JP2005239454A - Hydrogen storage material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lightweight and low cost hydrogen storage material acting at a relatively low temperature and useful for an energy conversion material or the like. <P>SOLUTION: The hydrogen storage material has a compound phase having a Ca<SB>3</SB>Si<SB>3</SB>H<SB>4</SB>type crystalline structure as a main phase. A hydrogen storage apparatus is constituted by housing the hydrogen storage material in a vessel. A negative electrode material for nickel-hydride cell is constituted by containing the hydrogen storage material. Further, a heat storage apparatus, a chemical heat pump, a metal hydride sensor and a light transmittance-variable element are constituted by using the hydrogen storage material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydrogen storage material capable of reversibly storing and releasing hydrogen.

In recent years, hydrogen energy has attracted attention as a clean alternative energy due to environmental problems such as global warming caused by carbon dioxide emissions and energy problems such as exhaustion of petroleum resources. For the practical application of hydrogen energy, it will be important to develop technology for safely storing and transporting hydrogen, and hydrogen energy conversion technology. A hydrogen storage alloy capable of reversibly storing and releasing hydrogen is expected as a hydrogen storage and transport medium and as an energy conversion material for hydrogen, and various alloys have been developed.
Osamu Yasuaki, “New edition of hydrogen storage alloy-its physical properties and applications-”, Agne Technology Center Co., Ltd., February 5, 1999, p. 1-18

For example, LaNi ₅ , TiFe and the like are known as practical hydrogen storage alloys. However, since LaNi ₅ and TiFe contain rare metals such as La, Ni, and Ti, it is difficult to secure their resources and the cost is high. In addition, since the alloy itself is heavy, the hydrogen content per unit weight of the hydride remains below 2 wt%. Further, hydrides such as LaNi ₅ alloy and TiFe alloy are used as negative electrode materials for nickel-hydride batteries. However, the theoretical electric capacity of these alloys is about 300 to 400 mAh / g. For this reason, further increase in capacity of the negative electrode material is desired.

On the other hand, magnesium hydride (MgH ₂ ) and yttrium hydride (YH _x ) are known as materials whose electrical conductivity and light transmittance change depending on the hydrogen content. However, the hydrogen storage / release temperature (operating temperature) of these materials is as high as 300 ° C. or higher. For this reason, not only the use conditions are limited, but it is not easy to change the hydrogen content.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a hydrogen storage material that is lightweight and inexpensive, can be operated at a relatively low temperature, and is useful as an energy conversion material or the like.

(1) The hydrogen storage material of the present invention is characterized in that the main phase is a compound phase having a Ca ₃ Si ₃ H ₄ type crystal structure. Here, the “main phase” means a phase present in a volume ratio of 30% or more among the compound phases contained in the hydrogen storage material or a phase having a larger volume ratio than other compound phases. . The compound phase having the Ca ₃ Si ₃ H ₄ type crystal structure is composed of only Ca, Si, and H, as well as when Ca, Si are partially substituted with other elements, etc. The aspect comprised including other elements other than H may be sufficient. Moreover, the hydrogen storage material of this invention may contain the phase which consists of impurities unavoidable on manufacture other than the said main phase. For example, when the hydrogen storage material is produced only from Ca, Si, and H, as impurities, Ca, Si, CaO, SiO ₂ , CaH ₂ , SiH ₄ , Ca ₂ Si, Ca ₅ Si ₃ , CaSi, Examples include binary alloys composed of Ca—Si such as Ca ₃ Si ₄ , Ca ₁₄ Si ₁₉ , and CaSi ₂ .

  The hydrogen storage material of the present invention is composed of Ca and Si as basic elements. Ca and Si are resource-rich and inexpensive elements. Ca and Si are relatively light. Therefore, the hydrogen storage material of the present invention having Ca and Si as basic constituent elements is a lightweight and inexpensive material. Moreover, the hydrogen content per unit weight is large. Furthermore, the hydrogen storage material of the present invention can release hydrogen at a relatively low temperature of 200 ° C. or less in a preferred composition. For this reason, it is highly practical.

The hydrogen storage material of the present invention releases hydrogen when heated. Thereafter, it becomes hydride again by reaction with hydrogen. This hydrogenation reaction becomes an exothermic reaction. Figure 1 shows an energy conversion cycle of Ca ₃ Si ₃ H ₄ which is an example of a hydrogen storage material of the present invention. As shown in FIG. 1, the reversible hydrogen release and occlusion reaction of the hydrogen storage material of the present invention allows mutual interaction between chemical energy (hydrogen), thermal energy (reaction heat), mechanical energy (pressure), and electrical energy (electric power). Conversion can be performed. Thus, the hydrogen storage material of the present invention is useful not only as a hydrogen storage / transport medium but also as an energy conversion material.

