JP6275561B2 - BODY, BODY MANUFACTURING METHOD, SOLID OXIDE FUEL CELL, AND WATER ELECTROLYTIC DEVICE - Google Patents

Description

  The present invention relates to a joined body, a manufacturing method of the joined body, a solid oxide fuel cell, and a water electrolysis apparatus.

  Conventionally, a solid oxide fuel cell using a solid electrolyte is known as a fuel cell. In a solid oxide fuel cell, a plurality of solid oxide fuel cells (sometimes referred to as single cells) each including a solid electrolyte layer, a fuel electrode, and an air electrode are usually used. In other words, a stack is formed by a large number of single cells, fuel gas is supplied to the fuel electrode, oxidant gas is supplied to the air electrode, and for example hydrogen in the fuel gas and oxygen in the oxidant gas, for example, are solid electrolytes. Electric power is generated by chemical reaction through the layers.

  For example, in a flat type solid oxide fuel cell, a plurality of single cells are stacked via an interconnector to form a stack. The air electrode and fuel electrode of each single cell and the interconnector are electrically connected via a current collector. The air electrode and the current collector are electrically connected by a bonding agent (sometimes referred to as a bonding layer). As the bonding agent, metal materials such as Pt and Ag, and conductive ceramics are used.

  For example, Patent Document 1 discloses a bonding agent including a transition metal oxide having a spinel crystal structure, and “a powder of each metal element constituting a spinel-based material is used as a starting material, and this powder is used during firing. By being oxidized, the bonding agent 300 having a spinel material is formed. The paste is sufficiently baked down because of the heat generated due to the oxidation reaction (= exothermic reaction) of the powder of each metal element. It is considered that this is based on the fact that the surface temperature rises locally and spinel crystals (composite oxide crystals) are synthesized and grown "(paragraph number 0034).

JP 2011-108621 A

  By the way, when the bonding agent represented by Patent Document 1 is used for bonding the air electrode and the current collector in the solid oxide fuel cell, only the initial electrical connection between the air electrode and the current collector is used. In addition, it is desirable that the electrical connection does not decrease over a long period of time. However, when the bonding agent described in Patent Document 1 is used, the thickness of the bonding agent in the direction from the air electrode toward the current collector decreases, and the electrical connection between the air electrode and the current collector decreases. Became clear by the inventors' research. This is considered to be due to the progress of sintering of the bonding agent by the operation of the solid oxide fuel cell.

  The present invention provides a joined body capable of maintaining an electrical connection between an air electrode and a current collector over a long period of time, a method for producing the joined body, a solid oxide fuel cell including the joined body, and It aims at providing the water electrolysis apparatus provided with the said joined_body | zygote.

Means for solving the problems are as follows:
(1) A solid electrolyte layer, a fuel electrode formed on one surface of the solid electrolyte layer, and an air electrode formed on the other surface of the solid electrolyte layer, the air electrode and the current collector Is a joined body joined by a joining layer,
The bonding layer includes a core inclusion particle having a core portion and a surface layer containing a conductive spinel oxide, and the core inclusion particle is disposed so as to allow conduction between the air electrode and the current collector. It is the joined body characterized by.

A preferred embodiment of (1) is as follows:
(2) The joined body according to (1), wherein the core-encapsulating particles include coarse core-encapsulating particles that extend from an interface between the joining layer and the air electrode to an interface between the joining layer and the current collector. It is.
(3) The bonding layer is the bonded body according to (1) or (2), in which a region between the core-encapsulating particles is porous.

Means for solving the another problem is as follows.
(4) a solid electrolyte layer, a fuel electrode formed on one surface of the solid electrolyte layer, and an air electrode formed on the other surface of the solid electrolyte layer, the air electrode and the current collector Is a method of manufacturing a joined body joined by a joining layer,
Including a joining step of placing and heating a joining paste containing a coarse metal powder and a fine metal powder between the air electrode and the current collector,
The coarse powder metal and the fine powder metal are metals that can react with oxygen to form a conductive spinel oxide, and the median diameter of the coarse powder is larger than the median diameter of the fine powder. This is a manufacturing method of the joined body.

Means for solving the another problem is as follows.
(5) A solid oxide fuel cell comprising the joined body according to any one of (1) to (3).

Means for solving the another problem is as follows.
(6) A water electrolysis apparatus including the joined body according to any one of (1) to (3).

  The bonding layer in the present invention includes core inclusion particles having a core portion and a surface layer, and these core inclusion particles are arranged so that the air electrode and the current collection portion can be conducted. The core-encapsulated particles are, for example, continuously disposed so that a plurality of core-encapsulated particles are in contact with each other from the interface between the bonding layer and the air electrode to the interface between the bonding layer and the current collector, and / or One core-encapsulated coarse particle extending from the interface between the bonding layer and the air electrode to the interface between the bonding layer and the current collector is disposed. The volume of the core-encapsulated particles is not greatly changed by sintering the bonding layer. Therefore, the connection between the air electrode and the current collector is maintained for a long period. The surface layer has conductivity because it contains a conductive spinel oxide. Therefore, in the bonding layer, the surface layer covering the core portion of the core-encapsulating particles serves as a flow path through which current flows, so that the air electrode and the current collector are electrically connected.

  Core-encapsulated particles having a core part and a surface layer can be produced by placing and heating a bonding paste containing a coarse metal powder and a fine metal powder between an air electrode and a current collecting part. it can. The surface layer of the core-encapsulated particles is a portion formed by the reaction of the surface portion of the coarse powder and the fine powder, and the core portion is a portion where the coarse powder does not react with the fine powder. Therefore, the size of the core-encapsulating particles depends on the size of the coarse powder contained in the bonding paste, and the core-encapsulating particles act like a support in the bonding layer. Even if there is no change and the thickness is reduced, the reduction amount is small. In addition, the thickness of the bonding paste and the bonding layer in the present specification refers to the length of the bonding paste and the bonding layer in the direction in which the single cells including the fuel electrode, the solid electrolyte layer, and the air electrode face each other.

  When the decrease in the thickness of the bonding layer relative to the bonding paste is large, when a solid oxide fuel cell stack is formed using a plurality of bonded bodies, the contact pressure between the air electrode, the bonding layer, and the current collector is mutually. Becomes small, and it becomes easy to peel off at these interfaces. In particular, when a solid oxide fuel cell stack is formed by laminating a plurality of assemblies and heating them in a state of being clamped at a predetermined pressure in the stacking direction of the assemblies, the tightening force in the stacking direction is loosened, The contact pressure between the bonding layer and the current collector is reduced, and peeling at these interfaces is remarkable. On the other hand, the thickness of the bonding layer in the present invention has almost no change with respect to the thickness of the bonding paste, and even after the solid oxide fuel cell stack is normally operated over a long period of time, the thickness of the bonding layer changes little. There is no. Therefore, since the mutual contact pressure among the air electrode, the bonding layer, and the current collector is maintained, it is difficult to peel off at these interfaces, and electrical connection can be ensured over a long period of time.

