JP6311952B1 - Interconnector, solid oxide fuel cell stack, and method for manufacturing solid oxide fuel cell stack - Google Patents

Abstract

The present specification discloses an interconnector. The interconnector disclosed in the present specification includes at least a first layer located on the fuel electrode side and a second layer located on the air electrode side, and the first layer is reducible. It has higher electrical conductivity and gas barrier properties than the second layer in the atmosphere, and the second layer has higher electrical conductivity and gas barrier properties than the first layer in the oxidizing atmosphere. Yes.

Description

  The present specification relates to an interconnector and use thereof.

  As a stack structure used in a solid oxide fuel cell (hereinafter, also simply referred to as SOFC), two or more cells including a fuel electrode layer, a solid electrolyte layer, and an air electrode layer are stacked via a separator layer. A stacked structure is disclosed (Patent Document 1).

  In addition, as an interconnection member (interconnector) for connecting SOFC cells, a member having a two-layer structure including a first layer containing a metallic conductive material and a second layer containing strontium titanate doped with lanthanum or the like Is disclosed (Patent Document 2). Furthermore, an interconnector is disclosed in which perovskite-type oxides such as strontium titanium ferrite doped with lanthanum or the like having different compositions so that the reduction expansion coefficients differ stepwise (Patent Document 3).

  The interconnector separates the oxidizing gas (typically air) from the reducing gas (typically a fuel gas such as hydrogen or methane) while physically and electrically connecting the single cells. It also serves as a separator.

International Publication No. 2009/119771 Special table 2010-515225 JP 2010-212036 A

  The interconnector interposed between the cells may be integrally sintered with the cells. For integral sintering of the interconnector and the cell, it is necessary to approximate the firing shrinkage and shrinkage behavior of the interconnector layer, fuel electrode layer, air electrode layer, and solid electrolyte layer. In particular, the material of the interconnector layer is not only electrically connected between the fuel electrode layer and the air electrode layer, but also has excellent conductivity, resistance to both gases and barrier properties for separation of reducing gas and oxidizing gas. Desired. Further, in an integrally sintered SOFC stack in which a plurality of cells are stacked by integral sintering, the performance of the interconnector is particularly important from the viewpoint of power generation characteristics and the like.

  Conventionally, a lanthanum-doped strontium titanate (LST) perovskite oxide has been used as an interconnector material. This material exhibits high conductivity in a reducing atmosphere, but when exposed to an oxidizing atmosphere. The conductivity is reduced. That is, although it is suitable for the fuel electrode, the performance as an interconnector is not sufficient on the air electrode side.

  The present inventors tried to protect the air electrode side of the LST layer with an air electrode material such as lanthanum strontium manganate (LSM). It was difficult to integrate because of the difference.

  Furthermore, the present inventors tried to approximate the linear expansion coefficient to an adjacent layer by mixing a zirconium oxide in which a rare earth used for a solid electrolyte was dissolved in LSM. It was found that the ionic conductivity due to zirconium oxide exceeded the expectation and significantly reduced the power generation performance of the integrally sintered SOFC stack.

  The present specification exhibits conductivity, resistance to reducing gas and oxidizing gas applied to SOFC, and further uses an interconnector suitable for integral sintering with a cell and the interconnector. Provide SOFC.

  The present inventors have focused on the fact that the fuel electrode side and the air electrode side of the interconnector are required to have different characteristics with respect to electrical conductivity and gas resistance. Then, we focused on integrating the materials satisfying these different characteristics with each other and with a single cell. According to the present specification, the following means are provided based on these findings and the like.

(1) An interconnector used for a solid oxide fuel cell, comprising a fuel electrode, a solid electrolyte, and an air electrode,
Comprising at least a first layer located on the fuel electrode side and a second layer located on the air electrode side;
The first layer has higher electrical conductivity and gas barrier properties than the second layer in a reducing atmosphere,
The second layer is an interconnector having higher electrical conductivity and gas barrier properties than the first layer in an oxidizing atmosphere.
(2) The interconnector according to (1), wherein the first layer includes a perovskite oxide doped with a rare earth element.
(3) The interconnector according to (1) or (2), wherein the second layer includes a conductive ceramic material and an oxide material of an element included in the solid electrolyte.
(4) The interconnector according to (3), wherein the ionic conductivity of the oxide material of the element contained in the solid electrolyte is lower than that of the oxide ion conductive material in the solid electrolyte.
(5) The interconnector according to any one of (1) to (4), wherein the first layer and the second layer are integrated by sintering.
(6) A solid oxide fuel cell stack including a plurality of single cells each including a fuel electrode, a solid electrolyte, and an air electrode,
A stack comprising the interconnector according to any one of (1) to (5) between at least two single cells.
(7) The stack according to (6), wherein at least two of the single cells are integrated by sintering through the interconnector.
(8) The stack according to (6) or (7), wherein the single cell has a thickness of 150 μm or more and 1000 μm or less.
(9) The stack according to any one of (6) to (8), wherein the fuel electrode has a thickness of 15 μm or more and 500 μm or less.
(10) A method for producing a solid oxide fuel cell stack including a plurality of unit cells each including a fuel electrode, a solid electrolyte, and an air electrode,
In obtaining a stack in which at least a first single cell and a second single cell are stacked via an interconnector,
A fuel electrode material layer including a material of the fuel electrode of the first single cell, an interconnector material layer including a material of the interconnector, and an air electrode material including a material of the air electrode of the second single cell. And integrating the precursor of the stack including at least a layer by firing,
With
The interconnector material layer includes a first material layer located on the fuel electrode material layer side, and a second material layer located on the air electrode material layer side,
The first material layer is configured to have higher electrical conductivity and gas barrier properties than a second layer obtained from the second material layer in a reducing atmosphere,
The manufacturing method, wherein the second material layer is configured to have higher electrical conductivity and gas barrier properties than the first layer obtained from the first material in an oxidizing atmosphere.

It is a figure which illustrates a part (single cell C) of the SOFC stack including this interconnector. It is a figure which illustrates a part (single cell C) of the SOFC stack including this interconnector. It is a figure which shows an example of the laminated structure of this interconnector. It is a figure which shows another example of the laminated structure of this interconnector. It is a figure which shows another example of the laminated structure of this interconnector. It is a figure which shows an example of a SOFC stack. It is a figure which shows a part of green sheet used at the manufacturing process of the SOFC stack of an Example. It is a figure which shows another part of green sheet used at the manufacturing process of the SOFC stack of an Example. It is a figure which shows another part of green sheet used at the manufacturing process of the SOFC stack of an Example. It is a figure which shows another part of green sheet used at the manufacturing process of the SOFC stack of an Example. It is a figure which shows a part of manufacturing process of the SOFC stack in an Example. It is a figure which shows another part of manufacturing process of the SOFC stack in an Example. It is a figure which shows the SOFC stack obtained in an Example.

  The present specification relates to an interconnector used for SOFC, an SOFC using the interconnector, and the like. The interconnector disclosed in the present specification (hereinafter, also simply referred to as the present interconnector) has electrical characteristics and different flow gas resistances suitable for the fuel electrode and the air electrode adjacent to the interconnector. Since the first layer and the second layer having the above and the like are provided, the connection performance can be exhibited while maintaining excellent conductivity and gas resistance as a whole.

  Further, according to the present interconnector, since the first layer in contact with the fuel electrode and the second layer in contact with the air electrode are provided, it is possible to easily control the adhesion between the fuel electrode and the air electrode. In addition, in the production of the stacked SOFC stack, it is also convenient to integrally sinter the single cells with each material layer of the interconnector.

  Hereinafter, representative and non-limiting specific examples of the present disclosure will be described in detail with reference to the drawings as appropriate. This detailed description is intended merely to provide those skilled in the art with details for practicing the preferred embodiments of the present invention and is not intended to limit the scope of the present disclosure. In addition, the additional features and disclosures disclosed below may be used separately from or in conjunction with other features and disclosures to provide further improved interconnectors and uses thereof.

  Further, the combinations of features and steps disclosed in the following detailed description are not essential in carrying out the present disclosure in the broadest sense, and are particularly only for explaining representative specific examples of the present disclosure. It is described. Moreover, various features of the representative embodiments described above and below, as well as those described in the independent and dependent claims, are described herein in providing additional and useful embodiments of the present disclosure. They do not have to be combined in the specific examples given or in the order listed.

  All features described in this specification and / or claims, apart from the configuration of the features described in the examples and / or claims, are individually disclosed as limitations on the original disclosure and claimed specific matters. And are intended to be disclosed independently of each other. Further, all numerical ranges and group or group descriptions are intended to disclose intermediate configurations thereof as a limitation to the original disclosure and claimed subject matter.

  In the present specification, the reducing atmosphere refers to a gas having a composition including one or more reducing gases. The reducing atmosphere is also a gas characterized by a reducing gas, and preferably contains a reducing gas as a main component. Moreover, it is preferable that a reducing atmosphere substantially consists of 1 type, or 2 or more types of reducing gas, or is a gas of the composition containing inert gas other than reducing gas. Examples of the reducing gas include hydrogen, carbon monoxide, and hydrogen sulfide. The reducing gas includes a gas that includes a reducing gas by reforming a gas that is not a reducing gas (for example, a hydrocarbon gas such as methane and water vapor) in a cell.

