JP3862594B2 - Method for activating hydrogen storage material - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for activating a hydrogen storage material, and more particularly, to a method for easily activating a hydrogen storage material used when storing hydrogen gas, which is a future clean energy medium.
[0002]
[Prior art]
Hydrogen can be easily converted into electric energy, mechanical energy, and thermal energy, and does not release harmful substances such as carbon dioxide. At that time, hydrogen is attracting attention as one of clean energy media.
[0003]
In order for hydrogen to become widespread in society as a next-generation energy medium, it is essential to develop hydrogen storage technology that controls demand and supply and provides efficient transportation. In recent years, with the aim of increasing the density of hydrogen storage, various material searches centering on various hydrogen storage alloys and carbon-based hydrogen storage materials have been vigorously developed.
[0004]
Mg, Ti, and V each store a large amount of hydrogen of 8.2 wt%, 4.1 wt%, and 3.9 wt% per unit metal weight. Especially, Mg and Ti are inexpensive, so that a low-cost storage system is constructed. Therefore, various hydrogen storage alloys based on Mg and Ti have been developed.
[0005]
For example, Mg ₂ Ni and TiFe have hydrogen storage amounts of 3.6 wt% and 1.8 wt%, respectively. However, since the surfaces of the above metals and alloys are usually covered with oxides or nitrides, the reactivity with hydrogen is low for the first time, and at the time of hydrogen occlusion, at a high temperature of 300 to 500 ° C., several to several tens MPa It is necessary to perform initial activation treatment several times under high-pressure hydrogen.
[0006]
Furthermore, once activated metal or alloy is sensitive to oxygen and nitrogen in the atmosphere and the surface will be recontaminated, so to maintain the characteristics after activation, handle it under an inert gas atmosphere, etc. It took great care.
[0007]
That is, after encapsulating the hydrogen storage material before activation in a hydrogen storage container, an activation treatment under high temperature and high pressure hydrogen is required before use, and a container having a strength capable of withstanding it is required. Therefore, the material and structure are remarkably limited, which is a serious problem particularly when a fuel cell vehicle hydrogen tank is required to be small and light.
[0008]
As a measure for solving the above problems, an activation method that does not require treatment under high temperature and high pressure hydrogen has been studied, and examples thereof include surface modification of metals and alloys with graphite. However, since carbon is dissolved in Mg, Ti, or V, and part of the carbon is changed to carbide, a decrease in hydrogen storage characteristics is observed.
[0009]
[Problems to be solved by the invention]
The present invention has been made under the state of the art as described above, and the object of the present invention is at least selected from Mg, Ti and V and Mg, Ti and V having high hydrogen storage capacity. It is an object of the present invention to provide a simple method for activating a hydrogen storage material that solves the need for treatment under high temperature and high pressure hydrogen when initially activating a hydrogen storage alloy containing one kind of metal.
[0010]
[Means for Solving the Problems]
In the present invention, when activating a hydrogen storage alloy containing Mg, Ti and V and at least one metal selected from Mg, Ti and V, the metal or the hydrogen storage alloy and hexagonal nitriding are used. A method of activating a hydrogen storage material that mechanically mixes with boron to refine at least a hexagonal boron nitride and reform the surface state of the metal or the hydrogen storage alloy, the metal or the hydrogen storage alloy The ratio of hexagonal boron nitride to the total weight of hexagonal boron nitride is 10 to 50 wt%, the crystallites of hexagonal boron nitride are refined to 20 nm or less, and the surface of the metal or the hydrogen storage alloy It is made to adhere to .
[0011]
Further, the crystallites of hexagonal boron nitride are refined to 20 nm or less and adhered to the surface of the metal or the hydrogen storage alloy.
[0012]
Further, the activation method is such that the ratio of hexagonal boron nitride to the total weight of the metal or hydrogen storage alloy and hexagonal boron nitride is in the range of 10 to 50 wt%, and a high energy ball mill is used as a mechanical mixing means. The activation method used. Further, the mechanical mixing is performed under an inert atmosphere such as in Ar gas.