(2) The hydrogen storage device of the present invention includes a container and a hydrogen storage material accommodated in the container, and the hydrogen storage material has a compound phase having a Ca ₃ Si ₃ H ₄ type crystal structure as a main phase. It is characterized by that. The hydrogen storage device of the present invention includes the above-described hydrogen storage material of the present invention. Therefore, the device is light and inexpensive and has a large hydrogen storage amount per unit weight. Thus, the hydrogen storage device of the present invention is suitable for transporting hydrogen and as a fuel tank of a fuel cell mounted on an automobile. Further, in a suitable composition of the hydrogen storage material, hydrogen is released at a relatively low temperature of 200 ° C. or lower. For this reason, hydrogen can be taken out simply and at low cost, and is highly practical.

  (3) The negative electrode material for nickel-hydride batteries of the present invention is characterized by including the hydrogen storage material of the present invention. The hydrogen storage material of the present invention is inexpensive because it contains no precious metal, and is harmless to the human body and the environment. As will be described in detail later, the theoretical electric capacity of the hydrogen storage material of the present invention is large. Therefore, the negative electrode material containing the hydrogen storage material of the present invention is inexpensive and safe and has a large theoretical electric capacity. Thus, by using the negative electrode material of the present invention, it is possible to constitute a nickel-hydride battery that has a high capacity, is easy to collect and recycle after use, and has little environmental impact.

  (4) The heat storage device of the present invention includes a heat source, the hydrogen storage material of the present invention, and a heat storage unit that releases hydrogen by heating from the heat source, and is connected to the heat storage unit and is discharged from the heat storage unit. And a hydrogen storage part for storing hydrogen. As described above, the hydrogen storage material of the present invention releases hydrogen by heating and releases heat when storing hydrogen. Therefore, when the hydrogen storage material of the present invention is heated by a heat source such as solar heat, geothermal power, wind power, and factory waste heat, hydrogen is released. If the released hydrogen is stored, heat is stored as chemical energy called hydrogen. When heat is required, for example, hydrogen is reacted with the hydrogen storage material in a state in which hydrogen is released. By doing so, the generated reaction heat can be taken out as thermal energy. The heat storage device of the present invention is inexpensive because the hydrogen storage material of the present invention is used, and can store even relatively low-temperature heat. Thus, according to the heat storage device of the present invention, it is possible to effectively recover and use thermal energy.

  (5) The chemical heat pump of the present invention has a first container having the hydrogen storage material of the present invention and a second material that can occlude and release hydrogen and whose equilibrium hydrogen pressure is different from that of the hydrogen storage material. A second container connected to the first container, and between the first container and the second container by a hydrogen storage and release reaction in each of the hydrogen storage material and the second material. It is characterized by transferring hydrogen by transferring hydrogen.

  In general, a chemical heat pump uses two types of materials that can occlude and release hydrogen. In the chemical heat pump of the present invention, the hydrogen storage material of the present invention is used as the first material, and a material having an equilibrium hydrogen pressure different from that of the hydrogen storage material of the present invention is used as the second material. These first material and second material are accommodated in a first container and a second container, respectively, and the two containers are connected so that hydrogen can move. Here, when a material having a lower equilibrium hydrogen pressure than the hydrogen storage material of the present invention is combined as the second material, a temperature rising type heat pump is obtained. On the other hand, when a material having a high equilibrium hydrogen pressure is combined as the second material, a cooling heat pump is obtained. For example, in the former case, the hydrogen storage material of the present invention in the first container is heated with relatively low-temperature factory waste heat or the like to release hydrogen. The released hydrogen moves to the second container and is stored in the second material. High temperature heat is obtained by the heat generated by this hydrogen storage.

  The chemical heat pump of the present invention is inexpensive because it uses the hydrogen storage material of the present invention, and operates with relatively low-temperature heat. Therefore, the chemical heat pump of the present invention is suitable for a cooling / heating system and the like in addition to recovery of solar heat, factory waste heat, etc., and temperature rise.

  (6) A metal hydride sensor of the present invention detects a temperature sensing part having the hydrogen storage material of the present invention and a hydrogen gas pressure connected to the temperature sensing part and released by the temperature rise of the temperature sensing part. A hydrogen gas pressure detecting unit. When the temperature sensitive part is heated, hydrogen is released from the hydrogen storage material of the present invention. The released hydrogen moves to the hydrogen gas detector, and the hydrogen gas pressure in the hydrogen gas detector increases. A predetermined driving means is operated by the increased pressure. Thus, in the metal hydride sensor of the present invention, thermal energy is converted into mechanical energy (pressure). The metal hydride sensor of the present invention is inexpensive because it uses the hydrogen storage material of the present invention, and operates with relatively low temperature heat.

