JP2005162552A - Composite material for hydrogen generation and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently generate hydrogen gas by a simple means even under mild conditions. <P>SOLUTION: The composite material comprises one or more kinds of aluminum metal from aluminum and aluminum alloys and a metal oxide in contact with the metal on the interface, and has ability of generating hydrogen to generate hydrogen gas by contact with water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The invention of this application is a new hydrogen generating composite material useful as a hydrogen source for fuel cells and the like, a method for producing the same, a method for generating hydrogen gas using the same, parts and devices for hydrogen generation, and a water circulation type The present invention relates to a fuel cell.

  Various solutions such as generation, storage, transportation and use of hydrogen have been proposed as clean energy sources. As one proposal for realizing a hydrogen society, a method has been proposed in which hydrogen gas is produced by thermochemical reaction of aluminum metal, which is light and easy to handle, using water (Patent Document 1).

  Aluminum is a trivalent metal in addition to being light in weight and has an extremely high electron density. However, it is easily contacted with water at room temperature and normal pressure, and it can easily form an immobile film that is resistant to corrosion from several nanometers to several tens of nanometers. It is a fact that has been formed for a long time, and the reaction does not proceed, and there is a big problem that the amount of hydrogen generated is negligible and the efficiency is poor. Therefore, the thermochemical reaction is performed at a high temperature of 200 ° C. or higher by constantly making a fresh surface of aluminum or by the above method. However, in such a high temperature thermochemical reaction, it is difficult to efficiently generate hydrogen gas, and the generator is large and expensive, so it is difficult to say that it is a practical hydrogen gas generation method. . On the other hand, as a method of generating hydrogen from a metal and water under milder conditions, a method of reacting a mixture of metal such as iron and zinc with aluminum and water (Patent Document 2), or indium on aluminum. Further, contrivances such as alloying gallium and reacting with water have been made (Patent Documents 3-4).

  However, in the method in which the mixed metal powder of aluminum, iron, and zinc is reacted with water, sufficient hydrogen must be used unless the solution is heated or under conditions shifted from an aqueous solution pH 7 (pure water) to an acid or alkali side. No gas generation occurs. In addition, in a method in which a material in which indium and gallium are alloyed and water are reacted, indium and gallium that are problematic in toxicity are difficult to handle, and it is difficult to consider as a general-purpose hydrogen gas generation method.

As described above, the conventional methods using metals or alloys as described above solve the problems such as severe reaction conditions for hydrogen generation, less generation of hydrogen gas, and difficult handling. 1) The amount of hydrogen generated relative to the weight ratio of the material is small, and the duration of generation is short.
2) Control of hydrogen generation rate and generation amount is not easy.
3) There is a problem that a power source, a reformer, a heat source, etc. are required.
JP-A-8-115733 JP 2002-104801 A JP 2002-161325 A JP 2003-12301 A

Therefore, the invention of this application solves the conventional problems as described above, and can maintain efficient hydrogen generation for a longer time even under harsh conditions. Control is relatively easy, does not require devices such as a power source or a heat source, and provides new technical means that can realize excellent operational effects such as easy handling. The challenge is to contribute to development.

  In order to solve the above problems, the invention of this application is first a composite material having at least one aluminum metal of aluminum and an aluminum alloy and a metal oxide in contact with the interface. Providing a hydrogen generating composite material that has a hydrogen generating ability to generate hydrogen gas upon contact with water, and second, a metal oxide contacts or adheres to the surface of aluminum metal particles The above-mentioned composite material for hydrogen generation is provided.

  In addition, according to the third aspect of the invention of this application, at least one kind of aluminum metal of aluminum and aluminum alloy and a metal oxide or metal oxide generating material in contact with the interface are placed in a non-oxidizing atmosphere. Provided is a method for producing a composite material for hydrogen generation, characterized by forming a composite material having a hydrogen generation capability of generating hydrogen gas by contact with water by heat treatment. In the fifth aspect of the method for producing a composite material for hydrogen generation described above, fifth, the composite material for hydrogen generation is characterized in that heat treatment is performed in a non-oxidizing atmosphere by evacuation or inert gas. Provide a method.

