JP4417806B2 - Hydrogen storage material and method for producing the same - Google Patents

Description

  The present invention relates to a hydrogen storage material using the hydrogen storage characteristics of Mg and a method for producing the same.

  In recent years, hydrogen has attracted attention as a clean energy source to replace fossil fuels such as oil and gas, which have a large impact on the environment. Hydrogen is a gas in a normal environment (normal temperature and normal pressure) and has a strong explosive property. Therefore, there is a need for a medium for safely storing and using hydrogen.

  As such a medium, Mg is expected to be a next-generation hydrogen storage material because it has the property of storing up to 7.6 wt% of its own weight of hydrogen. However, when Mg simple substance is used as a hydrogen storage material, a compound with hydrogen (hydride) is thermodynamically stable, and a general Mg bulk simple substance hardly causes a hydrogen releasing reaction in a temperature range of 300 ° C. or lower. For this reason, various materials based on Mg that have been treated to destabilize hydrides have been developed and studied.

As measures for destabilizing hydrides in Mg-based hydrogen storage materials, various research and development have been conducted mainly from the two viewpoints of alloying with elements having a catalytic function and introduction of nanostructures. Moreover, from the viewpoint of introducing a nanostructure, a conventional manufacturing method includes a powder process and a lamination process by vapor deposition or sputtering (see Patent Document 1 and Non-Patent Document 1).
JP 2002-105576 A “Nanocrystalline magnesium for hydrogen storage” by A. Zaluska, L .; Zaluski and J.M.

  However, it is known that in alloying with an element having a catalytic function, it is difficult to synthesize a single-phase compound by cooling and solidification from a liquid phase in many systems containing Mg. In the introduction of nanostructures, forced solid solution, alloying, and multiphase formation can be performed using a powder process with extremely strong processing, but generally reversibility in the reaction of the formed phase with hydrogen is poor. In addition, the lamination process by vapor deposition and sputtering can precisely control the lamination structure, but there has been no example of the structure change in the process of hydrogen storage / release so far, and the reversibility of the reaction can be maintained. Have difficulty.

  The present invention has been made in view of the above problems, and an object thereof is to provide a hydrogen storage material that is excellent in reversibility of the hydrogen storage / release process.

  The inventors have conducted intensive studies in order to solve the above-mentioned problems, and have found that the following means exert significant effects.

The technical means taken in claim 1 of the present invention includes at least one of a layer made of Mg and a layer made of Pd, and Mg _x Pd _(1-x) (x is 0.25, 0.45-0.5. , 0.6, 0.75, 5/7, 6/7) a layered structure formed by laminating layers composed of phases .

The technical means taken in claim 2 of the present invention is the hydrogen storage material according to claim 1, wherein the layer interval of the laminated structure is less than 1 micrometer .

The technical means taken in claim 3 of the present invention is configured to reversibly absorb and desorb hydrogen in a temperature range of 200 ° C. or less. Material.

The technical means taken in claim 4 of the present invention is to integrate a laminated body in which a layer made of Mg and a layer made of Pd or a powder mixture containing Mg and Pd are integrated. A structure having a laminated structure with an interval of less than 1 micrometer is formed by repeating strong processing with plastic deformation and compression-integrated molding of the processed material with respect to the bulk. It is a manufacturing method of material.

  The technical means taken in claim 5 of the present invention is the method for producing a hydrogen storage material according to claim 4, wherein the indirect rolling method and heat treatment at 200 ° C to 400 ° C are used in combination.

The technical means taken in claim 6 of the present invention is that the hydrogen storage material prepared by the method according to any one of claims 4 and 5 is subjected to heat treatment in a hydrogen atmosphere at 250 to 350 ° C. By simultaneously carrying out alloying by interdiffusion between solid phases and dissociation reaction accompanying hydrogenation, Mg _x Pd _(1-x) (x is 0.25, 0.45-0.5, 0. 6, 0.75, 5/7, 6/7 ) phase is produced, which is a method for producing a hydrogen storage material.

