JP2004290811A - Hydrogen storage material and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen storage material having a high hydrogen occluding capacity, and its manufacturing method. <P>SOLUTION: In manufacturing the hydrogen storage material using a hydrogen storing functional material developing the hydrogen occluding capacity by micronizing the hydrogen storing functional material by mechanical grinding under a hydrogen gas atmosphere, a metal component, which has a function for dissociating a hydrogen molecule into hydrogen atoms, is added to the hydrogen storing functional material on the way of the mechanical grinding of the hydrogen storing functional material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrogen storage capable of storing a large amount of hydrogen at a relatively low temperature and a method for producing the same. The hydrogen storage medium of the present invention is used as a hydrogen storage medium for a fuel cell vehicle, a medium for storing and transporting hydrogen gas, and for separating and purifying hydrogen gas.
[0002]
[Prior art]
Due to the depletion of fossil fuels and global environmental problems, natural energy and renewable energy are promising as secondary energy alternatives to fossil fuels. In particular, hydrogen gas is expected to be an important material in the energy cycle.
[0003]
However, the biggest problem using hydrogen as fuel is the storage of hydrogen as fuel. At present, as a means of storing hydrogen as a gas, there is storage of hydrogen by a high-pressure gas cylinder, but in order to increase the amount of stored hydrogen, it is necessary to increase the hydrogen pressure, and as the weight of the container increases, There are problems with the pressure resistance and reliability of valves and the like. As a means for storing hydrogen as a liquid, there is a method of storing liquid hydrogen in a heat insulating container. However, liquid hydrogen has a very low boiling point, requires a lot of energy for liquefaction, and a loss due to evaporation of 10 to 20% during supply of liquid hydrogen to an insulated container, and 8% of hydrogen even when insulated. Is said to evaporate, which is economically problematic.
[0004]
Recently, attention has been paid to carbon-based materials such as carbon nanotubes and activated carbon as hydrogen storage materials for solving these problems, and active research has been conducted.
[0005]
For example, Patent Document 1 proposes a method of storing hydrogen in carbon nanotubes. Patent Literature 2 proposes a method of adsorbing hydrogen on a fine structure using activated carbon. Further, Patent Document 3 proposed by the present inventor previously proposes a hydrogen storage material having high hydrogen storage capacity using graphite nanostructured by mechanical pulverization.
[0006]
[Patent Document 1]
JP-A-11-116219 [Patent Document 2]
WO98 / 30496 [Patent Document 3]
JP 2001-302224 A
[Problems to be solved by the invention]
However, although it is reported that the carbon nanotube of Patent Document 1 is produced by a thermal decomposition reaction and has a low yield and can store a large amount of hydrogen, it has a drawback that reproducibility cannot be obtained. Therefore, it is not preferable as an industrial production method. Further, the activated carbon of Patent Document 2 requires an extremely low temperature and a high pressure, such as a temperature of −173 ° C. or less and a hydrogen pressure of about 5 MPa, for storing hydrogen, which is not preferable as an industrial production method. On the other hand, Patent Document 3 mentioned above can store a relatively large amount of hydrogen at normal temperature and under low pressure, but it is still not enough.
[0008]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a hydrogen storage body having a high hydrogen storage capacity and a method for producing the same.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have developed a technique disclosed in Japanese Patent Application Laid-Open No. 2001-302224 to further improve the hydrogen storage capacity of nanostructured graphite by mechanical pulverization under a hydrogen gas atmosphere. The examination was repeated. As a result, if a metal component that functions as a catalyst and has a function of dissociating hydrogen molecules into hydrogen atoms is added during the mechanical grinding of graphite, the metal component is not thickly covered with the hydrogen storage function material, It has been found that the component can be supported in a highly dispersed state, and a high hydrogen storage capacity can be obtained by the action of the metal component. Such an effect can be similarly obtained not only for graphite but also for other hydrogen storage function materials that exhibit a hydrogen storage function by being finely divided by mechanical pulverization in a hydrogen gas atmosphere.