  Therefore, the joined body according to the present invention, the solid oxide fuel cell including the joined body, and the water electrolysis device can maintain electrical connection for a long period of time. Moreover, the manufacturing method of the conjugate | zygote which concerns on this invention can manufacture the conjugate | zygote which can maintain an electrical connection over a long period of time.

  Further, the bonding layer in the present invention has a porous region. Therefore, the air gap of the porous air electrode is not blocked by the bonding layer at the interface between the bonding layer and the air electrode, and the air permeability of the oxidant gas is secured in the bonding layer, and the oxidant gas is The air electrode can be sufficiently supplied.

FIG. 1 is a schematic perspective view showing an example of a solid oxide fuel cell stack in a solid oxide fuel cell of the present invention. FIG. 2 is a schematic cross-sectional explanatory view showing an XX cross section of the solid oxide fuel cell stack shown in FIG. FIG. 3 is an enlarged schematic cross-sectional view of a relevant part showing a joined body in the solid oxide fuel cell stack shown in FIG. FIG. 4 is a cross-sectional schematic explanatory diagram showing an enlarged view of a bonding layer in the bonded body shown in FIG. FIG. 5 is a schematic cross-sectional view showing another example of the solid oxide fuel cell stack in the solid oxide fuel cell of the present invention. FIG. 6 is a schematic cross-sectional explanatory view showing still another example of the solid oxide fuel cell stack in the solid oxide fuel cell of the present invention. FIG. 7 is an image obtained by photographing the cut surface of the sample of Example 1 with an SEM. FIG. 8 is a diagram obtained by mapping analysis with an image obtained by photographing the cut surface of the sample of Example 1 with EPMA. 8A is an image obtained by photographing the cut surface with EPMA, FIG. 8B is a diagram showing the concentration of Cu on the cut surface, and FIG. 8C is a diagram showing the concentration of Mn on the cut surface. FIG. 8D is a diagram showing the concentration of oxygen (O) on the cut surface.

  An embodiment of the solid oxide fuel cell according to the present invention will be described with reference to FIGS. A solid oxide fuel cell is a device that generates power by receiving supply of fuel gas and oxidant gas. The solid oxide fuel cell stack 100 shown in FIG. 1 is formed by stacking a plurality of plate-like single cells 1 as power generation units in series. As shown in FIG. 2, when the single cells 1 are stacked, the separators 51 are joined to the single cells 1, and the single cells 1 are stacked via the separators 51. Further, an interconnector 5 is provided between the single cells 1 and the end cells 52 and 53 are provided on both sides in the stacking direction of the single cells 1. As shown in FIG. 1, four columnar fixing members 12 to 15 are arranged in a cross section of the separator 51 joined to the single cell 1 so as to penetrate the end plates 52 and 53 in the stacking direction of the single cell 1. One is provided at each of the four corners of the substantially rectangular shape. Further, between the adjacent fixing members 12 to 15 and the fixing members 12 to 15, a hollow columnar fuel gas introduction pipe 16, a fuel gas outlet pipe 17, an oxidant gas introduction pipe 18, in the stacking direction of the single cells 1, And an oxidant gas outlet pipe 19 is provided. The solid oxide fuel cell stack 100 together with other devices forms a solid oxide fuel cell capable of generating electric power by being housed in a storage container (not shown). As long as the storage container does not impair the power generation performance of the solid oxide fuel cell stack 100, a conventionally known container can be used.

  The solid oxide fuel cell stack 100 includes a fixing member 12 to 15, a fuel gas introduction pipe 16, a fuel gas outlet pipe 17, an oxidant gas introduction pipe 18, and an oxidant gas outlet pipe 19. The laminated body of the several single cell 1 is integrated by applying pressing force to the end plates 52 and 53 using such a fastening member. The fuel gas introduction pipe 16, the fuel gas lead-out pipe 17, the oxidant gas lead-in pipe 18, and the oxidant gas lead-out pipe 19 have a plurality of the same as the fixing members 12 to 15 in addition to the gas lead-in / out function. It also has a function of integrating the laminated body of the single cells 1.

  As shown in FIG. 3, the unit cell 1 includes a solid electrolyte layer 2, a fuel electrode 3 formed on one surface of the solid electrolyte layer 2, and an air electrode formed on the other surface of the solid electrolyte layer 2. 4. The single cell 1 in the solid oxide fuel cell of this embodiment is a rectangular plate, but the shape is not particularly limited, and may be a disk. A current collector 6 is provided between the air electrode 4 and the interconnector 5, and the air electrode 4 and the current collector 6 are joined via a joining layer 7. A joined body 11 according to the present invention includes a single cell 1, a joining layer 7, and a current collector 6.

  The solid electrolyte layer 2 has ion conductivity capable of moving the oxidant gas introduced into the air electrode 4 as ions during operation of the solid oxide fuel cell. The solid electrolyte layer 2 can be formed of at least one of yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), samaria-added ceria (SDC), gadria-added ceria (GDC), and the like.

  The fuel electrode 3 is formed on the surface of the solid electrolyte layer 2 opposite to the surface on which the air electrode 4 is formed. As long as the fuel electrode 3 is in contact with a fuel gas such as hydrogen gas and functions as an anode in the fuel cell, the structure and material thereof are not particularly limited. The fuel electrode 3 has a porous structure and is formed so that fuel gas can pass therethrough. Examples of the material forming the fuel electrode 3 include zirconia ceramics such as zirconia stabilized by at least one of metals such as Ni and Fe and rare earth elements such as Y and Sc.

The air electrode 4 is formed on the surface of the solid electrolyte layer 2 opposite to the surface on which the fuel electrode 3 is formed. The structure and material of the air electrode 4 are not particularly limited as long as the air electrode 4 is in contact with an oxidant gas such as air and functions as a cathode in the fuel cell. The air electrode 4 has a porous structure and is formed so that an oxidant gas can pass therethrough. Examples of the material for forming the air electrode 4 include metals, metal oxides, metal composite oxides, and the like. Examples of the metal include metals such as Pt, Au, Ag, Pd, Ir, Ru, Ru, and alloys containing two or more metals. Examples of the metal oxide include oxides such as La, Sr, Ce, Co, Mn, and Fe, such as La ₂ O ₃ , SrO, Ce ₂ O ₃ , Co ₂ O ₃ , MnO ₂ , and FeO. . As the composite oxide, a composite oxide containing at least one of La, Pr, Sm, Sr, Ba, Co, Fe, Mn, etc., for example, a La _1-x Sr _x CoO ₃ based composite oxide ( LSC), La _1-x Sr _x FeO ₃ composite oxide (LSF), La _1-x Sr _x Co _1-y Fe _y O ₃ composite oxide (LSCF), La _1-x Sr _x MnO ₃ system Examples include composite oxides, Pr _1-x Ba _x CoO ₃ composite oxides (PBC), and Sm _1-x Sr _x CoO ₃ composite oxides (SSC). The air electrode 4 may be formed of a plurality of layers made of the above-described materials, for example. The thickness of the air electrode 4 is preferably 30 μm or more and 100 μm or less.

