JP2019212374A - Bonding structure of sofc, and conductive bonding material used therefor - Google Patents

Abstract

To provide a bonding structure of SOFC which enables the bonding with a high bonding strength while ensuring an electrical conduction property of an air electrode and an interconnector even in the case of using a metal interconnector with a spinel coating.SOLUTION: The bonding structure comprises: an air electrode of SOFC; a metal interconnector; and a bonding member for bonding them. The metal interconnector has a spinel layer on a surface of a metal substrate on a side opposed to the bonding member; the spinel layer includes a first spinel phase represented by the following general formula: MO. The bonding member includes: a perovskite phase represented by the general formula, ABO; and an oxide phase represented by the general formula, MO. In the formula, A is two or more elements selected from a group consisting of La, Sr and Ba, and B is one or more elements including at least Co, and Mis two or more elements selected from a group consisting of Ni, Fe, Co and Cu.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a connection structure for connecting an SOFC air electrode and an interconnector, and a conductive bonding material used therefor.

  Solid Oxide Fuel Cell (SOFC, hereinafter referred to simply as “SOFC”) is a type of fuel cell that has high power generation efficiency and low environmental impact among various types of fuel cells. Its demand is increasing because it has advantages such as being usable. An SOFC single cell is essentially composed of a dense layered solid electrolyte made of an oxygen ion conductor, and a porous structure of an air electrode (cathode) on one side of the solid electrolyte and the other side. A fuel electrode (anode) having a porous structure is formed. In general, a plurality of the single cells are stacked (stacked) and electrically connected to be used as an SOFC stack. For connection of single cells, an interconnector and a joining member that electrically connects the interconnector and the SOFC are used. In recent years, as an interconnector, the use of ferritic stainless steel having a thermal expansion coefficient close to that of yttria-stabilized zirconia (YSZ) which is a solid electrolyte and excellent in oxidation resistance has been studied.

JP 2011-108621 A

  About this metal interconnector, chromium (Cr) contained in ferritic stainless steel diffuses at a high temperature in the operating temperature of SOFC (for example, 700 ° C. or more), and particularly reacts with the air electrode material. There is a problem of degrading performance (chromium poisoning). Recently, the diffusion of chromium from the ferritic stainless steel is suitably suppressed by surface-treating the surface of the interconnector with a transition metal oxide having a spinel crystal structure (for example, see Patent Document 1). It was discovered that Therefore, as a metal interconnector for SOFC, the surface of a base material made of ferritic stainless steel is coated with a spinel transition metal oxide (hereinafter referred to as spinel coating).

  However, this spinel coating cannot be said to have sufficient bondability, and peeling and cracking occur when the temperature changes during operation of the SOFC, and the resistance at the bonding interface tends to increase. In particular, the SOFC is required to further improve heat cycle resistance for the purpose of rapid heating at start-up, time reduction at the time of shutdown during maintenance or abnormality. Therefore, when using the metal interconnector provided with the spinel coating, there is a problem that the bonding strength is inferior compared to the case of using the interconnector made of a ceramic material.

  The present invention has been created to solve the above-mentioned conventional problems, and the object thereof is, for example, even when a metal interconnector having a spinel coating is used, for example, an SOFC air electrode and an interconnector. It is to provide a bonding structure that can be bonded with high bonding strength while ensuring electrical conductivity.

In order to achieve the above object, the present invention provides a joining structure for joining an SOFC air electrode and a metal interconnector. The joining structure includes an SOFC air electrode, a metal interconnector, and a joining member that joins the air electrode and the metal interconnector. Here, the metal interconnector is provided on a metal base material containing at least Fe and Cr, and a surface of the metal base material on the side facing the joining member, and has a general formula: M ¹ ₃ O ₄ (however, the formula And M ¹ is one or more elements selected from transition metals.); And a spinel layer including a first spinel phase represented by: In addition, the bonding member has a general formula: ABO ₃ (wherein A is two or more elements selected from the group consisting of La, Sr and Ba, and B is one or more containing at least Co) And a perovskite phase represented by the general formula: M ² ₃ O ₄ (wherein M ² is selected from the group consisting of Ni, Fe, Co and Cu) And an oxide phase represented by;

  In the above configuration, the metal interconnector has a spinel layer on the surface, and the diffusion of Cr is suppressed. The SOFC air electrode is mainly composed of a perovskite transition metal oxide. And the joining member disclosed here contains the perovskite phase and oxide phase which are specified by the said general formula. When a joining member contains the said oxide phase, the physical joining property and electrical joining property with respect to the spinel layer of the surface of metal interconnectors are improved. The reason why such an effect is manifested is not clear, but at the operating temperature of SOFC, the perovskite type transition metal oxide exhibits band conduction, and the oxide phase having the above composition can be a spinel type transition metal oxide. Can exhibit hopping conduction. As a result, the joining member achieves good electrical conductivity. Further, since the joining member includes the perovskite phase and the oxide phase, the joining member exhibits high joining property to the spinel layer of the metal interconnector and also maintains high joining property to the SOFC air electrode. be able to. Since these are integrated by, for example, sintering, electrically good bonding is realized even at the bonding interface, and the interface resistance can be kept low. As a result, a joint structure having both joint strength and interface resistance characteristics is provided.

  In a preferable embodiment of the junction structure disclosed herein, the perovskite phase includes La and Sr as the element A, and Co as the element B. For example, the perovskite phase is preferably strontium cobaltite or lanthanum strontium cobaltite. Such a perovskite phase may have, for example, a crystal structure similar to or equal to a material widely used as an SOFC air electrode material and similar in thermal characteristics. With such a configuration, for example, a joining structure that can maintain the power generation performance of SOFC well even at a low temperature of about 600 ° C. or higher and 800 ° C. or lower is provided.

In a preferred embodiment of the junction structure disclosed herein, the oxide phase has any one selected from NiFe ₂ O ₄ , NiCo ₂ O ₄ , and CoFe ₂ O ₄ as a main phase.
Here, the “main phase” means that the spinel phase contains 50 mol% or more of the phase composed of any one of the above oxides. This improves the bonding property of the bonding material with the spinel layer on the surface of the metal interconnector. In addition, good bondability can be maintained even when a severe heat cycle is repeatedly applied, for example, from room temperature to a temperature range of about 600 ° C. to 800 ° C.

  In a preferable aspect of the bonding structure disclosed herein, in the bonding member, a mass ratio of the perovskite phase to the oxide phase is 90:10 to 20:80 as a perovskite phase: oxide phase. This provides a joint structure that can achieve good jointability between the air electrode and the metal interconnector.

  In a preferred embodiment of the joint structure disclosed herein, the metal substrate is ferritic stainless steel. Ferritic stainless steel has a coefficient of thermal expansion (CTE) close to yttria stabilized zirconia (YSZ), which is a solid electrolyte. Moreover, since ferritic stainless steel contains chromium at a relatively high concentration, it forms a dense and highly adherent oxidation-resistant passive film on the surface of the steel in an oxygen-containing atmosphere. As a result, the metal substrate can maintain good conductivity and oxidation resistance for a long time without corroding in the operating environment of SOFC. This suppresses the occurrence of internal stress at the joint with the air electrode and the metal interconnector due to a temperature change based on the operation and stop of the SOFC. This is preferable because a stable joint structure can be realized over a long period of time.

In another aspect, the technology disclosed herein provides a conductive joining material for forming a joining member that joins an air electrode of a solid oxide fuel cell and a metal interconnector. Here, the metal interconnector is provided on a surface of a metal base containing at least Fe and Cr, and on the surface of the metal base facing the joining member, and has a general formula: M ¹ ₃ O ₄ (however, M ¹ in the formula is one or more elements selected from transition metals.); A spinel layer including a first spinel phase represented by: The conductive bonding material has a general formula: ABO ₃ (wherein A is two or more elements selected from the group consisting of La, Sr and Ba, and B is one or more containing at least Co) A perovskite oxide powder having a perovskite type crystal structure represented by: and an alloy powder containing two or more elements selected from the group consisting of Ni, Fe, Co and Cu. Including. According to said structure, the perovskite oxide phase and the oxide phase derived from alloy powder are formed in a joining member. The oxide phase derived from this alloy powder mainly contains a spinel phase, and is superior in conductivity, for example, compared to an oxide phase derived from a simple metal or an oxide phase derived from a spinel oxide, This is preferable because the bondability to the metal interconnector can be good. Although the detailed reason is not clear, the improvement of the bondability is due to the fact that the spinel layer formed on the surface of the metal interconnector and the metal species contained in the alloy powder are easily dissolved. Conceivable. Cr poisoning is suppressed by the spinel layer including the first spinel phase. Thereby, for example, even at a low temperature of about 600 ° C. or higher and 800 ° C. or lower, it is possible to suitably form a bonding member having good bonding properties with a metal interconnector that can suppress Cr poisoning.

  In a preferred embodiment of the conductive bonding material disclosed herein, the average particle size of the alloy powder is smaller than the average particle size of the perovskite oxide powder. For example, the average particle size of the perovskite oxide powder is preferably 0.1 μm or more and 15 μm or less, and the average particle size of the alloy powder is preferably 0.1 μm or more and 10 μm or less. Thereby, even when the proportion of the alloy powder is reduced, it is preferable because the contribution by the alloy powder can be exhibited.

  In a preferred embodiment of the conductive bonding material disclosed herein, a metal component-containing powder is further included as a sintering aid. Moreover, it is preferable that Cu-containing powder is contained as the sintering aid, and at least one of the perovskite oxide powder and the alloy powder contains Cu at the B site. This is preferable in that the perovskite oxide powder and the alloy powder can start sintering from a lower temperature and can produce a bonded member having good bondability at a lower temperature. In addition, since the sintering aid is a Cu-containing powder, the sinterability of the perovskite oxide powder and the alloy powder is further improved, and a bonded member having excellent adhesion and bondability is produced. It is preferable because

  In a preferable embodiment of the conductive bonding material disclosed herein, the conductive bonding material includes a dispersion medium in which the perovskite oxide powder and the alloy powder are dispersed, and is in a paste form (including forms such as slurry and dispersion; the same applies hereinafter). Has been prepared. This is preferable because the uniform dispersibility of the perovskite oxide powder and the alloy powder can be improved, and a conductive bonding material that can suitably employ a supply method such as printing or coating is provided.

