JP6712119B2 - Solid oxide fuel cell stack - Google Patents

Description

The present invention relates to a solid oxide fuel cell stack. Specifically, the present invention relates to a solid oxide fuel cell stack having an interconnector having good gas sealing properties and adhesion to a solid electrolyte, and particularly excellent in conductivity and oxide ion insulation.

Unlike a heat engine that uses the process of thermal energy or kinetic energy, a fuel cell causes a fuel such as natural gas or hydrogen to react with oxygen in the air through a solid electrolyte, and continuously reacts with the chemical energy of the fuel. Is an energy converter that directly obtains electrical energy. Among them, the solid oxide fuel cell is a fuel cell that operates using a solid oxide (ceramic) as a solid electrolyte and using a fuel electrode as a negative electrode and an air electrode as a positive electrode. Further, the solid oxide fuel cell is known to have an advantage that high energy conversion efficiency can be obtained.

Since the solid oxide fuel cell has a small output per unit cell, a plurality of unit cells are connected in series to increase the output to generate electricity. A member that electrically connects adjacent unit cells is called an interconnector. An interconnector using ceramics (hereinafter also referred to as a ceramic interconnector) is known as a material thereof. As a characteristic of the ceramic interconnector, gas sealability that does not allow gas to permeate, conductivity, oxide ion insulation, and adhesion with a solid electrolyte are required.

Generally, a ceramic interconnector cannot have sufficient conductivity unless it has a small thickness (for example, about 100 μm or less). However, if the thickness of the ceramic interconnector is reduced in order to obtain sufficient conductivity and it is attempted to form such a thin ceramic interconnector on the surface of the porous electrode (fuel electrode or air electrode), it becomes porous. There is a risk that the ceramic interconnector will be taken into the wrong electrode. As a result, the ceramic interconnector may not be formed, or even if it is formed, the gas may not be sufficiently sealed because it is thin.

When the gas sealability of the ceramic interconnector is low, the fuel gas leaks from the fuel electrode side of the ceramic interconnector to the air electrode side and is mixed with air, which is not preferable. In order to improve the gas sealability of the ceramic interconnector, it is necessary to increase the denseness of the ceramic interconnector, and it is necessary to sinter the ceramic interconnector densely. In addition, when the conductivity of the ceramic interconnector is low, the resistance of the ceramic interconnector increases, and the output of the fuel cell decreases. Further, when the oxide ion insulation of the ceramic interconnector is low, oxide ions leak from the air electrode side of the ceramic interconnector to the fuel electrode side, and the efficiency of the fuel cell decreases. In addition, if the adhesion between the solid electrolyte and the ceramic interconnector is low, a gap such as a crack is created between the solid electrolyte and the ceramic interconnector, and the fuel gas leaks from this gap.

A lanthanum chromite (LaCrO ₃ ) based interconnector is widely used as a material for the ceramic interconnector. This LaCrO ₃ -based interconnector is generally known to have high conductivity but is difficult to sinter. Further, since it contains chromium (Cr), so-called Cr poisoning may occur.

Further, as a material for the ceramic interconnector, an SLT-based interconnector represented by SrLaTiO _{3 −δ} is widely used. It is known that this SLT-based interconnector has lower conductivity but better sinterability than the LaCrO ₃ -based interconnector. The SLT-based interconnector, for example, replaces the Sr site in the crystal lattice of SrTiO ₃ that is an insulator with lanthanum (La) to obtain SrLaTiO _{3 −δ} (SLT), thereby forming SrLaTiO _{3 −δ} (SLT). The conductivity is expressed by changing part of Ti ⁴⁺ of the Ti site in the crystal lattice to Ti ³⁺ . Note that δ is a value that is determined so as to satisfy the charge neutral condition.

JP-A-2013-030270 (Patent Document 1) discloses that when an interconnector containing strontium titanate is integrally fired with a base material containing a transition metal oxide such as NiO, the transition metal component contained in the base material is It has been reported that the diffusion causes a decrease in conductive carriers due to charge compensation, resulting in a decrease in conductivity of the interconnector.

Further, Japanese Patent Laid-Open No. 2010-212036 (Patent Document 2) does not contain an element that deteriorates battery performance, and has a reduced expansion coefficient for the purpose of forming an interconnector capable of achieving both low expansion coefficient and high conductivity. So as to increase or decrease in a stepwise manner, a portion having a different reduction expansion coefficient is composed by using a perovskite type oxide (LSTF oxide) represented by La _1-x Sr _x Ti _1-y Fe _y O _3-δ. It is described that a two-layer structure different from each other is used. Further, according to this document, it is described that two kinds of LSTF oxides having different compositions are diffusion-bonded by pressure firing to manufacture a composition-graded interconnector having a two-layer structure.

However, according to the knowledge of the present inventors, the interconnector described in Patent Document 2 has a high iron composition ratio, so that it exhibits oxide ion conductivity and is difficult to use as an interconnector. .. Therefore, none of the above documents has realized the manufacture of a solid oxide fuel cell stack having a ceramic interconnector having particularly excellent conductivity and oxide ion insulation.

JP 2013-030270 JP JP 2010-212036 JP

According to the experiments conducted by the present inventors, the substitution of the titanium (Ti) site of the SLT with iron (Fe) as a conductive carrier reduces the conductivity even when nickel (Ni) is solid-solved in the SLT. It was found to be difficult. On the other hand, by replacing the Ti site with Fe, oxygen deficiency occurs and the oxide ion conductivity is developed. As a result, it was found that the leakage of oxide ions consumes the fuel and lowers the power generation efficiency.

The present inventors have now found that the expression of oxide ion conductivity due to oxygen deficiency can be suppressed by further substituting the Ti site of Fe-substituted SLT with niobium (Nb). Further, by making Fe and Nb substituting for SLT have a specific composition ratio, it is possible to suppress the decrease in the conductivity of the interconnector due to the solid solution of Ni and also suppress the development of the oxide ion conductivity due to the substitution of Fe. It was found that it was possible (that is, the oxide ion insulating property was obtained). The present invention is based on these findings.

Therefore, it is an object of the present invention to provide a solid oxide fuel cell having a ceramic interconnector which is particularly excellent in conductivity and oxide ion insulation.

And, the solid oxide fuel cell stack according to the present invention,
A plurality of power generation elements in which a fuel electrode, a solid electrolyte and an air electrode are laminated at least sequentially,
At least an interconnector electrically connecting the air electrode of one adjacent power generating element of the plurality of power generating elements and the fuel electrode of the other power generating element, and the plurality of power generating elements are connected in series. A solid oxide fuel cell stack comprising:
The interconnector has the following formula (1):
_{Sr a La b Ti 1-c} -d Nb c Fe d O 3-δ (1)
(Where a, b, c and d are 0.1≦a≦0.8, 0.1≦b≦0.8, 0.05≦c≦0.2, and 0.2≦d≦ It is a positive real number that satisfies 0.5.)
It is characterized by comprising a perovskite type oxide represented by.

1 is a front view of a horizontal stripe type solid oxide fuel cell stack according to the present invention. FIG. 3 is a partial cross-sectional view of a vertical stripe type solid oxide fuel cell unit forming a vertical stripe solid oxide fuel cell stack according to the present invention. 1 is a perspective view showing a vertical stripe type solid oxide fuel cell stack according to the present invention. FIG. 3 is a schematic cross-sectional view of the vicinity of a power generation element that constitutes a solid oxide fuel cell stack according to the present invention 1 is one embodiment of a solid oxide fuel cell stack according to the present invention. 3 is an SEM photograph of an interconnector for connecting power generating elements that form a solid oxide fuel cell stack according to the present invention. It is a flowchart figure which shows the manufacturing process of the solid oxide fuel cell stack by this invention. FIG. 3 is a cross-sectional view of a region portion including two adjacent power generation elements formed in each manufacturing process of the solid oxide fuel cell stack according to the present invention. FIG. 3 is a cross-sectional view of a region portion including two adjacent power generation elements formed in each manufacturing process of the solid oxide fuel cell stack according to the present invention.

Definition The solid oxide fuel cell stack according to the present invention is a plurality of power generations in which a fuel electrode, a solid electrolyte and an air electrode are at least sequentially laminated, except that the composition of the interconnector satisfies the requirements described below. In the art, it is usually a solid oxide form comprising at least an element and the interconnector for electrically connecting the air electrode of one of these adjacent power generating elements and the fuel electrode of the other power generating element. Meaning the same as what is classified or understood as a fuel cell stack. The shape of the solid oxide fuel cell stack according to the present invention is not limited, and may be, for example, a cylindrical shape or a hollow plate shape having a plurality of gas passages formed therein.

The solid oxide fuel cell stack according to the present invention includes both so-called vertical stripe solid oxide fuel cells and horizontal stripe solid oxide fuel cells. In the present invention, the vertical stripe type solid oxide fuel cell means a solid oxide fuel cell in which one power generating element is formed on the surface of one support. The support may also serve as the fuel electrode or the air electrode. For example, a solid oxide fuel cell in which a solid electrolyte and an air electrode are sequentially laminated on the surface of a fuel electrode which functions as a support is mentioned. The horizontal stripe type solid oxide fuel cell means a solid oxide fuel cell in which a plurality of power generation elements are formed on the surface of one support.

