JP7103783B2 - Joining material and joining body - Google Patents

Description

The present invention relates to a joining material and a joining body.

A single cell of a solid oxide fuel cell (SOFC) has a structure in which a fuel electrode (anode), a solid electrolyte layer, and an air electrode (cathode) are laminated in this order. During SOFC operation, for example, at a high temperature of 600 ° C. or higher, oxygen-containing gas is supplied to the surface of the solid electrolyte layer on the air electrode side, fuel gas is supplied to the surface of the solid electrolyte layer on the fuel electrode side, and power generation is performed. Will be.

From the viewpoint of improving the output density and power generation efficiency, a single SOFC cell is practically used as an SOFC stack in which a plurality of SOFCs are electrically connected via an interconnector. The SOFC single cell and the interconnector are electrically connected by a current collector. Conventionally, this current collector has been formed of a material having excellent electron conductivity and durability at high temperatures, for example, a metal material such as Ni or Ag (see Patent Documents 1 to 3).

Japanese Unexamined Patent Publication No. 2008-200724 Japanese Unexamined Patent Publication No. 2008-293984 Japanese Unexamined Patent Publication No. 2009-205821

However, if the current collector on the fuel electrode side is made of the above metal material, the SOFC may repeatedly start and stop, causing problems such as peeling and cracking in the current collector. rice field. That is, the current collector on the fuel side is exposed to air and is in an oxidizing atmosphere when the SOFC is stopped. On the other hand, during the operation of the SOFC, it is exposed to a fuel gas (for example, hydrogen gas) to create a reducing atmosphere. Due to this change from the oxidizing atmosphere to the reducing atmosphere, the metal material is reduced in the current collecting section on the fuel side to change from the oxide state to the metal state. As a result, the volume of the metal material is reduced and the contact area between the fuel electrode and the interconnector is reduced. Further, if air is introduced when the SOFC is shut down, the current collector on the fuel side is exposed to an oxidizing atmosphere. As a result, in the current collector on the fuel side, the metal material is oxidized and returns from the metal state to the oxide state. As a result, the volume of the metal material expands. Repeated redox as described above may cause problems such as peeling and cracking in the current collector on the fuel side, which may reduce the durability and reliability of the SOFC stack.

The present invention has been made in view of this point, and an object of the present invention is a joint body provided with a current collector whose volume change during redox is suppressed, and a joint material capable of forming the current collector. Is to provide.

INDUSTRIAL APPLICABILITY The present invention provides a joint including a solid oxide fuel cell, a metal member, and a current collector for connecting the solid oxide fuel cell and the metal member. The current collector contains a main material made of a metal or an oxide thereof, and a general formula (1): AB _x O _3-δ (where x is 0 or 1, and A is at least one lanthanoid element. When x is 1, B contains at least one transition metal element, and δ is a value determined so as to satisfy the neutral condition of electric charge.); The above-mentioned metal of the above-mentioned main material and the above-mentioned metal calculated based on the electron microscope observation-energy dispersive X-ray analysis method (SEM-EDX: Scanning Electron Microscope-Energy Dispersive X-ray Spectroscope) in a reducing atmosphere. When the total with the auxiliary material is 100% by volume, the volume ratio of the metal of the main material is 50% by volume or more and 98% by volume or less.

The current collector contains, in addition to a metal as a main material or an oxide thereof, a reduction-expandable auxiliary material. As a result, the volume change during redox can be suppressed as compared with the conventional current collector made of only a metal material. As a result, in the current collector, even if the SOFC is repeatedly operated and stopped, problems such as peeling and cracking are less likely to occur. Further, the durability and reliability of the joined body can be improved as compared with the mode in which the current collector made of only the metal material is provided. Therefore, the junction provided with the current collector can stably exhibit high power generation performance.

In addition, Patent Documents 2 and 3 disclose a conductive bonding material containing a perovskite type oxide and a metal oxide, and a stack of a solid oxide fuel cell provided with the conductive bonding material. However, the joining materials disclosed in Patent Documents 2 and 3 are all composed mainly of perovskite-type oxides in which a small amount of metal oxides coexist. Therefore, the technique disclosed herein is clearly different from Patent Documents 2 and 3, for example, in the coexistence ratio of the perovskite type oxide and the metal oxide.

In a preferred embodiment disclosed herein, the main material comprises at least one of Fe, Ni, Cu, Ag, Ag—Pd alloys and oxides thereof. These materials have an excellent balance between cost and conductivity. Therefore, excellent conductivity and durability at high temperatures can be realized at a relatively low cost.

In a preferred embodiment disclosed herein, the auxiliary material has the following (A), (B): (A) x in the general formula (1) is 0, and A contains at least Ce. , Cerium-containing oxide; (B) Perovskite-type oxide in which x in the general formula (1) is 1, at least one of them. These materials are excellent in conductivity and durability at high temperatures. Therefore, the effects of the techniques disclosed herein can be better exerted.

In a preferred embodiment disclosed herein, the current collector is composed of the metal of the main material and the auxiliary material calculated based on the electron microscope observation-energy dispersive X-ray analysis method in a reducing atmosphere. When the total of the above is 100% by volume, the volume ratio of the metal of the main material is 80% by volume or more and 95% by volume or less. As a result, the effects of the techniques disclosed herein can be exerted at a higher level.

In a preferred embodiment disclosed herein, the solid oxide fuel cell has a fuel electrode, a solid electrolyte, and an air electrode, and the current collector is located between at least the fuel electrode and the metal member. Is placed. Since the volume change during redox is suppressed, the current collector is preferably used on the side of the fuel electrode that is repeatedly exposed to the oxidizing atmosphere and the reducing atmosphere when the SOFC is started and stopped. can.

In a preferred embodiment disclosed herein, the current collector has a coefficient of thermal expansion _Air (%) measured in a temperature range from 25 ° C. to 700 ° C. in an oxidizing atmosphere using a thermomechanical analyzer. The volume change rate at the time of oxidation-reduction obtained by subtracting the coefficient of thermal expansion E _red (%) measured in the above temperature range in the reducing atmosphere is −0.01% or more and + 0.18% or less. Thereby, the reduction shrinkage of the main material can be better suppressed, and the effect of the technique disclosed herein can be exhibited at a higher level.

