JP2006124802A - Hydrogen storage material, method for producing hydrogen storage material and method for releasing hydrogen from hydrogen storage material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen storage material in which the electron arrangement and spin state of a metal capable of an ionic bond with hydrogen atoms are changed, and the bonding strength between the metal and hydrogen atoms is controlled, thus the hydrogen releasing temperature thereof can be controlled. <P>SOLUTION: The hydrogen storage material 1 regarding the embodiment 1 in this invention has a structure where two magnesium atoms 11 capable of an ionic bond with two hydrogen atoms 10 and a metal atom 12 are comprised, and the metal atom 12 is arranged between the two magnesium atoms 11. By arranging (inserting) the metal atom 12 between the magnesium atoms 11 in this way, the electron arrangement and spin state of the magnesium atoms 11 are changed, and owing to the change, the bonding strength between the magnesium atoms 11 and the hydrogen atoms 10 is weakened. Thus, activation energy required for separating the hydrogen atoms 10 from the magnesium atoms 11 is reduced, and the hydrogen releasing temperature thereof can be lowered. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydrogen storage material capable of releasing hydrogen at a predetermined temperature, a method for producing the hydrogen storage material, and a hydrogen release method for the hydrogen storage material. For example, a hydrogen release temperature at a practical level based on magnesium hydride. The present invention relates to a hydrogen storage material that realizes (approximately 400 K), a method for producing the hydrogen storage material, and a hydrogen release method for the hydrogen storage material.

  In recent years, hydrogen has attracted attention as an energy source to replace fossil fuels such as petroleum in order to cope with global environmental problems such as ozone depletion and air pollution. A typical example using hydrogen is a fuel cell. A fuel cell reacts a fuel such as hydrogen, which is easily oxidized, with oxygen that is abundant in the atmosphere, and converts chemical energy generated by the chemical reaction into heat. Without direct conversion to electrical energy. In addition, when hydrogen is used as a fuel, since the reaction product with oxygen is only water, there is no risk of environmental destruction, and it is considered that it will become the mainstream of future energy.

  When a fuel cell is put into practical use, a hydrogen storage technology having the capability of temporarily storing hydrogen and supplying a necessary amount of hydrogen appropriately and stably when necessary is necessary. The hydrogen storage technology is roughly classified into a reforming system that reforms hydrocarbons and the like to supply hydrogen, and a pure hydrogen system that directly supplies hydrogen. In the former reforming method, the reformer is complicated, and CO poisoning occurs in which carbon monoxide (CO) generated when reforming hydrocarbon coats platinum (Pt) as an electrode catalyst. There is a problem. Therefore, the latter pure hydrogen method is desirable in the future in terms of improving efficiency and reducing carbon monoxide emissions.

By the way, hydrogen is a gas having a very low density, and even when stored under high pressure (200 atm), only hydrogen of 0.99 × 10 ²² cm ⁻³ can be stored. Moreover, when hydrogen is liquefied, it is necessary to cool it to an ultra-low temperature of 20K. Of course, if ultra-high pressure is used, hydrogen can be liquefied even at room temperature, but it is extremely difficult to ensure safety. As described above, the pure hydrogen system has many problems, and it is indispensable for practical use and widespread use to ensure safety, and to realize weight reduction and cost reduction.

Thus, magnesium hydride (MgH ₂ ) has attracted attention as a hydrogen storage material that is one form of the pure hydrogen system. Magnesium hydride is a substance produced by adsorbing two hydrogen atoms (H) by magnesium atoms (Mg), and has a high hydrogen storage capacity (hydrogen weight density = 7.66 wt%), and sodium in seawater. Since Mg present in a large amount next to (Na) can be easily produced at low cost by the electrolytic method, it is promising as a future hydrogen storage material. Moreover, in order to mount a fuel cell on a vehicle, it is necessary to be lightweight and small, but this point does not adversely affect magnesium hydride.

  However, magnesium hydride is in a thermodynamically very stable state because its component magnesium atom and hydrogen atom are bonded by an extremely strong ionic bond. Therefore, the activation energy required to release hydrogen atoms from magnesium hydride is high (573 K in terms of temperature), and it is necessary to supply thermal energy corresponding to the activation energy. In other words, unless magnesium hydride is heated to 573 K or higher, hydrogen atoms are not released from magnesium hydride. Conversely, at room temperature (300 K), a reaction in which hydrogen atoms are adsorbed on magnesium atoms proceeds. Resulting in.