In the present invention, the solid oxide fuel cell stack means a group of a plurality of power generating elements.

The solid oxide fuel cell system using the solid oxide fuel cell stack of the present invention is not limited to a particular one, and the manufacturing method thereof and other materials constituting the solid oxide fuel cell system are all known ones. Can be used.

Power Generation Element The solid oxide fuel cell stack according to the present invention has a plurality of power generation elements, and the power generation elements are connected in series. The power generation element is a laminated body in which a fuel electrode, a solid electrolyte, and an air electrode are sequentially laminated.

Support The solid oxide fuel cell stack according to the present invention may have a support. In the case of a vertical stripe type solid oxide fuel cell, it may or may not have a support. In the case of a horizontal stripe type solid oxide fuel cell, it has a support. In the case of having a support, a power generation element in which a fuel electrode, a solid electrolyte, and an air electrode are sequentially laminated on the surface of the support is formed. In the case of the horizontal stripe type solid oxide fuel cell, a plurality of power generating elements are formed in series on the surface of the support.

In the present invention, such a support is particularly limited as long as it is porous, has gas permeability, has mechanical strength for supporting the power generation element, and has electrical insulation properties. It can be used without being used. As the material of the support, one or more selected from the group consisting of MgO, calcia-stabilized zirconia (CSZ), and forsterite can be used. The preferred thickness of the support is 0.5-2 mm.

Inner electrode and outer electrode In the present invention, the fuel electrode may be an inner electrode or an outer electrode. That is, the power generation element may be a laminated body in which at least a fuel electrode as an inner electrode, a solid electrolyte, and an air electrode as an outer electrode are laminated. Alternatively, the power generation element may be a laminated body in which at least an air electrode as an inner electrode, a solid electrolyte, and a fuel electrode as an outer electrode are laminated.

According to a preferred aspect of the present invention, the inner electrode is a fuel electrode. The reason is as follows. That is, the support and the current collecting layer have a porous structure with good gas permeability. The support needs to hold the structure of the power generating element. Therefore, the support is thicker than the current collecting layer which is required only to have conductivity. That is, the support tends to have a lower gas permeability than the current collecting layer. Further, comparing the diffusion rates of oxygen gas and hydrogen gas, hydrogen gas is generally several times faster than oxygen gas. From these facts, when the inner electrode is an air electrode, oxygen, which is more difficult to permeate the support than hydrogen, permeates, so that the gas diffusion overvoltage is lower than that when the inner electrode is the fuel electrode. growing. As a result, the power generation performance tends to decrease. Therefore, the power generation performance is better when the inner electrode is the fuel electrode. When the inner electrode is the fuel electrode, the outer electrode is the air electrode.

Fuel Electrode In the present invention, the fuel electrode has porosity for permeating fuel gas, catalytic activity (electrode activity) for adsorbing hydrogen, conductivity, and oxide ion conductivity. The porosity of the fuel electrode may be smaller than that of the support.

Examples of the material forming such a fuel electrode include NiO/zirconium-containing oxides and NiO/cerium-containing oxides, and at least one of them is contained. Here, the NiO/zirconium-containing oxide means a mixture of NiO and zirconium-containing oxide uniformly in a predetermined ratio. Further, the NiO/cerium-containing oxide means a mixture of NiO and cerium-containing oxide uniformly at a predetermined ratio. Examples of the zirconium-containing oxide of the NiO/zirconium-containing oxide include zirconium-containing oxide doped with one or more of CaO, Y ₂ O ₃ , and Sc ₂ O ₃ . The cerium-containing oxide of NiO / cerium-containing oxide represented by the general formula _{Ce 1-y Ln y O 2} ( where, Ln is La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm , Yb, Lu, Sc, and Y, and a combination of at least one of them, such as 0.05≦y≦0.50). Since NiO is reduced to Ni in a fuel atmosphere, the oxides become Ni/zirconium-containing oxide or Ni/cerium-containing oxide, respectively.

In the present invention, the fuel electrode may have a single layer or multiple layers. As an example of the case where the inner electrode is a multi-layer fuel electrode, Ni/YSZ (yttria-stabilized zirconia) is used on the support side and Ni/GDC(Gd ₂ O ₃ -CeO ₂ ) (that is, A fuel electrode catalyst layer) is used. The preferable thickness of the fuel electrode is 10 to 200 μm. The preferable thickness of the fuel electrode catalyst layer is 0 to 30 μm.

Air Electrode In the present invention, the air electrode has porosity for allowing oxygen to permeate, catalytic activity (electrode activity) for adsorbing or ionizing oxygen, electrical conductivity, and oxide ion conductivity. Further, the porosity and conductivity of the air electrode may be smaller than those of the current collecting layer.

As a material forming such an air electrode, for example, La _1-x Sr _x CoO ₃ (where x=0.1 to 0.3) and LaCo _1-x Ni _x O ₃ (where x=0.1) are used. 0.6) lanthanum cobalt oxides such as, LaSrFeO ₃ system and the LaSrCoO ₃ based solid solution in which lanthanum ferrite oxide _{(La 1-m Sr m Co} 1-n Fe n O 3 ( where 0.05 <m<0.50, 0<n<1)) and the like. The air electrode may have a single layer or multiple layers. As an example of the case where the outer electrode is a multi-layered air electrode, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ (that is, the air electrode catalyst layer) is used on the solid electrolyte side, and La _0.6 Sr _0.4 Co _0.8 Fe _0.2 O ₃ (that is, the air electrode) can be used for the surface layer. The preferable thickness of the air electrode is 0.2 to 30 μm.

Solid Electrolyte In the present invention, the solid electrolyte has oxide ion conductivity, gas sealability, and electrical insulation. Examples of the material that constitutes such a solid electrolyte include lanthanum gallate-based oxides and stabilized zirconia in which one or more kinds selected from Y, Ca, and Sc as solid solution species are solid-dissolved. Suitable solid electrolyte in the present invention is a lanthanum gallate-based oxide Sr and Mg-doped, the general formula _La is more preferably _{1-a Sr a Ga 1-} b-c Mg b Co c O 3-δ (However, 0.05≦a≦0.3, 0<b<0.3, 0≦c≦0.15, δ is a value determined so as to satisfy the charge neutral condition) It is a system oxide (LSGM). LSGM expresses oxide ion conductivity by substituting Sr for the La site based on LaGaO ₃ . The solid electrolyte may be a single layer or multiple layers. When the solid electrolyte is a multi-layer, for example, a reaction suppressing layer can be provided between the fuel electrode and the solid electrolyte composed of LSGM. Specific examples of the reaction suppressing layer include ceria (Ce _1-x La _x O ₂ (provided that 0.3<x<0.5)) in which La is solid-dissolved. It is preferably Ce _0.6 La _0.4 O ₂ . The preferred thickness of the solid electrolyte is 5 to 60 μm. The preferable thickness of the reaction suppressing layer is 0 to 20 μm.

Current Collection Layer The solid oxide fuel cell stack according to the present invention has a current collection layer that electrically connects the outer electrode and the interconnector. This current collecting layer has gas (oxygen) permeability and conductivity for smoothly circulating electrons generated from the air electrode. In the present invention, when the outer electrode is an air electrode, the current collecting layer is a conductive paste containing a noble metal such as Ag or Pt, or La _0.6 Sr _0.4 Co _0.8 Fe _0.2 O _{3 −. It} can be formed by baking a paste containing a conductive oxide such as _δ . Further, when the outer electrode is a fuel electrode, the current collecting layer can be formed by baking a metal oxide such as NiO or Ni, or a paste containing a metal, which is reduced to obtain conductivity. Further, the current collecting layer preferably has a structure such as a porous structure or a mesh in order to obtain gas permeability. The preferable thickness of the current collecting layer is 10 to 200 μm.

Interconnector In the present invention, the interconnector means a ceramic interconnector. An interconnector included in a solid oxide fuel cell stack according to the present invention electrically connects an air electrode of one adjacent power generating element among a plurality of power generating elements and a fuel electrode of the other power generating element. Connecting. This interconnector has the following formula (1):
_{Sr a La b Ti 1-c} -d Nb c Fe d O 3-δ (1)
(Where a, b, c and d are 0.1≦a≦0.8, 0.1≦b≦0.8, 0.05≦c≦0.2, and 0.2≦d≦ It is a positive real number that satisfies 0.5.)
It is composed of a perovskite type oxide represented by. Here, “consisting of” means that the main component of the interconnector is a perovskite type oxide represented by the above formula (1). That is, it does not exclude a mode in which the interconnector contains other components, for example, a diffusion element described later. In other words, the interconnector contains the perovskite type oxide represented by the above formula (1) as a main component. The main component means that the interconnector contains 80 mol% or more of the perovskite type oxide represented by the above formula (1). The content is preferably 90 mol% or more, more preferably 95 mol% or more. Even more preferably, the interconnector is composed only of the perovskite type oxide represented by the above formula (1).

