Hydrogen adsorption material and method for manufacturing the same

Abstract

This invention provides a hydrogen adsorption material having a high hydrogen adsorption capacity, and a method for easily producing the same. [Solution] One aspect of the present invention is lithium-modified hydrogen boride containing lithium and hydrogen boride, wherein when the IR spectrum is measured by total internal reflection absorption, it is 1100 cm⁻¹. -1 More than 1500cm -1 Absorption peaks were observed within the following range, and the maximum value of these absorption peaks was 1300 cm⁻¹. -1 More than 1400cm -1 The absorption peak (Ia) is located within the following range, and its maximum value is 1200 cm². -1 More than 1300cm -1 This peak, which is the superimposed peak of the absorption peak (Ib) located within the following range, relates to lithium-modified hydrogen boride.

Description

[Technical Field]

[0001] One aspect of the present invention relates to a hydrogen adsorption material and a method for producing the same. [Background technology]

[0002] In recent years, hydrogen has attracted attention as a clean energy source as part of decarbonization efforts. In fuel cell vehicles, hydrogen is filled at high pressure (70 MPa), and there is a need for technology that can store hydrogen at lower pressures and in a lighter and denser form than compressed gas.

[0003] For example, Patent Document 1 contains (M x H 1-x B) n A metal-supported two-dimensional boron sheet-containing material is disclosed, having a two-dimensional network consisting of (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 atoms are arranged in a hexagonal ring, and the hexagons formed by the B atoms are connected to form a mesh-like two-dimensional network, and at least the M and B atoms are bonded by a three-center two-electron bond or a two-center two-electron bond. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-151415 [Overview of the project] [Problems that the invention aims to solve]

[0005] It has been reported that theoretically, the amount of hydrogen adsorbed by the resulting composite compound increases when alkali metal atoms and / or alkaline earth metal atoms can be dispersed at the atomic level onto hydrogen boride (HB) (Phys. Chem. Chem. Phys., 2018, 20, 30304-30311 and International Journal of Hydrogen Energy, 2021, 46, 39273-39283).

[0006] One method for imparting alkali metal atoms or alkaline earth metal atoms to compounds is vapor deposition in a vacuum. However, in vapor deposition methods, alkali metal atoms and alkaline earth metal atoms tend to aggregate, making it difficult to uniformly disperse these atoms at the atomic level into powder samples.

[0007] Furthermore, as described in Patent Document 1, there is a method of introducing alkali metals or alkaline earth metals by using them in the form of salts, ionizing them in a solvent, mixing them with the compound, and then drying them. However, in this case, the atoms are introduced into the compound in an ionized state, making it difficult to introduce them in atomic form.

[0008] Therefore, conventional technology has not established hydrogen adsorption materials that exhibit sufficient hydrogen adsorption capacity, nor a method for easily producing such hydrogen adsorption materials.

[0009] Therefore, one aspect of the present invention aims to provide a hydrogen adsorption material having a high hydrogen adsorption capacity, and a method for easily producing the same. [Means for solving the problem]

[0010] The inventors investigated various means to solve the above-mentioned problems. As a result, the inventors found that by mixing lithium metal and hydrogen boride under shear force, the amount of hydrogen adsorbed by the resulting lithium-modified hydrogen boride increases. Based on the above, the inventors have completed one embodiment of the present invention.