[0013]
[Action]
In order for hydrogen to be stored as a hydride inside the hydrogen storage material, hydrogen diffusion needs to occur through the material surface. Usually, the material surface is covered with an impurity film such as oxide and nitride, preventing initial hydrogen diffusion. The conventional activation method has been to reduce and remove impurity films such as oxides and nitrides by exposing the hydrogen storage material to high temperature and high pressure hydrogen. According to the activation method of the present invention, rapid activation is possible by mechanical mixing in the presence of hexagonal boron nitride without exposure to high temperature and high pressure hydrogen.
[0014]
The present invention will be described in more detail with reference to the drawings. The effect in the activation method of the present invention is manifested by the following two factors.
[0015]
FIG. 1 shows a conceptual diagram of changes in the hydrogen storage material in the activation treatment of the present invention. Reference numeral 1 denotes a hydrogen storage material at the start of the activation process of the present invention, and reference numeral 2 denotes a hydrogen storage material after the activation process of the present invention. First, the surface of the hydrogen storage material 3 is polished by mechanical mixing with the hexagonal boron nitride 4 to remove the impurity film 5 such as oxide and nitride. That is, the surface of the hydrogen storage material is cleaned, and a hydrogen diffusion path from the material surface to the inside is secured.
[0016]
The cleaned hydrogen storage material surface is then modified with hexagonal boron nitride 6 that is preferably microstructured to 20 nm or less, causing charge transfer from the hydrogen storage material to the microstructured boron nitride. Therefore, the electron density on the surface of the hydrogen storage material is reduced, and reoxidation and renitridation on the surface of the hydrogen storage material are suppressed. Here, when the hexagonal boron nitride crystallites are not miniaturized to 20 nm or less, the hexagonal boron nitride is difficult to be close to the hydrogen storage material due to steric hindrance, and the contact interface between the two decreases. Such electronic interaction is less likely to occur. Therefore, the activation effect is reduced.
[0017]
The activation effect can be seen even when the ratio of hexagonal boron nitride to the total weight of the hydrogen storage material and hexagonal boron nitride exceeds 50 wt%, but the ratio of the hydrogen storage material is small, so The amount of hydrogen occlusion with respect to the total weight of the material and hexagonal boron nitride is small, which is not preferable for practical use. When the ratio of hexagonal boron nitride is less than 10 wt%, the activation effect is limited.
[0018]
As described above, by securing a hydrogen diffusion path and suppressing re-oxidation and re-nitridation of the surface of the hydrogen storage material, the present invention does not require a reduction treatment under high temperature and high pressure hydrogen, and enables simple activation of the hydrogen storage material. Can be realized.
[0019]
【Example】
Examples of the present invention will be specifically described below, but the present invention is not limited to these examples.
[0020]
[Example 1]
Ti powder (0.9 g) and hexagonal boron nitride (hereinafter referred to as h-BN) powder (0.1 g) together with chrome steel balls (7 mmφ × 22) container for chrome steel planetary ball mill (capacity) 45 ml) and mechanically mixed for 1 hour at room temperature under an Ar gas atmosphere using a planetary ball mill apparatus. The rotation speed of the planetary ball mill device was 400 rpm.
[0021]
From the results of X-ray diffraction of the mixed powder sample after ball mill mechanical mixing, no peaks other than those attributed to Ti were observed, so by-products such as nitrides and borides that cause a decrease in hydrogen storage amount I knew it wasn't.
[0022]
On the other hand, the peak attributed to h-BN was broadened and the intensity was remarkably reduced, indicating that h-BN was refined to an almost disordered state. When the size of the crystallite was estimated from the X-ray diffraction and the Raman spectroscopic spectrum, it became clear that the crystallite of h-BN was refined to about 8 nm.
[0023]
In order to investigate the hydrogen storage rate of this sample, the change over time of the hydrogen storage amount of this sample at 25 ° C. was measured in a hydrogen atmosphere of 2 MPa. The result is shown in FIG. 7 is the time-dependent change in the hydrogen storage amount in Ti activated by h-BN, and 8 is the time-dependent change in the hydrogen storage amount in h-BN-free Ti. The h-BN-free Ti only occludes hydrogen slightly even after 24 hours, but with Ti activated by h-BN, hydrogen occlusion starts quickly, and the hydrogen occlusion amount is 3 after 24 hours. Reached 6 wt%. As can be seen from the above results, it was found that Ti can occlude a large amount of hydrogen under mild conditions of 25 ° C. without initial activation under high temperature and high pressure hydrogen by the activation method of the present invention.