In the present invention, in the perovskite type oxide represented by the above formula (1), the Ti site of SLT is substituted with Fe as a conductive carrier. Since Fe does not react with Ni contained in the fuel electrode, its conductivity does not decrease even if Ni is solid-dissolved in SLT substituted with Fe. On the other hand, in the SLT substituted with Fe, there is a tendency that oxygen deficiency occurs due to the substitution of the Ti site with Fe and the oxide ion conductivity is exhibited. However, in the perovskite type oxide represented by the above formula (1) contained in the interconnector of the present invention, pentavalent Nb having a higher valence than tetravalent Ti is contained in the Ti site of SLT substituted with Fe. Further, since it is substituted, the expression of oxide ion conductivity due to oxygen deficiency can be suppressed. That is, the conductivity can be improved by substituting the Ti site of SLT with Fe, and the expression of oxide ion conductivity can be suppressed by substituting the Ti site of SLT substituted with Fe with Nb. This makes it possible to obtain an interconnector having both conductivity and oxide ion insulation.

The composition ratio of Sr and La is within the range of 0.1≦a≦0.8 and 0.1≦b≦0.8, and the oxygen content (3-δ) is 3.00 or less. .. As a result, a dense film having a low porosity can be obtained. In addition, a stable perovskite structure can be maintained, an impurity phase such as La ₂ Ti ₂ O ₇ is not generated, and compactness failure due to sintering inhibition does not occur. More preferably, the interconnector of the present invention is configured such that each composition of Sr and La has an oxygen content of 2.95 or more and 3.00 or less. When the amount of oxygen is 2.95 or more, a stable perovskite structure can be maintained, an impurity phase such as TiO ₂ is not generated, and poor compactness due to sintering inhibition does not occur.

In the present invention, it is preferable that both the solid electrolyte and the interconnector contain strontium. In the present invention, it is more preferable that the amount of strontium contained in the interconnector is larger than the amount of strontium contained in the solid electrolyte. That is, the amount of strontium contained in the solid electrolyte is more preferably smaller than the amount of strontium contained in the interconnector. In the interconnector, the perovskite type oxide represented by the above formula (1) preferably contains 30 mol% or more and 50 mol% or less of strontium in the composition in terms of elements excluding oxygen. The solid electrolyte preferably contains 15 mol% or less of strontium in the composition, more preferably 2.5 mol% or more and 15 mol% or less, in terms of elements excluding oxygen. That is, as described above, the solid electrolyte has a general formula of La _1-a Sr _a Ga _1-b-c Mg _b Co _c O _3-δ (where 0.05≦a≦0.3 and 0<b<0. 0.3, 0≦c≦0.15, δ is a value determined so as to satisfy the charge neutrality condition), and it is preferable to include a lanthanum gallate-based oxide (LSGM).

In the present invention, the composition ratios of Nb and Fe of the perovskite type oxide represented by the formula (1) are 0.05≦c≦0.2 and 0.2≦d≦0.5, and The preferred ranges are 0.1≦c≦0.2 and 0.2≦d≦0.4. The composition ratio of Ti is calculated by 1-cd.

In the present invention, the composition ratio of Fe in the perovskite type oxide represented by the formula (1) is controlled within a specific range. This makes it possible to achieve both good adhesion to the solid electrolyte and good conductivity while controlling element diffusion into the solid electrolyte during firing. Further, by setting the composition ratio of Fe and Nb within a specific range, more excellent adhesion and conductivity with the solid electrolyte are realized.

In the present invention, the interconnector may include, as an unavoidable component, an element diffused from another member, that is, the fuel electrode, the air electrode and the solid electrolyte into the interconnector during firing. Examples of such elements include Ni, Y, Gd, Ce, Zr, La, Sr, Ga, Mg, Co and Fe. The amount of the diffused element varies depending on the constituent material of each member, the crystal structure, the firing temperature, the firing mode (eg, sequential firing or co-firing), and the like.

According to a preferred aspect of the present invention, the interconnector has a composition gradient in the composition range represented by the formula (1) in the thickness direction. This makes it possible to achieve both conductivity and oxide ion insulation.

Whether or not the perovskite oxide is contained in the interconnector can be determined by analyzing the interconnector using an X-ray diffractometer (XRD).

The composition and proportion of the perovskite type oxide contained in the interconnector can be obtained by the following method. An interconnector was cut out from the produced solid oxide fuel cell stack, and a thin film having a thickness of 100 nm to 200 nm was obtained by using a focused ion beam-scanning electron microscope (hereinafter, referred to as FIB-SEM). To process. This is evaluated by a scanning transmission electron microscope-energy dispersive X-ray spectroscopy (Scanning Transmission Electron Microscope-Energy Dispersive X-ray spectroscopy. Hereinafter, referred to as STEM-EDX) to obtain an element mapping. By quantitatively analyzing this elemental mapping using the thin film approximation method, the composition and proportion of the perovskite type oxide contained in the interconnector can be obtained.

According to a preferred embodiment of the present invention, the solid oxide fuel cell stack has an oxidation between the interconnector and the solid electrolyte of one power generating element and/or between the interconnector and the solid electrolyte of the other power generating element. It is preferable to have a physical ion insulating portion, and the oxide ion insulating portion is in contact with the interconnector and the solid electrolyte of one power generating element and/or the solid electrolyte of the other power generating element. Thereby, leakage of oxide ions can be suppressed, and as a result, the power generation output of the power generation element can be improved. This oxide ion insulating part has the formula (2): Sr _x La _y TiO _{3 −δ} (where x and y are 0.8≦x+y≦1.0 and 0.01<y≦0. It is preferably a positive real number that satisfies 1.). This makes it possible to suppress leakage of oxide ions.

According to a preferred aspect of the present invention, the interconnector is formed on the surface of the fuel electrode, has a first interconnector precursor having a specific composition, and is formed on the surface of the first interconnector precursor, It is formed by co-firing a first interconnector precursor and a second interconnector precursor having a specific composition different from that of the first interconnector precursor. Specifically, by firing, the elements contained in each of the first and second interconnector precursors are mutually diffused to form an interconnector. As a result, the interconnector can have a composition gradient in the composition range represented by the above formula (1) in the thickness direction. The composition of each interconnector precursor and the interdiffusion of elements between them will be described later.

The first interconnector precursor first interconnector precursor represented by the following formula _{(1 '): Sr a La} b Ti 1-c-d Nb c Fe d O 3-δ ( in formula, a, b, c And d are positive real numbers satisfying 0.1≦a≦0.8, 0.1≦b≦0.8, 0.1≦c≦0.3, and 0.3≦d≦0.6. It is preferably composed of a perovskite type oxide represented by Here, “consisting of” means that the main component of the first interconnector precursor is a perovskite type oxide represented by the above formula (1′). That is, it does not exclude an aspect in which the first interconnector precursor contains other components, for example, a diffusion element described later. In other words, the first interconnector precursor preferably contains the above formula (1′) as a main component. The main component means that the first interconnector precursor contains 80 mol% or more of the perovskite type oxide represented by the formula (1′). It is preferably 90 mol% or more, and more preferably 95 mol% or more. Even more preferably, the first interconnector precursor consists only of the perovskite type oxide represented by the above formula (1′). The composition ratio of Sr and La is preferably such that the oxygen amount (3-δ) is 3.00 or less. As a result, a dense film having a low porosity can be obtained. In addition, a stable perovskite structure can be maintained, an impurity phase such as La ₂ Ti ₂ O ₇ is not generated, and compactness failure due to sintering inhibition does not occur.

In the present invention, the first interconnector precursor is diffused into the first interconnector precursor from other members such as the fuel electrode, the air electrode, the second interconnector precursor and the solid electrolyte in the manufacturing process. Element may be included as an unavoidable component. Examples of such elements include Ni, Y, Gd, Ce, Zr, La, Sr, Ga, Mg, Co and Fe. The amount of the diffused element changes depending on the constituent material of each member, the crystal structure, the drying temperature, the firing temperature, the firing mode (for example, sequential firing or co-firing), and the like. The mechanism of element diffusion will be described later.

According to a preferred aspect of the present invention, the first interconnector precursor has a composition such that the composition ratio of Sr and La in the formula (1′) is such that the oxygen content is 2.95 or more and 3.00 or less. .. When the amount of oxygen is 2.95 or more, a stable perovskite structure can be maintained, an impurity phase such as TiO ₂ is not generated, and poor compactness due to sintering inhibition does not occur.

According to a preferred embodiment of the present invention, in the first interconnector precursor, in the formula (1′), the composition ratios of Nb and Fe are 0.1≦c≦0.3 and 0.3≦d≦. 0.6, and more preferable ranges are 0.1≦c≦0.25 and 0.3≦d≦0.5. The composition ratio of Ti is calculated by 1-cd.

