JP6572731B2 - Fuel cell stack - Google Patents

Description

  The present invention relates to a fuel cell stack, and more particularly to a fuel cell stack using a solid electrolyte as an electrolyte.

  Conventionally, as disclosed in Patent Document 1, a fuel cell stack in which flat fuel cell single cells each having an anode, a solid electrolyte layer, and a cathode are sandwiched by a separator is known. This document describes a technique of inserting a metal connecting member having a tongue piece in contact with the cathode surface between the two in order to maintain good contact between the cathode side separator and the fuel cell single cell. .

JP 2007-265896 A

  However, in general, a fuel cell stack that uses a solid electrolyte as an electrolyte is generally operated at about 700 ° C. to 900 ° C. Therefore, in the fuel cell stack, as the use at a high temperature proceeds, the metal connection member deteriorates due to creep, and the contact resistance between the cathode and the separator increases. Therefore, it is difficult for the fuel cell stack to improve power generation efficiency and durability.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a fuel cell stack that is advantageous for improving power generation efficiency and durability.

One aspect of the present invention, the first conductive oxide (41) or with the first conductive oxide and zirconium oxide-based oxide by Ri configured cathode (23), a plurality utilizing a solid electrolyte as the electrolyte A flat plate fuel cell single cell (2),
A metal separator (3) interposed between the fuel cell single cells, provided with a current collector (31), and provided with a coating layer (32) composed of a second conductive oxide (42) on the surface thereof; ,
A contact layer (4) disposed between the cathode and the separator,
The contact layer has an inner layer (40a) chemically bonded to the cathode and an outer layer (40b) chemically bonded to the inner layer and the covering layer;
The inner layer is composed Ri by third conductive oxide (43) and said first conductive oxide,
The outer layer is composed Ri by said third conductive oxide and the second conductive oxide,
The first conductive oxide is at least one transition metal perovskite oxide selected from the group consisting of lanthanum strontium cobaltite, lanthanum strontium iron cobaltite, and lanthanum strontium manganite,
The second conductive oxide is a manganese cobalt-based oxide having a spinel structure,
The third conductive oxide, Ri lanthanum nickel ferrite der,
The volume ratio of the third conductive oxide and the second conductive oxide in the outer layer is in the range of 6: 4 to 9: 1.
The volume ratio of the third conductive oxide and the first conductive oxide in the inner layer is in the range of 6: 4 to 9: 1.
It is in the fuel cell stack (1).

According to the fuel cell stack, the inner of the contact layer between the cathode and the separator is configured Ri by said third conductive oxide and the first conductive oxide. That is, the same material as the first conductive oxide contained in the cathode is combined with the third conductive oxide in the inner layer. Further, the outer layer is composed Ri by said third conductive oxide and said second conductive oxide in the contact layer. That is, in the outer layer, the same material as the second conductive oxide constituting the coating layer on the separator surface is combined with the third conductive oxide. Therefore, in the fuel cell stack, the sinterability at the interface between the inner layer and the cathode and the interface between the outer layer and the separator is promoted by heat treatment at the time of manufacture, and the bonding between the inner layer and the cathode by the chemical bond, And the separator are firmly joined. In addition, since the inner layer and the outer layer both contain the same third conductive oxide and are the same material, the bonding property between them is high. Therefore, the fuel cell stack is advantageous in that the contact resistance at the interface between the inner layer and the cathode and the interface between the outer layer and the separator is reduced, and the power generation efficiency and durability are improved. Since the contact layer is formed of a conductive oxide, it does not creep at the operating temperature like metal. Therefore, the contact layer can suppress microstructural changes during durability. Therefore, the fuel cell stack is advantageous in improving durability from this viewpoint.

  In addition, the code | symbol in the parenthesis described in the means to solve a claim and a subject shows the correspondence with the specific means as described in embodiment mentioned later, and limits the technical scope of this invention. It is not a thing.

FIG. 3 is an explanatory diagram schematically showing a part of a cross section in the fuel cell stack of Embodiment 1. FIG. 3 is an explanatory view schematically showing a microstructure around a contact layer in the fuel cell stack of Embodiment 1.

(Embodiment 1)
The fuel cell stack according to Embodiment 1 will be described with reference to FIGS. 1 and 2. As illustrated in FIGS. 1 and 2, the fuel cell stack 1 of the present embodiment includes a plurality of flat plate fuel cell single cells 2, a separator 3 interposed between the fuel cell single cells 2, and a cathode 23. The contact layer 4 is disposed between the separator 3 and the inner layer 40a and the outer layer 40b.