[0024]
[Example 2]
Put Ti powder (0.5g) and h-BN powder (0.5g) together with chrome steel balls (7mmφ × 22) in a chrome steel planetary ball mill device container (capacity 45ml), planetary ball mill Using an apparatus, mechanical mixing was performed at room temperature under an Ar gas atmosphere for 0.5 to 5 hours. The rotation speed of the planetary ball mill device was 400 rpm.
[0025]
When the size of the crystallite was estimated from the X-ray diffraction and Raman spectroscopic spectrum of the mixed powder sample after ball mill mechanical mixing, the crystallite size of h-BN decreased with the mechanical mixing time. It became 40, 20, 15, 5 nm by the process for 5 hours, respectively.
[0026]
In order to investigate the hydrogen storage rate of this sample, the change over time of the hydrogen storage amount of this sample at 25 ° C. was measured under a hydrogen atmosphere of 1 MPa. The result is shown in FIG. The smaller the h-BN crystallite size, the faster the hydrogen storage rate. When the h-BN crystallite size is 5 nm, the theoretical hydrogen storage amount (2.05 wt%) of this sample is reached in about 1 hour. It was. The smaller the crystallite size, the stronger the electronic interaction with the Ti surface, so the hydrogen storage rate increases.
[0027]
As is clear from the above results, it was found that high hydrogen storage activity can be obtained by refining h-BN crystallites to 20 nm or less and attaching them to the surface of Ti.
[0028]
[Example 3]
Ti powder and h-BN powder are placed in a chromium steel planetary ball mill container (capacity 45 ml) together with chrome steel balls (7 mmφ × 22), using a planetary ball mill apparatus under an Ar gas atmosphere, Mechanical mixing at room temperature for 1 hour. The rotation speed of the planetary ball mill device was 400 rpm. Here, various samples were prepared by changing the ratio of h-BN with respect to the total weight (1.0 g) of Ti and h-BN in the range of 5 to 90 wt%, and at 25 ° C under a hydrogen atmosphere of 3 MPa. The amount of hydrogen occlusion was evaluated. The result is shown in FIG. The amount of occlusion of hydrogen increases linearly as the h-BN content in the sample decreases. However, when the amount of occlusion is less than 10 wt%, no occlusion of hydrogen was observed, that is, no activation effect was observed. Even if the h-BN content exceeds 50 wt%, the activation effect is observed, but since the proportion of Ti responsible for hydrogen storage becomes small, the hydrogen storage amount becomes small, which is not practically preferable.
[0029]
As is clear from the above results, a large amount of hydrogen can be occluded when the ratio of hexagonal boron nitride to the total weight of Ti and h-BN is 10 to 50 wt%.
[0030]
[Example 4]
Put Mg powder (0.9 g) and h-BN powder (0.1 g) together with chrome steel balls (7 mmφ × 22) in a chrome steel planetary ball mill device container (capacity 45 ml). Planetary ball mill Using an apparatus, mechanical mixing was performed at room temperature under an Ar gas atmosphere for 1 hour. The rotation speed of the planetary ball mill device was 400 rpm.
[0031]
From the X-ray diffraction results of the mixed powder sample after ball mill mechanical mixing, no peaks other than those attributed to Mg were observed, so that by-products such as nitrides and borides that cause a decrease in hydrogen storage amount I knew it wasn't.
[0032]
On the other hand, the peak attributed to h-BN was broadened and the intensity was remarkably reduced, indicating that h-BN was refined to an almost disordered state. When the size of the crystallite was estimated from the X-ray diffraction and Raman spectroscopic spectrum, it became clear that the crystallite of h-BN was refined to about 12 nm.
