WO2018042474A1 - Cell for solid oxide fuel cell, solid oxide fuel cell stack, and solid oxide fuel cell - Google Patents

Abstract

The present invention provides a solid oxide fuel cell that is capable of suppressing the formation of cracks around a gas flow passage. The solid oxide fuel cell according to the present invention is provided with: a fuel electrode; an air electrode; a solid electrolyte that is disposed between the fuel electrode and the air electrode; a reducing gas flow passage; and an oxidizing gas flow passage. At least one of the reducing gas flow passage and the oxidizing gas flow passage has an opening shape, in which the width of the opening at the distal end with respect to the solid electrolyte is smaller than the width of the opening at the proximal end with respect to the solid electrolyte.

Description

Solid oxide fuel cell, solid oxide fuel cell stack and solid oxide fuel cell

The present specification discloses a solid oxide fuel cell, a solid oxide fuel cell stack, and a solid oxide fuel cell.

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

Generally, in order to achieve a high current density in SOFC, it is necessary to supply a sufficient amount of reducing gas and oxidizing gas to the fuel electrode and the air electrode, respectively. For this reason, another gas flow path (reducing gas flow path and oxidizing gas flow path) is formed in an electrode that is a porous body.

As such a gas flow path, those having a rectangular opening shape (Patent Document 1) and those having a circular shape (Patent Document 2) are disclosed. Moreover, what has the gas flow path formed in the interconnector separate from the cell is disclosed (Patent Document 3).

International Publication No. WO2009 / 119971 JP 2012-252963 A International Publication No. WO2012 / 133044

Since SOFC manufactures cells by stacking different materials and firing them integrally, shrinkage due to firing occurs. Such shrinkage does not occur uniformly throughout the cell. For this reason, there are cases where unintended deformation and distortion around the gas flow path, as well as cracks associated therewith, occur. As a result, sufficient power generation characteristics may not be obtained or may deteriorate over time. The present specification provides an integrally sintered SOFC that can suppress cracks generated around a flow path even when various materials shrink by firing.

As a result of intensive studies by the inventors, it has been found that the shape of the gas flow path, particularly the opening shape of the gas flow path, is a major cause of cracking. According to the present specification, the following means are provided based on the above findings.

(1) an anode,
The air electrode,
A solid electrolyte disposed between the fuel electrode and the air electrode;
A reducing gas flow path;
An oxidizing gas flow path, and
At least one of the reducing gas channel and the oxidizing gas channel has an opening shape in which a width of a distal end with respect to the solid electrolyte is smaller than a width of a proximal end with respect to the solid electrolyte, Solid oxide fuel cell.
(2) The solid oxide fuel cell according to (1), wherein a width of the distal end is 20% or more and 90% or less with respect to a width of the proximal end.
(3) The cell for a solid oxide fuel cell according to (1) or (2), wherein the thickness of the reducing gas channel is 15% or more and 85% or less with respect to the maximum thickness of the fuel electrode.
(4) The solid oxide fuel cell according to any one of (1) to (3), wherein a thickness of the oxidizing gas channel is 15% or more and 85% or less with respect to a maximum thickness of the air electrode. Cell.
(5) The solid oxide fuel according to any one of (1) to (4), wherein a width of the proximal end of the reducing gas channel and the oxidizing gas channel is not less than 200 μm and not more than 1000 μm. Battery cell.
(6) The cell for a solid oxide fuel cell according to any one of (1) to (5), wherein the thickness of the cell is 100 μm or more and 1000 μm or less.
(7) A solid oxide fuel cell stack in which a plurality of the solid oxide fuel cell cells according to any one of (1) to (6) are stacked via an interconnector.
(8) A solid oxide fuel cell using the solid oxide fuel cell stack of (7).

It is a figure which shows a part (single cell C) of the SOFC stack containing an interconnector. It is a figure which shows a part (single cell C) of the SOFC stack containing an interconnector. It is a figure which shows an example of the laminated structure of an interconnector. It is a figure which shows another example of the laminated structure of an interconnector. It is a figure which shows another example of the laminated structure of an 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.