  The separator 51 is provided around the single cell 1. As shown in FIG. 1, when the outer shape of the cross section of the solid oxide fuel cell stack 100 is rectangular, the separator 51 is placed on four sides of the rectangle shown in the cross section of the solid oxide fuel cell stack 100. It is formed in a frame plate shape along. The separator 51 is provided so as to separate the fuel gas chamber 31 through which the fuel gas flows and the oxidant gas chamber 41 through which the oxidant gas flows. The separator 51 is made of, for example, stainless steel such as SUS430, nickel base alloy, chromium base alloy, conductive ceramic, or the like.

  The interconnector 5 is a plate-like body, and is provided between the adjacent single cells 1 and has a function of taking out the current generated in the single cells 1 to an external circuit. The interconnector 5 is formed of the same material as the separator 51.

  The current collectors 6 and 8 include a current collector 6 on the air electrode 4 side that electrically connects the air electrode 4 and the interconnector 5, and a fuel electrode that electrically connects the fuel electrode 3 and the interconnector 5. And a three-side current collector 8. The current collectors 6 and 8 are provided between the air electrode 4 and the fuel electrode 3 and the interconnector 5, and the structure and material thereof are not particularly limited as long as they can be electrically connected. The current collectors 6, 8 have a shape that can be joined to at least a part of one surface of the air electrode 4 or the fuel electrode 3, and as such a shape, for example, viewed from a direction orthogonal to the stacking direction It is comb-shaped in a state where it is joined to the interconnector 5, and has a grid shape in which a plurality of rectangular bodies are aligned at a predetermined interval when viewed from the stacking direction, and is corrugated when viewed from a direction orthogonal to the stacking direction. Examples include corrugated plate shapes. The current collectors 6, 8 may be integrally formed of the same material as the interconnector 5, or may be formed of a conductive material different from the interconnector 5, and may be connected to the interconnector 5 by a brazing material or the like. It may be joined. The current collectors 6 and 8 are formed of a metal foam, metal felt, metal mesh, conductive ceramic porous body, etc. having a porous structure in order to relieve stress caused by the difference in thermal expansion coefficient of each member. Preferably it is done.

  The current collector 6 on the air electrode 4 side and the current collector 8 on the fuel electrode 3 side may be formed of the same structure and the same material, or may be different from each other. As shown in FIG. 3, the current collector 6 on the air electrode 4 side has, for example, a plurality of protrusions protruding from one surface of the interconnector 5, and a plurality of ones are formed on one surface of the interconnector 5. Forms are provided so as to be arranged in a grid pattern with a predetermined interval, and are formed so that an oxidant gas flows through a concave portion between the convex portions. As with the current collector 6 on the air electrode 4 side, a plurality of current collectors 8 on the fuel electrode 3 side are provided on the opposite side of the interconnector 5 from the side on which the current collector 6 on the air electrode 4 side is provided. The rectangular bodies are provided so as to be arranged in a grid pattern at a predetermined interval, and are formed so that fuel gas flows through the recesses.

  The fuel electrode 3 and the current collector 8 on the fuel electrode 3 side are joined by a joining layer 7 ′ on the fuel electrode 3 side, and both are electrically connected. The joining layer 7 ′ on the fuel electrode 3 side is formed of a conductive material, and examples of the conductive material include metals such as Ni and conductive ceramics.

  The air electrode 4 and the current collector 6 on the air electrode 4 side (hereinafter also simply referred to as a current collector) may be referred to as a bonding layer 7 on the air electrode 4 side (hereinafter simply referred to as a bonding layer). The two are electrically connected to each other, and the bonding layer 7 is interposed on at least a part of the facing surfaces of the air electrode 4 and the current collector 6.

  Below, the joining layer 7 which joins the said air electrode 4 and the said current collection part 6 which is the characteristic part of the conjugate | zygote 11 concerning this invention is demonstrated in detail. FIG. 4 is a cross-sectional schematic explanatory diagram showing an enlarged view of a bonding layer in the bonded body shown in FIG.

  The bonding layer 7 includes a core inclusion particle 21 having a core portion 22 and a surface layer 23 containing a conductive spinel oxide covering the core portion 22, and the core inclusion particle 21 is connected to the air electrode 4 and the collector. It arrange | positions so that electrical connection with the electric part 6 is possible. As shown in FIG. 4, the core inclusion particles 21 included in the bonding layer 7 include a plurality of core inclusions from the interface 9 between the bonding layer 7 and the air electrode 4 to the interface 10 between the bonding layer 7 and the current collector 6. The particles 21 b may be continuously arranged so as to be in contact with each other, or extend from the interface 9 between the bonding layer 7 and the air electrode 4 to the interface 10 between the bonding layer 7 and the current collector 6. A single core-encapsulating coarse particle 21a may be in a state of being disposed. Since the core-encapsulated particles 21 include an oxide having a spinel crystal structure in which the surface layer 23 has conductivity, at least the surface layer 23 has conductivity. Therefore, in the portion where the plurality of core-encapsulated particles 21b are continuously arranged so as to be in contact with each other, the surface layer 23 of the plurality of core-encapsulated particles 21b serves as a current flow path from the air electrode 4 to the current collector 6. In the portion where the current flows and one core-encapsulated coarse particle 21 a is disposed, the surface layer 23 of the one core-encapsulated coarse particle 21 a serves as a current flow path from the air electrode 4 to the current collector 6. Therefore, electrical connection is ensured between the air electrode and the current collector.

  The bonding layer 7 has the same length in the thickness direction of the bonding layer 7 of the core inclusion particles 21 appearing in a cross section when the bonding layer 7 is cut in the thickness direction of the bonding layer 7, that is, the direction in which the single cells 1 face each other. It is preferable to include the core inclusion particle 21 that is one-sixth or more of the thickness of the bonding layer 7 in the cross section, and more preferably to include the core inclusion particle 21 that is one-third or more. The inclusion of the core-encapsulating particles 21 is particularly preferable. In particular, it is preferable that almost all of the core-encapsulated particles 21 included in the bonding layer 7 have a size in the above range, for example, 90% or more of the core-encapsulated particles have a size in the above range. The core inclusion particles 21 preferably include core inclusion particles having the same length as the thickness of the bonding layer 7. That is, the bonding layer 7 preferably includes the core-encapsulated coarse particles 21a, and more preferably the core-encapsulated coarse particles 21a are dispersed in the bonding layer 7. For example, when the thickness of the bonding layer 7 is 30 μm, the length in the thickness direction of the bonding layer 7 of the core inclusion particles 21 is preferably in the range of 5 to 30 μm. It is preferable to include at least the core-encapsulating coarse particles 21a having a length in the thickness direction of 30 μm.