  The fuel cell single cell 2 is a solid electrolyte fuel cell that uses a solid electrolyte as an electrolyte. A fuel cell using solid oxide ceramics as a solid electrolyte is called a solid oxide fuel cell (SOFC). Specifically, the single fuel cell 2 has an anode 21, a solid electrolyte layer 22, and a cathode 23.

  In the present embodiment, an example in which an intermediate layer 24 is further provided between the solid electrolyte layer 22 and the cathode 23 is shown. The intermediate layer 24 is a layer mainly for suppressing the reaction between the cathode material and the solid electrolyte layer material. Moreover, although the example in which the anode 21 is composed of a single layer is shown, it may be composed of a plurality of layers. When the anode 21 is composed of a plurality of layers, the anode 21 includes an active layer (not shown) disposed on the solid electrolyte layer 22 side and a diffusion layer (not illustrated) disposed on the active layer opposite to the solid electrolyte layer 22 side. It is possible to adopt a configuration having The active layer is mainly a layer for enhancing the electrochemical reaction on the anode side. The diffusion layer is a layer capable of diffusing the supplied fuel gas. Specifically, the single fuel cell 2 is an anode support type in which an anode 21 as an electrode is a support.

  In the fuel cell unit cell 2, as an anode material, for example, a catalyst such as Ni or NiO and a solid electrolyte such as a zirconium oxide oxide such as yttria stabilized zirconia (YSZ) or scandia stabilized zirconia (ScSZ) are used. A mixture etc. can be illustrated. NiO becomes Ni in a reducing atmosphere during power generation. In the present embodiment, specifically, the anode material can be Ni or a mixture of NiO and yttria-stabilized zirconia. From the viewpoints of gas diffusion, electrical resistance, strength, and the like, the thickness of the anode 21 is preferably 100 to 800 μm, and more preferably 200 to 700 μm, for example.

  As the solid electrolyte used as the electrolyte in the fuel cell single cell 2, for example, the above-mentioned zirconium oxide-based oxide can be suitably used. As the solid electrolyte, yttria-stabilized zirconia is preferable from the viewpoints of ion conductivity, mechanical stability, compatibility with other materials, chemical stability in a fuel gas atmosphere, and the like. The thickness of the solid electrolyte layer 22 is preferably 3 to 20 μm, more preferably 5 to 15 μm, from the viewpoint of reducing ohmic resistance.

In the fuel cell unit 2, the intermediate layer material, for example, CeO _2, or, Gd in _{CeO 2, Sm, Y, La} , Nd, Yb, Ca, and one or more selected from Ho Examples include cerium oxide-based oxides such as ceria-based solid solutions doped with these elements. These can be used alone or in combination of two or more. The thickness of the intermediate layer 24 is preferably 1 to 20 μm, more preferably 5 to 15 μm, from the viewpoints of reducing ohmic resistance and suppressing element diffusion from the cathode 23.

In the single fuel cell 2, the cathode 23 includes a first conductive oxide 41. The first conductive oxide 4 1, specifically, lanthanum strontium cobaltite (hereinafter, sometimes referred to as "LSC".), Lanthanum strontium iron cobaltite (hereinafter, sometimes referred to as "LSCF".), And , lanthanum strontium manganite Ru least one transition metal Perubusukaito type oxide der selected from the group consisting of (hereinafter also referred to as "LSM".). If this is advantageous to the cathode active improvements. Moreover, the cathode 23 may contain the said zirconium oxide type oxide. The thickness of the cathode 23 is preferably 20 to 100 μm, more preferably 30 to 80 μm, from the viewpoints of gas diffusibility, electrode reaction resistance, current collection, and the like. The LSC mentioned above is specifically La _1-X Sr _X CoO _3-δ (0.2 ≦ X ≦ 0.7), and the LSCF is specifically La _1-X Sr _X Co _{1. -Y Fe Y O 3-δ (} 0.2 ≦ X ≦ 0.7,0.5 ≦ Y ≦ 0.95), LSM , _{specifically, La 1-X Sr X MnO} 3-δ (0 .1 ≦ X ≦ 0.5).