[0010]
The present invention has been completed based on such findings of the present inventors, and provides the following (1) to (7).
[0011]
(1) In producing a hydrogen storage body using a hydrogen storage function material that exhibits a hydrogen storage function by mechanically pulverizing it under a hydrogen gas atmosphere, it has a function of dissociating hydrogen molecules into hydrogen atoms. A method for producing a hydrogen storage body, comprising adding a metal component during the mechanical pulverization of the hydrogen storage function material.
(2) In the above (1), the metal component having a function of dissociating the hydrogen molecule into a hydrogen atom is Mn, Fe, Co, Ni, Pt, Pd, Rh, Li, B, Na, Mg, K, Ir. , Nd, La, Ca, V, Ti, Cr, Cu, Zn, Al, Si, Ru and Ag, or a hydrogen storage alloy characterized by being a hydrogen storage alloy. Production method.
(3) In the above (2), the metal component having a function of dissociating the hydrogen molecule into a hydrogen atom is one or more elemental metals selected from the above elements, one or more elemental metals selected from the above elements, or A method for producing a hydrogen storage body, which is in any form of an alloy, an oxide, a nitride, a chloride, or another compound containing two or more kinds of components.
(4) In the above items (1) to (3), the total amount of the metal component having a function of dissociating the hydrogen molecules into hydrogen atoms is 0.3 to 20.0% by mass of the mass of the hydrogen storage body. A method for producing a hydrogen storage body.
(5) The method for producing a hydrogen storage material according to any one of (1) to (4), wherein the hydrogen storage function material is graphite, amorphous carbon, activated carbon, carbon nanotube, or fullerene.
(6) In the above (5), after the hydrogen / carbon atomic ratio of the hydrogen storage function material reaches a range of 0.10 to 0.25, a metal component having a function of dissociating hydrogen molecules into hydrogen atoms is added. A method for producing a hydrogen storage body.
(7) A hydrogen storage produced by the method of (1) to (6).
[0012]
Embodiment of the present invention
Hereinafter, embodiments of the present invention will be described.
In the present invention, the function of dissociating hydrogen molecules into hydrogen atoms when producing a hydrogen storage body using a hydrogen storage function material that expresses a hydrogen storage function by mechanically pulverizing under a hydrogen gas atmosphere to produce a hydrogen storage function. Is added during the mechanical pulverization of the hydrogen storage functional material.
[0013]
In the present invention, in the process of miniaturizing a hydrogen storage functional material such as graphite by mechanical pulverization in a hydrogen gas atmosphere, hydrogen penetrates into the micronized hydrogen storage functional material, and the surface of the micronized hydrogen storage functional material And / or hydrogen is stored inside. Here, the term “inside” means between crystal grains, between layers, and in defects.
[0014]
As the hydrogen storage function material, a carbonaceous material such as graphite, amorphous carbon, activated carbon, carbon nanotube, and fullerene can be used. In this case, the form of hydrogen intrusion includes those with a carbon-hydrogen covalent bond and those without a covalent bond, and among these, hydrogen mainly without a covalent bond can be reversibly extracted, Effective as stored hydrogen. Among the carbonaceous materials, graphite is preferable because of its high hydrogen storage capacity. Since graphite crystals have a layered structure, a large amount of hydrogen can be stored between the surfaces and between layers during the pulverization process in a hydrogen atmosphere.
[0015]
In the technique disclosed in Patent Document 3 (Japanese Patent Application Laid-Open No. 2001-302224), hydrogen is stored in the process of crushing graphite in a hydrogen atmosphere as described above, and the hydrogen storage amount is about 3 mass% at maximum. However, a further increase in hydrogen storage is required.