  As will be described later, the core-encapsulated particles 21 included in the bonding layer 7 are heated by placing a bonding paste containing a coarse metal powder and a fine metal powder between the air electrode 4 and the current collector 6. Can be formed. The surface layer 23 is a portion formed by a reaction between the surface portion of the coarse powder and the fine powder, and the core portion 22 is a portion where the coarse powder does not react with the fine powder. Therefore, the size of the core inclusion particles 21 depends on the size of the metal coarse powder contained in the bonding paste. When the bonding layer is formed by the bonding paste containing only the metal fine powder, the metal fine powder is completely reaction-sintered and densified, and the thickness of the bonding layer is smaller than the thickness of the coating layer of the bonding paste. On the other hand, the bonding layer 7 in the present invention is formed of a bonding paste containing a metal coarse powder and includes core-encapsulating particles 21 having a core portion 22. The thickness of the bonding layer 7 hardly changes with respect to the paste. That is, the thickness of the bonding paste disposed between the air electrode 4 and the current collector 6 and the thickness of the bonding layer 7 formed by heating this are almost unchanged, and even if the thickness decreases, The amount of decrease is small.

  When forming the solid oxide fuel cell stack 100, as will be described later, a plurality of the joined bodies 11 are stacked via the interconnector 5, and the joined bodies 11 are clamped by the fastening members attached to the fixing members 12 to 15. The laminated body of the joined body 11 is integrated by heating in a state of being tightened at a predetermined pressure in the laminating direction. At this time, if the amount of decrease in the thickness of the bonding layer 7 is larger than the thickness of the bonding paste disposed between the air electrode 4 and the current collector 6, the fixing members 12 to 12 in the solid oxide fuel cell stack 100. 15 and the tightening force of the tightening member is loosened, the contact pressure between the air electrode 4, the bonding layer 7, and the current collector 6 is reduced, and separation at these interfaces 9 and 10 is facilitated. End up. On the other hand, the bonding layer 7 in the present invention has little change in the thickness of the bonding layer 7 with respect to the bonding paste before and after the heating of the solid oxide fuel cell stack 100, and hardly changes. Furthermore, the thickness of the bonding layer 7 hardly changes even after the solid oxide fuel cell stack 100 is normally operated over a long period of time. Therefore, the air electrode 4, the bonding layer 7, and the current collector 6 are in close contact with each other, and the contact pressure between the air electrode 4, the bonding layer 7, and the current collector 6 is maintained. 10 is difficult to peel off, thereby suppressing an increase in contact resistance and securing electrical connection over a long period of time.

  The thickness of the bonding layer 7 and the length in the thickness direction of the bonding layer 7 of the core inclusion particles 21 can be determined as follows. A portion including the air electrode 4, the bonding layer 7, and the current collector 6 is cut at an arbitrary surface in a direction in which the single cells 1 face each other. An image of the obtained cut surface is obtained by SEM (scanning electron microscope) or the like, and in the obtained image, an interface 9 between the air electrode 4 and the bonding layer 7 and an interface 10 between the current collector 6 and the bonding layer 7 are obtained. Are measured at at least five arbitrary positions. An arithmetic average of the measured values can be calculated and used as the thickness of the bonding layer 7. In addition, the length in the thickness direction of the bonding layer 7 of the core inclusion particles 21 can be obtained by measuring the maximum length in the thickness direction of the bonding layer 7 for all the core inclusion particles 21 present on the image. .

The surface layer 23 is provided on the surface of the core portion 22 and includes a conductive spinel oxide. The conductive spinel oxide is a metal oxide having a spinel crystal structure and is not particularly limited as long as it has conductivity. The conductive spinel oxide is an oxide represented by a composition formula of AB ₂ O ₄ and has two sites where cations called A site and B site are arranged in the crystal. As each metal element which occupies A site and B site, at least 1 type selected from the group which consists of Cu, Mn, Co, Fe, Cr, Ni, Zn etc. can be mentioned. Examples of the conductive spinel oxide include CuMn ₂ O ₄ , MnCo ₂ O ₄ , CoMn ₂ O ₄ , MnFe ₂ O ₄ , ZnMn ₂ O ₄ , CuFe ₂ O ₄ , NiMn ₂ O ₄ , and CoCr ₂ O _4. Etc. Among these, CuMn ₂ O ₄ is preferably contained in the surface layer 23 in terms of high conductivity. A part of the A site and the B site may be substituted with a metal element other than the metal elements described above. The surface layer 23 is entirely or mostly formed of a conductive spinel oxide, but may include a metal composed of the above-described metal element and / or an oxide other than the spinel oxide.

As will be described later, the core portion 22 may be formed by heating coarse metal particles contained in the bonding paste. Accordingly, the core portion 22 includes a metal that forms the coarse particles and / or a metal oxide that is formed by oxidizing the metal. The core portion 22 may be uniformly formed of the metal or the metal oxide. When the core portion 22 includes the metal and the metal oxide, the metal and the metal oxide are included. Things may be mixed with each other and in a dispersed state. Further, the core portion 22 is different from the metal or the metal oxide forming the central portion in a form such as a composition and a crystal structure so as to cover the central portion formed of the metal or the metal oxide. One or more layers may be formed. For example, the center part of the core part 22 may be formed with the said metal, and the outer peripheral part of this center part may be formed with the said metal oxide. Examples of the metal include metals or alloys containing at least one element selected from the group consisting of elements such as Cu, Mn, Co, Fe, Cr, Ni, and Zn. Examples of the metal oxide include metal oxides exemplified as the metal. Examples of the metal oxide include CuO, MnO ₂ , Mn ₃ O ₄ , CoO, Co ₂ O ₃ , FeO, Fe ₂ O ₃ , Cr ₂ O ₃ , NiO, and ZnO. The core part 22 is entirely or mostly formed of the metal and / or the metal oxide, and a part thereof may include a conductive spinel oxide included in the surface layer 23. .

As will be described later, the region 24 between the core-encapsulated particles 21 and the core-encapsulated particles 21 can be formed by heating fine metal particles contained in the bonding paste. Since the fine particles are almost completely reaction-sintered, the region 24 is entirely or mostly formed of a metal oxide formed by oxidizing the metal forming the fine particles. Examples of the metal oxide include metal oxides containing at least one element selected from the group consisting of elements such as Cu, Mn, Co, Fe, Cr, Ni, and Zn. Examples of the metal oxide include CuO, MnO ₂ , Mn ₃ O ₄ , CoO, Co ₂ O ₃ , FeO, Fe ₂ O ₃ , Cr ₂ O ₃ , NiO, and ZnO. When the fine particles remain without being completely reacted and sintered, the region 24 may contain a metal that forms the fine particles. In addition, a conductive spinel oxide included in the surface layer 23 may be included in the region 24. The region 24 is preferably formed of a conductive material. However, as described above, the bonding layer 7 has a flow path through which current flows due to the conductive spinel oxide included in the surface layer 23. Therefore, it is not necessary to have conductivity.