  Therefore, in order to lower the hydrogen release temperature, alloying of magnesium hydride and a transition metal having a catalytic action is performed by a mechanical alloying method. The mechanical alloying method is a method in which a component metal powder is mechanically mixed in a solid state without causing the component metal to be dissolved, and a chemical reaction is caused to form a compound. As shown in FIG. 8, the transition metal 101 is attached to the magnesium hydride 100 in which two hydrogen atoms 100b are adsorbed to the magnesium atom 100a without changing the composition of the magnesium hydride itself. (For example, refer nonpatent literature 1).

  FIG. 9 is a graph showing the potential characteristics of a conventional hydrogen storage material, and shows the potential energy required to separate hydrogen atoms from magnesium atoms in the structure of FIG. In the figure, the horizontal axis indicates the distance between magnesium atoms and hydrogen atoms, the vertical axis indicates the potential energy, and each solid line indicates that the transition metals are scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr ), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn) 3d transition metal potential characteristics, the broken line is the case of magnesium hydride alone The potential characteristics at are shown. As is apparent from the figure, the activation energy is reduced by attaching a transition metal to magnesium hydride. That is, the hydrogen release temperature of magnesium hydride can be lowered as shown in Table 1.

Journal of Alloys and Compounds, 2000, 305, p246-252

  However, if a transition metal is attached to magnesium hydride by the mechanical alloying method as described above, the hydrogen release temperature can be lowered. However, no detailed study has been conducted on the alloy type. As shown in “1”, when scandium and nickel are used, the hydrogen release temperature can be reduced to 500 K. However, alloy types having a practical level of hydrogen release temperature (approximately 400 K) have not yet been obtained. There is no current situation.

  As a result of studying the alloy state of magnesium hydride from a microscopic viewpoint, the present inventor has found a transition metal between a conventional case in which a transition metal is adhered to magnesium hydride and two magnesium hydrides. In addition to the knowledge that the hydrogen release characteristics released from magnesium hydride differ greatly from the case of arrangement (insertion), it was clarified that the cause is due to the electronic configuration and the spin state of the transition metal.

  The present invention has been made on the basis of this finding. By adopting a configuration in which a second metal different from the first metal is disposed between a plurality of first metals capable of ionic bonding with hydrogen atoms, Provided are a hydrogen storage material and a method for producing the hydrogen storage material that can change the electron configuration and spin state of one metal, control the bonding force between the first metal and a hydrogen atom, and control the hydrogen release temperature. Objective.

  In addition, the present invention charges a metal capable of ion-bonding with a hydrogen atom, thereby changing the electronic configuration and spin state of the metal itself, controlling the bonding force between the metal and the hydrogen atom, and controlling the hydrogen release temperature. An object of the present invention is to provide a method for releasing hydrogen from a hydrogen storage material.

  The hydrogen storage material according to the first invention includes a plurality of first metals capable of ion-bonding with hydrogen atoms, and a second metal different from the first metal, and the adsorption of hydrogen atoms to the first metal and / or Or it is a hydrogen storage material which discharge | releases the hydrogen atom from the said 1st metal, Comprising: The said 2nd metal is arrange | positioned between each 1st metal, It is characterized by the above-mentioned.

  In the first invention, a second metal different from the first metal is disposed between the plurality of first metals capable of ionic bonding with hydrogen atoms. Due to the influence of the second metal arranged between the first metals, the electron arrangement and the spin state of the first metal change, and the bonding force between the first metal and the hydrogen atom changes due to the change. As a result, the activation energy required to separate the hydrogen atom from the first metal changes, and the hydrogen release temperature changes. In other words, by arranging the second metal between the plurality of first metals, the electron arrangement and the spin state of the first metal are changed, and the bonding force between the first metal and the hydrogen atom is controlled, The hydrogen release temperature can be controlled.

  The hydrogen storage material according to a second invention is characterized in that, in the first invention, the second metal is a transition metal.

