JP5394767B2 - Method for producing hydrogen absorbing / releasing sheet - Google Patents

Description

  The present invention relates to a hydrogen storage / release sheet, and more particularly to a high-performance hydrogen storage / release sheet capable of stably absorbing and releasing hydrogen with high efficiency and a method for manufacturing the same.

Conventionally, there is a hydrogen storage alloy as the hydrogen storage / release material, which has been developed as a material for secondary batteries and fuel cells.
In general, the hydrogen storage alloy is basically used by putting a granular or massive hydrogen storage alloy in a storage container as it is. At this time, by repeating absorption and release of hydrogen, volume expansion and volume contraction accompanying a change in the crystal structure of the hydrogen storage alloy are repeated, and the granular or massive material is gradually atomized to several tens of μm. For this reason, the thermal conductivity characteristics are lowered, the gaps between the hydrogen storage alloys in the container are filled, and the hydrogen absorption / release performance is deteriorated and the airflow resistance is increased. In addition, there is a problem that the finely divided hydrogen storage alloy flows out of the hydrogen storage container by the air current. Furthermore, when the hydrogen absorption / release operation is controlled by temperature, the hydrogen storage alloy itself has a low thermal conductivity, which requires a complicated hydrogen storage container structure for improving the thermal conductivity.

On the other hand, it is also conceivable to carry a hydrogen storage alloy on a sheet. As a related technique, there is proposed a technique in which adsorbent particles such as activated carbon powder are confined between fibers in a sandwich structure using the wet papermaking method already proposed by the present applicant in Patent Document 1.
By using wood pulp fibers used for papermaking as the main material and attaching a fine hydrogen storage alloy to the fibers by wet papermaking, a space allowing the volume change of the hydrogen storage alloy is secured, and the hydrogen absorption It is conceivable to solve the problems caused by the deterioration of the discharge performance and the increase of airflow resistance.

Japanese Patent Application Laid-Open No. 2004-330631 “Adsorbent Sheet, Manufacturing Method and Manufacturing Apparatus”

However, the following problems remain even with the above solution.
(A) In an experiment conducted by the present inventors, when a structure mainly composed of cellulose fibers not refined is used, the maximum content of the hydrogen storage alloy that can prevent the hydrogen storage alloy attached to the sheet from dropping is low. However, the current hydrogen storage capacity is not sufficient. This is because the structure using cellulose fibers that have not been refined is configured to wrap the hydrogen storage alloy in the internal voids of the cellulose fibers.
(B) By using cellulosic fine fibers, it is possible to drop off the hydrogen storage alloy and increase the maximum content. However, since the heat resistant temperature is as low as 200 ° C. or less, a general hydrogen storage alloy was used. In this case, there is a problem that the heat treatment in the initial activation cannot be endured, the shape cannot be maintained, and the powder cannot be prevented from falling off.

(C) Even when a hydrogen storage alloy having a low initial activation temperature is used, in the structure mainly composed of cellulosic fibers, the shape of the hydrogen storage alloy is maintained, and the powder is pulverized by the thermal history during hydrogen absorption / release. There is a risk that it cannot be prevented from falling out.

This invention is made | formed in view of the said subject, The objective of this invention is providing the hydrogen absorption-release sheet | seat which can solve the said subject, and its manufacturing method.
An example of a specific purpose is as follows.
(A) While maintaining a high content of the hydrogen storage alloy, even if it is formed into various shapes such as a honeycomb structure, the shape retention is maintained high, and the dropping of the hydrogen storage alloy from the sheet can be strongly suppressed. To do.
(B) While maintaining a high content of the hydrogen storage alloy, the thermal conductivity is also increased so that hydrogen can be absorbed and released in a short time and with less energy.
(C) The heat resistance of the sheet is improved so that the hydrogen storage / release operation of the hydrogen storage alloy can be performed stably over a long period of time.
(D) Generally, the surface of a pulverized hydrogen storage alloy is easily poisoned, and often loses the ability to absorb and release hydrogen by operation in the air or water. In this case, the hydrogen absorption / desorption performance can be recovered by performing the activation treatment under the condition of 200 ° C. or higher under the high-pressure hydrogen atmosphere.
In addition, the subject of invention other than having described above, its solution means, and its effect are demonstrated in detail in description in the specification mentioned later.

