JP2007069184A - Hydrogen adsorbing material for adsorbing/desorbing hydrogen at low temperature and low-temperature hydrogen storage vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen adsorbing material for adsorbing/desorbing hydrogen at low temperature, in which low-temperature hydrogen gas to be generated by vaporization of liquid hydrogen can be stored in relatively large quantities and from which the stored hydrogen can be desorbed easily and to provide a low-temperature hydrogen storage vessel using the hydrogen adsorbing material. <P>SOLUTION: The hydrogen adsorbing material for adsorbing/desorbing hydrogen at low temperature contains h-BNH obtained by crushing h-BN (hexagonal boron nitride) mechanically in a hydrogen atmosphere. The low-temperature hydrogen storage vessel is formed by fixing the hydrogen adsorbing material for adsorbing/desorbing hydrogen at low temperature on the inner wall thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydrogen adsorbing material for low-temperature hydrogen adsorption / release and a low-temperature hydrogen storage container. More specifically, the present invention can store a relatively large amount of low-temperature hydrogen gas generated by evaporation of liquid hydrogen, and can The present invention relates to a hydrogen-adsorbing material for low-temperature hydrogen adsorption / release capable of easily releasing hydrogen and a low-temperature hydrogen storage container using the same.

  In recent years, hydrogen energy has attracted attention as a clean alternative energy because of environmental problems such as global warming caused by carbon dioxide emissions and energy problems such as the depletion of petroleum resources. Hydrogen is not only clean, but also the lightest fuel and is characterized by a high energy density per mass. However, hydrogen is a gas at normal temperature and normal pressure, and has a drawback that the amount of stored energy per unit volume is small. Therefore, in order to put hydrogen energy into practical use, it is important to develop technology for storing and transporting hydrogen safely and efficiently.

As a method of storing hydrogen,
(1) A first method for storing high-pressure hydrogen gas in a pressure vessel,
(2) a second method for storing liquid hydrogen in an insulated container;
(3) a third method in which hydrogen is physically or chemically adsorbed to a certain material;
Etc. are known.
As a material (hydrogen storage material) that can physically or chemically adsorb (store) hydrogen,
(1) Carbon materials such as activated carbon, fullerene and nanotubes,
(2) Hydrogen storage alloys such as LaNi ₅ and TiFe,
Etc. are known.

Non-Patent Document 1 discloses nanostructure h-BN obtained by pulverizing h-BN in a hydrogen atmosphere. In the same document,
(1) The size of h-BN crystals after grinding for 80 hours is about 3 nm,
(2) The hydrogen concentration measured by OCHA (oxygen-combustion hydrogen analysis) of this h-BN reaches 2.6 mass%, and
(3) Even if this h-BN is heated to 1173K, a part of hydrogen remains trapped in h-BN,
Is described.

P.Wang et al., Appl.Phys.Lett., Vol.80, No.2, 14 January (2002) 318-320

Of the various hydrogen storage methods described above, the first method is a very simple storage method. However, since the weight of the pressure vessel is large and the compression of hydrogen gas is limited, the hydrogen density per unit volume and unit weight is relatively small.
On the other hand, the third method is notable as a transportable hydrogen storage method because it can store hydrogen at a density equal to or higher than that of liquid hydrogen and does not require special containers or a large amount of energy for storage. Yes. However, since the carbon material has a low specific gravity, there is a drawback that the hydrogen density per unit volume is small.
In addition, hydrogen storage alloy
(1) Many of them contain rare metals such as La, Ni, Ti, etc., it is difficult to secure resources, and the cost is high.
(2) Since the weight of the alloy itself is large, the hydrogen density per unit weight is small, that is, an extremely heavy storage material is required to store a large amount of hydrogen.
(3) In the storage of hydrogen into the hydrogen storage alloy, hydrogen molecules are adsorbed on the metal surface, dissociate into hydrogen atoms, diffuse into the interior, and fill the gaps between the metal lattices. When the hydrogen concentration in the metal increases and hydrogen is dissolved in the alloy to some extent, a phase change occurs in a new compound phase called hydride. Therefore, in order to quickly release a large amount of hydrogen, it is necessary to heat.
There are disadvantages such as.
Furthermore, in the nanostructure h-BN, since hydrogen is strongly chemisorbed, it is extremely difficult to release the chemisorbed hydrogen in a practical temperature range.

