JP2008004392A - Hydrogen transmission metal layer/electrolyte composite, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the degradation of durability which is caused by the occurrence of air bubbles at the interface between a hydrogen transmission metal layer and an electrolyte layer of a hydrogen transmission metal layer/electrolyte composite. <P>SOLUTION: The hydrogen transmission metal layer/electrolyte comprises a hydrogen transmission metal layer 22 containing a noble metal having such activity as making hydrogen atom to be proton on one surface, and containing, near that one surface, a high solubility coefficient part 52 consisting of a high solubility coefficient material showing a hydrogen solubility coefficient higher than the average value of the hydrogen solubility coefficient in the hydrogen transmission metal layer 22. The hydrogen transmission metal layer/electrolyte composite comprises an electrolyte layer 21 which comprises a solid oxide having proton conductivity, and is provided on that one surface of the hydrogen transmission metal layer 22. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a composite of a hydrogen permeable metal layer and an electrolyte, and a fuel cell having the composite.

  As a kind of electrolyte having proton conductivity, an electrolyte made of a solid oxide is known, and such an electrolyte can be used, for example, as an electrolyte layer of a fuel cell. As a fuel cell including an electrolyte layer made of a solid oxide, a fuel cell in which a solid oxide layer having proton conductivity is formed on a hydrogen-permeable metal layer has been proposed (see, for example, Patent Document 1). With such a configuration, the electrolyte layer can be thinned and the proton conductivity in the electrolyte layer can be improved.

JP 2004-146337 A

  However, when power generation is continued for a long time using such a fuel cell, battery performance may be degraded. For example, when power generation is continued at a constant current, a voltage drop may occur gradually. When such deterioration in battery performance is observed, when the internal state of the fuel cell is examined, fine voids (voids) are observed in the vicinity of the interface between the hydrogen permeable metal layer and the electrolyte layer. Such air bubbles are considered to be formed by a certain gas generated in the fuel cell along with the power generation when the power generation is continued for a long time. When air bubbles are formed in the vicinity of the interface between the hydrogen permeable metal layer and the electrolyte layer in this way, the hydrogen permeable metal layer and the electrolyte layer are easily separated at the interface, and the effective area (power generation at the interface) In this case, the area of the interface that can actually be involved in proton transfer from the hydrogen-permeable metal layer to the electrolyte layer is reduced. It is considered that the battery performance deteriorates due to a decrease in durability and a decrease in effective area of the hydrogen permeable metal layer / electrolyte layer composite due to such peeling of the layer. The generation of air bubbles at the interface may occur not only when power generation is continued for a long time, but also when the power generation current in the fuel cell is increased, for example. In addition, the problem of air bubble formation at the interface is not limited to the fuel cell, but other devices using a composite including a hydrogen permeable metal layer and an electrolyte layer made of a solid oxide, such as a hydrogen pump and a hydrogen This is a problem that may occur in the density sensor as well.

  The present invention has been made in order to solve the above-described conventional problems, and the durability of the hydrogen permeable metal layer / electrolyte composite due to the generation of air bubbles at the interface between the hydrogen permeable metal layer and the electrolyte layer. It aims at suppressing the fall of property.

In order to achieve the above object, the hydrogen permeable metal layer / electrolyte composite of the present invention comprises:
A hydrogen permeable metal layer comprising a noble metal having an activity of protonating hydrogen atoms on one surface, wherein the hydrogen permeable metal layer has a higher hydrogen solubility coefficient than the average value of the hydrogen solubility coefficient. A hydrogen permeable metal layer having a high solubility coefficient portion made of a solubility coefficient material in the vicinity of the one surface;
And an electrolyte layer made of a solid oxide having proton conductivity provided on the one surface of the hydrogen permeable metal layer.

  According to the hydrogen permeable metal layer / electrolyte composite of the present invention configured as described above, in the hydrogen permeable metal layer, a high solubility coefficient is provided in the vicinity of the surface on which the electrolyte layer is formed and provided with the noble metal. When the hydrogen permeates through the hydrogen permeable metal layer, even when the activity of protonating hydrogen atoms in the noble metal becomes insufficient, excess hydrogen atoms can be absorbed by the high solubility coefficient portion. it can. Therefore, in the vicinity of the interface between the hydrogen permeable metal layer and the electrolyte layer, generation of air bubbles caused by the generation of hydrogen molecules can be suppressed, and the durability of the hydrogen permeable metal layer / electrolyte composite can be improved. , Performance degradation can be suppressed.