This specification relates to a cell for SOFC, a SOFC stack, and a SOFC. In particular, the present invention relates to a gas flow path formed in the SOFC cell. The SOFC disclosed in the present specification includes a reducing gas channel and an oxidizing gas channel. At least one of the reducing gas channel and the oxidizing gas channel has an opening shape in which the width of the distal end with respect to the solid electrolyte is smaller than the width of the proximal end with respect to the solid electrolyte. According to such an opening shape, the amount of the electrode material (fuel electrode material or air electrode material) existing on the distal side with respect to the solid electrolyte of the gas flow path is compared with the amount of the electrode material existing on the proximal side. And increase. Therefore, it is possible to effectively relieve stress applied to the gas flow path during firing. As a result, in addition to cracks in the fuel electrode, air electrode, and solid electrolyte around the gas flow path, deformation and distortion of the gas flow path, and in turn, peeling and cracking of the cell components can be suppressed. An excellent SOFC can be obtained.

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, additional features and disclosure disclosed below are further described in order to provide further improved solid oxide fuel cells, solid oxide fuel cell stack structures, methods of manufacturing the same, and the like. Or can be used separately or together with the disclosure.

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 containing 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, the 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. The oxidizing atmosphere is preferably composed of one or more oxidizing gases or a gas having a composition containing an inert gas in addition to the oxidizing gas. Examples of the oxidizing gas include oxygen, ozone, nitrous oxide, nitric oxide, and nitrogen dioxide.

(Interconnector)
The 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 a high electrical conductivity and a reducing gas barrier property in a reducing atmosphere. More specifically, the first layer 12 can have higher electrical conductivity and gas barrier properties than the second layer 14 described later in a reducing atmosphere. By providing the first layer 12, 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 the interconnector 10 only needs to exhibit integral sintering with the air electrode 4, electrical connectivity with the air electrode 4, and 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 expressed as (Ln _a M ¹ _b ) M ² O ₃ (however, a value that matches a perovskite structure such as a + b = 1). Is done. 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), and nickel (Ni). More than species. 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 oxides. 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 a 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, for example, the material of the fuel electrode 2 of the SOFC to which the interconnector is applied, the material of the air electrode 4, the operating temperature, the sintering temperature of the stack 30, and the like. The The first layer 12 is preferably made of a LaTiO ₃ oxide that exhibits high conductivity in a reducing atmosphere, and in particular, a (LaSr) TiO ₃ oxide such as La _0.3 Sr _0.7 TiO ₃ .

The first layer 12 may be configured by laminating 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 has the denseness that is generally provided in an interconnector. For example, the first layer 12 preferably has a relative density (according to Archimedes method) of 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 side of the interconnector 10 that is scheduled to be the air electrode 4 side or the air electrode 4 side (hereinafter simply referred to as the air electrode side). It is not limited to be positioned on 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 contains a conductive ceramic material and an oxide material of an element contained in the solid electrolyte. The second layer 14 includes an oxide material of an element contained in the solid electrolyte 6 by using a conductive ceramic material, exhibiting high conductivity and resistance in an oxidizing atmosphere, and integrity with the air electrode 4. Thus, the thermal expansion coefficient with the solid electrolyte 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 a 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, Ti, and other elements such as Cr, Fe, and Mg may be present 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, CeO doped with rare earth elements such as ZrO ₂ (zirconia), gadolinium (Gd), and Sm at least partially stabilized with rare earth elements such as yttrium (Y), scandium (Sc), and ytterbium (Yb). ₂ (ceria), LaGaO ₃ (lanthanum gallate) in which a part of La and Ga is substituted with an alkaline earth metal such as Sr or Mg.

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, in the interconnector, the ion conductivity may be restrained from limiting the performance of the interconnector. In order to adjust the ion conductivity of the oxygen ion conductive material, it is preferable to suppress the amount of rare earth element 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 interconnector 10 is applied is about 20% to 60%. When zirconia is used for the solid electrolyte, yttria or the like of about 6 mol% to 10 mol% 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 materials of the elements contained in the conductive ceramic material and the solid electrolyte are, for example, the material of the fuel electrode 2 of the SOFC to which the interconnector 10 is applied, the material of the air electrode 4, the operating temperature, and the sintering temperature of the stack, respectively. Etc. are selected as appropriate. The mixing 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 30% by mass. 70:30 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 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. May be. 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 has the denseness that is generally included in an interconnector. For example, the second layer 14 preferably has a relative density (according to Archimedes method) of 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 the interconnector will be described in detail later.