  Substances forming the core portion 22, the surface layer 23, and the region 24 can be specified as follows. First, a portion including the air electrode 4, the bonding layer 7, and the current collector 6 is cut at an arbitrary surface in a direction in which the single cells 1 face each other, and the obtained cut surface is photographed with EPMA and an element. Perform mapping analysis. The obtained image confirms the core inclusion particles 21 having the core portion 22 and the surface layer 23 and the region 24 around the core inclusion particles 21. By quantifying the element concentration after element mapping, the concentration of the element present in each of the core portion 22, the surface layer 23, and the region 24 is measured. Next, the cut surface is analyzed by an X-ray diffractometer (XRD), and the substance contained in the bonding layer 7 is identified. The substance contained in the bonding layer 7 is identified by comparing an X-ray diffraction chart obtained by XRD analysis with, for example, a JCPDS card. Next, based on the element detected by EPMA and the substance identified by XRD analysis, the substance forming each of the core portion 22, the surface layer 23, and the region 24 is specified. For example, when element A and B element are detected on the surface layer 23 by element mapping analysis by EPMA, and a diffraction peak of a spinel oxide containing A element and B element is confirmed by XRD, the surface layer 23 Can be determined to contain a spinel oxide containing an A element and a B element.

  The region 24 is porous. Since the region 24 is porous, the gap between the porous air electrode 4 is not blocked by the bonding layer 7 at the interface 9 between the bonding layer 7 and the air electrode 4. The air permeability of the oxidant gas is ensured, and the oxidant gas can be sufficiently supplied to the air electrode 4.

  The bonding layer 7 preferably has a porosity of 15 to 35%. As the porosity of the bonding layer 7 decreases, the air permeability of the oxidant gas deteriorates at the interface 9 between the bonding layer 7 and the air electrode 4, and as the porosity increases, the bonding layer 7 and the air electrode 4 The contact resistance at the interface 9 tends to increase and the conductivity tends to decrease. When the porosity is within the above range, it is possible to ensure both the air permeability of the oxidant gas in the bonding layer 7 and the maintenance of conductivity.

  Most of the pores in the bonding layer 7 are present in the region 24 between the core inclusion particles 21. When the coarse metal powder and the fine metal powder contained in the bonding paste are reaction-sintered, the coarse powder is arranged to form the core inclusion particles 21 having the core portion 22 and form the skeleton of the bonding layer 7. The In the region 24 between the core-containing particles 21 arranged so as to form a skeleton, the fine powder is reacted and sintered to reduce the volume and form pores. Therefore, the porosity can be adjusted by changing the particle size distribution, sintering conditions, etc. of the coarse powder and the fine powder.

  The porosity can be determined as follows. First, an image of the cut surface of the bonding layer 7 is obtained in the same manner as when the thickness of the bonding layer 7 is measured. In the obtained image, a line segment is drawn from one end of the image to the other end, and a plurality of line segments parallel to the line segment are drawn at intervals of, for example, 1 to 2 μm. What is necessary is just to set the space | interval of a line segment suitably according to the magnitude | size of a pore. The total length L of the pores existing on all the line segments and the total length Lt of all the line segments are measured, and the total length L of the pores with respect to the total length Lt of all the line segments is calculated. Calculated [(L / Lt) × 100] (%) and set this as the porosity.

  The bonding layer 7 preferably contains the core inclusion particles 21 in an area ratio of 10 to 35% on the cut surface of the bonding layer 7. When the bonding layer 7 contains the core-encapsulated particles 21 in the area ratio within the above range, the amount of decrease in the thickness of the bonding layer 7 with respect to the bonding paste before and after the heating of the solid oxide fuel cell stack 100 is further reduced. Thereby, the electrical conductivity between the air electrode 4 and the current collector 6 can be maintained over a long period of time.

  The area ratio of the core-encapsulated particles 21 can be obtained as follows. First, an image of the cut surface of the bonding layer 7 is obtained in the same manner as when the thickness of the bonding layer 7 is measured. In the obtained image, the core-containing particles 21 and other portions, that is, the regions 24 are distinguished and binarized. The total area S identified as the core inclusion particles 21 and the area St of the entire image are measured, and the total area S of the core inclusion particles 21 with respect to the area St including pores in the bonding layer 7 in the image is calculated [ (S / St) × 100] (%), which is the area ratio of the core-encapsulating particles 21.

  The bonding layer 7 includes core inclusion particles 21 having a core portion 22 and a surface layer 23, and the core inclusion particles 21 are arranged so that the air electrode 4 and the current collector 6 can be conducted. Accordingly, the bonding layer 7 has little change in the thickness of the bonding layer 7 with respect to the bonding paste before and after the heating of the solid oxide fuel cell stack 100, and hardly changes. Furthermore, the thickness of the bonding layer 7 hardly changes even after the solid oxide fuel cell stack 100 is normally operated over a long period of time. Therefore, the air electrode 4, the bonding layer 7, and the current collector 6 are in close contact with each other, and the contact pressure between the air electrode 4, the bonding layer 7, and the current collector 6 is maintained. Therefore, it is difficult to peel off at these interfaces 9 and 10, thereby suppressing an increase in contact resistance. Therefore, the solid oxide fuel cell provided with the joined body 11 can exhibit desired performance over a long period of time.

  Next, an example of a method for producing a solid oxide fuel cell according to the present invention will be described below.

  The method of manufacturing a solid oxide fuel cell according to this embodiment includes a bonding step of placing and heating a bonding paste including a coarse metal powder and a fine metal powder between the air electrode and the current collector. Including.

  The pre-process of the joining process includes a preparation process for preparing a joining paste, and a laminating process for forming a laminate by laminating the single cell 1 and the interconnector 5 including the current collector 6 via the joining paste. Including.

In the preparation step, a bonding paste including a coarse metal powder and a fine metal powder is prepared. The coarse powder metal and the fine powder metal are metals that can react with oxygen to form a conductive spinel oxide. Examples of the metal of the coarse powder and the fine powder include a metal powder containing an element that can occupy at least one of the A site and the B site in the spinel oxide represented by the composition formula of AB ₂ O _4. Examples thereof include metal powders containing at least one element selected from the group consisting of Cu, Mn, Co, Fe, Cr, Ni, Zn and the like. For example, when a metal made of an element that easily occupies the A site is adopted as the metal of the coarse powder, a metal made of an element that easily occupies the B site is adopted as the metal of the fine powder. Therefore, the type of the metal of the coarse powder is usually different from the type of the metal of the fine powder. The fine powder is preferably a metal having a melting point lower than that of the coarse powder. When the fine powder has a melting point lower than that of the coarse powder, when the bonding paste is heated and subjected to reaction sintering, the fine powder metal is likely to melt and become a liquid phase. It becomes easy to react. Examples of the combination of the coarse powder metal and the fine powder metal include Mn and Cu, and Mn and Co.