[0016]
Therefore, in the present invention, a metal component having a function of dissociating hydrogen molecules into hydrogen atoms is used as a catalyst component, and such a metal component is added during the mechanical pulverization of the hydrogen storage body. As a result, the metal component can be supported in a highly dispersed state, and a high hydrogen storage capacity can be obtained by the action of the metal component. The catalyst component is not particularly limited as long as it is a metal component having such a function, but Mn, Fe, Co, Ni, Pt, Pd, Rh, Li, B, Na, Mg, K, Ir, Nd, One, two or more selected from La, Ca, V, Ti, Cr, Cu, Zn, Al, Si, Ru and Ag, or a hydrogen storage alloy is preferable. The metal component that functions as a catalyst may be one or more elemental metals selected from the above elements, or an alloy containing one or two or more elements selected from the above elements. , Oxides, nitrides, chlorides and other compounds. Among the above elements, Pd is particularly good. In addition, the above-mentioned hydrogen storage alloy basically has no affinity between the exothermic metal A (for example, Ti, Zr, misch metal (Mm), Ca, etc.) which easily forms a stable hydride and hydrogen. endothermic metal B (eg, Ni, Fe, Co, Mn, etc.) are composed of, AB ₅ type (LaNi ₅ or MmNi _5, etc.), AB ₂ type _(e.g., Ti 1.2 _{Mn 1.8} and TiCr _1.8, etc.), AB-type (TiFe, etc.), _{a 2} B type _(Mg 2 Ni and _Mg 2 Cu or the like) can be mentioned.
[0017]
It is preferable that the total amount of the metal component having a function of dissociating hydrogen molecules into hydrogen atoms as described above is 0.3 to 20.0% by mass of the hydrogen storage function material. If the amount is less than 0.3 mass%, the function of dissociating hydrogen molecules into hydrogen cannot be effectively exhibited, and if it exceeds 20.0 mass%, not only the effect is saturated, but also the cost increases.
[0018]
In the present invention, the metal component having a function of dissociating hydrogen molecules into hydrogen atoms is added during the mechanical pulverization of the hydrogen storage function material.
[0019]
If a metal component serving as a catalyst component is supported before finely pulverizing the carbonaceous material, the carbonaceous material will cover the metal surface thickly when the carbon is finely pulverized, and the function as a catalyst will not be effectively exhibited. However, the effect of increasing the hydrogen storage amount is small. In particular, when the hydrogen storage functional material is a carbonaceous material, in addition to such a small increase effect of the hydrogen storage amount, hydrogen atoms generated by the catalytic action are often used for cutting graphene sheets, and methane and the like are used. A large amount of hydrocarbons is generated, the CH ₄ / H ₂ ratio increases, and the ratio of hydrogen in the released gas (hydrogen selectivity) decreases.
[0020]
On the other hand, in the present invention, since the metal component is added during the mechanical pulverization of the hydrogen storage function material, the surface of the metal component is not thickly coated with the hydrogen storage function material, and the metal component is highly dispersed. It can be supported in a state, and the catalytic action of the metal component is effectively exhibited, and the hydrogen atoms generated by dissociation on the surface of the metal component are effective in the hydrogen functional material from the interface between the metal component and the hydrogen storage functional material Hydrogen storage capacity is high. In particular, in the case where the hydrogen storage function material is a carbonaceous material such as graphite, when mechanical pulverization is started, no metal component functioning as a catalyst is present, and thus the end of the graphene sheet formed by pulverization is not present. Since hydrogen is bonded to the group (dangling bond) and the metal component is added in that state, the amount of hydrogen used for cutting the graphene sheet is small, and the CH ₄ / H ₂ ratio is low (the hydrogen selectivity is high). ). Therefore, a hydrogen storage body having a high hydrogen storage amount and high hydrogen selectivity can be obtained.
[0021]
The method of adding a metal component having a function of dissociating hydrogen molecules into hydrogen atoms is not particularly limited, but a metal component introduction container is connected via a valve to a pulverization container for mechanically pulverizing a hydrogen storage function material. A method of opening a valve after a predetermined time from the commencement of grinding of the hydrogen storage functional material, coating a metal component having a function of dissociating hydrogen molecules into hydrogen atoms on the surface of the grinding medium by plating or the like, or grinding the grinding medium itself. Is composed of a metal component having a function of dissociating hydrogen molecules into hydrogen atoms, and a metal component is gradually added during the pulverization process of the hydrogen storage function material.