  In this specification, an oxidizing atmosphere refers to a gas having a composition containing one or more oxidizing gases. The oxidizing atmosphere is a gas characterized by an oxidizing gas, and preferably contains an oxidizing gas as a main component. Moreover, it is preferable that the oxidizing atmosphere is substantially composed of one or more oxidizing gases, or is a gas having a composition containing an inert gas other than the oxidizing gas. Examples of the oxidizing gas include oxygen, ozone, nitrous oxide, nitric oxide, and nitrogen dioxide.

(Interconnector)
This interconnector is an interconnector used for SOFC, which includes a fuel electrode, a solid electrolyte, and an air electrode. Hereinafter, the interconnector will be described with reference to the drawings such as FIG. 1 as appropriate, and then the SOFC to which the interconnector is applied will be described. In FIGS. 1 and 2, the reducing gas channel 22 and the oxidizing gas channel 24 are explicitly shown so as to be parallel to each other.

(First layer)
The interconnector 10 includes at least a first layer 12. The first layer 12 is located on the fuel electrode 2 side in the interconnector 10. The first layer 12 may be on the side of the interconnector 10 that is scheduled to be the fuel electrode 2 side or the fuel electrode 2 side (hereinafter simply referred to as the fuel electrode side). It is not limited to be positioned on the fuel electrode 2 side. Moreover, what is necessary is just to join to the fuel electrode 2 directly or indirectly.

  The first layer 12 preferably has high electrical conductivity and reducing gas barrier properties in a reducing atmosphere. More specifically, the first layer 12 can have higher electrical conductivity and gas barrier properties than the second layer described later in a reducing atmosphere. By providing such a first layer, the fuel electrode 2 can be connected with high conductivity, and reducing gas such as hydrogen can be reliably shut off. On the other hand, the first layer 12 may have low electrical conductivity or substantially no electrical conductivity in an oxidizing atmosphere such as oxygen, and may not have resistance to the oxidizing atmosphere. As a result, the gas barrier property in the oxidizing atmosphere may be low or substantially absent. The first layer 12 in this interconnector may exhibit the integral sinterability with the air electrode 4, the electrical connectivity with the air electrode 4, and the resistance to oxidizing gas in the second layer 14 described later. Therefore, a conventionally known interconnector material can be easily applied.

For the first layer 12, a conductive ceramic material used as a conventionally known ceramic interconnector material used for SOFC can be appropriately selected and used. Examples of the conductive ceramic material include various known ABO ₃ perovskite oxides. For example, such an oxide is a perovskite oxide doped with a rare earth element, and is (Ln _a M ¹ _b ) M ² O ₃ (however, a numerical value matching the perovskite structure such as a + b = 1). It is expressed as Ln is a rare earth element, and examples thereof include elements having atomic numbers of 57 to 71. As the rare earth element, for example, an element having a relatively large ionic radius such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm) can be used, and La is preferably used. be able to. M ¹ represents an alkaline earth metal, and examples thereof include calcium (Ca), strontium (Sr), and barium (Ba), and one or more of them can be used. M ² is one or two selected from transition elements such as titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), etc. More than a seed. Is mentioned. Preferably, it is 1 type, or 2 or more types selected from Ti, Cr, Mn, Fe, and Co.

Examples of such conductive ceramic materials include LaCoO ₃ oxides, LaMnO ₃ oxides, La (CoFe) O ₃ oxides, LaCrO ₃ oxides in which La and Sr or Ca coexist at the A site, Examples include LaTiO ₃ acid compounds. In addition to Co, Mn, and Ti, other elements such as Cr, Fe, and Mg may exist at the B sites of various oxides. More specifically, (LaSr) MnO ₃ , (LaSr) CoO ₃ , (LaSr) (CoFe) O ₃ , (LaSr) TiO _3, LaCrMgO _{3 and the} like can be mentioned.

  The first layer 12 can contain one or more conductive ceramic materials. The first layer 12 includes such a ceramic material in part so that it can exhibit the characteristics as an interconnector, and may be substantially composed of the material, or only composed of the material. There may be. Preferably, the first layer 12 does not include a metal conductive material such as a metal or metal alloy. In the present specification, “substantially composed of a certain material” means that the material to be used does not include other materials that may greatly affect the characteristics imparted to the interconnector. ing.

The material used for the first layer 12 is appropriately selected in consideration of the material of the fuel electrode 2 of the SOFC to which the present interconnector is applied, the material of the air electrode 4, the operating temperature, the sintering temperature of the stack 30, and the like. Is done. For the first layer, it is preferable to use a LaTiO ₃ -based oxide exhibiting high conductivity in a reducing atmosphere, in particular, a (LaSr) TiO ₃ -based oxide such as La _0.3 Sr _0.7 TiO ₃ .

  The first layer 12 may be configured by stacking two or more first layers having different compositions. The two or more first layers 12 may contain a similar ceramic material, or may contain different ceramic materials. Moreover, you may have a continuous or intermittent gradient composition.

  The first layer 12 generally has the denseness that an interconnector has. For example, the relative density (according to Archimedes method) of the first layer 12 is preferably 93% or more, and more preferably 95% or more. Further, the thickness of the first layer 12 is not particularly limited, but can be set to 1 μm or more and 50 μm or less in consideration of the size and conductivity of the entire stack, for example. Moreover, Preferably it is also 1 micrometer or more and 30 micrometers or less. Furthermore, it can also be 1 μm or more and 20 μm or less.

(Second layer)
The interconnector 10 includes at least a second layer 14. The second layer 14 is located on the air electrode 4 side in the interconnector 10. The second layer 14 may be on the air electrode 4 side or the air electrode 4 side (hereinafter simply referred to as the air electrode side) in the present interconnector. It is not limited to be positioned closest to the air electrode 4 side. Moreover, what is necessary is just to join to the air electrode 4 directly or indirectly.

  The second layer 14 can have higher electrical conductivity and gas barrier properties than the first layer 12 in an oxidizing atmosphere. By providing the second layer 14, the air electrode 4 can be connected with high conductivity, and an oxidizing gas such as air can be reliably blocked. On the other hand, the second layer 14 may have low or substantially no electrical conductivity in a reducing atmosphere containing hydrogen gas or the like, and does not have resistance to the reducing atmosphere. The gas barrier property in a reducing atmosphere may be low or substantially absent.

  The second layer 14 preferably includes a conductive ceramic material and an oxide material of an element contained in the solid electrolyte. The second layer 14 exhibits high conductivity and resistance in an oxidizing atmosphere by using a conductive ceramic material, and integrity with respect to the air electrode 4, and includes an oxide material included in the solid electrolyte. The coefficient of thermal expansion of 6 can be adapted. According to such a configuration, it is possible to ensure the integrity with the air electrode 4, the compatibility of the thermal expansion coefficient, the resistance against the oxidizing gas, and the blocking property.

  The second layer 14 can include a conductive ceramic material and an oxide material of an element included in the solid electrolyte. The second layer 14 includes these ceramic materials in part so that the characteristics as an interconnector can be exhibited, and may be substantially composed of the material, or only composed of the material. It may be. Preferably, the second layer 14 does not include a metal conductive material such as a metal or metal alloy.

The conductive ceramic material used for the second layer 14 can be appropriately selected from known air electrode materials used as SOFC air electrode materials. For example, an ABO ₃ type perovskite oxide containing La or La and Sr can be mentioned. Examples of such perovskite oxides include transition metal perovskite oxides such as LaCoO ₃ oxides, LaMnO ₃ oxides, LaFeO ₃ oxides in which La or La and Sr or Ca coexist at the A site. Can be mentioned. Further, LaTiO ₃ based oxide or the like to coexist with La or La and Sr or Ca in the A site and the like. In addition, Co, Mn, and Ti may contain Cr, Fe, Mg, and the like as other elements at the B sites of various oxides. More specifically, (LaSr) MnO ₃ , (LaCa) MnO ₃ , LaCoO ₃ , (LaSr) CoO ₃ , (LaSr) (CoFe) O ₃ , (LaSr) (TiFe) O _{3 and the} like can be mentioned. The air electrode material used in the second layer 14 may be the same as or common to the material of the air electrode 4 in the single cell in which the interconnector is interposed, but may be different.

The oxide material of the element contained in the solid electrolyte is not particularly limited, and a known material can be appropriately selected and used. For example, ZrO ₂ (zirconia) stabilized at least partially with rare earth elements such as Y, Sc, Yb, CeO ₂ (ceria) doped with rare earth elements such as Gd, Sm, alkaline earth such as Sr and Mg Examples thereof include LaGaO ₃ (lanthanum gallate) in which a part of La and Ga is substituted with a similar metal.

