JP2005097036A - Multi-component glass material for hydrogen treatment and hydrogen treated composite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a material, a structure, and a unit for technologies relating to hydrogen energy. <P>SOLUTION: This material contains a glass 3, and the glass 3 has a function of decomposing hydrogen gas in the atmosphere and dissolving the hydrogen atom or, as a reverse reaction, discharging the dissolved hydrogen as a hydrogen molecule to the atmosphere depending on the partial pressure of the hydrogen, and also a function of decomposing a water molecule in the atmosphere and selectively dissolving the formed hydrogen atom or, as a reverse reaction, discharging the dissolved hydrogen as a water vapor molecule to the atmosphere by the reaction of the dissolved hydrogen with an oxygen in the atmosphere depending on the partial pressure of the water vapor in the atmosphere, and contains at least one selected from the group consisting of a titanium oxide, a niobium oxide, and a tungsten oxide. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to materials and structures and devices in hydrogen energy related technology. Specifically, in devices that produce hydrogen by thermochemically decomposing water, hydrogen atom sensors, hydrogen molecule sensors, hydrogen separation and purification devices, hydrogen storage devices such as various devices for hydrogen treatment, and these devices, The present invention relates to materials and structures having elementary functions such as decomposition of hydrogen-containing molecules such as water and hydrogen, dissolution and diffusion of hydrogen atoms, and release of hydrogen molecules.

  In order to cope with the global warming caused by the increase of carbon dioxide and the depletion of petroleum resources, it is becoming increasingly important to use hydrogen energy instead of the conventional use of fossil fuel. In order to effectively use hydrogen, various devices for processing hydrogen are required. For example, an apparatus for producing hydrogen, an apparatus for separating and purifying hydrogen, an apparatus for storing and transporting hydrogen, an apparatus for detecting hydrogen, an apparatus for converting hydrogen into electric energy (fuel cell), a hydrogen combustion engine, and the like. In these devices, various materials and structures are used to realize their functions. Typical examples are a hydrogen permselective membrane used in a hydrogen separation and purification apparatus and a proton conductive film used in a fuel cell.

Hereinafter, the hydrogen processing apparatus and the material for hydrogen processing required there will be described. First, technical issues related to hydrogen production will be described. Hydrogen production technology that constructs an ideal form of a hydrogen energy system is a method using water as a raw material and sunlight as an energy source in an energy consuming area. If water is used as a raw material, there is no generation of CO ₂ which is a problem in the decomposition of fossil fuels. Furthermore, since hydrogen returns to water again after energy conversion, it is reused as an energy transmission medium. Moreover, since water exists in many regions on the earth, there is no problem of resource depletion like fossil fuel.

  Methods for producing hydrogen from water using sunlight as an energy source are broadly classified into methods using light energy as photons and methods using heat. The former includes, for example, a photocatalytic method disclosed in Patent Document 1 in which water is decomposed by excited electrons and excited holes generated by photoexcitation of a solid catalyst. In this method, only light having a wavelength of about 500 nm or less can be used in practice. Therefore, there is an essential limitation that only about 1/4 of the total energy of sunlight reaching the ground surface can be used. Also, since oxygen and hydrogen are generated simultaneously on the solid surface, a process and energy are required to separate hydrogen from oxygen and water vapor.

  The temperature required for the one-step pyrolysis reaction of water to proceed significantly is about 3000 ° C. Therefore, in the method of producing hydrogen from water using sunlight as thermal energy, the development of technology for concentrating sunlight from a large area to a small space becomes an issue, and no practical system has been developed yet.

  In addition, as disclosed in Non-Patent Document 1 and Patent Document 2, studies have been made to generate hydrogen from water using a thermochemical reaction at a temperature of about 900 ° C. These have not been put into practical use until now because they have the disadvantage that they have to be large plants in order to construct complex processes.

  As a thermochemical decomposition method using a functional material, Patent Document 3 discloses a method of generating hydrogen from water vapor at a temperature of 400 ° C. by a catalytic reaction of zeolite. Since this method uses the catalytic function of the material as compared with the conventional thermochemical method, there is a possibility that a system with a simple configuration can be realized. However, in this reaction, oxygen is inevitably generated simultaneously with hydrogen, so that it has a drawback that an apparatus for efficiently separating hydrogen and oxygen is required as a post-treatment device, and it is a complete method for generating hydrogen. Not.

  Realize a system that can produce hydrogen from water at a temperature that can be reached by using an optical system with low concentration using solar heat, or at a temperature that can be obtained by industrial waste heat that is not effectively used and released into the atmosphere. Therefore, a new material for hydrogen treatment is necessary. The material used for the purpose of generating hydrogen from water vapor not only has the function of decomposing water vapor into hydrogen and oxygen on the surface like zeolite, but also simultaneously separates hydrogen and oxygen and incorporates hydrogen. It is desirable to have It will be easily understood that by using such materials, a simple hydrogen generation system using solar heat or industrial waste heat and using water as a raw material can be realized.

The material having a function of selectively taking in hydrogen is a material required for a hydrogen treatment apparatus for other purposes. As a representative example, a hydrogen separation and purification technique will be described. Currently, hydrogen is produced by steam reforming or the like using hydrocarbons such as natural gas, LPG or methanol as raw materials. In the steam reforming method, normally, other gases such as CO and H ₂ O are by-produced together with hydrogen. Therefore, in order to use hydrogen as an energy source, it is necessary to separate and purify hydrogen from the product gas mixture.