  (7) The light transmittance variable element of the present invention is characterized by comprising a base material and a counter hydrogen reaction film formed on the surface of the base material and containing the hydrogen storage material of the present invention. As will be described later, the light transmittance of the hydrogen storage material of the present invention varies depending on the hydrogen content. Further, with a suitable composition, hydrogen can be released at a relatively low temperature of 200 ° C. or lower. Therefore, the light transmittance variable element of the present invention is practical because the light transmittance changes at a relatively low temperature.

  The hydrogen storage material of the present invention is lightweight and inexpensive. Further, the hydrogen content per unit weight is large, and hydrogen can be released at a relatively low temperature. Therefore, it is useful as a hydrogen storage / transport medium, energy conversion material, and the like.

  Hereinafter, the hydrogen storage material, the hydrogen storage device, the negative electrode material for nickel-hydride battery, the heat storage device, the chemical heat pump, the metal hydride sensor, and the light transmittance variable element of the present invention will be described in order.

<Hydrogen storage material>
The hydrogen storage material of the present invention has a compound phase having a Ca ₃ Si ₃ H ₄ type crystal structure as a main phase. Examples of the compound having a Ca ₃ Si ₃ H ₄ type crystal structure include Ca ₃ Si ₃ H _x (0.6 ≦ x ≦ 4.5), Ca ₃ (Si _0.8 Ge _0.2 ) ₃ H _x (0.6 ≦ x ≦ 4.5), Ca ₃ (Si _0.5 Ge _0.5 ) ₃ H _x (0.6 ≦ x ≦ 4.5), Ca ₃ (Si _0.8 Ag _0.2 ) ₃ H _x (0.6 ≦ x ≦ 4) .5) and the like. The method for producing the hydrogen storage material of the present invention is not particularly limited. For example, it can be produced by hydrogenating a material mainly composed of CaSi having a CrB type crystal structure. As an example, the powder X-ray diffraction profile of the Ca ₃ Si ₃ H ₄ produced as such is shown in FIG. Table 1 below shows the crystallographic parameters obtained by Rietveld analysis of the data in FIG. That is, the material having the main phase of the compound X-ray diffraction profile shown in FIG. 2 and the crystallographic parameters shown in Table 1 is the hydrogen storage material of the present invention.

本発明の水素貯蔵材料の電気的特性は、エネルギーバンド構造から知ることができる。そこで、本発明の水素貯蔵材料である上記Ｃａ₃Ｓｉ₃Ｈ₄のエネルギーバンド構造を、一般化された密度勾配近似を用いた第一原理計算により求めた。図３に、Ｃａ₃Ｓｉ₃Ｈ₄のエネルギーバンド構造および状態密度分布を示す。図３に示すように、Ｃａ₃Ｓｉ₃Ｈ₄は、直接遷移型のエネルギーバンド構造をもち、そのバンドギャップの値は、約０．２５ｅＶであった。なお、第一原理計算により見積もられるバンドギャップの値は、実際より小さい値となることが知られている。このため、実際のバンドギャップの値は、より大きな値となると推定される。また、上記第一原理計算から、Ｃａ₃Ｓｉ₃Ｈ₄は、水素含有量を減少させるとバンドギャップが消滅し、金属状態となることがわかった。通常、バンドギャップが大きいほど、電気抵抗は大きくなり、電気伝導率は小さくなる。この知見に基づいて、Ｃａ₃Ｓｉ₃Ｈ₄の電気抵抗値を測定したところ、水素含有量が大きくなるほど電気抵抗値は大きくなった。これより、水素含有量を調整すれば、本発明の水素貯蔵材料の電気伝導率を調整することができることがわかる。なお、本発明の水素貯蔵材料は、好適な組成では、２００℃以下で水素を放出することができる。つまり、２００℃以下で水素の含有量を調整することができる。このため、本発明の水素貯蔵材料は、比較的低温下で作動可能な電気抵抗可変型電気伝導体として好適である。