  The coarse powder has a median diameter larger than that of the fine powder. The median diameter of the coarse powder is, for example, 6 to 15 μm. When the coarse powder has a median diameter larger than that of the fine powder and the median diameter is larger than 6 μm, only the surface portion of the coarse particles easily reacts with the fine powder when the bonding paste is heated and subjected to reaction sintering. It becomes easy to form the core-containing particles 21 having the core portion 22 and the surface layer 23. When the bonding paste contains coarse powder having a specific particle size, the thickness of the bonding layer 7 can be made difficult to change with respect to the thickness of the coating layer of the bonding paste. That is, the thickness of the bonding layer 7 that makes it difficult to change the thickness of the bonding layer 7 with respect to the thickness of the bonding paste coating layer varies depending on the particle size of the coarse powder. Therefore, the median diameter of the coarse powder may be appropriately determined according to the required thickness of the bonding layer 7. For example, when the required thickness of the bonding layer 7 is 30 μm, the median diameter of the coarse powder is preferably 6 to 10 μm. The median diameter of the fine powder only needs to react with the surface portion of the coarse powder. For example, the median diameter of the fine particles is 0.5 to 5 μm. The median diameter of the coarse powder and the fine powder can be measured using a laser diffraction particle size distribution analyzer. The median diameter is a particle diameter corresponding to 50% cumulative when the particle size distribution of the powder is expressed as a cumulative distribution, and is based on volume. When the particle size distribution of the metal powder containing the coarse powder and the fine powder is measured by a laser diffraction particle size distribution measuring device, the particle size of the coarse powder and the fine powder is different to the extent that two peaks appear. preferable.

  The coarse powder and the fine powder are preferably blended at a ratio of 2: 1 (mass ratio) to 1: 2 (mass ratio). When the coarse powder and the fine powder are blended in the above ratio, it is easy to form the core-encapsulated particles 21 having the core portion 22 and the surface layer 23, and the core-encapsulated particles 21 in a predetermined ratio are formed in the bonding layer 7. As a result, the core-encapsulated particles 21 serve as support columns of the bonding layer 7 and the amount of decrease in the thickness of the bonding layer 7 with respect to the thickness of the bonding paste is reduced.

  You may add a binder, a solvent, and another additive to the said joining paste as needed. Examples of the binder include methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral and the like. Examples of the solvent include ethanol, butanol, terpineol, acetone, xylene, toluene, vehicle, and the like. Examples of the other additive include a dispersant and a plasticizer.

  In the laminating step, first, the single cell 1 is manufactured by a conventionally known method, and the bonding is performed on at least one of the outer surface of the air electrode 4 and the surface of the current collector 6 facing the air electrode 4 in the single cell 1. After the paste is applied by screen printing or the like and dried at 80 ° C. to 150 ° C. as necessary to form a coating layer, the interconnector 5 having the single cell 1, the bonding paste coating layer, and the current collector 6; Are stacked to form a laminate.

  As an example of the manufacturing method of the single cell 1, first, the raw material powder having the components of the fuel electrode 3, the organic beads as the pore former, the butyral resin, the plasticizer, the dispersant, and the solvent are mixed to form a slurry. The prepared slurry is coated on a support by a doctor blade method or the like and dried to prepare a fuel electrode green sheet. Further, the green sheet for the solid electrolyte layer is produced in the same manner as the green sheet for the fuel electrode. Next, the obtained green sheet for fuel electrode and the obtained green sheet for solid electrolyte layer are laminated and sintered to produce a sintered laminate. Next, the paste prepared from the raw material powder having the components of the air electrode 4 described above is applied on the solid electrolyte layer 2 in the sintered laminate by screen printing or the like to form a paste layer. The air electrode 4 is formed by sintering. In this way, the single cell 1 is manufactured.

  In the joining step, the laminated body obtained in the laminating step is heated to join the air electrode 4 and the interconnector 5 provided with the current collector 6 via the joining layer 7.

  In the joining step, for example, a plurality of laminated bodies obtained in the laminating step are laminated as desired to form an assembly. The assembled body is tightened by a fastening member attached to the fixing members 12 to 15 penetrating in the stacking direction of the stacked body, and pressure in the stacking direction is applied to the assembled body. With the pressure applied, the assembly is put into an electric furnace or the like and heated to maintain a predetermined temperature in a temperature range of 600 ° C. or higher and 900 ° C. or lower, preferably 750 ° C. or higher and 850 ° C. or lower. 3 is maintained for 2 hours to 10 hours while a fuel gas is supplied to the air electrode 3 and an oxidant gas is supplied to the air electrode 4, and the joining paste is sintered by a reactive sintering method. Bonding is performed with the bonding layer 7. The bonding paste coating layer has a core having a surface layer 23 containing a conductive spinel oxide by reacting the surface portion of the coarse powder particles contained in the bonding paste with the fine powder after the bonding step. The encapsulated particles 21 are formed, and the fine powders react to form a porous region 24 containing a metal oxide, thereby forming the bonding layer 7.

The joining step may be performed on a laminated body in which at least the single cell 1, the joining paste, the current collector 6 and the interconnector 5 are laminated, or on an assembled body in which a plurality of the laminated bodies are laminated. You may go.
In the joining step, the laminate or the assembly may be heated with an electric furnace or the like, but after the solid oxide fuel cell stack 100 is assembled, the solid oxide fuel cell stack 100 is operated. The solid oxide fuel cell stack 100 may be heated by its own heat generation, and the air electrode 4 and the interconnector 5 including the current collector 6 may be joined via the joining layer 7.

  According to the method for manufacturing a solid oxide fuel cell of this embodiment, the core-containing particles 21 having the core portion 22 and the surface layer 23 are disposed so that the air electrode 4 and the current collector 6 can be electrically connected. Layer 7 can be manufactured easily. Therefore, according to the method for manufacturing the solid oxide fuel cell of this embodiment, the amount of decrease in the thickness of the bonding layer 7 with respect to the thickness of the bonding paste can be reduced. Thus, a solid oxide fuel cell capable of ensuring electrical connection with the battery 6 can be easily manufactured.

  The solid oxide fuel cell of the present invention can be used for various applications as a battery capable of outputting a high voltage. The solid oxide fuel cell of the present invention can be used, for example, as a power generation source in a small cogeneration system for home use or as a power generation source in a large cogeneration system for business use.

  The solid oxide fuel cell of the present invention is not limited to the above-described embodiment, and various modifications can be made within a range in which the object of the present invention can be achieved. For example, the single cell 1 in the solid oxide fuel cell is a rectangular plate-like body, but may be a cylindrical body as shown in FIG. 5 or a flat cylindrical body as shown in FIG.

  As shown in FIG. 5, a single cell 101 of a cylindrical solid oxide fuel cell includes, for example, a solid electrolyte layer 102 and an air electrode 104 stacked in this order on the outer peripheral surface of a cylindrical fuel electrode 103. The interconnector 105 is provided on the surface of the fuel electrode 103 in which the cell 101 is formed and is not covered with the solid electrolyte layer 102 and the air electrode 104. A current collector 106 is provided between the single cell 101 and the single cell 101. The current collector 106 is joined to the fuel electrode 103 of one single cell 101 via an interconnector 105, and the other single cell 101 is connected. The adjacent single cells 101 are connected in series to form a solid oxide fuel cell stack 110 by being bonded to the air electrode 104 via the bonding layer 107 of the present invention.