In the hydrogen permeable metal layer / electrolyte composite of the present invention,
The high solubility coefficient material may hold more hydrogen inside as the surrounding hydrogen concentration increases and release hydrogen as the surrounding hydrogen concentration decreases.

  With such a configuration, when the hydrogen permeable metal layer / electrolyte complex is continuously used, even if the state where the protonation activity in the noble metal is insufficient and the state where it is sufficient are repeated, the proton When the activation activity becomes insufficient, a predetermined effect can be obtained repeatedly.

  In such a hydrogen permeable metal layer / electrolyte composite according to the present invention, the high solubility coefficient material may be a hydrogen storage alloy. Alternatively, in the hydrogen permeable metal layer / electrolyte complex of the present invention, the high solubility coefficient material may be a carbon-based adsorbent.

  With such a configuration, even when any high solubility coefficient material is used, when the protonation activity becomes insufficient, the effect of suppressing the formation of air bubbles caused by the generation of hydrogen molecules can be repeatedly obtained. Can do.

In the hydrogen permeable metal layer / electrolyte composite of the present invention,
The high solubility coefficient portion is formed in a continuous layer shape in the vicinity of the interface with the electrolyte layer in the hydrogen permeable metal layer,
The hydrogen permeable metal layer may include the noble metal in a region on the high solubility coefficient portion and including an interface with the electrolyte layer.

  With such a configuration, by forming the high solubility coefficient portion in a continuous layer shape, excess hydrogen atoms can be efficiently absorbed in the vicinity of the entire interface with the electrolyte layer, and hydrogen molecules are generated. It is possible to suppress the formation of air bubbles resulting from the above.

  The present invention can be realized in various forms other than the above. For example, the present invention can be realized in the form of a fuel cell, a hydrogen pump, or a hydrogen concentration sensor including the hydrogen permeable metal layer / electrolyte composite according to the present invention. Is possible.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Fuel cell configuration:
B. Production method:
C. Operation during power generation:
D. Variation:

A. Fuel cell configuration:
FIG. 1 is a schematic cross-sectional view showing an outline of the configuration of a single cell 20 constituting a fuel cell according to a preferred embodiment of the present invention. The unit cell 20 includes a hydrogen permeable metal layer / electrolyte complex 23 composed of a hydrogen permeable metal layer 22 and an electrolyte layer 21, a cathode 24 formed on the electrolyte layer 21, and gas separators 27 and 29. ing. Between the gas separator 27 and the hydrogen permeable metal layer 22, an in-cell fuel gas channel 30 through which a fuel gas containing hydrogen passes is formed. Further, between the gas separator 29 and the cathode 24, there is formed an in-single cell oxidizing gas flow path 32 through which an oxidizing gas containing oxygen passes. Hereinafter, a structure including the hydrogen permeable metal layer 22, the electrolyte layer 21, and the cathode 24 is referred to as an MEA (Membrane Electrode Assembly) 40. Although the single cell 20 is shown in FIG. 1, the actual fuel cell of this embodiment has a stack structure in which a plurality of the single cells 20 of FIG. 1 are stacked. Although illustration is omitted, in order to adjust the internal temperature of the stack structure, a refrigerant flow path through which a refrigerant passes may be provided between each single cell or every time a predetermined number of single cells are stacked. good.

  FIG. 2 is an enlarged schematic cross-sectional view showing the configuration of the hydrogen permeable metal layer 22 shown in FIG. 1 in more detail. The hydrogen permeable metal layer 22 is formed from a hydrogen permeable layer 50 formed of a metal having hydrogen permeability and a solubility coefficient of hydrogen in the hydrogen permeable metal formed on the hydrogen permeable layer 50 and constituting the hydrogen permeable layer 50. A high solubility coefficient part 52 made of a high solubility coefficient material exhibiting a high hydrogen solubility coefficient, and a catalyst layer 54 formed on the high solubility coefficient part 52 and comprising a noble metal having an activity of protonating hydrogen atoms. . Such a hydrogen permeable metal layer 22 is a layer that allows hydrogen flowing through the fuel gas flow channel 30 in the single cell to pass therethrough and delivers it as protons to the electrolyte layer 21 and functions as an anode electrode in the fuel cell. Hereinafter, each layer constituting the hydrogen permeable metal layer 22 will be described in more detail.