  As a method for separating hydrogen from a mixed gas containing hydrogen, there are a method of absorbing and separating impurities using an adsorbent, a method of separating using an organic, inorganic, or metal / alloy hydrogen separation membrane (membrane separation method). . Among them, the membrane separation method can be said to be an excellent method from the viewpoints of energy utilization efficiency, separation efficiency, simplicity of the apparatus, and ease of operation. Hydrogen separation membranes used in membrane separation methods include porous membranes and non-porous membranes. A porous membrane has a limit in the selectivity of hydrogen, which is the minimum molecular species, in principle.

  The hydrogen storage alloy has a function of reversibly absorbing or releasing hydrogen according to the hydrogen partial pressure in the atmosphere. In particular, Pd and Pd-based alloys have excellent hydrogen selectivity and hydrogen permeability and have been industrialized for some applications. In the hydrogen separation and purification method using such a metal / alloy non-porous membrane, hydrogen is dissociated into atoms and permeated, so that in principle, high-purity hydrogen that does not contain other components can be produced.

  A typical hydrogen separation and purification membrane is a Pd-silver Ag alloy membrane having a thickness of about 0.2 mm, and is used at a temperature of about 400 ° C. at which the hydrogen diffusion coefficient becomes a practical value. However, apart from its use in industrial fields with high added value such as the semiconductor industry, the price of Pd becomes an obstacle in order for Pd-based alloys to be used more generally.

In order to solve this problem, a method using a lower-priced alloy such as vanadium V (Patent Document 4) has been proposed, but these alloy films contain high-temperature reformed gas containing carbon monoxide, water vapor, and the like. When used for a long time, it has a disadvantage that its performance deteriorates. For this reason, it is necessary to coat the surface with a Pd thin film. However, in that case, a new problem arises that the coated Pd and the base metal form an alloy layer and deteriorate the hydrogen permeation performance.
In order to solve such problems, Patent Document 5 proposes a multilayer membrane having a structure in which an inorganic layer having hydrogen transport properties is inserted between a metal plate such as Pd and a metal plate such as iron Fe as a hydrogen separation membrane. . Here, examples of the hydrogen permeable film made of an inorganic material include SiO ₂ , WO ₃ , SrCeO _{3 and the} like.

However, each of these inorganic material films has the following drawbacks. SiO ₂ is a substance that exhibits good hydrogen selectivity in a hydrogen molecule permeable membrane and has a large hydrogen diffusion coefficient in glass. However, compared with the hydrogen diffusion coefficient in metal, it is two orders of magnitude smaller and the solubility of hydrogen is low, so that the permeation ability is small for use as a hydrogen permeable membrane.

Since SrCeO ₃ exhibits its function in an environment where moisture is replenished at 800 ° C., preferably 900 ° C. (see, for example, Patent Document 6), the above-described configuration cannot realize stable hydrogen permeability. Have.

In addition, since SiO ₂ and oxide crystals have a smaller thermal expansion coefficient than metal, there is a disadvantage that when a composite film is made of a metal, there is a high possibility of causing cracks in the film due to a difference in thermal expansion coefficient. Have. WO ₃ is chemically unstable and cannot withstand long-term use at high temperatures.
Japanese Patent No. 2526396 Japanese Patent Publication No.55-3282 JP-A-11-171501 Japanese Examined Patent Publication No. 6-98281 JP-A-7-185277 JP 2003-2610 A JP 2002-201041 A Applied Physics Vol.63, No.8, 831 J. et al. Appl. Published by Phys 91, 1650, 2002

  The present invention has been made to solve such problems, and its purpose is to produce hydrogen by thermochemically decomposing water, and more particularly, materials and structures and apparatuses in hydrogen energy related technology. Devices, hydrogen atom sensors, hydrogen molecule sensors, hydrogen separation and purification devices, hydrogen storage devices such as hydrogen storage devices, and in these devices, decomposition of hydrogen-containing molecules such as water and hydrogen, dissolution of hydrogen atoms The object is to provide a hydrogen processing material and a hydrogen processing complex that are responsible for elementary functions such as diffusion and release of hydrogen molecules.

First, the fundamental discovery leading to the present invention will be described. The inventors have a function in which an oxide glass containing TiO ₂ , Nb ₂ O ₅ , and WO ₃ reversibly absorbs and releases hydrogen depending on the hydrogen molecular partial pressure in the atmosphere like a hydrogen storage alloy. It has also been found that these glasses absorb hydrogen atoms efficiently in a hydrogen atom atmosphere. This property also means that these materials have a very high hydrogen selectivity. Conventionally, as disclosed in, for example, Patent Document 7, it has been known that hydrogen exists in a multicomponent glass, but it is not known to have such properties.

The second discovery is that these glass materials have a large hydrogen diffusion coefficient over a wide composition range. The oxide glass having the highest hydrogen diffusion coefficient known so far is silica glass. The diffusion coefficient of hydrogen at 500 ° C. is about 6 × 10 ⁻⁷ cm ² / s. On the other hand, the glass system according to the present invention has a value of about 10 ⁻⁶ cm ² / s, which is one digit larger.

  The third discovery is that when one surface of a sheet glass made from the glass material of the present invention is exposed to a water vapor atmosphere at a temperature below the glass transition point, water atoms in the atmosphere are decomposed and generated on the glass surface. The only thing that selectively dissolves and diffuses in the glass.