  In the second invention, since the second metal is a transition metal, the bonding force between the first metal and the hydrogen atom is weaker than when the first metal is a simple substance. Therefore, the activation energy required for separating the hydrogen atom from the first metal is reduced, and the hydrogen release temperature can be lowered.

  A hydrogen storage material according to a third invention is characterized in that, in the first invention or the second invention, the first metal is a magnesium atom, and the second metal contains an iron atom or a manganese atom.

  In the third invention, an iron atom or a manganese atom is arranged between the magnesium atom and the magnesium atom. The iron atom or the manganese atom has a great influence on the electronic arrangement and the spin state of the magnesium atom, and has a great effect of reducing the activation energy necessary for separating the hydrogen atom from the magnesium atom. For example, when the iron atom is arranged between the magnesium atoms, the activation energy required to separate the distance between the hydrogen atom and the magnesium atom to 4.5 angstroms can be lowered to 2.0 eV, The hydrogen release temperature can be lowered to 400K. Similarly, when the manganese atom is arranged between magnesium atoms, the activation energy can be lowered to 1.5 eV, and the hydrogen release temperature can be further lowered to 300K.

  According to a fourth aspect of the present invention, there is provided a method for producing a hydrogen storage material, comprising: a plurality of first metals that can be ionically bonded to hydrogen atoms; and a second metal that is different from the first metal. A method for producing a hydrogen storage material that adsorbs and / or releases hydrogen atoms from the first metal, wherein the second metal is disposed between the first metals.

  In the fourth invention, a second metal different from the first metal is disposed between the plurality of first metals capable of ionic bonding with hydrogen atoms. By disposing the second metal between the plurality of first metals, the electron arrangement and the spin state of the first metal are changed, the bonding force between the first metal and hydrogen atoms is controlled, and the hydrogen release temperature is controlled. Can be controlled. As a method of disposing the second metal between the first metal, the first metal and the second metal are alternately irradiated using the MBE method (molecular beam epitaxial growth method), In addition to the method of forming the multilayer film, a thin film formation method such as MOCVD (metal organic chemical vapor deposition), or by dissolving the first metal and the second metal in a solid state, There is a melting method that is inserted between the first metals.

  According to a fifth aspect of the present invention, there is provided the method for producing a hydrogen storage material according to the fourth aspect, wherein the second metal includes a plurality of types of atoms, and the composition ratio of the plurality of types of atoms is adjusted to adjust the hydrogen atoms. The discharge temperature is specified.

  In the fifth invention, the second metal responsible for adjusting the bonding force between the first metal and the hydrogen atom is composed of a plurality of types of atoms. Depending on the type of atoms constituting the second metal, the influence on the binding force between the first metal and hydrogen atoms is different, so by adjusting the composition ratio of the atoms constituting the second metal, the release of hydrogen atoms The temperature can be specified. For example, when the second metal consists of two types of atoms, if each of them is a simple substance, the hydrogen release temperature becomes the first temperature and the second temperature, respectively. It can set so that it may become the temperature between 1st temperature and 2nd temperature, The hydrogen discharge | release temperature is specified by the composition ratio of the atom which comprises a 2nd metal.

  According to a sixth aspect of the present invention, there is provided a method for releasing hydrogen from a hydrogen storage material comprising a metal ion-bondable with a hydrogen atom, wherein the hydrogen storage material adsorbs the hydrogen atom on the metal and / or releases the hydrogen atom from the metal. A method for releasing hydrogen from a hydrogen storage material that releases hydrogen atoms, wherein the hydrogen storage material is charged.

  In the sixth aspect of the invention, the hydrogen storage material made of a metal ionically bonded to hydrogen atoms is charged. Due to the influence of charging, the electron arrangement and the spin state of the metal itself change, and the bonding force between the metal and the hydrogen atom changes due to the change. When positively charged, the contribution ratio of electrons to the ionic bond with the hydrogen atom becomes small, so that the bonding force between the metal and the hydrogen atom becomes weak. That is, the activation energy required to separate the hydrogen atom from the metal is lowered, and the hydrogen release temperature can be lowered. Further, since the characteristics of the hydrogen storage material itself are not changed into an alloy with a metal, the hydrogen content per weight is not reduced. In other words, it is possible to control the hydrogen release from the hydrogen storage material by keeping the temperature substantially constant and charging the hydrogen storage material.