  As shown in FIG. 6, the unit cell 201 in the solid oxide fuel cell having a flat cylindrical body has a substantially elliptic cylindrical shape, and includes a support substrate 211 including a flat portion and arc-shaped portions on both sides of the flat portion. . Both surfaces of the flat portion are formed substantially parallel to each other, and the fuel electrode 203 and the solid electrolyte layer 202 are laminated in this order so as to cover one surface of the flat portion of the support substrate 211 and the arc-shaped portions on both sides. A single cell 201 is formed by laminating an air electrode 204 on the solid electrolyte layer 202 on the surface. In addition, an interconnector 205 is provided on the surface of the flat portion not covered with the fuel electrode 203 and the solid electrolyte layer 202. A current collector 206 is provided between the single cell 201 and the single cell 201. The current collector 206 is joined to the support substrate 211 via the interconnector 205, and is connected to the air electrode 204 of the other single cell 201. Bonded via the inventive bonding layer 207, whereby adjacent unit cells 201 are connected in series to form a solid oxide fuel cell stack 210.

  The solid oxide fuel cell of the present invention can be used as a water electrolysis apparatus for electrolyzing water and producing hydrogen by carrying out the reverse reaction. For example, by supplying water vapor to the fuel electrode side and supplying power between the fuel electrode and the air electrode, the water vapor of the fuel electrode is electrolyzed, oxygen is generated on the air electrode side, and oxygen is generated on the fuel electrode side. Hydrogen is generated. Therefore, the solid oxide fuel cell provided with the joined body of the present invention can be used as a water electrolysis device.

<Example 1>
[Preparation of sample]
(Preparation of bonding paste)
20 g (median diameter 8 μm) of coarse powder, 30 g of Cu (median diameter 2.7 μm) as fine powder, and 50 g of vehicle as solvent were stirred with a spatula and mixed three times with three rolls. A paste was obtained. The vehicle was prepared by mixing Etocel 4CPS and butyl carbitol in a ratio of 1: 4. The median diameter of the coarse powder and the fine powder was measured with a laser diffraction particle size distribution analyzer (HORIBA LA-750).

(Production of single cell)
To the YSZ powder (100 parts by weight), a butyral resin, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol were added and mixed in a ball mill to prepare a slurry. A green sheet for a solid electrolyte layer having a thickness of 10 μm was prepared from the obtained slurry by a doctor blade method.

  Organic beads (10% by weight with respect to the mixed powder) as a pore former, butyral resin, with respect to the mixed powder (100 parts by weight) of NiO powder (60 parts by weight) and YSZ powder (40 parts by weight) Then, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol were added and mixed by a ball mill to prepare a slurry. A green sheet for a fuel electrode having a thickness of 250 μm was prepared from the obtained slurry by a doctor blade method.

  The fuel electrode green sheet and the solid electrolyte layer green sheet were laminated and sintered to produce a sintered laminate.

  On the solid electrolyte layer of the sintered laminate, a paste prepared by LSCF fine powder, etosel as an organic binder and butyl carbitol as a solvent is applied by screen printing to the surface of the solid electrolyte layer in the sintered laminate. A paste layer was formed, and the paste layer was sintered at 1000 ° C. to form an air electrode having a thickness of 30 μm. A single cell 1 was thus obtained.

(Production of interconnector with current collector)
A plate material made of stainless steel was cut to produce an interconnector 5 having a current collecting portion 6 in which prismatic projections were arranged in a grid pattern on one side of the plate material at a predetermined interval.

(Application of bonding paste)
A bonding paste was printed on the entire surface of the current collector 6 of the interconnector 5 facing the air electrode 4 by screen printing. Subsequently, it was dried at 100 ° C. for 30 minutes to obtain an interconnector 5 having a current collector 6 on which a bonding paste was printed. The thickness of the bonding paste was measured with a micrometer and found to be 32 μm.

(Production of solid oxide fuel cell stack)
The air electrode 4, the bonding paste, the current collector 6, and the interconnector 5 in the single cell 1 were laminated so as to be in this order to form a laminate. Six laminates were laminated to form an assembly, and the assembly was clamped by a fastening member attached to a fixing member penetrating in the stacking direction, and pressure in the stacking direction was applied to the assembly. . This assembly is put into an electric furnace or the like and heated up, and kept at 850 ° C. for 3 hours while flowing hydrogen into the fuel electrode 3 and air into the air electrode 4, and the air electrode 4 and the current collector 6 are joined to each other. A solid oxide fuel cell stack 100 was obtained as a sample joined in Step 7.

[An endurance test]
Assuming normal operation of the solid oxide fuel cell, put the sample in an electric furnace with an ambient temperature of 750 ° C., and conduct an energization treatment for 1000 hours in a current density range of 0.3 to 0.6 A / cm ^2. Went.

[Observation of bonding layer]
As shown in FIG. 7, after the endurance test, the cut surface obtained by cutting the sample along the plane in the stacking direction was photographed with an SEM (1000 times), and in the obtained SEM image, the air electrode 4 and the bonding layer 7. The distance between the interface 9 and the current collector 6 and the interface 10 between the bonding layer 7 was measured at 20 arbitrary positions. When the arithmetic average of these measured values was calculated as the thickness of the bonding layer 7, it was 30 μm. The thickness of the bonding layer 7 was 2 μm less than the thickness of the bonding paste. This reduction in thickness is due to volatilization of the solvent contained in the bonding paste.

  As shown in FIG. 7, in the SEM image, a plurality of core-encapsulated particles 21 having a core portion 22 and a surface layer 23 were confirmed. In these core-encapsulated particles 21, coarse core-encapsulated particles 21 a extending from the interface 9 between the air electrode 4 and the bonding layer 7 to the interface 10 between the bonding layer 7 and the current collector 6 were confirmed. The length in the thickness direction of the bonding layer 7 of the core-encapsulated particles 21 observed in the SEM image was in the range of 4 to 32 μm. The area ratio [(S / St) × 100] (%) of the total area S of the core-encapsulating particles 21 to the area St including pores in the bonding layer 7 in the image was 39 area%. It was.

  Moreover, it was confirmed from the SEM image that the region 24 around the core-encapsulated particles 21 is porous. In the SEM image, a plurality of line segments were drawn at intervals of 2 μm, and the porosity was measured as described above to be 22.5%.

