JP6654764B2 - 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 excellent conductivity and gas sealing properties.

  Fuel cells, unlike heat engines that go through the process of thermal energy or kinetic energy, react a fuel such as natural gas or hydrogen with oxygen in the air through a solid electrolyte to continuously convert the fuel from the chemical energy of the fuel. It is an energy converter that obtains electrical energy directly. Among them, the solid oxide fuel cell is a fuel cell that uses a solid oxide (ceramic) as a solid electrolyte and operates as a battery having a fuel electrode as a negative electrode and an air electrode as a positive electrode. Also, solid oxide fuel cells are known to have the advantage that high energy conversion efficiency can be obtained.

  The solid oxide fuel cell has a small output per unit cell, and therefore, generates electric power by increasing the output by connecting a plurality of unit cells in series. A member that electrically connects adjacent cells is called an interconnector. As the material, an interconnector using ceramic (hereinafter, also referred to as a ceramic interconnector) is known. As characteristics of the ceramic interconnector, gas sealability that does not allow gas to permeate, conductivity, oxide ion insulation, and adhesion to a solid electrolyte are required.

  In general, a ceramic interconnector cannot have sufficient conductivity unless the thickness is small (for example, about 100 μm or less). However, when the thickness of the ceramic interconnector is reduced to obtain sufficient conductivity, and such a thin ceramic interconnector is to be formed on the surface of a porous electrode (a fuel electrode or an air electrode), a porous interconnector is required. There is a possibility that the ceramic interconnector may be taken into an undesired electrode. As a result, there is a possibility that the ceramic interconnector cannot be formed, or even if the ceramic interconnector can be formed, the gas interconnectability may not be sufficiently obtained because it is thin.

  If 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 mixes with air, which is not preferable. In order to enhance the gas sealing property of the ceramic interconnect, it is necessary to increase the density of the ceramic interconnect, and it is required to sinter the ceramic interconnect densely. Further, when the conductivity of the ceramic interconnector is low, the resistance of the ceramic interconnector increases, and the output of the fuel cell decreases. Furthermore, if 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 is reduced. In addition, when the adhesion between the solid electrolyte and the ceramic interconnector is low, a gap such as a crack is generated between the solid electrolyte and the ceramic interconnector, and fuel gas leaks from this gap.

As the material of the ceramic interconnector, lanthanum chromite (LaCrO ₃₎ system interconnector is widely used. It is known that this LaCrO ₃ type interconnector generally has high conductivity but is difficult to be sintered. Further, since chromium (Cr) is contained, so-called Cr poisoning may occur.

Further, as a material for the ceramic interconnector, an SLT-based interconnector represented by SrLaTiO3 _-δ is widely used. The SLT system interconnector, compared with LaCrO ₃ system interconnector, although low conductivity, sinterability is known to be good. The SLT-based interconnector replaces, for example, Sr sites in the crystal lattice of SrTiO ₃ , which is an insulator, with lanthanum (La) to obtain SrLaTiO _{3 -δ} (SLT), so that SrLaTiO _{3 -δ} (SLT) The conductivity is exhibited by partially changing Ti ⁴⁺ of the Ti site in the crystal lattice to Ti ³⁺ . Here, δ is a value determined so as to satisfy the charge neutral condition.

Japanese Patent Application Laid-Open No. 2008-270203 (Patent Document 1) aims to provide an SLT-based ceramic interconnector that simultaneously improves conductivity and improves adhesion to a solid electrolyte while maintaining good airtightness. I have. In order to achieve this object, the ceramic interconnector is divided into an airtight part formed on the fuel electrode side and a conductive part formed on the air electrode side and having higher conductivity than the airtight part. It describes that it has a two-layer structure. According to this document, the material of the airtight emphasis moiety with _{Sr 1-3x / 2 La x Ti 1} + y O 3-δ, the material of the conductive focus moiety Using _{Sr 1-3z / 2} La z TiO ₃ Have been. In a portion where airtightness is emphasized, excessive Sr is not preferable because it hinders sintering, and when La is too large or too small, the conductivity of the ceramic interconnector is reduced, so that 0.15 ≦ x ≦ 0.4. Further, Ti is set to satisfy 0.2 ≦ y ≦ 0.4 from the viewpoint of improving the adhesion and the conductivity of the ceramic interconnector. In the portion where the conductivity is important, the substitution ratio of La to Sr is important for improving the conductivity, and 0.2 ≦ z ≦ 0.4.