The electrical characteristics of the hydrogen storage material of the present invention can be known from the energy band structure. Therefore, the energy band structure of the Ca ₃ Si ₃ H ₄ , which is the hydrogen storage material of the present invention, was determined by first-principles calculation using a generalized density gradient approximation. FIG. 3 shows the energy band structure and state density distribution of Ca ₃ Si ₃ H ₄ . As shown in FIG. 3, Ca ₃ Si ₃ H ₄ had a direct transition type energy band structure, and the value of the band gap was about 0.25 eV. It is known that the band gap value estimated by the first principle calculation is smaller than the actual value. For this reason, the actual band gap value is estimated to be a larger value. Further, from the above first principle calculation, it was found that Ca ₃ Si ₃ H ₄ disappears when the hydrogen content is reduced, and the band gap disappears and becomes a metal state. Usually, the larger the band gap, the greater the electrical resistance and the lower the electrical conductivity. Based on this knowledge, when the electrical resistance value of Ca ₃ Si ₃ H ₄ was measured, the electrical resistance value increased as the hydrogen content increased. From this, it can be seen that the electric conductivity of the hydrogen storage material of the present invention can be adjusted by adjusting the hydrogen content. In addition, the hydrogen storage material of this invention can discharge | release hydrogen at 200 degrees C or less in a suitable composition. That is, the hydrogen content can be adjusted at 200 ° C. or lower. For this reason, the hydrogen storage material of this invention is suitable as an electrical resistance variable type electric conductor which can operate | move under comparatively low temperature.

  Similarly to the electrical conductivity, the light transmittance is also related to the band gap. Therefore, if the hydrogen content is adjusted, the light transmittance of the hydrogen storage material of the present invention can be adjusted. Therefore, the hydrogen storage material of the present invention is suitable as a light transmittance variable element that can operate at a relatively low temperature. The light transmittance variable element using the hydrogen storage material of the present invention will be described in detail later.

  In general, the thermal conductivity of metals is proportional to temperature, and the thermal conductivity of insulators and semiconductors increases in proportion to the cube of temperature. As described above, the hydrogen storage material of the present invention can take both a metal state and a semiconductor state depending on the hydrogen content. For this reason, desired heat conductivity can be easily obtained by adjusting hydrogen content. Therefore, according to the hydrogen storage material of the present invention, it is possible to easily realize a heat conductor having a thermal conductivity corresponding to the application.

The phenomenon in which thermal energy and electrical energy are mutually converted in a solid is called a thermoelectric effect. Generally, a performance index ZT (ZT = TS ² / ρκ, T: absolute temperature, S: Seebeck coefficient, ρ = electric resistance value, κ: thermal conductivity) is used as an index of thermoelectric conversion efficiency. As a condition of an excellent thermoelectric material, it is required that the Seebeck coefficient is large and the electric resistance value and the thermal conductivity are small. For the Ca ₃ Si ₃ H ₄ , the Seebeck coefficient, electrical resistance, and thermal conductivity were measured, and the figure of merit ZT was calculated. As a result, it was confirmed that Ca ₃ Si ₃ H ₄ has excellent thermoelectric properties. . Moreover, in the hydrogen storage material of this invention, it is possible to adjust an electrical resistance value and heat conductivity by adjusting hydrogen content. Thus, the hydrogen storage material of the present invention is suitable as a thermoelectric material having desired thermoelectric characteristics.

  Utilizing the property that the electrical conductivity, light transmittance, and thermal conductivity change depending on the hydrogen content, for example, a hydrogen gas detection element that detects hydrogen gas can be configured from the hydrogen storage material of the present invention. it can. The hydrogen gas detection element can be produced, for example, by forming a thin film made of the hydrogen storage material of the present invention on the surface of a substrate. The hydrogen storage material of the present invention is lightweight and inexpensive, has a large hydrogen content per unit weight, and can release hydrogen at a relatively low temperature of 200 ° C. or less with a suitable composition. Taking advantage of these advantages, the hydrogen storage material of the present invention can be used in various apparatuses described below.

<Hydrogen storage device>
The hydrogen storage device of the present invention includes a container and a hydrogen storage material accommodated in the container, and the hydrogen storage material has a compound phase having a Ca ₃ Si ₃ H ₄ type crystal structure as a main phase. The container is not particularly limited as long as it can be used under conditions such as high pressure. A normally used pressure vessel may be used. And what is necessary is just to discharge | release and occlude hydrogen by filling the said hydrogen storage material in a container and adjusting temperature and pressure to predetermined conditions.

<Negative electrode material for nickel-hydride batteries>
The negative electrode material for nickel-hydride batteries of the present invention includes the hydrogen storage material of the present invention. As an example of the hydrogen storage material of the present invention, Ca ₃ Si ₃ H ₄ will be described. Ca ₃ Si ₃ H ₄ contains four H atoms for three Ca atoms and three Si atoms. Therefore, the theoretical electric capacity ΔQ of Ca ₃ Si ₃ H ₄ is calculated as 524.25 mAh / g from the following equation (i). In formula (i), F is a Faraday constant, and M _av is an average atomic weight of Ca ₃ Si ₃ H ₄ in a state where hydrogen is lost.
ΔQ = ΔX [H / M] × 1000 × F / 3600 / M _av
= (4 / (3 + 3)) × 1000 × 96485/3600 / 34.0082 (i)
Thus, the theoretical electric capacity of the hydrogen storage material of the present invention is large. For this reason, the theoretical electric capacity of the negative electrode material of the present invention containing the same material is increased.