  Sixth, the present invention provides a method for generating hydrogen gas, characterized in that the hydrogen generating composite material is brought into contact with water.

  And, the invention of this application provides, in a seventh aspect, a hydrogen generating part or device characterized in that the hydrogen generating composite material is at least a part of its configuration, and in the eighth, Provided is a water circulation type fuel cell characterized by using these parts or devices.

  According to the invention of this application as described above, it is possible to easily and efficiently generate hydrogen even under conditions that are more relaxed than in the past, and to achieve the following effects. .

  (1) A large amount of total hydrogen gas is generated based on the weight and volume of the material.

  (2) Easy control of supply speed and gas generation during supply.

  (3) No power source / reformer and heat source are required.

  (4) There is no emission of carbon monoxide and carbon dioxide when hydrogen is generated.

  (5) Simple hydrogen storage and supply system.

  (6) Easy to store, transport, transport and handle, safe.

  (7) There is no impact on health problems in use.

  (8) Easy handling of materials.

  The material of the invention of this application can be applied as a hydrogen energy source in various industrial fields such as power generation, automobiles, and aerospace, and is particularly promising as a hydrogen source for fuel cells such as automobiles that have recently attracted attention. In addition, the materials of the invention of this application, and parts and devices using the same, can produce hydrogen by circulating and using the water generated in the fuel cell, and have the function of a reserve energy source and a reserve battery. ing.

  The invention of this application has the features as described above, and the embodiments thereof will be described below.

The composite material for hydrogen generation of the invention of this application is basically (A) aluminum metal particles comprising at least one of aluminum and an aluminum alloy,
(B) A metal oxide is used as its component.

  The aluminum alloy of the aluminum metal particles (A) may be a binary alloy with various elements or a multi-element alloy as long as the aluminum activity is expressed, and it is workable, formable, and stable. For example, it may be an alloy with one or more of various elements such as titanium, zirconium, iron, tin, niobium, tantalum, silicon, copper, iron, molybdenum, and zinc. Further, the aluminum content in the alloy can also be determined in consideration of the activity of aluminum for generating hydrogen.

  On the other hand, the metal oxide (B) may be an oxide of various elements, and preferably aluminum, titanium, zirconium, hafnium, chromium, indium, magnesium, manganese, tin, zinc, lead, gallium, copper, vanadium, One or more of niobium, tantalum, molybdenum, tungsten, screws, anticene, boron, phosphorus, iron, nickel, cobalt, etc. are considered. Among these, oxides of aluminum, titanium, and magnesium are illustrated as preferable examples. Alumina, titania, magnesia, etc.

  Further, the metal oxide (B) may be a mixture or composite oxide of two or more kinds. Examples include silica / alumina, titania / silica, natural or synthetic zeolite, alumina / boria, alumina / niobium oxide, and the like.

  The metal oxide (B) of the invention of this application contains an acid hydrate or hydroxide.

  As for the metal oxide (B) as described above, as long as the form of the metal oxide in the finally formed composite becomes an oxide, an acid hydrate and a hydroxide in the production thereof, As starting materials for metal oxides, oxides, halides such as chlorides and bromides other than hydroxides, and organic acid salts such as oxalates and acetates can also be used. These oxides preferably have a surface area of a certain level or more and are not easily reduced.

In the composite material for hydrogen generation of the invention of this application, in addition to the above components (A) and (B), ceramics, resins, metals, alloys and the like as shaping materials and stabilizing materials may be used in combination.

In any form, in the composite material for hydrogen generation of the invention of this application, by adding a very small amount of metal oxide to aluminum, the hydrogen gas generation amount is improved as compared with aluminum alone. There is no big deal in the composition. However, if the aluminum ratio is low, the amount of hydrogen gas generated is reduced. On the other hand, if the aluminum ratio is too high, unreacted aluminum remains or the hydrogen gas generation rate is slow. The effect of the present invention can be confirmed when the content of the metal oxide in the aluminum-based composite material of this application is 1 to 99% by volume. From a practical viewpoint, the preferable range is 5 to 95%, more preferably 10 to 90%, and further 40% 90%, although it depends on manufacturing conditions and application fields.