Second interconnector precursor The second interconnector precursor has the following formula (2): Sr _x La _y TiO _{3 −δ} (where x and y are 0.8≦x+y≦1.0, respectively). And a positive real number satisfying 0.01<y≦0.1.) is preferable. Here, “consisting of” means that the main component of the second interconnector precursor is a perovskite type oxide represented by the above formula (2). It does not exclude an aspect in which the second interconnector precursor contains other components, for example, a diffusion element described below. In other words, it is preferable that the second interconnector precursor contains the above formula (2) as a main component. The main component means that the second interconnector precursor contains 80 mol% or more of the perovskite type oxide represented by the formula (2). The content is preferably 90 mol% or more, more preferably 95 mol% or more. Even more preferably, the second interconnector precursor consists only of the perovskite type oxide represented by the above formula (2). This makes it possible to achieve both sufficient compactness and conductivity. According to a more preferred embodiment of the present invention, it is preferable that the composition ratio of Sr and La satisfy the relationship of 0.8≦x+y≦0.9 and 0.01<y≦0.1. Thereby, the denseness can be further enhanced. Further, Ti may be replaced with Nb. Thereby, the conductivity can be further increased. As a preferable specific example of such an oxide, Sr _x La _y Ti _1-z Nb _z O _3-δ (0.8≦x+y≦1.0, 0.01<y≦0.1, 0.05≦ z≦0.2).

In the present invention, the second interconnector precursor is diffused into the second interconnector precursor from other members, such as the fuel electrode, the air electrode, the first interconnector precursor and the solid electrolyte, in the manufacturing process. Element may be included as an unavoidable component. Examples of such elements include Ni, Y, Gd, Ce, Zr, La, Sr, Ga, Mg, Co, Fe and Nb. The amount of the diffused element changes depending on the constituent material of each member, the crystal structure, the drying temperature, the firing temperature, the firing mode (for example, sequential firing or co-firing), and the like. The mechanism of element diffusion will be described later.

According to a preferred aspect of the present invention, the interconnector and the solid electrolyte are
A first interconnector precursor formed on the surface of the fuel electrode,
A dry coating of the solid electrolyte formed on the surface of the first interconnector precursor;
It is formed by co-firing the first interconnector precursor and the second interconnector precursor formed on the surface of the dry coating of the solid electrolyte. By co-firing, the elements contained in each of the first interconnector precursor, the second interconnector precursor, and the dry coating of the solid electrolyte diffuse into each other. Here, before firing, the first interconnector precursor and the second interconnector precursor are in contact with portions in contact with each other by forming a dry coating film of the solid electrolyte in a portion between them. It is preferable to have a part that does not. That is, the first interconnector precursor and the second interconnector precursor are the dry coating of the solid electrolyte of one power generating element and/or the solid electrolyte of the other power generating element adjacent to a part between them. A dry film is formed. As a result, during co-firing, the element diffuses between the interconnector precursors in the area where they are in contact with each other, and the element does not diffuse between the interconnector precursors in the area where they are not in contact with each other. In the portion where the interconnector precursors are not in contact with each other, each precursor is in contact with the dry film of the solid electrolyte, so that element diffusion occurs between each precursor and the dry film of the solid electrolyte.

In this aspect, the second interconnector precursor represented by the above formula (2) having a large amount of Sr and having high reactivity with the dry film of the solid electrolyte is formed on the surface of the dry film of the solid electrolyte. By doing so, both react with each other according to the mechanism of element diffusion described below during co-firing, and the adhesion between the solid electrolyte and the interconnector can be improved. As a result, the gas sealing property between the solid electrolyte and the interconnector can be improved.

The co-firing temperature is preferably 1250° C. or higher and lower than 1400° C. As a result, the elements contained in each of the first interconnector precursor, the second interconnector precursor, and the dry coating of the solid electrolyte diffuse into each other.

Further, in this aspect, the portion of the second interconnector precursor that is not in contact with the first interconnector precursor is made of the perovskite oxide represented by the above formula (2) even after firing. Is preferred. Here, "consisting of" means that the main component of the portion of the second interconnector precursor which is not in contact with the first interconnector precursor is a perovskite oxide represented by the above formula (2). Means That is, it does not exclude an aspect in which the portion of the second interconnector precursor that is not in contact with the first interconnector precursor contains other components, for example, a diffusion element described below. In other words, the portion of the second interconnector precursor that is not in contact with the first interconnector precursor preferably contains the above formula (2) as a main component. The main component means that the perovskite oxide represented by the above formula (2) is contained in an amount of 80 mol% or more in the portion of the second interconnector precursor that is not in contact with the first interconnector precursor. Means The content is preferably 90 mol% or more, more preferably 95 mol% or more. Even more preferably, the part of the second interconnector precursor that is not in contact with the first interconnector precursor consists only of the perovskite type oxide represented by the above formula (2). As a result, a portion of the second interconnector precursor that is not in contact with the first interconnector precursor is formed as an oxide ion insulating portion. As a result, leakage of oxide ions can be suppressed, and the power generation output of the power generation element can be improved. The oxide ion insulating portion thus formed is formed between the interconnector and the solid electrolyte of one power generating element adjacent to the interconnector and/or between the interconnector and the solid electrolyte of the other power generating element. ..

In the present invention, the mechanism of element diffusion by firing, specifically, the element diffusion between the first and second interconnector precursors, and the mechanism of elemental interdiffusion between each interconnector precursor and the solid electrolyte. Is considered as follows, but the present invention is not limited thereto.

Mechanism of interdiffusion ( interdiffusion mechanism of the first interconnector precursor and the second interconnector precursor)
By burning the first interconnector precursor and the second interconnector precursor in contact with each other, the elements contained in the first interconnector precursor and the second interconnector precursor drive the concentration gradient. As a result, heat is diffused from a higher concentration to a lower concentration. Specifically, Sr diffuses from the second interconnector precursor to the first interconnector precursor, La diffuses from the first interconnector precursor to the second interconnector precursor, and Ti is the first. Diffuses from the second interconnector precursor to the first interconnector precursor. As a result, a solid layer firmly adhered is formed. That is, it is possible to obtain an interconnector excellent in airtightness. Further, it is possible to obtain an interconnector having a composition gradient within the composition range represented by the formula (1) in the thickness direction. Further, Fe and Nb are diffused from the first interconnector precursor to the second interconnector precursor, thereby suppressing a decrease in conductivity of the interconnector due to solid solution of Ni and improving oxide ion insulation. be able to.

(Mutual diffusion mechanism of second interconnector precursor and solid electrolyte)
The second interconnector precursor exhibits conductivity by substituting La for SrTiO ₃ as a base. Further, the solid electrolyte exhibits oxide ion conductivity by substituting Sr based on LaGaO ₃ . When the second interconnector precursor and the solid electrolyte are brought into contact with each other and fired, La contained in the second interconnector precursor diffuses into the solid electrolyte and approaches a stable SrTiO ₃ crystal. Further, Sr contained in the solid electrolyte diffuses into the second interconnector precursor and approaches a stable LaGaO ₃ crystal. Since both SrTiO ₃ and LaGaO ₃ are oxide ion-insulating, in the second interconnector and the solid electrolyte, the part where the second interconnector precursor and the solid electrolyte are in contact with each other is an element by firing. The diffusion makes it oxide-ion insulating.

(Mutual diffusion mechanism of the first interconnector precursor and solid electrolyte)
The first interconnector precursor exhibits conductivity by substituting La for Sr sites and Nb, Fe for Ti sites based on SrTiO ₃ . Further, the solid electrolyte expresses oxide ion conductivity by substituting Sr for the La site based on LaGaO ₃ . When the first interconnector precursor and the solid electrolyte are brought into contact with each other and fired, La contained in the first interconnector precursor diffuses into the solid electrolyte and approaches a stable SrTiO ₃ crystal. Further, Sr contained in the solid electrolyte diffuses into the first interconnector precursor and approaches a stable LaGaO ₃ crystal. Further, Fe and Nb thermally diffuse from the first interconnector precursor to the solid electrolyte by using the concentration gradient as a driving force. Since both SrTiO ₃ and LaGaO ₃ are oxide ion-insulating, in the first interconnector precursor and the solid electrolyte, the portion where the first interconnector precursor and the solid electrolyte are in contact with each other is fired. Oxide ion insulating property is obtained by element diffusion due to.

In the present invention, the lower limit of the electrical conductivity of the interconnector in the atmosphere of 700° C. is preferably 0.05 S/cm or more, more preferably 0.1 S/cm or more. There is no upper limit because the higher the conductivity, the better, but it is preferably 0.16 S/cm or less. This makes it possible to improve the conductivity of the interconnector and improve the power generation performance of the solid oxide fuel cell stack.

In the present invention, the upper limit of the porosity of the interconnector is preferably 1% or less, more preferably 0.1% or less. The lower limit is preferably 0% or more. This makes it possible to secure the gas sealability of the interconnector and improve the power generation efficiency of the solid oxide fuel cell stack. Further, the preferable thickness of the interconnector is 5 to 50 μm.