In contrast, the second method is
(1) A large amount of energy is consumed to liquefy hydrogen.
(2) A special insulated container is required for storage of liquid hydrogen.
However, the volume of hydrogen can be greatly reduced by liquefaction. Therefore, the second method is the most realistic hydrogen storage method at present.
However, even when liquid hydrogen is stored in a heat insulating container, there is a problem that liquid hydrogen tends to evaporate due to heat entering from the outside. Further, there has never been an example in which specific means for reducing such an evaporation loss of liquid hydrogen has been proposed.

The problem to be solved by the present invention is a low-temperature hydrogen that can store a relatively large amount of low-temperature hydrogen gas generated by evaporation of liquid hydrogen and can easily release the stored hydrogen. An object of the present invention is to provide a hydrogen adsorption material for adsorption / release and a low-temperature hydrogen storage container using the same.
Another object of the present invention is to provide a low-temperature hydrogen storage container that can reduce the evaporation loss of liquid hydrogen.

In order to solve the above problems, the hydrogen adsorption material for low-temperature hydrogen adsorption / release according to the present invention comprises h-BNH obtained by mechanically pulverizing h-BN in a hydrogen atmosphere.
Moreover, the low-temperature hydrogen storage container according to the present invention is composed of the hydrogen adsorption material for low-temperature hydrogen adsorption / release according to the present invention fixed to the inner wall thereof.

  The amount of adsorbed and released hydrogen at a low temperature (for example, around −196 ° C.) of h-BNH is at least twice that of h-BN. Therefore, if this is used for the inner wall material of the heat insulating container for storing liquid hydrogen, low-temperature hydrogen gas generated by evaporation of liquid hydrogen can be temporarily stored in h-BNH. Moreover, since h-BNH has a low thermal conductivity, the evaporation loss of liquid hydrogen can be further reduced by using it for the inner wall of the heat insulating container. Further, when a container (boil-off hydrogen storage container) in which h-BNH is fixed to the inner wall is connected to the heat insulating container in which liquid hydrogen is stored, the evaporated hydrogen gas can be temporarily stored. Therefore, the evaporation loss of liquid hydrogen can be further reduced.

Hereinafter, an embodiment of the present invention will be described in detail.
The hydrogen adsorption material for low temperature hydrogen adsorption / release according to the present invention contains h-BNH.
Here, “h-BNH” refers to a material obtained by mechanically pulverizing h-BN (hexagonal boron nitride) in a hydrogen atmosphere. h-BNH is considered that hydrogen is chemisorbed on h-BN. Hydrogen chemisorbed on h-BNH is relatively stable, and it is difficult to release it in a practical temperature range. However, h-BNH has a property of physically adsorbing a relatively large amount of hydrogen at a low temperature. The physically adsorbed hydrogen can be easily released by setting the temperature higher than the adsorption temperature. Also, reversible hydrogen adsorption / release is extremely easy.
The amount of physical adsorption of hydrogen on h-BNH depends on the specific surface area of h-BNH. In general, the higher the specific surface area of h-BNH, the greater the amount of physical adsorption of hydrogen. In order to adsorb a relatively large amount of hydrogen, the specific surface area of h-BNH is preferably 300 m ² / g or more, and more preferably 500 m ² / g or more.

The hydrogen adsorption material for low temperature hydrogen adsorption / release according to the present invention may be composed of only h-BNH, or may be a complex containing other components. Specifically, as other ingredients,
(1) Other hydrogen adsorption materials having properties similar to h-BNH,
(2) binder,
and so on.

Examples of other hydrogen adsorbing materials having properties similar to h-BNH include carbon such as graphite, activated carbon, fullerene, and carbon nanotube. Carbon has a property of physically adsorbing a relatively large amount of hydrogen at a low temperature, and depending on the type, carbon can adsorb a larger amount of hydrogen than h-BNH. However, since carbon has a high thermal conductivity, in order to keep adsorbing low-temperature hydrogen, it is necessary to store it in a special heat insulating container and block heat entering from the outside.
On the other hand, since h-BNH has a low thermal conductivity, the structure of the heat insulating container can be simplified. Further, when this is combined with carbon, a hydrogen adsorbing material having high heat insulating properties and capable of adsorbing and releasing a large amount of hydrogen is obtained. In particular, activated carbon is suitable as a material to be used in combination with h-BNH because it has a large amount of hydrogen adsorption at low temperatures.