  By selecting and adjusting the volume ratio of the aluminum metal particles (A) and the metal oxide (B), the particle size of the aluminum metal particles (A), and their types, the rate and amount of hydrogen generation, and the duration Can be controlled.

  And the thing of the structure where the metal oxide (B) with a smaller particle diameter contacts or adheres to the surface of the aluminum metal particle (A) with a larger particle diameter in a granular form or a foil piece shape is suitable.

  That is, in the invention of this application, a metal oxide is uniformly dispersed at the interface of aluminum metal to form a composite of aluminum metal and metal oxide, which is brought into contact with water to generate hydrogen gas. As mentioned earlier, aluminum metal usually forms a passive film at the interface in the presence of water and water vapor, and the reaction between aluminum and water does not proceed, but the new material of this application should be used. Thus, hydrogen gas can be produced continuously and efficiently under mild conditions.

As a specific example, a composite of aluminum metal and gamma alumina can be exemplified. An example is a mixture of fine aluminum powder and aluminum hydroxide in a constant mixing ratio, a constant pressure applied to prepare a pre-sintered body, and sintered in a vacuum of about 600 ° C. In this case, a composite in which aluminum hydroxide is changed to fine particles of γ · Al ₂ O ₃ during the sintering process, and porous and high surface area γ · Al ₂ O ₃ is present on the entire surface of the aluminum metal particles. Produces. Since this composite is covered with alumina particles, aluminum is quite stable even in the air, and oxidation of aluminum hardly occurs. The sintering temperature may be low, and aluminum hydroxide may be anhydrous or boehmite normal composite. The aluminum-based composite that generates hydrogen may be a molded body as shown in the above example, but may be used in a powder form.

  The composite material for hydrogen generation of the invention of this application can be manufactured as a sintered body as described above, for example. That is, at least one kind of aluminum metal powder of aluminum and aluminum alloy and a metal oxide or a metal oxide generating material are mixed, and sintered in a non-oxidizing atmosphere, whereby the particles of the aluminum metal and the metal are mixed. It is to produce a composite material for hydrogen generation that is mainly composed of oxides and generates hydrogen by contact with water.

  In this method, it is considered as one of preferable modes that sintering is performed after forming a pre-fired body, or sintering is performed in an inert gas or in a non-oxidizing atmosphere by vacuum exhaust.

  In addition to the above method, the method for producing the composite material for hydrogen generation according to the invention of this application may be a mixture of aluminum metal powder and metal oxide or precursor thereof in a powder form and mechanically mixed, or a massive aluminum metal. And metal oxide pulverized in a ball mill, or metal oxide part powder dispersed in dissolved aluminum, and the composite was pulverized. Any method can be used as long as it can form a uniformly attached complex. It is considered that a uniform and overall dispersion of the metal oxide on the surface of powdered aluminum metal having a certain high surface area is a desirable method for the efficient generation of hydrogen gas. In any of the methods, since the progress of surface oxidation of the aluminum metal is not desirable, it is preferable to employ a method for preventing oxidation as much as possible in the course of the manufacturing method.

The greatest feature of the aluminum-based hydrogen generating composite material according to the invention of this application is that hydrogen gas is easily generated even under mild conditions such as room temperature by contacting with pure water.
When this reaction is carried out under optimal conditions, hydrogen is released continuously until the aluminum metal is almost exhausted. For example, when a sample reacted after having generated hydrogen gas for a certain long time is measured by X-ray diffraction (XRD), as shown in FIG. 7, aluminate hydrate Boebmite, AlO (OH) together with gamma alumina is used. ) Is detected. In addition, when the form is observed with an electron microscope, the shape of the aluminum-based composite material gradually changes, and finally the reaction products in completely different forms as shown in FIG. 1, FIG. 7 and FIG. Is observed. From such an analysis result, it is considered that the reaction represented by the following equation occurs.