As will be described later, the interconnector 10 is preferably manufactured at the same time as the single cell stack is manufactured by interposing between the single cells in the manufacturing process of the SOFC stack 30. For example, an unsintered laminated body appropriately including the material layer of the first layer 12 and the material layer of the second layer 14 may be prepared as an 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 interconnector 10 as a whole is not particularly limited, but can adopt a form corresponding 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 whole thickness of the interconnector 10 is not specifically limited, For example, it can be 1 micrometer or more and 100 micrometers 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 10 is 8 × 10 ⁻⁶ K ⁻¹ or more and 12 × 10 ⁻⁶ K ⁻¹ or less. It is preferable. It is because peeling with 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 and sufficient interconnector characteristics as a whole. Further, in the production of the integrally sintered type metal material-free (in other words, all ceramics) SOFC stack 30, the material layer of the ceramic first layer 12 corresponding to the fuel electrode and the ceramic material corresponding to the air electrode By applying each 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. The layer 12 and the second layer 14 are also integrally sintered with each other. 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 30 can be improved.

(Solid oxide fuel cell (SOFC) stack)
The SOFC stack disclosed herein can include an interconnector between at least two single cells. According to such an SOFC stack, these single cells can be connected and separated with high electrical conductivity and gas barrier properties, and when they are 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 an 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, Y, Sc, Sm, Gd or the like can be used. Specifically, 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 can be mentioned.

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. The average pore diameter in the case of a spherical shape 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 can be provided with an anode buffer layer 2a that is smaller than the portion proximal to the first layer 12 of the interconnector 10 or distal to the interconnector 10. 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 a reducing gas flow path 22 (described later) is provided in the fuel electrode 2 and the fuel electrode 2 itself is provided with a convex portion 26 that follows the reducing gas flow path 22, the fuel electrode buffer layer 2a. Follows the convex portion 26 well, and even in a thin layer, the reducing gas flow path (disappearing member for forming the reducing gas flow path in the SOFC manufacturing process) 22 is disposed in the fuel electrode 2. It can be surely included. As a result, it is possible to avoid the direct contact of the top surface of the reducing 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 a form having the convex portion 26 that follows the reducing gas flow path 22, the thickness of the fuel electrode 2 itself can be reduced, and occurs when the SOFC stack 30 is started and stopped. The deposition fluctuation of the fuel electrode 2 due to oxidation and reduction of Ni contained in the fuel electrode 2 can be suppressed, and the separation, deformation and destruction in the SOFC stack 30 can be suppressed.

(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. 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 can be about 1 μm or more and 5 μm or less. .

(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, the adhesion of the interconnector 10 to the first layer 12 can be improved. 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 related to the pores, that is, the average pore diameter, the pore diameter distribution, and the 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 the 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 smaller particle size distribution, and the fuel electrode buffer layer 2a has a smaller average particle size. And / or an anode material containing a spherical pore former having a larger 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 reducing 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 micrometers or more and 400 micrometers or less, More preferably, it can be 50 micrometers or more and 300 micrometers 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 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 its porosity 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 may vary depending on the presence or absence of the oxidizing gas flow path 24 (described later) and the flow path form, but may be, for example, 15 μm or more and 500 μm or less. It can be set to 20 μm or more and 500 μm or less. Further, for example, the thickness may 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, examples of the solid electrolyte material include the oxygen ion conductive materials already exemplified.

The solid electrolyte 6 is dense and preferably has the same relative density as the interconnector 10 from the viewpoint of blocking gas permeation. 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.