As a method for combining h-BNH with other hydrogen-adsorbing materials having properties similar to h-BNH such as carbon, specifically,
(1) A method of mixing h-BNH powder and powder of other hydrogen adsorption material,
(2) A method of forming a mixture of h-BNH powder and powder of other hydrogen adsorption material into a predetermined shape such as a pellet shape or a tile shape,
(3) A method of arranging h-BNH compacts and other hydrogen-adsorbing material compacts randomly or regularly.
(4) a combination of these methods,
and so on.
In this case, the ratio between h-BNH and the other hydrogen-adsorbing material can be arbitrarily selected according to the purpose. For example, when carbon (for example, activated carbon) having a larger amount of hydrogen adsorption than h-BNH is used as another hydrogen adsorption material, the amount of hydrogen adsorption increases as the carbon ratio increases. However, since carbon generally has a higher thermal conductivity than h-BNH, the higher the ratio, the lower the heat insulation. In order to obtain moderate heat insulation and relatively high hydrogen adsorption characteristics, the h-BNH: carbon ratio (weight ratio) is preferably 1: 1 to 4.

Examples of the binder include fluorine resins such as polytetrafluoroethylene, acrylic resins, urethane resins, polyester resins, polypropylene resins, and epoxy resins. As described above, h-BNH or carbon may be used as a powder, but when the powder is molded and used, it can be easily fixed to the inner wall of the hydrogen storage container. Further, since there is little scattering of the powder at the time of hydrogen adsorption / release, there is an advantage that the structure of the filter installed in the vicinity of the valve can be simplified or eliminated.
However, these materials generally have poor moldability, and there are cases where a molded body having a practically sufficient strength cannot be obtained by molding only powder. In such a case, it is preferable to add a binder to the h-BNH powder or a mixture obtained by adding a powder such as carbon thereto.
In this case, the addition amount of the binder is not particularly limited, and an optimum addition amount is selected according to the composition of the powder, the kind of the binder, and the like so that the desired strength can be obtained. Usually, a binder of about 1 wt% to 2 wt% is added to the powder.

Next, the manufacturing method of the hydrogen adsorption material for low temperature hydrogen adsorption / release according to the present invention will be described. As described above, h-BNH is obtained by mechanically pulverizing h-BN in a hydrogen atmosphere.
Generally, when the hydrogen pressure at the time of pulverization is low, a sufficient amount of h-BNH cannot be obtained due to a lack of hydrogen. In order to efficiently produce h-BNH, the hydrogen pressure is preferably 0.5 MPa or more, and more preferably 1 MPa or more.
On the other hand, more pressure than necessary has no real benefit. Therefore, the hydrogen pressure during pulverization is preferably 3 MPa or less, and more preferably 2 MPa or less.

The “mechanical pulverization process” refers to a process (so-called “mechanical grinding (MG) process”) in which mechanical energy is applied to a starting material by rotation, vibration, impact, or the like, and the mixture is uniformly mixed while being pulverized. The kind of pulverizer used for the treatment is not particularly limited, and various pulverizers such as a planetary ball mill, a rotary mill, and a vibration mill can be used.
In general, as the energy (or acceleration) during pulverization increases, the pulverization can be performed in a relatively short time. In addition, when h-BN is mechanically pulverized in a hydrogen atmosphere, h-BNH having a large specific surface area is generally obtained as the pulverization time is increased and / or the energy during pulverization is increased.
On the other hand, if an excessive pulverization treatment is performed, the pulverized h-BNH may re-aggregate during the pulverization, and the specific surface area may decrease. Therefore, it is preferable to select the optimum processing conditions according to the type of pulverizer to be used, the amount of powder charged into the pulverizer, and the like. For example, when performing MG processing using a planetary ball mill, it is preferable to perform pulverization processing for several hours to 100 hours at an acceleration of about 2 to 5 G.

