the second step is separated by liquid-phase chromatography. Specifically, the second dispersion obtained in the second step is separated by liquid-phase chromatography using silica gel as the stationary phase and a mixture of methanol and chloroform as the mobile phase to remove impurities and obtain a purified metal-supported two-dimensional borohydride sheet-containing material.

[0054] The solution containing the metal-supported two-dimensional borohydride sheet-containing material recovered by separation using liquid phase chromatography is dried naturally or dried by heating to finally obtain only the metal-supported two-dimensional borohydride sheet-containing material.

[0055] Examples of analytical methods for the product obtained by the method for producing a metal-supported two-dimensional boron-hydride sheet-containing material of this embodiment include X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), and energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) performed within a transmission electron microscope.

[0056] In X-ray photoelectron spectroscopy (XPS), for example, an X-ray photoelectron spectrometer (trade name: JPS9010TR) manufactured by JEOL Ltd. is used to irradiate the surface of the product with X-rays and measure the energy of the photoelectrons generated, thereby analyzing the constituent elements of the product and their electronic states. In this analysis, if photoelectrons having the energy of photoelectrons originating from the metal elements constituting the raw material metal diboride are hardly detected, and only photoelectrons having the energy of photoelectrons originating from boron and the metal elements introduced in steps 2 to 4 are detected, then it can be said that the product is composed of boron and the introduced metal elements.

[0057] In observations using a transmission electron microscope (TEM), for example, a transmission electron microscope (product name: JEM-2100F TEM / STEM) manufactured by JEOL Ltd. is used to observe the product and analyze its shape (appearance), etc. If a film-like (sheet-like) substance is observed in this analysis, the product can be said to be a two-dimensional sheet-like substance. By performing energy dispersive X-ray analysis (EDS) in the transmission electron microscope, the presence or absence of metal elements in the TEM-observed portion of the product can be observed. If, in this analysis, almost no X-ray energy due to the metal elements constituting the raw material metal diboride is detected and no peak for the metal element (e.g., Mg) appears, it can be said that the metal elements constituting the metal diboride are not present. Furthermore, by performing electron energy loss spectroscopy (EELS) in the transmission electron microscope, the constituent elements in the TEM-observed portion of the product can be observed. In this analysis, if only X-ray energy attributable to boron and the metal elements introduced in steps 2 to 4 is detected, it can be said that the product is composed of boron and the metal elements introduced in steps 2 to 4.

[0058] According to the method for producing a metal-supported two-dimensional borohydride sheet-containing material of this embodiment, the above-mentioned metal-supported two-dimensional borohydride sheet-containing material can be easily produced.

[0059] Furthermore, according to the method for producing a metal-supported two-dimensional borohydride sheet-containing material of this embodiment, the composition of the final metal-supported two-dimensional borohydride sheet-containing material, i.e., the amount of metal introduced, can be quantitatively controlled by adjusting the pH of the second dispersion. ｘ H １－ｘ B) ｎ In this case, the value of x can be adjusted.

[0060] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0061] [Preparation of two-dimensional borohydride sheet] Magnesium diboride (purity: 99%, manufactured by Rare Metallic Co., Ltd.) was added to acetonitrile, and 60 mL of an ion exchange resin having a sulfo group (Amberlite (registered trademark) IR120B, manufactured by Organo Corporation) was added by volume and stirred with a glass rod to prepare a mixed solution of magnesium diboride and ion exchange resin. The amount of magnesium diboride added to acetonitrile was 5 mg / mL. At this time, ion exchange resin was added in an amount 3.0 times the ion exchange capacity. After stirring this mixed solution at 25 ° C. for 72 hours, this mixed solution was filtered through a membrane filter with a pore size of 0.2 μm, and the filtrate was collected. Thereafter, the product was obtained by drying for 30 minutes under reduced pressure using a 70 ° C. oil bath under a nitrogen atmosphere.