Al + 2H ₂ O → AlO (OH) + 3 / 2H ₂ (1)
2Al + 3H ₂ O → Al ₂ O ₃ + 3H ₂ (2)
That is, it is considered that aluminum metal is changed to boehmite having a part of crystallinity while generating hydrogen in the presence of water (in addition, the formation of alumina of the formula (2) uses alumina as a metal oxide. In the case of use, the formation cannot be confirmed.) Theoretically, a very large amount of hydrogen of 1.1 moles per aluminum atom is generated, but water and water are heated at a temperature higher than room temperature. As a result of the reaction, a practically theoretical hydrogen generation amount has been confirmed.

  Such generation of hydrogen gas can be performed by any method as long as the aluminum-based composite material of the invention of this application is brought into contact with a suitable molded body and / or powder and water or water vapor. is there. For example, a method of suspending a composite powder or compact in a tank reactor containing water, a method of passing or contacting water or water vapor to a cylindrical reactor filled with a composite powder or compact, etc. It can be illustrated. When water is used for generation of hydrogen gas, sufficient generation of hydrogen gas can be achieved with pure water, but an aqueous solution shifted from pH 7 to the acid or alkali side can also be used. In addition, when the composite material and water are brought into contact with each other, hydrogen gas can be generated near room temperature, but the generation rate of hydrogen gas can be increased by increasing the temperature. The amount of hydrogen gas generated can be controlled by changing the amount of contact between the composite material and water / steam, the reaction temperature, and the like.

  Accordingly, examples will be described below. Of course, the invention is not limited by the following examples.

<Example 1>
Commercially available aluminum hydroxide Al (OH) ₃ and aluminum powder (particle size of about 3 microns) are respectively 10: 0, 9: 1, 8: 2, 7: 3, 6: 4, 5: 5, 4 : 6: 3: 7, 2: 8, 1: 9, 0:10, and a pre-sintered body was prepared by applying a pressure of about 120 Mpa. The pre-sintered body sintered in a vacuum of about 600 ° C. is subjected to # 0, # 1, # 2, # 3, # 4, # 5, # 6, # 7, # 7, according to the volume content of aluminum. # 8, # 9 and # 10 samples were named. Sample # 0 is from 100% aluminum hydroxide, and sample number # 10 is from 100% aluminum. The surface areas of the samples up to sample numbers # 0, # 1, # 2, # 3, # 4, # 5 and # 6 are 225, 214, 184, 147, 119, 92, 8.4 (unit m ² / g, respectively). )Met. The surface area of the samples after # 7 was the same as that of # 6. FIG. 1 is a scanning electron microscope (SEM) photograph of sample # 4. The particles with the A mark in the figure are identified as Al-rich by EDX analysis (FIG. 2), indicating that they are Al particles. It can be confirmed that γ · Al ₂ O ₃ is fully adhered around the Al particles. FIG. 3 is an enlarged photograph thereof.

FIG. 4 shows the result of X-ray analysis of this material. It can be seen that there are peaks of the Al phase (a) and the γ · Al ₂ O ₃ phase (b). It seems that γ · Al ₂ O ₃ was formed by the following reaction at about 400 ° C. during heating.

2Al (OH) ₃ → γ · Al ₂ O ₃ + 3H ₂ O
When 0.5 g of these samples was put into a beaker containing a large amount of pure water at room temperature, gas generation was observed when any of the samples was used. Gas chromatography analysis confirmed that the generated gas was hydrogen gas. FIG. 5 shows the transition of the hydrogen generation amount up to around 20 hours. From FIG. 5, in the samples # 1 to # 9, the amount of hydrogen gas generated increases with time, and the amount of hydrogen gas generated is within a range of 10.40% by volume of the aluminum metal composition. It is confirmed that there are many. In the samples # 0 and # 10, the gas generation amount per 0.5 g was 4.0 μmol and 17.28 μmol after 71 hours and 22 hours, respectively. The above results clearly show that the generation of hydrogen gas is significantly promoted by the composite of aluminum metal and alumina.