  What is necessary is just to form the negative electrode of a nickel-hydride battery from the negative electrode material of this invention according to the already well-known method. For example, first, the negative electrode material of the present invention is powdered with an average particle size of about 20 to 60 μm. Next, this negative electrode material powder, a conductive material such as nickel or carbon, and a binder such as polytetrafluoroethylene (PTFE) or polyethylene are mixed and pressure-bonded to a porous nickel plate or the like serving as a current collector. Then, the formed negative electrode, a positive electrode using nickel hydroxide as a positive electrode active material, and a separator sandwiched between the positive electrode and the negative electrode are sealed in a battery case together with an electrolytic solution, so that a nickel-hydride battery is obtained. That's fine.

<Heat storage device>
Hereinafter, an embodiment of the heat storage device of the present invention will be described. In FIG. 4, the model figure of the thermal storage apparatus of this embodiment is shown. As shown in FIG. 4, the heat storage device 1 includes a heat source 2, a heat storage container 3, and a hydrogen tank 4. As the heat source 2, natural energy such as solar heat, high-temperature air heat (wind power), geothermal heat, or waste heat discharged from a factory is used. The heat storage container 3 accommodates Ca ₃ Si ₃ H ₄ which is the hydrogen storage material of the present invention. The heat storage container 3 is heated by the heat source 2. The heat storage container 3 is included in the heat storage part which comprises the heat storage apparatus of this invention. The hydrogen tank 4 is connected to the heat storage container 3 by piping. The hydrogen tank 4 is included in the hydrogen storage part which comprises the heat storage apparatus of this invention.

First, when storing heat, the heat storage container 3 is heated by the heat source 2 using predetermined heat. Then, hydrogen is released from Ca ₃ Si ₃ H ₄ in the heat storage container 3. The released hydrogen moves through the piping to the hydrogen tank 4 and is stored in the hydrogen tank 4. In other words, heat is stored as chemical energy called hydrogen. On the other hand, when using the stored heat, hydrogen is supplied from the hydrogen tank 4 to the heat storage container 3. At this time, the pressure of the supplied hydrogen is set higher than the equilibrium hydrogen pressure of Ca ₃ Si ₃ H ₄ at the temperature in the heat storage container 3. Then, in the heat storage container 3, CaSi in a state where hydrogen is released absorbs the hydrogen and generates heat. This reaction heat is used as heat energy. Thus, according to the heat storage device 1, it is possible to effectively recover and use thermal energy.

  The heat storage device of the present invention is not limited to the above embodiment. For example, in the said embodiment, you may change a hydrogen tank into the hydrogen storage container which accommodated the material which occludes hydrogen. In this embodiment, hydrogen released from the heat storage container is occluded by the material in the hydrogen storage container. Therefore, when it is desired to use heat, the hydrogen storage container is heated to release hydrogen from the material in the container, and the hydrogen is supplied to the heat storage container.

Moreover, in the said embodiment, heat transport can be performed by changing a hydrogen tank into the heat receiving container which accommodated the material which occludes hydrogen. In this embodiment, first, the heat storage container is heated to release hydrogen from Ca ₃ Si ₃ H ₄ in the heat storage container. Next, the released hydrogen is moved through a pipe to a heat receiving container at a transport destination. In the heat receiving container, the accommodated material absorbs hydrogen and generates heat. Here, the material stored in the heat receiving container may be any material that can occlude hydrogen at the hydrogen pressure released from the hydrogen storage material of the present invention in the heat storage container. And the material which has the reaction heat corresponding to the heat energy to utilize at a transport destination should just be selected suitably. In the above embodiment, when it is desired to obtain a heat quantity substantially equal to the heat quantity supplied to the heat storage container at the transportation destination, the material accommodated in the heat receiving container may be, for example, CaSi having a CrB type crystal structure.

<Chemical heat pump>
Hereinafter, an embodiment of the chemical heat pump of the present invention will be described. Here, the case where the chemical heat pump of the present invention is used as a cooling heat pump will be described. In FIG. 5, the model figure of the cooling cycle using the chemical heat pump of this embodiment is shown. In FIG. 5, (a) shows the regeneration process, and (b) shows the cooling process. As shown in FIG. 5, the chemical heat pump 5 includes a first container 6 and a second container 7.