  It is preferable that the ionic conductivity of the oxide material of the element contained in the solid electrolyte used for the second layer 14 is reduced as compared with the oxygen ion conductive material used for the solid electrolyte. This is because the ionic conductivity in the interconnector may prevent the performance of the interconnector from being limited. In order to adjust the ion conductivity of the oxygen ion conductive material, it is preferable to suppress the amount of rare earth oxide added to the oxygen ion conductive material. For example, it is preferable that the addition rate of the rare earth element oxide in the partially stabilized oxide used in the solid electrolyte to which the present interconnector 10 is applied is about 20% to 60%. When zirconia is used for the solid electrolyte, about 6 to 10 mol% of yttria or the like is generally added. For example, the rare earth element oxide as the stabilizing material used for the second layer 14 is preferably added in an amount of about 1.5 mol% to 5 mol% with respect to an oxide material such as zirconia. More preferably, it is about 2 mol% or more and 4 mol% or less.

  The oxide material of the element contained in the conductive ceramic material and the solid electrolyte is, for example, the material of the fuel electrode 2 of the SOFC to which the present interconnector 10 is applied, the material of the air electrode 4, the operating temperature, and the stack sintering. The temperature is appropriately selected in consideration of the temperature and the like. The blending ratio of the conductive ceramic material and the air electrode material is not particularly limited. For example, the conductive ceramic material and the oxide material of the element contained in the solid electrolyte are 30:70 to 70 by mass ratio. : 30 or the like, or 40:60 to 60:40.

  The second layer 14 may be configured by stacking two or more second layers having different compositions. The two or more second layers may contain a similar ceramic material, or may contain different ceramic materials. Moreover, you may have a continuous or stepwise gradient composition.

  In the present interconnector 10, the first layer 12 and the second layer 14 may be directly integrated with each other, and one or more other third layers are interposed between these layers. It may be interposed. The first layer 12 and the second layer 14 are preferably integrated by sintering. More preferably, they are integrated by direct sintering without a special intervening layer.

  The second layer 14 generally has the denseness that the interconnector has. For example, the relative density (according to Archimedes method) of the second layer 14 is preferably 93% or more, and more preferably 95% or more. The thickness of the second layer 14 is not particularly limited. For example, considering the overall size and conductivity of the stack 30, for example, the thinnest portion of the second layer 14 is 1 μm or more and 50 μm or less. It can be. Moreover, Preferably it is also 1 micrometer or more and 30 micrometers or less. Furthermore, it can also be 1 μm or more and 20 μm or less.

  The lamination form of the first layer 12 and the second layer 14 in the interconnector 10 is not particularly limited, and is appropriately determined depending on the single cell structure in the SOFC to which the interconnector 10 is applied. Various forms of this interconnector will be described in detail later.

  As will be described later, the interconnector 10 is preferably manufactured at the same time as a single cell stack is manufactured by interposing between the single cells in the manufacturing process of the SOFC stack 30. For example, a green laminate appropriately including the material layer of the first layer 12 and the material layer of the second layer 14 may be prepared as the interconnector precursor and used for the manufacturing process of the SOFC stack 30. . In addition, for example, the material layer of the first layer 12 and the material layer of the second layer 14 may be laminated in a necessary order and used for the manufacturing process of the SOFC stack 30. The SOFC and its manufacturing method will be described in detail later.

  The form of the present interconnector 10 as a whole is not particularly limited, but can adopt a form according to the SOFC stack 30 to be applied. For example, when applied to a flat plate type SOFC, a flat plate or the like is obtained. Moreover, although the thickness of the whole interconnector 10 is not particularly limited, for example, it can be 1 μm or more and 100 μm or less in the thinnest part. Preferably, it can be 2 μm or more and 60 μm or less, and more preferably 2 μm or more and 40 μm or less.

The thermal expansion coefficient (20 ° C. to 1000 ° C.) of each of the first layer 12 and the second layer 14 of the interconnector is 8 × 10 ⁻⁶ K ⁻¹ or more and 12 × 10 ⁻⁶ K ⁻¹ or less. Preferably there is. This is because peeling within the air electrode layer or the fuel electrode layer can be suppressed within this range. Considering the residual stress of the stack structure, it is more preferably 9.5 × 10 ⁻⁶ K ⁻¹ or more and 11.5 × 10 ⁻⁶ K ⁻¹ or less.

  The interconnector 10 described above has interconnect characteristics suitable for the fuel electrode 2 of one single cell to be connected and the air electrode 4 of the other single cell, that is, conductivity, gas resistance, and shut-off property. Therefore, it is possible to provide a thin layer as a whole and sufficient interconnector characteristics. Further, in the manufacture of the integrally sintered metal material-free (in other words, all ceramics) SOFC stack 30, the ceramic material layer corresponding to the fuel electrode and the ceramic material material corresponding to the air electrode are used. By applying each material layer of the material layer of the second layer 14, the first layer 12 and the second layer 14 are integrally sintered to the fuel electrode 2 and the air electrode 4, respectively. Layer 12 and second layer 14 are also integrally sintered together. Therefore, excellent conductivity and gas barrier properties can be reliably realized, the stacking process of the stack 30 can be simplified and made efficient, and the integral sinterability of the stack 20 can be improved.

(Solid oxide fuel cell (SOFC) stack)
The SOFC stack disclosed herein can include this interconnector between at least two single cells. According to such an SOFC stack, these single cells are connected and separated with high electrical conductivity and gas barrier properties, and when integrally sintered to the cells, the electrical conductivity and In addition to improved gas barrier properties, the SOFC stack manufacturing process is simplified. Hereinafter, an SOFC stack in which SOFC single cells are stacked with this interconnector will be described with reference to FIGS.

(Single cell)
A cell (power generation element) C in the SOFC includes a fuel electrode 2, a solid electrolyte 6, and an air electrode 4. More specifically, it has a structure in which the fuel electrode 2 and the air electrode 4 are laminated via a solid electrolyte 6.

(Fuel electrode)
The fuel electrode 2 is not particularly limited, and can be a porous body made of one or more conductive ceramic materials applied to the SOFC fuel electrode. For example, the fuel electrode material can include zirconia or ceria in which a rare earth element is dissolved, and Ni / NiO. As the rare earth element, for example, yttrium (Y), scandium (Sc), samarium (Sm), gadolinium (Gd), or the like can be used. Specific examples include Ni cermet containing yttria partially stabilized or stabilized zirconia (YSZ), scandia partially stabilized or stabilized zirconia (ScSZ), gadolinia solid solution ceria (GDC) and Ni / NiO.

  The fuel electrode 2 is porous, and its porosity is appropriately set, but is preferably 15% or more, more preferably about 20% or more and 40% or less. In the present specification, the porosity can be measured from the area ratio of the pore portion and the dense portion of a cross-sectional image obtained by scanning a plurality of cross-sections created by mechanical cutting and polishing with a scanning electron beam microscope. . For example, for each of the five cut surfaces, the pores and dense portions of the layer are binarized by image processing in a field of view of 500 μm × 500 μm including the layer, and the area ratio is obtained, and the average of all cut surfaces is taken. Can determine the porosity.

  The pore shape in the fuel electrode 2 can be any shape such as an indefinite shape, a fiber shape, or a spherical shape. In the case of a spherical shape, the average pore diameter is preferably 1 μm or more and 10 μm or less. More preferably, it is 2 μm or more and 5 μm or less. In the present specification, the average pore diameter is assumed to be obtained by connecting a plurality of spherical pores to a pore portion of a cross-sectional image photographed by a scanning electron microscope with a plurality of cross sections created by mechanical cutting and polishing. It can be measured from the average diameter. For example, for each of the five cut surfaces, the pores and dense portions of the layer are binarized by image processing in a 500 μm × 500 μm visual field including the layer, and circular approximation is performed for all pores included in the visual field The average pore diameter can be obtained by obtaining the diameter of the cut and taking the average of all the cut surfaces.

(Fuel electrode buffer layer)
The anode 2 may have a substantially single porosity and / or average pore diameter, but may have a different distribution with respect to these. For example, as shown in FIG. 2, in the portion of the fuel electrode 2 that is distal from the solid electrolyte 6 or proximal to the first layer 12 of the interconnector 10, the porosity and / or the average pore diameter is set as the solid electrolyte 6. The anode buffer layer 2a can be provided smaller than the portion proximal to the first layer 12 of the interconnector 10 or distal to the distal portion thereof. By doing so, the adhesion between the fuel electrode 2 and the interconnector (first layer) 10 can be enhanced, and the integrity can be improved and peeling can be suppressed. On the other hand, when the gas flow path 22 is provided in the fuel electrode 2 and the fuel electrode 2 itself is provided with the convex portion 26 that follows the gas flow path 22, the fuel electrode buffer layer 2a is formed on the convex portion 26. The gas flow path (disappearing member for forming the gas flow path in the SOFC manufacturing process) 22 can be surely included in the fuel electrode 2 even if it is a thin layer by following well. Thereby, it is possible to avoid the direct contact of the top surface of the gas flow path 22 with the first layer 12 of the interconnector 10, and to reduce the resistance of the conductive path of the fuel electrode 2.