Further, Japanese Patent 2013-030270 (Patent Document _2), containing the _{Sr x Ln y TiO 3-δ} , Ni, Fe, and at least one transition metal selected from Co and Cu, at least two layers A ceramic interconnector having a structure is disclosed. According to this document, the two-layer structure has a porous layer (first layer) formed on the fuel electrode side with a relative density of less than 95% and a dense layer formed on the air electrode side with a relative density of 95% or more. It is a layer (second layer), and it is described that high conductivity is obtained by the porous layer and good gas sealing property is obtained by the dense layer.

  However, the interconnector described in Patent Literature 1 has a two-layer structure including a portion that emphasizes airtightness and a portion that emphasizes conductivity, and the functions of each layer are separated, and the airtightness provided on the fuel electrode side is provided. It is difficult to achieve both excellent airtightness and conductivity depending on the important part. Further, the first layer provided on the fuel electrode side of the interconnect described in Patent Document 2 has a conductivity obtained by being porous, and does not have a conductivity obtained by denseness. .

JP 2008-270203 A JP 2013-030270 A

  The present inventors have recently provided a dense and conductive intermediate layer between the fuel electrode and the interconnector, separately from the interconnector, so that the interconnector can be attached to the fuel electrode when the interconnector is formed. It has been found that incorporation can be suppressed and the interconnector can be formed as a thin layer. Further, it has been found that since the intermediate layer has conductivity, the conductivity of the interconnector is not impaired, and good conductivity can be obtained. Further, the inventors have found that the gas sealing property of the interconnector can be complemented by the intermediate layer, and good gas sealing property can be obtained. And it was found that such a two-layer structure of the intermediate layer and the interconnector can achieve both excellent conductivity and gas sealing properties as a solid oxide fuel cell stack. The present invention is based on the above findings.

  Accordingly, an object of the present invention is to provide a solid oxide fuel cell stack having an intermediate layer and an interconnector having excellent conductivity, gas sealing properties, and adhesion to a solid electrolyte.

And, the solid oxide fuel cell stack according to the present invention,
Fuel electrodes, solid electrolyte and a plurality of power generating elements formed by laminating the air electrode at least sequentially,
At least an interconnector for electrically connecting an air electrode of one of the plurality of power generation elements and a fuel electrode of the other power generation element, wherein the plurality of power generation elements are connected in series A solid oxide fuel cell stack comprising:
An intermediate layer having a porosity of 1% or less and a conductivity of 700 S / cm or more in an air atmosphere at 700 ° C. is formed between the interconnector and the fuel electrode of the other adjacent power generating element. It is characterized by becoming.

1 is a front view of a horizontal-striped solid oxide fuel cell stack according to the present invention. 1 is a partial cross-sectional view of a vertical stripe type solid oxide fuel cell unit constituting a vertical stripe type solid oxide fuel cell stack according to the present invention. 1 is a perspective view illustrating a vertical stripe type solid oxide fuel cell stack according to the present invention. FIG. 2 is a schematic cross-sectional view of one embodiment in the vicinity of an adjacent power generating element constituting a solid oxide fuel cell stack according to the present invention. It is a schematic diagram which shows another aspect near the adjacent power generation element which comprises the solid oxide fuel cell stack by this invention. It is a schematic diagram which shows another aspect near the adjacent power generation element which comprises the solid oxide fuel cell stack by this invention. It is a schematic diagram which shows another aspect near the adjacent power generation element which comprises the solid oxide fuel cell stack by this invention. It is a schematic diagram which shows another aspect near the adjacent power generation element which comprises the solid oxide fuel cell stack by this invention. It is a schematic diagram which shows another aspect near the adjacent power generation element which comprises the solid oxide fuel cell stack by this invention. It is a schematic diagram which shows another aspect of the electric power generation element which comprises the solid oxide fuel cell stack by this invention.

Definition The solid oxide fuel cell stack according to the present invention has an intermediate layer provided between the interconnector and the fuel electrode separately from the interconnector, and the intermediate layer satisfies the requirements described below. Other than the above, the fuel electrode, the solid electrolyte and the air electrode are laminated at least in order, and a plurality of power generating elements, and the air electrode of one adjacent power generating element and the fuel electrode of the other power generating element are electrically connected to each other. It means the same thing that is usually classified or understood in the art as a solid oxide fuel cell stack, comprising at least the interconnector to be connected. 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 flow paths formed therein.