[0033]
In order to investigate the hydrogen storage rate of this sample, the change over time of the hydrogen storage amount of this sample at 200 ° C. was measured under a hydrogen atmosphere of 2 MPa. The result is shown in FIG. 13 is the change over time of the hydrogen storage amount in Mg activated by h-BN, and 14 is the change over time in the hydrogen storage amount in h-BN-free Mg. The h-BN-free Mg hardly absorbs hydrogen even after 24 hours, but Mg activated by h-BN immediately starts to absorb hydrogen, and the hydrogen storage amount is 6.3 wt after 24 hours. % Reached.
[0034]
As is clear from the above results, it was found that Mg can occlude a large amount of hydrogen at a relatively low temperature of 200 ° C. without initial activation under high temperature and high pressure hydrogen by the activation method of the present invention.
[0035]
[Example 5]
V powder (0.9 g) and h-BN powder (0.1 g) are placed in a chrome steel planetary ball mill device container (capacity 45 ml) together with chrome steel balls (7 mmφ × 22). Using an apparatus, mechanical mixing was performed at room temperature under an Ar gas atmosphere for 1 hour. The rotation speed of the planetary ball mill device was 400 rpm.
[0036]
From the results of X-ray diffraction of the mixed powder sample after ball mill mechanical mixing, no peaks other than those attributed to V were observed, so that by-products such as nitrides and borides that cause a decrease in hydrogen storage amount I knew it was n’t there.
[0037]
On the other hand, the peak attributed to h-BN was broadened and the intensity was remarkably reduced, indicating that h-BN was refined to an almost disordered state. When the size of the crystallite was estimated from the X-ray diffraction and the Raman spectroscopic spectrum, it became clear that the crystallite of h-BN was refined to about 8 nm.
[0038]
In order to investigate the hydrogen storage rate of this sample, the change over time of the hydrogen storage amount of this sample at 25 ° C. was measured in a hydrogen atmosphere of 2 MPa. The result is shown in FIG. 15 is the time-dependent change in the hydrogen storage amount in V activated by h-BN, and 16 is the time-dependent change in the hydrogen storage amount in h-BN-free V. The h-BN-free V hardly absorbs hydrogen even after 24 hours, but in the case of V activated by h-BN, the hydrogen storage starts quickly, and the hydrogen storage amount becomes 3.2 wt% after 24 hours. Reached.
[0039]
As is clear from the above results, it was found that V can occlude a large amount of hydrogen under mild conditions of 25 ° C. without initial activation under high temperature and high pressure hydrogen by the activation method of the present invention.
[0040]
[Example 6]
Put Mg ₂ Ni powder (0.9 g) and h-BN powder (0.1 g) together with chrome steel balls (7 mmφ × 22) in a chrome steel planetary ball mill device container (capacity 45 ml) Using a mold ball mill apparatus, mechanical mixing was performed at room temperature under an Ar gas atmosphere for 2 hours. The rotation speed of the planetary ball mill device was 400 rpm.
[0041]
From the X-ray diffraction results of the mixed powder sample after ball mill mechanical mixing, no peaks other than those attributed to Mg ₂ Ni were observed. I found that there was no life.
[0042]
On the other hand, the peak attributed to h-BN was broadened and the intensity was remarkably reduced, indicating that h-BN was refined to an almost disordered state. When the size of the crystallite was estimated from the X-ray diffraction and Raman spectroscopic spectrum, it became clear that the crystallite of h-BN was refined to about 5 nm.
[0043]
In order to investigate the hydrogen storage rate of this sample, the change over time of the hydrogen storage amount of this sample at 200 ° C. was measured under a hydrogen atmosphere of 2 MPa. The result is shown in FIG. 17 is the change over time of the hydrogen storage amount in Mg ₂ Ni activated by h-BN, and 18 is the change over time in the hydrogen storage amount in h ₂ BN-free Mg ₂ Ni. h-BN-free Mg ₂ Ni only occludes 0.6 wt% hydrogen after 10 hours. However, Mg ₂ Ni activated by h-BN immediately starts hydrogen occlusion, and hydrogen occlusion. The amount reached 3.2 wt% after 10 hours.