[0011] That is, the gist of one aspect of the present invention is as follows. (1) A lithium-modified borohydride containing lithium and borohydride, when measured by the total reflection absorption method for the IR spectrum, has an absorption peak in the range of 1100 cm -1 or more and 1500 cm -1 or less, and the absorption peak is a peak obtained by superimposing an absorption peak (Ia) having a maximum value in the range of 1300 cm -1 or more and 1400 cm -1 or less and an absorption peak (Ib) having a maximum value in the range of 1200 cm -1 or more and 1300 cm -1 or less. Lithium-modified borohydride. (2) The lithium-modified borohydride according to (1), wherein the area ratio (Ia / Ib) of the separated absorption peak (Ia) to the absorption peak (Ib) is in the range of 0.5 or more and 0.8 or less. (3) The lithium-modified borohydride according to (1) or (2), wherein the molar ratio (B / Li) of boron to lithium calculated by ICP is in the range of 0.8 or more. (4) The lithium-modified borohydride according to any one of (1) to (3), wherein the molar ratio (H / B) of hydrogen calculated by TPD to boron calculated by ICP is in the range of 1.2 or less. (5) The lithium-modified borohydride according to any one of (1) to (4), which has a hydrogen release peak in the range of 500 °C or more and 600 °C or less at the peak top in the temperature-hydrogen intensity curve obtained by TPD measurement. (6) A method for producing a lithium-modified borohydride containing lithium and borohydride, the method including a step of adding a shearing force to mix lithium metal and borohydride. (7) The method according to (6), wherein the mixing is carried out in an inert atmosphere using a mortar and a pestle.

Advantages of the Invention

[0012] According to one aspect of the present invention, a hydrogen adsorption material having a high hydrogen adsorption amount and a method for easily producing the same are provided.

Brief Description of the Drawings

[0013] [Figure 1] This is a diagram schematically showing the structure of lithium-modified borohydride of one aspect of the present invention (in the structure, the molar ratio of hydrogen to boron (H / B) is 1). [Figure 2] (A) It is a graph showing the hydrogen adsorption amount at 298K at each pressure of Li / HB, HB, and LiB2, and (B) it is a graph showing the hydrogen adsorption amount at 77K at each pressure of Li / HB and HB. [Figure 3] (A) It is a graph showing the IR spectrum of HB by the total reflection absorption (ATR) method, and (B) it is a graph showing the IR spectrum of Li / HB by the total reflection absorption (ATR) method. [Figure 4] (A) It is a graph showing the EEM spectrum of HB, and (B) it is a graph showing the EEM spectrum of Li / HB. [Figure 5] (A) It is a graph showing the hydrogen release amount of HB at each temperature, and (B) it is a graph showing the hydrogen release amount of Li / HB at each temperature.

Mode for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments of one aspect of the present invention will be described in detail. In this specification, the features of one aspect of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of one aspect of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the hydrogen adsorption material of one aspect of the present invention and its manufacturing method are not limited to the following embodiments, and can be implemented in various forms with changes, improvements, etc. that can be made by those skilled in the art without departing from the gist of one aspect of the present invention.

[0015] The lithium-modified borohydride of one aspect of the present invention contains lithium and borohydride.

[0016] In one embodiment of the present invention, the IR spectrum obtained by total internal reflection absorption (ATR) of lithium-modified hydrogen boride shows 1100 cm⁻¹. -1 More than 1500cm -1 Absorption peaks (hereinafter also referred to as peaks (Iab)) are observed within the following range.

[0017] The peak (Iab) is not a single absorption peak, but rather has a shape formed by the overlapping of two or more absorption peaks. In one embodiment, the peak (Iab) is two absorption peaks, i.e., the maximum value (peak top) is 1300 cm⁻¹. -1 More than 1400cm -1 The absorption peaks (hereinafter also referred to as peak (Ia)) located within the following range, and the maximum value of 1200 cm², are as follows: -1 More than 1300cm -1 This peak is formed by superimposing absorption peaks (hereinafter also referred to as peak (Ib)) that exist within the following range. In this embodiment, the area ratio (Ia / Ib) of the separated peak (Ia) and peak (Ib) is usually in the range of 0.5 to 0.8, and in one embodiment, it is in the range of 0.6 to 0.7.

[0018] Here, the IR spectrum obtained by ATR is measured in an inert atmosphere, such as an argon atmosphere, and at room temperature, such as between 20°C and 25°C.