In the present invention, the porosity can be measured by the following method.
<Method of obtaining from SEM image>
The solid oxide fuel cell stack was cut out so as to include an interconnector, and the interconnector was observed with a scanning electron microscope (for example, S-4100 manufactured by Hitachi, Ltd.) at an acceleration voltage of 15 kV, a secondary electron image, and a magnification of 100 to Observe at 10000 times to obtain a SEM image. The SEM image is evaluated by image processing software (for example, Winroofver 6.5.1, manufactured by MITANI CORPORATION). As a result, a histogram in which the horizontal axis represents the luminance and the vertical axis represents the appearance frequency is obtained. In this histogram, a region whose brightness is lower than the average value of the minimum and maximum brightness is a low brightness region, and a region whose brightness is higher than the average value is a high brightness region. The low-luminance region is determined to be a pore, and the high-luminance region other than the pore is determined to be an interconnector, thereby performing binarization processing. Then, the porosity can be obtained from the following formula.
Porosity (%)=integral value of low brightness region/integral value of overall appearance frequency×100

In the present invention, in order to confirm that the interconnector has a desired porosity obtained by the above method, the porosity obtained by the following method can be used as one index.
<Method to obtain by measuring with Archimedes method>
A raw material powder for an interconnector is uniaxially pressed under a load of 900 kgf/cm ² and fired at 1300° C. for 2 hours in the atmosphere to obtain a test piece. This test piece is measured by the Archimedes method in accordance with JIS R 1634 to obtain the porosity.

In the present invention, the conductivity can be measured by the following method.
<Method of measuring terminal voltage>
A solid oxide fuel cell stack is prepared. The current collection on the fuel electrode side is performed by pasting a current collecting metal on the exposed portion of the fuel electrode of one of the adjacent power generating elements with silver paste and baking it. Current collection on the side of the air electrode including the interconnector is performed by sticking a current collecting metal with silver paste and baking it on the exposed portion of the fuel electrode of the other adjacent power generating element. Current collection on the side of the air electrode that does not include the interconnector is performed by bonding a current collecting metal to the air electrode of the adjacent one of the power generation elements with silver paste and baking it. After that, under the following power generation conditions, by connecting a potential line and a current line to the fuel electrode of one adjacent power generation element and the fuel electrode of the other power generation element, respectively, and connecting the potential line to the air electrode, the voltage between the terminals can be taking measurement.
Fuel gas: (H ₂ +3% H ₂ O) and N ₂ mixed gas (mixing ratio is H ₂ :N ₂ =7:4 (vol:vol))
Fuel utilization rate: 7%
Oxidizing gas: Air Operating temperature: 700°C
Current density: 0.4 A/cm ²
The voltage (V) between terminals connected to the fuel electrode of one power generating element and the fuel electrode of the other power generating element and the voltage between terminals (V') connected to the fuel electrode and air electrode of one power generating element are measured. .. Using these, the conductivity of the interconnector is calculated by the following formula.
Conductivity=Current density×Air electrode area/(V'-V)*(Interconnector film thickness)/(Interconnector area)
The areas of the interconnector and the air electrode are obtained by stripping the interconnector and the air electrode from the solid oxide fuel cell stack after the power generation test and using a caliper or the like.

In the present invention, in order to confirm that the interconnector has a desired conductivity obtained by measuring the voltage between terminals, the conductivity obtained by the following method can be used as an index.

<Method of measuring by 4-terminal method>
A test piece for measuring conductivity is produced by uniaxially pressing a raw material powder of an interconnector under a load of 900 kgf/cm ² and firing it at 1300° C. for 2 hours in an air atmosphere. The electrical conductivity of this test piece is measured at 700° C. in an air atmosphere by a direct current four-terminal method based on JIS R 1650-2.

Structure of Solid Oxide Fuel Cell Stack FIG. 1 is a front view showing a horizontal stripe solid oxide fuel cell stack as one embodiment of the present invention. In the lateral stripe type solid oxide fuel cell stack 210, 13 power generation elements 10 are connected in series to a support 201.

FIG. 2 is a partial cross-sectional view of a vertical stripe type solid oxide fuel cell unit which constitutes a vertical stripe type solid oxide fuel cell stack according to one embodiment of the present invention. The vertical stripe type solid oxide fuel cell unit 16 includes a fuel cell 84 and inner electrode terminals 86 connected to the vertical ends of the fuel cell 84. The fuel cell 84 is a tubular structure extending in the vertical direction, and has an inner electrode layer 90, an outer electrode layer 92, and an inner electrode on the surface of a cylindrical porous support 91 that forms a fuel gas flow passage 88 inside. It comprises a solid electrolyte 94 between the layer 90 and the outer electrode layer 92. In the vertical stripe type solid oxide fuel cell stack, the interconnector and the air electrode are connected by a metal such as Ag or conductive ceramics.

Since the inner electrode terminals 86 attached to the upper end side and the lower end side of the fuel cell 84 have the same structure, the inner electrode terminal 86 attached to the upper end side will be specifically described here. The upper portion 90a of the inner electrode layer 90 includes a solid electrolyte 94, an outer peripheral surface 90b exposed to the outer electrode layer 92, and an upper end surface 90c. The inner electrode terminal 86 is connected to the outer peripheral surface 90b of the inner electrode layer 90 via the conductive sealing material 96, and further, is brought into direct contact with the upper end surface 90c of the inner electrode layer 90 so that the inner electrode layer 90 is It is electrically connected. A fuel gas passage 98 communicating with the fuel gas passage 88 of the inner electrode layer 90 is formed in the center of the inner electrode terminal 86.

FIG. 3 is a perspective view showing a vertical stripe type solid oxide fuel cell stack as one embodiment of the present invention. The vertical stripe solid oxide fuel cell unit 14 includes 16 vertical stripe solid oxide fuel cell units 16, and the lower end side and the upper end side of these vertical stripe solid oxide fuel cell units 16 are respectively It is supported by a ceramic lower support plate 68 and an upper support plate 100. Through holes 68a and 100a through which the inner electrode terminals 86 can pass are formed in the lower support plate 68 and the upper support plate 100, respectively.

A current collector 102 and an external terminal 104 are attached to the vertical stripe type solid oxide fuel cell unit 16. The current collector 102 includes the fuel electrode connecting portion 102a electrically connected to the inner electrode terminal 86 attached to the inner electrode layer 90 serving as a fuel electrode, and the entire outer peripheral surface of the outer electrode layer 92 serving as an air electrode. Is integrally formed with the air electrode connecting portion 102b electrically connected to. The air electrode connecting portion 102b is formed by a vertical portion 102c extending vertically on the surface of the outer electrode layer 92, and a large number of horizontal portions 102d extending horizontally from the vertical portion 102c along the surface of the outer electrode layer 92. Has been done. In addition, the fuel electrode connecting portion 102a linearly extends obliquely upward or obliquely downward from the vertical portion 102c of the air electrode connecting portion 102b toward the inner electrode terminal 86 positioned in the vertical direction of the fuel cell unit 16. It is extended.

The upper end and the lower end of the two vertical striped solid oxide fuel cell unit 16 located at the end of the vertical striped solid oxide fuel cell stack 14 (the left side and the front side in FIG. 3). The external terminals 104 are connected to the inner electrode terminals 86, respectively. These external terminals 104 are connected to the external terminals 104 (not shown) of the vertical stripe solid oxide fuel cell unit 16 at the ends of the adjacent vertical stripe solid oxide fuel cell stacks 14 and are described above. Thus, all of the 16 vertical stripe solid oxide fuel cell units 16 are connected in series.

FIG. 4 is a schematic view showing one embodiment of the horizontal striped solid oxide fuel cell stack 210 according to the present invention, and shows the vicinity of the power generation element 10 in the horizontal striped solid oxide fuel cell stack. FIG. 4 shows a type in which the inner electrode is the fuel electrode. The solid oxide fuel cell stack 210 includes a support 201, a (first/second) fuel electrode 202 (that is, a fuel electrode layer 202a and a fuel electrode catalyst layer 202b), and a (first/second) solid. The electrolyte 203 (that is, the reaction suppressing layer 203a and the solid electrolyte layer 203b), the air electrode 204, the current collecting layer 205, and the interconnector 206 are included. Here, (first/second) is a single layer or two layers, and in the case of two layers, it means having a first layer and a second layer.

FIG. 5 is one preferred embodiment of the solid oxide fuel cell stack according to the present invention. An oxide ion insulating portion 308 is formed between the solid electrolyte 304 of one power generating element and the interconnector 306, and the oxide ion insulating portion 308 contacts the interconnector 306 and the solid electrolyte 304 of one power generating element. doing. Further, the oxide ion insulating portion 308 is formed between the solid electrolyte 304 of the other power generating element and the interconnector 306, and the oxide ion insulating portion 308 is formed by the interconnector 306 and the solid electrolyte 304 of the other power generating element. Is in contact with. Thereby, leakage of oxide ions can be suppressed, and as a result, the power generation output of the power generation element can be improved. Although FIG. 5 shows a mode in which two oxide ion insulating portions are formed, a mode in which only one of them is formed is also included in the scope of the present invention.