  In this embodiment, the hydrogen permeable layer 50 is formed of a metal film made of palladium (Pd). Palladium has an activity of dissociating hydrogen molecules into hydrogen atoms in addition to the property of allowing hydrogen to permeate mainly as hydrogen atoms. Therefore, hydrogen flowing through the fuel gas flow path 30 in the single cell is dissociated into hydrogen atoms on the surface of the hydrogen permeable layer 50 and permeates through the hydrogen permeable layer 50 mainly as hydrogen atoms. In addition, the thickness of the hydrogen permeable layer 50 can be 30-100 micrometers, for example.

In the present embodiment, the high solubility coefficient portion 52 is constituted by a layer made of a hydrogen storage alloy having a hydrogen solubility coefficient larger than that of palladium constituting the hydrogen permeable layer 50. A hydrogen storage alloy is an alloy that stores hydrogen as the surrounding hydrogen gas concentration increases and releases hydrogen as the surrounding hydrogen gas concentration decreases, and when hydrogen diffuses into the interior in an atomic state, An alloy that forms a metal hydride by forming a solid solution with hydrogen between crystal lattices. In general, a hydrogen storage alloy that achieves both storage and release of hydrogen is produced by appropriately combining a metal that easily absorbs hydrogen and a metal that hardly absorbs hydrogen at a predetermined ratio. Specifically, as the hydrogen storage alloy constituting the high solubility coefficient portion 52, for example, a LaNi ₅ alloy, a TiFe alloy, a Mg ₂ Ni alloy, or a Fe _0.9 Ni _0.1 Ti alloy can be used. In the present embodiment, the high solubility coefficient portion 52 is formed in a continuous layer, and the thickness of the high solubility coefficient portion 52 can be set to 0.1 to 5 μm, for example.

  In the present embodiment, the catalyst layer 54 is formed of palladium in the same manner as the hydrogen permeable layer 50. In addition to the properties described above, palladium has an activity of generating protons from hydrogen atoms. Therefore, hydrogen atoms that have passed through the hydrogen permeable layer 50 and the high solubility coefficient portion 52 and reached the catalyst layer 54 are protonated in the catalyst layer 54 and delivered to the electrolyte layer 21. In addition, the thickness of the catalyst layer 54 should just be the thickness which can implement | achieve the above-mentioned catalyst activity in the interface with the electrolyte layer 21 in the hydrogen permeable metal layer 22, for example, can be 0.01-2 micrometers. .

Further, the electrolyte layer 21 shown in FIG. 1 described above is a layer made of a solid electrolyte having proton conductivity. In this embodiment, the electrolyte layer 21 is formed of a perovskite solid oxide. Specifically, for example, the electrolyte layer 21 may be formed of BaCe _0.8 Y _0.2 O ₃ or SrZr _0.8 In _0.2 O ₃ . it can. Since the electrolyte layer 21 is formed on the dense hydrogen permeable metal layer 22, it is possible to sufficiently reduce the thickness. Thus, since the membrane resistance of the electrolyte layer 21 can be reduced by forming the electrolyte layer 21 thinner, the temperature is lower than the operating temperature of the conventional solid electrolyte fuel cell, which is about 200 to 600 ° C. This makes it possible to operate the fuel cell. In addition, the thickness of the electrolyte layer 21 can be 0.1-5 micrometers, for example.

  The cathode 24 is a metal layer formed on the electrolyte layer 21 and is formed of a noble metal having catalytic activity that promotes an electrochemical reaction. In this embodiment, the cathode 24 is made of palladium. In the case where the cathode 24 is composed of another kind of noble metal that does not have hydrogen permeability, such as platinum (Pt), the cathode 24 is formed to be sufficiently thin so that the outside of the cathode 24 (oxidizing gas channel 32 in the single cell) is formed. Side) and the electrolyte layer 21 may be ensured.