  A hydrogen release method for a hydrogen storage material according to a seventh aspect of the invention is characterized in that, in the sixth aspect of the invention, the release temperature of the hydrogen atom is specified by adjusting the charge amount of the hydrogen storage material.

  In the seventh aspect of the invention, since the influence on the binding force between the metal and the hydrogen atom differs depending on the charge amount of the hydrogen storage material, the discharge temperature of the hydrogen atom can be specified by adjusting the charge amount. it can. For example, when the hydrogen storage material is magnesium hydride ionically bonded to hydrogen atoms, the hydrogen release temperature from the magnesium hydride is determined by the magnitude of the charge amount of the magnesium hydride, and depends on the magnitude of the charge amount. descend.

  The method for releasing hydrogen of a hydrogen storage material according to an eighth invention is characterized in that, in the sixth invention or the seventh invention, the hydrogen storage material is any one of the hydrogen storage materials of the first invention to the third invention.

  In the eighth invention, by arranging the second metal between the plurality of first metals, the electron arrangement and the spin state of the first metal are changed, and the bonding force between the first metal and the hydrogen atom is controlled. In addition to controlling the hydrogen release temperature, by charging the hydrogen storage material, the electron configuration and the spin state of the metal itself are changed by the effect of charging, and the bonding force between the first metal and the hydrogen atom is controlled. Thus, the hydrogen release temperature is controlled. Thereby, the control area | region of hydrogen discharge | release temperature becomes wider by each effect | action, and it becomes possible to utilize for more various uses.

  According to the present invention, since the second metal different from the first metal is arranged between the plurality of first metals capable of ion bonding with the hydrogen atom, the second metal arranged between the first metals. As a result, the electron arrangement and the spin state of the first metal change, and the bonding force between the first metal and the hydrogen atom changes due to the change. Accordingly, by disposing the second metal between the plurality of first metals, the electron arrangement and the spin state of the first metal are changed, and the bonding force between the first metal and the hydrogen atom is controlled to release the hydrogen. The temperature can be controlled.

  According to the present invention, since the second metal is a transition metal, the bonding force between the first metal and the hydrogen atom can be weakened compared to the case where the first metal is a simple substance. The activation energy required for separating a hydrogen atom from one metal is lowered, and the hydrogen release temperature can be lowered.

  According to the present invention, since the iron atom or the manganese atom having a large influence on the electronic arrangement and the spin state of the magnesium atom is arranged between the magnesium atom and the magnesium atom, the hydrogen atom is separated from the magnesium atom. The effect of reducing the activation energy required to achieve this is great. For example, when the iron atom is arranged between the magnesium atoms, the activation energy required to separate the distance between the hydrogen atom and the magnesium atom to 4.5 angstroms can be lowered to 2.0 eV. And the hydrogen release temperature can be lowered to 400K. Similarly, when the manganese atom is arranged between magnesium atoms, the activation energy can be lowered to 1.5 eV, and the hydrogen release temperature can be further lowered to 300K.

  According to the present invention, the degree of the influence on the bonding force between the first metal and the hydrogen atom differs depending on the type of atom constituting the second metal responsible for adjusting the bonding force between the first metal and the hydrogen atom. Thus, the emission temperature of hydrogen atoms can be specified by adjusting the composition ratio of atoms constituting the second metal.

  According to the present invention, by charging a hydrogen storage material composed of a metal ionically bonded to a hydrogen atom, the electron configuration and the spin state of the metal itself are changed, and the change between the metal and the hydrogen atom is caused by the change. Control the binding force. When positively charged, the contribution ratio of electrons to the ionic bond with the hydrogen atom becomes small, so that the bonding force between the metal and the hydrogen atom becomes weak. That is, the activation energy required to separate the hydrogen atom from the metal is lowered, and the hydrogen release temperature can be lowered. Further, since the characteristics of the hydrogen storage material itself are not changed into an alloy with a metal, the hydrogen content per weight is not reduced.