  Furthermore, if a hydrogen storage alloy is laminated and compounded in advance on the opposing surface of this glass, the diffused hydrogen is distributed and dissolved in the alloy layer and released as hydrogen molecules according to the hydrogen partial pressure in the alloy side atmosphere. Was also observed.

In addition, the thermal expansion coefficient of these glasses is about 10 ⁻⁵ / K, and has a value closer to that of metal as compared with SiO ₂ and oxide crystals. For this reason, in particular, a laminated composite with a hydrogen storage alloy can be easily realized. This laminated composite has excellent performance as a hydrogen treatment body such as a hydrogen separation and purification membrane.

  By the above invention, the material used as the foundation | substrate which implement | achieves the hydrogen production apparatus which used water as a raw material, and the waste heat of about 500 degrees C or less etc. as an energy source, and the foundation | substrate material which implement | achieves a hydrogen selective membrane are realizable. A material having a function of absorbing hydrogen, transmitting hydrogen, and releasing hydrogen is widely applicable to other hydrogen treatment apparatuses. Furthermore, a laminated composite made of this material and a hydrogen storage alloy can be used in various types of hydrogen treatment apparatuses by further strengthening the hydrogen treatment function of this material.

The multicomponent oxide glass material having the hydrogen absorption / release function of the present invention will be described. Hydrogen absorption / diffusion / release in glass containing any one of TiO ₂ , Nb ₂ O ₅ , and WO ₃ is considered to proceed by the following mechanism.

When these glasses are placed in an atmosphere having a hydrogen partial pressure of about several hundred degrees Celsius or higher than that in the atmosphere, Ti ⁴⁺ , Nb ⁵⁺ , W ^6+, etc., which are easily reducible ions near the glass surface, are hydrogen. By extracting electrons from the hydrogen atoms generated by decomposing the molecules, they themselves are reduced to Ti ³⁺ , Nb ⁴⁺ , and W ⁵⁺ .

The existence state of hydrogen atoms, ie protons, from which electrons have been removed shows various changes depending on the glass composition. For example, it combines with surrounding oxygen ions to form a hydroxyl group —OH. Or it may melt | dissolve in a lattice as a pseudo free ion, without couple | bonding with a specific ion. Regardless of the mode of existence, protons have a role of charge compensation around reduced ions having excessive negative charges. Such proton / electron pairs can easily move on the neighboring Ti ⁴⁺ , Nb ⁵⁺ , and W ⁶⁺ , and as a result, hydrogen atoms diffuse at a high speed. These phenomena can be confirmed by electron spin resonance absorption measurement and light absorption measurement in the visible-near infrared-infrared region.

  Since the dissolution and diffusion of hydrogen proceeds even at temperatures below the glass transition point, glass does not crystallize or undergo major changes in the skeletal structure that forms glass at such temperatures due to absorption and dissolution of hydrogen. . Therefore, it will be understood that this glass material can be used stably for a long time.

  When glass that has absorbed and melted hydrogen is placed in an atmosphere of low hydrogen partial pressure, the dissolved hydrogen is released from the glass into the atmosphere as hydrogen molecules in the reverse process. The atmosphere of low hydrogen partial pressure is realized by a method of reducing the total pressure by a vacuum pump or circulating a gas inert to hydrogen such as nitrogen or an inert gas. By these methods, hydrogen or a mixed gas of hydrogen and an inert gas can be obtained.

  The composition of the glass of the present invention will be described. The glass of the present invention has a function of decomposing hydrogen to dissolve generated hydrogen atoms by the level of hydrogen partial pressure in the atmosphere, or releasing dissolved hydrogen into the atmosphere as hydrogen molecules as a reverse reaction, and Combined with the function of decomposing water molecules and selectively dissolving the generated hydrogen atoms by the level of the partial pressure of water vapor in the atmosphere, or releasing dissolved hydrogen as water vapor molecules by reaction with oxygen in the atmosphere as a reverse reaction As long as it is a multicomponent glass containing at least one oxide of titanium oxide, niobium oxide, and tungsten oxide, other components are not limited. For example, phosphate, silicate, borate, germane It may be an acid salt system and a mixed glass thereof.

  Since the diffusion coefficient of hydrogen increases as the distance between adjacent Ti, Nb and W ions decreases, it is desirable that the content of these cations is large. The total content of Nb + Ti + W is preferably 15% or more, more preferably 20% or more in terms of mol% of cations constituting the glass. However, if the total amount of these cations increases, the thermal stability of the glass deteriorates and it becomes easy to crystallize during the glass production process, so the range is the total content of Nb + Ti + W in terms of mol% of cations constituting the glass. The amount is preferably 60% or less, more preferably 55% or less. Moreover, in order to contain these cations in large quantities, it is preferable that it is a phosphate glass, The range is the mol% display of the cation which comprises glass, P: 20-50%, Nb: 0 More preferably, they are 50%, Ti: 0-20%, W: 0-40%.

  For the purpose of increasing the solubility of hydrogen, the glass of the present invention can further contain at least one or more cations that are reduced by reacting with hydrogen in addition to Ti, Nb, and W. The cation species is not limited as long as it is a cation that increases the solubility of hydrogen, but it is preferably a more easily reducible cation than Ti, Nb, and W. Examples of such cations include Fe, Mo, and V. Etc.