  In addition, by providing the fuel electrode 2 with the form having the convex portion 26 that follows the gas flow path 22, the thickness of the fuel electrode 2 itself can be reduced, and the fuel electrode that is generated when the SOFC stack 30 is started and stopped. 2 can suppress fluctuations in the deposition of the fuel electrode 2 due to oxidation / reduction of Ni contained in 2, and can suppress separation, deformation and destruction in the SOFC stack 30.

(Average pore size of fuel electrode buffer layer)
The fuel electrode buffer layer 2a is also, for example, 40% of the average pore diameter of the solid electrolyte 6 side of the fuel electrode 2 (a layer in contact with the solid electrolyte 6 side of the fuel electrode 2, hereinafter also referred to as the fuel electrode main layer 2b). It is preferably 90% or less. By such a small average pore diameter, the followability to the curved surface / deformed surface such as the convex portion 26 of the fuel electrode buffer layer 2a is improved. More preferably, it is about 50% or more and 80% or less. Further, for example, when the pores of the fuel electrode buffer layer 2a are spherical together with the fuel electrode main layer 2b, the average pore diameter is smaller than that of the fuel electrode main layer 2b and should be about 1 μm or more and 5 μm or less. it can.

(Porosity distribution of fuel electrode buffer layer)
In addition, the pore size distribution (pore size distribution) when the pores of the fuel electrode buffer layer 2a are spherical is preferably more polydisperse than the fuel electrode main layer 2b. By being polydisperse, followability to various curved surfaces and deformed surfaces can be imparted. For example, the pore size distribution of the fuel electrode buffer layer 2a is preferably a distribution in which 50% or less of the pores exist in the average value ± 0.2σ. In this specification, the pore size distribution is based on the assumption that a plurality of spherical pores are connected to the pores of a cross-sectional image taken with a scanning electron microscope for a plurality of cross sections created by mechanical cutting and polishing. It can be measured from the average diameter.

(Porosity of fuel electrode buffer layer)
The porosity of the fuel electrode buffer layer 2a can be made smaller than the porosity of the fuel electrode main layer 2b. In addition to improving the followability to a deformed surface such as a curve, it is possible to improve the adhesion of the interconnector 10 to the first layer 12. The porosity of the fuel electrode buffer layer 2a is preferably 40% or more and 80% or less, more preferably 60% or more and 80% or less of the porosity of the fuel electrode main layer 2b.

  The fuel electrode buffer layer 2a can have one or more of the above three characteristics regarding pores, average pore diameter, pore diameter distribution, and porosity. Preferably, three can be provided.

  Further, when the fuel electrode 2 includes the fuel electrode main layer 2b and the fuel electrode buffer layer 2a, the gradient composition related to such pores may be continuous or stepwise. The pores can be formed by using a pore-forming agent that forms pores reflecting the shape of carbon or a high-molecular material such as starch or acrylic after being burned down. For example, in the fuel electrode 2, in order to adjust the average pore size and / or pore size distribution of spherical pores, spherical pore formers having different particle sizes and / or particle size distributions can be used. Moreover, in order to adjust a porosity, the usage-amount of arbitrary pore forming agents can be changed. For example, the fuel electrode main layer 2b is formed from a fuel electrode material containing a spherical pore former having a larger average particle size and / or a smaller particle size distribution, and the fuel electrode buffer layer 2a has a smaller average particle size. And / or a fuel electrode material containing a spherical pore former having a large particle size distribution. A method for controlling pores in ceramics is a method well known to those skilled in the art.

  The thickness of the fuel electrode 2 is not particularly limited, and may be, for example, 15 μm or more and 500 μm or less, although it varies depending on the presence or absence of the gas channel 22 and the channel configuration. More preferably, it can be 20 μm or more and 500 μm or less. More preferably, it can be 50 μm or more and 400 μm or less, and preferably 50 μm or more and 300 μm or less. As will be described later, the thicknesses of the fuel electrode 2 and the air electrode 4 are not necessarily constant in one layer. Therefore, the description regarding the thickness of the fuel electrode 2 and the air electrode 4 means that one layer exists in the range of such thickness unless it mentions especially.

  Further, the thickness of the fuel electrode buffer layer 2a is not particularly limited, but may be, for example, 5 μm or more and 50 μm or less, and may be, for example, 5 μm or more and 20 μm or less.

(Air electrode)
The air electrode 4 is not particularly limited, and may be a porous body made of one or more conductive ceramic materials applied to the SOFC air electrode 4. For example, examples of the air electrode material include the conductive ceramic materials already exemplified as the material of the second layer 14 of the interconnector 10.

  The air electrode 4 is porous, and the porosity thereof is appropriately set, but is preferably 15% or more, more preferably about 20% or more and 40% or less. When the pores in the air electrode 4 are spherical, the average pore diameter is preferably 1 μm or more and 10 μm or less. More preferably, it is 2 μm or more and 5 μm or less.

  The thickness of the air electrode 4 is not particularly limited, and varies depending on the presence or absence of the oxidizing gas flow path 24 and the flow path form. For example, the thickness can be 15 μm or more and 500 μm or less, and for example, 20 μm or more and 500 μm. It can be as follows. More preferably, it can be 50 μm or more and 400 μm or less.

(Solid electrolyte)
The solid electrolyte 6 is not particularly limited, and can be a dense body made of one or more oxygen ion conductive materials applied to the SOFC solid electrolyte. For example, as the solid electrolyte material, already exemplified oxygen ion conductive materials can be mentioned.

  The solid electrolyte 6 is dense and preferably has the same relative density as the interconnector 10 from the viewpoint of blocking gas permeability. Further, the thickness of the solid electrolyte 6 is not particularly limited, but can be set to, for example, 1 μm or more and 100 μm or less. More preferably, it can be 3 μm or more and 40 μm or less, and further preferably 5 μm or more and 30 μm or less.

(Gas flow path)
The single cell C of the SOFC includes gas flow paths 22 and 24 for a reducing gas containing hydrogen supplied to the fuel electrode 2 and an oxidizing gas containing oxygen supplied to the air electrode 4, respectively. . The gas flow paths 22 and 24 can be formed over one or two layers constituting a single cell. That is, the gas flow paths 22 and 24 may be provided in the fuel electrode 2 and the air electrode 4, respectively, or may be provided in the interconnector 10, and may be provided across the fuel electrode 2 and the interconnector 10. It may be provided over the air electrode 4 and the interconnector 10.

  For example, as shown in FIG. 1, these gas flow paths 22, 24 may be included so as to be completely embedded in the thickness range of the fuel electrode 2 and the air electrode 4. By carrying out like this, the increase in the volume of an interconnector with high resistance can be controlled, and the fall of power generation performance can be controlled. Or although not shown in figure, in the interconnector 10 which contact | connects the fuel electrode 2 and the air electrode 4, it can also provide so that it may open to the fuel electrode 2 side and the air electrode 4 side. By carrying out like this, the volume of the fuel electrode 2 can be suppressed and the volume fluctuation accompanying the oxidation reduction of Ni can be suppressed.

  Further, for example, in a form as shown in FIG. 2, at least the gas flow path 22 can be provided in the fuel electrode 2. That is, the fuel electrode 2 is included so as to cover the gas flow path 22, but only a part of the thickness of the gas flow path 22 is provided.

  For example, as shown in FIG. 2, the fuel electrode 2 has one or more convex portions 26 that protrude outward from the single cell C based on the outer shape, arrangement pattern, and the like of the gas flow path 22. Can be provided. By doing so, the layer thickness of the fuel electrode 2 can be reduced, and the volume fluctuation of the fuel electrode 2 due to the oxidation / reduction of Ni (according to the start and stop of SOFC) due to the increase in the volume of the fuel electrode 2 can be suppressed. it can.

  The fuel electrode 2 having the convex portion 26 based on the gas flow path 22 to be present has a thickness that does not satisfy the thickness (thickness or height in the stacking direction) of the gas flow path 22 in a region where the gas flow path 22 is not formed. It is formed by providing the fuel electrode 2. That is, the fuel electrode 2 is provided with a thickness of less than 100% of the thickness of the gas flow path 22. By carrying out like this, the thickness of the fuel electrode 2 can be reduced effectively and oxidation-reduction tolerance can be improved. In addition, the thickness of the first layer 12 of the interconnector 10 can be appropriately reduced, and the electrical resistance can be reduced. For example, in this region, the fuel electrode 2 can be 90% or less, for example, 80% or less, further, for example, 70% or less, further, for example, 60% or less, etc. In the region, the fuel electrode 2 is 1% or more of the thickness of the gas flow path 22, for example, 10% or more, for example, 20% or more, and further, for example, 30% or more. . Typically, the thickness of the fuel electrode 2 can be not less than 30% and not more than 70% of the thickness of the gas channel 22 in the gas channel non-formation region.