  The gas separators 27 and 29 are gas-impermeable members made of a conductive material such as carbon or metal. On the surfaces of the gas separators 27 and 29, predetermined uneven shapes for forming the above-described single-cell in-cell fuel gas flow channel 30 and single-cell in-cell oxidizing gas flow channel 32 are formed. In the single cell 20 shown in FIG. 1, between the MEA 40 and the gas separator, a member having conductivity and gas permeability, for example, a metal porous body such as foam metal or metal mesh, carbon paper, etc. It is good also as arrange | positioning a carbon porous body.

  As the fuel gas supplied to the fuel cell, a hydrogen-rich gas obtained by reforming a hydrocarbon-based fuel may be used, or a high-purity hydrogen gas may be used. For example, air can be used as the oxidizing gas supplied to the fuel cell.

B. Production method:
Below, the manufacturing method of the single cell 20 is demonstrated. FIG. 3 is an explanatory diagram showing a manufacturing process of the MEA 40 constituting the single cell 20.

  When creating the MEA 40, first, the hydrogen permeable layer 50 is prepared (step S100). In this embodiment, a palladium metal film is prepared as the hydrogen permeable layer 50.

  Next, a high solubility coefficient portion 52, that is, a layer made of a hydrogen storage alloy is formed on one surface of the hydrogen permeable layer 50 prepared in step S100 (step S110). The layer made of a hydrogen storage alloy can be formed, for example, by a physical vapor deposition method (PVD) such as a sputtering method or a PLD method or a chemical vapor deposition method (CVD) using the above-described hydrogen storage alloy as a film forming material. Alternatively, instead of Step S110, a layer made of a hydrogen storage alloy is prepared as a metal foil separate from the hydrogen permeable layer 50, and this metal foil is clad-bonded onto the hydrogen permeable layer 50 prepared in Step S100. Later, a process of rolling the whole to a predetermined film thickness may be performed.

  Next, a catalyst layer 54 made of palladium is formed on the high solubility coefficient portion 52 formed in step S110 (step S120). The catalyst layer 54 can be formed by, for example, sputtering, PVD, or CVD.

  Thereafter, the electrolyte layer 21 is formed on the catalyst layer 54 in the hydrogen permeable metal layer 22 to produce the hydrogen permeable metal layer / electrolyte complex 23 (step S130). The electrolyte layer 21 is formed by forming a film on the hydrogen permeable metal layer 22 while generating the solid oxide described above. As a film forming method, for example, PVD, CVD, a sputtering method or a sol-gel method can be used.

  Next, the cathode 24 is formed on the electrolyte layer 21 (step S140), and the MEA 40 is completed. The cathode 24 can be formed by, for example, PVD or CVD.

  When assembling the fuel cell, the gas separators 27 and 29 are arranged so as to sandwich the MEA 40 manufactured according to FIG. 3 to form the single cell 20, and a predetermined number of the single cells 20 are stacked.

C. Operation during power generation:
FIG. 4 is an explanatory view showing the state in the vicinity of the interface between the hydrogen permeable metal layer 22 and the electrolyte layer 21 during power generation of the fuel cell of this example. When the fuel cell generates power, the hydrogen gas flowing through the fuel gas flow path in the single cell dissociates into hydrogen atoms, permeates through the hydrogen permeable metal layer 22, and is transferred to the electrolyte layer 21 as protons. At this time, as described above, hydrogen atoms that permeate through the hydrogen permeable metal layer 22 are protonated at the interface with the electrolyte layer 21. When the protonation activity on the surface of the hydrogen permeable metal layer 22 becomes insufficient as compared with the amount of hydrogen atoms that pass through the hydrogen permeable metal layer 22, the vicinity of the interface between the hydrogen permeable metal layer 22 and the electrolyte layer 21 is near. Then, hydrogen atoms are accumulated. FIG. 4A shows that the proton permeable activity in the catalyst layer 54 formed at the interface with the electrolyte layer 21 in the hydrogen permeable metal layer 22 is insufficient compared to the amount of hydrogen atoms that permeate through the hydrogen permeable metal layer 22. It shows how to do. For example, when the amount of output current in the fuel cell increases or when the power generation operation of the fuel cell is continued for a long time, the protonation activity in the catalyst layer 54 tends to become insufficient.