[0022]
【Example】
Hereinafter, examples of the present invention will be described in comparison with comparative examples.
Here, the result of using graphite as the hydrogen storage function material will be described.
[0023]
1. 1.95 g of finely divided graphite prepared graphite powder (artificial graphite manufactured by Kishida Chemical Co., Ltd., average particle size: 36 μm) was placed in a 250 mL zirconia mill container having an inner volume of 250 mL, and after evacuation of the inside of the mill container, hydrogen gas was introduced at 1.0 MPa. did. The mechanical pulverization was performed at 20 ° C. using a planetary ball mill (Fritsch P5) at a revolution number of 250 r. p. Milling was performed for a predetermined time at m. The crushed balls used were 60 zirconia balls (φ10 mm) having the same composition and hardness as the container. As the mill vessel, a vessel equipped with a connection valve for introducing hydrogen gas or vacuum evacuation and a sample introduction valve for adding a metal component having a function of dissociating hydrogen molecules into hydrogen atoms was used.
[0024]
2. Addition of metal component having a function of dissociating hydrogen molecules into hydrogen atoms The addition of a metal component having a function of dissociating hydrogen molecules into hydrogen atoms was performed as follows.
[0025]
First, a metal component having a function of dissociating a predetermined amount of hydrogen molecules into hydrogen atoms with respect to the amount of graphite before milling was measured in a high-purity glove box and placed in a sample introduction container.
[0026]
Next, the hydrogen pressure of the mill container that has been milled for a predetermined time is measured by a pressure gauge, and the above-described sample introduction container is attached to the connection valve of the mill container and evacuated, and hydrogen equivalent to that of the mill container milled for a predetermined time is measured. Hydrogen was introduced until pressure.
[0027]
Open the valve between the sample introduction container into which the hydrogen was introduced and the mill container, add a metal component having the function of dissociating a predetermined amount of hydrogen molecules into hydrogen atoms, and milling together with the milling time before addition Milling was performed until the time reached 80 hours.
[0028]
3. Take out the sample The sample after milling is taken out in a glove box in a high-purity argon atmosphere to minimize the effects of oxidation and moisture adsorption, transferred to a heating vessel in an argon atmosphere, and subjected to a test. Evacuated.
[0029]
4. Measurement of hydrogen release amount and CH ₂ / H ₂ ratio Graphite in a heating vessel evacuated was heated in an electric furnace from room temperature to 900 ° C. at a heating rate of 10 ° C./min, and gas released from graphite was reduced to 20 ° C. After cooling, the gas pressure was measured by a pressure gauge and collected in a gas cylinder having an inner volume of 50 mL.
[0030]
The released gas was introduced into a gas chromatograph (manufactured by Shimadzu Corporation, GC9A, TCD detector, column: Molecular Sieve 5A) through a pipe, and the amount of released hydrogen and the amount of released methane were measured. A typical chart at this time is shown in FIG. The amount of hydrogen stored was a value obtained by dividing the amount of hydrogen by the amount of graphite before heating. The carbon-to-hydrogen atomic ratio was determined by calculating the amount of hydrogen atoms from the amount of released hydrogen and the amount of carbon atoms from the amount of graphite before heating. The CH ₄ / H ₂ ratio was a value obtained by dividing the amount of methane obtained by gas chromatography by the same amount of hydrogen.
[0031]
5. Ni, Co, Fe, Pd, and Pt were used as raw materials used and metal components having a function of dissociating gaseous hydrogen molecules into hydrogen atoms, and the following materials were used as the raw materials.