The first container 6 contains Ca ₃ Si ₃ H ₄ which is the hydrogen storage material of the present invention. The first container 6 is heated by the heat source 8. The second container 7 is connected to the first container 6 by piping. The second container 7 contains LaNi ₅ as the second material. Here, the equilibrium hydrogen pressure of LaNi ₅ is higher than that of Ca ₃ Si ₃ H ₄ .

First, let the 1st container 6 and the 2nd container 7 be the same temperature (outside temperature). Then, (a) the first container 6 is heated by the heat source 8 in the regeneration process. Then, the temperature and pressure in the first container 6 rise, and hydrogen is released from Ca ₃ Si ₃ H ₄ . The released hydrogen moves to the second container 7 through the pipe. The hydrogen supplied to the second container 7 is occluded in LaNi ₅ . LaNi ₅ is hydrogenated to LaNi ₅ H _x (6 ≦ x ≦ 7). At this time, the reaction heat generated is released to the outside. Next, (b) the heating of the first container 6 is stopped in the cooling process. Then, the temperature of the first container 6 decreases and becomes the same temperature as the second container 7. Therefore, hydrogen returns to the first container 6 having a low equilibrium hydrogen pressure. Moreover, since the release of hydrogen stops and hydrogen is no longer supplied to the second container 7, the pressure in the second container 7 decreases. As a result, LaNi ₅ H _x (6 ≦ x ≦ 7) in the second container 7 takes heat from the outside and releases hydrogen. This endothermic reaction provides a cooling effect. On the other hand, the hydrogen released from the second container 7 moves to the first container 6 through the pipe. The hydrogen supplied to the first container 6 is occluded in CaSi in a state where hydrogen is released. At this time, the reaction heat generated is released to the outside. Thus, if the chemical heat pump of the present invention is used as a cooling heat pump, it is possible to continuously cool indoors.

  The chemical heat pump of the present invention is not limited to the above embodiment. For example, a material having a lower equilibrium hydrogen pressure than the hydrogen storage material of the present invention may be used as the second material. For example, ZrNi etc. are mentioned. In this case, the chemical heat pump of the present invention is a temperature rising type heat pump. That is, the first container is heated with a relatively low temperature heat source to release hydrogen from the hydrogen storage material of the present invention. The released hydrogen moves to the second container and is stored in the second material. High temperature heat is obtained by the heat generated by this hydrogen storage. Thus, if the chemical heat pump of this invention is used as a temperature rising type heat pump, high temperature heat can be taken out from low temperature heat.

<Metal hydride sensor>
Hereinafter, an embodiment of the metal hydride sensor of the present invention will be described. FIG. 6 shows the operating principle of the metal hydride sensor of this embodiment. As shown in FIG. 6, the metal hydride sensor 9 includes a temperature sensing unit 10 and a hydrogen gas pressure detection unit 11. The temperature sensing unit 10 contains Ca ₃ Si ₃ H ₄ which is the hydrogen storage material of the present invention. The hydrogen gas pressure detection unit 11 includes a cylinder 110 and a piston 111. The cylinder 110 is connected to the temperature sensing unit 10 by piping. A filter 12 is disposed in the piping.

When the temperature of the temperature sensing unit 10 rises, hydrogen is released from Ca ₃ Si ₃ H ₄ . The released hydrogen moves to the cylinder 110 through the pipe. As a result, the hydrogen gas pressure in the cylinder 110 increases, and the piston 111 moves to the right side in the figure. Predetermined work is performed by driving the piston 111.

<Light transmittance variable element>
The light transmittance variable element of the present invention is composed of a base material and a counter hydrogen reaction film formed on the surface of the base material and containing the hydrogen storage material of the present invention. The substrate is not particularly limited as long as it can form a hydrogen reaction film on the surface and can maintain the shape and light transmittance of the element itself. For example, materials such as silica glass and fluororesin can be used.

  The hydrogen reaction film formed on the surface of the substrate contains the hydrogen storage material of the present invention. The hydrogen reaction membrane may contain, for example, a high hydrogen dissociation material in addition to the hydrogen storage material of the present invention. Here, the high hydrogen dissociation ability material means a material having a high hydrogen dissociation ability, that is, a material mainly performing a catalytic function of dissociating hydrogen. Among materials having high hydrogen dissociation ability, those having high hydrogen permeability are preferable. When hydrogen permeability is high, dissociated hydrogen atoms are likely to diffuse. Examples of such a high hydrogen dissociation material include palladium, palladium alloy, nickel, nickel alloy and the like. One kind or two or more kinds of these may be used. By containing a high hydrogen dissociation ability material in the hydrogen reaction membrane, the hydrogen content of the hydrogen storage material of the present invention can be changed more rapidly. The content of the high hydrogen dissociation-capable material in the hydrogen reaction membrane is not particularly limited. For example, the hydrogen storage material of the present invention and the high hydrogen dissociation material may be mixed to form a hydrogen reaction membrane, and the thin film made of the hydrogen storage material of the present invention and the thin film made of the high hydrogen dissociation material May be stacked to form a hydrogen reaction film.