Further, as another aspect of the present invention, a joining material used for forming the current collecting portion in the production of the joining body is disclosed. From the viewpoint of handleability and the like, the bonding material preferably contains a solvent and is prepared in the form of a paste.

It is a perspective view which shows typically the SOFC stack which concerns on one Embodiment. It is a TMA measurement chart of Comparative Example 1. It is a TMA measurement chart of Comparative Example 4.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as appropriate. It should be noted that matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention (for example, the configuration of a single cell of SOFC which does not characterize the present invention, the manufacturing process of SOFC, etc.) , Can be grasped as a design matter of a person 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 the present specification and the common general technical knowledge in the art. Further, in the following drawings, members / parts having the same function may be described with the same reference numerals, and duplicate description may be omitted or simplified. Further, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

In the present specification, the "coefficient of thermal expansion" is an average linear expansion coefficient α measured in a temperature range from room temperature (25 ° C.) to 700 ° C. using a thermomechanical analysis (TMA). Say. The unit is K ^-1 . Unless otherwise specified, the atmosphere for measuring the coefficient of thermal expansion is an oxidizing atmosphere (typically, an atmosphere having an oxygen partial pressure of about 0.2 atm).

The average linear expansion coefficient α is such that the length of the test piece is L ₁ to L ₂ by changing the temperature of the test piece having a length L ₀ at room temperature from T ₁ to T ₂ (T ₁ <T ₂ ). When changed, the ratio of the amount of change in length ΔL = (L ₂ -L ₁ ) to the length L ₀ at room temperature, that is, ΔL / L ₀ is defined as “thermal expansion ε”, and such thermal expansion ε is defined as temperature. It is obtained by dividing by the difference ΔT = (T2 _- T ₁ ). In other words, the coefficient of linear expansion α can be calculated by the following formula (Equation I).
α = (L ₂ -L ₁ ) / {L ₀ × (T ₂ -T ₁ )} ・ ・ ・ (Equation I)
The measurement of the coefficient of linear expansion α is based on, for example, JIS Z 2285: 2003 “Measurement method of coefficient of linear expansion of metal materials” and JIS R 1618: 2002 “Measurement method of thermal expansion by thermomechanical analysis of fine ceramics”. Can be carried out.

Further, in the present specification, the “reduction expansion amount” refers to the coefficient of thermal expansion _Oredo measured in a temperature range from room temperature (25 ° C.) to 700 ° C. in a reducing atmosphere (typically in 100% hydrogen gas). It is a value (E _red -E _air ) obtained by subtracting the coefficient of thermal expansion E _air (%) measured in the above temperature range from (%). Then, in the present specification, when this value exceeds 0%, in other words, when _Red > _Air , it is said that it has "reduction swelling property". The coefficient of thermal expansion E is a value obtained by multiplying the above-mentioned thermal expansion ε by 100 and converting it into a percentage.

Further, in the following description, when expressing the compounding ratio (preparation ratio) in the joining material for forming the current collecting portion, the unit of "mass%" is mainly used, and the current collecting portion (joining layer) is used. When expressing the abundance ratio in a state, the unit of "volume%" is mainly used. Further, in the present specification, "A to B (where A and B are arbitrary values)" shall mean A or more and B or less unless otherwise specified.

<SOFC stack (joint)>
First, a solid oxide fuel cell (SOFC) will be described.
FIG. 1 is a perspective view schematically showing the SOFC stack 1 according to the embodiment. The SOFC stack 1 is a flat plate type. The SOFC stack 1 includes a plurality of SOFC single cells 10A and 10B, a plurality of metal metal connectors 20 and 20A, and a first current collector 30 and a second current collector 40. The SOFC stack 1 has a stack structure in which SOFC single cells 10A and 10B are stacked in a predetermined stacking direction via metal interconnectors 20 and 20A. The first current collector 30 and the second current collector 40 are interposed between the SOFC single cells 10A and 10B and the metal interconnectors 20 and 20A, respectively, and the SOFC single cells 10A and 10B and the metal interconnector 20 are respectively interposed. , 20A is joined. The SOFC stack 1 is an example of a bonded body. The SOFC stack 1 can be manufactured according to a conventionally known method.

The configurations of the single cells 10A and 10B may be the same as those of the conventional ones, and are not particularly limited. In this embodiment, the single cells 10A and 10B each include a first fuel pole 12, a second fuel pole 14, a solid electrolyte layer 16, and an air pole 18, respectively.

The first fuel pole 12 is formed thicker than the second fuel pole 14, the solid electrolyte layer 16, and the air pole 18. The first fuel pole 12 has a function as a support substrate. The first fuel pole 12 is a so-called fuel pole support. The first fuel pole 12 contains a conductive material. The conductive material is, for example, a nickel-based metal material containing a nickel (Ni) component (for example, nickel). The conductive material may be, for example, a cermet of a nickel-based metal material and zirconia stabilized with a stabilizer. In that case, the ratio of the metal material to the stabilized zirconia is not particularly limited, but the mass ratio is generally 90:10 to 40:60, for example, 80:20 to 45:55.

The properties of the conductive material are not particularly limited, but are typically in the form of powder. The average particle size of the conductive material (particle size corresponding to a cumulative 50% from the fine particle side in the volume-based particle size distribution measured by the laser diffraction / light scattering method; the same applies hereinafter) is approximately 0.01 to 5 μm, for example. It is 0.1 to 2 μm. When the conductive material is a cermet of a metal material and stabilized zirconia, the average particle size of both is approximately the same (for example, within ± 0.5 μm) from the viewpoint of improving the homogeneity and durability of the first fuel electrode 12. It is good to be.

The average thickness (length in the stacking direction) of the first fuel electrode 12 is not particularly limited, but is generally 0.3 to 2 mm, for example 0.5 to 1 mm. The first fuel pole 12 is a porous body. The porosity of the first fuel electrode 12 (a value calculated by dividing the void volume obtained by the mercury intrusion method by the apparent volume and multiplying by 100; the same applies hereinafter) is not particularly limited, but is approximately 20 to 50 volumes. %, For example, 30-40% by volume. The coefficient of thermal expansion of the first fuel electrode 12 is not particularly limited, but is, for example, 11 × 10 ^-6 to 14 × 10 ^-6 / K.