The separator 3 is made of metal. The metal includes an alloy. Specific examples of the metal constituting the separator 3 include ferritic stainless steel, ferritic heat-resistant chromium alloy, and the like. The separator 3 includes a current collector 31 and a coating layer 32 made of a second conductive oxide 42 on the surface thereof. The multi-layer 32 may cover part of the surface of the current collector 31 such as the tip of the current collector 31 or may cover the entire surface of the current collector 31. Specifically, the current collector 31 exemplifies, for example, a protrusion such as an emboss formed on the surface of the separator 3, a current collector (not shown) such as a stainless mesh provided on the surface of the separator 3, and the like. be able to. That is, as for the separator 3, a part of separator body may have a current collection function, or the current collector may be provided in the separator 3 separately. In the present embodiment, the current collector 31 is a protrusion such as an emboss formed on the surface of the separator 3. In addition, it is made into the channel | path of oxidant gas between protrusion parts.

The second conductive oxide 4 2, specifically, manganese cobalt oxide having a spinel type structure (hereinafter sometimes referred to as "MC".) Ru Der. Manganese cobalt-based oxides prevent Cr from transpiration when the separator 3 contains Cr, and are effective in suppressing Cr poisoning of the cathode 23. Therefore, in this case, it is advantageous for suppressing Cr poisoning of the cathode 23. Incidentally, MC, _{specifically, Mn 3-X Co X O} 4 can be (1.5 ≦ X ≦ 2).

In the contact layer 4, the inner layer 40a is in contact with the cathode 23 is configured Ri good third conductive oxide 43 and the first conductive oxide 4 1. On the other hand, the outer layer 40b is in contact with the inner layer 40a and the cover layer 32 is composed Ri good third conductive oxide 43 and the second conductive oxide 4 2.

The third conductive oxide 4 3 in the contact layer 4, specifically, run-Tan nickel ferrite (hereinafter, sometimes referred to as "LNF".) Ru Der. Lanthanum nickel ferrite has a lower electrical resistance than other conductive oxides. Therefore, in this case, the electron conductivity of the skeleton of the contact layer 4 can be ensured, and an electron conduction path between the cathode 23 and the separator 3 can be easily secured. Therefore, in this case, it becomes easy to obtain the fuel cell stack 1 that is advantageous for improving the power generation efficiency, coupled with the above-described effects. Incidentally, LNF, _{specifically,} may be a _{LaNi 1-X Fe X O 3} -δ (0.3 ≦ X ≦ 0.7).

The first conductive oxide 41 in the inner layer 40 a is the same as the first conductive oxide 41 in the cathode 23. In the case where the first conductive oxide 41 is as described above, it is easy to suppress an increase in electrical resistance of the inner layer 40a. In particular, when the third conductive oxide 43 is LNF, the first conductive oxide 41 is composed of the above-described conductive oxide, thereby improving the bondability between the inner layer 40a and the cathode 23, and the inner layer 40a. This is advantageous for reducing the contact resistance at the interface with the cathode 23. The second conductive oxide 42 in the outer layer 40b is the same as the second conductive oxide 42 in the coating layer 32. When the second conductive oxide 42 is as described above, it is easy to suppress an increase in the electrical resistance of the outer layer 40b. In particular, when the third conductive oxide 43 is LNF, the second conductive oxide 42 is made of the above-described MC, thereby improving the bonding property between the outer layer 40b and the separator 3, and the outer layer 40b and the separator 3 This is advantageous for reducing the contact resistance at the interface. The “same thing” mentioned above does not require that the chemical compositions are strictly the same, but may be the same as the conductive oxide even if the chemical compositions are different. means. For example, La _0.6 Sr _0.4 CoO _3-δ and La _0.4 Sr _0.6 CoO _3-δ have different chemical compositions. However, these are all lanthanum strontium cobaltite and are evaluated as being of the same type. The same applies to other conductive oxides. The “same thing” mentioned above includes those having different particle diameters.

  In the fuel cell stack 1, the inner layer 40 a has a lower concentration of the first conductive oxide 41 from the cathode 23 side toward the separator 3 side, and the outer layer 40 b is a second layer from the separator 3 side toward the cathode 23 side. It can be set as the structure where the density | concentration of the conductive oxide 42 becomes low. In this case, a large amount of the same material as that of the first conductive oxide 41 included in the cathode 23 can be present near the interface with the cathode 23 in the inner layer 40a. Further, a large amount of the same material as the second conductive oxide 42 contained in the coating layer 32 on the surface of the separator 3 can be present near the interface with the separator 3 in the outer layer 40b. Therefore, in this case, the sinterability at the interface between the inner layer 40a and the cathode 23 and the interface between the outer layer 40b and the separator 3 is easily promoted, and the bonding between the inner layer 40a and the cathode 23, the outer layer 40b and the separator 3 It becomes easier to strengthen the bonding. Therefore, in this case, the contact resistance at the interface between the inner layer 40a and the cathode 23, and the outer layer 40b and the separator 3 is reliably reduced, and the fuel cell stack 1 that easily improves the power generation efficiency and durability can be obtained. . The concentration mentioned above can be measured by EDX or EPMA.