  The h-BNH thus obtained can be used as a powder, but when it is used as a molded body, it is molded at an appropriate pressure. The molding method is not particularly limited, and various methods such as mold molding and CIP molding can be used. Moreover, it is preferable that the pressure at the time of molding is a pressure that does not crush the pores of h-BNH. Moreover, when shaping | molding, you may add other hydrogen adsorption materials and binders, such as a predetermined amount of carbon, to h-BNH as needed.

Next, a method of using the hydrogen adsorption material for low temperature hydrogen adsorption / release according to the present invention will be described.
The boiling point of liquid hydrogen is −252.6 ° C., and the hydrogen gas immediately after evaporation from the liquid hydrogen has a temperature of this level. The evaporated hydrogen accumulates in the upper part of the storage container and is heated by the heat entering from the inner wall of the upper part of the container, and the temperature gradually rises. Also, the hydrogen gas taken out from the storage container is supplied to a hydrogen gas consumption source (for example, a fuel cell) through a pipe, but is also heated by the heat entering through the pipe at that time, and the temperature is increased. Increasing gradually.

The hydrogen adsorbing material according to the present invention is used as a hydrogen adsorbing material for adsorbing and releasing relatively low temperature hydrogen gas, such as hydrogen gas obtained by evaporating liquid hydrogen. In general, the hydrogen adsorption amount of h-BNH increases as the temperature of the hydrogen gas decreases. In order to efficiently adsorb and release hydrogen using the hydrogen adsorbing material according to the present invention, the temperature of the hydrogen gas (or hydrogen adsorbing material) at the time of adsorption is preferably −100 ° C. or less, more preferably − It is 150 degrees C or less, More preferably, it is -190 degrees C or less.
In addition, when releasing the adsorbed hydrogen, it is only necessary to heat the hydrogen adsorbing material to a temperature higher than the adsorption temperature. Since hydrogen is only physically adsorbed mainly to h-BNH, the adsorbed hydrogen can be easily released by raising the temperature.

Next, the operation of the hydrogen adsorption material for low temperature hydrogen adsorption / release according to the present invention will be described.
h-BN has a crystal structure similar to graphite, and has a scaly crystal structure in which sheets of B atoms and N atoms are stacked in the c-axis direction. As shown in FIG. 1A, each sheet has a structure in which six-membered rings in which B atoms and N atoms are alternately arranged are periodically arranged. When such h-BN is mechanically pulverized in a hydrogen atmosphere, as shown in FIG. 1B, the BN bond in the sheet surface is broken to form nano-sized BN. At the same time, it is considered that hydrogen is chemisorbed on the bonds of B and / or N that have become free after the bond is broken, and new B—H and / or N—H bonds are formed. h-BNH refers to nano-sized h-BN containing such chemisorbed hydrogen.

Hydrogen chemisorbed on h-BNH is relatively stable, and in order to release it, it is necessary to heat it to a relatively high temperature (600 ° C. or higher). Accordingly, it is difficult to release the chemisorbed hydrogen in a practical temperature range.
However, when h-BNH is brought into contact with relatively low temperature hydrogen, a relatively large amount of hydrogen is adsorbed. This is because h-BNH is a nanocrystallite, as shown in FIG. 1C, and has many edge portions, and hydrogen is considered to be physically adsorbed on this edge portion. In addition, h-BNH has a hydrogen adsorption amount at a low temperature that is twice or more that of h-BN. Details of the reason are unknown, but it is probably due to interaction with chemisorbed hydrogen.

  Next, a liquid hydrogen storage system using the low-temperature hydrogen storage container according to the present invention will be described. FIG. 2 shows an example of a liquid hydrogen storage system. In FIG. 2, the liquid hydrogen storage system 10 includes a first low-temperature hydrogen storage container (hereinafter referred to as “liquid hydrogen storage container”) 20 and a second low-temperature hydrogen storage container (hereinafter referred to as “boil-off hydrogen storage”). 40).