The second fuel pole 14 is interposed between the first fuel pole 12 and the solid electrolyte layer 16. The second fuel pole 14 has higher catalytic activity than the first fuel pole 12. The second fuel electrode 14 is a so-called fuel electrode active layer. The constituent material of the second fuel pole 14 may be the same as that of the first fuel pole 12, and may be partially or completely different. The second fuel pole 14 may contain the same nickel-based metal material (for example, nickel) as the first fuel pole 12 from the viewpoint of enhancing the integrity with the first fuel pole 12. The second fuel electrode 14 may contain an oxide ion conductor, for example, stabilized zirconia, from the viewpoint of enhancing the harmony of thermal expansion with the solid electrolyte layer 16. The average thickness of the second fuel pole 14 is not particularly limited, but is typically smaller than that of the first fuel pole 12, and is generally 100 μm or less, for example, 20 to 50 μm. The second fuel electrode 14 is a porous body. The porosity of the second fuel pole 14 is not particularly limited, but is typically smaller than that of the first fuel pole 12, and is approximately 5 to 30% by volume, for example, 10 to 20% by volume.

The solid electrolyte layer 16 is interposed between the second fuel pole 14 and the air pole 18. The solid electrolyte layer 16 has a function of separating the gas on the side of the first fuel pole 12 and the second fuel pole 14 and the gas on the side of the air pole 18. The solid electrolyte layer 16 has oxygen ion conductivity. The solid electrolyte layer 16 is an oxide ion conductor. The solid electrolyte layer 16 is, for example, zirconia stabilized with a stabilizer such as yttria, for example YSZ (Yttria stabilized zirconia), or ceria doped with a doping agent such as gadlinia, for example GDC (Gadolinia doped ceria). .. The average thickness of the solid electrolyte layer 16 is not particularly limited, but is generally 1 to 20 μm, for example, 3 to 10 μm. The content ratio of the stabilizer and the doping agent is not particularly limited, but is preferably about 5 to 10 mol% when the entire oxide ion conductor is 100 mol%. The solid electrolyte layer 16 is densely formed from the viewpoint of preventing gas leakage. The porosity of the solid electrolyte layer 16 is not particularly limited, but is generally 0.2 to 5% by volume, for example, 0.5 to 3% by volume.

The air electrode 18 is, for example, a perovskite-type oxide such as a lanthanum cobaltate (LaCoO ₃ ) type, a lanthanum manganate (LaMnO ₃ ) type, or a lanthanum ferrite (LaFeO ₃ ) type. The air electrode 18 is a porous body. The porosity of the air electrode 18 is not particularly limited, but is generally 5 to 50% by volume, for example, 10 to 30% by volume.

In this embodiment, the single cells 10A and 10B each have a four-layer structure, but the present invention is not limited to this. In the single cells 10A and 10B, for example, the first fuel pole 12 and the second fuel pole 14 may be composed of one layer having a constant porosity. Further, the single cells 10A and 10B may further have a layer other than the above. For example, a reaction inhibitor containing a layer for stabilizing the interface between the solid electrolyte layer 16 and the air electrode 18 such as zirconia stabilized with a stabilizer and / or ceria doped with a doping agent. It may have layers.

Further, the single cells 10A and 10B are so-called fuel pole supported type (ASC: Anode-Supported Cell) cells provided with the first fuel pole 12. However, the single cells 10A and 10B may be, for example, a so-called electrolyte-supported cell (ESC) cell in which the solid electrolyte layer 16 is thickened, and the air electrode 18 is thickened, so-called air. It may be a cathode-supported cell (CSC) cell. Further, it may be a metal-supported cell (MSC) having a porous metal sheet on the surface of the first fuel pole 12 or the second fuel pole 14 on the side away from the solid electrolyte layer 16.

The metal interconnectors 20 and 20A are for electrically connecting a plurality of single cells 10A and 10B to each other. The metal interconnector 20A located in the center of FIG. 1 is interposed between the two single cells 10A and 10B to connect the single cells 10A and 10B in series. However, the metal interconnectors 20 and 20A may be arranged so that the single cells 10A and 10B are connected in parallel. The metal interconnectors 20 and 20A are made of, for example, nickel, stainless steel, austenitic alloys, ferritic alloys and the like. The metal interconnectors 20 and 20A are examples of metal members. The coefficient of thermal expansion of the metal connectors 20 and 20A is not particularly limited, but is typically 10 × 10 ^-6 to 15 × 10 ^-6 / K, for example, 10 × 10 ^-6 to 12 × 10 ^-6 / K. ..

A plurality of grooves are formed on the cell facing surface 21 on the side of the metal interconnectors 20 and 20A facing the air electrode 18, and an oxygen-containing gas flow path 22 is provided. The oxygen-containing gas flow path 22 is connected to a first gas pipe (not shown) and communicates with a source of oxygen-containing gas (for example, hydrogen gas). Further, a plurality of grooves are formed on the cell facing surface 25 on the side of the metal interconnectors 20 and 20A facing the first fuel pole 12, and a fuel gas flow path 26 is provided. The fuel gas flow path 26 is connected to a second gas pipe (not shown) and communicates with a fuel gas (for example, air) supply source.

The first current collecting unit 30 and the second current collecting unit 40 have a function of physically and electrically connecting the metal interconnectors 20 and 20A and the single cells 10A and 10B. The first current collector 30 and the second current collector 40 have high bonding strength, excellent conductivity at high temperatures, are chemically stable at high temperatures, and have volume changes due to temperature changes. It is required to be small. The first current collecting unit 30 and the second current collecting unit 40 are densely formed from the viewpoint of reducing the current collecting resistance. The first current collector 30 connects the cell facing surfaces 25 of the metal interconnectors 20 and 20A and the first fuel poles 12 of the single cells 10A and 10B. The second current collector 40 connects the cell facing surfaces 21 of the metal interconnectors 20 and 20A and the air poles 18 of the single cells 10A and 10B.

In this embodiment, the first current collecting unit 30 and the second current collecting unit 40 are formed so as to cover the cell facing surfaces 21 and 25 of the metal interconnectors 20 and 20A, respectively. However, the first current collecting unit 30 and the second current collecting unit 40 need only be formed in at least a part where the metal interconnectors 20 and 20A and the single cells 10A and 10B are in contact with each other, and the cell facing surfaces 21, It is not necessary to cover the entire surface of 25.