  The technical means taken in claim 9 of the present invention is configured to absorb and release hydrogen reversibly in a temperature range of 200 ° C. or lower, and the hydrogen storage according to claim 7 or 8. Material.

  According to the present invention, a hydrogen storage material that is excellent in reversibility of hydrogen storage / release reaction and excellent in practicality is obtained. In addition, hydrogen storage / dissociation pressure is higher than that of Mg alone, and hydrogen can be stored / released at a temperature lower than that of conventional hydrogen storage materials such as Mg alone. Moreover, the hydrogen storage material concerning this invention can be manufactured using simple equipments, such as a rolling mill and the heating furnace which controlled atmosphere, and is excellent in productivity. In addition, since the heat treatment temperature can be lower than the temperature at which Mg evaporates, contamination of the material, in particular, oxidation and composition deviation hardly occur, and a high-purity and high-quality hydrogen storage alloy can be obtained.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  An outline of a method for producing a hydrogen storage material according to the present invention is shown in FIG. Here, the hydrogen storage material is manufactured so as to have a structure in which at least two of a layer made of Mg, a layer containing at least one element other than Mg, and a layer containing an Mg-containing alloy are alternately stacked. Therefore, for example, a case where Mg and Pd are used as starting materials will be described. The manufacturing process includes a lamination / rolling process and a heat treatment process.

  First, the lamination / rolling process will be described. The starting materials Mg and Pd are formed as a thin plate-like or foil-like Mg layer 1 and Pd layer 2, respectively. The Mg layer 1 and the Pd layer 2 of the starting material are alternately laminated, and both surfaces of the laminate (bulk) 3 are sandwiched and joined by protective plates 4 and 4. Further, the laminate 3 is rolled (strong processing with plastic deformation). Rolling is an indirect rolling method in which compression and stretching are performed with a pair of rotating rolls 5 and 5 while sandwiching both surfaces of the laminate 3 with the protective plates 4 and 4. The protective plates 4 and 4 are peeled off from the rolled laminate 3 and the laminate 3 is folded or overlapped with another rolled laminate, and then rolled while being sandwiched between the protective plates 4 and 4 again. . In this way, the Mg and Pd fine laminate 3 is formed by repeating rolling and compression-integrated molding after rolling as necessary.

  After repeating the rolling until the internal structure of the laminated body 3 has a desired microstructure, the laminated body 3 is heat-treated in a controlled atmosphere so as not to be oxidized using a heating device 6 such as an electric furnace. The heat treatment is performed at a predetermined temperature in a temperature range of 200 ° C to 400 ° C. At this time, the reaction does not proceed at temperatures lower than 200 ° C., and at 400 ° C. or higher, the vapor pressure of Mg is high and compositional deviation occurs.

  The heat treatment is more preferably performed at a predetermined temperature in a temperature range of 250 ° C. to 350 ° C. in a hydrogen atmosphere. At this time, hydrogen occlusion / release does not proceed at a temperature of 250 ° C. or lower, and when it is heat-treated at a temperature of 350 ° C. or higher, hydrogen storage / release characteristics at a low temperature deteriorate.

  By the heat treatment, forced solid solution / chemical reaction proceeds, and an intermetallic compound phase is generated. In addition, when the heat treatment is performed in a hydrogen atmosphere, by performing hydrogen absorption and desorption, generation of an intermetallic compound phase due to forced solid solution / compounding and secondary generation due to dissociation of the compound phase accompanying the hydrogenation reaction are performed. A fine microstructure is formed.

  In the rolling process, since the indirect rolling method in which the laminate 3 is sandwiched and stretched between the protective plates 4 and 4 is used, the stress concentration during the compression by the rotary rolls 5 and 5 is dispersed. Accordingly, non-uniformity caused by material damage due to stress concentration, slight setting errors, etc., is alleviated in the rolling process.

  In addition, since a process of stacking materials after rolling, for example, folding and rolling again is repeated, a desired Mg—Pd layer interval can be formed very easily in the laminate 3. For example, layer spacing on the order of nanometers (less than 1 micrometer) can be easily obtained. Note that the same effect can be obtained by increasing the initial thickness of the laminated body 3 or performing multi-stage rolling with respect to the repeated lamination and rolling.