[0062] "Infrared Spectroscopic Analysis" The obtained product was analyzed using an infrared spectroscopic analyzer (trade name: FTIR ALPHA II, manufactured by Bruker), and it was confirmed that a two-dimensional borohydride sheet was obtained.

[0063] Example 1 A dispersion was prepared by dispersing 68.1 mg of the above-described two-dimensional borohydride sheet in 50 mL of distilled water. 50 mL of aqueous sodium hydroxide solution (1.0 mol / L, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was collected and diluted 10 times with distilled water using a 500 mL measuring flask. The diluted aqueous sodium hydroxide solution was added dropwise to the dispersion using an automatic potentiometric titrator (manufactured by HANNA Instruments). The temperature of the dispersion was adjusted to 25°C. The aqueous sodium hydroxide solution was added dropwise to the dispersion while stirring it at 1300 rpm using a magnetic stirrer (trade name: Hot Stirrer (50 Hz) SRS311HA, manufactured by ADVANTEC). The pH of the dispersion was measured using the pH meter of the automatic potentiometric titrator from before the addition of the aqueous sodium hydroxide solution to the dispersion until the addition was completed. The relationship between the amount of sodium hydroxide aqueous solution added and the pH of the dispersion is shown in Figure 2. Next, the dispersion was transferred to a Schlenk flask, and the atmosphere inside the Schlenk flask was replaced with argon. Next, the Schlenk flask containing the dispersion was immersed in an oil bath at 50°C, and the pressure inside the Schlenk flask was reduced, thereby concentrating the dispersion and evaporating the water contained in the dispersion, thereby obtaining a product. Next, the Schlenk flask containing the obtained product was immersed in an oil bath at 70°C, and the pressure inside the Schlenk flask was reduced, thereby drying the product for 30 minutes. Through the above steps, approximately 63.0 mg of product was obtained.

[0064] [Evaluation] "X-ray Diffraction" The obtained product was analyzed using an X-ray diffractometer (trade name: MINI FLEX, manufactured by Rigaku Corporation). The results are shown in Figure 3. The results shown in Figure 3 indicate that the product is a substance composed of an amorphous structure.

[0065] "Infrared Spectroscopic Analysis" The obtained product was analyzed using an infrared spectroscopic analyzer (trade name: FTIR ALPHA II, manufactured by Bruker). The results are shown in Figure 4. In Figure 4, NaOH-HB (pH 7) indicates the product of Example 1, and SS20230707 indicates the above-mentioned two-dimensional borohydride sheet. From the results shown in Figure 4, it can be seen that in infrared absorption spectroscopy, the B-H stretching vibration in NaHB was shifted to the lower wavenumber side due to electron injection from Na, compared to HB (red). 500 cm －１ ~1500cm －１ The fact that the intensity of the B-H-B vibration shown by is relatively smaller than the intensity of the B-H stretching vibration indicates that Na has exchanged with H in the BHB binding site. Since Na has a large mass, there is no signal related to Na in the X-ray diffraction spectrum shown in Figure 4.

[0066] "Thermal Desorption Spectroscopy" The obtained product was subjected to thermal desorption spectrometry (TDS). The obtained product was heated from 25°C to 1200°C at a heating rate of 10°C / min, and the released gas was sampled and subjected to mass analysis using a quadrupole mass analyzer. Here, the amount of released hydrogen (mass number 2) was measured. The analysis results are shown in Figure 5. For comparison, the above-mentioned two-dimensional boron hydride sheet was also subjected to thermal desorption spectrometry in the same manner. The analysis results are shown in Figure 6. From the results shown in Figures 5 and 6, it was found that the product of Example 1 released less hydrogen at 200°C than the two-dimensional boron hydride sheet. It was also found that the product of Example 1 released more hydrogen at 1100°C than the two-dimensional boron hydride sheet. Furthermore, the product of Example 1 was found to release less hydrogen than the two-dimensional borohydride sheet, indicating that some of the hydrogen was replaced by sodium, and that the presence of sodium made some of the hydrogen less susceptible to recombination and desorption.