The liquid hydrogen storage container 20 is a container for storing the liquid hydrogen 12, and is a molded body (hereinafter simply referred to as "molded body") made of the container 22 and a hydrogen adsorbing material according to the present invention fixed to the inner wall thereof. 24.
The container 22 has a heat insulating structure in which a blocking material is filled between the inner wall and the outer wall.
The molded body 24 may be composed only of h-BNH, or may be a composite of h-BNH and another hydrogen adsorption material (for example, carbon). In general, the higher the h-BNH content in the molded body 24, the higher the heat insulation. The thickness of the molded body 24 is not particularly limited, and can be arbitrarily selected according to the characteristics required for the liquid hydrogen storage container 20. In general, the thicker the molded body 24, the greater the amount of hydrogen gas adsorbed and the higher the heat insulation of the liquid hydrogen storage container 20.
Since the molded body 24 has a function as a heat insulating material in addition to a function as a hydrogen adsorbing material, it is preferably fixed to the entire inner wall of the container 22, but a part of the container 22 (for example, the container 22). It may be fixed to the inner wall of the inner wall or the like. Moreover, the fixing method of the molded object 24 is not specifically limited, Various methods, such as an adhesive agent and a bolt stop, can be used.

A heater 26 for heating the liquid hydrogen 12 and a liquid level meter 28 for measuring the remaining amount of the liquid hydrogen 12 are provided in the container 22.
A filling pipe 30 for filling the liquid hydrogen 12 is connected to the upper part of the container 22. A filling port 30 a for filling the liquid hydrogen 12 into the container 22 is provided at the tip of the filling pipe 30. In addition, an opening / closing valve 30 b for opening and closing the filling pipe 30 is provided in the vicinity of the container 22.

Further, a supply pipe 32 for sending the vaporized hydrogen gas to a hydrogen consumption source (for example, a fuel cell stack) is connected to the container 22. The supply pipe 32 is provided with a backflow valve (gas / liquid) 32a, a heat exchanger 32b, and an automatic shut-off valve 32c.
The backflow valve (gas / liquid) 32 a is for sending only hydrogen gas supplied to the supply pipe 32 to the hydrogen consumption source and returning liquid hydrogen condensed in the supply pipe 32 to the container 22.
The heat exchanger 32b also sends a part of the hydrogen gas supplied into the supply pipe 32 into the heat exchange pipe, and exchanges heat between the hydrogen gas in the supply pipe 32 and the hydrogen gas in the heat exchange pipe. To increase the internal pressure of the hydrogen gas in the supply pipe 32.
Furthermore, the automatic shut-off valve 32c is an automatic control valve for supplying an appropriate amount of hydrogen to the hydrogen consumption source. When the hydrogen pressure (flow rate) exceeds the pressure (flow rate) required for the hydrogen consumption source, it automatically The supply pipe 32 is shut off.

The boil-off hydrogen storage container 40 is for temporarily storing surplus hydrogen gas generated in the liquid hydrogen storage container 20, and includes a container 42 and a hydrogen adsorbing material according to the present invention fixed to the inner wall of the container 42. And a second hydrogen-adsorbing material (hereinafter simply referred to as “filler”) 46 filled in the container 42.
The container 42 includes a heat insulating structure in which a blocking material is filled between the inner wall and the outer wall.
The compact 44 may be composed of only h-BNH, or may be a composite of h-BNH and another hydrogen adsorbing material (for example, carbon). In general, the higher the h-BNH content in the molded body 44, the higher the heat insulation. The thickness of the molded body 44 is not particularly limited, and can be arbitrarily selected according to the characteristics required for the boil-off hydrogen storage container 40. In general, as the thickness of the molded body 44 increases, the amount of evaporated hydrogen gas adsorbed increases, and the heat insulation of the boil-off hydrogen storage container 40 increases.
Since the molded body 44 has a function as a heat insulating material in addition to a function as a hydrogen adsorbing material, it is preferably fixed to the entire inner wall of the container 42, but a part of the container 42 (for example, the container 42). It may be fixed to the inner wall of the inner wall or the like. Moreover, the fixing method of the molded object 44 is not specifically limited, Various methods, such as an adhesive agent and a bolt stop, can be used.