In the fuel cell stack 1, the volume ratio of the third conductive oxide 43 and the second conductive oxide 42 in the outer layer 40b is specifically in the range of 6 : 4 to 9: 1 . The volume ratio of the third conductive oxide 43 and the second conductive oxide 42 in the outer layer 40b can be preferably in the range of 6.5: 3.5 to 8.5 to 1.5. . In this case, since the third conductive oxide 43 forming the skeleton of the contact layer 4 can be sufficiently secured, it is easy to secure an electron conduction path in the outer layer 40b. At this time, according to the configuration in which the third conductive oxide 43 is LNF and the second conductive oxide 42 is MC, the electrical resistance of the outer layer 40b is lower because LNF has a lower electrical resistance than MC. The increase is easily suppressed, and the above effect can be easily obtained.

In the fuel cell stack 1, the volume ratio of the third conductive oxide 43 and the first conductive oxide 41 in the inner layer 40a is specifically in the range of 6 : 4 to 9: 1 . The volume ratio of the third conductive oxide 43 and the first conductive oxide 41 in the inner layer 40a can be preferably in the range of 6.5: 3.5 to 8.5 to 1.5. . In this case, since the third conductive oxide 43 that forms the skeleton of the contact layer 4 can be sufficiently secured, it is easy to secure an electron conduction path in the inner layer 40a. At this time, according to the configuration in which the third conductive oxide 43 is LNF and the first conductive oxide 41 is at least one selected from LSC, LSFC, and LSM, LNF is more than LSC or the like. Since the electric resistance is low, an increase in the electric resistance of the inner layer 40a can be easily suppressed, and the above effect can be easily obtained.

  In the fuel cell stack 1, the thickness of the outer layer 40b can be equal to or less than the thickness of the inner layer 40a, preferably less than the thickness of the inner layer 40a. In many cases, the second conductive oxide 42 has a higher electric resistance than the first conductive oxide 41. Therefore, in this case, it is easy to reduce the electrical resistance of the entire contact layer 4, and the fuel cell stack 1 that is advantageous for improving the power generation performance can be obtained.

  In the fuel cell stack 1, the thickness of the inner layer 40a is specifically 0.4 to 0.8 mm, preferably 0.5 to 0.6 mm, from the viewpoint of, for example, reduction in electrical resistance and bonding strength. It can be. Further, the thickness of the outer layer 40b can be specifically set to 0.1 to 0.4 mm, preferably 0.2 to 0.3 mm, for example, from the viewpoint of reduction of electric resistance, bonding strength, and the like. . Specifically, the thickness of the entire contact layer 4 can be set to 0.5 to 1.2 mm, preferably 0.7 to 0.9 mm, for example, from the viewpoint of reduction in electrical resistance, bonding strength, and the like. .

  The fuel cell stack 1 can be manufactured, for example, as follows, but is not limited thereto.

  A fuel cell single cell 2, a separator 3, an inner layer forming paste (not shown), and an outer layer forming paste (not shown) are prepared. Specifically, the inner layer forming paste may include a third conductive oxide powder, a first conductive oxide powder, and a binder. Specifically, the outer layer forming paste can include a third conductive oxide powder, a second conductive oxide powder, and a binder.

  Next, the outer layer forming paste is applied to the surface of the coating layer 32 in the current collector 31 of the separator 3 using a coating method such as a screen printing method. Next, an inner layer forming paste is applied to the surface of the applied outer layer forming application layer (not shown) to form an inner layer forming application layer (not shown). Next, the fuel cell single cells 2 and the separators 3 are alternately stacked to form a stack. At this time, the separator 3 is arranged so that the current collector 31 side faces the cathode 23 side of the single fuel cell 2. In addition, as for the fuel cell single cell 2, the cell outer periphery may be supported by the flame | frame (not shown). Alternatively, the inner layer forming paste and the outer layer forming paste can be sequentially applied to the position corresponding to the current collector 31 on the surface of the cathode 23 of the fuel cell single cell 2 and then stacked.