(Reducing gas channel and oxidizing gas channel)
The single cell C of the SOFC has a reducing gas flow path 22 for a reducing gas containing hydrogen supplied to the fuel electrode 2 and an oxidizing gas containing oxygen supplied to the air electrode 4. An oxidizing gas channel 24 is provided. Hereinafter, for convenience of explanation, both are also simply referred to as “ gas flow paths 22 and 24”. 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. The reducing gas flow path 22 may be provided across the fuel electrode 2 and the interconnector 10, and the oxidizing gas flow path 24 may be provided across the air electrode 4 and the interconnector 10.

For example, as shown in FIG. 1, these gas flow paths 22 and 24 can 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 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. That is, the reducing gas flow path 22 only needs to be defined by the fuel electrode 2 at least a part of the outer periphery thereof. Similarly, at least part of the outer periphery of the oxidizing gas channel 24 only needs to be defined by the air electrode 4.

Further, for example, in the form shown in FIG. 2, at least the reducing 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 reducing gas passage 22, but only a part of the thickness of the reducing gas passage 22 is provided.

For example, as shown in FIG. 2, the fuel electrode 2 has one or more convex shapes convex toward the outside of the single cell C based on the outer shape, arrangement pattern, etc. of the reducing gas flow path 22. A portion 26 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 internal reducing gas channel 22 has a thickness (thickness or height in the stacking direction) of the reducing gas channel 22 in a region where the reducing gas channel 22 is not formed. ), The fuel electrode 2 is provided with a thickness not satisfying the above. That is, the fuel electrode 2 is provided with a thickness of less than 100% of the thickness of the reducing gas channel 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 of the thickness of the reducing gas flow path 22, for example, 80% or less, further, for example, 70% or less, and further, for example, 60% or less. Further, in this region, the fuel electrode 2 is 1% or more of the thickness of the reducing gas channel 22, for example, 10% or more, for example, 20% or more, and further, for example, 30% or more. It is. Typically, the thickness of the fuel electrode 2 can be 30% or more and 70% or less of the thickness of the reducing gas channel 22 in the gas channel non-formation region.

For example, in this region, the fuel electrode 2 is 90% or less of the maximum height of the reducing gas flow path 22 in the fuel electrode 2, for example, 80% or less, further, for example, 70% or less, further, for example, 60% or less, It can be 50% or less, further 40%, for example 30%, or 20% or less. Further, in this region, the fuel electrode 2 is 1% or more of the thickness of the reducing gas flow path 22, for example, 5% or more, for example, 10% or more. Typically, the thickness of the fuel electrode 2 can be 5% to 50% of the maximum height of the reducing gas channel 22 in the gas channel non-formation region.

Further, 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 a convex shape based on the reducing gas channel 22 is formed. The fuel electrode 2 that is in close contact with the portion 26 and encloses or covers the reducing gas flow path 22 can be easily formed. Although not particularly limited, it is preferable to mainly include the fuel electrode buffer layer 2 a in the upper part of the reducing gas channel 22.

Furthermore, by providing the first layer 12 of the interconnector 10 having suitable characteristics with respect to the fuel electrode 2 having the surface form including the convex portion 26 corresponding to one or more reducing gas flow paths 22. The electric conductivity and gas in the oxidizing atmosphere derived from the air electrode 4 of the adjacent single cell C are ensured by ensuring the electric conductivity and gas barrier property in the reducing atmosphere and further including the second layer 14. Interceptability can be secured. Thus, according to the ceramic two-layer containing structure of the interconnector 10, in accordance with not only the characteristics of the adjacent electrodes but also the surface form having changes, the surface that has changed in this way exhibits excellent followability and adhesion. The SOFC stack 30 having good integrity, moldability, and shape can be constructed by buffering the form. Further, according to the ceramic two-layer containing structure of the interconnector 10, the existence form of the two layers according to the electrode surface having such a change, that is, the thickness and arrangement pattern of each layer is also changed, so that the interconnector and the stack 30 are obtained. Performance can be optimized.