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

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

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

Support The solid oxide fuel cell stack according to the present invention may have a support. When the fuel cell is 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 generating element in which a fuel electrode, a solid electrolyte, and an air electrode are sequentially stacked on the surface of the support is formed. In the case of a horizontal stripe type solid oxide fuel cell, a plurality of power generation 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 generating element, and has electrical insulation. Not used. As the material of the support, at least one 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 generating element may be a laminate in which at least the fuel electrode as the inner electrode, the solid electrolyte, and the air electrode as the outer electrode are laminated. Alternatively, the power generating element may be a laminate in which an air electrode as an inner electrode, a solid electrolyte, and a fuel electrode as an outer electrode are at least laminated.

  According to a preferred embodiment 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 adopt a porous structure having 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 that requires only conductivity. That is, the support tends to have lower gas permeability than the current collecting layer. When 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 that is harder to permeate than the hydrogen passes through the support, so that the gas diffusion overvoltage is lower than when the inner electrode is a fuel electrode. growing. As a result, power generation performance tends to decrease. Therefore, when the inner electrode is the fuel electrode, the power generation performance is better. When the inner electrode is a fuel electrode, the outer electrode is an air electrode.

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

Examples of a material forming such a fuel electrode include NiO / zirconium-containing oxide, NiO / cerium-containing oxide, and the like, and include at least any of these. Here, NiO / zirconium-containing oxide means that NiO and zirconium-containing oxide are uniformly mixed at a predetermined ratio. In addition, the NiO / cerium-containing oxide means that NiO and the cerium-containing oxide are uniformly mixed at a predetermined ratio. Examples of the zirconium-containing oxide of NiO / zirconium-containing oxide include a zirconium-containing oxide doped with at least one 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 is a combination of at least one of 0.05 ≦ y ≦ 0.50). Since NiO is reduced to Ni in a fuel atmosphere, the oxides become Ni / zirconium-containing oxides or Ni / cerium-containing oxides, respectively.

In the present invention, the fuel electrode may be a single layer or a multilayer. As an example 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 ) (ie, (A fuel electrode catalyst layer). The preferred thickness of the fuel electrode is 10 to 200 μm. The preferred thickness of the fuel electrode catalyst layer is 0 to 30 μm.

Intermediate Layer The solid oxide fuel cell stack according to the present invention has an intermediate layer formed between the interconnector and the fuel electrode of the other adjacent power generating element. This intermediate layer has a porosity of 1% or less, a conductivity in an air atmosphere at 700 ° C. of 0.05 S / cm or more, and is dense and conductive. By providing a dense intermediate layer between the fuel electrode and the interconnector separately from the interconnector, it is possible to prevent the interconnector from being taken into the fuel electrode when the interconnector is formed. The connector can be formed as a thin layer. Further, since the intermediate layer has conductivity, good conductivity can be obtained without impairing the conductivity of the interconnector. Furthermore, the gas sealing property of the interconnector can be complemented by the denseness of the intermediate layer, and good gas sealing property can be obtained. As a result, due to the two-layer structure of the intermediate layer and the interconnector, it is possible to achieve both excellent conductivity and gas sealing properties as a solid oxide fuel cell stack.

(Porosity)
In the present invention, the porosity of the intermediate layer is 1% or less. A preferred upper limit is 0.5% or less, and more preferably 0.4% or less. Further, a preferable lower limit is 0% or more. Thereby, the conductivity and the gas sealing property of the interconnector can be complemented. The porosity is measured using the following method.