  In addition, the method of manufacturing the laminate 3 is preferably the method or a method of mixing powder materials and integrating them by warm extrusion or pressing, but a method of manufacturing a multilayer film by sputtering or the like is also possible. .

  The manufacturing method of the said laminated body 3 is realizable only by using general equipments, such as a rolling mill and an atmosphere control heat treatment furnace, and generally does not require high vacuum sealed space like vapor deposition, sputtering, etc.

  The ratio of Mg and Pd determines the initial lamination thickness ratio from each molar volume, and the fineness of the structure can be controlled by heat treatment conditions such as the initial plate thickness, the number of rollings, and the number of annealings.

  In addition, since the degree of compound formation can be set under heat treatment conditions, it is very easy to design and control the structure of the compound phase after the heat treatment or the compound phase and the remaining metal phase. This makes it possible to produce not only single-phase intermetallic compounds, but also hydrogen-absorbing composite alloys in which Pd, which has a catalytic effect, or Mg is dispersed in the phase to obtain a hydrogen-absorbing material with a large hydrogen-absorbing capacity. It becomes.

  Moreover, since the laminated body before heat treatment is a metal mixture, plastic working is possible and the degree of freedom in shape is large.

  Further, the heat treatment temperature in the reaction process in the present invention is about 400 ° C. at the maximum, but this temperature range can be treated in a general heating furnace. In this temperature range, the vapor pressure of Mg is sufficiently low, and there is little compositional deviation, oxidation, and contamination.

(Example) Hereinafter, an example of the present invention will be described in detail. A thin plate having a thickness of 5 mm was cut out from a commercially available Mg ingot, and a 65 μm-thick Mg foil was produced through each process of warm rolling and cold rolling. Using this Mg foil and a commercially available Pd foil (20 μm thick) as a base material, these were cut into rectangles (2 × 3 cm) and stacked alternately as Mg, Pd, Mg, Pd, etc. It was joined with a hydraulic press (700 kgf / cm ² ) sandwiched between (stainless steel plate). In this case, the molar ratio of the stacked Mg and Pd is approximately 2: 1.

  The laminate is sandwiched between the two protective plates, rolled to a thickness of about half of the initial thickness with a two-roll rolling mill, the rolled laminate is folded in half and sandwiched between the protective plates again. Rolled. This process was repeated about 40 times to produce a Mg—Pd mixed laminate. A schematic view of a cross section of the prepared mixed laminate is shown in FIG. This was held at 300 ° C. for 24 hours in a heating apparatus in a hydrogen atmosphere to perform diffusion / hydrogenation heat treatment.

Fig. 2 shows the results of X-ray diffraction using Cu-Kα rays after vacuuming the hydrogen storage alloy after heat treatment, and phase identification and quantification by Rietveld analysis using Rietan-2000. 3 shows. In the material after the heat treatment, single Mg is not detected, and Pd generated by dissociation of the intermetallic compound and the compound phase (that is, _x of Mg _x Pd _(1-x) is 0,0.75,5 / 7. , 6/7 product). In addition, as a result of electron beam diffraction performed on the isolated Pd phase (shown in FIG. 4), regular lattice reflection that cannot be observed with single Pd was confirmed. This is because the amount of Pd-rich compound phase (that is, _x of Mg _x pd _(1-x) is 0.25, 0.45-0.5, 0.6 product) is formed.

  FIG. 5 shows a transmission electron microscope (TEM) photograph of the microstructure formed secondarily by the heat treatment. It can be seen that in addition to the Pd phase indicated by symbol A and the compound phase indicated by symbol C, a microcrystalline region indicated by symbol B is formed at the interface. It can also be seen that the compound phase of the symbol C is composed of ultrafine grains having a crystal grain size of the order of nanometers.