  For example, in the region, the fuel electrode 2 is 90% or less of the maximum height of the gas flow path 22 in the fuel electrode 2, for example, 80% or less, further, for example, 70% or less, and further, for example, 60% or less, For example, it can be 50% or less, moreover, for example, 40%, further, for example, 30%, for example, 20% or less. Further, in this region, the fuel electrode 2 is 1% or more of the thickness of the gas flow path 22, for example, 5% or more, for example, 10% or more. As a typical rule, the thickness of the fuel electrode 2 can be 5% or more and 50% or less of the maximum height of the gas passage 22 in the gas passage non-formation region.

  Furthermore, in order to form such a fuel electrode 2, as described above, the fuel electrode 2 is formed of the fuel electrode main layer 2 b and the fuel electrode buffer layer 2 a, so that the convex portion 26 based on the gas flow path 22 is formed. It is possible to easily form the fuel electrode 2 that is in close contact with and encloses or covers the gas flow path 22. Although not particularly limited, it is preferable to mainly include the fuel electrode buffer layer 2 a in the upper part of the gas flow path 22.

  Furthermore, by including the first layer 12 of the present interconnector 10 having suitable characteristics for the fuel electrode 2 having a surface configuration including a convex portion 26 corresponding to one or more gas flow paths 22, By ensuring the electrical conductivity and gas barrier property in a reducing atmosphere and further comprising the second layer 14, the electrical conductivity and gas barrier in the oxidizing atmosphere derived from the air electrode 4 of the adjacent single cell C Can be secured. As described above, according to the ceramic two-layer containing structure of the interconnector 10, the following characteristics and the adhesiveness are exhibited in accordance with the surface form having changes as well as the characteristics of the adjacent electrodes, and thus changed. The surface morphology can be buffered to build a SOFC stack 30 with good integrity, moldability, and shape. Further, according to the ceramic two-layer containing structure of the present interconnector 10, the presence pattern of the two layers, that is, the thickness and arrangement pattern of each layer are changed according to the electrode surface having such a change, so that the interconnector 10 and the stack 30 are changed. Performance can be optimized.

  Various forms of the gas flow path 22 in the fuel electrode 2 have been described. However, the above-described internal form can also be applied to the gas flow path 24 in the air electrode 4.

  The thickness of the gas flow paths 22 and 24 (that is, the thickness or flow path height along the stacking direction of the elements in the cell C) is determined depending on the portion where the gas flow paths 22 and 24 are provided (in the interconnector or the electrode) or the gas flow Although it varies depending on the road pattern and the like and is not particularly limited, for example, it can be 50 μm or more and 400 μm or less. For example, the thickness of the gas flow path 22 in the fuel electrode 2 is preferably 100 μm or more and 200 μm or less, and the thickness of the gas flow path 24 in the air electrode 4 is preferably 150 μm or more and 300 μm or less.

  The pattern of each gas flow path 22 and 24 of reducing gas and oxidizing gas is not particularly limited, and various patterns can be adopted. Although it depends on the form of the SOFC, for example, in the case of a flat plate type SOFC, in a plan view, a pattern in which a plurality of linear flow paths are arranged at regular intervals, and a plurality of U-shaped flow paths having different sizes are provided. Examples include a pattern arranged on the inner side in order of decreasing size, a pattern in which one or more continuous flow paths are arranged.

  The thickness of the single cell (fuel electrode, air electrode, solid electrolyte) C configured in this way is not particularly limited, and can be, for example, 100 μm or more and 1000 μm or less. Moreover, it is preferably 150 μm or more and 1000 μm or less. Furthermore, it can be preferably 200 μm or more and 1000 μm or less. Further, it can be preferably 300 μm or more and 600 μm or less.

  Moreover, the surface of the fuel electrode 2 and / or the air electrode 4 of the single cell C can also be provided with a convex portion 26 or the like based on the external form and arrangement pattern of the gas flow paths 22 and 24 contained therein.

  The single cell C and the SOFC stack 30 of the SOFC can be appropriately provided with a seal portion 20 for sealing each gas supplied to the fuel electrode 2 and the air electrode 4. Although the form of the seal part 20 is not specifically limited, For example, a well-known seal structure can be suitably employ | adopted besides the seal part disclosed by international publication WO2009 / 119971.

(Structure of this interconnector for SOFC and SOFC stack)
The SOFC disclosed in this specification can include the interconnector 10 or a part thereof with respect to the single cell C, and the SOFC stack 30 includes at least two single cells C via the interconnector 10. And have a connected structure. As shown in FIGS. 1 and 2, the unit cell C in which the fuel electrode 2, the air electrode 4, and the solid electrolyte 6 are stacked is connected to another unit cell C via the interconnector 10 to form a SOFC stack 30. doing. The first layer 12 and the second layer 14 of the interconnector 10 can take various laminated forms according to the mode of each power generating element in the SOFC.

  For example, in the case of a flat plate SOFC, a form as shown in FIG. In the form shown in FIG. 3, the gas flow path is omitted as appropriate. FIG. 3A shows a form in which the first layer 12 and the second layer 14 are flat layers. In this embodiment, each gas flow path 22, 24 may be in the interconnector or in the electrode. However, in the case of being in the electrode, the gas flow path is included in the layer thickness of the electrode. Thus, the convex portion due to the gas flow path does not appear on the electrode surface.

  3B is a layer having one or more curved portions 12a corresponding to one or more convex portions 26 based on the gas flow path 22 in which the first layer 12 is inherent in the fuel electrode 2. The second layer 14 is a layer having a filling portion 14b that fills the portion of the first layer 12 that is not the curved portion 12a, that is, the bottom portion 12b and has a substantially uniform thickness as the entire interconnector 10. The form is shown. Here, the first layer 12 is a wavy or corrugated layer having a substantially uniform thickness. Further, the second layer 14 includes a covering portion 14a having a relatively thin layer thickness in the curved portion 12a corresponding to or around the reducing gas flow path 22, and corresponds to the space between the reducing gas flow paths 22. The bottom portion 12b is provided with a relatively thick filling portion 14b. According to this interconnector form, the first layer 12 can be applied to the fuel electrode 2 in a necessary and sufficient form while ensuring a uniform thickness as a whole. Further, the second layer 14 allows the interconnector 10 to have a substantially flat and uniform thickness as a whole.

  Furthermore, FIG. 3C differs from FIG. 3B in that the second layer 14 for the air electrode 4 has a curved portion 14c and a bottom portion 14d following a surface form having a convex portion 28 based on the gas flow path 24 of the air electrode 4. The first layer 12 has a filling portion 12d that fills the bottom portion 14d of the second layer 14 and has a covering portion that thinly covers the curved portion 14c. The form provided with the part 12c is shown. In other words, the first layer 12 is relatively thin in the curved portion 14 c corresponding to or around the oxidizing gas flow channel 24, and the first layer is formed in the bottom portion 14 d between the oxidizing gas flow channels 24. 12 is relatively thick. Also in this form, the second layer can be applied to the air electrode 4 in a necessary and sufficient form. In addition, the second layer 12 allows the interconnector 10 to have a substantially flat and uniform thickness as a whole.

(Restricted layer)
As shown in FIG. 4, the SOFC single cell C or SOFC stack 30 may comprise at least one constraining layer 40 in the stack. The constraining layer 40 can include at least a non-porous layer 42 including a conductive ceramic material and an oxide material of an element included in the solid electrolyte. By providing the constraining layer 40, the shrinkage rate deviation in the plane (xy plane) of the laminate is suppressed, and the firing behavior is adjusted so as to suppress warping and bending in the stacking direction (z direction). Can do. As a result, deformation and distortion of the gas flow paths 22 and 24, cracks and peeling in the fuel electrode 2, the air electrode 4 and the solid electrolyte 6, etc., and cracks in the cell, etc. are suppressed, and the SOFC single cell excellent in power generation characteristics and integrity C and SOFC stack 30 can be obtained.

As the conductive ceramic material used for the constraining layer 40, the conductive ceramic material suitable for the air electrode 4 described above can be used. Moreover, as an oxide material of the element contained in the solid electrolyte, an oxygen ion conductive material suitable for the solid electrolyte 6 described above can be used. By setting it as this composition, the thermal expansion coefficient of the constraining layer 40 can be adjusted easily, and the firing behavior by the constraining layer 40 can be adjusted. The thermal expansion coefficient (20 ° C. to 1000 ° C.) of the constraining layer 40 is preferably 10 × 10 ⁻⁶ K ⁻¹ or more and 15 × 10 ⁻⁶ K ⁻¹ or less. This is because if it is within this range, peeling does not easily occur at the interface with the interconnector 10 or the air electrode 4. Considering the residual stress of the SOFC stack 30, it is more preferably 10 × 10 ⁻⁶ K ⁻¹ or more and 12 × 10 ⁻⁶ K ⁻¹ or less.

  The constraining layer 40 includes at least a non-porous layer 42. The non-porous layer 42 can have the same denseness as the solid electrolyte 6 and the interconnector 10. Moreover, as a porosity, it is preferable that it is 10% or less, More preferably, it is 5% or less. The thickness of the non-porous layer 42 is not particularly limited, but may be, for example, 10 μm to 200 μm, preferably 50 μm to 100 μm.