  In a preferred embodiment of the conductive bonding material disclosed herein, the conductive bonding material prepared in a paste form, having a firing shrinkage rate of 3% or less when dried at 150 ° C. and then fired at 850 ° C. . Thereby, the shrinkage | contraction at the time of baking can be suppressed and a joining member can be produced with sufficient adhesiveness with metal interconnectors.

  As described above, according to the technology disclosed herein, a conductive bonding material capable of bonding an SOFC air electrode and a metal interconnector with good adhesion and bondability is provided. Therefore, the technology disclosed herein includes an SOFC including a fuel electrode, a solid electrolyte, and an air electrode, a metal interconnector, and a joining member that joins the air electrode and the metal interconnector. A stack is also provided. Here, the joining member is composed of a fired product of the conductive joining material described above. The conductive bonding material can form the bonding member suitably by firing at a low temperature of 900 ° C. or lower, for example. Therefore, since it is not necessary to expose the SOFC to a high temperature of, for example, 1000 ° C. or higher when stacking the SOFC, it is provided that migration and deterioration of various components in the SOFC single cell are suppressed.

It is a disassembled perspective view which shows typically the SOFC stack which concerns on one Embodiment. (A) is a SEM image which shows the EDX analysis area | region about the junction structure which concerns on one Embodiment, (b)-(g) is an element map of La, Sr, Fe, Co, Cr, O, respectively. It is a XRD analysis result after baking (1) Fe-Ni alloy paste and (2) Fe-Co alloy paste. (A)-(d) is a figure explaining the mode of the image analysis of Co map.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification (for example, conductive bonding materials and bonding members) and matters necessary for the implementation of the present invention (for example, a single SOFC that does not characterize the present invention). The cell configuration, SOFC manufacturing and operation processes, etc.) can be grasped as design matters of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Further, in the present specification, the notation “X to Y” indicating a numerical range means “X or more and Y or less” unless otherwise specified.

[SOFC stack]
FIG. 1 is an exploded perspective view schematically showing a SOFC stack 1 according to an embodiment. The SOFC stack 1 provided by the technology disclosed herein includes a plurality of SOFC single cells 10A and 10B and a plurality of metal interconnectors 50 and 50A. The SOFC stack 1 has a stack structure in which SOFC single cells 10A and 10B are stacked via metal interconnectors 50 and 50A. The SOFC stack 1 can be manufactured according to a known manufacturing method.

The configuration of the single cells 10A and 10B may be the same as the conventional one, and is not particularly limited. In the present embodiment, each of the unit cells 10A and 10B is based on the solid electrolyte layer 30, and the air electrode (cathode) 20 is provided on one surface of the solid electrolyte layer 30, and the fuel electrode (anode) 40 is provided on the other surface. Is integrated.

The solid electrolyte layer 30 is located between the air electrode 20 and the fuel electrode 40. The solid electrolyte layer 30 has a role of selectively transmitting oxygen ions (O ²⁻ ). The solid electrolyte layer 30 also has a role of separating the gas flowing through the air electrode 20 and the gas flowing through the fuel electrode 40. The solid electrolyte layer 30 is formed of a dense thin layer made of an oxygen ion conductive material. Examples of the oxygen ion conductive material include zirconia stabilized with a stabilizer such as yttria (for example, YSZ: Yttria stabilized zirconia) and ceria doped with a dopant such as gadolinia (for example, GDC: Gadolinia doped ceria). Etc.

The air electrode 20 has a role of supplying oxygen ions at a relatively high concentration to one surface of the solid electrolyte layer 30. The air electrode 20 is supplied with an oxygen-containing gas (typically air or the like) containing oxygen as a raw material for oxygen ions. The air electrode 20 generates oxygen ions from oxygen. The air electrode 20 is a porous body made of an oxygen ion / electron composite conductive material in order to efficiently generate oxygen ions. The oxygen ion electron composite conductive material is a perovskite oxide mainly composed of lanthanum cobaltite (LaCoO ₃ ) or lanthanum manganite (LaMnO ₃ ) from the viewpoint of low reactivity with the solid electrolyte.

The fuel electrode 40 has a role of relatively reducing the concentration of oxygen ions on the other surface of the solid electrolyte layer 30. A fuel gas that can react with oxygen ions and consume oxygen ions is supplied to the fuel electrode 40. The fuel gas is typically hydrogen (H ₂ ) or hydrocarbon (eg, methane; CH ₄ ), ammonia (NH ₃ ), and the like. The fuel electrode 40 has a role of promoting the reaction between oxygen ions and fuel gas. Further, the fuel electrode 40 has a role of receiving electrons emitted by consumption of oxygen ions and conducting them to an external load. The fuel electrode 40 is a porous body made of, for example, a catalyst material having a catalytic action. The catalyst material is, for example, a nickel-based metal material (for example, Ni or NiO) or a cermet of a nickel-based metal material and a solid electrolyte material (for example, yttria-stabilized zirconia).

  The metal interconnectors 50 and 50A are elements for electrically connecting the plurality of single cells 10A and 10B to each other and taking out the electrons generated in the single cells 10A and 10B to the outside. A metal interconnector 50A located in the center of FIG. 1 is interposed between two single cells 10A and 10B and connects the single cells 10A and 10B in series. However, the single cells 10A and 10B may be connected in parallel. A spinel layer (not shown) is provided on the surfaces of the metal interconnectors 50 and 50A. Thereby, the diffusion of Cr from the metal interconnectors 50 and 50A can be suppressed.

The metal interconnector 50A is stacked with the single cell 10A so that the cell facing surface 52 faces the air electrode 20. The metal interconnector 50A is stacked with the single cell 10B so that the cell facing surface 54 faces the fuel electrode 40. The cell facing surface 52 on the side facing the air electrode 20 of the metal interconnector 50, 50A is formed with, for example, a plurality of grooves, and constitutes an oxygen-containing gas flow path 53 for flowing an oxygen-containing gas. Yes. The oxygen-containing gas channel 53 is connected to an oxygen-containing gas supply source (not shown). Further, for example, a plurality of groove portions are formed on the cell facing surface 54 of the metal interconnectors 50, 50A facing the fuel electrode 40, and a fuel gas flow path 55 for flowing the fuel gas is formed. Yes. The fuel gas channel 55 is connected to a fuel gas supply source (not shown). The metal interconnectors 50 and 50A and the single cell 10A are hermetically joined by the joining member 60. The metal interconnector 50, the joining member 60, and the single cells 10A and 10B are joined together to form the joining structure disclosed herein.
In FIG. 1, the joining member 60 is provided on the entire surface of the air electrode 20 on the side facing the metal interconnector 50. Thereby, a work process can be simplified and the joining member 60 can be provided. However, the joining member 60 can also be provided only between the cell facing surface 52 and the air electrode 20. Moreover, the joining member 60 can also be provided in part or all of the surface of the metal interconnectors 50 and 50A. Further, the joining member 60 can be provided between the cell facing surface 54 and the fuel electrode 40.

At the time of SOFC power generation, the temperature of the SOFC stack 1 is raised to a high temperature range of 600 ° C. or higher, for example, about 600 to 900 ° C. Further, at such an operating temperature, the oxygen-containing gas channel 53 is supplied with an oxygen-containing gas, for example, air (Air). A fuel gas, for example, hydrogen (H ₂ ) is supplied to the fuel gas channel 55. When gases having different oxygen partial pressures are supplied to one surface and the other surface of the solid electrolyte layer 30, a difference in oxygen concentration occurs. This becomes an electromotive force, and oxygen is decomposed at the air electrode 20 to form oxygen ions. The oxygen ions move inside the solid electrolyte layer 30 from the air electrode 20 toward the fuel electrode 40. In the fuel electrode 40, oxygen ions and the fuel gas react to generate water (H ₂ O), and electrons are emitted. Thereby, the production | generation of the electrical energy by SOFC is implement | achieved.

  In this embodiment, each of the single cells 10A and 10B has a three-layer structure. However, the structure of the single cells 10A and 10B is not limited to this. The single cells 10A and 10B may have layers other than those described above. For example, a reaction suppression layer (not shown) for stabilizing the interface between the solid electrolyte layer 30 and the air electrode 20 may be provided. The reaction inhibition layer can be composed of a porous body made of, for example, YSZ or GDC.

  Further, the unit cells 10 </ b> A and 10 </ b> B can form the fuel electrode 40 thicker than the solid electrolyte layer 30 and the air electrode 20. Such single cells 10A and 10B are anode-supported cells (ASC) cells in which the anode 40 also has a function as a support. On the other hand, the single cells 10A and 10B may be, for example, an electrolyte-supported cell (ESC) cell in which the solid electrolyte layer 30 is thickened, or an air electrode supported type in which the air electrode 20 is thickened. (Cathode-Supported Cell: CSC) cell may be used. Further, it may be a metal-supported cell (MSC) provided with a porous metal sheet outside the fuel electrode 40 (on the side opposite to the solid electrolyte layer 30). Furthermore, the form of the single cells 10A and 10B is not particularly limited. Although not specifically shown, the single cells 10A and 10B are, for example, a flat plate type, a MOLB type, a vertical stripe cylindrical type (Tubular), or a flat cylindrical type (Flat tubular) in which the peripheral side surface of the cylinder is vertically crushed. ), And various structures such as a monolithic laminated type.

[Metal interconnector]
Here, although not specifically illustrated, the metal interconnectors 50 and 50A used in the SOFC stack 1 include a metal base material and a spinel layer.