Although the present invention can be expressed in many aspects, for example, typical ones are configured as follows.
The hydrogen absorbing / releasing sheet of the present invention is composed of fine hydrogen absorbing / releasing particles having an average particle diameter of 0.001 to 1 mm, synthetic polymer fibers and inorganic fibers that are easily fibrillated, and the hydrogen absorbing / releasing particles are 70 wt% or more and 95 wt%. % Or less in the range.
As a typical material for the hydrogen absorption / release particles, there are hydrogen storage alloy particles.
According to the present invention, a fine synthetic polymer fiber that takes a fine network structure under predetermined conditions and hydrogen absorption / release particles are mixed together under appropriate conditions, so that a high content of hydrogen absorption / release particles is contained inside the network structure. It is possible to encapsulate at a rate, and it is possible to strongly suppress the dropping of particles after the sheet is formed.
Further, because of this network structure, the entire surface of the hydrogen absorbing / desorbing particles is not covered, and the hydrogen absorbing / releasing performance is not affected.

  The method for producing a hydrogen absorbing / releasing sheet according to the present invention includes a fibrillation dispersion step in which a fine polymer fiber structure is formed in a solution by stirring and dispersing the synthetic polymer fibers that are easily fibrillated in the solution. And adhering the hydrogen absorbing / releasing particles to the mesh fiber structure by adding fine hydrogen absorbing / releasing particles having an average particle diameter of 0.001 to 1 mm to the formed fine mesh fiber structure while stirring. A particle supporting step, an inorganic fiber dispersing step in which inorganic fibers are mixed and stirred and dispersed in the solution, a paper making solution adjusting step to finally form a uniform hydrogen absorbing and releasing particle mixed solution, and the adjusted paper making solution. Using a papermaking process for producing a sheet by a wet papermaking method and a drying process for drying the obtained papermaking sheet, and the content of hydrogen absorbing / releasing particles in the dried sheet is 70% by weight or more 9 Or less by weight%, and stable and adjusting the degree of fibrillation of synthetic polymer fibers in the fibrillated dispersion step to allow carrying the hydrogen absorption and desorption particles.

  In the present invention, even if the content of hydrogen absorbing / releasing particles is a high content of 70% by weight or more and 95% by weight or less, synthetic polymer fibers that are easy to be fibrillated are used in advance, and further the synthetic high fiber in the fibrillation dispersion step. Since the degree of fibrillation of the molecular fiber is adjusted, the hydrogen absorbing / releasing particles can be adhered to the fine mesh fiber structure, and the hydrogen absorbing / releasing particles are encased in a relatively large internal space. Unlike this, the hydrogen absorbing / releasing particles can be stably supported without falling off the sheet.

The fibrillation dispersion step and the inorganic fiber dispersion step can be performed almost simultaneously. However, it is easier to adjust the degree of fibrillation of the synthetic polymer fiber when the fibrillation / dispersion step → the particle supporting step → the inorganic fiber dispersion step → the papermaking solution adjustment step is performed in this order.
In the present specification, “fibril” means fine fibers constituting fibers. “Fibrillation” refers to a phenomenon in which a single fiber is divided into many fibrils, or a phenomenon in which fine fibers inside the fiber appear on the fiber surface by some action and become dispersed.

  As a method for fibrillating highly crystalline orientation fibers, there is a method of processing in a solution so that one fiber is divided into many fibrils by strongly beating and stirring. As another method, there is a method in which fibers before being put into a solution are easily torn and dispersed in the machine direction by mechanical or chemical treatment.

The hydrogen absorbing / releasing sheet of the present invention is characterized in that both the synthetic polymer fiber and the inorganic fiber are fibers that can withstand a temperature of 200 ° C. to 400 ° C.
With this configuration, both the synthetic polymer fiber and the inorganic fiber can be activated without lowering the moldability by withstanding temperatures of 200 ° C. to 400 ° C., and the hydrogen absorbing / releasing particles carried on the fiber can be contained in the container. The capability of absorbing or releasing hydrogen in the state of being accommodated in the container can be provided. On the other hand, if the temperature cannot be withstand at 200 ° C., the fiber loses the ability to hold the hydrogen absorbing / releasing particles, causing a problem that the supported hydrogen absorbing / releasing particles fall off.