The manufacturing method of the light transmittance variable element of the present invention is not particularly limited, and may be performed in accordance with a generally performed thin film forming method. For example, the hydrogen reaction film may be formed by sputtering, flash evaporation, or the like. Hereinafter, as an example of the light transmittance variable element of the present invention, an example of a method for manufacturing a light transmittance variable element in which three layers of palladium film / Ca ₃ Si ₃ H ₄ film / palladium film are laminated on the substrate surface will be described. To do.

First, a palladium film having a thickness of about 20 nm is formed on the surface of a transparent silica glass plate having a thickness of about 0.3 mm by an RF magnetron sputtering method in an argon atmosphere. Next, a CaSi film having a thickness of about 50 nm is formed on the surface of the formed palladium film by the same method as described above. Further, a palladium film having a thickness of about 20 nm is formed on the surface of the formed CaSi film by the same method as described above. The thin film laminate thus obtained is exposed to a hydrogen atmosphere, and the CaSi film is hydrogenated to form a Ca ₃ Si ₃ H ₄ film.

<Others>
As described above, according to the hydrogen storage material of the present invention, heat energy can be converted into mechanical energy called pressure. With this hot metal energy conversion function, a chemical compressor, a chemical engine, a metal hydride actuator, or the like can be configured using the hydrogen storage material of the present invention.

  Based on the above embodiment, four types of hydrogen storage materials of the present invention were produced. Hereinafter, it demonstrates in order.

(1) Production of Ca ₃ Si ₃ H _x (0.6 ≦ x ≦ 4.5) Ca particles (purity 99.5%) and Si powder (purity 99.999%) are mixed, and an argon gas atmosphere The solution was melted at high frequency. Further, heat treatment was performed at 950 ° C. for 30 hours in an argon gas atmosphere, followed by water cooling to obtain a Ca _0.5 Si _0.5 ingot. The obtained ingot was pulverized into a powder form in a glove box filled with argon gas. This powder was hydrogenated under conditions of a temperature of 100 ° C. and a hydrogen pressure of 9 MPa to obtain Ca ₃ Si ₃ H _x (0.6 ≦ x ≦ 4.5). The obtained Ca ₃ Si ₃ H _x (0.6 ≦ x ≦ 4.5) was subjected to X-ray diffraction measurement by a powder method using CuΚα rays. From the X-ray diffraction profile, it was confirmed that Ca ₃ Si ₃ H _x (0.6 ≦ x ≦ 4.5) is substantially composed of a single phase and has a Ca ₃ Si ₃ H ₄ type crystal structure.

(2) Production of Ca ₃ (Si _0.8 Ge _0.2 ) ₃ H _x (0.6 ≦ x ≦ 4.5) Ca grains (purity 99.5%), Si powder (purity 99.999%), Ge The powder (purity 99.9%) was mixed and high-frequency dissolved in an argon gas atmosphere. Furthermore, heat treatment was performed at 950 ° C. for 30 hours in an argon gas atmosphere, followed by water cooling to obtain an ingot of Ca _0.5 (Si _0.8 Ge _0.2 ) _0.5 . The obtained ingot was pulverized into a powder form in a glove box filled with argon gas. This powder was hydrogenated under conditions of a temperature of 100 ° C. and a hydrogen pressure of 9 MPa to obtain Ca ₃ (Si _0.8 Ge _0.2 ) ₃ H _x (0.6 ≦ x ≦ 4.5). X-ray diffraction measurement was performed on the obtained Ca ₃ (Si _0.8 Ge _0.2 ) ₃ H _x (0.6 ≦ x ≦ 4.5) in the same manner as described above. From the X-ray diffraction profile, it is confirmed that Ca ₃ (Si _0.8 Ge _0.2 ) ₃ H _x (0.6 ≦ x ≦ 4.5) is substantially composed of a single phase and has a Ca ₃ Si ₃ H ₄ type crystal structure. It was done.