[0019] Furthermore, the IR spectrum of hydrogen boride measured under the same conditions showed a value of 1100 cm⁻¹. -1 More than 1500cm -1 Absorption peaks are observed within the following range, but the maximum value of these absorption peaks is 1300 cm. -1 More than 1400cm -1 The following is a single peak located within the specified range, which is presumed to be an absorption peak based on the vibration of BHB. Therefore, in lithium-modified hydrogen boride according to one embodiment of the present invention, peak (Ia) is presumed to be an absorption peak based on the vibration of BHB, and peak (Ib) is presumed to be an absorption peak based on the vibration of Li-B.

[0020] In one embodiment of the present invention, lithium-modified hydrogen boride has an absorption peak in the IR spectrum measured by ATR in which two absorption peaks overlap within the aforementioned range, indicating that in the lithium-modified hydrogen boride, lithium is not ionized and is uniformly dispersed at the atomic level within the hydrogen boride.

[0021] In lithium-modified hydrogen boride according to one embodiment of the present invention, the molar ratio of boron to lithium (B / Li) calculated by ICP (Inductively Coupled Plasma) is typically in the range of 0.8 or more, in one embodiment in the range of 1.0 or more, in one embodiment in the range of 1.2 or more, in one embodiment in the range of 1.4 or more, in one embodiment in the range of 1.6 or more, in one embodiment in the range of 1.8 or more, and in one embodiment in the range of 1.9 or more. The upper limit of the molar ratio of boron to lithium (B / Li) calculated by ICP is not limited. The molar ratio of boron to lithium (B / Li) calculated by ICP is typically in the range of 2.1 or less, in one embodiment in the range of 2.0 or less.

[0022] Here, the measurement conditions for ICP are known in the art. In one embodiment, the ICP was quantitatively analyzed using an ICP emission spectrometer ICPS-8100 manufactured by Shimadzu Corporation, with measurement wavelengths of lithium and boron set to 670.785 nm and 249.773 nm, respectively.

[0023] Furthermore, in lithium-modified hydrogen boride according to one embodiment of the present invention, the molar ratio (H / B) of hydrogen calculated by TPD (Temperature-Programmed Desorption) to boron calculated by ICP is usually in the range of 1.2 or less, and in one embodiment, in the range of 1.1 or less. The lower limit of the molar ratio (H / B) of hydrogen calculated by TPD to boron calculated by ICP is not limited. The molar ratio (H / B) of hydrogen calculated by TPD to boron calculated by ICP is usually in the range of 0.9 or more, and in one embodiment, in the range of 1.0 or more.

[0024] In addition, lithium-modified hydrogen boride according to one embodiment of the present invention has a hydrogen release peak in the temperature-hydrogen intensity curve obtained by TPD measurement, where the maximum value (peak top) is in the range of 500°C to 600°C. More specifically, in lithium-modified hydrogen boride according to one embodiment of the present invention, the amount of released hydrogen increases as the temperature rises from around 100°C, reaches a maximum value in the range of 150°C to 250°C, and then gradually decreases while repeatedly increasing and decreasing as the temperature rises, but increases again as the temperature rises from around 360°C, reaches a maximum value in the range of 500°C to 600°C, and then decreases as the temperature rises. In this case, lithium-modified hydrogen boride according to one embodiment of the present invention has at least a hydrogen release peak in the temperature-hydrogen intensity curve obtained by TPD measurement where the maximum value is in the range of 150°C to 250°C, and a hydrogen release peak where the maximum value is in the range of 500°C to 600°C. Furthermore, with hydrogen boride (HB) alone, no peak indicating hydrogen release (with a peak top) is observed in the temperature-hydrogen intensity curve obtained by TPD measurement in the range of 500°C to 600°C.

[0025] Here, the measurement conditions for ICP are as described above. TPD is measured by quantifying the hydrogen generated simultaneously with heating when the sample is heated at a heating rate of 10 K / min in an apparatus combining a high-sensitivity differential thermal balance with a quadrupole mass spectrometer.

[0026] When the molar ratio of boron to lithium calculated by ICP in lithium-modified hydrogen boride, and the molar ratio of hydrogen calculated by TPD to boron calculated by ICP, fall within the aforementioned range, it can be confirmed that lithium is stably modified into hydrogen boride in lithium-modified hydrogen boride.