  Even if it is a cation other than the above, there is no limit to containing a cation that is necessary for producing a more thermally and chemically more stable glass and one that does not significantly reduce the diffusion coefficient and solubility of hydrogen. Further, anions other than oxygen such as fluorine and chlorine can be contained as long as the thermal and chemical stability, hydrogen diffusion coefficient and solubility are not significantly reduced.

  When the glass of the present invention is compared with a hydrogen storage alloy used for hydrogen treatment such as Pd, the function of dissociating hydrogen molecules into hydrogen atoms and the function of releasing dissolved hydrogen atoms into the atmosphere as hydrogen molecules are particularly poor. In some cases, there is a problem of further increasing the amount of hydrogen absorbed and released.

  This problem is solved by laminating with a hydrogen storage alloy film by utilizing the unique property of the glass of the present invention, that is, the property of being substantially dissolved in the glass as hydrogen atoms, like hydrogen in the metal. I can do it. Examples of such a metal film include Ni, Pd, Pt, and alloys containing any one of these. By this method, hydrogen molecules in the atmosphere are rapidly dissociated and adsorbed on the surface of the metal alloy, occluded, and then diffused into the glass. Alternatively, dissolved hydrogen in the glass diffuses into the metal alloy film and can be quickly desorbed as hydrogen molecules on the surface thereof.

  It is also possible to combine glass with a metal / alloy by a method other than the above-described lamination composite. The glass of the present invention can contain an appropriate amount of Pd or the like as a kind of constituent cation in advance when producing the glass. By heating this glass in a hydrogen atmosphere, Pd ions are reduced by hydrogen to generate Pd atoms. Since Pd atoms can easily move in the glass under heating, they aggregate and become Pd metal fine particles. The Pd fine particles present on the glass surface can dissociate and adsorb hydrogen molecules in the atmosphere, or extract dissolved hydrogen in the glass and desorb it as hydrogen molecules from its own surface. A composite function can be realized.

  As described above, it will be understood that the glass of the present invention is effective as a hydrogen separation membrane because it has a function of dissolving, diffusing and releasing hydrogen. In particular, the glass transition point of oxide glass can be set higher than, for example, the operating temperature of a hydrogen separation membrane applied to a reformed gas. Therefore, as a hydrogen selective membrane used at such a high temperature, the hydrogen selectivity and durability are excellent. It is possible to supply a hydrogen selective membrane. This embodiment will be described in detail in Example 3. Furthermore, the hydrogen permeation ability can be further improved by employing a multilayer structure in which the surface of the hydrogen selective membrane made of the glass of the present invention is coated with a hydrogen storage alloy.

  The glass of the present invention can decompose and absorb hydrogen selectively by decomposing a compound containing hydrogen on the glass surface. Especially in the case of water, the industrial effect is large as described in the background art. In particular, compared with the water decomposition catalyst using zeolite disclosed in Patent Document 3, the glass of the present invention has a function of decomposing water and simultaneously separating hydrogen and oxygen and incorporating hydrogen into the glass. It will be understood that by utilizing this function, a simplified water thermochemical decomposition apparatus can be obtained. The specific embodiment will be described in detail in Example 4.

In addition, the glass of the present invention is utilized as a hydrogen atom sensor that selectively detects only hydrogen atoms from a mixed atmosphere of hydrogen molecules and hydrogen atoms by utilizing the fact that the absorption capacity for hydrogen molecules and hydrogen atoms in the gas phase is different. You can also
As described in Non-Patent Document 2, in recent years, there is a technique for generating hydrogen atoms by bringing hydrogen molecules into contact with a tungsten wire heated to about 2000K. However, the hydrogen atom concentration in the atmosphere must be measured by two-photon laser induced fluorescence spectroscopy, vacuum ultraviolet absorption, or the like, and there is a problem that the measurement is complicated and the apparatus is expensive.

  If the hydrogen-absorbing glass of the present invention is used, hydrogen atoms are absorbed and colored simply by heating to about several hundred degrees Celsius in the apparatus. Therefore, the hydrogen atom concentration in the apparatus can be determined simply by measuring the light absorption of this glass. Can be determined. It is desirable that the glass used here does not contain this in order to prevent contamination of the apparatus and sample due to alkali scattering.

  Patent Document 7 discloses a method of heat-treating in an atmosphere containing hydrogen gas as a method for coloring glass, but the hydrogen absorption rate is significantly different between a hydrogen molecule atmosphere and a hydrogen atom atmosphere. There is no idea to make a hydrogen atom sensor using the difference.

  Hydrogen dissolved in the glass of the present invention exists as a pair of electrons dissociated and captured by protons and transition metal ions. Therefore, the glass of the present invention exhibits high proton conductivity while maintaining electronic insulation, particularly when hydrogen is dissolved at a high concentration. Therefore, it can also be used as proton conductors for various electrochemical devices related to hydrogen, hydrogen fuel cells, water solid-state electrolysis devices, electrochemical hydrogen purification devices, and the like.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.

Examples of the hydrogen absorption / release function of the hydrogen-treated glass material will be described. The procedure for producing and treating the glass material is as follows. By using Nb ₂ O ₅ , WO ₃ , Ba (PO ₃ ) ₂ , NaPO ₃ , Na ₂ CO ₃ as starting materials and dissolving at 1050 to 1150 ° C. for 2 hours, it is shown in Composition 1 to Composition 10 in Table 1. A glass was prepared. A sample having a size of about 20 mm × 20 mm and a thickness of 10 mm was cut out from the glass, and optical polishing was performed on two surfaces having a size of 20 mm × 20 mm.