{Circle around (1)} Ni, Co, Fe metal fine particles: Ni manufactured by Vacuum Metallurgy Co., Ltd .: average particle diameter 20 nm, specific surface area: 43.8 m ² / g
Co: average particle size 20 nm, specific surface area: 47.9 m ² / g
Fe: average particle size 20 nm, specific surface area: 46.0 m ² / g
{Circle around (2)} Pd and Pt fine particles: Ishifuku Metal Industries Pd: average particle size 0.5 μm, specific surface area: 1.2 m ² / g
Pt: average particle size 0.5 μm, specific surface area: 10.1 m ² / g
[0032]
The following were used as the hydrogen gas and the argon gas.
Hydrogen gas: G17N
Argon gas: α 2 6N
[0033]
FIGS. 2 and 3 show the relationship between the addition time and the hydrogen release rate, and the addition of 3 mass% Pd fine particles and 3 mass% Fe fine particles as metal components having a function of dissociating hydrogen molecules into hydrogen atoms. ₄ shows the relationship between time and the CH ₄ / H ₂ ratio. The addition time of 0 hours indicates that the metal component was added before the pulverization of graphite.
[0034]
As shown in FIGS. 2 and 3, in any case, rather than adding a metal component having a function of dissociating hydrogen molecules into hydrogen atoms before mechanical pulverization (milling), rather than adding a metal component having a function of dissociating hydrogen molecules into hydrogen atoms (milling) ( (10 hours, 20 hours), it was confirmed that the hydrogen release rate (corresponding to the hydrogen storage amount) was increased, the CH ₄ / H ₂ ratio was reduced, and the hydrogen selectivity was improved.
[0035]
FIG. 4 shows the relationship between the milling time and the hydrogen storage amount (release amount) and the hydrogen carbon atom ratio. FIG. 5 is an enlarged view of the relationship between the milling time and the hydrogen carbon atom ratio in FIG. 50 hours).
[0036]
Under these conditions, the hydrogen carbon atom ratio (H / C) was in the range of 0.10 to 0.25 by milling graphite for 5 to 25 hours. It is needless to say that the milling time for obtaining the hydrogen carbon atom ratio in such a range is not defined as described above, and the milling time varies depending on the conditions.
[0037]
From the results of FIGS. 4 and 5, hydrogen molecules are dissociated into hydrogen atoms in graphite having a hydrogen-carbon ratio of 0 (milling time 0), 0.193 (milling time 15 hours), and 0.323 (milling time 48 hours). Fine particles of Pd and Fe were added as metal components having a function, and the amount of gas released from room temperature to 900 ° C. in vacuum was measured to determine the amount of hydrogen released and the mass ratio of hydrogen methane. The results are shown in FIGS. 6 shows the relationship between the Pd addition rate and the hydrogen release rate, FIG. 7 shows the relationship between the Pd addition rate and the CH ₄ / H ₂ ratio, FIG. 8 shows the relationship between the Fe addition rate and the hydrogen release rate, and FIG. 9 shows the Fe addition. ₃ shows the relationship between the ratio and the CH ₄ / H ₂ ratio, respectively. 6A to 9B, (a) shows the whole, and (b) is an enlarged view of a metal component of 0 to 3 mass%.
[0038]
As shown in these figures, in the relationship between the hydrogen release rate and the addition rate, although the hydrogen carbon atom ratio of the graphite before addition was not significantly different between the samples of 0.193 and 0.323, the hydrogen carbon atom ratio Is 0.323, the CH ₄ / H ₂ ratio is increased and the selectivity of hydrogen is inferior.
[0039]
Next, 3 mass% of various metal components having a function of dissociating hydrogen molecules into hydrogen atoms are added to the graphite having the above-mentioned hydrogen-carbon atom ratios. The relationship between the release rate and the CH ₄ / H ₂ ratio was determined. The result is shown in FIG.
[0040]
As shown in FIG. 10, although the values of the hydrogen release rate and the CH ₄ / H ₂ ratio differ depending on the type of the metal element, hydrogen molecules are converted to graphite with a hydrogen carbon atom ratio in the range of 0.10 to 0.25. High hydrogen selectivity was obtained in nanographite to which a metal having a function of dissociating into atoms was added.