  The filler 46 is made of a material that can adsorb a low-temperature hydrogen gas such as h-BNH or carbon. The filler 46 is not required to have much heat insulation, so it is preferable to use carbon having a large hydrogen adsorption amount. The filler 46 may be a powder or a molded body having an appropriate size and shape. When a molded body is used as the filler 46, it is possible to suppress the scattering of powder during the adsorption and release of hydrogen, simplify the structure of the filter provided at the hydrogen filling port and / or the discharge port, or omit the filter itself. There is.

  The boil-off hydrogen storage container 40 and the liquid hydrogen storage container 20 are connected by a connection pipe 48 branched from the supply pipe 32. The connection pipe 48 is provided with a boil-off valve 48a for opening and closing the connection pipe 48. A safety valve 50 is provided between the branch point of the connection pipe 48 and the supply pipe 32 and the boil-off valve 48a. Further, the container 42 is provided with a supply pipe 52 for supplying hydrogen gas released from the boil-off hydrogen storage container 40 to a hydrogen consumption source (for example, a fuel cell). The supply pipe 52 is provided with a shutoff valve 52a for opening and closing the supply pipe 52.

Next, a method for using the liquid hydrogen storage system 10 shown in FIG. 2 will be described. First, with the automatic shut-off valve 32c, boil-off valve 48a, safety valve 50, and shut-off valve 52a closed, the on-off valve 30b is opened, and the liquid hydrogen 12 is filled into the container 22 from the filling port 30a. After filling, the on-off valve 30b is closed. If left in this state, the liquid hydrogen 12 evaporates due to heat flowing from outside the container 22, and the container 22 is filled with hydrogen gas. A part thereof is adsorbed to the molded body 24.
If it is left to stand without using hydrogen gas, the adsorption of hydrogen by the molded body 24 is saturated and the internal pressure of the container 22 increases. When the internal pressure of the container 22 exceeds a certain value, the boil-off valve 48a is opened. When the boil-off valve 48 a is opened, the hydrogen gas in the container 22 flows into the boil-off hydrogen storage container 40, and the hydrogen gas is adsorbed by the compact 44 and the filler 46. When the adsorption of hydrogen by the molded body 44 and the filler 46 is saturated, the internal pressure of the container 42 rises. Therefore, when the internal pressure of the container 42 exceeds a certain level, the safety valve 50 is opened to remove a part of the excess hydrogen gas. Discharge.

When hydrogen gas is used, first, the liquid hydrogen 12 is heated by the heater 26 with the automatic shut-off valve 32c, the boil-off valve 48a, and the safety valve 50 closed, and the internal pressure of the container 22 is increased. Next, when the automatic shut-off valve 32 c is opened, the hydrogen gas is supplied to the hydrogen consumption source through the supply pipe 32. In this case, the supplied hydrogen gas is mainly hydrogen gas generated by evaporation of the liquid hydrogen 12, but also includes hydrogen gas released from the molded body 24.
When supplying hydrogen gas, liquid hydrogen is separated from the hydrogen gas by the backflow valve (gas / liquid) 32a, and only hydrogen gas is sent to the hydrogen consumption source. Further, the internal pressure of the hydrogen gas in the supply pipe 32 is increased as appropriate by the heat exchanger 32b. When the hydrogen pressure (flow rate) supplied to the hydrogen consumption source becomes more than necessary, the automatic shutoff valve 32c is closed and the supply of hydrogen gas is stopped.
Moreover, when using the hydrogen stored in the boil-off hydrogen storage container 40, it is only necessary to open the shut-off valve 52a. When the shut-off valve 52a is opened, the hydrogen gas released from the molded body 44 and the filler 46 is supplied to the hydrogen consumption source through the supply pipe 52.

Conventional liquid hydrogen storage containers are simply structured to store liquid hydrogen in an insulated container. Therefore, there is a problem that liquid hydrogen gradually evaporates due to heat entering through the outer wall of the heat insulating container, and hydrogen evaporation loss is large.
On the other hand, in the liquid hydrogen storage system 10 according to the present invention, the hydrogen adsorption material for low temperature hydrogen adsorption / release according to the present invention is fixed to the inner wall of the liquid hydrogen storage container 20, so that the liquid hydrogen storage system 10 enters through the outer wall of the heat insulation container. The amount of heat to be reduced can be reduced. A part of the evaporated hydrogen gas is adsorbed by the hydrogen adsorbing material for low-temperature hydrogen adsorption / release. Therefore, hydrogen evaporation loss can be reduced compared to conventional containers.
Furthermore, since the boil-off hydrogen storage container 40 is connected to the liquid hydrogen storage container 20, the liquid hydrogen storage system 10 according to the present invention can store a large amount of evaporated hydrogen gas. Therefore, hydrogen evaporation loss can be further reduced as compared with the case where only the liquid hydrogen storage container 20 is used.