(3) Production of Ca ₃ (Si _0.5 Ge _0.5 ) ₃ H _x (0.6 ≦ x ≦ 4.5) Ca grains (purity 99.5%), Si powder (purity 99.999%), Ge The powder (purity 99.9%) was mixed and high-frequency dissolved in an argon gas atmosphere. Further, heat treatment was performed at 950 ° C. for 30 hours in an argon gas atmosphere, followed by water cooling to obtain a Ca _0.5 (Si _0.5 Ge _0.5 ) _0.5 ingot. The obtained ingot was pulverized into a powder form in a glove box filled with argon gas. This powder was hydrogenated under the conditions of a temperature of 100 ° C. and a hydrogen pressure of 9.5 MPa to obtain Ca ₃ (Si _0.5 Ge _0.5 ) ₃ H _x (0.6 ≦ x ≦ 4.5). X-ray diffraction measurement was performed on the obtained Ca ₃ (Si _0.5 Ge _0.5 ) ₃ H _x (0.6 ≦ x ≦ 4.5) in the same manner as described above. From the X-ray diffraction profile, it is confirmed that Ca ₃ (Si _0.5 Ge _0.5 ) ₃ H _x (0.6 ≦ x ≦ 4.5) is substantially composed of a single phase and has a Ca ₃ Si ₃ H ₄ type crystal structure. It was done.

(4) Production of Ca ₃ (Si _0.8 Ag _0.2 ) ₃ H _x (0.6 ≦ x ≦ 4.5) Ca grains (purity 99.5%), Si powder (purity 99.999%), Ag The powder (purity 99.9%) was mixed and high-frequency dissolved in an argon gas atmosphere. Further, after heat treatment at 660 ° C. for 24 hours in an argon gas atmosphere, water cooling was performed to obtain an ingot of Ca _0.5 (Si _0.8 Ag _0.2 ) _0.5 . The obtained ingot was pulverized into a powder form in a glove box filled with argon gas. This powder was hydrogenated under conditions of a temperature of 150 ° C. and a hydrogen pressure of 9 MPa to obtain Ca ₃ (Si _0.8 Ag _0.2 ) ₃ H _x (0.6 ≦ x ≦ 4.5). X-ray diffraction measurement was performed on the obtained Ca ₃ (Si _0.8 Ag _0.2 ) ₃ H _x (0.6 ≦ x ≦ 4.5) in the same manner as described above. From the X-ray diffraction profile, it is confirmed that Ca ₃ (Si _0.8 Ag _0.2 ) ₃ H _x (0.6 ≦ x ≦ 4.5) is substantially composed of a single phase and has a Ca ₃ Si ₃ H ₄ type crystal structure. It was done.

An energy conversion cycle of Ca ₃ Si ₃ H ₄ which is an example of a hydrogen storage material of the present invention. Shows the powder X-ray diffraction profile of the Ca ₃ Si ₃ H _4. The energy band structure and state density distribution of the same Ca ₃ Si ₃ H ₄ are shown. It is a model figure of one Embodiment of the thermal storage apparatus of this invention. It is a model figure of the cooling cycle using the chemical heat pump of this invention. The operation principle of the metal hydride sensor of the present invention is shown.

Explanation of symbols

1: Thermal storage device 2: Heat source 3: Thermal storage container (thermal storage unit) 4: Hydrogen tank (hydrogen storage unit)
5: Chemical heat pump 6: First container 7: Second container 8: Heat source 9: Metal hydride sensor 10: Temperature sensing unit 11: Hydrogen gas pressure detection unit 110: Cylinder 111: Piston 12: Filter

Claims (7)

A hydrogen storage material whose main phase is a compound phase having a Ca ₃ Si ₃ H ₄ type crystal structure. A container, and a hydrogen storage material accommodated in the container,
The hydrogen storage material is characterized in that the main phase is a compound phase having a Ca ₃ Si ₃ H ₄ type crystal structure.   A negative electrode material for a nickel-hydride battery comprising the hydrogen storage material according to claim 1. A heat source,
A heat storage part having the hydrogen storage material according to claim 1 and releasing hydrogen by heating from the heat source;
A hydrogen storage unit connected to the heat storage unit and storing hydrogen released from the heat storage unit;
A heat storage device comprising: A first container having the hydrogen storage material according to claim 1;
A second container capable of storing and releasing hydrogen, having a second material whose equilibrium hydrogen pressure is different from that of the hydrogen storage material, and connected to the first container;
A chemical heat pump for transferring heat by transferring hydrogen between the first container and the second container by a hydrogen storage and release reaction in each of the hydrogen storage material and the second material. A temperature sensing part having the hydrogen storage material according to claim 1;
A hydrogen gas pressure detection unit connected to the temperature sensing unit for detecting the hydrogen gas pressure released by the temperature rise of the temperature sensing unit;
A metal hydride sensor comprising: A substrate;
A hydrogen-reactive membrane comprising a hydrogen storage material according to claim 1 formed on the surface of the substrate;
A light transmittance variable element comprising:

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