The metal base material is a main component of the metal interconnector, and has an electronic conductivity, heat resistance, and CTE close to the single cells 10A and 10B (particularly, the solid electrolyte layer 30) in the operating temperature range of the SOFC. Desired. From this point of view, the metal interconnectors 50 and 50A can be preferably made of an iron-chromium alloy (Fe—Cr alloy) containing at least iron (Fe) and chromium (Cr). Examples of the Fe—Cr alloy include ferritic stainless steel, austenitic stainless steel, and austenitic / ferritic stainless steel, and any of these may be used. Among these, from the viewpoint of suitably forming a passive film showing good heat resistance and oxidation resistance in an oxygen atmosphere, the metal substrate is preferably an Fe—Cr alloy containing about 11 to 32% of Cr. . More preferably, it can be made of ferritic stainless steel. Although the specific composition of the ferritic stainless steel is not strictly limited, for example, from the viewpoint that the ferrite phase can be maintained in the operating temperature range of SOFC, about 16 Cr represented by SUS403 or the like is used. Fe-Cr alloys containing at least% are preferred. The Fe—Cr alloy is more preferably one in which carbon (C) and nitrogen (N) are reduced to about 300 ppm or less (preferably 150 ppm or less) in order to improve corrosion resistance at high temperatures. It is also preferable to contain elements such as molybdenum (Mo), titanium (Ti), niobium (Nb), etc., in order to refine crystal grains and improve corrosion resistance. Such ferritic stainless steel has a relatively low electrical resistance and a low thermal expansibility compared to martensitic stainless steel and austenitic stainless steel. The CTE of ferritic stainless steel is, for example, approximately 7 to 12 × 10 ⁻⁶ / K. Such ferritic stainless steel can be expected to relax the temperature gradient in the cell because this alloy material has good thermal conductivity and mechanical strength.

The spinel layer is provided on at least the surface of the metal substrate facing the bonding member 60. The spinel layer includes a first spinel phase having a spinel crystal structure represented by a general formula: M ¹ ₃ O ₄ ; Here, in the above general formula, M ¹ includes one or more elements selected from transition metals. A spinel layer having such a crystal structure has semiconducting conductivity, and can have good electrical conductivity in the operating temperature range of SOFC. Here, as the transition metal, an element (transition element) existing between the third group and the eleventh group in the periodic table can be considered. The transition metal is not particularly limited. For example, chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), titanium (Ti), vanadium (V), Preferred examples include yttrium (Y), tungsten (W), and the like. In a preferred embodiment of the spinel layer disclosed herein, M ¹ can further contain zinc (Zn) in addition to the transition metal. Any of these may be used alone or in combination of two or more.

More specifically, the oxide having a spinel type crystal structure is an oxide represented by a composition formula of A ^S B ^S ₂ O ₄ , and includes two cation sites of the A ^S site and the B ^S site in the crystal. have. The transition metal or the like occupies the ^AS site and the ^BS site in the spinel crystal structure. Examples of the elements occupying the ^{A S} site, Fe, Mn, Co, Cu , or any one of Ni and Zn are preferred. As the element which occupies a ^{B S} site, Cr, Co, or any one of Mn and Fe are preferred. Mn, C, Fe may be disposed at any ^{A S} sites and ^{B S} sites. Examples of the combination of a transition metal occupying the A ^S sites and ^{B S} site, for example, manganese spinel _(Mn 3 _{O 4,} etc.), cobalt - manganese spinel _{(MnCo 2 O 4, CoMn 2} O 4 , etc.), cobalt - iron Spinel (CoFe ₂ O ₄ etc., nickel-iron spinel (NiFe ₂ O ₄ etc.), nickel-cobalt spinel (NiCo ₂ O ₄ etc., iron-manganese spinel (FeMn ₂ O ₄ etc.), copper-manganese spinel (CuMn ₂ O ₄ etc.), iron-zinc-manganese spinel ((Fe, Zn) Mn ₂ O ₄ etc.) are preferable examples.The spinel layer is more preferably nickel cobaltite spinel, nickel iron. A spinel and a cobalt iron spinel are preferred.

  Note that the spinel layer provided on the surface of the metal substrate may be realized by preparing a metal interconnector obtained by applying the spinel coating containing the first spinel phase to the surface of the metal substrate. Alternatively, it is realized by using a metal interconnector obtained by applying a spinel precursor coating capable of forming the first spinel phase by heat treatment (typically heating in an oxidizing atmosphere) on the surface of the metal substrate. May be. When the metal interconnector having such a spinel precursor coating is used, the spinel precursor coating is heat-treated when the metal interconnector and the SOFC are joined with a joining material described later, or during the operation of the SOFC, so that the spinel layer is heat-treated. It becomes. Thereby, the metal interconnector can have a spinel layer on the surface of the metal substrate.

  The thickness of the spinel layer is not particularly limited, but for example, it is suitably about 10 μm or less, for example, about 7 μm or less, and preferably about 5 μm or less. For example, the thickness of the spinel layer is suitably about 0.5 μm or more, and preferably about 1 μm or more.

In addition, formation of a passive film such as Cr ₂ O ₃ is unavoidable on the surface of the metal substrate in an oxygen-containing atmosphere. It is also said that the Cr ₂ O ₃ coating on the surface is responsible for Cr poisoning of the air electrode. The metal interconnectors 50 and 50A disclosed herein are provided with the spinel layer on at least the surface connected to the air electrode. Thereby, in the spinel layer, Cr moving from a metal substrate (for example, a passive film) can be supplemented, and diffusion of Cr can be suppressed. From this point of view, it is allowed that a chromium-containing compound derived from a metal substrate exists in the spinel layer or at the interface between the spinel layer and the metal substrate.

[Joint material]
The joining member 60 disclosed here is an element that mechanically connects the SOFC air electrode 20 and the metal interconnectors 50 and 50A. Further, the joining member 60 plays a role of electrically connecting the air electrode 20 and the metal interconnectors 50 and 50A in the operating environment of the SOFC. The bonding member 60 includes a perovskite phase represented by a general formula: ABO ₃ ; and an oxide phase represented by a general formula: M ² ₃ O ₄ ; In the above general formula, A is one or more elements selected from the group consisting of La, Sr and Ba, and B is one or more elements including at least a transition metal element. M ² is one or more elements selected from transition metals.

  Regarding the perovskite phase, in the above general formula, A is an element occupying the A site in the perovskite crystal structure, and includes one or more of lanthanum (La), strontium (Sr), and barium (Ba). it can. In addition to these elements, the A site can contain any of lanthanoid elements (Ln) from lanthanum (Ln) having an atomic number of 57 to lutetium (Lu) having an atomic number of 71. Among the lanthanoid elements, for example, cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), etc. have a relatively large ionic radius. An element is preferable. Any two kinds of elements may be contained in the A site, or three or more kinds of elements may be contained in combination.

Regarding the perovskite phase, in the above general formula, B contains at least cobalt (Co). Although the detailed reason is not clear, according to the study by the inventors, the perovskite phase tends to have high contact resistance if it does not contain Co even if it is a small amount in the B site. Further, when Co is contained in the B site, a high oxygen reduction ability can be expressed at a relatively low temperature. Therefore, in the technology disclosed herein, the perovskite phase contains Co as an essential element. The perovskite phase can contain a transition metal element other than Co at the B site. Since this transition metal element is the same as the element that can be included in the B ^s site in the spinel layer, repeated description is omitted. In the perovskite phase, as long as at least Co is contained in the B site, the ratio and the content of other elements are not particularly limited. The transition metal element other than Co contained in the perovskite phase is not particularly limited, but is preferably the first transition element (3d transition element), among which titanium (Ti), manganese (Mn), It is preferable that 1 type (s) or 2 or more types selected from the group which consists of iron (Fe), nickel (Ni), and copper (Cu) are contained. In particular, a combination of Co and Mn is preferable because an oxide phase having excellent oxygen reduction ability can be obtained. In this case as well, a third element may be included in the B site in addition to Co and Mn as long as the effects of the present application are not impaired.

  The perovskite phase preferably contains La and Sr simultaneously at the A site. More specifically, the perovskite phase preferably contains lanthanum, strontium, and cobaltite as the main phase. Thereby, even when the operating temperature of the SOFC is lowered, it is preferable because it can exhibit suitable electrical and electronic mixed conductivity. Furthermore, for example, from the viewpoint of further improving the bondability with the air electrode, the main phase is a perovskite oxide that is the same as the perovskite oxide included in the air electrode to be bonded or a common element. It is preferable to do. The B site preferably contains Fe in addition to Co. By including Fe, the sintering start temperature of the perovskite phase is lowered, and this joining member 60 can be manufactured at a relatively low temperature. In other words, it means that the single cells 10A and 10B and the metal interconnectors 50 and 50A can be joined at a relatively low temperature. Further, the B site preferably contains Cu in addition to Co. By including Cu, the bonding member 60 maintains good adhesion and bonding properties with the metal interconnectors 50 and 50A even under long-term operating conditions, and the durability of the SOFC stack 1 is preferably enhanced.

The oxide phase contains an oxide represented by the general formula: M ² ₃ O ₄ ; Here, in the above general formula, M ² includes two or more elements selected from the group consisting of Ni, Fe, Co, and Cu. In other words, the oxide phase is a double oxide phase containing two or more elements selected from the group consisting of Ni, Fe, Co, and Cu. For example, the oxide phase can include at least one element that is the same as or common to the first spinel phase included in the spinel layer of the metal interconnector. Thereby, the joining member can improve mechanical joining property with a metal interconnector. Furthermore, this oxide phase may preferably have a spinel crystal structure. In other words, the oxide phase may be in a form including a second spinel phase. The second spinel phase may have the same composition as the first spinel phase or a different composition. Thereby, the joining member can improve the electrical joining property with a metal interconnector.

The composition of the oxide phase is not limited as long as it includes any metal element selected from Ni, Fe, Co, and Cu. M ² preferably contains any one metal element selected from Ni, Fe, Co and Cu in a proportion of 0.5 equivalent or more (50 mol% or more in the metal element). More preferably, the second spinel phase is the main phase. Such an oxide phase can have semiconducting conductivity like the first spinel phase. As a result, good electrical conductivity can be provided in the operating temperature range of the SOFC.
Examples of oxides that can be included in such an oxide phase include cobalt-iron-based oxides (for example, CoFe ₂ O ₄ ), nickel-iron-based oxides (for example, NiFe ₂ O ₄ ), and nickel-cobalt. A suitable example is a system oxide (for example, NiCo ₂ O ₄ ). When these oxide phases have a spinel type crystal structure, in addition to the good bondability with the spinel layer of the metal interconnector, the ferritic stainless steel and CTE as the base material are close, More preferably, it has a spinel crystal structure.