  According to the present invention, the influence exerted on the bonding force between the metal and the hydrogen atom differs depending on the charge amount of the hydrogen storage material. Therefore, the discharge temperature of the hydrogen atom can be specified by adjusting the charge amount. For example, when the hydrogen storage material is magnesium hydride ionically bonded to hydrogen atoms, the hydrogen release temperature from the magnesium hydride is determined by the magnitude of the charge amount of the magnesium hydride, and depends on the magnitude of the charge amount. descend.

  According to the present invention, by arranging the second metal between the plurality of first metals, the electron arrangement and the spin state of the first metal are changed, and the bonding force between the first metal and the hydrogen atom is controlled. In addition to controlling the hydrogen release temperature, by charging the hydrogen storage material, the electron configuration and the spin state of the metal itself are changed by the effect of charging, and the bonding force between the first metal and the hydrogen atom is controlled. , Control the hydrogen release temperature. Thereby, the control region of the hydrogen release temperature becomes wider by each action, and it has excellent effects such as being able to be used for more various uses.

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.

(Embodiment 1)
FIG. 1 is a schematic diagram showing the structure of a hydrogen storage material according to Embodiment 1 of the present invention.
The hydrogen storage material 1 according to Embodiment 1 of the present invention includes a plurality of first metals (here, two magnesium atoms 11) and a second metal (here, metals) capable of ionic bonding with two hydrogen atoms 10. And a structure in which the metal atom 12 is disposed between two magnesium atoms 11. The metal atom 12 is a transition metal such as a 3d transition metal, a 4d transition metal, or a 5d transition metal. By supplying hydrogen atoms 10 to such a hydrogen storage material 1, magnesium atoms 11 constituting the hydrogen storage material 1 adsorb the hydrogen atoms 10 to become magnesium hydride 15 (FIG. 2A). By heating to a predetermined temperature, the magnesium hydride 15 releases the hydrogen atoms 10 (FIG. 2B). That is, by controlling the temperature of the hydrogen storage material 1, the adsorption and release of the hydrogen atoms 10 can be controlled.

  For the hydrogen storage material 1 having such a structure, a density functional theory known per se (for example, Physical Review, published on November 9, 1964, Vol. 136, p864-871, Physical Review, November 15, 1965) When the hydrogen atom 10 approaches or separates from the magnesium atom 11 on the basis of Japanese publication, vol. 140, p1133-1138), the potential energy with respect to the distance of the hydrogen atom 10 from the magnesium atom 11 is calculated by an electronic computer. It was found that the material 1 has a potential characteristic as shown in FIG.

  In FIG. 3, each solid line shows potential characteristics when the metal atom 12 is a 3d transition metal of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, and a broken line shows the case of magnesium hydride alone. The potential characteristics at are shown.

  In the case of magnesium hydride alone, for example, an energy of 3.5 eV (activation energy) is required to separate the distance between the hydrogen atom 10 and the magnesium atom 11 to 4.5 angstroms. When arranged between the magnesium atoms 11 of the two magnesium hydrides 15 and 15, the distance between the hydrogen atoms 10 and the magnesium atoms 11 is 4.5 angstroms at an activation energy of 2.0 eV. It becomes possible. Further, when Mn is used as the metal atom 12, the distance between the hydrogen atom 10 and the magnesium atom 11 can be separated by 4.5 angstroms with an activation energy of 1.5 eV. In other words, the activation energy necessary for separating the hydrogen atom 10 from the magnesium hydride 15 can be controlled by arranging the metal atom 12 between the magnesium atoms 11 and 11 of the two magnesium hydrides 15 and 15. it can.

  This is because by arranging an iron atom or a manganese atom between the magnesium atoms 11 of the two magnesium hydrides 15, the electron configuration and the spin state of the magnesium atom 11 are changed, and the magnesium atom 11 is caused by the change. It is presumed that the bond strength between the hydrogen atom 10 and the hydrogen atom 10 is weakened, and the activation energy necessary for separating the hydrogen atom 10 from the magnesium atom 11 is reduced.

  Further, it is known that the activation energy and the hydrogen release temperature have a relationship as shown in FIG. 4, and based on this relationship, the hydrogen storage material 1 has a relationship as shown in “Table 2”. It was found to have a hydrogen release temperature. In particular, when an iron atom is used as the metal atom 12, the hydrogen release temperature can be lowered to 400K. Similarly, when a manganese atom is used, the hydrogen release temperature can be lowered to 300K. Thus, for example, by arranging a manganese atom between two magnesium hydrides 15 and 15, the hydrogen atom 10 can be separated from the magnesium hydride 15 at room temperature. That is, it can be set as the hydrogen storage material which can discharge | release the hydrogen atom 10 at normal temperature.