  From these results, it was confirmed that a change in the composition ratio of Mg and a constituent element other than Mg (Pd in this example) was accompanied by a hydrogen storage / release reaction using the hydrogen storage material of this example. This indicates that the hydrogen storage alloy is destabilized by the hydrogen storage reaction.

  As described above, in this embodiment, alloying and secondary microstructure formation are performed simply by performing machining (lamination / rolling process) and heat treatment (heat treatment process) in a lower temperature range than melting. Is called. Therefore, alloy contamination, especially oxidation and compositional deviation, which cannot be avoided by other methods, is very small. That is, it is possible to produce a high purity alloy without using special equipment.

  Further, in this example, about 0.5 g of the heat-treated hydrogen storage material produced through the lamination / rolling process and the heat treatment process is put into a SUS316 container (volume 3.5 ml), and PCT characteristic evaluation is performed at 200 ° C. by the Siebelz method. (Maximum pressure 3.3 MPa) was performed.

The results of the PCT characteristic evaluation are shown in FIG. In this temperature range, although the Mg hydride MgH ₂ is thermodynamically stable, the hydrogen occlusion / release reaction proceeds reversibly in the sample prepared by this method. . Furthermore, the hydrogen storage / dissociation pressure in this hydrogen storage / release process is higher than that of Mg. This is because the hydrogen storage alloy is destabilized due to a change in the composition ratio between Mg and a constituent element other than Mg (Pd in this embodiment) in the hydrogen storage reaction as described above. That is, the complex secondary microstructure introduced into the alloy indicates that the hydrogen storage and release process has been activated, and it is reversibly high at a much lower temperature compared to conventional hydrogen storage alloys. This shows that hydrogen is stored and released at a dissociation pressure and a high storage capacity.

  Explanatory drawing which shows the manufacturing process of the hydrogen storage material in one Example of this invention.   The schematic diagram of the cross section of the Mg-Pd type laminated body in one Example of this invention.   Explanatory drawing which shows the result of the X-ray-diffraction profile and Rietveld analysis of the laminated body in one Example of this invention after heat processing.   The electron-diffraction pattern of the Pd phase of the laminated body in one Example of this invention after heat processing.   The micro structure photograph of the laminated body after heat processing in one Example of this invention.   Explanatory drawing which shows the isothermal hydrogen storage characteristic (PCT characteristic evaluation result by the Siebelz method) of the laminated body after heat processing in one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mg layer, 2 ... Pd layer, 3 ... Laminated body, 4 ... Protection board, 5 ... Rotating roll, 6 ... Heating device

Claims (6)

At least one of a layer made of Mg and a layer made of Pd, and Mg _x Pd _(1-x) (x is 0.25, 0.45-0.5, 0.6, 0.75, 5/7, 6 / 7) A hydrogen storage material characterized by having a layered structure formed by laminating layers composed of phases .   2. The hydrogen storage material according to claim 1, wherein the layer interval of the laminated structure is less than 1 micrometer.   3. The hydrogen storage material according to claim 1, wherein the hydrogen storage material is configured to reversibly store and release hydrogen in a temperature range of 200 ° C. or lower. Strong processing and processing accompanied by plastic deformation for a laminated body in which a layer made of Mg and a layer made of Pd are laminated, or a bulk in which a powder mixture containing Mg and Pd is integrated A method for producing a hydrogen storage material, characterized in that a structure having a laminated structure with a layer interval of less than 1 micrometer is formed by repeating subsequent compression-integral molding of the material.   The method for producing a hydrogen storage material according to claim 4, wherein an indirect rolling method and a heat treatment at 200 ° C. to 400 ° C. are used in combination. The hydrogen storage material prepared by the method according to any one of claims 4 and 5 is subjected to heat treatment at 250 to 350 ° C in a hydrogen atmosphere, and alloying and hydrogenation by interdiffusion between solid phases during the heat treatment. By simultaneously carrying out the dissociation reaction associated with Mg _x Pd _(1-x) (x is 0.25, 0.45-0.5, 0.6, 0.75, 5/7, 6/7 ) A method for producing a hydrogen storage material, comprising generating a phase.