[0044]
As is clear from the above results, according to the method for activating a hydrogen storage material of the present invention, a large amount of hydrogen can be produced at a relatively low temperature of 200 ° C. without initial activation of Mg ₂ Ni under high temperature and high pressure hydrogen. I found that it can be occluded.
[0045]
[Example 7]
TiFe powder (0.9 g) and h-BN powder (0.1 g) are placed in a chrome steel planetary ball mill container (capacity 45 ml) together with chrome steel balls (7 mmφ × 22), and a planetary ball mill Using an apparatus, mechanical mixing was performed at room temperature under an Ar gas atmosphere for 2 hours. The rotation speed of the planetary ball mill device was 400 rpm.
[0046]
From the X-ray diffraction results of the mixed powder sample after ball mill mechanical mixing, no peaks other than those attributed to TiFe were observed, so there was no by-product of nitride and boride causing a decrease in hydrogen storage capacity. I understood it.
[0047]
On the other hand, the peak attributed to h-BN was broadened and the intensity was remarkably reduced, indicating that h-BN was refined to an almost disordered state. When the size of the crystallite was estimated from the X-ray diffraction and Raman spectroscopic spectrum, it became clear that the crystallite of h-BN was refined to about 5 nm.
[0048]
In order to investigate the hydrogen storage rate of this sample, the change over time of the hydrogen storage amount of this sample at 25 ° C. was measured in a hydrogen atmosphere of 2 MPa. The result is shown in FIG. 19 is the time-dependent change of the hydrogen storage amount in TiFe activated by h-BN, and 20 is the time-dependent change of the hydrogen storage amount in h-BN-free TiFe. The h-BN-free TiFe only occluded 0.1 wt% hydrogen after 24 hours. However, TiFe activated by h-BN started to quickly absorb hydrogen, and the hydrogen occlusion amount was 24 hours. Later, it reached 1.5 wt%.
[0049]
As is clear from the above results, it was found that TiFe can occlude a large amount of hydrogen under mild conditions of 25 ° C. without initial activation under high temperature and high pressure hydrogen by the activation method of the present invention.
[0050]
[Example 8]
Put Ti _1.2 CrV powder (0.9 g) and h-BN powder (0.1 g) into a chrome steel planetary ball mill device container (capacity 45 ml) together with chrome steel balls (7 mmφ × 22). Using a planetary ball mill apparatus, mechanical mixing was performed for 2 hours at room temperature in an Ar gas atmosphere. The rotation speed of the planetary ball mill device was 400 rpm.
[0051]
From the X-ray diffraction results of the mixed powder sample after ball mill mechanical mixing, no peaks other than those attributed to Ti _1.2 CrV were observed, so that nitrides, borides, etc. that cause a decrease in hydrogen storage amount It turned out that there was no by-product.
[0052]
On the other hand, the peak attributed to h-BN was broadened and the intensity was remarkably reduced, indicating that h-BN was refined to an almost disordered state. When the size of the crystallite was estimated from the X-ray diffraction and Raman spectroscopic spectrum, it became clear that the crystallite of h-BN was refined to about 10 nm.
[0053]
In order to investigate the hydrogen storage rate of this sample, the change over time of the hydrogen storage amount of this sample at 25 ° C. was measured in a hydrogen atmosphere of 2 MPa. The result is shown in FIG. 21 is the time-dependent change of the hydrogen storage amount in Ti _1.2 CrV activated by h-BN, and 22 is the time-dependent change of the hydrogen storage amount in h-BN-free Ti _1.2 CrV. The h-BN-free Ti _1.2 CrV only occluded 0.7 wt% hydrogen after 10 hours, but Ti _1.2 CrV activated by h-BN started hydrogen occlusion quickly. The hydrogen storage amount reached 2.9 wt% after 10 hours.
[0054]
As is clear from the above results, it can be seen that Ti _1.2 CrV can occlude a large amount of hydrogen under mild conditions of 25 ° C. without initial activation under high temperature and high pressure hydrogen by the activation method of the present invention. It was.
[0055]
In Examples 1 to 8, a powder of hydrogen storage alloy containing at least one kind of metal selected from Mg, Ti and V and Mg, Ti and V by a ball mill and hexagonal boron nitride are Ar. The gas atmosphere, that is, the inertness is not limited to the atmosphere, and the process can be performed in the air. In this case, the hydrogen storage capacity is somewhat reduced.