  When a hydrogen storage material is used as a hydrogen supply source for a fuel cell, it is necessary to temporarily store hydrogen atoms and supply a necessary amount of hydrogen atoms appropriately and stably when necessary. It is common to control the temperature of the material. Accordingly, there is a demand for a material from which hydrogen atoms are released at a temperature slightly higher than room temperature. For example, a hydrogen storage material in which manganese atoms are arranged and a hydrogen storage material in which iron atoms are arranged are mixed, and the composition ratio is determined. Thus, the hydrogen release temperature can be adjusted. Thus, it can be set as the hydrogen storage material which can discharge | release hydrogen at the temperature suitable for the application to utilize.

  The gist of the present embodiment is to provide a hydrogen storage material from which hydrogen atoms are released at a desired temperature, which is difficult in the prior art by arranging metal atoms between each magnesium atom of two magnesium hydrides. The purpose is to control the strength of the ionic bond between the magnesium atom and the hydrogen atom so that the hydrogen atom is released in the temperature range below 500K.

  Next, the manufacturing method of the hydrogen storage material which concerns on Embodiment 1 of this invention is demonstrated. FIG. 5 is an explanatory diagram for explaining a method for producing a hydrogen storage material according to Embodiment 1 of the present invention. Hereinafter, the case where a magnesium atom is used as a metal atom will be described.

  First, magnesium wires 51a and manganese wires 52a were alternately irradiated on the surface of the substrate 50 as a base by MBE (FIG. 5A), and the magnesium layers 51 and the manganese layers 52 were alternately stacked. A multilayer film is formed (FIG. 5B). The irradiation pressure, irradiation time, and substrate temperature of the magnesium wire 51a and the manganese wire 52a are appropriately adjusted so that the thicknesses of the magnesium layer 51 and the manganese layer 52 are 2 monolayers (atomic layers) and 1 monolayer, respectively.

  In this way, the magnesium layer 51 is arranged above and below each manganese layer 52, and the manganese atoms located in the manganese layer 52 are in one monolayer below the magnesium layer arranged above the manganese layer 52. It changes the electron configuration and the spin state of the magnesium atom located and the magnesium atom located in the upper monolayer of the magnesium layer arranged below the manganese layer 52.

  Next, the hydrogen atoms 10 are adsorbed to each magnesium layer 51 by supplying the hydrogen atoms 10 under a temperature environment of less than 300K. The number of adsorbed hydrogen atoms is approximately twice the number of magnesium atoms constituting the magnesium layer 51, and a larger amount of hydrogen atoms 10 can be stored as compared with a gas state having the same volume. Further, since the adsorption and release of the hydrogen atoms 10 can be easily controlled by the temperature, the safety is dramatically improved as compared with the case of the gas state.

  In this example, after forming a multilayer film in which magnesium layers and manganese layers are alternately stacked, hydrogen atoms are supplied to the multilayer film so that the hydrogen atoms are adsorbed by the magnesium atoms constituting the magnesium layer. However, a multilayer film in which magnesium hydride layers in which hydrogen atoms are previously adsorbed on magnesium atoms and manganese layers are alternately stacked may be formed.

  Further, the method for forming a multilayer film using the MBE method has been described. However, the method is not limited to the MBE method, and a known technique such as the MOCVD method can be used, and a method suitable for the multilayer film to be formed is appropriately selected. select. Also, a solid state manganese atom and magnesium atom may be dissolved by a melting method so that the manganese atom is inserted between the magnesium atoms, and a method in which the composition becomes uniform is preferable.