[0067] "X-ray Photoelectron Spectroscopy Measurement" The bond energy of the obtained product was measured using an X-ray photoelectron spectrometer (trade name: JPS 9010 TR, manufactured by JEOL Ltd.). The results are shown in Figure 7. From the results shown in Figure 7, it was confirmed that a signal of sodium appeared.

[0068] "UV-Visible Absorption Spectroscopy" UV-Visible absorption spectroscopy was performed on the obtained product using a UV-Visible absorption spectrometer (product name: Duett, manufactured by HORIBA). Acetonitrile was used as the solvent. The concentration of the product in the solution dispersed in acetonitrile was 1 mg / mL. The results are shown in Figure 8. In Figure 8, NaOH-HB (pH 7) represents the product of Example 1, and SS20230707 represents the above-mentioned two-dimensional borohydride sheet. The results shown in Figure 8 indicate that the product of Example 1 has lower absorption around 320 nm and higher absorption around 370 nm compared to the two-dimensional borohydride sheet. This indicates that the introduction of sodium changes the light absorption characteristics.

[0069] From the amount of sodium hydroxide solution dropped at pH 7 shown in FIG. 2, the amount of reacted hydrogen ions (H + Table 1 shows the results when two types of two-dimensional borohydride sheets were used to obtain the product.

[0070]

[0071] From the results shown in Table 1, although it depends greatly on the two-dimensional borohydride sheet used as the raw material, the H substituted for Na + It was found that the ratio of Na was about 6 atomic % to 8 atomic %. ｘ H （１－ｘ） It was found that a substance such as B (0.06≦x≦0.08) could be synthesized.

[0072] Example 2: A dispersion was prepared by dispersing 23.5 mg of the two-dimensional borohydride sheet in 30 mL of distilled water. 50 mL of aqueous sodium hydroxide solution (1.0 mol / L, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was collected and diluted 10 times with distilled water in a 500 mL measuring flask to a concentration of 0.1 mol / L. The diluted aqueous sodium hydroxide solution was added dropwise to the dispersion using an automatic potentiometric titrator (manufactured by HANNA Instruments). The temperature of the dispersion was adjusted to 25°C. The aqueous sodium hydroxide solution was added dropwise to the dispersion while stirring it at 1300 rpm using a magnetic stirrer (trade name: Hot Stirrer (50 Hz) SRS311HA, manufactured by ADVANTEC). The pH of the dispersion was measured using a pH meter on a potentiometric automatic titrator from before the sodium hydroxide aqueous solution was added dropwise to the end of the addition. The relationship between the amount of sodium hydroxide added and the pH of the dispersion is shown in Figure 9. Next, the dispersion was transferred to a Schlenk flask, and the atmosphere inside the Schlenk flask was replaced with argon. The Schlenk flask containing the dispersion was then immersed in a 45°C oil bath, and the Schlenk flask was depressurized to concentrate the dispersion and evaporate the water contained in the dispersion, thereby obtaining a product. The Schlenk flask containing the obtained product was then immersed in a 70°C oil bath, and the Schlenk flask was depressurized to dry the product for 30 minutes. Approximately 26.4 mg of product was obtained through the above process.

[0073] In the same manner as in Example 1, the amount of reacted hydrogen ions (H + ) was calculated, and the H + It was found that the ratio of Na was about 4 atomic % to 5 atomic %. ｘ H （１－ｘ） It was found that a substance such as B (0.04≦x≦0.05) could be synthesized.