[0056]
【The invention's effect】
As described above, according to the present invention, a hydrogen storage alloy containing at least one kind of metal selected from Mg, Ti and V and Mg, Ti and V and hexagonal boron nitride are hexagonal. Mechanical mixing is performed so that the ratio of hexagonal boron nitride to the total weight of boron nitride is 10 to 50 wt%, and the crystallites of hexagonal boron nitride are refined to 20 nm or less, and the metal or the hydrogen occlusion is obtained. By adhering to the surface of the alloy, a hydrogen storage alloy containing Mg, Ti and V and at least one metal selected from Mg, Ti and V is treated at room temperature without treatment under high temperature and high pressure hydrogen. Initial activation can be easily performed in the vicinity.
[Brief description of the drawings]
FIG. 1 is a diagram showing a change in a hydrogen storage material in an activation process of the present invention.
FIG. 2 is a diagram showing the effect of the present invention on Ti.
FIG. 3 is a graph showing changes over time in the amount of hydrogen occlusion in samples having various h-BN crystallite sizes.
FIG. 4 is a graph showing the relationship between h-BN content and hydrogen storage amount.
FIG. 5 is a diagram showing the effect of the present invention in Mg.
FIG. 6 is a diagram showing the effect of the present invention in V.
FIG. 7 is a graph showing the effect of the present invention on Mg ₂ Ni.
FIG. 8 is a diagram showing the effect of the present invention on TiFe.
FIG. 9 is a diagram showing the effect of the present invention in Ti _1.2 CrV.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Hydrogen storage material at the time of start of activation processing of this invention 2 Hydrogen storage material after activation processing of this invention 3 Hydrogen storage material 4 Hexagonal boron nitride 5 Impurity film 6 Microstructured hexagonal boron nitride 7 h Change with time of hydrogen storage amount in Ti activated by BN 8 Change with time of hydrogen storage amount in h-BN-free Ti 9 Change with time of hydrogen storage amount of sample mixed for 0.5 hour 10 1 hour machine Change in Hydrogen Occlusion of Sample Mixed with Time 11 Change over Time in Hydrogen Occlusion of Sample Mixed for 2 Hours 125 Change over Time of Hydrogen Occluded in Sample Mixed for 5 Hours 13 Activated by h-BN Change with time of hydrogen storage amount in Mg 14 Change with time of hydrogen storage amount in Mg without addition of h-BN 15 Change with time of hydrogen storage amount in V activated by h-BN 16 No addition of h-BN in V Change with time of hydrogen storage amount in Mg ₂ Ni activated by h-BN 17 Change with time of hydrogen storage amount in Mg ₂ Ni without addition of h-BN 19 Time change of hydrogen storage amount in Mg ₂ Ni activated by h-BN Change over time of hydrogen storage amount in TiFe 20 h-BN non-addition time change of hydrogen storage amount in TiFe 21 Change over time of hydrogen storage amount in Ti _1.2 CrV activated by h-BN 22 No addition of h-BN Temporal change of hydrogen storage amount in Ti _1.2 CrV

Claims (3)

When activating a hydrogen storage alloy containing at least one metal selected from Mg, Ti and V and Mg, Ti and V, the metal or the hydrogen storage alloy and hexagonal boron nitride are used. A method of activating a hydrogen storage material that mechanically mixes to refine at least hexagonal boron nitride and reforms the surface state of the metal or the hydrogen storage alloy ,
The ratio of hexagonal boron nitride to the total weight of the metal or hydrogen storage alloy and hexagonal boron nitride is 10 to 50 wt%,
A method for activating a hydrogen storage material , wherein the crystallites of hexagonal boron nitride are refined to 20 nm or less and adhered to the surface of the metal or the hydrogen storage alloy . Oite to claim 1, method for activating the hydrogen storage material characterized by using a high energy ball mill as a means of mechanical mixing. 3. The method for activating a hydrogen storage material according to claim 1, wherein the mechanical mixing is performed in an inert gas atmosphere.

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