  Next, heat treatment is performed. Specifically, for example, the heat treatment is preferably performed at a temperature higher than the operating temperature of the fuel cell stack 1. In this case, when the fuel cell stack 1 is operated, it is difficult for changes in the bonding state at the interface between the inner layer 40a and the cathode 23 and the interface between the outer layer 40b and the separator 3 to occur, and the bonding stability is improved. When the operating temperature of the fuel cell stack 1 is 700 ° C., for example, the heat treatment temperature can be 850 ° C., for example. The heat treatment may be performed by increasing the temperature when the fuel cell stack 1 is operated, or may be performed separately from the temperature increase when the fuel cell stack 1 is operating.

According to the fuel cell stack 1, inner layer 40a of the contact layer 4 between the cathode 23 and the separator 3 is composed Ri goodness the third conductive oxide 43 and the first conductive oxide 4 1 . That is, the same material as the first conductive oxide 41 included in the cathode 23 is combined with the third conductive oxide 43 in the inner layer 40 a. Further, the outer layer 40b of the contact layer 4 is composed Ri goodness the third conductive oxide 43 and the second conductive oxide 4 2. In other words, the outer layer 40 b is composed of the same material as the second conductive oxide 42 constituting the coating layer 32 on the surface of the separator 3 in the third conductive oxide 43. Therefore, in the fuel cell stack 1, the sinterability at the interface between the inner layer 40a and the cathode 23 and the interface between the outer layer 40b and the separator 3 is promoted by heat treatment or the like during manufacture, and the inner layer 40a and the cathode are chemically bonded. The bonding between the outer layer 40b and the separator 3 becomes strong. Further, since the inner layer 40a and the outer layer 40b both include the same third conductive oxide 43 and are made of the same material as the skeleton, both have high bonding properties. Therefore, in the fuel cell stack 1, the contact resistance at the interface between the inner layer 40a and the cathode 23 and the interface between the outer layer 40b and the separator 3 is reduced, which is advantageous in improving the power generation efficiency and durability. Since the contact layer 4 is made of a conductive oxide, it does not creep at the operating temperature like a metal. Therefore, the contact layer 4 can suppress a change in the microstructure during durability. Therefore, the fuel cell stack 1 is also advantageous for improving durability from this viewpoint.

(Experimental example)
<Single fuel cell>
NiO powder (average particle size: 0.8 μm), 8YSZ powder (average particle size: 0.4 μm), carbon (pore forming agent), polyvinyl butyral (binder), isoamyl acetate, 2-butanol and ethanol ( A slurry was prepared by mixing the mixed solvent) with a ball mill. The mass ratio of NiO powder and 8YSZ powder was 60:40. The slurry was applied in a layer form on a plastic substrate using a doctor blade method and dried to prepare an anode forming sheet. The average particle diameter is the particle diameter (diameter) d50 when the volume-based cumulative frequency distribution measured by the laser diffraction / scattering method shows 50% (hereinafter the same).

Mixing yttria-stabilized zirconia (hereinafter 8YSZ) powder (average particle size: 0.4 μm) containing 8 mol% Y ₂ O ₃ , polyvinyl butyral, isoamyl acetate, 2-butanol and ethanol with a ball mill. A slurry was prepared. The slurry was applied in a layer form on a plastic substrate using a doctor blade method and dried to prepare a solid electrolyte layer forming sheet.

  For intermediate layer formation by mixing ceria (hereinafter, 10GDC) powder (average particle size: 0.8 μm) doped with 10 mol% Gd, ethyl cellulose (binder), and terpineol (solvent) with a ball mill. A paste was prepared.

A cathode forming paste was prepared by mixing LSC powder (La _0.6 Sr _0.4 CoO _3-δ , average particle size: 1 μm), ethyl cellulose, and terpineol with a ball mill.

  A solid electrolyte layer forming sheet was laminated on the anode forming sheet to obtain a laminate. The obtained laminate was pressure-bonded using a hydrostatic press (CIP) molding method, and then degreased. The CIP molding conditions were a temperature of 80 ° C., a pressing force of 50 MPa, and a pressing time of 10 minutes.

  The laminate was fired at 1350 ° C. for 2 hours. As a result, a sintered body in which the solid electrolyte layer (10 μm) was joined to the anode (400 μm) was obtained.

  The intermediate layer forming paste was printed on the surface of the solid electrolyte layer in the sintered body by a screen printing method and baked at 1100 ° C. for 120 minutes to form an intermediate layer (thickness 5 μm).