[0074] Example 3: A dispersion was prepared by dispersing 6.1 mg of the above-described two-dimensional borohydride sheet in 50 mL of distilled water. 50 mL of aqueous sodium hydroxide solution (1.0 mol / L, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was collected and diluted 10-fold with distilled water in a 500 mL measuring flask to a concentration of 0.1 mol / L. The diluted aqueous sodium hydroxide solution was added dropwise to the dispersion using an automatic potentiometric titrator (manufactured by HANNA Instruments). The temperature of the dispersion was adjusted to 25°C. The aqueous sodium hydroxide solution was added dropwise to the dispersion while stirring it at 1300 rpm using a magnetic stirrer (trade name: Hot Stirrer (50 Hz) SRS311HA, manufactured by ADVANTEC). The pH of the dispersion was measured using a pH meter on a potentiometric automatic titrator from before the sodium hydroxide aqueous solution was added dropwise to the end of the addition. The relationship between the amount of sodium hydroxide added and the pH of the dispersion is shown in Figure 10. Next, the dispersion was transferred to a Schlenk flask, and the atmosphere inside the Schlenk flask was replaced with argon. The Schlenk flask containing the dispersion was then immersed in a 50°C oil bath, and the Schlenk flask was depressurized to concentrate the dispersion and evaporate the water contained in the dispersion, thereby obtaining a product. The Schlenk flask containing the obtained product was then immersed in a 70°C oil bath, and the Schlenk flask was depressurized to dry the product for 30 minutes. Approximately 4.5 mg of product was obtained through the above process.

[0075] In the same manner as in Example 1, the reacted hydrogen ions (H + ) was calculated, and the H + It was found that the ratio of Na was about 5 atomic % to 6 atomic %. ｘ H （１－ｘ） It was found that a substance such as B (0.05≦x≦0.06) could be synthesized.

[0076] Example 4: A dispersion was prepared by dispersing 15.1 mg of the above-described two-dimensional borohydride sheet in 30 mL of distilled water. 50 mL of aqueous sodium hydroxide solution (1.0 mol / L, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was collected and diluted 10 times with distilled water in a 500 mL measuring flask to a concentration of 0.1 mol / L. The diluted aqueous sodium hydroxide solution was added dropwise to the dispersion using an automatic potentiometric titrator (manufactured by HANNA Instruments). The temperature of the dispersion was adjusted to 25°C. The aqueous sodium hydroxide solution was added dropwise to the dispersion while stirring it at 1300 rpm using a magnetic stirrer (trade name: Hot Stirrer (50 Hz) SRS311HA, manufactured by ADVANTEC). The pH of the dispersion was measured using a pH meter on a potentiometric automatic titrator from before the sodium hydroxide aqueous solution was added dropwise to the end of the addition. The relationship between the amount of sodium hydroxide added and the pH of the dispersion is shown in Figure 11. Next, the dispersion was transferred to a Schlenk flask, and the atmosphere inside the Schlenk flask was replaced with argon. The Schlenk flask containing the dispersion was then immersed in a 45°C oil bath, and the Schlenk flask was depressurized to concentrate the dispersion and evaporate the water contained in the dispersion, thereby obtaining a product. The Schlenk flask containing the obtained product was then immersed in a 70°C oil bath, and the Schlenk flask was depressurized to dry the product for 40 minutes. Approximately 25.6 mg of product was obtained through the above process.

[0077] In the same manner as in Example 1, the amount of reacted hydrogen ions (H + ) was calculated, and the H + It was found that the ratio of Na was about 8 atomic % to 9 atomic %. ｘ H （１－ｘ） It was found that a substance such as B (0.08≦x≦0.09) could be synthesized.