The hydrogen absorbing / releasing sheet of the present invention is characterized in that an aromatic polyamide fiber that is easily fibrillated is employed as the synthetic polymer fiber.
With this configuration, the aromatic polyamide fiber that is easily fibrillated becomes a fine network structure by vigorously stirring in water, and the hydrogen absorbing / releasing particles can be held and fixed therein. Even if it is included at a high content as described above, it is difficult for fine particles to fall off.

The hydrogen absorption / release sheet of the present invention is characterized in that carbon-based fibers are employed as the inorganic fibers.
If it is this structure, carbon fiber has a high thermal conductivity and there exists an advantage which can perform the absorption / release operation | movement of hydrogen with a short time and less energy compared with the sheet | seat which does not contain carbon fiber.
The hydrogen storage / release sheet of the present invention is characterized in that metal fibers are employed as the inorganic fibers.
If it is this structure, a metal fiber has the high heat conductivity, and there exists an advantage which can perform the absorption / release operation | movement of hydrogen with a short amount of energy compared with the sheet | seat which does not contain a carbon fiber.

  As described above, according to the present invention, the content of the hydrogen absorbing / releasing material can be set to a high content of 70 wt% to 95 wt% by fibrillating the synthetic polymer fiber to improve its supporting performance. It is possible to prevent the hydrogen storage alloy from falling off and to have stable performance. Further, the shape retainability can be maintained at a high level, the thermal conductivity can be increased, and the operation of absorbing and releasing hydrogen can be performed in a short time and with less energy, so that a simple heat generating device can be configured. Furthermore, the heat resistance of the sheet can be improved, the hydrogen absorption / release operation of the hydrogen absorption / release material can be stably performed over a long period of time, and the activation treatment can be performed under conditions of 200 ° C. or higher.

FIG. 1 is an electron micrograph of a hydrogen storage / release sheet according to this embodiment. FIG. 2 is a view showing a schematic microstructure of a hydrogen absorption / release sheet mainly composed of wood pulp fibers as a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the case where a hydrogen storage alloy is employed as the hydrogen storage / release material will be described as an example.
As described above, even with a structure mainly composed of wood pulp fibers, it is possible to suppress the dropping of the hydrogen storage alloy to some extent. However, in the experiments conducted by the present inventors, a structure mainly composed of wood pulp fibers is The upper limit of the content of the hydrogen storage alloy capable of preventing the occlusion of the storage alloy from the fiber structure is about 50% by weight of the sheet.
A possible reason for this is that in the structure mainly composed of wood pulp fibers, even when the fibers are stirred and dispersed in the solution, the fiber diameter is large (40 μm to 50 μm), and therefore the fine particles are fixed (fibers). The surface area and the internal voids are small, and the content of fine particles cannot be increased. In addition, in the structure mainly composed of wood pulp fibers, the direction of the fibers is easily aligned in the same direction when viewed in fine units, and the hydrogen storage alloy can only be supported by enclosing the hydrogen storage alloy in the internal voids of the fiber structure. Seems to be a factor.

FIG. 2 is a view schematically showing such a wood pulp fiber structure 5.
As shown in FIG. 2, the wood pulp fibers 1 extend in the direction of the arrow 2 and are entangled with each other, and the fine hydrogen storage alloy particles 4 are attached so as to wrap in the internal voids 3 generated by the entanglement between the fibers 1. ing. With such a structure, the tensile strength as a sheet and ease of papermaking are improved, but the internal voids 3 are large, the number of particles 4 that leak out is large, and the surface of the fiber structure 5 is on the surface. Since the adhering voids are not easily formed, the content of the hydrogen storage alloy cannot be increased.

  In addition, because the fiber diameter is large and the fiber direction of the sheet-like material is easily aligned in the same direction during papermaking, heat is mainly generated on the sheet surface with a small number of fine voids to which the hydrogen storage alloy adheres. Since it is transmitted through the fiber, the thermal conductivity is extremely small. For this reason, when it is going to control hydrogen absorption-and-release operation with temperature, the above-mentioned special apparatus for improving thermal conductivity is needed.