Method for Producing Solid Oxide Fuel Cell Stack The method for producing a solid oxide fuel cell stack according to the present invention is not limited to a particular method. The solid oxide fuel cell stack according to the present invention is manufactured, for example, as follows. In the following description, the case where the inner electrode is the fuel electrode and the outer electrode is the air electrode will be described as an example.

The support 301 can be manufactured as follows, for example. First, a solvent (water, alcohol, etc.) is added to the raw material powder to prepare a kneaded clay. At this time, as an optional component, a dispersant, a binder, a defoaming agent or a pore-forming agent, or a combination thereof may be added. A sheet forming method, a press forming method, an extrusion forming method, or the like is used for forming the kneaded material, but when forming a support having a gas flow passage formed therein, it is preferable to use the extrusion forming method. In the case of molding a multi-layered support, a method of molding the upper layer by coating or printing can be used in addition to multi-layer extrusion molding in which the multi-layers are integrally extrusion-molded. Specific examples of the coating method include a slurry coating method for coating a raw material slurry, a tape casting method, a doctor blade method, and a transfer method. Specific examples of the printing method include a screen printing method and an inkjet printing method. Next, the produced kneaded material is shaped and dried to obtain a support precursor. This support precursor is preferably calcined (800° C. or higher and lower than 1100° C.) to obtain a porous support calcined body, and then the support calcined body is calcined alone. The support may be obtained, or the support may be obtained by firing at least with a fuel electrode or the like. The firing temperature is preferably 1100°C or higher and lower than 1400°C.

The interconnector 306 can be manufactured as follows, for example. First, a raw material powder is prepared. The raw material powder can be produced, for example, by a solid phase method. That is, the metal oxide powder as a raw material is weighed so as to have a desired composition ratio, mixed in a solution, and then the solvent is removed to obtain a powder, which is then calcined at, for example, 1150° C. Make a powder. A solvent (water, alcohol, etc.) and, if necessary, a molding aid such as a dispersant and a binder are added to this raw material powder to prepare a slurry or paste. This slurry or paste is coated and dried (80° C. or more and 1100° C. or less, preferably 300° C. or more and 1100° C. or less) to form a dried film, which is then baked (1100° C. or more and less than 1400° C., preferably 1250° C.). The interconnector can be obtained by subjecting the interconnector to a temperature of 1°C or higher and lower than 1400°C. The coating can use the same method as described above. Alternatively, each dry film may be formed as a transfer sheet in advance, and the transfer film may be attached to the layered body.

The fuel electrode 302, the solid electrolyte 304, and the air electrode 307 can be manufactured as follows, for example. A solvent (water, alcohol, etc.) and, if necessary, a molding aid such as a dispersant and a binder are added to each raw material powder to prepare a slurry or paste. This slurry or paste is coated and dried (80° C. or more and 1100° C. or less, preferably 300° C. or more and 1100° C. or less) to form a dried film, which is then baked (1100° C. or more and less than 1400° C., preferably 1250° C.). The temperature of the fuel electrode 302, the solid electrolyte 304, and the air electrode 307 can be obtained by performing the heating at a temperature of not less than 1°C and less than 1400°C). The coating can use the same method as described above. Alternatively, each dry film may be formed as a transfer sheet in advance, and the transfer film may be attached to the layered body.

According to a preferred embodiment of the production method of the present invention, the firing is preferably performed each time each layer is formed. That is, according to this aspect, after the dry coating of the fuel electrode 302 is formed on the surface of the support 301 or the calcined body thereof, the step of firing to form the fuel electrode 302 and the dry coating of the interconnector 306 are formed. After that, a step of firing to form the interconnector 306, a step of forming a dry coating of the solid electrolyte 304, a step of firing to form the solid electrolyte 304, and a step of forming a dry coating of the air electrode 307 and then firing to air At least forming a pole 307. The current collecting layer is formed after the air electrode 307 is formed.

According to a preferred aspect of the manufacturing method of the present invention, the interconnector 306 forms the first interconnector precursor 303 and the second interconnector precursor 305, and then co-fires them (1250° C. or more and less than 1400° C.). To be formed.

The first interconnector precursor 303 and the second interconnector precursor 305 can be produced, for example, as follows. First, a raw material powder is prepared. The raw material powder can be produced, for example, by a solid phase method. That is, the raw material metal oxide powder is weighed so as to have a desired composition ratio, mixed in a solution and then the solvent is removed, and the obtained powder is fired at, for example, 1150° C. Make a powder. A solvent (water, alcohol, etc.) and, if necessary, a molding aid such as a dispersant and a binder are added to this raw material powder to prepare a slurry or paste. Each of the interconnector precursors can be formed by coating this slurry or paste and drying (80°C or more and 1100°C or less, preferably 300°C or more and 1100°C or less). The coating can use the same method as described above. Alternatively, each dry film may be formed as a transfer sheet in advance, and the transfer film may be attached to the layered body.

According to a preferred aspect of the production method of the present invention, the interconnector 306 and the solid electrolyte 304 are formed after forming a dry coating film of the first interconnector precursor 303, the second interconnector precursor 305, and the solid electrolyte 304. Is co-fired (1250° C. or higher and lower than 1400° C.). Specifically, the interconnector 306 and the solid electrolyte 304 form a first interconnector precursor 303, and a step of forming a dry coating film of the solid electrolyte 304 on the surface of the first interconnector precursor 303. A step of forming the second interconnector precursor 305 on the surface of the dry coating of the first interconnector precursor and the solid electrolyte 304, and the dry coating of the first interconnector precursor 303 and the solid electrolyte 304 and the second And the interconnector precursor 305 are co-fired (1250° C. or higher but lower than 1400° C.) to form the interconnector 306 and the solid electrolyte 304. By adopting such a manufacturing method, the elements contained in the interconnector precursor and the elements contained in the solid electrolyte mutually diffuse during co-firing. That is, when the element contained in the interconnector precursor and the element contained in the solid electrolyte are the same, they diffuse each other. Examples of such elements include strontium and lanthanum. Thereby, the adhesion between the interconnector and the solid electrolyte can be improved.

According to a preferred embodiment of the manufacturing method of the present invention, the step of producing the support 301 (step 1), the step of forming a dry coating of the fuel electrode 302 (step 2), the dry coating of the first interconnector precursor 303. (Step 3), a step of forming a dry film of the solid electrolyte 304 (step 4), a step of forming a dry film of the second interconnector precursor 305 (step 5), then the support 301, the fuel A step (step 6) of co-firing (1250° C. or more and less than 1400° C.) a laminated body composed of the dried film of the electrode 302, the first interconnector precursor 303, the solid electrolyte 304 and the second interconnector precursor 305, and then It comprises a step of forming a dry film of the air electrode 307 (step 7) and a step of baking the whole (1100° C. or higher and lower than 1400° C., preferably 1250° C. or higher and lower than 1400° C.) (step 8). FIG. 7 shows a flowchart of this manufacturing process. Further, an example of each step is shown in FIGS.

In the above aspect of the manufacturing method according to the present invention, the support 301 or the calcined body thereof is dried on the fuel electrode 302, the first interconnector precursor 303, the solid electrolyte 304, and the second interconnector precursor 305. After forming the coating film, co-firing is performed in which a laminated body composed of these is fired at once. In this embodiment, the firing is preferably performed in an oxidizing atmosphere so that the solid electrolyte 304 and the first and second interconnector precursors (303 and 305) are not modified by the diffusion of the dopant. More preferably, a mixed gas of air and oxygen is used, and firing is performed in an atmosphere having an oxygen concentration of 20% by mass or more and 30% by mass or less.

In the above aspect of the manufacturing method according to the present invention, at least the first interconnector precursor 303, the dry coating of the solid electrolyte 304, and the second interconnector precursor 305 are co-fired (1250°C or higher and lower than 1400°C). Preferably.

In the present invention, in the laminated body, the second interconnector precursor 305 made of SLT having a large amount of Sr and having high reactivity with LSGM is formed on the surface of the dry film of the solid electrolyte 304 (for example, LSGM). Therefore, due to element diffusion occurring between the second interconnector precursor 305 and the dry coating of the solid electrolyte 304 due to firing, they react with each other to improve the adhesion, and as a result, the solid electrolyte 304 It is possible to improve the gas sealability between the connector and the interconnector 306.

According to another aspect of the manufacturing method of the present invention, the firing forms a dry coating of the first interconnector precursor 303, the solid electrolyte 304, and a dry coating of each member other than the second interconnector precursor 305. It is preferable to carry out each time. That is, according to this aspect, after forming the dry film of the fuel electrode 302 on the surface of the dry film of the support 301 or the calcined body thereof, firing (1100° C. or more and less than 1400° C., preferably 1250° C. or more and less than 1400° C. ) To form the fuel electrode 302, and after forming a laminated compact including the first interconnector precursor 303, the dry coating of the solid electrolyte 304, and the second interconnector precursor 305, co-firing (preferably Is 1250° C. or higher and lower than 1400° C.) to form a laminated fired body, and a dry coating film of the air electrode 307 is formed and fired together with the laminated fired body (1100° C. or higher but lower than 1400° C., preferably 1250° C. or higher 1400° C. (Below °C) to form an air electrode. The current collecting layer is formed after the air electrode 307 is formed.