Example 1
h-BN (5 g) was placed in a chrome steel container (volume: 300 ml) together with 40 chrome steel balls (outer diameter 9.5 mm) and subjected to MG treatment with a planetary ball mill P-5 (manufactured by FRITSCH). The MG treatment was performed for 0 to 100 hours under a hydrogen gas atmosphere (1 MPa), room temperature, and grinding energy of 5 G (motor rotation speed 1300 rpm).
(Comparative Example 1)
MG treatment of h-BN was performed under the same conditions as in Example 1 except that the atmosphere during MG treatment was an argon atmosphere (0.1 MPa).

FIG. 3 shows infrared absorption spectra of h-BNH (MG treatment time: 24 hours) after hydrogen MG treatment and h-BN before MG treatment. FIG. 3 shows that absorption of stretching vibration based on the B—H bond (2520 cm ⁻¹ ) and the N—H bond (3440 cm ⁻¹ ) is observed by the hydrogen MG treatment, that is, by hydrogen MG treatment, It can be seen that -H bond and N-H bond are newly generated.
FIG. 4 shows an X-ray diffraction pattern of h-BNH after hydrogen MG treatment (MG treatment time: 24 hours). From FIG. 4, it can be seen that microcrystals are formed by the MG treatment.
Further, FIGS. 5A and 5B show TEM photographs of h-BN before hydrogen MG treatment and h-BNH after hydrogen MG treatment (MG treatment time: 24 hours), respectively. From FIG. 5, it can be seen that the several μm h-BN crystal is cracked in the hexagonal plane direction (perpendicular to the c-plane) by hydrogen MG treatment to form a microcrystal of several tens of nm.

Next, the hydrogen physical adsorption amount of h-BNH treated with hydrogen MG and h-BN treated with MG in an argon atmosphere was measured. The hydrogen adsorption conditions were temperature: −196 ° C. and hydrogen gas pressure: 2 MPa. FIG. 6 shows the relationship between the MG processing time and the hydrogen adsorption amount. Table 1 shows the relationship between the h-BNH MG treatment time and the specific surface area.
The specific surface area of h-BNH reached a maximum (320 m ² / g) when the MG treatment time was 24 hours. When the MG treatment time was further increased, the specific surface area of h-BNH was decreased. This is thought to be due to the reaggregation of h-BNH caused by excessive MG treatment. The specific surface area of h-BN showed almost the same tendency, and the specific surface area reached the maximum (about 300 m ² / g) after 24 hours of MG treatment.
Further, the physical adsorption amount of hydrogen in h-BNH reached the maximum (about 1.3 wt%) when the MG treatment time was 24 hours. The hydrogen physical adsorption amount of h-BNH has a correlation with the specific surface area, and the physical adsorption amount increased as the specific surface area increased. This is presumably because h-BNH is broken in the hexagonal plane direction by hydrogen MG treatment and many edges appear (see FIG. 5B), and hydrogen is physically adsorbed at this site.
Furthermore, the amount of hydrogen physically adsorbed by h-BNH was more than twice that of h-BN having a substantially equivalent specific surface area. This is considered to be due to the interaction with hydrogen chemisorbed on h-BNH.

Since h-BNH treated with hydrogen MG (MG treatment time: 24 hours) chemically adsorbs about 2 wt% of hydrogen, there is a total amount of hydrogen adsorbed of about 3 wt% at −196 ° C. Further, if the MG treatment is optimized, h-BNH can be made into nanocrystals of about 10 nm, so that the specific surface area can be sufficiently up to about 500 m ² / g. When the specific surface area is 500 m ² / g, the physical adsorption amount of hydrogen is about 1.5 wt%.