<Method to obtain from SEM image>
The manufactured solid oxide fuel cell stack is cut out to include an intermediate layer, and the intermediate layer is subjected to an acceleration voltage of 15 kV, a secondary electron image, a magnification of 100 to 100, using a scanning electron microscope (for example, S-4100 manufactured by Hitachi, Ltd.). Observe at 10000x and obtain SEM image. This SEM image is evaluated by image processing software (for example, Winroofver 6.5.1, manufactured by MITANNI CORPORATION). As a result, a histogram in which the horizontal axis is luminance and the vertical axis is appearance frequency is obtained. In this histogram, an area whose luminance is lower than the average of the minimum and maximum values of the luminance is a low luminance area, and an area whose luminance is higher than the average is a high luminance area. The low-luminance area is determined to be a pore, and the high-luminance area other than the pore is determined to be an intermediate layer, thereby performing a binarization process. Thereafter, the porosity can be obtained from the following equation.
Porosity (%) = Integral value of low-luminance area / Integral value of overall appearance frequency × 100

  In the present invention, in order to confirm that the intermediate layer has a desired porosity obtained by the above method, the porosity obtained by the following method can be used as one index.

<Method obtained by Archimedes method>
A test piece is obtained by uniaxially pressing the raw material powder of the intermediate layer under a load of 900 kgf / cm ² and firing at 1300 ° C. for 2 hours in an air atmosphere. The test piece is measured by the Archimedes method based on the provisions of JIS R 1634 to obtain a porosity.

(Conductivity)
In the present invention, the conductivity of the intermediate layer at 700 ° C. in the atmosphere is 0.05 S / cm or more, and preferably 0.1 S / cm or more. Thereby, the conductivity of the interconnector can be complemented. There is no upper limit because the higher the conductivity, the better, but it is preferably 0.16 S / cm or less, more preferably 0.15 S / cm or less. The conductivity can be measured by the following method. That is, a test piece for measuring the conductivity is prepared by uniaxially pressing the raw material powder of the intermediate layer under a load of 900 kgf / cm ² and firing at 1300 ° C. for 2 hours in the air atmosphere. The conductivity of this test piece is measured at 700 ° C. in an air atmosphere by a direct current four-terminal method based on the provisions of JIS R 1650-2.

(Crystal stability)
In the present invention, the crystal structure of the intermediate layer does not change under the atmosphere at 700 ° C. and under the reducing atmosphere at 700 ° C. That is, the intermediate layer has crystal stability. Thereby, the intermediate layer does not deteriorate during the operation of the solid oxide fuel cell stack, and the gas sealing property of the interconnector can be complemented. Evaluation of crystal stability can be performed using the following method.

A test piece is obtained by uniaxially pressing the raw material powder of the intermediate layer under a load of 900 kgf / cm ² and firing at 1300 ° C. for 2 hours in an air atmosphere. After the test piece was heat treated for 10 hours at temperature of 700 ℃ in air atmosphere, ground to a BET1m ² / g~3m ² / g in a mortar. The diffraction intensity of the obtained pulverized product at 2θ = 20 ° to 90 ° is measured by a powder X-ray diffractometer (XRD). Then, after heat-treating this ground material at 700 ° C. in a hydrogen atmosphere for 10 hours, the obtained ground material is measured for diffraction intensity at 2θ = 20 ° to 90 ° by a powder X-ray diffractometer by the same measuring method. . By comparing the obtained diffraction intensities and confirming that there is no change in the crystal structure, it is confirmed that the crystal is stable.

(composition)
In the present invention, the intermediate layer is represented by the general formula _{Sr a La b Ti 1-c} -d A c B d O 3-δ ( However, a, b, c and d are 0.1 ≦ a ≦ 0.8, Is a positive real number satisfying 0.1 ≦ b ≦ 0.8, 0.1 ≦ c ≦ 0.3, and 0.3 ≦ d ≦ 0.6, and A is 1 selected from Nb, V, and Ta , And B is at least one element selected from Fe and Co.). Here, "consisting of", means that the main component of the intermediate layer is a perovskite oxide represented by the general formula _{Sr a La b Ti 1-c} -d A c B d O 3-δ I do. The embodiment in which the intermediate layer contains other components, for example, a diffusion element described later is not excluded. In other words, it is preferred that the intermediate layer are those which comprise a perovskite oxide represented by the general formula _{Sr a La b Ti 1-c} -d A c B d O 3-δ as a main component. The main component means that in the intermediate layer, the formula _{Sr a La b Ti 1-c} -d A c perovskite oxide represented by B d _{O 3-δ} is contained more than 80 mol% . It is preferably contained in an amount of 90 mol% or more, more preferably 95 mol% or more. Still more preferably, the intermediate layer is composed of only the perovskite oxide represented by the above general formula. The composition ratio of Sr and La is preferably in a range of 0.1 ≦ a ≦ 0.8 and 0.1 ≦ b ≦ 0.8, and a composition in which the oxygen amount (3-δ) is 3.00 or less is preferable. Thus, 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 poor denseness due to sintering inhibition does not occur.