The present invention will be specifically described based on the following examples and comparative examples, but the present invention is not limited to these specific examples.

Example 1
(Preparation of Kneaded Material A for Support)
A high-purity forsterite (Mg ₂ SiO ₄ containing 0.05% by mass CaO) raw material powder was adjusted to have an average particle diameter of 0.7 μm. 100 parts by weight of this powder, 20 parts by weight of solvent (water), 8 parts by weight of binder (methyl cellulose), 0.5 parts by weight of lubricant, and 15 parts by weight of pore former (acrylic resin particles having an average particle diameter of 5 μm). Was mixed with a high-speed mixer, then kneaded with a kneader (kneader), and deaerated with a vacuum kneader to prepare a kneaded material for extrusion molding. Here, the average particle size is a value measured by the standard of JIS R1629 and shown as a 50% size (the same applies hereinafter).

(Preparation of fuel electrode slurry)
NiO powder and 10YSZ (10 mol% Y ₂ O ₃ -90 mol% ZrO ₂ ) powder were wet mixed at a weight ratio of 65:35 to obtain a dry powder. The average particle size of the obtained dry powder was adjusted to 0.7 μm. 150 parts by weight of this powder, 100 parts by weight of solvent (carbitol), 6 parts by weight of binder (soluble polymer), 2 parts by weight of dispersant (nonionic surfactant), and defoaming agent (organic polymer) 2 After mixing with 1 part by weight, the mixture was sufficiently stirred to prepare a slurry.

(Preparation of slurry for fuel electrode catalyst layer)
After producing a mixture of NiO powder and _{GDC10 (10mol% GdO 1.5 -90mol%} CeO 2) powder in coprecipitation, followed by heat treatment to obtain a powder for the fuel electrode catalyst layer. The mixing ratio of the NiO powder and the GDC10 powder was 50/50 by weight. The average particle diameter of the obtained powder for fuel electrode catalyst layer was adjusted to be 0.5 μm. 100 parts by weight of this powder, 100 parts by weight of solvent (carbitol), 5 parts by weight of binder (soluble polymer), 2 parts by weight of dispersant (nonionic surfactant), and defoaming agent (organic polymer) 2 After mixing with 1 part by weight, the mixture was sufficiently stirred to prepare a slurry.

(Preparation of slurry for reaction suppression layer)
As the material of the reaction inhibition layer was used powder 50 parts by weight of the cerium complex oxide _{LDC40 (40mol% LaO 1.5 -60mol%} CeO 2). This material powder is mixed with 0.04 part by weight of Ga ₂ O ₃ powder as a sintering aid, and further 100 parts by weight of solvent (carbitol), 4 parts by weight of binder (soluble polymer), dispersant (nonionic interface). 1 part by weight of an activator and 1 part by weight of an antifoaming agent (organic polymer type) were mixed and sufficiently stirred to prepare a slurry.

(Preparation of slurry for solid electrolyte)
As a material for the solid electrolyte, LSGM powder having a composition of La _0.9 Sr _0.1 Ga _0.8 Mg _0.2 O ₃ was used. 50 parts by weight of this LSGM powder, 100 parts by weight of solvent (carbitol), 4 parts by weight of binder (soluble polymer), 1 part by weight of dispersant (nonionic surfactant), and defoaming agent (organic polymer type) After mixing with 1 part by weight, the mixture was sufficiently stirred to prepare a slurry.

(Preparation of slurry for air electrode)
As the material of the air electrode, a powder having a composition of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ was used. 40 parts by weight of this powder, 100 parts by weight of a solvent (carbitol), 2 parts by weight of a binder (soluble polymer), 1 part by weight of a dispersant (nonionic surfactant), and 1 defoaming agent (organic polymer) After mixing with 1 part by weight, the mixture was thoroughly stirred to prepare a slurry.

(Preparation of raw material powder for first interconnector precursor)
The production of the raw material powder for the first interconnector precursor was performed by the solid phase method. Strontium, lanthanum, titanium, niobium, and iron have the composition ratio of the perovskite-type oxide represented by Sr _0.37 La _0.52 Ti _0.50 Nb _0.10 Fe _0.40 O _3-δ , The raw material metal oxide powder was weighed, mixed in a solution, and then the solvent was removed to obtain a powder, which was fired at 1050° C. and pulverized to obtain a first raw material powder for an interconnector precursor. It was made.

(Preparation of slurry for first interconnector precursor)
As a material for the first interconnector precursor, a raw material powder for the first interconnector precursor having a composition of Sr _0.37 La _0.52 Ti _0.50 Nb _0.10 Fe _0.40 O _3-δ is used. I was there. 40 parts by weight of this powder, 100 parts by weight of solvent (carbitol), 4 parts by weight of binder (soluble polymer), 1 part by weight of dispersant (nonionic surfactant), and 1 part by weight of defoaming agent (organic polymer). After mixing with 1 part, agitated thoroughly to prepare a slurry.

(Preparation of raw material powder for second interconnector precursor)
The production of the raw material powder for the second interconnector precursor was performed by the solid phase method. The powder of the metal oxide as the raw material was weighed and mixed in the solution so that the composition ratio of the perovskite type oxide represented by Sr _0.90 La _0.04 TiO _3-δ of strontium, lanthanum and titanium was obtained. After that, the solvent was removed and the obtained powder was fired at 1050° C. and pulverized to prepare a second raw material powder for an interconnector precursor.

(Preparation of slurry for second interconnector precursor)
As a material for the second interconnector precursor, a raw material powder for a second interconnector precursor having a composition of Sr _0.90 La _0.04 TiO _3−δ was used. 40 parts by weight of this powder, 100 parts by weight of solvent (carbitol), 4 parts by weight of binder (soluble polymer), 1 part by weight of dispersant (nonionic surfactant), and defoaming agent (organic polymer) 1 After mixing with 1 part by weight, the mixture was thoroughly stirred to prepare a slurry.

(Preparation of solid oxide fuel cell stack)
Using the kneaded clay and each slurry obtained as described above, a solid oxide fuel cell stack was manufactured by the following method.

A cylindrical molded body was produced from the porous kneaded material A for a support by an extrusion molding method. After drying at room temperature, it was heat-treated at 1100° C. for 2 hours to prepare a calcined body of the support. On this support surface, a fuel electrode, a fuel electrode catalyst layer, a first interconnector precursor, a reaction suppressing layer, a solid electrolyte, and a second interconnector precursor were formed in this order by a slurry coating method, and dried. A laminated molded body having a dry film laminated thereon was obtained. This laminated compact was co-fired at 1300° C. for 2 hours. It is believed that during this firing, interdiffusion of elements occurs between the first and second interconnector precursors and between each interconnector precursor and the solid electrolyte.

Next, an air electrode was formed on the surface of the solid electrolyte and fired at 1100° C. for 2 hours to prepare a solid oxide fuel cell stack. The support had an outer diameter of 10 mm and a wall thickness of 1 mm after co-firing. The produced solid oxide fuel cell stack had a fuel electrode thickness of 100 μm, a fuel electrode catalyst layer thickness of 10 μm, a reaction suppression layer thickness of 10 μm, and a solid electrolyte thickness of 30 μm. The thickness of the interconnector was 15 μm, and the thickness of the air electrode was 20 μm. Further, the outer diameter of the support was measured with a micrometer at a portion where no film was formed. The thickness of each member was obtained by cutting the produced solid oxide fuel cell stack and observing the cross section three times with a scanning electron microscope (SEM) at an arbitrary magnification of 30 to 2000 times. Of these, the maximum and minimum values are added and divided by two. The cutting location was the central portion of the portion where the air electrode was formed. FIG. 6 is an SEM image showing a laminated structure in which a fuel electrode, an interconnector and an air electrode are formed in this order from the bottom. In the figure, the upper side of the dotted line is the portion derived from the second interconnector precursor, and the lower side of the dotted line is the portion derived from the first interconnector precursor. The following evaluations were performed on the obtained solid oxide fuel cell stack. The results are shown in Table 1.

Examples 2-13
A solid oxide fuel cell stack was obtained in the same manner as in Example 1 except that the composition of the first interconnector precursor and the second interconnector precursor were changed to those shown in Table 1. .. The following evaluations were performed on the obtained solid oxide fuel cell stack. The results are shown in Table 1.

Comparative Example 1
The same procedure as in Example 1 was performed except that the first interconnector precursor was not provided and the composition of the second interconnector precursor was Sr _0.55 La _0.30 TiO _{3 -δ,} and solid oxidation was performed. A solid fuel cell stack was obtained. The following evaluations were performed on the obtained solid oxide fuel cell stack. The results are shown in Table 1.

Comparative example 2
A solid oxide fuel was prepared in the same manner as in Example 1, except that the composition of the first interconnector precursor was Sr _0.40 La _0.55 Ti _0.50 Fe _0.50 O _3-δ. A battery cell stack was obtained. The following evaluations were performed on the obtained solid oxide fuel cell stack. The results are shown in Table 1.