  The present invention forms a fine mesh fiber structure in the solution by stirring and dispersing synthetic polymer fibers such as aromatic polyamides that are easily fibrillated based on such a viewpoint. After that, a fine hydrogen storage alloy having an average particle diameter of 0.001 to 1 mm is added to the fine mesh fiber structure while stirring, thereby the hydrogen storage alloy is put into the fine voids in the mesh fiber structure. I try to make it adhere. And the sheet | seat is manufactured by the wet papermaking method using the adjusted papermaking solution, The obtained papermaking sheet is dried and a hydrogen absorption / release sheet | seat is manufactured.

As shown in the electron micrograph of FIG. 1, the fiber structure of the hydrogen absorption / release sheet manufactured in this way has a messy extending direction of fibrils, and a network-like fiber structure is formed. Even when the content of the hydrogen storage alloy particles is increased to a range of 70% by weight or more and 95% by weight or less, the particles of the hydrogen storage alloy enter the fine voids of the mesh-like fiber structure, thereby strengthening the particles. It will be difficult to drop off because it will be held.
In addition, even when actually formed into a pleated structure, a honeycomb structure, or a wound structure, the attached hydrogen storage alloy does not fall off. Furthermore, the way in which heat is transferred to the hydrogen storage alloy can be increased by making the hydrogen storage alloy fine particles and blending the carbon fibers.
Also, since synthetic polymer fibers are used, processing into pleats, honeycomb shapes, etc. is also good.
In addition, it is preferable that the length of the synthetic polymer fiber constituting the network-like fiber structure is in the range of 0.1 mm to 3.0 mm.
Moreover, as a hydrogen storage alloy to be used, known alloys such as a titanium alloy, a rare earth alloy, and a Laves phase alloy can be used.

Specific examples will be described below.
Example 1
Aramid fibers that can be fibrillated (Jsp 8026 made by Teijin Techno Products) 15.63 g (solid content 8%) are put into a mixing vessel containing 2 liters of water, and dispersed at high speed to form a fine mesh in the solution. A shaped structure was formed. Next, 10.0 g of TiFe-based hydrogen storage alloy (Ti _1.15 FeO _0.024 manufactured by Hokkaido University) having a specific gravity of 6 previously atomized to 1 mm or less was added while stirring the water in the mixing vessel. As a result, a material in which fine particles of TiFe-based hydrogen storage alloy (hydrogen storage / release material) adhered to the inside and the surface of the aramid fiber network structure was obtained. Thereafter, 1.39 g of carbon fiber having good thermal conductivity (3 mm chop product manufactured by Toho Rayon) was blended and stirred for a predetermined time to prepare a uniform hydrogen absorption / release mixed solution. The obtained mixed solution was formed into a sheet by a hand-sheet test apparatus and dried to obtain a 25 cm square hydrogen absorption / release sheet.
The content of the TiFe-based hydrogen storage alloy in the obtained hydrogen storage / release sheet was about 80% by weight. The weight% is obtained by dividing the weight of the hydrogen storage alloy (hydrogen storage / release material) by the total weight of (hydrogen storage alloy + aramid fiber + carbon fiber).
The produced hydrogen absorption / release sheet was subjected to an activation treatment at 200 ° C. under hydrogen pressure for 30 minutes.
The hydrogen absorption / release characteristics of the fabricated hydrogen absorption / release sheet were evaluated. As a result, when the hydrogen storage alloy was used as it was, hydrogen absorption started after 10 seconds, whereas the hydrogen absorption / release sheet was 1 second, and it was proved that the hydrogen absorption / release characteristics were excellent.
Also, an experiment was conducted to determine whether the obtained hydrogen absorption / release sheet could be formed into a pleated structure, a honeycomb structure, or a wound structure to maintain the shape.