Next, the diffusion coefficient of hydrogen was evaluated by the following method. A glass sample manufactured by the method described above was subjected to heat treatment at 500 ° C. for 5 hours in an H ₂ atmosphere to diffuse hydrogen atoms. Diffusion hydrogen releases electrons to reduce Ti, Nb, or W, and itself becomes a proton. In the glass of this example, W ⁶⁺ is reduced to W ⁵⁺ and the glass is colored blue-black. After cutting a 20 mm × 10 mm 1 mm thick sample vertically from the center of the polished surface and performing double-sided optical polishing, the visible light absorption spectrum was measured while moving the position from the surface before cutting to the inner direction every 500 μm. . The effective cross-sectional area of the light absorption measurement is approximately 100 μmφ. As a result of analyzing the absorption intensity profile at 610 nm for each measurement position in the depth direction using a diffusion theoretical formula, the diffusion coefficient at 500 ° C. was calculated to be about 4 × 10 ⁻⁶ cm ² / sec.

Next, the evaluation of the hydrogen concentration dissolved and diffused in the glass will be described. Glass shown in composition 1 of Table 1, cut out 5mm thick sample at approximately 10 mm × 10 mm, after performing two-sided optically polished surface of 10 mm × 10 mm, 500 ° C. The sample in _{H 2} atmosphere, 24 hours The entire glass was colored blue-black. From the electron spin resonance absorption measurement, it was confirmed that the reduced / colored species generated in the glass was W ⁵⁺ and the concentration thereof, that is, the concentration of hydrogen atoms was approximately 1 × 10 ¹⁸ atoms / cm ³ . .

Five samples were used, and temperature programmed desorption analysis was performed by the following method. First, these samples were placed in the apparatus, the degree of vacuum was reduced to 10 ⁻⁸ Torr or less, and then the samples were heated to 100 ° C. After the degree of vacuum became 10 ⁻⁹ Torr or less, the sample was heated to 500 ° C. in about 20 minutes and held at 500 ° C. for about 5 hours. A gas (hydrogen) having a molecular weight of 2 generated in the apparatus immediately after the start of temperature increase was measured with a quadrupole mass spectrometer. As a result, as shown in FIG. 1, it was confirmed that the amount of generated hydrogen was larger than that of the comparative example.

In this example, the hydrogen dissolution / release function of the Pd / glass / Pd laminated composite will be described. The procedure for producing and treating the glass material is as follows. Using Nb ₂ O ₅ , WO ₃ , Ba (PO ₃ ) ₂ , NaPO ₃ , Na ₂ CO ₃ as starting materials, and melting at 1050 to 1150 ° C. for 2 hours, glass of composition 1 in Table 1 was produced. . A sample having a thickness of about 10 mm × 10 mm and a thickness of 5 mm was cut out from the glass and double-sided optical polishing was performed on a 10 mm × 10 mm surface.

Next, the evaluation of the hydrogen concentration dissolved and diffused in the glass will be described. To form a film of Pd approximately 10nm thickness using a sputter ion device optically polished surface of the double-side polishing _sample, 500 ° C. with 3.5% H ₂ -96.5% _N 2 atmosphere, a heat treatment of 24 hours The whole glass was colored blue-black. From the electron spin resonance absorption measurement, it was confirmed that the reduced / colored species generated in the glass was W ⁵⁺ and the concentration thereof, that is, the concentration of hydrogen atoms was approximately 3 × 10 ¹⁸ atoms / cm ³ . .

Next, the hydrogen releasing function of the Pd / glass / Pd laminated composite will be described. Using the above five colored samples, temperature programmed desorption analysis was performed by the following method. First, these samples are placed in a room temperature vacuum apparatus and depressurized. After the degree of vacuum became 10 ⁻⁸ Torr or less, the sample was heated and degassed to 100 ° C. After the degree of vacuum became 10 ⁻⁹ Torr or less, the sample was heated to 500 ° C. in about 20 minutes and held at that temperature for about 13 hours. A gas (hydrogen) having a molecular weight of 2 generated in the apparatus immediately after the start of temperature increase was measured with a quadrupole mass spectrometer. As a result, as shown in FIG. 1, it was confirmed that the amount of hydrogen generated was larger than that in Example 1. Further, when Pd was removed by polishing from the sample after completion of the measurement, the glass was only slightly blue-black. That is, most of the dissolved hydrogen is released from the Pd film forming surface into the atmosphere.

Next, Comparative Example 1 will be described. After processing SiO ₂ glass to a size of about 10 mm × 10 mm and a thickness of 5 mm and performing double-sided optical polishing on a 10 mm × 10 mm surface, a Pd film of about 10 nm is formed, and 500 ° C./24 in H ₂ atmosphere is formed. Heat treatment for hours was performed. As a result of performing temperature programmed desorption analysis by the same method as in Example 1 using five of these samples, it was confirmed that the amount of generated hydrogen was small compared to Example 1 as shown in FIG. It was.

  Next, a hydrogen separation and purification membrane using the hydrogen treatment complex of the present invention will be described. The hydrogen-absorbing glass of the present invention is used as a hydrogen separation and purification membrane having excellent hydrogen selectivity by processing into a plate shape and forming a film of Pd on both surfaces or by depositing Pd fine particles in the glass. be able to.