(Embodiment 2)
FIG. 6 is an explanatory diagram for explaining a hydrogen release method for a hydrogen storage material according to Embodiment 2 of the present invention.
In the method for releasing hydrogen of a hydrogen storage material according to Embodiment 2, magnesium hydride 25, which is a hydrogen storage material 2 in which magnesium atoms 21 are ion-bonded to two hydrogen atoms 20, is charged. Specifically, the magnesium hydride 25 (hydrogen storage material 2) is positively charged by removing the electrons 30 constituting the magnesium hydride 25. As a method for charging the magnesium hydride 25, there are an electron beam irradiation method for irradiating an electron beam, light, and X-rays, a light irradiation method, an X-ray irradiation method, and a voltage application method for applying a voltage. Further, the voltage application method includes a method of applying a voltage by installing an electrode, a method of applying a stress by adhering a piezoelectric element, and the like.

  When the hydrogen atom 20 approaches or separates from the magnesium atom 21 with respect to the charged magnesium hydride 25 based on a density functional theory known per se, the potential energy with respect to the distance of the hydrogen atom 20 from the magnesium atom 21 is expressed. When calculated by an electronic computer, it was found that the magnesium hydride 25 has potential characteristics as shown in FIG.

  In FIG. 7, each solid line shows potential characteristics when the total charge amount of magnesium hydride 25 is +1, +0.75, +0.50, +0.25 in units of elementary charge e, and a broken line shows hydrogenation. The potential characteristics when magnesium 25 is uncharged are shown. The charge amount is basically an integer having the elementary charge e as a unit, and the above total charge amount means the charge amount per one magnesium hydride 25. That is, when the total charge amount of the magnesium hydride 25 is +1, it means that one electron 30 is removed from one magnesium hydride 25. Similarly, when the total charge amount is +0.75, This means that three electrons 30 are removed from the magnesium hydride 25, and the total charge amounts of +0.50 and +0.25 are respectively two, four and four electrons 30 from the magnesium hydride 25. It means removing.

  When the magnesium hydride 25 is uncharged, for example, an activation energy of 3.5 eV is required to separate the distance between the hydrogen atom 20 and the magnesium atom 21 to 4.5 angstroms. When the total charge amount is +1, the distance between the hydrogen atom 20 and the magnesium atom 21 can be separated by 4.5 angstroms with an activation energy of 1.2 eV. That is, the activation energy required to separate the hydrogen atom 20 from the magnesium hydride 25 can be controlled by charging the magnesium atom 21 (magnesium hydride 25).

  Further, based on the above-described relationship between the activation energy and the hydrogen release temperature (see FIG. 4), it was found that the charged magnesium hydride 25 has a hydrogen release temperature as shown in “Table 3”. In particular, when the total charge amount of the magnesium hydride 25 is +0.50, the hydrogen release temperature can be lowered to 480 K. Similarly, when the total charge amount is +0.75, The discharge temperature can be lowered to 360K.

  This is because when the magnesium hydride 25 is positively charged, the electron configuration and the spin state of the magnesium atom 21 are changed, and the bonding force between the magnesium atom 21 and the hydrogen atom 20 is weakened due to the change. It is presumed that the activation energy necessary for separating the atoms 20 has decreased. In the magnesium hydride 25, the positively charged magnesium atom 21 and the negatively charged hydrogen atom 20 are in an extremely stable state due to ionic bonds, and the hydrogen atom 20 is charged when desorbed from the magnesium atom 21. It becomes so-called neutral. Therefore, when the magnesium hydride 25 is positively charged in advance, the hydrogen atom 20 can be brought close to neutrality and the interaction caused by the ionic bond between the magnesium atom 21 and the hydrogen atom 20 can be weakened. In this way, the hydrogen release temperature of the magnesium hydride 25 can be lowered without alloying. In other words, it is possible to control the hydrogen release from the hydrogen storage material by keeping the temperature substantially constant and charging the hydrogen storage material.

  Further, for example, the total charge amount of the magnesium hydride 25 can be adjusted by adjusting the irradiation intensity and irradiation time for irradiating the electron beam, and the hydrogen release temperature can be adjusted by adjusting the total charge amount of the magnesium hydride 25. Therefore, hydrogen atoms can be released at a temperature suitable for the application to be used. In particular, since only the magnesium atom 21 that contributes to the adsorption and release of hydrogen atoms is a constituent element, the hydrogen content per weight is not reduced.