  Whether or not the intermediate layer contains a perovskite oxide can be determined by analyzing the intermediate layer using an X-ray diffractometer (XRD).

  The composition and ratio of the perovskite oxide contained in the intermediate layer can be specified by the following method. An intermediate layer is cut out from the manufactured solid oxide fuel cell stack, and a thin film having a thickness of 100 nm to 200 nm is obtained by using a focused ion beam-scanning electron microscope (hereinafter, referred to as FIB-SEM). Process into This is evaluated by scanning transmission electron microscopy-energy dispersive X-ray spectrum (hereinafter, referred to as STEM-EDX) to obtain element mapping. The composition and ratio of the perovskite-type oxide contained in the intermediate layer can be obtained by quantitatively analyzing the element mapping using the thin film approximation method.

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

According to a preferred embodiment of the present invention, in the perovskite-type oxide represented by the general formula, the composition ratio of Sr and La 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 denseness due to inhibition of sintering does not occur.

  In the perovskite oxide represented by the above general formula, the oxygen amount (3-δ) is equal to the sum of the valence of the cation of each element and the sum of the valence of the oxide ion which is a divalent anion. The amount of oxygen at the time. In the present invention, the valence of each element is calculated assuming that Sr is divalent, La and Fe are trivalent, Ti and Co are tetravalent, and Nb, V and Ta are pentavalent.

  According to a preferred embodiment of the present invention, in the perovskite-type oxide represented by the general formula, the respective composition ratios of the element A and the element B are 0.1 ≦ c ≦ 0.3, 0.3 ≦ d ≦ 0 .6. The composition ratio of Ti is determined by 1-cd.

  According to a preferred aspect of the present invention, in the perovskite-type oxide represented by the general formula, each composition ratio of Sr and La is 0.2 ≦ a ≦ 0.5, 0.4 ≦ b ≦ 0.7. It is. More preferably, 0.29 ≦ a ≦ 0.4 and 0.5 ≦ b ≦ 0.6. This makes it possible to form an intermediate layer having a low porosity and a high conductivity.

  According to a preferred aspect of the present invention, in the perovskite-type oxide represented by the general formula, the respective composition ratios of the element A and the element B are 0.1 ≦ c ≦ 0.25, 0.3 ≦ d ≦ 0 .5.

  According to a more preferred aspect of the present invention, in the perovskite oxide represented by the general formula, the element A is Nb, and the element B is Fe. In this embodiment, in the intermediate layer, the Ti site of the SLT as a conductive carrier is replaced with Fe. Therefore, conductivity is improved. On the other hand, in the SLT substituted with Fe, oxygen deficiency tends to occur due to the substitution of the Ti site with Fe, and oxide ion conductivity tends to appear. However, in the intermediate layer constituting the present invention, since the Ti site of the SLT substituted with Fe is further substituted with pentavalent Nb having a higher valence than tetravalent Ti, oxide ion conduction due to oxygen deficiency is caused. Sex can be suppressed. In other words, the conductivity is improved by replacing the Ti site of the SLT with Fe, and the occurrence of the oxide ion conductivity is suppressed by replacing the Ti site of the SLT substituted with Fe with Nb. It is possible to obtain an intermediate layer capable of satisfying both the properties and the oxide ion insulating property.

  In the above aspect, the composition ratio of Fe in the intermediate layer is controlled to a specific range. That is, the composition ratio of Fe preferably satisfies the above-mentioned range of d. Thereby, while controlling element diffusion from the intermediate layer to the solid electrolyte at the time of firing, good adhesion between the intermediate layer and the solid electrolyte and good conductivity are both achieved. Further, it is preferable that the composition ratio of Fe and Nb be in a specific range. That is, it is preferable that the above ranges of c and d are satisfied. Thereby, more excellent adhesion and conductivity between the intermediate layer and the solid electrolyte are realized.