  In the fuel cell of this embodiment, when the protonation activity in the catalyst layer 54 is insufficient and the concentration of hydrogen atoms partially increases, the high solubility coefficient portion 52 provided near the interface with the electrolyte layer 21 is It absorbs hydrogen atoms that are being accumulated near the interface. FIG. 4B schematically shows how excess hydrogen atoms are absorbed by the high solubility coefficient portion 52.

  On the other hand, in the case where the high solubility coefficient portion 52 is not provided in the hydrogen permeable metal layer, a reaction in which hydrogen atoms accumulated in the vicinity of the interface recombine to generate hydrogen molecules proceeds. Air bubbles (voids) are formed by hydrogen molecules (hydrogen gas). FIG. 4C schematically shows how air bubbles are formed by hydrogen gas in the vicinity of the interface in the hydrogen permeable metal layer 22.

The mechanism of the formation of air bubbles resulting from the generation of hydrogen molecules and the suppression of air bubble formation by providing the high solubility coefficient portion 52 can be considered as follows. That is, it is considered that the reaction that generates hydrogen molecules in the vicinity of the interface of the hydrogen permeable metal layer 22 proceeds at a relatively weak site in terms of crystal structure such as a crystal grain boundary. Here, if the hydrogen partial pressure due to the hydrogen molecules generated at the grain boundary is assumed to be P _H2 , this hydrogen partial pressure P _H2 is the concentration of hydrogen dissolved in the metal existing around the grain boundary (dissolution amount S). In the case where the temperature is constant, the following equation (1) is established (Sieverts' law).

S = K√ (P _H2 ) (1)
Where K is the solubility coefficient of hydrogen in the metal around the grain boundary.

  Here, in this embodiment, since the hydrogen storage alloy having a higher hydrogen solubility coefficient K is arranged around the grain boundary where hydrogen molecules are generated, the hydrogen concentration (dissolution amount S) in the hydrogen permeable metal layer 22 is set. Is a predetermined value, the partial pressure of hydrogen in the grain boundary can be suppressed to a lower value from the equation (1) than in the case where no hydrogen storage alloy is arranged. Thereby, even if the hydrogen concentration (dissolution amount S) in the hydrogen permeable metal layer 22 is increased, the increase in the hydrogen partial pressure in the grain boundary can be suppressed, and the growth of the grain boundary to air bubbles can be suppressed. .

  On the other hand, when the high solubility coefficient portion 52 made of a hydrogen storage alloy is not provided, when the hydrogen concentration (dissolution amount S) in the hydrogen permeable metal existing around the grain boundary increases, the hydrogen in the grain boundary The partial pressure rises more quickly. And the grain boundary wall surface is expanded by the pressure rise in a grain boundary, and the growth from a grain boundary to an empty bubble advances.

  According to the fuel cell of this example configured as described above, in the hydrogen permeable metal layer 22, the high solubility coefficient portion 52 is disposed in the vicinity of the interface with the electrolyte layer 21, so that the hydrogen permeable metal layer Even when the protonation activity in the catalyst layer 54 is insufficient with respect to the amount of hydrogen atoms that permeate through 22, the high solubility coefficient portion 52 absorbs excess hydrogen atoms, thereby generating hydrogen near the interface. It is possible to suppress the generation of air bubbles caused by molecules. Thus, in the vicinity of the interface between the hydrogen permeable metal layer 22 and the electrolyte layer 21, the generation of air bubbles due to the generation of hydrogen molecules is suppressed, so that the gap between the hydrogen permeable metal layer 22 and the electrolyte layer 21 is reduced. It is possible to suppress a decrease in the durability of the fuel cell due to the peeling of the fuel cell and a decrease in the effective area between the hydrogen permeable metal layer 22 and the electrolyte layer 21.