FIG. 6 shows X-ray diffraction data after the reaction of the aluminum composite material after hydrogen gas was generated for about 1 day by the reaction of the sample # 2 and water. Compared to FIG. 4, several new peaks are detected. From the analysis result of this peak, it was confirmed that it was newly generated in the aluminate hydrate Boehmite, AlO (OH). 7 and 8 are scanning electron microscope (SEM) photographs of the # 4 sample after reacting with water for 37 hours and 20 days, respectively. In particular, the composite material after the reaction for 20 days (FIG. 8) has changed to a feather shape completely different from that before the reaction (FIGS. 1 and 3). It was confirmed that the reaction with the liquid reached the inside of the particle.
<Example 2>
In the same manner as in Example 1, a sample having a volume ratio of aluminum metal to alumina of 30:70 was prepared. This sample was reacted with distilled water at room temperature and pressure for about 10 days. The change with time in the amount of hydrogen gas generated is shown in FIG. A large amount of hydrogen was observed during the first 4 days, but the amount of hydrogen generated thereafter tended to saturate. Thereafter, when the temperature is raised, the amount of hydrogen gas generated increases, but the amount of hydrogen gas generated in the first 50 hours is about 4300 micromol, and about 50% of the supplied aluminum is used for hydrogen gas generation. I understood.
<Example 3>
A composite material of aluminum metal and titanium oxide was prepared in the same manner as in Example 1 except that titanium oxide particles were used instead of aluminum hydroxide as a starting material. The volume ratio of the aluminum metal powder and titanium oxide powder of the prepared sample was 30:70. When 0.5 g of this sample was put into a beaker containing pure water, continuous gas generation was observed as in the case of the aluminum-alumina composite material. Although the amount of gas generated seemed to be slightly less than that of the alumina-alumina composite, it was confirmed that the generated gas was hydrogen gas.

It is a scanning electron microscope (SEM) photograph of unreacted sample # 4. It is the figure which showed the result of the elemental analysis by EDX (The particle | grains of Al-rich were specified). It is a SEM high magnification photograph of unreacted sample # 4. It is the figure which showed the X-ray-analysis result of unreacted sample # 4. It is the figure which showed the time-dependent behavior of the hydrogen release amount from sample # 1 to sample # 9. It is the figure which showed the X-ray-diffraction data after about 1 day reaction of sample # 2. It is the surface SEM photograph of the sample after making sample # 4 react for 37 hours. It is the surface SEM photograph of the sample after making sample # 4 react about 20 days. It is the figure which showed the time-dependent change of the hydrogen gas generation amount at the time of making sample # 3 sample react for about 10 days.

Claims (8)

  It is a composite material having at least one kind of aluminum metal of aluminum and aluminum alloy and a metal oxide in contact with the interface, and has a hydrogen generating ability to generate hydrogen gas by contact with water. A composite material for hydrogen generation.   2. The composite material for hydrogen generation according to claim 1, wherein a metal oxide contacts or adheres to the surface of the aluminum metal particles.   By heat-treating at least one kind of aluminum metal of aluminum and aluminum alloy and a metal oxide or metal oxide generating material in contact with the interface in a non-oxidizing atmosphere, hydrogen gas is brought into contact with water. A method for producing a composite material for hydrogen generation, comprising forming a composite material having the ability to generate hydrogen.   4. The method for producing a composite material for hydrogen generation according to claim 3, wherein sintering is performed.   4. The method for producing a composite material for hydrogen generation according to claim 3, wherein the heat treatment is performed in a non-oxidizing atmosphere by evacuation or inert gas.   A method for generating hydrogen gas, comprising bringing the hydrogen generating composite material according to claim 1 or 2 into contact with water.   A hydrogen generating component or apparatus comprising the composite material for generating hydrogen of claim 1 or 2 as at least a part of the structure.   A water-circulating fuel cell using the component or apparatus according to claim 7.