As shown in FIG. 1, the reducing gas channel 22 has a width at the distal end (upper side in the drawing) with respect to the solid electrolyte 6 and a proximal end (lower side in the drawing) with respect to the solid electrolyte 6 when viewed in cross section. An opening shape smaller than the width of the side) can be provided. The relative volume of the reducing gas channel 22 is preset based on the size of the SOFC in which it is formed and the material of each element. In the present specification, by adopting the above-described configuration, the amount of the fuel electrode material in the vicinity of the interface between the fuel electrode 2 and the interconnector 10 can be increased without changing the volume of the reducing gas passage 22. . For this reason, the stress applied to the periphery of the reducing gas flow path 22 during the firing of SOFC can be relaxed suitably.

The opening shape of the reducing gas channel 22 is not limited to the trapezoidal shape shown in FIG. 1 as long as the width of the distal end with respect to the solid electrolyte 6 is smaller than the width of the proximal end. The shape can be taken. For example, in addition to a tapered opening shape configured so that the opening width gradually decreases from the proximal end to the distal end, the opening shape between the distal end and the proximal end is convex outward. Various shapes such as a shape in which the opening width is expanded and a part of the opening width is larger than that of the distal end can be adopted. Further, the ratio of the width of the distal end to the solid electrolyte 6 with respect to the width of the proximal end is not particularly limited. For example, it may be a semicircular shape as shown in FIG. 2, a triangular shape, a polygonal shape, or the like in which the width of the distal end from the solid electrolyte 6 is difficult to define. The opening shape may not be symmetrical in the width direction.

In order to relieve such stress more suitably, the opening shape of the reducing gas flow path 22 is clear at the outer peripheral edge of the distal end (upper side of the drawing) with respect to the solid electrolyte 6 as shown in FIG. It is preferable not to have a corner (that is, a curved surface shape or a curved shape).

Various forms of disposing the reducing gas flow path 22 in the fuel electrode 2 have been described, but the above forms can also be applied to the oxidizing gas flow path 24 in the air electrode 4. In addition, as for the opening shape of these gas flow paths 22 and 24, only any one can also take the shape mentioned above, and both can also take the shape mentioned above. Preferably, the reducing gas channel 22 has the above-described opening shape. More preferably, both the reducing gas channel 22 and the oxidizing gas channel 24 have the above-described opening shape. By applying such a form, cracks and peeling can be further suppressed.

The thickness of the gas flow paths 22 and 24 (that is, the height in the direction along the stacking direction of the elements in the cell C) depends on the thickness of the fuel electrode 2 and the air electrode 4, but is not particularly limited. For example, the maximum thickness of the fuel electrode 2 and the air electrode 4 can be 15% or more and 85% or less. Preferably they are 20% or more and 80% or less, More preferably, they are 30% or more and 70% or less. Moreover, the thickness of the gas flow paths 22 and 24 can be 50 micrometers or more and 400 micrometers or less, for example. Preferably, the thickness of the reducing gas channel 22 is not less than 100 μm and not more than 200 μm, and the thickness of the oxidizing gas channel 24 is not less than 150 μm and not more than 300 μm.

The width of the proximal end of the gas flow paths 22 and 24 with respect to the solid electrolyte 6 (that is, the width in the surface direction of each element when the gas flow paths 22 and 24 are viewed in cross section) is not particularly limited. For example, it can be 200 μm or more and 1000 μm or less. Preferably they are 250 micrometers or more and 800 micrometers or less, More preferably, they are 300 micrometers or more and 600 micrometers or less.

The width of the distal end with respect to the solid electrolyte 6 of the gas flow path 22, 24 is not particularly limited as long as it is smaller than the width of the proximal end. % Or less. Preferably, it is 50% or more and 80% 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. Patterns that are arranged on the inside in order of decreasing size, patterns in which one or more spiral flow paths are arranged, patterns that are arranged so that the flow paths extend radially from the center, and in a grid pattern Examples include a pattern in which a flow path is 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.

Further, the surface of the fuel electrode 2 and / or the air electrode 4 of the single cell C can 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 that are included.

The SOFC single cell C and the SOFC stack 30 can appropriately include 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.

(Interconnector structure for SOFC and SOFC stack)
The SOFC disclosed in this specification may 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 connected via the interconnector 10. Has a structured. 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 through an interconnector 10 to form a SOFC stack 30. ing. The first layer 12 and the second layer 14 of the interconnector 10 can take various laminated forms depending on the mode of each power generation element in the SOFC.