(Thickness)
According to a preferred embodiment of the present invention, the thickness of the intermediate layer is larger than the thickness of the interconnector. Thereby, it is possible to prevent the interconnector from being taken into the fuel electrode when the interconnector is formed. Specifically, the thickness of the intermediate layer is preferably 10 μm or more and 100 μm or less. When the thickness is 10 μm or more, gas sealing properties can be obtained, and when it is 100 μm or less, conductivity can be obtained. A more preferable thickness is 15 μm or more and 50 μm or less. The thickness of the intermediate layer can be determined by the following method. First, the manufactured solid oxide fuel cell stack is cut so as to include the intermediate layer. Then, this section is observed three times with a scanning electron microscope (SEM) at an arbitrary magnification of 30 to 2000 times, and the thickness is obtained by adding the maximum value and the minimum value of the obtained values and dividing by two. Can be.

Interconnector (composition)
In the present invention, the interconnector is made of ceramic. That is, in the present invention, the interconnector means a ceramic interconnector. Interconnector general formula _{Sr x La y TiO 3-δ} ( here, x and y are positive real number satisfying 0.8 ≦ x + y ≦ 1.0, and 0.01 <y ≦ 0.1. ) Is preferably made of a perovskite oxide. Here, "consisting of" is meant to be a perovskite oxide main component of the interconnector is represented by the general formula _{Sr x La y TiO 3-δ} . That is, this does not exclude an aspect in which the interconnector includes another component, for example, a diffusion element described later. In other words, it is preferred interconnector are those which comprise a perovskite oxide represented by the general formula Sr x _La y TiO _3-δ as a main component. The main component in the interconnector, perovskite oxide represented by the general formula _Sr x _La y TiO _3-δ means that it contains more than 80 mol%. It is preferably contained in an amount of 90 mol% or more, more preferably 95 mol% or more. Even more preferably, the interconnector is made of only the perovskite oxide represented by the above general formula. When the main component of the interconnector is an oxide having such a composition ratio, sufficient denseness and conductivity can be achieved at the same time. The interconnector exhibits conductivity by replacing La with SrTiO ₃ as a base. According to a more preferred aspect of the present invention, the composition ratio of Sr and La preferably satisfies the relationship of 0.8 ≦ x + y ≦ 0.9 and 0.01 <y ≦ 0.1. Thereby, denseness can be further improved. Further, Ti may be replaced with Nb. Thereby, the conductivity can be further increased. Preferred examples of such _{oxides, 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 interconnector may include, as an unavoidable component, an element diffused into the interconnector from another member, for example, a fuel electrode, an air electrode, a solid electrolyte, an intermediate layer, or the like during firing. Such elements include Ni, Y, Gd, Ce, Zr, La, Sr, Ga, Mg, Co and the like. The amount of the element to be diffused varies depending on the constituent material of each member, the crystal structure, the firing temperature, the mode of firing (for example, sequential firing or co-firing), and the like.

  Whether or not a perovskite oxide is contained in the interconnector can be determined in the same manner as in the intermediate layer.

  The composition and ratio of the perovskite oxide contained in the interconnector can be obtained by the same method as that for the intermediate layer.

  In the present invention, the interconnector preferably does not contain Fe. Thereby, expression of oxide ion conductivity can be suppressed. When the intermediate layer contains Fe, it is difficult to completely suppress oxide ion conductivity. Therefore, when the intermediate layer is used as an interconnector, oxide ion conductivity cannot be completely suppressed, and there is a possibility that oxide ion leakage may occur. This undesirably reduces the output of the fuel cell. Therefore, in the present invention, the interconnector and the intermediate layer are provided as separate layers.

(Thickness)
In the present invention, the thickness of the interconnector is preferably smaller than the thickness of the intermediate layer. Specifically, the thickness is preferably 5 μm or more and 15 μm or less.

(conductivity)
In the present invention, the electrical conductivity of the interconnector is preferably 0.01 S / cm or more, more preferably 0.02 S / cm or more at 700 ° C. in an air atmosphere. There is no upper limit because the higher the conductivity, the better, but it is preferably 0.1 S / cm or less, more preferably 0.04 S / cm or less. The conductivity can be measured by the same method as the method for measuring the conductivity of the intermediate layer.

(Porosity)
In the present invention, the porosity of the interconnector is preferably 0.8% or more, and more preferably 1% or more. The upper limit is preferably at most 2.4%, more preferably at most 1.7%. The porosity can be measured using the method obtained from the above-mentioned SEM image.