(Example 2)
H-BNH after hydrogen MG treatment (MG treatment time: 24 hours), super activated carbon (MSC30, manufactured by Kansai Thermal Chemical Co., Ltd.) or graphite (specific surface area: 10 m ² / g or less, manufactured by Aldrich, catalog No. 496596-113.4G) was mixed 1: 1 by weight. About the obtained mixture, the physical adsorption amount of hydrogen was measured on the conditions of temperature: -196 degreeC and hydrogen gas pressure: 2MPa.
(Comparative Example 2)
Super activated carbon (MSC30, manufactured by Kansai Thermal Chemical Co., Ltd.), boron powder (specific surface area: 10 m ² / g or less, manufactured by High Purity Chemical Co., catalog No. BBE01PB), and boron carbide powder (specific surface area: 10 m ² / g or less, high-purity chemical stock, catalog No. BBI03PB), the physical adsorption amount of hydrogen was measured under the same conditions as in Example 2.

Table 2 shows the amount of physical adsorption of hydrogen of various materials. Table 2 also shows the hydrogen physical adsorption amount of h-BNH (MG treatment time: 24 hours) obtained in Example 1.
From Table 2,
(1) Super activated carbon has a large amount of hydrogen adsorption, but poor heat insulation.
(2) B and B ₄ C have moderate heat insulation properties, but the hydrogen adsorption amount is small.
(3) h-BNH has a slightly lower hydrogen adsorption amount than super activated carbon, but has high heat insulation properties.
(4) A mixture of h-BNH and super activated carbon or graphite has a relatively large amount of hydrogen adsorption, and has an appropriate heat insulating property.
I understand that.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

The hydrogen adsorption material for low temperature hydrogen adsorption / release according to the present invention can be used as a hydrogen storage material for storing low temperature hydrogen gas generated by evaporation of liquid hydrogen.
The low-temperature hydrogen storage container according to the present invention may be used as hydrogen storage means for storing liquid hydrogen supplied to a hydrogen consumption source such as a fuel cell or low-temperature hydrogen gas generated by evaporation of liquid hydrogen. it can.

It is a schematic diagram which shows the crystal structure of h-BN and h-BNH obtained by carrying out MG process of this in hydrogen atmosphere. It is a schematic block diagram of the liquid hydrogen storage system using the low-temperature hydrogen storage container which concerns on this invention. It is an infrared absorption spectrum of h-BN and h-BNH. It is an X-ray diffraction pattern of h-BNH. FIG. 5 (a) is a TEM photograph of h-BN, and FIG. 5 (b) is a TEM photograph of h-BNH. It is a figure which shows the relationship between MG processing time of h-BNH and h-BN, and hydrogen adsorption amount.

Explanation of symbols

10 Liquid hydrogen storage system 20 Low temperature hydrogen storage container (liquid hydrogen storage container)
22 Container 24 Hydrogen adsorption material for low temperature hydrogen adsorption / release (molded body)
40 Low temperature hydrogen storage container (boil-off hydrogen storage container)
42 Container 44 Hydrogen adsorption material for low temperature hydrogen adsorption / release (molded body)
46 Filler (Carbon)

Claims (7)

  A hydrogen adsorption material for low temperature hydrogen adsorption / release containing h-BNH obtained by mechanically pulverizing h-BN in a hydrogen atmosphere. ^{2. The} hydrogen adsorption material for low-temperature hydrogen adsorption / release according to claim 1, wherein the h-BNH has a specific surface area of 300 m ² / g or more.   The hydrogen adsorption material for low-temperature hydrogen adsorption / release according to claim 1 or 2, comprising a composite of the h-BNH and carbon.   A hydrogen adsorption material for low-temperature hydrogen adsorption / release obtained by molding the powder containing the h-BNH according to any one of claims 1 to 3.   A low-temperature hydrogen storage container in which the hydrogen-adsorbing material for low-temperature hydrogen adsorption / release according to claim 4 is fixed to an inner wall thereof.   The low-temperature hydrogen storage container according to claim 5, wherein the second hydrogen-adsorbing material is further filled therein. The low-temperature hydrogen storage container according to claim 6, wherein the second hydrogen adsorption material is carbon.

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