In addition to the above-mentioned required properties, the first current collecting unit 30 is required to have a small volume change during redox and excellent resistance to a redox cycle (redox resistance). The first current collector 30 disclosed herein includes a main material and an auxiliary material. The first current collector 30 may be composed of a main material and an auxiliary material, and may contain a third component in addition to the main material and the auxiliary material. Examples of the third component include elements contained in the peripheral members of the first current collector 30, such as aluminum (Al), silicon (Si), and chromium (Cr). The total of the main material and the auxiliary material in the total mass (100%) of the first current collector 30 is approximately 20% by mass or more, typically 50% by mass or more, preferably 70% by mass or more. ..

The main material undergoes a redox reaction as the SOFC stack 1 starts and stops. The main material is reducing shrinkage at a high temperature of, for example, 600 ° C. or higher. That is, the main material has a property that the volume decreases when the periphery of the first current collector 30 changes from an oxidizing atmosphere to a reducing atmosphere at a high temperature. In other words, in the main material, the coefficient of thermal expansion E _red (%) in the reducing atmosphere and the coefficient of thermal expansion E _air (%) in the oxidizing atmosphere are E _air -E _red > 0, that is, E _air >. It is a material related to E _red . The effect of the technique disclosed here is that when the difference between the above _Air and the above _Red of the main material is large, for example, _Air -E _red ≥ 0.1%, and further, _Air -E _red ≥ 0. It works better when it is .2%.

The main material is metal or metal oxide. The type of metal of the main material is not particularly limited, but in general, the smaller the atomic number in the periodic table of elements and / or the larger the negative value of the standard electrode potential (V vs. SHE), the more easily it is oxidized. Tend. Examples of metals that are easily oxidized include metals belonging to the 3rd and 4th periods of the Periodic Table of the Elements. As another example, for example, magnesium (Mg), aluminum (Al), and titanium (Mg), aluminum (Al), and titanium (in descending order of the negative value of the standard electrode potential described in the Chemical Handbook (5th edition) of Maruzen Publishing Co., Ltd.) Metals such as Ti), manganese (Mn), zinc (Zn), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), tin (Sn), lead (Pb), copper (Cu), etc. Is difficult to oxidize at room temperature, but is rapidly oxidized in a temperature environment of, for example, 300 ° C. or higher. When one or more of such metal species are used as the main material, the effects of the techniques disclosed herein are better exhibited. Among them, iron groups (Fe, Co, Ni) and Cu are preferable from the viewpoint of improving conductivity, and Fe, Ni, Cu are more preferable from the viewpoint of the balance between cost and conductivity. In particular, from the viewpoint of enhancing the integrity with the first fuel pole 12 and the harmony of thermal expansion, the main material is the same metal type (for example, nickel) as the first fuel pole 12, and / or the metal interconnectors 20, 20A. May contain the same metal species as.

From the viewpoint of improving conductivity, simple substances of noble metals such as platinum (Pt), palladium (Pd), and silver (Ag) and alloys thereof, for example, Ag-Pd alloy and Pt-Pd alloy are preferable. Among them, Ag and Ag—Pd alloys are more preferable from the viewpoint of the balance between cost and conductivity.

The properties of the metal of the main material are not particularly limited, but are typically in the form of powder. The average particle size of the main material is approximately 0.01 to 5 μm, for example 0.1 to 2 μm. From the viewpoint of improving the bondability and integrity with the first fuel electrode 12, the average particle size of the main material of the first current collector 30 is substantially the same as the average particle size of the conductive material of the first fuel electrode 12 ( For example, ± 0.5 μm).

The auxiliary material causes a redox reaction as the SOFC stack 1 starts and stops. The by-product is reductively expandable, for example, at a high temperature of 600 ° C. or higher. That is, the auxiliary material has a property that the volume increases, contrary to the main material, when the periphery of the first current collector 30 changes from an oxidizing atmosphere to a reducing atmosphere at a high temperature. In other words, the relationship between the coefficient of thermal expansion E _red (%) in the reducing atmosphere and the coefficient of thermal expansion E _air (%) in the oxidizing atmosphere is E _red -E _air > 0, that is, E _red > E _air . It is in. From the viewpoint of better exerting the effects of the techniques disclosed herein, it is preferable that the above-mentioned _Red and the above-mentioned _{Air of the auxiliary materials are E red-E air ≥ 0.2} %, and E _red -E. More preferably, _air ≥ 0.4%, for example, _Red -E _air ≥ 0.42%. Further, although not particularly limited, when E _red -E _air ≤ 1.5%, for example, E _red -E _air ≤ 1.0%, it becomes easy to fine-tune the volume change during redox. Therefore, it is preferable.

The auxiliary material is the following general formula (1):
AB _x O _3-δ ... (1);
It is one kind or two or more kinds of compounds represented by. This compound can exhibit high conductivity at high temperatures. In the general formula (1), x is 0 or 1. δ is a value determined so as to satisfy the neutral condition of electric charge, typically −1.2 ≦ δ ≦ 1.2, for example -1 ≦ δ ≦ 1. The A site contains one or more lanthanoid elements (Ln), such as lanthanum (La), cerium (Ce), samarium (Sm), neodymium (Nd), gadolinium (Gd) and the like. The A site may further contain one or more elements other than Ln. As an example of the elements that can be contained in the A site, a monovalent alkali metal element or a divalent alkaline earth metal element (Ae), for example, magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba). ) Etc. can be mentioned.

In the above general formula (1), when x is 1, the B site is one or more of transition metal elements, for example, titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe). , Cobalt (Co), nickel (Ni), copper (Cu) and the like. The B site may further contain one or more elements other than the transition metal element. An example of an element that can be contained in the B site is a metal element having a valence of 3 or more and classified as a main group element or a rare earth element.

In a preferred embodiment, x in the general formula (1) is 0, and the A site contains at least Ce. That is, the auxiliary material has the following general formula (2):
( ^AI _y Ce _1-y ) O _3-δ ... (2);
It contains a cerium-containing oxide represented by.
Y in the general formula (2) is a real number satisfying 0 ≦ y <1. y is preferably 0.01 ≦ y ≦ 0.2, for example 0.05 ≦ y ≦ 0.1. When 0 <y, ^AI is one or more of the elements other than Ce in the examples of the elements that can be contained in the A site of the general formula (1). Among them, it is preferable to include one kind or two or more kinds of Ln, for example, Sm, Nd, Gd and the like. Note that δ is the same as the above general formula (1).