[0078] Example 5: A dispersion was prepared by dispersing 20.0 mg of the above-described two-dimensional borohydride sheet in 30 mL of distilled water. 50 mL of calcium hydroxide aqueous solution (1.0 mol / L) was collected and diluted 10 times with distilled water using a 500 mL measuring flask. The diluted calcium hydroxide aqueous solution was added dropwise to the dispersion using an automatic potentiometric titrator (manufactured by HANNA Instruments). The temperature of the dispersion was adjusted to 25°C. The calcium hydroxide aqueous solution was added dropwise to the dispersion while stirring it at 1000 rpm using a magnetic stirrer (trade name: Hot Stirrer (50 Hz) SRS311HA, manufactured by ADVANTEC). The pH of the dispersion was measured using the pH meter of the automatic potentiometric titrator from before the calcium hydroxide aqueous solution was added to the dispersion until the addition was completed. The relationship between the amount of calcium hydroxide aqueous solution added and the pH of the dispersion is shown in Figure 12. Next, the dispersion was transferred to a Schlenk flask, and the atmosphere inside the Schlenk flask was replaced with argon. Next, the Schlenk flask containing the dispersion was immersed in an oil bath at 50°C, and the pressure inside the Schlenk flask was reduced, thereby concentrating the dispersion and evaporating the water contained in the dispersion, thereby obtaining a product. Next, the Schlenk flask containing the obtained product was immersed in an oil bath at 70°C, and the pressure inside the Schlenk flask was reduced, thereby drying the product for 30 minutes. Through the above steps, approximately 18.4 mg of product was obtained.

[0079] [Evaluation] "Infrared Spectroscopic Analysis" The obtained product was analyzed using an infrared spectroscopic analyzer (product name: FTIR ALPHA II, manufactured by Bruker). The results are shown in FIG. 13. From the results shown in FIG. 13, it can be seen that when hydrogen in the two-dimensional borohydride sheet is replaced with calcium, the 2500 cm －１ The position of the BH vibration changes, and the calcium-derived vibration shifts to 1000 cm －１ Infrared spectroscopy revealed that the product of Example 5 (Ca ｘ H （１－ｘ）In B), it was found that the BH stretching vibration shifted to a lower wavenumber due to electron injection from calcium. Because calcium has a large mass, there is no signal related to calcium in the X-ray diffraction spectrum shown in Figure 13.

[0080] [Example 6] A dispersion was prepared by dispersing 88.2 mg of the above-described two-dimensional borohydride sheet in 50 mL of distilled water. 50 mL of potassium hydroxide aqueous solution (1.0 mol / L) was collected and diluted 10 times with distilled water using a 500 mL measuring flask. The diluted potassium hydroxide aqueous solution was added dropwise to the dispersion using an automatic potentiometric titrator (manufactured by HANNA Instruments). The temperature of the dispersion was adjusted to 25°C. The potassium hydroxide aqueous solution was added dropwise to the dispersion while stirring the dispersion at 1000 rpm using a magnetic stirrer (trade name: Hot Stirrer (50 Hz) SRS311HA, manufactured by ADVANTEC). The pH of the dispersion was measured using the pH meter of the automatic potentiometric titrator from before the potassium hydroxide aqueous solution was added to the dispersion until the addition was completed. The relationship between the amount of potassium hydroxide aqueous solution added and the pH of the dispersion is shown in Figure 14. Next, the dispersion was transferred to a Schlenk flask, and the atmosphere inside the Schlenk flask was replaced with argon. Next, the Schlenk flask containing the dispersion was immersed in an oil bath at 50°C, and the pressure inside the Schlenk flask was reduced, thereby concentrating the dispersion and evaporating the water contained in the dispersion, thereby obtaining a product. Next, the obtained product was dispersed in 3 mL of methanol to obtain a dispersion, and the dispersion was separated using a centrifuge. Next, the Schlenk flask containing the supernatant obtained by centrifugation was immersed in an oil bath at 50°C, and the Schlenk flask was reduced in pressure, thereby drying the product for 30 minutes. Approximately 37.2 mg of product was obtained through the above process.

[0081] [Evaluation] "X-ray Diffraction" The obtained product was analyzed using an X-ray diffractometer (trade name: MINI FLEX, manufactured by Rigaku Corporation). The results are shown in Figure 15. The results shown in Figure 15 revealed that the product was a substance composed of an amorphous structure.