  In the joining member 60, since the oxide phase is contained even a little, the joining property with the spinel layer on the surface of the metal interconnector can be improved. Here, from the viewpoint of clearly expressing the effect of improving the bondability, the ratio of the oxide phase in the total of the perovskite phase and the oxide phase should exceed 5% by mass, and preferably 10% by mass or more. 15 mass% or more is more preferable, and 20 mass% or more is particularly preferable. However, when the ratio of the oxide phase becomes excessive, the bondability with the air electrode may be lowered. From this viewpoint, the ratio of the oxide phase in the total of the perovskite phase and the oxide phase is preferably less than 90% by mass, preferably 80% by mass or less, more preferably 75% by mass or less, and 70% by mass or less. Is particularly preferred.

  In addition, although mentioned later, the joining member 60 can be preferably comprised as a sintered compact of powder material. In this case, the joining member 60 may include a sintering aid component that is a component that assists the sintering of the powder as other components other than the perovskite phase and the oxide phase. The sintering aid can be a metal component (typically a transition metal component) having a lower melting point than the components constituting the perovskite phase and the oxide phase. The fired product is typically a metal-containing component such as a metal oxide (typically a transition metal oxide). From this, the joining member 60 can include a metal component-containing phase derived from the sintering aid in addition to the perovskite phase and the oxide phase.

  In the bonding member 60, the perovskite phase and the oxide phase are preferably main constituents of the bonding member 60. The total of the perovskite phase and the oxide phase is preferably 50 parts by mass or more, more preferably 75 parts by mass or more, further preferably 80 parts by mass or more, when the mass of the bonding member 60 is 100 parts by mass. 85 parts by mass or more is particularly preferable, and may be 90 parts by mass or more. Although it is expected that it is difficult to completely eliminate crystal phases other than the perovskite phase and the oxide phase, the bonding member 60 may be composed of only the perovskite phase and the oxide phase. On the other hand, when the joining member 60 includes the metal component-containing phase derived from the sintering aid, the metal component-containing phase is approximately 25 when the total of the perovskite phase and the oxide phase is 100 parts by mass. It may be contained in a proportion of less than or equal to parts by mass. The proportion of the metal component-containing phase is more preferably 20 parts by mass or less, further preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less. The lower limit of the ratio of the metal component-containing phase is not particularly limited, but is suitably 1 part by mass or more, for example, 3 parts by mass or more in order to exert the effect of adding the sintering aid.

  In addition, the ratio of said perovskite phase and an oxide phase can be grasped | ascertained by results, such as EDX analysis of a junction cross section, as shown in below-mentioned Test Example 1, for example. That is, the area ratio between the perovskite phase and the oxide phase in an arbitrary cross section of the joint portion can directly reflect the volume ratio between the perovskite phase and the oxide phase in the joint portion. For example, from the concentration distribution of each element in the cross section of the junction structure, the distribution area of each phase is divided by the image analysis technique, and the total area (unit is, for example, pixel) for each phase is calculated. The volume ratio of the perovskite phase and the oxide phase in the part can be grasped.

  Although not necessarily limited to this, it is preferable that the perovskite phase and the oxide phase have the same or larger perovskite phase than the oxide phase. More specifically, as an example, when the joining member 60 includes a first sintered particle portion including a perovskite phase and a second sintered particle portion including an oxide phase, the average of the first sintered particle portion The diameter is preferably larger than the average diameter of the second sintered particle part. The average diameter (size) here refers to, for example, the first sintered particle portion and the oxide phase including a perovskite phase distinguished by elemental analysis or the like when an arbitrary cross section of the bonding member 60 is observed with a microscope. It can judge based on the biaxial average diameter with the 2nd sintered particle part containing. As the biaxial average diameter of the first sintered particle portion and the second sintered particle portion, an arithmetic average value obtained by measuring the biaxial average diameter of 10 or more for each sintered particle portion may be employed. Although the microscope used for observation is not particularly limited, a microscope capable of observation at a magnification suitable for observing the structure of the bonding member 60 can be used. For example, a high-power microscope, a scanning electron microscope, a transmission electron microscope, or the like. More specifically, for example, the perovskite phase is preferably about 0.1 μm or more, and preferably 15 μm or less. Moreover, it is preferable that an oxide phase is about 0.1 micrometer or more, and it is preferable that it is 10 micrometers or less. Although not particularly limited, the size of the perovskite phase is preferably about 1 to 20 times the size of the oxide phase, and more preferably about 2 to 10 times. The perovskite phase may be integrally sintered as a whole to form, for example, a matrix. In this case, the oxide phase can be observed as a phase interspersed with islands in the perovskite phase matrix.

  The air electrode 20 has a porous structure. Typically, the air electrode 20 has a porous structure with a porosity of about 10 to 60%. On the other hand, the metal interconnectors 50 and 50A have a dense metal structure at the atomic level. Therefore, it is preferable that the joining member 60 that joins them and has the same or similar composition as the air electrode as described above has a porous structure with a porosity of about 10 to 60%. Thereby, since the joining member 60 becomes easy to relieve | moderate the thermal stress accompanying the difference of CTE between the air electrode 20 and the metal interconnectors 50 and 50A, it is preferable.

Moreover, it is preferable that CTE in 25 to 800 degreeC of the joining member 60 is 19.3 * 10 < ^-6 > / K or less. For example, the CTE of lanthanum cobaltite is about 20 × 10 ⁻⁶ / K. On the other hand, the CTE of the Cr—Fe alloy constituting the metal interconnectors 50 and 50A is significantly low as 7 to 12 × 10 ⁻⁶ / K as described above. According to the study by the present inventors, the long-term joining property in the operating environment with the Cr—Fe alloy can be improved by reducing the CTE to about 19 × 10 ⁻⁶ / K or less. We have knowledge. The CTE of the joining member 60 is more preferably 18.9 × 10 ⁻⁶ / K or less, and particularly preferably 18.8 × 10 ⁻⁶ / K or less. The CTE of the joining member 60 greatly depends on the composition of the perovskite phase and the oxide phase. For example, when the perovskite phase and the oxide phase contain Fe or Cu at the B site, CTE can be greatly reduced. In such a case, the CTE is more preferably 18.7 × 10 ⁻⁶ / K or less, for example, 18 × 10 ⁻⁶ / K or less. The lower limit of CTE is not particularly limited, and may be, for example, more than 17 × 10 ⁻⁶ / K, more preferably 17.5 × 10 ⁻⁶ / K or more, and more preferably 17.8 × 10 ⁻⁶ / K or more. can do.

  In addition, CTE in this specification means an average linear expansion coefficient measured in a temperature range from room temperature (25 ° C.) to 800 ° C. using a thermomechanical analyzer (TMA) unless otherwise specified. The value obtained by dividing the change in the length of the sample in this temperature range by the measured temperature difference. The coefficient of thermal expansion should be measured according to the method for measuring the linear expansion coefficient of metallic materials specified in JIS Z2285: 2003 or the method for measuring thermal expansion by thermomechanical analysis of fine ceramics specified in JIS R1618: 2002. Can do.

[Conductive bonding material]
Since the joining member 60 includes the porosity and the CTE as described above, it is preferable that the joining member 60 is made of, for example, a powder sintered body. Therefore, the technique disclosed herein provides a conductive bonding material that can preferably manufacture the bonding member 60. This conductive bonding material includes perovskite oxide powder and alloy powder.

(Perovskite oxide powder)
The perovskite oxide powder forms a perovskite phase in the bonding member 60. In other words, the perovskite oxide powder is sintered to form a perovskite phase. Although the composition of the raw material and the fired body may differ strictly depending on the firing, the joining member disclosed herein can be produced by firing at a relatively low temperature of, for example, 600 ° C. to 800 ° C. From this, the composition of the perovskite oxide powder can be made substantially the same as the composition of the perovskite phase.

  On the other hand, if the average particle size of the perovskite oxide powder is too large, it is not preferable because the reactivity between the perovskite oxide powder and the alloy powder does not become uniform when firing to produce a bonded member. The average particle size of the perovskite oxide powder is suitably about 5 μm or less, preferably about 4 μm or less, and more preferably about 3 μm or less. The lower limit of the average particle size of the perovskite oxide powder is not particularly limited, but from the viewpoint of handling properties, for example, about 0.1 μm or more can be used as a guide.

(Alloy powder)
Further, the alloy powder forms an oxide phase in the bonding member 60. In other words, the alloy powder is oxidized and sintered by firing to form an oxide phase (typically a double oxide phase). Therefore, the composition of the alloy powder can include the one corresponding to the metal element contained in the oxide phase. Specifically, the alloy powder includes an alloy composed of two or more selected from the group consisting of nickel (Ni), cobalt (Co), iron (Fe), and copper (Cu). The alloy powder may be an alloy composed of only two or more of the above four kinds of metal elements, or may be an alloy powder containing the above two kinds of metal elements and other elements. May be. It is preferable that the alloy powder is formed by forming an alloy rather than a mixture of powders of a single metal because the reactivity (oxidation) during firing can proceed uniformly and satisfactorily. In addition, an oxide obtained after firing is preferable because a favorable double oxide (typically, an oxide having a spinel structure) can be suitably formed.

  The average particle size of the alloy powder is not particularly limited. For example, it may be of a size that can be satisfactorily mixed with the perovskite oxide powder. For example, the average particle size of the alloy powder is suitably about 10 μm or less, preferably about 9 μm or less, and more preferably about 8 μm or less. The lower limit of the average particle diameter of the alloy powder is not particularly limited, but from the viewpoint of handling properties, for example, about 0.1 μm or more can be used as a guide. The perovskite oxide powder and the alloy powder can be considered to generally correspond to the particle diameter of the perovskite phase or oxide phase only when the particles constituting them are present independently.