[0027] Lithium-modified hydrogen boride according to one aspect of the present invention does not exhibit luminescence even when irradiated with light of a wavelength between 250 nm and 650 nm.

[0028] Furthermore, when hydrogen boride is irradiated with light of a wavelength of 332 nm, it exhibits luminescence with a maximum peak around 400 nm. Therefore, the fact that lithium-modified hydrogen boride according to one aspect of the present invention does not exhibit luminescence indicates that lithium-modified hydrogen boride according to one aspect of the present invention is a substance with different properties from hydrogen boride.

[0029] Figure 1 shows the structure of lithium-modified hydrogen boride in one embodiment of the present invention, where the molar ratio of hydrogen to boron (H / B) is 1. B has a six-membered ring network with B:H = 1:1, and H exists as BHB bridging the BB of the six-membered ring, but may also form BH bonds as Terminal BH around edges or defects. Li is located on top of the BHB, but may also be located in the center of the six-membered ring, on top of B, and / or on top of H of BH. Note that the six-membered ring is flexible and does not have to be perfectly planar.

[0030] The hydrogen adsorption amount of lithium-modified hydrogen boride in one aspect of the present invention is in the range of 0.17% to 0.19% by mass at a pressure of 2.6 MPa, 5.0% to 5.3% by mass at a pressure of 6.1 MPa, and 1.0% to 1.1% by mass at a pressure of 10 MPa, relative to the total mass of lithium-modified hydrogen boride, at 298 K.

[0031] The hydrogen adsorption amount of lithium-modified hydrogen boride in one embodiment of the present invention is in the range of 0.057% to 0.071% by mass at a pressure of 0.20 MPa, 0.25% to 0.34% by mass at a pressure of 1.1 MPa, and 2.5% to 3.0% by mass at a pressure of 11 MPa, relative to the total mass of lithium-modified hydrogen boride, at 77 K.

[0032] Therefore, lithium-modified hydrogen boride according to one aspect of the present invention has a larger hydrogen adsorption capacity than hydrogen boride alone, typically three times or more, and can therefore be used as a hydrogen adsorption material.

[0033] Lithium-modified hydrogen boride according to one aspect of the present invention can be produced by a process of mixing lithium metal and hydrogen boride under the application of shear force. "Mixing under the application of shear force" means that the lithium metal and hydrogen boride are mixed while being crushed by repeated compression and / or expansion as they come into contact with and / or collide with each other.

[0034] In one aspect of the present invention, the mixing is carried out under an inert atmosphere, for example, under an inert gas atmosphere, such as nitrogen gas or argon gas.

[0035] In one aspect of the present invention, mixing is not limited to any method that can apply shear force to the raw materials, and can be carried out using, for example, a mortar and pestle, a ball mill, or other grinding equipment.

[0036] In one embodiment of the present invention, the mixing time is not limited. The mixing time is typically in the range of 20 minutes to 40 minutes, and in one embodiment, in the range of 25 minutes to 35 minutes.

[0037] In one aspect of the present invention, the mixing temperature is not limited. The mixing temperature is typically in the range of 20°C to 25°C, and in one embodiment, in the range of 22°C to 24°C.

[0038] A method for producing lithium-modified hydrogen boride according to one aspect of the present invention is as follows. (1) A physical mixture is obtained by physically mixing metallic lithium and hydrogen boride. Here, "physical mixing" refers to stirring the metallic lithium and hydrogen boride, for example, by moving them up and down and / or rotating them in a sealed container until they become uniform. (2) The physical mixture is hand-milled in an agate mortar in an inert gas. The hand-milling is carried out for the mixing time and at the mixing temperature. (3) In order to remove adsorbed water, etc., vacuum drying is performed at a temperature of 60°C to 100°C, for example 80°C, for a period of 16 hours to 48 hours, for example about 32 hours.