In another preferred embodiment, x in the general formula (1) is 1. That is, the by-product contains a perovskite-type oxide represented by ABO ₃ . As an example of the perovskite type oxide, an LTF oxide containing La, Ti and Fe, an LSTF oxide containing La, Sr, Ti and Fe, an LCTF oxide containing La, Ca, Ti and Fe, La and Examples include LSC oxides containing Sr and Co, LSCF oxides containing La, Sr, Co and Fe, LSM oxides containing La, Sr and Mn, and SSC oxides containing Sm, Sr and Co. Be done.

When x in the general formula (1) is 1, the A site preferably contains La. The A site preferably further contains a divalent alkaline earth metal such as Ca and Sr. Further, the B site preferably contains at least one of metals belonging to the 4th period of the Periodic Table of the Elements, for example, Ti, Fe, Co, and Ni. From the viewpoint of improving the reduction expandability, it is preferable that Ti is contained in the B site. From the viewpoint of improving conductivity, it is preferable that Fe is contained in the B site.

As a preferable example of the perovskite type oxide, the following general formula (3):
(La _1-α Ae _α ) (BI ¹ _-β Fe _β ) O _3-δ ... (3);
The composite oxide represented by is mentioned.
Α in the above general formula (3) is a real number satisfying 0 ≦ α <1. α is typically 0.1 ≦ α ≦ 0.7, preferably 0.2 ≦ α ≦ 0.6, for example 0.2 ≦ α ≦ 0.4. When 0 <α, Ae is, for example, Mg, Ca, Sr, Ba, or the like.
Further, β is a real number satisfying 0 ≦ β <1. β is typically 0.1 <β ≦ 0.99, preferably 0.5 ≦ β ≦ 0.95, for example 0.6 ≦ β ≦ 0.9. When β <1, BI is one or more of the elements other than Fe in the examples as the elements that can be contained in the B site of the above general formula ( ¹ ). Among them, it is preferable to contain one or more kinds of transition metal elements, for example, Ti and Co. Note that δ is the same as the above general formula (1).

The first current collecting unit 30 disclosed here has a ratio of V1 when the total of the occupied volume V1 of the metal of the main material and the occupied volume V2 of the auxiliary material is 100% by volume in a reducing atmosphere. It is 50 to 98% by volume. In other words, V1: V2 = 50:50 to 98: 2. As a result, volume expansion during redox is suppressed. From the viewpoint of improving the bondability between the first current collector 30 and the metal interconnectors 20 and 20A and reducing the contact resistance, the ratio of V1 is 80 to 95% by volume, in other words, V1: V2 = More preferably, it is 80:20 to 95: 5. The ratio of V1: V2 can be calculated by image analysis based on the SEM-EDX image of the first current collector 30. The detailed calculation method will be described in the column of Examples. Further, the ratio of V1: V2 can be adjusted by, for example, the mixing ratio (preparation ratio) of the main material and the auxiliary material in the joining material used for forming the first current collector 30.

The coefficient of thermal expansion of the first current collector 30 is equivalent to that of the first fuel pole 12 of the single cells 10A and 10B and the metal interconnectors 20 and 20A (approximately ± 2 × ^10-6 / K ^, preferably ± 1 × 10-. ⁶ / K) is preferable. The coefficient of thermal expansion of the first current collector 30 is typically 10 × 10 ^-6 to 20 × 10 ^-6 / K, for example 11 × 10 ^-6 to 16 × 10 ^-6 / K.

In the first current collector 30, the volume change rate at the time of redox is suppressed to a small value, and the redox resistance is improved as compared with the conventional case. In the first current collecting unit 30, the volume change rate at the time of redox obtained by subtracting the coefficient of thermal expansion E _red (%) in the reducing atmosphere from the above-mentioned coefficient of thermal expansion E _air (%) in the oxidizing atmosphere is determined. It is preferably about −0.31 to + 0.19%, and more preferably −0.01% to + 0.18%. The value of the volume change rate is represented here as a positive value in the case of reduction contraction and a negative value in the case of reduction expansion. The range of the volume change rate can be realized by adjusting, for example, the mixing ratio of the main material and the auxiliary material in the joining material, the type of the main material, and the general formulas (2) and (3) of the auxiliary material. can.

The first current collector 30 having the above configuration has less volume expansion due to redox than, for example, a conventional current collector made of a metal material. Therefore, even when the SOFC stack 1 is repeatedly operated and stopped, the first current collecting unit 30 is preferably maintained in denseness, and the current collecting resistance is unlikely to increase. In other words, it has excellent resistance to the cycle of the oxidizing atmosphere and the reducing atmosphere (redox resistance). Further, the first current collector 30 is typically excellent in conductivity as compared with the conductive joining material as described in Patent Documents 2 and 3. Therefore, the first current collector 30 can maintain high conductivity for a long period of time, and is excellent in durability and reliability.

The second current collector 40 is typically made of the same material as the air electrode 18, for example, a perovskite type such as a lanthanum cobaltate (LaCoO ₃ ) type, a lanthanum manganate (LaMnO ₃ ) type, or a lanthanum ferrite (LaFeO ₃ ) type. It is composed of oxides. However, the second current collector 40 may be made of the same material as the first current collector 30.

During operation of the SOFC stack 1, the temperature of the SOFC stack 1 is raised to a high temperature of about 600 ° C. or higher, for example, about 600 to 900 ° C. An oxygen-containing gas, for example, air (Air) is supplied to the oxygen-containing gas flow path 22 of the metal interconnectors 20 and 20A. Fuel gas, for example, hydrogen gas (H ₂ ), is supplied to the fuel gas flow path 26 of the metal interconnectors 20 and 20A. In the SOFC single cells 10A and 10B, oxygen is reduced at the air electrode 18 to become oxide ions. The oxide ions reach the first fuel pole 12 and the second fuel pole 14 via the solid electrolyte layer 16, oxidize hydrogen, and emit electrons. This generates electrical energy. That is, power generation is performed.