  A hydrogen separation and purification membrane having a Pd / glass / Pd three-layer structure will be described with reference to FIG. In FIG. 2, 1 is a hydrogen inflow side Pd thin film, 2 is a hydrogen outflow side Pd thin film, 3 is a hydrogen-soluble glass of the present invention, and 5 is a porous ceramic having hydrogen permeability. Since the hydrogen-treated glass material of the present invention is a material having excellent hydrogen selectivity as described above, pinholes are present in the hydrogen inflow side Pd thin film 1 formed on the hydrogen inflow side glass surface. However, molecules other than hydrogen do not permeate the glass, and even if carbon monoxide or water vapor contacts the glass, the hydrogen permeability is not affected. For this reason, the film thickness of the hydrogen inflow side Pd thin film 1 can be 100 nm or less.

  The glass itself of the present invention has a small hydrogen diffusion coefficient and solubility compared to the hydrogen storage alloy, and a sufficient hydrogen permeation amount cannot be obtained when the thickness is increased. For this reason, the thickness of the glass is preferably 1 micrometer or less. Hydrogen atoms that have passed through the hydrogen-treated glass layer are released as hydrogen molecules on the surface of the hydrogen outflow side Pd thin film 2. Since this Pd thin film only needs to have a function of releasing hydrogen, its film thickness can be made 100 nm or less.

  As described above, the total thickness of the Pd thin film / glass / Pd thin film three-layer structure hydrogen separation / purification membrane is on the order of 1 micrometer, so that the mechanical strength is insufficient as a self-supporting membrane. In the example of FIG. 2, this is compensated by supporting it with a porous ceramic 5 having gas permeability.

  FIG. 3 shows an example in which an Nb metal plate that is a non-porous hydrogen permeable material is used as a support. In this structure, hydrogen passes through the hydrogen-soluble glass 3 and the Nb metal plate 4 and is released as hydrogen molecules on the surface of the outflow side Pd thin film 2. Also in this case, the thickness of the Pd thin film can be made 100 nm or less as in the case of FIG.

  Subsequently, a method for increasing the amount of permeated and purified hydrogen when purifying hydrogen using the hydrogen treatment complex will be described. Among materials constituting an alloy / glass / alloy three-layer structure composite, the one having the smallest diffusion coefficient is a glass material. Therefore, in order to increase the hydrogen flux passing through the glass layer, it is effective to increase the difference in hydrogen concentration between both end surfaces of the glass on the hydrogen inflow side and the outflow side. This is because the amount of hydrogen atoms that permeate the hydrotreated glass is proportional to the difference in the end face concentration between the inflow side and the outflow side. In order to control the difference in hydrogen concentration between the two end faces, it is utilized that the equilibrium solubility of hydrogen in the alloy varies with the potential (Fermi energy) of the alloy. By giving a positive potential and a negative potential to the hydrogen inflow Pd thin film 1 and the hydrogen outflow Pd thin film in FIG. 2 and FIG. Can be changed.

  The production of hydrogen by decomposing water in a one-step reaction requires ultra-high temperatures, so several elementary processes that are realized at relatively low temperatures are combined. By utilizing the glass / hydrogen storage alloy laminated composite of the present invention, a separation-free process that can decompose water and selectively extract hydrogen can be realized.

The reaction proceeds in the following five-stage continuous process.
First reaction: Evaporation of water using waste heat, sunlight, etc. as a heat source Second reaction: Hydrogen atom generation by water decomposition on the surface of a solid oxide such as glass Third reaction: Selection of hydrogen atoms into the solid Diffusion 4th reaction: partitioning / diffusion of hydrogen atoms into the alloy layer 5th reaction: desorption of hydrogen molecules from the alloy layer surface

  The most important technical element that enables this series of reactions is the function of decomposing water on its surface, selectively taking in the produced hydrogen and separating it from oxygen. This phenomenon has not been known so far, but has been newly found through the inventors' research. Even in the catalytic reaction of zeolite described in Patent Document 3 or the widely known photocatalytic reaction (for example, Patent Document 1), some substance (catalyst) reacts with water, and as a result, water is decomposed and hydrogen is converted. The point of generation is the same as the above phenomenon. However, in these known techniques, the produced hydrogen is not separated from water or water vapor and oxygen, and both are mixed outside the catalyst. On the other hand, in the operation of the present invention, decomposed hydrogen is taken into the glass, and water vapor and oxygen remain outside the glass. Therefore, in the present invention, unlike the conventional thermochemical decomposition method such as UT-3 (see Non-Patent Document 1), there is substantially no intermediate product, so the hydrogen generation system is very simple. It will be something.

  Below, the Example which produces | generates hydrogen from water using the hydrogen processing body in connection with this invention is described in detail. FIG. 4 schematically shows the configuration of this apparatus. The apparatus includes a water vapor holding vessel 11, a reaction element 12 made of a glass material / Pd composite that realizes water decomposition and hydrogen uptake reaction, a holding plate 13 made of a porous material that mechanically holds the reaction element 12, hydrogen A takeout container 14 and a hydrogen storage means 18 containing a hydrogen storage alloy are installed. The basic function of this apparatus is to store hydrogen in the hydrogen storage alloy in the hydrogen storage means 18 via the hydrogen take-out container 14 by filling the water vapor holding container with water vapor of about 200 ° C. to 500 ° C.