In the present invention, the intermediate layer and the interconnector are integrally configured to electrically connect 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. Is what you do. Therefore, in the present invention, an integral structure of the intermediate layer and the interconnector is defined as a conductive portion.

  In the present invention, the conductivity of the conductive portion is preferably 0.03 S / cm or more, and more preferably 0.05 S / cm or more. There is no upper limit since the higher the conductivity, the better, but it is preferably 0.15 S / cm or less, more preferably 0.13 S / cm or less. As a result, it is possible to suppress a decrease in output in the conductive portion and exhibit high power generation performance as a solid oxide fuel cell stack.

The conductivity of the conductive portion can be determined by the following method. Under the evaluation conditions described below, a potential line and a current line are connected to the fuel electrode of one of the power generating elements adjacent to the interconnector, and a potential difference between the interconnector and the fuel electrode terminal of the adjacent one of the power generating elements while flowing current. Measure A. Thereafter, a through hole is provided to penetrate the interconnector and the intermediate layer and reach the fuel electrode of one of the adjacent power generating elements, and the potential line and the current line are connected to the fuel electrode below the through hole via the Ag paste. . A potential line and a current line are also connected to the fuel electrode of the other adjacent power generating element. The potential difference B between the terminals of the fuel electrode of the other adjacent power generating element below the interconnector through-hole and the fuel electrode of the adjacent other power generating element is measured while flowing a current. Using the measured potential difference, the conductivity is determined from the following equation.
Conductivity = current ÷ (potential difference A−potential difference B) × (film thickness of interconnect + film thickness of intermediate layer) ÷ conductive area of interconnect The conductive area of the interconnect is sandwiched between the air electrode and the intermediate layer. This is the area of the interconnector, which can be determined using, for example, a caliper.
(Evaluation conditions)
Fuel gas: mixed gas of (H ₂ + 3% H ₂ O) and N ₂ (mixing ratio is H ₂ : N ₂ = 7: 4 (vol: vol))
Oxidizing gas: air Operating temperature: 700 ° C
Current: 1A

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, conductivity, and oxide ion conductivity. The porosity and conductivity of the air electrode may be smaller than those of the current collecting layer.

As a material constituting 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 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)). The cathode may be a single layer or multiple layers. As an example where the outer electrode is a multi-layer air electrode, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ (that is, an air electrode catalyst layer) is used on the solid electrolyte side. La _0.6 Sr _0.4 Co _0.8 Fe _0.2 O ₃ (that is, an 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 sealing properties, and electrical insulation properties. Examples of a material constituting such a solid electrolyte include a lanthanum gallate-based oxide, and stabilized zirconia in which at least one selected from Y, Ca, and Sc is dissolved as a solid solution. 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 (Where 0.05 ≦ a ≦ 0.3, 0 <b <0.3, 0 ≦ c ≦ 0.15, and δ are values determined so as to satisfy the charge neutrality condition) Based oxide (LSGM). LSGM expresses oxide ion conductivity by replacing La site with Sr based on LaGaO ₃ . The solid electrolyte may be a single layer or a multilayer. When the solid electrolyte is a multilayer, for example, a reaction suppression layer can be provided between the fuel electrode and the solid electrolyte composed of LSGM. Specific examples of the reaction inhibiting layer, ceria is solid-solved _{La (Ce 1-x La x} O 2 ( where, 0.3 <x <0.5)) and the like. Preferably, it is Ce _0.6 La _0.4 O ₂ . The preferred thickness of the solid electrolyte is 5 to 60 μm. The preferred thickness of the reaction suppression layer is 0 to 20 μm.

In the present invention, it is preferable that both the solid electrolyte and the intermediate layer contain strontium. According to a preferred embodiment of the present invention, the amount of strontium contained in the solid electrolyte is smaller than the amount of strontium contained in the intermediate layer. Specifically, the solid electrolyte preferably contains strontium in a composition of 15 mol% or less, more preferably 2.5 mol% or more and 15 mol% or less in terms of an element excluding oxygen. That is, the solid electrolyte mentioned above general formula _{La 1-a Sr a Ga 1} -b-c Mg b Co c O 3-δ ( where, 0.05 ≦ a ≦ 0.3,0 <b <0.3, 0 ≦ c ≦ 0.15, δ is a value determined so as to satisfy the charge neutrality condition.) It is preferable to include a lanthanum gallate-based oxide (LSGM).