<Joining material>
Next, the joining material disclosed here will be described. The joining material disclosed here can be suitably used for forming the first current collector 30 of the SOFC stack 1 described above. The joining material includes the above-mentioned two types of materials, that is, a main material and an auxiliary material. The joining material disclosed here typically has a mass ratio of main material: auxiliary material = 99: 1 to 64: 36 when the total of the main material and the auxiliary material is 100% by mass. For example, it is preferable that the main material: auxiliary material = 95: 5 to 88:12.

The joining material may be composed of a main material and an auxiliary material, and may contain other optional components in addition to the main material and the auxiliary material. As other optional ingredients, various additive ingredients commonly used in this type of application can be considered. Examples of additive components are solvents, binders, dispersants, thickeners, plasticizers, sintering aids, defoamers, antioxidants, preservatives, antistatic agents, pH regulators, colorants (pigments, dyes). Etc.) etc. are exemplified.

In a preferred embodiment, the bonding material contains a solvent and is prepared in the form of a paste (including an ink form and a slurry form). In the following, the paste-like joining material may be simply referred to as "paste". As the solvent, from the viewpoint of workability, storage stability and the like, it is preferable to use a high boiling point organic solvent having a boiling point of about 200 ° C. or higher, for example, 200 to 300 ° C. as a main component. Specific examples of the high boiling point organic solvent include alcohol solvents having an −OH group such as tarpineol, mentanol, texanol, dihydroterpineol, and benzyl alcohol, 2,2,4-trimethyl-1,3-pentanediol-1-. Ester-based solvents such as monoisobutyrate and isobornyl acetate, which have an ester-binding group (RC (= O) -OR') in the main chain, ethyl diglycol acetate, butyl glycol acetate, butyl diglycol acetate, Examples include ether solvents such as butyl cellosolve acetate, butyl carbitol acetate, and butyl carbitol, which have an ether bond group (-COC-) in the main chain, hydrocarbon solvents such as toluene and xylene, and mineral spirits. Be done. Among them, an alcohol solvent can be preferably used.

As the binder, for example, one that can be evaporated and removed by heating and firing at 500 ° C. or higher can be preferably used. Specific examples of the binder include cellulose-based polymers (cellulose derivatives) such as methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; ester-based polymers such as methacrylate esters; polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, and poly. Acrylic polymers such as butyl methacrylate; Ethylene polymers such as polyethylene oxide; Nitrile-based polymers such as polyacrylonitrile and polymetallylonitrile; Urethane-based polymers such as polyurethane; Polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride Polyvinylfluoride , Vinyl-based polymers such as vinyl acetate; rubbers such as styrene-butadiene rubber; and the like. Among them, a cellulosic polymer such as ethyl cellulose can be preferably used from the viewpoint of excellent combustion decomposition during firing and environmental consideration.

The ratio of the main material and the auxiliary material to the total paste is not particularly limited, but from the viewpoint of achieving high density after firing, the total of the main material and the auxiliary material is approximately 50% by mass or more in terms of mass ratio, which is typical. It is preferable that the content is 60 to 95% by mass, for example, 70 to 90% by mass. The ratio of the organic solvent to the entire paste is not particularly limited, but from the viewpoint of workability when applying the paste and the viewpoint of realizing the first current collecting unit 30 having high homogeneity, the mass ratio is approximately 5. It is preferably from 20% by mass, typically 10 to 15% by mass. When the paste contains a binder, the ratio of the binder to the entire paste is not particularly limited, but the mass ratio is generally 1 to 10% by mass, for example, 2 to 5% by mass.

The first current collector 30 of the SOFC stack 1 can be formed as follows, for example, by using the above paste. That is, first, the paste is applied to the cell facing surfaces 25 of the metal interconnectors 20 and 20A. Next, the surfaces of the single cells 10A and 10B on the side of the first fuel pole 12 are superposed on the applied paste to form a complex. The complex is dried at room temperature and then calcined at, for example, 800-900 ° C. As a result, a first current collector 30 that electrically and physically connects the first fuel poles 12 of the single cells 10A and 10B and the cell facing surfaces 25 of the metal interconnectors 20 and 20A is formed. be able to. Then, the SOFC stack 1 including the single cells 10A and 10B, the metal interconnectors 20 and 20A, and the first current collector 30 can be obtained. The first current collecting unit 30 formed by using the paste disclosed here has excellent redox resistance as compared with the conventional one, and it is unlikely that the current collecting resistance will increase even when the start and stop are repeated. Therefore, the SOFC stack 1 can stably exhibit high power generation performance for a long period of time.

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

(Test Example I)
[Preparation of joining material]
First, NiO powder as the main material (average particle size: 0.5 μm) and LSTF (La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O ₃ ) powder as the auxiliary material (average particle size: 0.5 μm) was prepared. Next, the prepared powder was prepared by mixing the NiO powder and the LSTF powder or using them alone at the “preparation ratio” shown in Table 1. Next, this prepared powder, an organic solvent (alcohol-based), and an organic binder (ethyl cellulose) are mixed so as to have a mass ratio of 100: 15: 3, and a paste-like bonding material (Examples 1 to 7) is mixed. , Comparative Examples 1 to 3) were prepared.

[Measurement of volume change rate during redox]
First, each of the joining materials prepared above is molded so as to have dimensions of 4 mm × 5 mm × 20 mm after firing, and fired at 1100 ° C. in the air to prepare two test pieces for measurement. did. Next, the thermomechanical analyzer (model: TMA8310) manufactured by Rigaku Co., Ltd. was used to measure the thermal expandability by the differential expansion method. The thermal expansion was measured in an oxidizing atmosphere (air) or a reducing atmosphere (100% H ₂ ) in a temperature range from room temperature (25 ° C.) to 700 ° C., respectively. Note that FIG. 2 shows a TMA measurement chart of Comparative Example 1 as an example.

Next, the following (Formula II):
Coefficient of thermal expansion E (%) = {(L ₂ -L ₁ ) / L ₀ } × 100 ... (Equation II);
L ₀ = L ₁ = 20 (mm), L ₂ substitutes the length of the test piece at 700 ° C, and the coefficient of thermal expansion from 25 ° C to 700 ° C in the oxidizing atmosphere (air) _Air ( %) And the coefficient of thermal expansion E _red (%) from 25 ° C. to 700 ° C. in the reducing atmosphere (H ₂ ) were calculated.
Then, the volume change rate (%) at the time of redox was calculated by subtracting E _red (%) from E _air (%), that is, by E _air (%) _{−E red} (%).
The results are shown in the "Volume change rate" column of Table 1. The values in Table 1 are shown as positive when the volume decreases (shrinks) due to the change from the oxidizing atmosphere to the reducing atmosphere, and increases (expands) when the volume increases (expands) due to the change from the oxidizing atmosphere to the reducing atmosphere. Is shown as a minus.