  Next, the reaction will be described in detail. The water vapor is generated from water as a raw material by a heater placed outside the apparatus shown in FIG. 4 and introduced into the water vapor holding container 11 from the water vapor inlet 15. Excess water vapor is removed from the water vapor exhaust port 16. The pressure of water vapor is approximately 1 atmosphere. The reaction for generating water vapor from water is realized with a yield of 100%. By converting water into water vapor, free energy of about 15 kcal / mol can be obtained.

The reaction element 12 is a laminated composite of the hydrogen-soluble glass and Pd thin film of the present invention. The composition of the glass used in this example was 30.7PO _5/2 -18.5NbO _5/2 -15.4WO ₃ -6.2BaO-29.2LiO _1/2 (mol%). A glass disk having a diameter of 25 mm was prepared in accordance with the method described above, and this was optically polished to a thickness of 100 μm. About 10 nm of Pd was formed on one side of the disk using an ion sputtering apparatus. The Pd surfaces were combined with the porous holding plate side, and attached to the reactor. The circumference of the reaction element is sealed to the reactor with a ceramic seal to ensure electrical insulation and airtightness.

The water vapor in the water vapor holding container 11 is decomposed into hydrogen and oxygen on the glass surface of the reaction element 12. The generated oxygen is removed from the water vapor holding vessel 11 together with excess water vapor from the water vapor exhaust port 16. Hydrogen dissolves in the hydrogen-soluble glass layer of the reaction element 12 and diffuses therein to reach the Pd film. The diffusion coefficient of hydrogen in the glass used in this example was 4.5 × 10 ⁻⁸ cm ² / s to 1 × 10 ⁻⁵ cm ² / s at 300 ° C. to 500 ° C.

  The dissolution / diffusion reaction of hydrogen into the glass layer ends when the hydrogen atom concentration in the glass forming the reaction element reaches an equilibrium with the adsorbed hydrogen concentration on the surface. Therefore, in order to continuously advance the reaction and take out hydrogen, it is necessary to remove hydrogen atoms in the reaction element. The basic means for this is to release hydrogen from the Pd constituting the surface of the water vapor take-out container into the atmosphere in the hydrogen take-out container 14. In a state where the hydrogen partial pressure is low, hydrogen is released into the atmosphere at a release pressure corresponding to the hydrogen concentration in Pd. In this example, the air in the hydrogen take-out container 14 was purged with an inert gas in advance to reduce the hydrogen partial pressure. The released hydrogen is cooled to the outside temperature and collected in a hydrogen storage alloy having a lower discharge pressure in the hydrogen storage means 18. Hydrogen is continuously generated and collected from water by the above method.

  Means (potential assist method) for increasing the unit area of the reaction element 12 exposed to water vapor and the yield of hydrogen per unit time using the water-splitting hydrogen production apparatus described above will be described with reference to FIG. However, the reaction conditions such as reaction temperature, water vapor partial pressure and oxygen partial pressure in the water vapor holding container, glass composition and thickness, alloy composition and thickness, and hydrogen partial pressure in the hydrogen take-out container 14 are all optimal conditions. Is set. One way to increase the yield is to increase the concentration gradient between the water vapor side surface and the alloy side surface of the glass layer.

  As described above, this can be realized by the structure schematically shown in FIG. 5 using the fact that the hydrogen concentration in the hydrogen storage alloy can be increased or decreased by controlling the Fermi level. In this case, the water vapor is at an equilibrium potential with the metal water vapor holding container 11 that is grounded. The hydrogen concentration in the glass 21 is determined by the equilibrium condition with the water vapor. Reference numeral 22 denotes a reference electrode attached to the surface on the water vapor side of the glass. Although not necessarily required, it is assumed that the reference electrode 22 and the hydrogen releasing alloy 23 are the same metal. The hydrogen concentration of the reference electrode is determined by the equilibrium relationship with the glass in contact. The hydrogen concentration in the hydrogen releasing alloy can be increased or decreased by raising or lowering the potential of the hydrogen releasing alloy on the order of 0.1 V with respect to the value of the reference electrode. By such an operation, the concentration gradient of hydrogen in the glass can be increased. At the same time, the hydrogen releasing equilibrium pressure of the hydrogen releasing alloy can be controlled. In the potential control in this configuration, there is no steady current. Therefore, most of the electric potential control power is used for increasing the free energy of hydrogen, and the power loss is extremely small.

  A second example of the potential assist method for increasing the hydrogen concentration in the glass and increasing the hydrogen yield will be described. In FIG. 6, the reference electrode 22 is dispersed over the entire glass surface using a porous electrode such as platinum black that is inert to water vapor. Similar to the case of FIG. 5, the potential of the hydrogen releasing alloy 23 can be controlled to an arbitrary value on the order of 0.1 V with respect to the reference electrode. The potentials of the reference electrode and the hydrogen-releasing alloy can be controlled independently of the water vapor holding container 11 and the hydrogen material taking-out container 14 that are grounded. In this configuration, the water vapor concentration on the glass surface in contact with the water vapor is substantially defined by the potential of the reference electrode. Accordingly, such a configuration can increase the hydrogen concentration in the glass and consequently increase the hydrogen yield. In this case, the hydrogen flux in the glass can be increased by controlling the potential of the hydrogen releasing alloy with respect to the reference electrode, the discharge pressure of the hydrogen releasing alloy can be controlled, and the loss of power supply is extremely small as described above. Same as the case.