  Although the hydrogen storage alloy has an excellent function of storing hydrogen according to the surrounding hydrogen concentration, the diffusion coefficient of hydrogen is smaller than that of palladium. That is, the hydrogen permeation rate inside is slower than that of palladium. Therefore, in order to increase the hydrogen permeation rate in the entire hydrogen permeable metal layer 22 and ensure the fuel cell performance, it is desirable to form the high solubility coefficient portion 52 sufficiently thin. Therefore, the thickness of the high solubility coefficient portion 52 may be appropriately set in consideration of the balance between the hydrogen permeation rate in the hydrogen permeable metal layer 22 and the effect of the high solubility coefficient portion 52 absorbing hydrogen. .

D. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

D1. Modification 1:
In the embodiment, the high solubility coefficient portion 52 formed on the hydrogen permeable layer 50 is formed in a continuous layer shape using a hydrogen storage alloy, but may be formed in a discontinuous shape. For example, it can be formed in a plurality of layers dissociated from each other formed on the surface of the hydrogen permeable layer 50, so-called islands. In order to form the high solubility coefficient portion 52 in an island shape, when the high solubility coefficient portion 52 is formed by sputtering, PVD, or CVD as in the embodiment, the high solubility coefficient portion 52 is sufficiently thin, for example, 0. What is necessary is just to form by thickness about 0.01-0.1 micrometer.

  Even in the case where the hydrogen storage alloy is arranged in a so-called island shape, in the portion where the hydrogen storage alloy is arranged, the solubility coefficient K in the equation (1) is increased similarly to the example, so that the hydrogen content at the grain boundary or the like is increased. The increase in pressure is suppressed and the growth of air bubbles is suppressed. Further, when the hydrogen storage alloy is arranged in an island shape, in the vicinity of the hydrogen storage alloy that is slightly away from the arranged hydrogen storage alloy, many hydrogen atoms dissolve in the hydrogen storage alloy, so The hydrogen concentration dissolved in the hydrogen permeable metal is relatively lowered. That is, the dissolution amount S becomes small in the above-described equation (1). Therefore, even in such a region, the hydrogen partial pressure at the grain boundary is suppressed, and the growth of air bubbles is suppressed at the entire interface of the hydrogen permeable metal layer 22. As described above, even if the shape is other than the layer shape, the effect of suppressing the bubble growth can be obtained if the high solubility coefficient portion is arranged in the vicinity of the grain boundary. In the case where the hydrogen storage alloy is arranged in an island shape, in order to obtain a sufficient effect of suppressing bubble growth over the entire interface of the hydrogen permeable metal layer 22, the degree of dispersion of the hydrogen storage alloy is increased. It is desirable to do.

D2. Modification 2:
In the embodiment, the catalyst layer 54 is formed so as to cover the entire interface with the electrolyte layer 21 in the hydrogen permeable metal layer 22, but may have a different shape. For example, the catalyst layer 54 may be formed in a so-called island shape on the high solubility coefficient portion 52 formed in a continuous layer shape as in the embodiment. It suffices if the hydrogen permeable metal layer 22 has an activity to protonate hydrogen atoms at the interface with the electrolyte layer 21, and by providing the high solubility coefficient portion 52 in the vicinity of such a catalyst layer, the protonation activity can be increased. When it becomes insufficient, the generation of air bubbles at the interface can be suppressed.

  Further, the catalyst layer 54 may be composed of a noble metal other than palladium, as long as it has an activity of protonating hydrogen atoms. Here, when the precious metal used has protonation activity but does not have sufficient hydrogen permeation performance, the catalyst layer 54 may be formed in a so-called island shape rather than as a dense film.

D3. Modification 3:
In the embodiment, the high solubility coefficient portion 52 is made of a so-called hydrogen storage alloy, but the high solubility coefficient portion 52 may be made of a different material, and the hydrogen solubility is higher than the average value of the entire hydrogen permeable metal layer 22. If the high solubility coefficient portion 52 is made of a material having a high coefficient, the same effect can be obtained. The material constituting the high solubility coefficient portion 52 may be a material other than metal. For example, the high solubility coefficient portion 52 may be constituted by a carbon-based adsorbent (activated carbon, carbon nanotube, carbon nanohorn, etc.). In order to form the high solubility coefficient portion 52 made of these carbon-based adsorbents, the carbon-based adsorbent is formed on the hydrogen permeable layer 50 by PVD such as PLD method or aerosol deposition method using the carbon-based adsorbent as a film forming material. A film may be formed. Like the carbon-based adsorbent and the hydrogen storage alloy described above, the high solubility coefficient portion 52 is made of a material that retains more hydrogen inside as the surrounding hydrogen concentration increases and releases hydrogen as the surrounding hydrogen concentration decreases. If comprised, when continuing the electric power generation by a fuel cell, a predetermined effect can be repeatedly obtained.