[0039] In one embodiment of the present invention, lithium-modified hydrogen boride can be easily produced in which lithium is uniformly dispersed at the atomic level in hydrogen boride without ionization by mechanochemically mixing lithium metal and hydrogen boride by applying shear force. [Examples]

[0040] The following describes several embodiments relating to one aspect of the present invention, but it is not intended that the embodiments of the present invention are limited to those shown in these embodiments.

[0041] 1. Preparation of lithium-modified hydrogen boride (1) HB (185.8 mg) and metallic Li (15.6 mg) cut into small pieces with scissors were prepared. (2) The HB and Li prepared in (1) were hand-milled in a mortar in a glove box under an argon atmosphere at 25°C for 30 minutes. (3) After mixing (2), a gray product (120.6 mg, also known as "Li / HB") was obtained.

[0042] ICP was measured for the obtained Li / HB mixture. ICP was quantitatively analyzed using a Shimadzu ICPS-8100 ICP emission spectrometer, with measurement wavelengths of 670.785 nm and 249.773 nm for lithium and boron, respectively. As a result, while the initial molar ratio was HB:Li = 1:0.14, the molar ratio determined by ICP was B:Li = 1:0.52 (0.66:0.34).

[0043] 2. Evaluation of lithium-modified hydrogen boride 2-1. PCT (P: pressure, C: storage capacity, T: temperature) evaluation For the Li / HB, HB, and LiB2 prepared as described above, the amount of hydrogen adsorbed at each pressure was measured at 298K (25°C) or 77K using a Microtrac-Bel BELSORP HP. The Li:B (molar ratio) of the LiB2 used as a comparative example was 3:7 in ICP measurement. Each sample underwent pretreatment heating (80°C, degassed for 32 hours) before measurement. For room temperature (298K) measurements, the sample tube containing the sample was immersed in a constant temperature bath (298K). For 77K measurements, the sample tube was immersed in a Dewar flask filled with liquid nitrogen.

[0044] The results are shown in Figure 2. In Figure 2, Li / HB measurements were performed four times and HB and LiB2 measurements were performed twice each at 298K, and Li / HB and HB measurements were performed twice each at 77K. From Figure 2, it was found that under the temperature conditions of 298K and 77K, the amount of hydrogen adsorption of the obtained Li / HB increased by more than three times compared to HB or LiB2 alone without Li modification.

[0045] 2-2. IR Spectrum Evaluation For Li / HB and HB, IR spectra were measured using the total internal reflection absorption (ATR) method with a Bruker Alpha spectrometer (ALPHAII, Bruker, Billerica, MA, USA). Measurements were performed 16 times in an argon atmosphere and in a glove box at room temperature (25°C).

[0046] The results are shown in Figure 3. From Figure 3B, the obtained Li / HB is 1100 cm³. -1 More than 1500cm -1 The absorption peak (Iab) was found to be present in the following range.

[0047] The resulting Li / HB absorption peak (Iab) is not a single absorption peak, but rather two absorption peaks, i.e., a maximum value of 1300 cm⁻¹. -1 More than 1400cm -1 The absorption peak (Ia) and maximum value are located within the following range: 1200 cm².-1 More than 1300cm -1 The following range (1280cm) -1 The peak was formed by superimposing absorption peaks (Ib) that were present in the vicinity.

[0048] The area ratio (Ia / Ib) between the separated absorption peak (Ia) and the absorption peak (Ib) was 0.68.

[0049] Furthermore, as shown in Figure 3A, the IR spectrum of HB measured under the same conditions is 1100 cm⁻¹. -1 More than 1500cm -1 Absorption peaks were observed within the following range, but the maximum value of these absorption peaks was 1300 cm⁻¹. -1 More than 1400cm -1 There was a single peak located within the following range.

[0050] Therefore, peak (Ia) is presumed to be an absorption peak based on the vibration of BHB, and peak (Ib) is presumed to be an absorption peak based on the vibration of Li-B.

[0051] From these results, it was found that in the obtained Li / HB, lithium was not ionized and was uniformly dispersed at the atomic level in hydrogen boride.