In this example, glass having the composition described in paragraph 0062 was used as a material that decomposes water and takes in hydrogen. However, this material is not limited to this, and TiO ₂ , Nb ₂ O ₅ , WO ₃ A glass containing any one component of MoO ₃ , V ₂ O ₅ , Fe ₂ O ₃ , Sb ₂ O ₅ , GeO ₂ , and CeO ₂ or a mixture thereof can be used.

  In this embodiment, in order to generate water vapor, a heater installed outside the water vapor holding container 11 is used. However, the present invention does not limit the production of water vapor to a heater. Rather, as a better means from the viewpoint of maintaining the environment, it is also possible to apply a method of producing water vapor using solar heat or a method of producing water vapor using various unused industrial waste heat.

  Moreover, although water vapor | steam was introduce | transduced into the water vapor holding container from the exterior, it is also possible to apply the method of producing | generating water vapor | steam by putting water into the water vapor holding container 11 directly and heating a holding container. In this case, in order to remove the generated oxygen, it is effective to increase the reaction efficiency to use an oxygen absorbent such as iron powder. In addition, since the generated oxygen is an active atom, application using strong oxidizability is possible.

  In this embodiment, a porous material is used for the support of the reaction element, but it is also possible to use a metal alloy plate that is permeable to hydrogen. In this embodiment, Pd is used as the metal film. However, the present invention is not limited to this, and a metal having a hydrogen diffusion coefficient larger than that of the glass material can be widely used.

  The present invention solves technical problems of materials related to hydrogen production, separation and purification, storage, sensing, and the like, among various technologies related to a hydrogen clean energy system that requires rapid development. For example, with regard to hydrogen production, hydrogen treatment materials and materials for building a quasi-ideal hydrogen production system using water as a raw material and unused heat or solar heat obtained with a simple condensing system as an energy source. A complex is provided. The materials and composites according to the present invention have a function of reversibly absorbing or releasing hydrogen depending on the hydrogen concentration in the atmosphere. Accordingly, by using the material or composite according to the present invention, a hydrogen separation and purification apparatus, a hydrogen sensing system, and the like with high hydrogen selectivity, high durability, and high cost competitiveness are provided.

The figure which shows the temperature-programmed desorption curve of Example 1, Example 2, and a comparative example. It is a figure which shows the structure 1 of a hydrogen selective membrane. It is a figure which shows the structure 2 of a hydrogen selective membrane. It is a basic conceptual diagram of a hydrogen generator. It is a figure explaining the electric potential assist in a hydrogen generator. It is a figure explaining the electric potential assist in a hydrogen generator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inflow side Pd thin film 2 Outflow side Pd thin film 3 Glass 4 Nb metal plate 5 Porous ceramic 11 Water vapor holding container 12 Reaction element 13 Holding plate 14 Hydrogen extraction container 15 Water vapor introduction port 16 Water vapor exhaust port 18 Hydrogen storage means 22 Reference electrode 23 Hydrogen releasing alloy

Claims (11)

  Due to the high and low partial pressure of hydrogen in the atmosphere, it has the function of decomposing hydrogen and dissolving the generated hydrogen atoms, or as a reverse reaction, releasing dissolved hydrogen into the atmosphere as hydrogen molecules. Depending on the pressure level, water molecules are decomposed to selectively dissolve generated hydrogen atoms, or as a reverse reaction, dissolved hydrogen is released as water vapor molecules by reaction with oxygen in the atmosphere. A multi-component glass material for hydrogen treatment containing at least one of niobium and tungsten oxide.   The multi-component glass material for hydrogen treatment according to claim 1, wherein the total content of Nb + Ti + W is 15% or more in terms of mol% of cations constituting the glass.   The multi-component glass material for hydrogen treatment according to claim 2, wherein the total content of Nb + Ti + W is 15 to 60% in terms of mol% of cations constituting the glass.   The multicomponent glass material for hydrogen treatment according to claim 3, wherein the total content of Nb + Ti + W is 20 to 55% in terms of mol% of cations constituting the glass.   It is a phosphate glass, The multicomponent glass material for hydrogen treatment of any one of Claims 1-4 characterized by the above-mentioned.   The molar percentage of cations constituting the glass, P: 20 to 50%, Nb: 0 to 50%, Ti: 0 to 20%, W: 0 to 40%. The multicomponent glass material for hydrogen treatment according to any one of 5.   A hydrogen treatment composite comprising the multi-component glass material for hydrogen treatment according to any one of claims 1 to 6 and a hydrogen storage alloy laminated or dispersed on the glass material.   8. The hydrogen treatment composite according to claim 7, wherein the hydrogen storage alloy is Palladium Pd, Nickel Ni, Platinum Pt and an alloy containing at least one of them.   A hydrogen-selective membrane comprising the multi-component glass material for hydrogen treatment according to any one of claims 1 to 6 or the hydrogen treatment complex according to claim 7 or 8 and formed into a film shape.   The hydrogen selective membrane according to claim 9, further comprising means for applying a potential difference between the front and back of the multi-component glass material for hydrogen treatment or the hydrogen treatment composite. The multi-component glass material for hydrogen treatment according to any one of claims 1 to 6 or the hydrogen treatment complex according to claim 7 or 8 and a steam generating means for generating steam, and the steam generating means A hydrogen generator in which the generated water vapor is brought into contact with a multi-component glass material for hydrogen treatment or a hydrogen treatment composite.

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