  A cathode forming paste was printed on the surface of the intermediate layer in the sintered body by a screen printing method and baked at 1000 ° C. for 2 hours to form a layered cathode (thickness: 60 μm).

  In this way, the anode, the solid electrolyte layer, the intermediate layer, and the cathode were laminated in this order and joined to each other, and a fuel cell single cell using the anode as a support was prepared.

<Separator>
A separator made of ferritic stainless steel was prepared. The separator has, on one side, a current collecting part made up of a plurality of protrusions and a coating layer (thickness 10 μm made of Mn _1.5 Co _1.5 O ₄ ) coated on the surface of the current collecting part. ing.

<Inner layer forming paste, outer layer forming paste>
Ethyl cellulose (binder) and terpineol (solvent) were blended at a mass ratio of 7: 3, and a vehicle was prepared using a kneader.

LNF powder (LaNi _0.6 Fe _0.4 O _3-δ , average particle size: 1.0 μm) and LSC powder (La _0.6 Sr _0.4 CoO _3-δ , average particle size: 1.0 μm) Was mixed at a volume ratio of 8: 2, and dry mixed with a ball mill to obtain a mixed powder A. Similarly, the above LNF powder and MC powder (Mn _1.5 Co _1.5 O ₄ , average particle diameter: 0.5 μm) were mixed at a volume ratio of 8: 2, and mixed by dry mixing in a ball mill. Powder B was obtained.

  The mixed powder A and the vehicle were blended at a mass ratio of 4: 5 and kneaded with three rolls to prepare an inner layer forming paste. Similarly, the mixed powder B and the vehicle were blended at a mass ratio of 4: 5 and kneaded with three rolls to prepare an outer layer forming paste.

<Fuel battery cell stack>
The outer layer forming paste and the inner layer forming paste were printed in this order on the surface of the coating layer at the front end of the current collector of the separator by using a screen printing method. Next, fuel cell single cells and separators were alternately stacked to form a stack. This was then heat treated at 850 ° C. for 2 hours. As a result, a fuel cell stack was obtained in which the cathode of the single fuel cell and the coating layer in the current collector of the separator were chemically bonded to the contact layer. The contact layer had a thickness of 0.7 mm, the inner layer had a thickness of 0.5 mm, and the outer layer had a thickness of 0.2 mm.

  The present invention is not limited to the above embodiments, and can be applied to various embodiments without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Fuel cell single cell 21 Anode 23 Cathode 3 Separator 31 Current collection part 32 Coating layer 4 Contact layer 40a Inner layer 40b Outer layer 41 1st conductive oxide 42 2nd conductive oxide 43 3rd conductive oxidation object

Claims (3)

The first conductive oxide (41) or with the first conductive oxide and zirconium oxide-based oxide by Ri configured cathode (23), a plurality of flat-plate utilizing a solid electrolyte as the electrolyte fuel cell single Cell (2);
A metal separator (3) interposed between the fuel cell single cells, provided with a current collector (31), and provided with a coating layer (32) composed of a second conductive oxide (42) on the surface thereof; ,
A contact layer (4) disposed between the cathode and the separator,
The contact layer has an inner layer (40a) chemically bonded to the cathode and an outer layer (40b) chemically bonded to the inner layer and the covering layer;
The inner layer is composed Ri by third conductive oxide (43) and said first conductive oxide,
The outer layer is composed Ri by said third conductive oxide and the second conductive oxide,
The first conductive oxide is at least one transition metal perovskite oxide selected from the group consisting of lanthanum strontium cobaltite, lanthanum strontium iron cobaltite, and lanthanum strontium manganite,
The second conductive oxide is a manganese cobalt-based oxide having a spinel structure,
The third conductive oxide, Ri lanthanum nickel ferrite der,
The volume ratio of the third conductive oxide and the second conductive oxide in the outer layer is in the range of 6: 4 to 9: 1.
The volume ratio of the third conductive oxide and the first conductive oxide in the inner layer is in the range of 6: 4 to 9: 1.
Fuel cell stack (1). The inner layer has a lower concentration of the first conductive oxide from the cathode side toward the separator side,
2. The fuel cell stack according to claim 1, wherein the outer layer has a lower concentration of the second conductive oxide from the separator side toward the cathode side. The fuel cell stack according to claim 1 or 2 , wherein a thickness of the outer layer is equal to or less than a thickness of the inner layer.

Images