  The perovskite oxide powder and the alloy powder may have the same or different average particle diameter. When the average particle size is varied, it is preferable that the perovskite oxide powder is relatively small and the alloy powder is relatively large. The alloy powder has a lower melting point than the perovskite oxide powder. In addition, the alloy powder has a smaller CTE than the perovskite oxide powder. Therefore, by making the perovskite oxide powder smaller than the alloy powder, it is possible to suppress an increase in the firing shrinkage rate due to the perovskite oxide powder. Further, by making the perovskite oxide powder smaller than the alloy powder, the effect of reducing the CTE with a smaller amount can be exhibited.

For example, the CTE of typical lanthanum cobaltite is about 22 × 10 ⁻⁶ / K. On the other hand, the CTEs of manganese cobaltite and ferritic stainless steel can be about 13 × 10 ⁻⁶ / K and about 7 to 12 × 10 ⁻⁶ / K, respectively. Therefore, the CTE of the joining member is not particularly limited to adjust the CTE of, for example, preferably 14 × 10 ⁻⁶ / K or more to 19 × 10 ⁻⁶ / K or less, but the size of the alloy powder is not limited to perovskite. The size of the oxide powder is preferably 1 times or more, more preferably 1.4 times or more, still more preferably 5 times or more, still more preferably 7 times or more, and may be, for example, 10 times or more. The upper limit of the size of the perovskite oxide powder with respect to the alloy powder is not particularly limited, but considering the preferable range of the particle diameter, for example, 30 times or less, preferably 20 times or less, typically about 15 times or less. It is good to do.

  In the conductive bonding material, the ratio between the perovskite oxide powder and the alloy powder is related to the ratio between the perovskite phase and the oxide phase in the bonding member 60. For example, the CTE of the joining member 60 can be reduced as the alloy powder having a relatively small CTE increases. From this viewpoint, it is preferable that the ratio of the alloy powder in the total of the perovskite oxide powder and the alloy powder exceeds 5% by mass. The ratio of the alloy powder is more preferably 7% by mass or more, further preferably 10% by mass or more, more preferably 15% by mass or more, and particularly preferably 20% by mass or more. However, an excessive amount of alloy powder is not preferable because the bondability with the air electrode can be lowered. Accordingly, the proportion of the alloy powder is suitably less than about 80% by mass, preferably 75% by mass or less, more preferably 70% by mass or less, further preferably 65% by mass or less, and particularly preferably 60% by mass or less. For example, the alloy powder can be 20 mass% or more and 50 mass% or less.

(Dispersion medium)
Note that the conductive bonding material disclosed herein can contain other components such as a dispersion medium in addition to the above powder material, as long as the object of the present invention is not deviated. Such other components can be adjusted in light of various criteria such as the method of forming the SOFC single cells 10A, 10B.

The above-mentioned powdery conductive joining material may be used for joining the SOFC single cells 10A, 10B and the metal interconnector 50A by compression molding or the like. The adhesive bonding material may be prepared and used in the form of a paste (including ink, slurry, suspension, etc.) dispersed in a dispersion medium. The dispersion medium used at this time may be any dispersion medium that can disperse the above-mentioned first and second oxide powders and, if necessary, the sintering aid satisfactorily. Various dispersion media can be used without particular limitation. Typically, as such a dispersion medium, a mixture of an organic binder and an organic solvent for viscosity adjustment can be considered.
As the organic solvent, for example, one kind of high-boiling organic solvents such as ethylene glycol and diethylene glycol derivatives (glycol ether solvents), toluene, xylene, butyl carbitol (BC), terpineol, or two or more kinds are used. Can be used in combination.

  Moreover, as an organic binder, the various resin component which shows viscosity can be included. Any resin component may be used as long as it can impart a good viscosity and a film-forming ability (including, for example, printability and adhesion to a substrate) to prepare a paste. What is used can be used without particular limitation. Examples thereof include those mainly composed of acrylic resin, epoxy resin, phenol resin, alkyd resin, cellulosic polymer, polyvinyl alcohol, rosin resin and the like. Among these, it is particularly preferable that a cellulosic polymer such as ethyl cellulose is contained. The dispersion medium may contain any additive that can be generally used for this type of dispersion medium, such as a dispersant and a plasticizer.

  The ratio of the dispersion medium can be appropriately adjusted according to the purpose of use of the conductive bonding material. For example, it can be appropriately adjusted according to the form of the cell facing surface 52 of the metal interconnector 50A, the method employed for the molding, and the like. As an example, the paste-like conductive bonding material can be preferably used for supplying the cell facing surface 52 of the metal interconnector 50A by a technique such as printing. In this case, the ratio of the dispersion medium to the entire paste-like conductive bonding material is preferably about 5% by mass to 60% by mass, more preferably 7% by mass to 50% by mass, and more preferably 10% by mass. The content is particularly preferably 40% by mass or less. The organic binder contained in the vehicle is, for example, about 1% by mass to 15% by mass of the entire paste, preferably about 1% by mass to 10% by mass, and more preferably about 1% by mass to 7% by mass. The ratio is exemplified. By adopting such a configuration, for example, the powder component of the conductive bonding material can be easily formed (coated) as a layered body (for example, a coating film) with a uniform thickness, is easy to handle, and further from the coated material. It is preferable because it does not take a long time to remove the dispersion medium.

  In preparing the paste, for example, a known three-roll mill can be used for mixing the powdery conductive bonding material and the dispersion medium. Thereby, the perovskite oxide powder, the alloy powder and the firing aid can be mixed uniformly. Moreover, these powder materials can be uniformly dispersed in a dispersion medium. As a result, a paste-like conductive bonding material can be obtained. By adjusting the viscosity of the paste-like conductive bonding material to an appropriate viscosity according to the desired application, the conductive bonding material can be simply supplied to the desired position in the desired form in the form of coating or printing. Is possible.

  The conductive bonding material is supplied between the cell facing surface 52 of the metal interconnector 50A and the air electrode 20 of the SOFC single cell 10A. That is, for example, after supplying the conductive bonding material to the cell facing surface 52 of the metal interconnector 50A, the single cells 10A are overlapped so that the air electrode 20 side of the single cell 10A comes into contact with the conductive bonding material. In this manner, the single cells 10A and 10B and the metal interconnectors 50 and 50A are stacked and then fired. In this case, the firing temperature can be about 1000 to 1150 ° C. as in the conventional case, but according to the technique disclosed herein, the firing temperature is 900 ° C. or less, for example, about 700 to 900 ° C. it can. The firing time can be, for example, about 1 to 5 hours. Thereby, the binder, the dispersion medium, and the like contained in the conductive bonding material disappear, and the perovskite oxide powder and the alloy powder are sintered to form the bonding member 60. At the same time, the joining member 60 can firmly join the SOFC air electrode 20 and the metal interconnector 50A with good adhesion.

  Note that the firing temperature of the conductive bonding material is substantially the same as the firing temperature of the SOFC air electrode 20. Further, the perovskite oxide powder and alloy powder constituting the conductive bonding material may have the same composition as the air electrode material. Therefore, the technology disclosed herein provides such a conductive bonding material as a material for forming the air electrode 20.

(Air electrode forming material)
The air electrode (cathode) 20 has a porous structure like the fuel electrode 40. In general, the air electrode 20 has a larger porosity than the joining member 60. Although the porosity of the air electrode 20 is not particularly limited, the porosity is 10% in order to satisfy both the ratio of the three-phase interface due to the fuel gas for the electrochemical reaction, the solid electrolyte layer, the air electrode, etc. and the appropriate strength. It is preferably 50% or less (preferably 10% or more and 40% or less, for example, 15% or more and 30% or less).

  Therefore, when a conductive bonding material is used as the air electrode forming material, a pore former may be added to the conductive bonding material. The pore former is a material blended with the electrode forming material in order to form an electrode such as the air electrode 20 in a porous structure, and various materials that disappear when the electrode is manufactured (fired) may be used. it can. For example, as the pore former, granular synthetic resin material, carbon powder, natural organic powder, or the like can be preferably used.

  As the granular resin material, a particulate material made of various synthetic resins that can disappear when the electrode is baked (typically when baking at about 700 to 900 ° C.) can be used. Typically, so-called resin beads can be preferably used. Such a granular resin material can be easily obtained with a uniform particle size, and since the surface form is smooth, it can maintain good fluidity when a slurry for electrode formation is prepared. Is preferable. Moreover, it is also preferable in that an electrode having a desired porous structure (for example, a porous structure having a sharp pore size distribution) can be formed. The type of resin constituting such a granular resin material is not particularly limited. For example, typically, polyolefin resins such as polyethylene and polypropylene, polystyrene such as polystyrene, styrene / acrylonitrile copolymer, acrylonitrile / butadiene / styrene polymer, and the like. Examples of such resins include acrylic resins, acrylic resins, vinyl ester resins, and composites thereof.

Various carbon powders can also be used as the pore former. Since such carbon powder is almost burned off at 700 ° C. to 900 ° C., almost all of the carbon powder is suitable for burning out when the electrode is fired. The carbon powder is not particularly limited in its crystal structure, manufacturing method, etc., and various carbon materials represented by graphite (natural graphite and modified products thereof, artificial graphite) and the like can be used.
Examples of natural organic powders include, among various types of plants containing starch, seeds (endosperm) containing a large amount of starch, powdered parts such as tuberous root, and starch powder extracted from such parts. Good. For example, typically, glutinous rice flour, rice flour, barley flour, wheat flour, oat flour, corn flour, pea bean flour, potato flour, sweet potato flour, cassava flour, katsu flour, sago flour, amaranth flour, banana flour Examples thereof include food powders such as arrow root powder and canna powder, and starch powders such as potato starch, corn starch and tapioca powder.