[0052] 2-3. EEM Spectral Evaluation Excitation-fluorescence matrix (EEM) spectra were measured for Li / HB and HB using a Duetta fluorescence absorbance analyzer (manufactured by Horiba, Ltd.). The measurements were performed using a 1 cm cell after preparing solutions by dispersing each sample in acetonitrile at a concentration of 1 mg / ml.

[0053] The results are shown in Figure 4. From Figure 4, it was found that the obtained Li / HB did not emit light.

[0054] Furthermore, when irradiated with light of a wavelength of 332 nm, HB exhibited emission with a maximum peak around 400 nm.

[0055] Therefore, the fact that Li / HB does not exhibit luminescence indicates that Li / HB is a substance with different properties from HB.

[0056] 2-4. TPD Evaluation For Li / HB and HB, the amount of hydrogen released from the compounds was measured using a system combining a high-sensitivity differential thermal balance (STA-2500 Regulus, NETZSCH, Tokyo, Japan) with a quadrupole mass spectrometer (Microvision 2, MKS Instruments). 10 mg of the sample was weighed into an alumina cup and heated using the STA-2500 Regulus at a heating rate of 10 K / min. The hydrogen generated simultaneously with heating was quantified using Microvision 2.

[0057] The results are shown in Figure 5. From Figure 5, it was found that the obtained Li / HB (Figure 5B) has a hydrogen emission peak at 200°C, which was also observed in HB (Figure 5A), as well as a hydrogen emission peak around 550°C.

[0058] By comparing the integrated intensity after subtracting background noise from TPD measurements using Li / HB (10 mg) with the calibration curve, it was found that Li / HB releases 0.35 ± 0.03 mmol of H2 (equivalent to 0.70 ± 0.06 mmol of H).

[0059] Based on the ICP and TPD results, the molar ratio of H, B, and Li in Li / HB can be calculated as follows. First, the molar ratio of B to Li in Li / HB is 0.66:0.34. The total amount of boron and lithium per 10 mg of Li / HB is 10 - 0.70 = 9.3 ± 0.06 mg. Therefore, (B + Li) is 9.3 / (10.8 × 0.66 + 6.9 × 0.34) = 0.98 mmol (calculated using an atomic weight of 10.8 for B and 6.9 for Li). Thus, H:B:Li = 0.7:(0.66 × 0.98):(0.34 × 0.98), so the molar ratio of H, B, and Li in Li / HB is H:B:Li = 1 ± 0.09:0.92 ± 0.09:0.48 ± 0.09.

Claims

1. Lithium-modified hydrogen boride containing lithium and hydrogen boride, When the IR spectrum was measured by total internal reflection absorption, 1100 cm⁻¹ －１ More than 1500cm －１ Absorption peaks were observed in the following range: The absorption peak in question has a maximum value of 1300 cm⁻¹. －１ More than 1400cm －１ The absorption peak (Ia) is located within the following range, and its maximum value is 1200 cm⁻¹. －１ More than 1300cm －１ This peak is a superimposed peak of the absorption peak (Ib) that exists within the following range: Lithium-modified hydrogen boride.

2. The lithium-modified hydrogen boride according to claim 1, wherein the area ratio (Ia / Ib) of the separated absorption peak (Ia) to the absorption peak (Ib) is in the range of 0.5 or more and 0.8 or less.

3. The molar ratio of boron to lithium (B / Li) calculated by ICP is in the range of 0.8 or higher. The molar ratio (H / B) of hydrogen calculated by TPD and boron calculated by ICP is in the range of 1.2 or less. Lithium-modified hydrogen boride according to claim 1 or 2.

4. The lithium-modified hydrogen boride according to claim 1 or 2, wherein the temperature-hydrogen intensity curve obtained by TPD measurement has a hydrogen release peak whose peak top is in the range of 500°C to 600°C.

5. A method for producing lithium-modified hydrogen boride containing lithium and hydrogen boride, comprising the step of mixing lithium metal and hydrogen boride by applying a shear force.

6. The method according to claim 5, wherein the mixing is carried out in an inert atmosphere using a mortar and pestle.

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