  The gist of the present embodiment is to provide a method for releasing hydrogen of a hydrogen storage material in which hydrogen atoms are released at a desired temperature. The magnesium hydride 25 is charged, and a temperature of less than 500 K, which has been difficult in the past. The purpose is to control the strength of the ionic bond between the magnesium atom 21 and the hydrogen atom 20 so that the hydrogen atom 20 is released in the region.

  In the first embodiment, the metal atom 12 is disposed between the magnesium atoms 11 of the two magnesium hydrides 15, and in the second embodiment, the magnesium hydride 25 is charged, so that the magnesium atoms 11 (21) and Although the strength of the ionic bond with the hydrogen atom 10 (20) is controlled, the strength of the ionic bond between the magnesium atom and the hydrogen atom may be controlled by combining the two. In this case, the control region of the hydrogen release temperature is further widened, and it can be used for more various applications.

  In each embodiment, the case of a magnesium atom as a metal atom capable of ionic bonding has been described. However, an alkali metal and alkaline earth metal having the same ionic bond may be used, and an alkali metal and alkaline earth metal may be used. The release temperature of hydrogen adsorbed on the metal can be controlled.

  As mentioned above, although the hydrogen storage material which concerns on this invention, the manufacturing method of a hydrogen storage material, and the hydrogen discharge | release method of a hydrogen storage material were shown and demonstrated concrete embodiment, this invention is not limited to these. . A person skilled in the art can add various changes or improvements to the configurations and functions of the invention according to the above-described embodiments without departing from the gist of the present invention.

It is a schematic diagram which shows the structure of the hydrogen storage material which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the mode of adsorption | suction of the hydrogen atom to a hydrogen storage material, and discharge | release of the hydrogen atom from a hydrogen storage material. It is a graph which shows the potential characteristic of the hydrogen storage material which concerns on Embodiment 1 of this invention. It is a graph which shows the relationship between activation energy and hydrogen discharge | release temperature. It is explanatory drawing for demonstrating the manufacturing method of the hydrogen storage material which concerns on Embodiment 1 of this invention. It is explanatory drawing for demonstrating the hydrogen release method of the hydrogen storage material which concerns on Embodiment 2 of this invention. It is a graph which shows the potential characteristic of the hydrogen storage material which concerns on Embodiment 2 of this invention. It is a schematic diagram which shows the structure of the conventional hydrogen storage material. It is a graph which shows the potential characteristic of the conventional hydrogen storage material.

Explanation of symbols

1, 2 Hydrogen storage material 10,20 Hydrogen atom 11,21 Magnesium atom 15,25 Magnesium hydride 30 Electron 50 Substrate 51 Magnesium layer 52 Manganese layer

Claims (8)

A plurality of first metals ion-bondable with hydrogen atoms, and a second metal different from the first metal, adsorbing hydrogen atoms to the first metal and / or hydrogen atoms from the first metal A hydrogen storage material that releases,
The hydrogen storage material, wherein the second metal is disposed between the first metals. The hydrogen storage material according to claim 1, wherein the second metal is a transition metal. The first metal is a magnesium atom;
The hydrogen storage material according to claim 1 or 2, wherein the second metal includes an iron atom or a manganese atom. A plurality of first metals ion-bondable with hydrogen atoms, and a second metal different from the first metal, adsorbing hydrogen atoms to the first metal and / or hydrogen atoms from the first metal A method for producing a hydrogen storage material that performs release, comprising:
The method for producing a hydrogen storage material, wherein the second metal is disposed between the first metals. The second metal includes a plurality of types of atoms;
The method for producing a hydrogen storage material according to claim 4, wherein a release temperature of the hydrogen atom is specified by adjusting a composition ratio of the plurality of types of atoms. A hydrogen release method for a hydrogen storage material comprising a metal capable of ion-bonding with a hydrogen atom and releasing a hydrogen atom from a hydrogen storage material that adsorbs a hydrogen atom to the metal and / or releases a hydrogen atom from the metal. And
A method for releasing hydrogen from a hydrogen storage material, wherein the hydrogen storage material is charged. The method for releasing hydrogen of the hydrogen storage material according to claim 6, wherein the release temperature of the hydrogen atom is specified by adjusting the charge amount of the hydrogen storage material. The hydrogen storage material according to any one of claims 1 to 3, wherein the hydrogen storage material is the hydrogen storage material according to any one of claims 1 to 3.

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