  In forming the air electrode 20, in addition to the conductive bonding material and the pore former, other components such as a dispersion medium can be included. As described above, the dispersion medium may be the same material as that used when preparing the paste-like conductive bonding material. The ratio of the dispersion medium can be adjusted according to the method of forming the air electrode 20. In general, the air electrode 20 is formed by using a paste-like air electrode forming material on the solid electrolyte layer 30 of a SOFC half cell (a half cell comprising the fuel electrode 40 and the solid electrolyte layer 30) by a method such as screen printing or a doctor blade method. To be fired. In this case, the dispersion medium is preferably about 5 mass% or more and 60 mass% or less of the entire paste. The supply of the air electrode forming material can be appropriately adjusted so that the air electrode 20 obtained after firing has a predetermined shape and dimensions. The shape of the air electrode 20 can be changed as appropriate according to the shape of the solid electrolyte layer 30. The thickness of the air electrode 20 is typically about 1 μm to 200 μm, preferably about 5 μm to 100 μm, more preferably 10 μm to 100 μm, but is not limited to such thickness.

  Note that the SOFC manufacturing method may be in accordance with a conventionally known manufacturing method and does not require any special treatment, and thus detailed description thereof is omitted. Thereby, at least a part of the SOFC air electrode 20 can be constituted by a fired product of the conductive bonding material (air electrode forming material) disclosed herein. In this case, the firing of the air electrode 20 and the firing at the time of stacking of the SOFC can be performed simultaneously.

  Hereinafter, some test examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the test examples.

[Test Example 1]
[Preparation of joining materials]
Fe-Co alloy powder and perovskite oxide powder were prepared as bonding materials. Specifically, an Fe-50% Co alloy powder (manufactured by Epson Atmix Co., Ltd.) having an average particle size (D ₅₀ (Alloy)) of 8.0 μm and an average particle size (D ₅₀ (ABO ₃ )). Is a perovskite oxide (La _0.6 Sr _0.4 CoO ₃ ) powder having a composition represented by the general formula: La _0.6 Sr _0.4 CoO ₃ ; The ratio (mass%) of the alloy powder occupying the total of the perovskite type oxide powder was changed and mixed in 12 ways between 0.1 and 100 mass% as shown in Table 1 below. And to this mixed powder, ethyl cellulose as a binder and terpineol as an organic solvent were added and mixed by a three-roll mill to prepare bonding pastes of Examples 1-1 to 1-12. The binder was blended at a ratio of 3 parts by mass and the organic solvent was blended at a ratio of 20 parts by mass with respect to a total of 100 parts by mass of the Fe—Co alloy powder and the perovskite oxide powder.

[CTE measurement]
The CTE of the joint (baked product) obtained by firing the bonding paste of each example was measured. That is, first, the bonding paste of each example was filled in a mold corresponding to a predetermined test piece size, dried, and then fired at 1100 ° C. to obtain a fired body. And it was set as the test piece for CTE measurement by shape | molding so that the dimension of a sintered body might be set to 4 mm x 5 mm x 20 mm. Using this test piece, the thermal expansion coefficient (CTE) in a temperature range of room temperature (25 ° C.) to 800 ° C. was measured using a thermomechanical analyzer (manufactured by Rigaku Corporation, TMA8310). The thermal expansion coefficient was determined from the average linear expansion coefficient measured by the differential expansion method in the atmosphere according to the method of measuring thermal expansion by thermomechanical analysis of fine ceramics of JIS 1618: 2002. The results are shown in the “CTE” column of Table 1 below.

[Jointability test]
[Production of SOFC for evaluation]
A SOFC for evaluation of bondability was produced by the following procedure.
First, a mixed powder of 48 to 58 mass% with a mass ratio of 60:40 of nickel oxide (NiO, average particle diameter 0.5 μm) powder and 8% yttria stabilized zirconia (8% YSZ, average particle diameter 0.5 μm) powder. And kneading by adding 24% by mass of an organic solvent (xylene), 8.5% by mass of an organic binder (polyvinyl butyral; PVB), 5-15% by mass of a pore forming material (carbon component) and 4.5% by mass of a plasticizer. Thus, a paste-like composition for forming a fuel electrode support was prepared. The fuel electrode support green sheet having a thickness of 0.5 to 1.0 mm was formed by repeatedly applying and drying the fuel electrode support forming composition on the carrier sheet by the doctor blade method.

  Next, a composition for forming a fuel electrode is prepared by mixing 48% by mass of NiO powder, 32% by mass of YSZ powder, 18% by mass of an organic solvent (terpineol) and 2% by mass of a binder (ethyl cellulose; EC) as described above. A product was prepared. This fuel electrode forming composition was supplied onto the fuel electrode support green sheet by screen printing and dried to form a fuel electrode green sheet having a thickness of about 10 μm.

  A paste-like solid is obtained by kneading 65% by mass of 8% YSZ (average particle size 0.5 μm) powder, 4% by mass of a binder (EC) and 31% by mass of an organic solvent (terpineol) as a solid electrolyte material. An electrolyte layer forming composition was prepared. This was supplied to the fuel electrode green sheet in a sheet form by a screen printing method and dried to form a solid electrolyte layer green sheet having a thickness of about 10 μm.

  Further, 10% gadolinium-doped ceria powder (10% GDC, average particle size 0.5 μm) powder 65% by mass, binder (EC) 4% by mass, organic solvent (terpineol) 31% by mass as a reaction preventing layer material By kneading, a paste-like composition for forming a reaction preventing layer was prepared. This was supplied on the solid electrolyte layer green sheet in a sheet form by screen printing and dried to form a reaction prevention layer green sheet having a thickness of about 5 μm.

  The thus-prepared laminated green sheet is cut into a circle and cofired at 1350 ° C., so that the fuel electrode support, the fuel electrode layer, the solid electrolyte layer, and the reaction prevention layer are integrally laminated in this order in an SOFC half cell. Got. In addition, the shape of the half cell after baking was adjusted so that it might become a circle with a diameter of 20 mm.

  Next, lanthanum strontium cobalt ferrite (LSCF) powder having an average particle diameter of 1 μm is used as an air electrode material, and a binder (EC) and a dispersion medium (TE) are used as the air electrode material, and LSCF: EC: TE = 80: 3: 17. By mixing at a mass ratio, a paste-like composition for forming an air electrode was prepared. The air electrode forming green sheet was formed by supplying the air electrode forming composition onto the SOFC half-cell reaction-preventing layer prepared above in the form of a circular sheet by screen printing and drying. Then, the SOFC for evaluation was obtained by baking the air electrode layer green sheet at 1100 ° C. together with the half cells to form a layered air electrode. The screen printing conditions were adjusted so that the air electrode had a diameter of 10 mm and a thickness of about 30 μm.

[Joint strength with cathode]
By applying the prepared bonding pastes of Examples 1-1 to 1-12 to the cathode surface of the SOFC for evaluation so that the dry film thickness is about 40 μm, drying, and firing at 850 ° C., A bonding layer was formed. The physical (mechanical) bondability between this bonding layer and the SOFC cathode was evaluated.
Specifically, the bonding strength between the bonding layer and the cathode was evaluated in accordance with a crosscut test defined in JIS K5600-5-6: 1999. In the cross-cut test, first, a grid pattern of 25 squares was formed by making six parallel cuts at 1 mm intervals at a position 5 mm or more away from the end of the bonding layer. Then, a transparent pressure-sensitive adhesive tape with a width of 24 mm (adhesion strength: 4.01 N / mm) is applied to cover the lattice pattern, and the tape is peeled off in a direction where the angle formed by the tape is about 60 °. The area ratio (peeling area ratio) P (%) of the peeled portion in the area (25 squares) was calculated.

As shown below, the evaluation symbols corresponding to the peeled area ratio P of the joining member are shown in the “cathode joining strength” column of Table 1. In addition, the following evaluation symbols generally correspond to the score of the cross-cut test of the Japan Paint Inspection Association, “×” is 0 point, “△” is 2 points, “◯” is 4-6 points In addition, “◎” corresponds to 8 to 10 points.
×: 65 <P
Δ: 35 <P ≦ 65
○: 5 <P ≦ 35
A: 0 ≦ P ≦ 5

[Joint strength with metal IC]
Instead of the above-mentioned SOFC cathode, each of the prepared bonding pastes of Examples 1-1 to 1-12 was applied to the surface of a metal interconnector (IC) so that the dry film thickness was about 40 μm and dried. After that, the bonding layer was formed by firing at 850 ° C. The physical (mechanical) bondability between the bonding layer and the metal IC was evaluated in the same manner as in the test for the cathode, and the result is shown in the “IC bonding strength” column of Table 1.

In addition, as a metal IC, a ferritic stainless steel plate provided with a precursor layer of Co ₃ O ₄ coating was used. Specifically, this metal IC is obtained by forming a Co film by Co plating after strike-treating Ni on the surface of a ferritic stainless steel plate and performing a pretreatment. This metallic IC is by heat treatment sintering of the 850 ° C., are designed to Co ₃ O ₄ coating composed mainly of Co ₃ O ₄ spinel phase on the outermost surface. The Co plating was formed so that the thickness of the Co ₃ O ₄ coating was about 5 μm. In this metallic IC, Cr can precipitate on the surface of the stainless steel plate by the heat treatment, but the diffusion of Cr (Cr poisoning) is suppressed by the presence of the Co ₃ O ₄ coating on the outermost surface. .

[Contact resistivity]
The electrical bondability between the bonding member obtained by firing the bonding paste and the metal IC was evaluated. Specifically, the prepared pastes of Examples 1-1 to 1-12 were applied to the surface of the ferritic stainless steel plate (25 mm × 25 mm) provided with the same Co ₃ O ₄ coating as described above. By applying and firing at 850 ° C., a thin-layer joining member having a thickness of about 30 μm was produced. Then, the electrical resistance was evaluated by measuring the contact resistance generated between the obtained joining member and the metal IC. The contact resistance was calculated from the slope of the IV curve when a voltage was swept at ± 10 mV in an environment of 700 ° C. using a resistivity meter (model: potentiostat manufactured by Solartron, SI1287). The obtained contact resistivity was indicated by an evaluation symbol in the “contact resistance” column of Table 1. Each evaluation symbol corresponds to the following contact resistivity.