(Example 2)
Aramid fiber used in Example 1 was formed into a sheet by the same method as in Example 1 except that 7.8 g (solid content 8%), TiFe-based hydrogen storage alloy 11.25 g, and carbon fiber 0.69 g were blended. A hydrogen absorption / release sheet of 25 cm square was obtained.
The content of the TiFe-based hydrogen storage alloy in the obtained hydrogen storage / release sheet was about 90% by weight.
The produced hydrogen absorption / release sheet was subjected to activation treatment at 200 ° C. under hydrogen pressure for 30 minutes.
The hydrogen absorption / release characteristics of the fabricated hydrogen absorption / release sheet were evaluated. As a result, when the hydrogen storage alloy was used as it was, hydrogen absorption started after 10 seconds, whereas the hydrogen storage / release sheet was 2 seconds, and it was proved that the hydrogen storage / release characteristics were excellent.
Also, an experiment was conducted to determine whether the obtained hydrogen absorption / release sheet could be formed into a pleated structure, a honeycomb structure, or a wound structure to maintain the shape.

(Comparative Example 1)
The hydrogen absorption / release characteristics of the hydrogen absorption / release sheet obtained in the same manner as in Example 1 except that the activation treatment was not performed were evaluated.
As a result, no hydrogen was absorbed.
Also, an experiment was conducted to determine whether the obtained hydrogen absorption / release sheet could be formed into a pleated structure, a honeycomb structure, or a wound structure to maintain the shape.
(Comparative Example 2)
A 25 cm square hydrogen absorption / release sheet was obtained in the same manner as in Example 1 except that 5.0 g of a natural fiber (solid content 25%) that can be refined was used instead of an aramid fiber.
The content of the TiFe-based hydrogen storage alloy in the obtained hydrogen storage / release sheet was about 80% by weight.
The produced hydrogen absorption / release sheet was subjected to activation treatment at 200 ° C. under hydrogen pressure for 30 minutes.
The hydrogen absorption / release characteristics of the fabricated hydrogen absorption / release sheet were evaluated. As a result, when the hydrogen storage alloy was used as it was, hydrogen absorption started after 10 seconds, whereas the hydrogen storage / release sheet was 2 seconds, and it was proved that the hydrogen storage / release characteristics were excellent.
On the other hand, an attempt was made to form and process the obtained hydrogen absorption / release sheet into a pleated structure, a honeycomb structure, and a wound structure, but these structures could not retain the shape.
Table 1 below summarizes the above experimental results.

As shown in Table 1, by using an aramid fiber or the like that forms a fine network fiber structure when stirred and dispersed in a solution as described in Example 1, it is 80% to 90% by weight. It has been found that even when the content is dramatically increased, it is possible to strongly suppress the dropping of the hydrogen storage alloy particles from the aramid fiber and maintain a practically no problem shape retention level.
Also, the absorption start time was short and the hydrogen absorption / release reactivity was good. Furthermore, it has been proved that hydrogen can be absorbed and released with a simple temperature change device with good thermal conductivity.
In addition, entanglement with the hydrogen storage alloy particles is increased by thinning the fiber, and dropping off from the aramid fiber can be suppressed. Moreover, since the aramid fiber is fibrillated and shrinks during drying, the adhesion between the materials is promoted and the occlusion of the hydrogen storage alloy particles is reduced. Thus, if it is the sheet | seat of a present Example, it will become possible to mix | blend an alloy with a high content rate to a sheet | seat.

Claims (1)

  Synthetic polymer fibers that are easily fibrillated are stirred and dispersed in the solution, thereby forming a fibrillation dispersion step for forming a fine mesh fiber structure in the solution, and a fine mesh fiber structure formed. A particle supporting step for adhering the hydrogen absorbing / releasing particles to the mesh fiber structure by adding fine hydrogen absorbing / releasing particles having an average particle size of 0.001 to 1 mm while stirring, and mixing inorganic fibers into the solution An inorganic fiber dispersion step for stirring and dispersing, a papermaking solution adjusting step for finally forming a uniform hydrogen absorbing / releasing particle mixed solution, and a papermaking step for producing a sheet by a wet papermaking method using the adjusted papermaking solution, A drying step of drying the resulting paper sheet, and the content of hydrogen absorbing / releasing particles in the dried sheet is 70 wt% or more and 95 wt% or less, and stably absorbs and releases hydrogen Hydrogen absorption and desorption method of manufacturing a sheet and adjusts the degree of fibrillation of synthetic polymer fibers in the fibrillated dispersion step to allow carrying the child.