[Analysis of bonding layer]
The cut surface obtained by cutting the sample along the plane in the stacking direction was subjected to image photographing and element mapping analysis with EPMA. 8A is an image obtained by photographing the cut surface with EPMA, FIG. 8B is a diagram showing the concentration of Cu on the cut surface, and FIG. 8C is a diagram showing the concentration of Mn on the cut surface. FIG. 8D is a diagram showing the concentration of oxygen (O) on the cut surface. As shown in FIG. 8 (a), core-encapsulated particles 21 having a core part 22 and a surface layer 23 on the cut surface are observed, as shown in FIGS. 8 (b), (c) and (d). Mn oxide was detected in the core portion 22, Mn oxide and Cu oxide were detected in the surface layer 23, and Cu oxide was detected in the region 24 around the core inclusion particles 21.
Further, the bonding layer 7 on the cut surface was analyzed from 2θ = 10 ° to 80 ° by XRD (manufactured by Rigaku Corporation: RINT-TTRIII). As a result, diffraction peaks corresponding to CuO and spinel oxide (for example, CuMn ₂ O ₄ , Mn ₃ O ₄ ) were obtained.
Since Mn, Cu and O were detected on the surface layer 23 by the mapping analysis and a diffraction peak of CuMn ₂ O ₄ was confirmed by the XRD analysis, the surface layer 23 had CuMn ₂ O ₄ which is a conductive spinel oxide. Is determined to be included.
Mn and O were detected in the core part 22 by the mapping analysis, and the diffraction peak of Mn ₃ O ₄ was confirmed by the XRD analysis. Therefore, it is determined that the core part 22 contains Mn ₃ O ₄ .
Cu and O were detected in the region 24 around the core-encapsulated particles 21 by the mapping analysis, and the diffraction peak of CuO was confirmed by the XRD analysis. Therefore, it is determined that the region contains CuO.

[Evaluation of conductivity]
Before and after the endurance test, the sample was supplied with 1 L / min of hydrogen containing 3% water at room temperature (25 ° C.) on the fuel electrode 3 side and 2 L / min of air on the air electrode 4 side at an ambient temperature of 700 ° C. The difference between the voltage when the current was passed between the current collector 6 on the air electrode 4 side and the current collector on the fuel electrode 3 side and the voltage when the current was turned off was measured by the current interruption method. . As the current interruption method measuring instrument, KIKUSUI FC IMPEDANCE METER KFM2150 was used. In order to subtract the load, a loader of KIKUSUI PLZ 1004W was also used. While subtracting a 20 A load from the sample with a loader, the voltage was measured by the current interruption method, and the average value of the measured values of the six laminates was determined as the average voltage. A high voltage means a low electrical resistance. The average voltage of the sample before the durability test was 802 mV, the average voltage of the sample after the durability test was 800 mV, and the average voltage deterioration rate was 0.25%.

<Comparative Example 1>
In the above-mentioned “Preparation of bonding paste”, the same procedure as in Example 1 was used except that Mn fine powder (median diameter: 3.2 μm) and Cu fine powder (median diameter: 2.7 μm) were used as starting materials. A sample was prepared.
As a result of measuring the thickness of the bonding paste in the same manner as in Example 1, it was 29 μm.

  The durability test was conducted in the same manner as in Example 1, and the thickness of the bonding layer after the durability test was measured. As a result, it was 16 μm. When the cut surface of the bonding layer after the durability test was observed with an SEM, the core-encapsulated particles observed in the bonding layer of Example 1 could not be confirmed and had a dense structure.

  The conductivity of the samples before and after the durability test was evaluated in the same manner as in Example 1. The average voltage of the sample before the durability test was 802 mV, the average voltage of the sample after the durability test was 777 mV, and the average voltage deterioration rate was 3.11%.

In the sample of Example 1, the bonding layer 7 is formed using a bonding paste including a metal coarse powder and a metal fine powder, and the bonding layer 7 includes core-encapsulated particles 21 each having a core portion 22 and a surface layer 23. As a result, the amount of decrease in thickness between the bonding paste and the bonding layer 7 was small. The core-encapsulated particles 21 are relatively large, and there are also core-encapsulated particles 21 having a size equivalent to the thickness direction of the bonding layer 7. The amount of decrease in the thickness of the layer 7 is small. Moreover, since the core inclusion particle 21 has the core part 22 and is difficult to sinter, the outer shape of the core inclusion particle 21 is maintained even after the endurance test, and the reduction in thickness is small.
On the other hand, in the sample of Comparative Example 1, since the joining layer is formed using a joining paste that contains only fine metal powder and does not contain coarse metal powder, the joining paste is densified by sintering. The amount of decrease in thickness was larger than that in Example 1.
The sample of Example 1 has a low average voltage deterioration rate before and after the durability test and maintains conductivity, whereas the sample of Comparative Example 1 has a higher average voltage deterioration rate than the sample of Example 1. , Conductivity is reduced.
From these results, compared with the sample of Comparative Example 1 in which the amount of decrease in the thickness of the bonding layer is large before and after the durability test, the sample of Example 1 in which the amount of decrease in the thickness of the bonding layer is small, the average voltage deterioration rate is small. It can be seen that conductivity is maintained.

1, 101, 201 Single cell 2, 102, 202 Solid electrolyte layer 3, 103, 203 Fuel electrode 4, 104, 204 Air electrode 5, 105, 205 Interconnector 6, 8, 106, 206 Current collector 7, 107 207 Bonding layer 9, 10 Interface 11 Bonded body 12, 13, 14, 15 Fixing member 16 Fuel gas introduction pipe 17 Fuel gas outlet pipe 18 Oxidant gas inlet pipe 19 Oxidant gas outlet pipe 21, 21a, 21b Core inclusion particle 22 Core portion 23 Surface layer 24 Region 31 Fuel gas chamber 41 Oxidant gas chamber 51 Separator 52, 53 End plates 100, 110, 210 Solid oxide fuel cell stack 211 Support substrate

Claims (6)

A joined body having a solid electrolyte layer, a fuel electrode, and an air electrode, wherein the air electrode and the current collector are joined by a joining layer,
The bonding layer includes a core inclusion particle having a core portion and a surface layer containing a conductive spinel oxide, and the core inclusion particle is disposed so as to allow conduction between the air electrode and the current collector. A joined body characterized by.   2. The joined body according to claim 1, wherein the core-encapsulated particles include coarse core-encapsulated particles that extend from an interface between the joining layer and the air electrode to an interface between the joining layer and the current collector.   The joined body according to claim 1 or 2, wherein the joining layer has a porous region between the core-containing particles. A method for producing a joined body having a solid electrolyte layer, a fuel electrode, and an air electrode, wherein the air electrode and the current collector are joined by a joining layer,
Including a joining step of placing and heating a joining paste containing a coarse metal powder and a fine metal powder between the air electrode and the current collector,
The coarse powder metal and the fine powder metal are metals that can react with oxygen to form a conductive spinel oxide, and the median diameter of the coarse powder is larger than the median diameter of the fine powder. A method for manufacturing a joined body.   A solid oxide fuel cell comprising the joined body according to claim 1.   The water electrolysis apparatus provided with the joined body as described in any one of Claims 1-3.

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