D4. Modification 4:
In the embodiment, the hydrogen permeable layer 50 is formed of palladium, but may have a different configuration. For example, the hydrogen permeable layer 50 can be formed of a palladium alloy such as a Pd—Ag (23%) alloy. Alternatively, the hydrogen permeable layer 50 is formed on at least one surface of a layer made of a group 5 metal having hydrogen permeability such as vanadium (V), niobium (Nb), tantalum (Ta), or a group 5 metal alloy with a palladium layer. Or you may form by the laminated film in which the palladium alloy layer was formed. The palladium layer or the palladium alloy layer exhibits an activity of dissociating hydrogen by being disposed on the surface of the fuel gas flow channel 30 in the single cell. Examples of the layer made of a group 5 metal alloy include a V—Cr (15%) alloy and an Nb—Ni (10%) alloy.

D5. Modification 5:
In the embodiment, a perovskite solid oxide is used as the solid oxide constituting the electrolyte layer 21, but different types of solid oxides may be used. For example, pyrochlore type solid oxide such as La ₂ Zr ₂ O ₇ and Sm ₂ Zr _1.8 Y _0.2 O ₇ , monazite type solid oxide such as LaPO ₄ , aragonite type solid oxide such as LaBO ₃ , SiO ₂ —P ₂ Glass solid oxides such as O ₅ and SiO ₂ —H ₂ SO ₄ can be used. Even when these solid oxides are used, the same effect of suppressing the formation of air bubbles can be obtained by providing the high solubility coefficient portion 52 in the vicinity of the interface with the solid oxide in the hydrogen permeable metal layer.

D6. Modification 6:
In the embodiment, the hydrogen permeable metal layer 22 is formed as a metal thin film having hydrogen permeability, that is, a self-supporting film, but may have a different configuration. For example, hydrogen permeability can be obtained by supporting a hydrogen permeable metal on a plate member having gas permeability (such as a thin plate made of stainless steel with a large number of holes, or a porous body made of metal or ceramic). A metal layer can be formed. With such a configuration, the hydrogen permeable metal layer can be further reduced in thickness.

D7. Modification 7:
In the embodiment, the hydrogen permeable metal layer / electrolyte composite composed of the hydrogen permeable metal layer 22 and the electrolyte layer 21 is used in the solid oxide fuel cell, but it may be configured differently. For example, the same hydrogen-permeable metal layer / electrolyte complex as in the examples can be used in devices such as a hydrogen pump and a hydrogen concentration sensor. As an example, the configuration of a hydrogen pump provided with the hydrogen permeable metal layer / electrolyte complex of the present invention will be described below.

  FIG. 5 is a schematic cross-sectional view showing a schematic configuration of a hydrogen pump 220 including the hydrogen-permeable metal layer / electrolyte layer composite of the present invention. The hydrogen pump 220 has the same hydrogen permeable metal layer / electrolyte complex 23 as in the embodiment, and has a configuration similar to that of the single cell in the embodiment. The hydrogen pump 220 of FIG. 5 further includes an electrode 224, holders 227 and 229, and a power source 250 in addition to the hydrogen permeable metal layer / electrolyte complex 23.

  Here, the electrode 224 is formed in the same manner as the cathode 24 of the single cell 20. Further, the holders 227 and 229 have grooves having a predetermined shape on the surface thereof. In the hydrogen pump 220, the groove forms a mixed gas channel 230 or a hydrogen channel 232 between the holders 227 and 229 and the adjacent hydrogen permeable metal layer 22 or electrode 224. In the mixed gas channel 230, a mixed gas containing hydrogen supplied from the outside flows. In the hydrogen flow path 232, the hydrogen gas extracted from the mixed gas flows by the action of the hydrogen pump 220, and the hydrogen gas is discharged from the hydrogen flow path 232 to the outside of the hydrogen pump.