For example, in the case of a flat plate type SOFC, there is 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 form, 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. In this state, 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 is different from FIG. 3B in that the second layer 14 for the air electrode 4 has a curved portion 14c and a bottom portion following the surface form having a convex portion 28 based on the oxidizing gas flow path 24 of the air electrode 4. 14d, which is a wavy or corrugated layer having a substantially uniform thickness. The first layer 12 has a filling portion 12d that fills the bottom portion 14d of the second layer 14, and the curved portion 14c is thinly covered. The form provided with the coating | coated part 12c to perform 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 14 can be applied to the air electrode 4 in a necessary and sufficient form. Further, the second layer 14 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 a non-porous layer 42 including at least a conductive ceramic material and an oxide material of an element included in the solid electrolyte. By providing such a 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 peeling is less likely to occur at the interface with the interconnector 10 or the air electrode 4 within this range. 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.

The constraining layer 40 can further include a porous layer 44 that is porous including the conductive ceramic material and the oxide material of the element contained in the solid electrolyte, like the non-porous layer 42. 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 that 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 contained 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 be the same, which may be different in composition (formulation), 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 and the solid electrolyte. The oxide material of the element can be 30:70 to 70:30 or the like, or 40:60 to 60:40 by mass ratio.

Further, each of the layers 42 and 44 can appropriately contain an additive in order to enhance the sinterability or improve the heat resistance during high-temperature firing. 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 pore shape 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.

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

The constraining layer 40 can be provided at any site in the SOFC. That is, the constraining layer 40 can be provided on either one or both of the fuel electrode 2 side and the air electrode 4 side in the single cell C, and at least a part of the plurality of single cells C included in the stack 30. A constraining 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, the interconnector 10 exhibits conductivity and resistance to reducing gas and oxidizing gas applied to the SOFC, and is suitable for integral sintering with the cell C. It has become. As a result, according to the 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.

Also, the SOFC stack manufacturing method disclosed in the present specification can include a step of forming a reducing gas channel and an oxidizing gas channel. In this manufacturing method, at least one of the reducing gas channel and the oxidizing gas channel has an opening shape in which the width of the distal end with respect to the solid electrolyte is smaller than the width of the proximal end with respect to the solid electrolyte. It can be constituted as follows.

According to this manufacturing method, when the SOFC stack is integrally sintered, stress generated around the gas flow path can be relieved, and cracking of the stack and peeling of various members can be suppressed, thereby improving the yield. Can be made.

The manufacturing method of the SOFC stack in the present specification can generally conform to a known manufacturing method of an integrally sintered 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.

Also, the firing method of the laminate (stack precursor) of the material layers of each element of the SOFC stack can generally conform to the manufacturing method of a known integrally sintered 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 above 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) as necessary at a temperature of about 60 ° C. to 120 ° C. This pressure-bonded body can be degreased at a temperature in the range of 300 ° C to 500 ° C.

It should be noted that methods for producing the slurry and the green sheet itself are 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.

The method of forming gas flow paths in the fuel electrode, air electrode and interconnector is 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. Specifically, the above-mentioned configuration is made by processing methods such as cutting, laser, punching, etc. of polymer materials such as acrylic, polyethylene, polystyrene, etc., which will be the disappearing material, laser printing, punching, etc. Then, when the cells are integrally fired, the lost material is burned away, whereby a cavity serving as a gas flow path having the shape disclosed in this specification can be obtained.

Also, an electrode green sheet including a sealing material layer that becomes 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 adopting an interconnector, a fuel electrode buffer layer, and a constraining layer as appropriate, advantages according to each element can be exhibited in the manufacturing method, and SOFC with excellent power generation characteristics, integrity, etc. You can get a stack.

Hereinafter, an outline of an example of this manufacturing method will be described. 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.

In addition, the application of the flow path forming material is in the range of 15% to 85% with respect to the maximum thickness of the fuel electrode material layer and the air electrode material layer, and the width is in the range of 200 μm to 1000 μm. As shown in FIG.