  Similarly to the non-porous layer 42, the constraining layer 40 can further include a porous layer 44 that is porous including an electroconductive ceramic material and an oxide of an element contained in the solid electrolyte. The provision of the non-porous layer 42 and the porous layer 44 makes it easier to adjust the firing behavior. The porosity of the porous layer 44 is not particularly limited as long as it is larger than that of the non-porous layer 42. For example, the porosity can be 10% or more and 50% or less. This is because within this range, it is easy to adjust the firing behavior by the combination with the non-porous layer 42. The thickness of the porous layer 44 is not particularly limited, but may be, for example, 10 μm or more and 200 μm or less, preferably 50 μm or more and 100 μm or less.

  Note that the non-porous layer 42 can also function as the interconnector 10 with respect to the air electrode 4 when disposed at the terminal end of the SOFC single cell C and the SOFC stack 30 on the air electrode 4 side. Therefore, for example, in this case, the second layer 14 of the interconnector 10 can be omitted.

  When the constraining layer 40 includes the non-porous layer 42 and the porous layer 44, the stacked form is not particularly limited, but the non-porous layer 42 and the porous layer 44 can be alternately provided. . When both of these layers are provided, the number and thickness of each layer may be different or the same, but from the viewpoint of adjusting the firing behavior, the number of layers of the non-porous layer 42 and the porous layer 44 is the same. Are the same number and / or the total thickness of each layer is preferably the same.

  The non-porous layer 42 and the porous layer 44 as the constraining layer 40 can each include a conductive ceramic material and an oxide material of an element included in the solid electrolyte. In these two types of layers 42 and 44, the same type of conductive ceramic material and the oxide material of the element contained in the solid electrolyte may be used, or at least one of them may be different. Preferably, these two types of layers 42 and 44 may have the same composition (formulation) but may be the same, but use the same type of material. When a plurality of non-porous layers 42 are provided, the same aspect as described above is applied to the non-porous layers 42 with respect to the oxide material of the element contained in the conductive ceramic material and the solid electrolyte. . When a plurality of porous layers 44 are provided, the same aspects as described above are applied to the porous layers 44 with respect to the conductive ceramic material and the oxide material of the element contained in the solid electrolyte.

  The mixing ratio of the conductive ceramic material and the oxide material of the element contained in the solid electrolyte in these two types of layers 42 and 44 is not particularly limited. For example, it is included in the conductive ceramic material: solid electrolyte. The oxide material of the element to be used can be 30:70 to 70:30 or the like, or 40:60 to 60:40, by mass ratio.

  Moreover, each layer 42 and 44 can contain an additive suitably, respectively, in order to improve sinterability or to improve the heat resistance at the time of high temperature baking. For example, in addition to the various additives described above, ceria and the like can be added from the viewpoint of heat resistance. A high-temperature heat-resistant additive such as ceria is not particularly limited, but is preferably added to the porous layer 44. The content of these additives is not particularly limited, and can be, for example, 0.5% by mass or more and 10% by mass or less based on the total ceramic materials (including additives) in each layer 42 and 44. Preferably, it can be 2 mass% or more and 8 mass% or less.

  The shape of the pores in the porous layer 44 is not particularly limited, but spherical pores can be formed. In the case of a spherical shape, the average pore diameter is not particularly limited, but can be, for example, 0.5 μm or more and 5 μm or less. This is because if the thickness is less than 0.5 μm and more than 5 μm, it is difficult to sufficiently adjust the firing behavior.

  The adjustment of the porosity and the average pore diameter in the ceramic material is well known to those skilled in the art, and a person skilled in the art can appropriately produce a ceramic layer having the intended porosity and average pore diameter.

  The constraining layer 40 can be provided at any site in the SOFC. That is, the constraining layer can be provided on one or both of the fuel electrode 2 side and the air electrode 4 side in the single cell C, and also constrains at least a part of the plurality of single cells C included in the stack 30. A layer 40 may be provided. It can also be provided on one or both of the outermost sides of the stack 30.

  For example, as shown in FIG. 4, on the anode 2 side of the SOFC single cell C, the first layer 12 of the interconnector 10 applied to the single cell C, that is, the first layer The constraining layer 40 can be provided so as to be located outside the cell C rather than 12. On the air electrode 4 side, when the air electrode 4 contains a flow path, the air electrode 4 is provided with a constraining layer 40 so as to be located on the outside of the cell C with respect to the air electrode 4. be able to.

  In these cases, the lamination form of the non-porous layer 42 and the porous layer 44 as the constraining layer 40 is not particularly limited. For example, the non-porous layer 42 is provided with respect to the first layer 12 and the air electrode 4. Furthermore, the porous layer 44 can be further provided on the outer side as required. Preferably, the outermost layer includes a porous layer 44. Further, in such a laminated form, it is preferable that the non-porous layer 42 and the porous layer 44 are arranged symmetrically with the solid electrolyte 6 in between from the viewpoint of controlling the firing behavior.

  Further, for example, as shown in FIG. 4, in the SOFC stack 30, the end portion on the fuel electrode 2 side (one end portion along the stacking direction of the stack 30) and / or the end portion on the air electrode 4 side (of the stack 30 The other end along the stacking direction) can be provided.

  As described above, this interconnector 10 exhibits conductivity and resistance to reducing gas and oxidizing gas applied to SOFC, and is suitable for integral sintering with the cell C. It has become. As a result, according to the present interconnector 10, it is possible to obtain a SOFC and SOFC stack excellent in power generation characteristics and integrity without complicating the manufacturing process.

(SOFC stack manufacturing method)
In the SOFC stack manufacturing method disclosed in the present specification, in order to obtain a stack in which at least a first single cell and a second single cell are stacked via an interconnector, the anode of the first single cell is used. A precursor of a stack including at least a fuel electrode material layer including the material of the above, an interconnector material layer including the material of the interconnector, and an air electrode material layer including the material of the air electrode of the second single cell. The process of integrating by can be provided. In this manufacturing method, the interconnector material layer includes a first layer located on the fuel electrode material layer side, and a second layer located on the air electrode material layer side. The second layer has higher electrical conductivity and gas barrier properties than the second layer in a reducing atmosphere, and the second layer has higher electrical conductivity and gas barrier properties than the first layer in an oxidizing atmosphere. be able to.

  According to this manufacturing method, a layer having suitable interconnector characteristics (conductivity and gas barrier properties) can be applied to each of the fuel electrode and the air electrode, and excellent conductivity and integrity can be exhibited. it can. In addition, since the first layer and the second layer are suitable for integral sintering with the cell elements, the stack can be integrally sintered without complicating the manufacturing process. Furthermore, since the first layer and the second layer can exhibit independent characteristics, the thickness and pattern can be appropriately set according to various aspects of the fuel electrode and the air electrode.

  The manufacturing method of the SOFC stack in this specification can generally conform to a manufacturing method of a known sintered integrated SOFC stack. A person skilled in the art can implement this production method by appropriately referring to, for example, the method disclosed in International Publication WO2009 / 119971.

  The manufacturing method of the SOFC stack is not particularly limited, but generally, a green sheet containing a material of a single cell and one or more elements constituting the stack is prepared in advance and laminated, or such a material is appropriately selected. While directly laminating the layers as a slurry, they are laminated in the required order and fired integrally. A person skilled in the art can appropriately determine and implement what kind of elements the green sheet is prepared or supplied as a slurry, and further the order of lamination and the like within a range where an SOFC stack can be obtained.

  In addition, the method for firing the laminate (stack precursor) of the material layers of each element of the SOFC stack can generally conform to a known method for producing a sintered monolithic SOFC stack. That is, the stack precursor is fired so that a ceramic material constituting the precursor is at least partially sintered to obtain a dense or porous desired fired body. Preferably, all elements are co-sintered. For example, the heat treatment can be performed at a temperature of 1250 ° C. to 1550 ° C., and preferably 1250 ° C. to 1500 ° C. More preferably, it is 1250 degreeC or more and 1400 degrees C or less. It can be fired in air. The firing time at the firing temperature is not particularly limited, and can be, for example, about 1 to several hours.

  Prior to firing, the stack precursor was pressed by cold isostatic pressing (CIP) at a temperature of about 60 ° C. to 120 ° C. as necessary. This crimped body can be degreased at a temperature in the range of 300 ° C to 500 ° C.

  In addition, the preparation method of a slurry and green sheet itself is well-known to those skilled in the art. For example, the slurry for each layer can be prepared by adding appropriate amounts of a binder resin, an organic solvent, etc., with the material of each element as the main component. In addition, the green sheet is a green sheet precursor obtained by casting the prepared slurry using a casting method such as a tape casting method using a coating apparatus such as a knife coater or a doctor blade, or using a screen printing method or a spray method. Can be obtained. In addition, a green sheet (unfired ceramic green sheet) can be obtained by heat-treating the obtained sheet precursor according to a conventional method after drying according to a conventional method.

  Also, methods for producing a fuel electrode, an air electrode, and a porous layer of a constraining layer are well known to those skilled in the art. For example, a person skilled in the art can include a desired average pore diameter, porosity, pore size distribution, etc. and appropriate porosity by including a particulate disappearance material in the formulation of the slurry according to a known method or by including a pore-forming agent. It is possible to produce a green sheet that can express the quality by firing. The disappearing material itself is well known, and various materials are commercially available.