  The power source 250 is a DC constant voltage power source and is connected to the holders 227 and 229. The positive side of the power supply 250 is connected to the holder 229, and the negative side is connected to the holder 227. When the hydrogen pump 220 is driven, a mixed gas is supplied to the mixed gas flow path 230 while applying a voltage between both holders by the power source 250. Thereby, hydrogen in the mixed gas loses electrons in the hydrogen permeable metal layer 22 and moves as protons in the electrolyte layer 21, and the protons receive electrons again at the electrode 224 and become hydrogen gas. In this way, by using the hydrogen pump 220, high purity hydrogen is extracted from the mixed gas.

  As described above, the present invention is applied to an apparatus having an electrolyte layer having proton conductivity, and the durability of the apparatus is improved by including the hydrogen permeable metal layer / electrolyte layer composite of the present invention as the electrolyte layer. Can be made.

2 is a schematic cross-sectional view illustrating an outline of a configuration of a single cell 20. FIG. 3 is an enlarged schematic cross-sectional view of a hydrogen permeable metal layer 22. FIG. It is explanatory drawing showing the manufacturing process of MEA40. FIG. 3 is an explanatory diagram showing a state in the vicinity of an interface between a hydrogen permeable metal layer 22 and an electrolyte layer 21. 2 is a schematic cross-sectional view illustrating a schematic configuration of a hydrogen pump 220. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Single cell 21 ... Electrolyte layer 22 ... Hydrogen permeable metal layer 23 ... Electrolyte complex 24 ... Cathode 27, 29 ... Gas separator 30 ... Fuel gas flow path in single cell 32 ... Oxidized gas flow path in single cell 40 ... MEA
DESCRIPTION OF SYMBOLS 50 ... Hydrogen permeable layer 52 ... High solubility coefficient part 54 ... Catalyst layer 220 ... Hydrogen pump 224 ... Electrode 227,229 ... Holder 230 ... Mixed gas flow path 232 ... Hydrogen flow path 250 ... Power supply

Claims (6)

A hydrogen permeable metal layer / electrolyte composite,
A hydrogen permeable metal layer comprising a noble metal having an activity of protonating hydrogen atoms on one surface, wherein the hydrogen permeable metal layer has a higher hydrogen solubility coefficient than the average value of the hydrogen solubility coefficient. A hydrogen permeable metal layer having a high solubility coefficient portion made of a solubility coefficient material in the vicinity of the one surface;
A hydrogen permeable metal layer / electrolyte composite comprising: an electrolyte layer formed on the one surface of the hydrogen permeable metal layer and made of a solid oxide having proton conductivity. The hydrogen-permeable metal layer / electrolyte composite according to claim 1,
The high solubility coefficient material retains more hydrogen inside as the surrounding hydrogen concentration increases and releases hydrogen as the surrounding hydrogen concentration decreases. Hydrogen permeable metal layer / electrolyte composite. The hydrogen-permeable metal layer / electrolyte composite according to claim 2,
The high solubility coefficient material is a hydrogen storage alloy. Hydrogen permeable metal layer / electrolyte composite. The hydrogen-permeable metal layer / electrolyte composite according to claim 2,
The high solubility coefficient material is a carbon-based adsorbent. Hydrogen permeable metal layer / electrolyte composite. The hydrogen-permeable metal layer / electrolyte composite according to claim 1,
The high solubility coefficient portion is formed in a continuous layer shape in the vicinity of the interface with the electrolyte layer in the hydrogen permeable metal layer,
The hydrogen permeable metal layer includes the noble metal in a region on the high solubility coefficient portion and including an interface with the electrolyte layer. Hydrogen permeable metal layer / electrolyte complex. A fuel cell,
A hydrogen permeable metal layer / electrolyte composite according to any one of claims 1 to 5,
A cathode electrode provided on the electrolyte layer,
A fuel cell in which a fuel gas containing hydrogen flows is formed on the hydrogen permeable metal layer, and an oxidizing gas channel containing oxygen is formed on the cathode electrode.

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