Evaluation (Analysis of composition and ratio of perovskite type oxide contained in interconnector)
The composition of the interconnector was specified by the following method. An interconnector was cut out from the produced solid oxide fuel cell stack and processed into a thin film of 100 nm to 200 nm by FIB-SEM. Elemental mapping was obtained by evaluating this thin film by STEM-EDX. By quantitatively analyzing this elemental mapping using the thin film approximation method, the composition ratio and the ratio of the perovskite type oxide contained in the interconnector were specified. The results are shown in Table 1. The main component of the composition of the interconnector was the same as that of the raw material powder.

(Measurement of OCV)
A power generation test was performed using the obtained solid oxide fuel cell stack. The current collection on the fuel electrode side was carried out by sticking a current collecting metal on the exposed part of the fuel electrode with silver paste and baking it. The current collection on the air electrode side was carried out by pasting a current collecting metal on the exposed part of the adjacent fuel electrode with a silver paste.

A power generation test was performed under the following power generation conditions, and an electromotive force after operating for 0 hour; OCV (V) was measured. The results are shown in Table 1.
Fuel gas: (H ₂ +3% H ₂ O) and N ₂ mixed gas (mixing ratio is H ₂ :N ₂ =7:4 (vol:vol))
Oxidizing gas: Air Operating temperature: 700℃

(Measurement of marginal fuel utilization rate)
Under the conditions of the above-mentioned power generation test, a power generation test was conducted by energizing the device at a current density of 0.4 A/cm ² . After that, the supply amount of the fuel gas was gradually reduced, the hydrogen supply amount immediately before the potential suddenly dropped was measured, and the limit fuel utilization rate was calculated from the following equation. The results are shown in Table 1.
Marginal fuel utilization rate = (amount of hydrogen used for power generation) / (amount of hydrogen supply just before the potential suddenly drops) x 100
The amount of hydrogen used for power generation is the amount of current (C/s)×60 (s)×22.4 (L/mol)÷Faraday constant (C/mol)×1/2 (valence)×power generation It is calculated by the number of elements.

(Measurement of terminal voltage)
Under the following power generation conditions, the voltage between the terminals was measured by connecting a potential line and a current line to the fuel electrode of one adjacent power generating element and the fuel electrode of the other adjacent power generating element. The results are shown in Table 1.
Fuel gas: (H ₂ +3% H ₂ O) and N ₂ mixed gas (mixing ratio is H ₂ :N ₂ =7:4 (vol:vol))
Fuel utilization rate: 7%
Oxidizing gas: Air Operating temperature: 700°C
Current density: 0.4 A/cm ²

10: power generation element, 210: solid oxide fuel cell stack, 301: support, 302: fuel electrode, 303: first interconnector precursor, 304: solid electrolyte, 305: second interconnector precursor , 306: interconnector, 307: air electrode, 308: oxide ion insulation part

Claims (12)

A plurality of power generation elements in which a fuel electrode, a solid electrolyte and an air electrode are laminated at least sequentially,
At least an interconnector electrically connecting the air electrode of one adjacent power generating element of the plurality of power generating elements and the fuel electrode of the other power generating element, and the plurality of power generating elements are connected in series. A solid oxide fuel cell stack comprising:
The interconnector has the following formula (1):
_{Sr a La b Ti 1-c} -d Nb c Fe d O 3-δ (1)
(Where a, b, c and d are 0.1≦a≦0.8, 0.1≦b≦0.8, 0.05≦c≦0.2, and 0.2≦d≦ Ri positive real number der satisfying 0.5, the 3-[delta], Ru value der not exceed 3.)
A solid oxide fuel cell stack comprising a perovskite oxide represented by The solid oxide fuel cell stack according to claim 1, wherein the interconnector has a composition gradient in the composition range represented by the formula (1) in the thickness direction. Between the interconnector and the solid electrolyte of one power generating element and/or between the interconnector and the solid electrolyte of the other power generating element, there is an oxide ion insulating portion, and the oxide ion insulating portion is The solid oxide fuel cell stack according to claim 1 or 2, which is in contact with the interconnector and the solid electrolyte of the one power generation element and/or the solid electrolyte of the other power generation element. The oxide ion insulation part is Sr _x La _y TiO _{3 −δ} formula (2)
(In the formula, x and y are positive real numbers that satisfy 0.8≦x+y≦1.0 and 0.01<y≦0.1.)
The solid oxide fuel cell stack according to claim 3, which comprises: The solid oxide fuel cell stack according to claim 1, wherein the solid electrolyte is a lanthanum gallate-based oxide doped with Sr and Mg. The interconnector is
Formed on the surface of the fuel electrode, the following formula (1′):
_{Sr a La b Ti 1-c} -d Nb c Fe d O 3-δ formula (1 ')
(Where a, b, c and d are 0.1≦a≦0.8, 0.1≦b≦0.8, 0.1≦c≦0.3, and 0.3≦d≦ Ri positive real number der satisfying 0.6, the 3-[delta], Ru value der not exceed 3.)
A first interconnector precursor consisting of
It is formed on the surface of the first interconnector precursor and has the following formula (2):
Sr _x La _y TiO _3-δ formula (2)
(Wherein, x and y, 0.8 ≦ x + y ≦ 1.0 , and 0.01 <Ri positive real number der satisfying y ≦ 0.1, the 3-[delta], the value der not exceeding 3 )
The solid oxide fuel cell stack according to any one of claims 1 to 5, which is formed by co-firing with a second interconnector precursor consisting of. The interconnector and the solid electrolyte are
The first interconnector precursor formed on the surface of the fuel electrode,
A dry coating of a solid electrolyte formed on the surface of the first interconnector precursor;
It is formed by co-firing the first interconnector precursor and the second interconnector precursor formed on the surface of the dry coating of the solid electrolyte,
The first interconnector precursor and the second interconnector precursor have a portion of a space between the first and second interconnector precursors, which is a dry coating of the solid electrolyte of the one power generating element and/or a dry solid electrolyte of the other power generating element. The solid oxide fuel cell stack according to claim 6 , which has a portion in contact with each other and a portion not in contact with each other by forming the coating film. The solid oxide form according to claim 6 or 7, wherein the portion of the second interconnector precursor that is not in contact with the first interconnector precursor is of the formula (2) even after firing. Fuel cell stack. A plurality of power generation elements in which a fuel electrode, a solid electrolyte and an air electrode are laminated at least sequentially,
At least an interconnector electrically connecting the air electrode of one adjacent power generating element of the plurality of power generating elements and the fuel electrode of the other power generating element, and the plurality of power generating elements are connected in series. A method of manufacturing a solid oxide fuel cell stack, comprising:
Forming the fuel electrode,
Forming the interconnector,
Forming the solid electrolyte,
At least comprising the step of forming the air electrode,
The interconnector is
Formula (1) below:
_{Sr a La b Ti 1-c} -d Nb c Fe d O 3-δ (1)
(Where a, b, c and d are 0.1≦a≦0.8, 0.1≦b≦0.8, 0.05≦c≦0.2, and 0.2≦d≦ Ri positive real number der satisfying 0.5, the 3-[delta], Ru value der not exceed 3.)
A method for producing a solid oxide fuel cell stack, comprising a perovskite oxide represented by On the surface of the fuel electrode, the following formula (1′):
_{Sr a La b Ti 1-c} -d Nb c Fe d O 3-δ formula (1 ')
(Where a, b, c and d are 0.1≦a≦0.8, 0.1≦b≦0.8, 0.1≦c≦0.3, and 0.3≦d≦ Ri positive real number der satisfying 0.6, the 3-[delta], Ru value der not exceed 3.)
A step of forming a first interconnector precursor consisting of
On the surface of the first interconnector precursor, the following formula (2):
Sr _x La _y TiO _3-δ formula (2)
(Wherein, x and y, 0.8 ≦ x + y ≦ 1.0 , and 0.01 <Ri positive real number der satisfying y ≦ 0.1, the 3-[delta], the value der not exceeding 3 )
Forming a second interconnector precursor consisting of
The solid oxide fuel cell stack according to claim 9, comprising a step of co-firing the first interconnector precursor and the second interconnector precursor to form the interconnector. Manufacturing method. Forming a dry coating of the solid electrolyte on the surface of the first interconnector precursor,
Forming the second interconnector precursor on the surface of the dry coating of the first interconnector precursor and the solid electrolyte;
11. The step of co-firing the first interconnector precursor, the dry coating of the solid electrolyte, and the second interconnector precursor to form the interconnector and the solid electrolyte. The method for producing a solid oxide fuel cell stack according to item 4. The first interconnector precursor and the second interconnector precursor are a dry coating of the solid electrolyte of one power generating element and/or a solid electrolyte of the other power generating element adjacent to a part between them. The method for producing a solid oxide fuel cell stack according to claim 11, comprising a portion that is in contact with each other and a portion that is not in contact with each other when the coating film is formed.