[Measurement of composition of bonding material layer]
First, the test piece whose thermal expansion property was measured in the reducing atmosphere in the measurement of the volume change rate was taken out after the temperature of the thermomechanical analyzer had dropped to room temperature. Next, this test piece was subjected to CP (Cross section polisher) processing to obtain a cross section, and then observed with an SEM to obtain an SEM observation image. Next, the obtained SEM observation image was subjected to elemental mapping of Ni (Ka line) and Ti (Ka line) with EDX. Then, using the image processing software (Image-Pro Plus) manufactured by Nippon Roper Co., Ltd., the SEM-EDX image was analyzed and the area occupied by each constituent material was calculated.

Specifically, first, the result of element mapping of Ni was converted (binarized) into a black-and-white image, and then the contour of the Ni particles was traced to calculate the area of the main material (Ni particles). Similarly, after converting (binarizing) the result of element mapping of Ti into a black-and-white image, the area of the secondary material (LSTF particles) was calculated by tracing the contour of Ti. Then, the ratio of each area to the total of the area of Ni particles and the area of LSTF particles was calculated. This cross-sectioning, SEM-EDX mapping, and image analysis processing are performed in multiple fields (here, 3 to 5 fields for each example), and the obtained area ratios are arithmetically averaged to obtain Ni particles and LSTF particles. The volume ratio was obtained. Although the element mapping of Ti was performed here when calculating the area of the LSTF particles, for example, La or Sr can also be used.
The results are shown in the column of "Joint material layer (reducing atmosphere)" in Table 1.

[Measurement of joint strength]
First, each of the joining materials prepared above was applied to a metal plate and fired in the air at 850 ° C. As the metal plate, ferritic stainless steel used as a material for the interconnector was used. As a result, each bonding material layer was formed on the metal plate.
Next, a grid test was carried out according to JIS K5400 8.5: 1990 “Adhesion-goban test”. Specifically, first, a lattice pattern of 10 × 10 = 100 squares was formed by making 11 parallel cuts at intervals of 1 mm in each of the formed bonding material layers. Next, an adhesive tape was attached so as to cover the lattice pattern, and the adhesive tape was rubbed with an eraser to adhere to the bonding material layer. Next, the adhesive tape was peeled off in a direction in which the angle formed by the bonding material layer was 90 °. Then, the joint strength was evaluated from the ratio of the peeled squares (peeling area ratio:%) among all the squares (100 squares) of the grid.
The results are shown in the "Joint strength" column of Table 1. In Table 1, the evaluation points of the JIS grid test are shown as "◎" for 8 points or more, "○" for 4 to 6 points, "△" for 2 points, and "×" for 0 points. There is.

[Making a half cell]
First, NiO powder (average particle size: 0.5 μm) and 8YSZ powder (average particle size: 0.5 μm) were mixed at a mass ratio of 6: 4 to prepare a mixed powder. Next, the mixed powder, the organic solvent (xylene), the organic binder, the pore-forming material (carbon), and the plasticizer were mixed in a mass ratio of 53: 24: 8.5: 10: 4.5. The mixture was mixed so as to obtain a paste for forming a fuel electrode support. This paste for forming a fuel electrode support was formed into a sheet having a thickness of 0.5 to 1.0 mm by a doctor blade method to obtain a fuel electrode support sheet.
Next, NiO powder (average particle size: 0.5 μm), 8YSZ powder (average particle size: 0.5 μm), an organic solvent (tarpineol), and an organic binder (ethyl cellulose) were added in a mass ratio of 48: The mixture was mixed so as to have a ratio of 32:18: 2 to obtain a paste for forming a fuel electrode layer. This fuel electrode layer forming paste was applied onto the fuel electrode support sheet prepared above by the screen printing method to form the fuel electrode layer.

Next, 8YSZ powder (average particle size: 0.5 μm), an organic solvent (tarpineol), and an organic binder (ethyl cellulose) are mixed so as to have a mass ratio of 65:31: 4, and an electrolyte membrane is formed. It was used as a forming paste. This electrolyte film forming paste was applied onto the fuel electrode layer formed above by screen printing to form an electrolyte film having a thickness of 10 μm.
Next, the laminate (fuel electrode support sheet / fuel electrode layer / electrolyte membrane) laminated and molded above was co-fired at 1350 ° C. to prepare a half cell.

[Measurement of contact resistance]
First, each of the joining materials prepared above was applied to the surface of the half cell produced above on the fuel electrode side in an area of □ 10 mm × 10 mm. Next, a metal interconnector made of stainless steel (SUS430) was placed on the coated joint material and fired at 850 ° C. As a result, a test piece in which the SOFC cell and the interconnector were integrated via the bonding material layer was produced. Next, terminals made of Pt are attached to the fuel electrode and the metal interconnector of the test piece, respectively, and in a reducing atmosphere (atmosphere of 100% H ₂ ), at a temperature of 700 ° C., between the fuel electrode and the metal interconnector. The contact resistance was measured. Specifically, it was swept at DC ± 10 mV and 1 mV / sec, and the contact resistance was calculated from the slope of the graph of the voltage value and the current value at that time.

The results are shown in the "contact resistance" column of Table 1. In Table 1, the case where the volume resistance is 0.02 Ω ・ cm ² or less is “◎”, and the case where the volume resistance is more than 0.02 Ω ・ cm ² and 0.05 Ω ・ cm ² or less is “〇”. , When the volume resistance exceeds 0.05 Ω ・ cm ² and is 0.1 Ω ・ cm ² or less, it is relatively “△”, and when the volume resistance exceeds 0.1 Ω ・ cm ² , it is “×”. Shown.