[0041]
【The invention's effect】
As described above, according to the present invention, in producing a hydrogen storage body using a hydrogen storage function material that exhibits a hydrogen storage function by mechanically pulverizing under a hydrogen gas atmosphere, Is added during the mechanical pulverization of the hydrogen storage functional material, so that the metal component is not thickly covered by the hydrogen storage functional material, and the metal component is highly dispersed. It can be supported in a state, and a high hydrogen storage capacity can be obtained by the action of the metal component.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a chart showing a result obtained by introducing a gas released from graphite into a gas chromatograph and measuring a hydrogen release amount and a methane release amount.
FIG. 2 is a graph showing the relationship between the addition time, the hydrogen release rate, and the CH ₄ / H ₂ ratio when 3 mass% Pd fine particles are used as a metal component having a function of dissociating hydrogen molecules into hydrogen atoms.
FIG. 3 is a graph showing the relationship between the addition time, the hydrogen release rate, and the CH ₄ / H ₂ ratio when 3 mass% Fe fine particles are used as a metal component having a function of dissociating hydrogen molecules into hydrogen atoms.
FIG. 4 is a diagram showing a relationship between a milling time, a hydrogen storage amount (release amount), and a hydrogen carbon atom ratio.
FIG. 5 is an enlarged view of the relationship between the milling time and the hydrogen carbon atom ratio in FIG. 4 (milling time 0 to 50 hours).
FIG. 6 is a graph showing a relationship between a Pd addition rate and a hydrogen release rate.
FIG. 7 is a diagram showing a relationship between a Pd addition rate and a CH ₄ / H ₂ ratio.
FIG. 8 is a diagram showing a relationship between an Fe addition rate and a hydrogen release rate.
FIG. 9 is a graph showing the relationship between the Fe addition ratio and the CH ₄ / H ₂ ratio.
FIG. 10 shows the hydrogen carbon atom ratio when various metal components having a function of dissociating hydrogen molecules into hydrogen atoms are added to graphite of each hydrogen carbon atom ratio at 3 mass%, and the hydrogen release rate from pulverized graphite. FIG. 5 is a graph showing the relationship between the ratio and the CH ₄ / H ₂ ratio.

Claims (7)

In producing a hydrogen storage body using a hydrogen storage material that exhibits a hydrogen storage function by mechanically pulverizing it under a hydrogen gas atmosphere, a metal component that has the function of dissociating hydrogen molecules into hydrogen atoms is used. And adding the hydrogen storage functional material during mechanical pulverization of the hydrogen storage functional material. The metal component having a function of dissociating the hydrogen molecule into a hydrogen atom includes Mn, Fe, Co, Ni, Pt, Pd, Rh, Li, B, Na, Mg, K, Ir, Nd, La, Ca, V, The method for producing a hydrogen storage body according to claim 1, wherein the hydrogen storage body is one or more selected from Ti, Cr, Cu, Zn, Al, Si, Ru, and Ag, or a hydrogen storage alloy. The metal component having a function of dissociating the hydrogen molecule into a hydrogen atom is one or two or more simple metals selected from the above elements, and an alloy containing one or two or more selected from the above elements 3. The method for producing a hydrogen storage body according to claim 2, wherein the hydrogen storage body is in the form of any one of oxides, oxides, nitrides, chlorides, and other compounds. 4. The method according to claim 1, wherein the total amount of the metal component having a function of dissociating the hydrogen molecules into hydrogen atoms is 0.3 to 20.0 mass% of the mass of the hydrogen storage function material. 5. The method for producing a hydrogen storage according to claim 1. The method for producing a hydrogen storage body according to any one of claims 1 to 4, wherein the hydrogen storage function material is graphite, amorphous carbon, activated carbon, carbon nanotube, or fullerene. 6. A metal component having a function of dissociating hydrogen molecules into hydrogen atoms after the hydrogen / carbon atomic ratio of the hydrogen storage function material reaches a range of 0.10 to 0.25. The method for producing a hydrogen storage material according to item 1. A hydrogen storage material produced by the method according to claim 1.

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