×: 0.1Ωcm ² than △: 0.05Ωcm ² ultra 0.1Ωcm ² following ○: 0.02Ωcm ² ultra 0.05Ωcm ² following ◎: 0.02Ωcm ² below

[EDX analysis]
In addition, while observing the cross section of the joined portion of the joined member produced in Example 1-5 and the metal IC with a scanning electron microscope (SEM), about a part of the observation region, Energy dispersive X-ray spectrometry (EDX) was performed. As an EDX analyzer, JSM-6610LA manufactured by JEOL Ltd. was used, and an observation region (image data) of 2000 times by a scanning electron microscope (SEM) was used for La L line, Sr L line, Fe Element maps of each element were obtained by detecting K-rays, Co-K-rays, Cr-K-lines, and O-K-lines. The results are shown in FIG. 2 shows (a) SEM image, (b) La map, (c) Sr map, (d) Fe map, (e) Co map, (f) Cr map, and (g) O map. ing. In each element map, the position where the target element is detected is displayed relatively white (brighter). Further, as shown for the SEM image, the lower band-like portion in the vertical direction of each figure corresponds to the ferritic stainless steel plate, the upper side corresponds to the joining member, and the interface (near the center) corresponds to the spinel layer.

[Ratio of oxide phase]
Further, the ratio of the perovskite phase to the oxide phase in the cross section of the joint portion in each example was examined by an image analysis method based on the element map (for example, Co, Fe, etc.) obtained by the EDX analysis. For image analysis, image analysis software Image J (1.45p) manufactured by National Institutes of Health (NIH) was used. FIGS. 4A to 4D illustrate how the Co map of Example 1-5 was analyzed.
Specifically, first, the region of the junction was cut out from the elemental map shown in (a) (here, Co map) so that the entire region was occupied by the junction, and subjected to image analysis (see b to d). Next, the entire image was subjected to Make Binary (binarized image creation) processing in the Binary (binarization) submenu to obtain a binary image shown in (b). Here, a region where a large amount of Co is detected is represented by white, and a region where a large amount of Co is not detected is represented by black. Next, after performing Despeckle (noise removal) processing in the Niose submenu, Dilate processing is performed in the Binary (binarization) submenu, and Remove Outliers (removing outliers in the Niose submenu). ) After processing, the figure shown in (c) was obtained by performing Erode processing in the Binary (binarization) submenu. The outlier removal conditions were Radius: 2 pixels, Threshold: 50, and Which Outliers: bright. By the above processing, the Co map was distinguished into an oxide phase region (white) and a perovskite phase region (black). Next, Analyze Particles (particle analysis) processing is performed, and as shown in (d), the number of oxide phase regions (white) in this binary image is counted and the area (unit: pixel) is measured. did. From this result, the following formula: oxide phase area ratio (%) = area of oxide phase region (number of pixels in white part) ÷ total area of junction analysis (total number of pixels) × 100); The area ratio was calculated and shown in Table 1.

[Evaluation]
As shown in Table 1, it was found that the proportion of the oxide phase in the joint obtained after firing increased as the proportion of the Co—Fe alloy contained in the joining paste increased. In Example 1-12, the area ratio of 0% is due to the fact that the whole became an oxide phase and could not be binarized, and actually means 100% of the oxide phase. In addition, as for the physical properties of the joint part, the joint member obtained by preparing a joining paste by adding alloy powder (Alloy) to the perovskite oxide powder (ABO ₃ ) having a relatively large CTE. It was found that CTE can be changed according to the mixing ratio (mass ratio) of the alloy powder. CTE of the joining member obtained by firing the bonding paste of this example, it was confirmed that changes in the range of ^{19.2 × 10 -6 /K~18.0×10 -6 / K} . Further, as shown in Examples 1-1 and 1-2, when the amount of alloy powder added to the perovskite oxide powder of the bonding paste is small, the bonding strength between the formed bonding member and the cathode is sufficient. However, as in the prior art, it is not possible to achieve good bonding with a metal IC, and the bonding strength is extremely low. This is because a spinel layer (spinel coating) is formed on the surface of the metal IC by firing, and the bonding property between the spinel layer and the bonding member using only the perovskite oxide powder is not good. Although not specifically shown, the bonding strength with the metal IC is further reduced with a bonding paste to which no alloy powder is added. From this, it was found that by adding an alloy powder to the bonding paste, the bonding property between the spinel layer of the metal IC and the bonding member can be improved. Further, when the bondability between the bonding member and the metal IC is evaluated by contact resistance, the ratio of the alloy powder added to the bonding paste is preferably about 5 mass% or more, and preferably about 10 mass% or more. It was found that it is more preferable to set the content to about 20% by mass or more.

  On the other hand, as shown in Examples 1-3 to 12, by including a certain amount of alloy powder in the bonding paste, the bonding strength of both the bonding member, the cathode, and the metal IC can be sufficiently increased. I knew it could be higher. However, if excessive alloy powder is included in the bonding paste, the bonding strength with the metal IC can be sufficiently obtained, but as shown in Examples 1-11 and 1-12, the bonding strength with the cathode is On the other hand, it turned out that it fell. Therefore, the ratio of the alloy powder added to the bonding paste is preferably about 80% by mass or less, preferably about 70% by mass or less, and more preferably about 50% by mass or less. I found out.

Moreover, from the result of the EDX analysis, as shown in the SEM image of FIG. 2, it can be confirmed that the joined member is formed on the spinel layer formed on the surface of the dense stainless steel plate. . As shown in (d) Fe map and (f) Cr map, it can be seen that Fe and Cr are present at a higher concentration in the position of the ferritic stainless steel plate than in other parts. Further, for example, as can be seen from the comparison of (e), (f), and (g), it can be seen that a Co ₃ O ₄ coating as a spinel layer is formed on the surface of the stainless steel plate by heat treatment. Then, as shown in (d) and (e), Fe and Co derived from Fe—Co alloy particles are detected in a round and high concentration at the location where the alloy powder was present in the joining member. I understood it. On the other hand, as shown in (b) and (c), at the position corresponding to the Fe—Co alloy particles, the element to be measured (La, Sr) that is not Fe or Co is detected in a round and low concentration. I understood. In addition, since the Fe—Co alloy powder in the bonding paste is easily oxidized by firing, O is detected at a high concentration at a position corresponding to the Fe—Co alloy particles as shown in FIG. It was found that the -Co alloy was oxidized. Although not specifically shown, Fe and Co constitute a spinel-type double oxide mainly composed of CoFe ₂ O ₄ and partially form a small amount of Co ₃ O ₄ and Fe ₃ O _4. Has been confirmed. Furthermore, as can be seen from (b), (c), (e), and (g), La, Sr, and Co that constitute the perovskite type oxide powder are present at locations where no alloy powder is present in the joining member. , O was confirmed to be present at a substantially uniform concentration.

Here, as shown in (f) Cr map, Cr can be confirmed in the region of the ferritic stainless steel plate, but the presence of Cr cannot be confirmed in the region of the joining member. According to the conventional joining structure of the metal IC and the cathode, Cr in the stainless steel moves toward the surface in order to form a passive layer made of Cr ₂ O ₃ on the stainless steel surface. It diffused inside and reached the cathode. Then, it reacts with Sr of LSCF, which is a cathode material, to form SrCrO _4, which causes a reduction in the reaction efficiency of the cathode. On the other hand, in the joining structure disclosed here, Cr is hardly seen in the joining member. In other words, by coating the surface of the stainless steel plate with the spinel layer, Cr diffused from the stainless steel plate can be supplemented by the spinel layer, and the diffusion of Cr to the joining member and the cathode can be suppressed. Further, as described above, according to the bonding member disclosed herein, the bonding between the metal IC having the spinel layer and the bonding member can be strengthened, and the contact resistance at the bonding interface can be kept low. Can do. Therefore, the joined body disclosed here realizes high strength and low resistance joining between the metal IC and the cathode while suppressing the Cr poisoning of the cathode even when the metal IC is used. It was confirmed that

[Test Example 2]
[Preparation of joining materials]
In the same manner as in Test Example 1, bonding pastes of Examples 2-1 to 2-5 were prepared. However, the mixing ratio (mass% ratio) of the alloy powder (Alloy) and the perovskite oxide powder (ABO ₃ ) in the bonding paste was constant at 20:80. Further, the average particle diameter of the alloy (Fe-50% Co) powder and the perovskite oxide (La _0.6 Sr _0.4 CoO ₃ ) powder and the combination thereof were changed as shown in Table 2 below. The other conditions were the same as in Test Example 1.

  Using the prepared bonding pastes of Examples 2-1 to 2-5, the bonding strength between the bonding member and the cathode or the metal IC and the contact resistance were examined in the same manner as in Test Example 1. The results are shown in Table 2 below.

As shown in Examples 2-1, 2-3, and 2-4 of Table 2, the average particle diameter of the powder constituting the bonding paste is various bondability, whether it is small or large for the alloy powder. It can be seen that no effect is seen. However, with respect to the perovskite type oxide powder, it has been found that when the particle size is relatively small, the bonding between the bonding member, the cathode, and the metal IC is good. Particularly in this test example, since the ratio of the alloy powder to the perovskite oxide powder is relatively small, if the average particle size of the perovskite oxide powder is too large, the perovskite oxide in the sintered bonded member There is a possibility that the porosity of the powder cannot be sufficiently filled with the alloy powder, and the bondability is deteriorated. However, it has been found that relatively good bonding can be realized by setting the average particle size of the perovskite oxide powder to be smaller than that of the alloy powder.

[Test Example 3]
[Preparation of joining materials]
The composition of the alloy powder and the composition of the perovskite type oxide powder were changed as shown in Table 3 below, and other conditions (average particle diameter and blending of each powder) were as described in Example 1-5 of Test Example 1 above. In the same manner, the bonding pastes of Examples 3-1 to 3-5 were prepared. As the alloy powder, an Fe—Co alloy, an Fe—Ni alloy, or a Cu—Fe alloy was used.