  Methods for forming gas flow paths in the fuel electrode, air electrode and interconnector are also well known to those skilled in the art. If it is a person skilled in the art, according to a known method, disposing a disappearing material capable of forming a desired gas flow path pattern on a green sheet of a fuel electrode material, and further laminating a green sheet of a fuel electrode material, etc. can do.

  In addition, an electrode green sheet including a sealing material layer serving as a seal portion adjacent to the fuel electrode material layer and the air electrode material layer can be manufactured as appropriate.

  In this manufacturing method, by appropriately adopting the fuel electrode buffer layer and the constraining layer in addition to the present interconnector, the advantages according to each element can be exhibited in the manufacturing method, and the power generation characteristics, integrity, etc. are excellent. A SOFC stack can be obtained.

  Below, an example of the outline | summary of this manufacturing method is demonstrated. A solid electrolyte green sheet was prepared from a slurry containing a solid electrolyte material. A fuel electrode green sheet is prepared from a fuel electrode slurry containing a fuel electrode material and a pore former and a seal slurry containing a seal material, and a flow path forming material made of a lost material is formed thereon by screen printing or the like. Further, the fuel electrode slurry and the sealing slurry are applied in a predetermined pattern until, for example, the height is about 30% to 70% of the height of the flow path forming material. Furthermore, the slurry for the first layer of the interconnector is applied with a substantially uniform thickness along the surface form including the convex portion of the fuel electrode material layer. Further, after that, the slurry for the second layer of the interconnector is applied to the surface of the first layer slurry so as to cover the convex portion of the fuel electrode material layer and become a substantially flat layer surface. Prepare a green sheet containing layers. In addition, the fuel electrode buffer slurry containing the fuel electrode buffer material can be further added as a separate fuel electrode slurry.

  In addition, a green sheet for an air electrode is produced from an air electrode slurry containing an air electrode material and a pore former and a sealing slurry containing a seal material, and a flow path forming material made of a disappearing material is screen printed thereon. Further, the air electrode slurry and the sealing slurry were applied in a predetermined pattern to produce a green sheet including the air electrode material layer. Also, a non-porous constraining layer material slurry and a sealing slurry are applied to the green sheet including the air electrode material layer to prepare an air electrode side termination green sheet.

  Separately, a non-porous constraining layer green sheet and a fuel electrode side termination green sheet are prepared using the non-porous constraining layer slurry and the sealing slurry. Further, a porous constraining layer green sheet is prepared using the porous constraining layer slurry and the sealing material.

  An appropriate number of these green sheets, for example, 2 or more and 30 or less, and for example, 5 or more and 20 or less may be stacked to produce a SOFC stack precursor. This precursor is fired at a predetermined temperature after pressure bonding and degreasing treatment.

  For example, an SOFC stack including the present interconnector can be obtained by the manufacturing process as described above. It is also possible to manufacture an SOFC stack having an interconnector structure corresponding to a specially shaped fuel electrode. Furthermore, an SOFC stack that also includes an anode buffer layer can be manufactured. Furthermore, an SOFC stack with a constraining layer can also be provided.

  The SOFC stack described above is further connected to a current collector or the like as necessary, to which a reducing gas and an oxidizing gas supply source are appropriately connected, and further provided with a heating device, so that a SOFC is provided. You can build a system.

  Note that the SOFC stack manufacturing method described above is merely an example of the SOFC stack manufacturing method disclosed in this specification. Therefore, according to a conventionally known SOFC manufacturing method, an appropriate combination of a stack of green sheets including at least one layer constituting a SOFC single cell or a SOFC stack, or a laminate by directly applying a slurry to a constituent layer, etc. SOFC single cells and SOFC stacks can be manufactured.

  Hereinafter, examples in which the disclosure of the present specification is embodied will be described, but the disclosure of the present specification is not limited to the following examples.

  In this embodiment, the SOFC stack is manufactured. Hereinafter, the ceramic material of each element in the SOFC stack is shown, and then the manufacturing process of the stack shown in FIGS. 5A to 5D will be described.

(Raw material of SOFC stack)
(1) Solid electrolyte Zirconia (ZrO) stabilized with 8 mol% of yttria (Y ₂ O ₃ ) added (8 mol% yttria stabilized zirconia: 8YSZ)
(2) Fuel electrode Mixture of nickel oxide (NiO) 60% by mass and 8YSZ 40% by mass (3) Air electrode La _0.8 Sr _0.2 MnO ₃ 50% by mass, 8YSZ 45% by mass and ceria (CeO ₂ ) 5% by mass (4) Fuel side interconnector (first layer of this interconnector)
La _0.3 Sr _0.7 TiO ₃
(5) Air-side interconnector (second layer of this interconnector)
La _0.8 Sr _0.2 MnO ₃ 50% by mass, 3YSZ 45% by mass and ceria 5% by mass (6) Seal part 8YSZ
(7) Constrained layer A mixture of La _0.8 Sr _0.2 MnO ₃ 50 mass%, 8 YSZ 45 mass% and ceria (CeO ₂ ) 5 mass%.

(2) Production process (2-1) Production of green sheet (green sheet for solid electrolyte)
A solid electrolyte raw material, a polyvinyl butyral binder, and ethanol as an organic solvent (hereinafter simply referred to as a solvent) were mixed to obtain a solid electrolyte slurry. Then, as shown to FIG. 5A, the green sheet 101 for solid electrolytes was created by the doctor blade method.

(Green sheet for fuel electrode)
20 parts by mass of acrylic particles in which 50% or more of the particles are distributed in an average particle diameter of 10 μm and an average particle diameter of ± 0.1σ with respect to 100 parts by mass of the fuel electrode raw material, and this mixed powder and polyvinyl butyral binder And a solvent were mixed to obtain a slurry for a fuel electrode. Also, 20 parts by mass of acrylic particles having an average particle diameter of 5 μm smaller than the previous acrylic particles and 50% or less of particles distributed within ± 0.1σ of the average particle diameter are added to 100 parts by mass of the fuel electrode raw material. The mixed powder, polyvinyl butyral binder, and mixed liquid were mixed to obtain a first slurry for the fuel electrode buffer. A second fuel electrode buffer slurry was prepared in the same manner except that 12 parts by mass of acrylic particles used in the fuel electrode slurry (corresponding to 60% of the fuel electrode slurry) were used.

  Next, a seal part slurry, a polyvinyl butyral binder, and a solvent were mixed to obtain a seal part slurry. Thereafter, as shown in FIG. 5B (a), the fuel electrode slurry and the seal portion slurry are sealed at the center of the green sheet using a doctor blade having a plurality of coating ports, and sealed at both ends. The fuel electrode green sheet 102 was prepared so as to include the portion 102b.

  Next, as shown in FIG. 5B (b), a line-and-line in which a plurality of linear flow path forming materials 103 are arranged at regular intervals using an acrylic resin composition on the fuel electrode green sheet 102. A pattern of the space-shaped flow path forming material 103 was produced by a screen printing method. Thereafter, as shown in FIG. 5B (c), on the pattern-printed fuel electrode green sheet 102, the slurry for the fuel electrode is flown by the doctor blade method until the height becomes about 60% of the height of the flow path forming material. The fuel electrode material layer 104a was formed by directly laminating between the path forming materials 103. In addition, the seal part 104b was simultaneously formed in the both ends of the fuel electrode material layer 104a using the slurry for seal parts. The layer including the fuel electrode material layer 104 a is also referred to as a fuel electrode material layer 104.

  Further, as shown in FIG. 5C (d), the first fuel electrode buffer slurry is laminated with a constant thickness so as to cover the whole including the flow path forming material 103 by the doctor blade method. 1 fuel electrode buffer material layer 105a was formed. Also at this time, seal portions 105b were formed at both ends at the same time. The corrugated layer including the first fuel electrode buffer material layer 105 a is also referred to as a first fuel electrode buffer material layer 105.

  Next, as shown in FIG. 5C (e), the fuel electrode side interconnector material layer 106 is formed by applying a slurry for the fuel electrode side interconnector in a corrugated shape following the first fuel electrode buffer material layer 105 by the doctor blade method. Formed.

  After that, as shown in FIG. 5C (f), the air electrode side interconnector slurry is laminated so as to fill the space between the convex portions due to the flow path forming material 103 and cover the fuel electrode side interconnector material layer 106. Thus, a green sheet 110 including the air electrode side interconnector material layer 107 was produced.

(Green sheet for air electrode)
20 parts by mass of acrylic particles in which 50% or more of the particles are distributed in an average particle diameter of 10 μm and an average particle diameter of ± 0.1σ with respect to 100 parts by mass of the air electrode raw material, and this mixed powder, polyvinyl butyral binder Then, a solvent was mixed to prepare an air electrode slurry. Thereafter, as shown in FIG. 5D (a), the air electrode slurry and the seal portion slurry are sealed at the center of the green sheet with the air electrode material layer 112a and at both ends, using a doctor blade having a plurality of coating ports. The air electrode green sheet 112 was prepared so as to include the portion 112b.