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

These SOFC stack precursors can be prepared by laminating these green sheets so as to include an appropriate number, for example, 2 to 30 or less, for example, 5 to 20 or less. This precursor is fired at a predetermined temperature after pressure bonding and degreasing treatment.

For example, an SOFC stack including an 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.

This example is an example of manufacturing an SOFC stack. Hereinafter, the ceramic material of each element in the SOFC stack will be 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% 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 interconnector)
La _0.3 Sr _0.7 TiO ₃
(5) Air side interconnector (second layer of 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%, 8YSZ 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 solvent 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 (equivalent to 60% of the fuel electrode slurry) were used.

Next, a seal portion slurry, a polyvinyl butyral binder, and a solvent were mixed to obtain a seal portion 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.

Thereafter, as shown in FIG. 5C (f), the slurry for the air electrode side interconnector is filled between the convex portions due to the fuel electrode flow path forming material 103 so as to cover the fuel electrode side interconnector material layer 106. The green sheet 110 including the air electrode side interconnector material layer 107 was produced by laminating.

(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, a 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) Green Sheet Lamination and SOFC Stack Production Next, the produced green sheets were laminated in the following order. 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 laminated. did. Further, the solid electrolyte green sheet 101 is laminated, and then, as shown in FIG. 6A (c), the fuel electrode layer 102b of the fuel electrode green sheet 110 is laminated so that the lowermost cell precursor 201 is formed. The air electrode side interconnector material layer 107 was formed thereon. 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) for 42 minutes at a temperature of 100 MPa and 80 ° C. 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 fuel electrode buffer layer slurry was used instead of the first fuel electrode buffer layer slurry.

The outline 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 thickness of the air electrode side interconnector 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 replaced with a mixture of La _0.8 Sr _0.2 MnO ₃ 50 mass%, “3YSZ” 45 mass%, and ceria 5 mass%, La _0.8 Sr _{0 .2} A SOFC stack of Comparative Example 1 was manufactured by the same manufacturing process as the SOFC stack described above except that a mixture of 50% by mass of MnO _3, 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 includes the 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). In addition, 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.

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

Further, in the stack of the present embodiment, the opening shape of the gas flow path is such that the width at the distal end with respect to the solid electrolyte is smaller than the width at the proximal end, so that the interconnector and the fuel electrode or the air electrode It was possible to improve the bonding strength. When the cross-sectional structure of the gas flow path of the stack of this example was observed with a microscope, it was confirmed that the opening shape of the gas flow path was substantially trapezoidal.

Claims (8)

1. An anode,
   The air electrode,
   A solid electrolyte disposed between the fuel electrode and the air electrode;
   A reducing gas flow path;
   An oxidizing gas flow path, and
   At least one of the reducing gas channel and the oxidizing gas channel has an opening shape in which a width of a distal end with respect to the solid electrolyte is smaller than a width of a proximal end with respect to the solid electrolyte, Solid oxide fuel cell.
2. The solid oxide fuel cell according to claim 1, wherein the width of the distal end is 20% or more and 90% or less with respect to the width of the proximal end.
3. The cell for a solid oxide fuel cell according to claim 1 or 2, wherein the thickness of the reducing gas channel is 15% or more and 85% or less with respect to the maximum thickness of the fuel electrode.
4. The solid oxide fuel cell according to any one of claims 1 to 3, wherein a thickness of the oxidizing gas channel is 15% or more and 85% or less with respect to a maximum thickness of the air electrode.
5. The solid oxide fuel cell according to any one of claims 1 to 4, wherein a width of the proximal end of the reducing gas channel and the oxidizing gas channel is 200 μm or more and 1000 μm or less.
6. 6. The cell for a solid oxide fuel cell according to claim 1, wherein the cell has a thickness of 100 μm or more and 1000 μm or less.
7. A solid oxide fuel cell stack in which a plurality of the solid oxide fuel cell cells according to any one of claims 1 to 6 are laminated via an interconnector.
8. A solid oxide fuel cell using the solid oxide fuel cell stack according to claim 7.

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