These alloys are oxidized by firing, and the Fe—Co alloy is converted into an oxide phase having CoFe ₂ O ₄ as a main phase, and the Fe—Ni alloy is converted into an oxide phase having NiFe ₂ O ₄ as a main phase. The Cu—Fe alloy changes to an oxide phase having CuFe ₂ O ₄ as a main phase. Therefore, in place of the alloy powder, Co ₃ O ₄ , NiO, and Fe ₂ O ₃ , which are oxides stable at high temperatures, were used to prepare bonding pastes of Examples 3-6 to 8-8.

Further, as Example 3-9, a bonding paste using only a perovskite type oxide powder without using an alloy powder was used, and as Example 3-10, only MnCo ₂ O ₄ having a spinel structure was used as a powder. The bonding paste was prepared by using MnCo ₂ O ₄ having a spinel structure instead of the alloy powder as Example 3-11.

Then, using the prepared bonding pastes of Examples 3-1 to 11-11, similarly to Test Example 1, the CTE of the bonding member, the bonding strength between the bonding member and the cathode or the metal IC, and the contact resistance were examined. It was. The results are shown in Table 3 below.
For reference, an XRD analysis result of a fired body obtained by firing a paste containing only an Fe—Ni alloy and a paste containing only an Fe—Co alloy (see Example 1-12) at 850 ° C. is shown in FIG. The results are shown in 1) and (2).

  As shown in Examples 3-1 to 3-5, if the alloy powder has a composition composed of two or more of Fe, Co, Ni, and Cu, it has good bondability to the cathode and the metal IC. It was found that a joining member having the same can be formed. However, in Example 3-5 using the perovskite type oxide powder containing only La at the A site, the bondability to the cathode and the metal IC is better than that of Examples 3-1 and 3-4, for example. Nevertheless, the result was a high contact resistance. Accordingly, it has been found that the perovskite oxide powder added to the bonding paste preferably contains a second element (here, Sr) in addition to La at the A site.

As shown in FIG. 3, when the bonding pastes of Examples 3-1 and 3-2 are fired, the alloy powder is fired to have a spinel phase as a main phase and other oxide phases as subphases. It can be seen that a fired body (joining member) is obtained. From this, the alloy powders used in the bonding pastes of Examples 3-1 to 3-5 are oxidized by firing, and the bonding member mainly includes CoFe ₂ O ₄ , NiFe ₂ O ₄ , CuFe ₂ O _{4, and the} like. It can be said that it exists in the form of a double oxide. On the other hand, in Examples 3-6 to 3-8, an oxide powder (Co ₃ O ₄ , NiO, or Fe ₂ O ₃ ) of any one of the above elements is used instead of the alloy powder. A bonding paste is prepared to form a bonded body. Therefore, Co, Ni, and Fe are present in the joined bodies of Examples 3-6 to 3-8 in the form of Co ₃ O ₄ , NiO, and Fe ₂ O ₃ . The CTE for the joining members in Examples 3-6 to 3-8 is not significantly different from the CTE in the joining member in Example 3-1. Nevertheless, in the joined bodies of Examples 3-6 to 3-8, the bondability to the metal IC is greatly reduced, and the contact resistance is also greatly increased. From this, it is understood that elements such as Fe, Co, Ni, and Cu in the joining member are contained at least in the form of an oxide having a spinel crystal structure. It can be seen that it is preferable to improve the characteristics. In other words, it can be said that elements such as Fe, Co, Ni, and Cu are not present as stable oxides in the bonding paste, but are preferably added in the form of an alloy, for example. In addition, Fe, Co, Ni, Cu and the like are not present as a single metal, but are present in the form of two or more alloys, so that it is easy to suitably form a spinel phase in the joining member during firing, It can be said that it is preferable because good bonding with a metal IC can be realized.

  On the other hand, in Example 3-9 in which the alloy paste is not included in the bonding paste, a spinel layer is formed on the surface of the metal IC, but no spinel phase is formed in the bonding member. As a result, although it was possible to suppress the diffusion of Cr from the metallic IC by the spinel layer, it was confirmed that the bonding strength between the metallic IC provided with the spinel layer and the bonding member was significantly reduced.

Since the surface of the stainless steel plate used as the metal IC was provided with a precursor layer of Co ₃ O ₄ coating, a spinel layer was formed on the metal IC by firing. By this spinel layer, Cr diffused from the stainless steel plate toward the joining member can be captured, and the diffusion of Cr to the joining member and the cathode can be suppressed. Here, if the spinel layer is not formed on the surface of the stainless steel plate of the metal IC, Cr contained in the stainless steel plate can diffuse in the joining member and reach the cathode. As a result, the diffused Cr reacts with Sr contained in the lanthanum strontium cobaltite (La _0.6 Sr _0.4 CO ₃ ) contained in the joining member and the cathode to form SrCrO ₄ , and the properties of the joining member and the cathode are improved. make worse. On the other hand, in the joining structure disclosed here, a spinel layer is provided on the surface of the metallic IC, and a spinel phase is also present in the joining member. Accordingly, the diffusion of Cr can be suppressed by the spinel layer, the bonding between the metal IC having the spinel layer and the bonding member can be strengthened, and the contact resistance at the bonding interface can be suppressed low. . Therefore, the joined body disclosed here can realize strong joining between the metallic IC and the cathode while suppressing Cr poisoning of the cathode even when the metallic IC is used.

Further, the bonding pastes of Examples 3-10 and 3-11 include MnCo ₂ O ₄ powder having a spinel crystal structure instead of the alloy powder, and the bonding member also includes a MnCo ₂ O ₄ phase. The general CTE of ferritic stainless steel used as a metal IC is as low as about 7 × 10 ^{−6 to} 12 × 10 ⁻⁶ / K, and the CTE of the spinel layer provided on the surface of the metal IC is, for example, MnCo ₂ It is about 13 × 10 ⁻⁶ / K in O ₄ (bulk). Therefore, the joining members of Examples 3-10 and 3-11 have the same MnCo ₂ O ₄ phase as that of the spinel layer provided on the surface of the metal IC, and are close to the CTE from the viewpoint of the metal IC. It is thought that the bonding was improved. However, it was confirmed that the joining member of Example 3-10 was formed from a paste containing no perovskite oxide powder, so that the joining property with the cathode was not good and the contact resistance was increased. Moreover, although the joining member of Example 3-11 contains perovskite-type oxide powder, the joining property between both the cathode and the metal IC is good, but the contact resistance is high, and the electrical properties of the joining member and the spinel layer are high. It is considered that general bonding is not good. This also shows that elements such as Fe, Co, Ni, and Cu added to the bonding paste are preferably in the form of an alloy rather than in the form of an oxide.
Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

1 SOFC stack 10, 10A, 10B Single cell 20 Air electrode (cathode)
30 Solid electrolyte 40 Fuel electrode (anode)
50, 50A Metal interconnectors 52, 54 Cell facing surface 53 Air flow path 55 Fuel gas flow path

Claims (13)

An air electrode of a solid oxide fuel cell, a metal interconnector, and a joining member that joins the air electrode and the metal interconnector,
The metal interconnector is
A metal substrate containing at least Fe and Cr;
Provided on the surface of the metal substrate facing the joining member, represented by the general formula: M ¹ ₃ O ₄ (wherein M ¹ is one or more elements selected from transition metals); A spinel layer including a first spinel phase,
The joining member is
General formula: ABO ₃ (wherein A is two or more elements selected from the group consisting of La, Sr and Ba, and B is one or more elements including at least Co); Perovskite phase,
An oxide phase represented by the general formula: M ² ₃ O ₄ (wherein M ² is two or more elements selected from the group consisting of Ni, Fe, Co and Cu);
Including junction structure.   2. The junction structure according to claim 1, wherein the perovskite phase includes La and Sr as the element A and Co as the element B. 3. The junction structure according to claim 1, wherein the oxide phase has any one selected from NiFe ₂ O ₄ , NiCo ₂ O ₄ , and CoFe ₂ O ₄ as a main phase.   The mass ratio of the perovskite phase and the oxide phase in the bonding member is 90:10 to 20:80 as a perovskite phase: oxide phase, according to any one of claims 1 to 3. Junction structure.   The joining structure according to claim 1, wherein the metal base material is ferritic stainless steel. A conductive joining material for forming a joining member for joining an air electrode of a solid oxide fuel cell and a metal interconnector,
Here, the metal interconnector is
A metal substrate containing at least Fe and Cr;
Provided on the surface of the metal substrate facing the joining member, and has a general formula: M ¹ ₃ O ₄ (wherein M ¹ includes one or more elements selected from transition metals) A spinel layer containing a first spinel phase represented by:
The conductive bonding material is
General formula: ABO ₃ (wherein A is two or more elements selected from the group consisting of La, Sr and Ba, and B is one or more elements including at least Co); A perovskite oxide powder having a perovskite crystal structure;
And an alloy powder containing two or more elements selected from the group consisting of Ni, Fe, Co, and Cu.   The conductive bonding material according to claim 6, wherein an average particle size of the perovskite oxide powder is smaller than an average particle size of the alloy powder. The perovskite oxide powder has an average particle size of 0.1 μm to 5 μm,
The conductive bonding material according to claim 7, wherein an average particle size of the alloy powder is 0.1 μm or more and 10 μm or less.   The conductive bonding material according to claim 6, further comprising a metal component-containing powder as a sintering aid. As the sintering aid, containing Cu-containing powder,
The conductive bonding material according to claim 9, wherein the perovskite oxide powder contains Cu at the B site.   The conductive bonding material according to any one of claims 6 to 10, wherein the conductive bonding material includes a dispersion medium in which the perovskite oxide powder and the alloy powder are dispersed and is prepared in a paste form. The conductive bonding material prepared in the paste form,
The conductive bonding material according to claim 11, wherein a firing shrinkage rate when dried at 850 ° C. after drying at 150 ° C. is 3% or less. A solid oxide fuel cell comprising a fuel electrode, a solid electrolyte, and an air electrode;
A metal interconnector;
A joining member for joining the air electrode and the metal interconnector;
With
The said joining member is a SOFC stack comprised with the baked product of the electroconductive joining material of any one of Claims 6-12.