  Next, as shown in FIG. 5D (b), a line and space in which a plurality of linear flow path forming materials are arranged at regular intervals using an acrylic resin composition on the air electrode green sheet 112. A pattern of the flow path forming material 113 was created by screen printing. Thereafter, as shown in FIG. 5D (c), on the air electrode green sheet 112 on which the pattern is printed, the slurry for the air electrode is formed by the doctor blade method, and the entire height of the flow path forming material 113 and the flow path shape material 113 are formed. The air electrode material layer 114a was formed by directly stacking so as to cover the top surface. Also at this time, the seal portion 114b was formed at both ends at the same time to produce the green sheet 115 for the air electrode.

(Green sheet for constraining layer)
As shown in FIG. 5A (b), a constrained layer raw material, a polyvinyl butyral binder, and a solvent are mixed to obtain a slurry for a nonporous constrained layer, and a green sheet 120 for a nonporous constrained layer is obtained by a doctor blade method. Was made.

  As shown in FIG. 5A (b), a slurry obtained by adding 10 parts by mass of acrylic particles to 100 parts by mass of the raw material of the constraining layer, a polyvinyl butyral binder, and a solvent are mixed to obtain a slurry for the porous constraining layer. Then, a green sheet 121 for a porous constrained layer was produced by a doctor blade method.

(2-2) Lamination of Green Sheet and Production of SOFC Stack Next, the produced various green sheets were laminated in the following order. That is, as shown in FIGS. 6A (a) to 6 (b), a porous constraining layer green sheet 121 is laminated, a non-porous constraining layer green sheet 120 is laminated, and an air electrode green sheet 115 is further laminated. did. Further, the solid electrolyte green sheet 101 is laminated, and then, as shown in FIG. 6A (c), the fuel electrode green sheet 110 is laminated so that the fuel electrode layer is in contact with each other to form the lowermost cell precursor 201. did. Further, as shown in FIG. 6B (d), the air electrode green sheet 115, the solid electrolyte green sheet 101, and the fuel electrode green sheet with respect to the air electrode side interconnector material layer 107 of the fuel electrode green sheet 110. 110 was stacked to form a second cell precursor 202. Further, as shown in FIG. 6B (e), similarly, green sheets are laminated to form the third cell precursor 203, and the non-porous constraining layer is formed on the air electrode side interconnector material layer 107. A green sheet 120 for a stack was laminated, and a green sheet 121 for a porous constrained layer was further laminated to obtain a stack precursor 130 of this example.

(2-3) Firing The stack precursor 130 was subjected to pressure bonding by cold isostatic pressing (CIP) at 100 MPa and a temperature of 80 ° C. for 2 minutes. The pressure-bonded body was degreased at a temperature of 400 ° C., and then held at a temperature of 1400 ° C. for 2 hours to be fired to obtain a stack of examples.

  A stack of another example was obtained in the same manner as described above except that the second slurry for the fuel electrode buffer layer was used instead of the first slurry for the fuel electrode buffer layer.

  An overview of the stack of the example obtained by firing is shown in FIG. 6C. As shown in FIG. 6C, in the stack 30 of this embodiment, the thickness of the solid electrolyte 6 is about 20 μm, the thickness of the fuel electrode 2 between the reducing gas flow paths 22 is about 50 μm, and the reducing gas flow The thickness of the passage 22 is about 100 μm, the thickness of the air electrode 4 between the oxidizing gas passages 24 is about 50 μm, the thickness of the oxidizing gas passage 24 is about 200 μm, and the fuel electrode side interconnector (first Layer) 12 was about 10 μm, and the air electrode side interconnector (second layer) 14 was about 10 to 100 μm (minimum portion to maximum portion).

As a comparative example, an SOFC stack of the following mode was also produced at the same time. That is, the second layer material of the interconnector is changed to a mixture of La _0.8 Sr _0.2 MnO ₃ 50% by mass, “3YSZ” 45% by mass and ceria 5% by mass, La _0.8 Sr _0.2 MnO ₃ 50% by mass, A SOFC stack of Comparative Example 1 was produced by the same production process as the SOFC stack described above except that a mixture of 45% by mass of “8YSZ” and 5% by mass of ceria was used. Further, in the green sheet 110, the first fuel electrode buffer slurry is applied in such a thickness as to cover the entire height of the flow path forming member 103 to flatten the surface of the fuel electrode material layer as described above. A SOFC stack of Comparative Example 2 was produced in the same manufacturing process as the SOFC stack. Furthermore, a SOFC stack of Comparative Example 3 was manufactured by the same manufacturing process as the SOFC stack described above except that the first fuel electrode buffer layer was not provided.

It was confirmed that the stack of this example was provided with a stack having excellent integrity and electrical conductivity by including the first layer and the second layer as interconnectors. For example, when 3YSZ is used as the oxide material of the element contained in the solid electrolyte in the air electrode side interconnector (second layer), the air electrode / air electrode side interconnector / fuel electrode side interconnector / fuel electrode The electric resistance value was 0.13 Ω · cm ² , whereas in Comparative Example 1 using 8YSZ instead of 3YSZ, it was 0.54 Ω · cm ² .

  In addition, the stack of the present embodiment has a corrugated fuel electrode side interconnect by causing the fuel electrode side interconnector (first layer) to follow an electrode (fuel electrode) having a convex portion based on the gas flow path. The volume of the fuel electrode could be suppressed by providing the air electrode side interconnector (second layer) so as to fill the non-convex portion of the fuel electrode interconnector as a connector. As a result, it is possible to suppress the fuel electrode and hence the stack volume fluctuation due to the oxidation and reduction accompanying the start and stop of the SOFC. For example, assuming that the total amount of Ni used in the stack of Comparative Example 2 is 100, the amount of Ni used in the stack of this example was 40%.

  In addition, the stack of this embodiment has a fuel electrode buffer layer, so that the adhesion and integrity between the fuel electrode and the fuel electrode side interconnector (first layer) are improved, and the fuel electrode has a convex shape. The top surface of the reducing gas channel was well covered. When the cross-sectional structure around the reducing gas flow path between the stack of this example and the stack of Comparative Example 3 (without the fuel electrode buffer layer) was observed with a microscope, the fuel electrode side interconnector (No. 1). It should be noted that the stack of another embodiment including the second fuel electrode buffer layer having a porosity lower than that of the fuel electrode is also the adhesion and integrity between the fuel electrode and the fuel electrode side interconnector (first layer). Thus, it was possible to closely follow the convex portion of the fuel electrode, and to cover the top surface of the reducing gas channel well.

  In addition, the cell without the constraining layer was greatly deformed, while the cell with the constraining layer could be sintered flat.

Claims (10)

An interconnector used for a solid oxide fuel cell, comprising a fuel electrode, a solid electrolyte, and an air electrode,
Comprising at least a first layer located on the fuel electrode side and a second layer located on the air electrode side;
The first layer has higher electrical conductivity and gas barrier properties than the second layer in a reducing atmosphere,
The second layer is an interconnector having higher electrical conductivity and gas barrier properties than the first layer in an oxidizing atmosphere.   The interconnector according to claim 1, wherein the first layer contains a perovskite oxide doped with a rare earth element.   The interconnector according to claim 1, wherein the second layer includes a conductive ceramic material and an oxide material of an element contained in the solid electrolyte.   The interconnector according to claim 3, wherein the ion conductivity of the oxide material of the element contained in the solid electrolyte is lower than that of the oxide ion conductive material in the solid electrolyte.   The interconnector according to claim 1, wherein the first layer and the second layer are integrated by sintering. A solid oxide fuel cell stack including a plurality of single cells each including a fuel electrode, a solid electrolyte, and an air electrode,
A stack comprising the interconnector according to claim 1 between at least two single cells.   The stack of claim 6, wherein at least two of the single cells are integrated by sintering through the interconnector.   The stack according to claim 6 or 7, wherein the single cell has a thickness of 100 µm or more and 1000 µm or less.   The stack according to claim 6, wherein the fuel electrode has a thickness of 15 μm or more and 500 μm or less. A method for producing a solid oxide fuel cell stack comprising a plurality of single cells comprising a fuel electrode, a solid electrolyte and an air electrode,
In obtaining a stack in which at least a first single cell and a second single cell are stacked via an interconnector,
A fuel electrode material layer including a material of the fuel electrode of the first single cell, an interconnector material layer including a material of the interconnector, and an air electrode material including a material of the air electrode of the second single cell. And integrating the precursor of the stack including at least a layer by firing,
With
The interconnector material layer includes a first material layer located on the fuel electrode material layer side, and a second material layer located on the air electrode material layer side,
The first material layer is configured to have higher electrical conductivity and gas barrier properties than a second layer obtained from the second material layer in a reducing atmosphere,
The manufacturing method, wherein the second material layer is configured to have higher electrical conductivity and gas barrier properties than the first layer obtained from the first material in an oxidizing atmosphere.