As shown in Table 1, the higher the charging ratio of NiO powder in the bonding material, the higher the ratio of Ni in the bonding material layer in the reducing atmosphere, and the volume change rate during redox is NiO alone. There was a tendency to approach the value of (Comparative Example 3).
In addition, from the evaluation results shown in Table 1, the following configuration:
(1) A bonding material obtained by blending NiO powder and LSTF powder in a mass ratio of NiO: LSTF = 64: 36 to 99: 1 (preferably, a mass ratio of NiO: LSTF = 88: 12 to 97: 3). To form a bonding material layer using;
(2) In a reducing atmosphere, Ni and LSTF form a bonding material layer of Ni: LSTF = 50: 50 to 98: 2 (preferably Ni: LSTF = 80: 20 to 95: 5) in volume ratio. To do;
Therefore, the reduction expansion property and the reduction contraction property of the bonding material layer could be offset. As a result, the volume change rate of the bonding material layer could be suppressed in the range of −0.31 to +0.19% (preferably +0.004 to +0.17%). Further, a bonding material layer having high bonding strength and low contact resistance has been realized. It is considered that the reason for this is that the reduction shrinkage of the main material is canceled by the auxiliary material and the absolute value of the volume change rate of the bonding material layer is suppressed to a small value, so that the redox resistance is improved.

(Test Example II)
Similar to Test Example I above, except that 10 GDC (Gd _0.1 Ce _0.9 O ₂ ) was used instead of LSTF as a secondary material and the "preparation ratio" of the joint material was adjusted as shown in Table 2. Then, Examples 8 to 11 and Comparative Examples 4 and 5 were evaluated. The results are shown in Table 2. Table 2 also shows the results of Comparative Example 3 in Test Example I. Further, FIG. 3 shows a TMA measurement chart of Comparative Example 4 as an example.

As shown in Table 2, when GDC was used instead of LSTF as a secondary material, the same results as in Test Example I were obtained. That is, the following configuration:
(1) Forming a bonding material layer using a bonding material in which NiO powder and GDC powder are mixed at a mass ratio of NiO: GDC = 61: 39 to 99: 1;
(2) Ni and GDC form a bonding material layer having a volume ratio of Ni: GDC = 50: 50 to 98: 2 in a reducing atmosphere;
Therefore, the reduction expansion property and the reduction contraction property of the bonding material layer could be offset. As a result, the volume change rate could be suppressed in the range of −0.11% to + 0.19%.

(Test Example III)
Examples 12 to 14 were evaluated in the same manner as in Example 5 of Test Example I above, except that the types of the main material and the auxiliary material included in the joint material were changed as shown in Table 3. As the LCTF as the auxiliary material, La _0.8 Ca _0.2 Ti _0.1 Fe _0.9 O ₃ was used. Further, in Example 14, LSTF (La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O ₃ ) having a composition ratio different from that of Example 5 was used. The results are shown in Table 3. Table 3 also shows the results of Example 5 in Test Example I.

As shown in Table 3, even when the type of the metal of the main material and / or the type of the perovskite type oxide of the auxiliary material was changed, the effects of the techniques disclosed herein were fully exhibited.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above.

For example, the SOFC single cells 10A and 10B shown in FIG. 1 are of the planar type, but are not limited thereto. The SOFC single cell can have various other shapes. For example, a conventionally known polygonal type, a cylindrical type (Tubular), or a flat cylindrical type (Flat Tubular) in which the peripheral side surface of the cylinder is vertically crushed can be used. Further, the shapes and sizes of the metal interconnectors 20 and 20A can also be appropriately changed according to the shapes of the single cells 10A and 10B.

Further, in the SOFC stack 1 shown in FIG. 1, the metal member is the metal interconnectors 20 and 20A, but the present invention is not limited to this. The metal member may be a member that is electrically and / or physically connected to the SOFC single cells 10A and 10B. The metal member may be, for example, a gas pipe connected to the fuel poles (first fuel pole 12 and second fuel pole 14) of the single cells 10A and 10B. In that case, the interconnector may be made of a material other than metal, such as carbon or ceramic.

1 SOFC stack 10A, 10B SOFC single cell 12 1st fuel pole 20, 20A interconnector (metal member)
30, 40 Current collector

Claims (6)

Solid oxide fuel cell and
With metal parts
A current collector that connects the solid oxide fuel cell and the metal member,
With
The solid oxide fuel cell has a fuel electrode, a solid electrolyte, and an air electrode.
The current collector is arranged between the fuel electrode and the metal member.
The current collector
The main material consisting of metal or its oxide,
General formula (1): A BO _3-δ (where A contains at least one lanthanoid element , B contains at least one transition metal element, and δ satisfies the charge neutrality condition. It is a value to be determined.); Including a reduction-expandable auxiliary material composed of a perovskite-type oxide represented by;
In a reducing atmosphere, when the total of the metal of the main material and the auxiliary material calculated based on the electron microscope observation-energy dispersive X-ray analysis method is 100% by volume, the metal of the main material A bonded body having a volume ratio of 50% by volume or more and 98% by volume or less. The main material comprises at least one of Fe, Ni, Cu, Ag, Ag—Pd alloys and oxides thereof.
The joined body according to claim 1. When the total of the metal and the sub-material of the main material calculated based on the electron microscope observation-energy dispersive X-ray analysis method is set to 100% by volume, the current collecting unit is in a reducing atmosphere. The volume ratio of the metal of the main material is 80% by volume or more and 95% by volume or less.
The joined body according to claim 1 or 2 . The current collector is measured in the temperature range from the thermal expansion coefficient _Air (%) measured in the temperature range of 25 ° C. to 700 ° C. in the oxidizing atmosphere using a thermomechanical analyzer in the reducing atmosphere. The rate of change in volume during oxidation-reduction obtained by subtracting the coefficient of thermal expansion E _red (%) is −0.01% or more and + 0.18% or less.
The bonded body according to any one of claims 1 to 3 . A joining material used for forming the current collector in the production of the joining body according to any one of claims 1 to 4 .
A powdery main material composed of a metal oxide and a general formula (1): ABO _3-δ (where A contains at least one lanthanoid element and B contains at least one transition metal element, δ Is a value determined so as to satisfy the neutral condition of the electric charge.); A bonding material containing a reduction-expandable powdery auxiliary material made of a perovskite-type oxide represented by . The joining material according to claim 5 , wherein the joining material contains a solvent and is prepared in the form of a paste.

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