[0082] "Infrared Spectroscopic Analysis" The obtained product was analyzed using an infrared spectroscopic analyzer (trade name: FTIR ALPHA II, manufactured by Bruker). The results are shown in Figure 16. From the results shown in Figure 16, it can be seen that when potassium is introduced, the position of the BH vibrational peak decreases. This is thought to be because the bond is weakened by electron injection from potassium. Furthermore, the change in absorption peak depending on the amount of potassium introduced is shown in Figure 17. The results shown in Figure 17 are also summarized in Figure 18. From the results shown in Figures 17 and 18, it can be seen that as the amount of potassium introduced increases, the amount of decrease in the position of the BH vibrational peak increases. This is thought to be because the bond is weakened due to the increase in the amount of electron injection from potassium.

[0083] "X-ray photoelectron spectroscopy measurement" The bond energy of the obtained product was measured using an X-ray photoelectron spectroscopy device (trade name: JPS 9010 TR, manufactured by JEOL Ltd.). The results are shown in Figure 19. For comparison, the bond energy of a two-dimensional borohydride sheet was also measured in the same manner. The results are shown in Figure 20. The results shown in Figures 19 and 20 confirmed the appearance of a potassium signal.

[0084] "Thermal Desorption Spectrometry" The obtained product was subjected to thermal desorption spectrometry (TDS). The obtained product was heated from 25°C to 1200°C at a heating rate of 10°C / min, and the released gas was sampled and subjected to mass analysis using a quadrupole mass analyzer. Here, the amount of released hydrogen (mass number 2) was measured. The analysis results are shown in Figure 21. For comparison, thermal desorption spectrometry was also performed on the above-mentioned two-dimensional borohydride sheet. In Figure 21, HBKT20230926 vs KOH (pH 3) represents the product produced at pH 3, HBKT20230926 vs KOH (pH 6) represents the product produced at pH 6, and HBKT20230926 represents the two-dimensional borohydride sheet. From the results shown in Figure 21, it was found that the product of Example 6 released less hydrogen at 200°C than the two-dimensional boron hydride sheet. It was also found that the product of Example 6 released more hydrogen at 1100°C than the two-dimensional boron hydride sheet. Furthermore, it was found that the total amount of released hydrogen was reduced compared to the two-dimensional boron hydride sheet. This indicates that some of the hydrogen was replaced with potassium, and that the presence of potassium made it difficult for some of the hydrogen to undergo recombination and desorption.

[0085] The metal-supported two-dimensional borohydride sheet-containing material obtained by the method for producing a metal-supported two-dimensional borohydride sheet-containing material of the present invention can be used as a hydrogen storage material, an electrode material, etc.

Claims

1. A step of dispersing a two-dimensional boron hydride sheet in water to prepare a first dispersion liquid; a step of adding a hydroxide containing an alkali metal or a Group 2 element to the first dispersion liquid to prepare a second dispersion liquid having a pH of 4 or more and 9 or less; and a step of obtaining a product by concentrating and drying the second dispersion liquid. A method for producing a metal-supported two-dimensional boron hydride sheet-containing substance.

2. The method for producing a metal-supported two-dimensional boron hydride sheet-containing substance according to claim 1, wherein the pH of the second dispersion liquid is 6.5 or more and 7.5 or less.

3. The product has a two-dimensional network composed of (M ｘ H １－ｘ B) ｎ (where M is an alkali metal atom or a Group 2 element, H is a hydrogen atom, B is a boron atom, 0.01 ≦ x < 1, n ≧ 6), and the B is arranged in a hexagonal ring, and has a network-like two-dimensional network formed by the connection of the hexagons formed by the B. At least the M and the B are bonded by a three-center two-electron bond or a two-center two-electron bond or an ionic bond, and it is a metal-supported two-dimensional boron hydride sheet-containing substance. The method for producing a metal-supported two-dimensional boron hydride sheet-containing substance according to claim 1.

Images