Current Collection Layer The solid oxide fuel cell stack according to the present invention has a current collection layer for electrically connecting the outer electrode and the interconnector. The current collecting layer has gas (oxygen) permeability and conductivity for smoothly flowing electrons generated from the air electrode. In the present invention, when the outer electrode is an air electrode current collector layer and a conductive paste containing the noble metal such as Ag or _{Pt, 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 . In the case where 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 is preferably a porous or mesh-like structure in order to obtain gas permeability. The preferred thickness of the current collecting layer is 10 to 200 μm.

Structure of Solid Oxide Fuel Cell Stack FIG. 1 is a front view showing a horizontal stripe type solid oxide fuel cell stack as one embodiment of the present invention. In the horizontal stripe type solid oxide fuel cell stack 210, 13 power generating 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 constituting a vertical stripe type solid oxide fuel cell stack according to one embodiment of the present invention. The vertical striped solid oxide fuel cell unit 16 includes a fuel cell 84 and inner electrode terminals 86 connected to the upper and lower ends of the fuel cell 84, respectively. The fuel cell 84 is a tubular structure extending in the up-down direction. An inner electrode layer 90, an outer electrode layer 92, and an inner electrode layer 92 are formed on a cylindrical porous support 91 forming a fuel gas flow path 88 therein. And 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 and the lower end of the fuel cell 84 have the same structure, the inner electrode terminal 86 attached to the upper end will be specifically described here. The upper portion 90a of the inner electrode layer 90 includes an outer peripheral surface 90b and an upper end surface 90c exposed to the solid electrolyte 94 and the outer electrode layer 92. The inner electrode terminal 86 is connected to the outer peripheral surface 90b of the inner electrode layer 90 via a conductive sealing material 96. Further, the inner electrode terminal 86 comes into direct contact with the upper end surface 90c of the inner electrode layer 90, and It is electrically connected. At the center of the inner electrode terminal 86, a fuel gas flow path 98 communicating with the fuel gas flow path 88 of the inner electrode layer 90 is formed.

  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-type solid oxide fuel cell stack 14 includes 16 vertical stripe-type solid oxide fuel cell units 16, and the lower end and the upper end of these vertical stripe-type solid oxide fuel cell units 16 are respectively It is supported by a ceramic lower support plate 68 and an upper support plate 100. The lower support plate 68 and the upper support plate 100 have through holes 68a and 100a, respectively, through which the inner electrode terminals 86 can pass.

  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 a fuel electrode connecting portion 102a electrically connected to the inner electrode terminal 86 attached to the inner electrode layer 90 serving as the fuel electrode, and the entire outer peripheral surface of the outer electrode layer 92 serving as the air electrode. And the air electrode connecting portion 102b that is electrically connected thereto. 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 number of horizontal portions 102d extending horizontally from the vertical portion 102c along the surface of the outer electrode layer 92. Have been. In addition, the fuel electrode connecting portion 102a extends linearly obliquely upward or obliquely downward from the vertical portion 102c of the air electrode connecting portion 102b toward the inner electrode terminal 86 located in the vertical direction of the fuel cell unit 16. Extending.

  The upper and lower ends of the two vertical stripe-shaped solid oxide fuel cell units 16 located at the ends of the vertical stripe-shaped solid oxide fuel cell stack 14 (in FIG. 3, at the far left and front sides at the left end). 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 type solid oxide fuel cell unit 16 at the end of the adjacent vertical stripe type solid oxide fuel cell stack 14, and are described above. Thus, all of the sixteen vertical stripe type solid oxide fuel cell units 16 are connected in series.

  FIG. 4 is a schematic view showing one embodiment of the solid oxide fuel cell stack according to the present invention, and shows the vicinity of an adjacent power generating element in the horizontal stripe type solid oxide fuel cell stack. On the surface of the support 201, a fuel electrode 202, a solid electrolyte 204, and an air electrode 206 are sequentially laminated. The air electrode 206 of one adjacent power generation element and the fuel electrode 202 of the other power generation element are electrically connected by an interconnector 205. An intermediate layer 203 is provided between the fuel electrode 202 and the interconnector 205.

  FIG. 5 is a schematic view showing one embodiment of the solid oxide fuel cell stack according to the present invention, and shows the vicinity of one of the power generating elements adjacent to each other in the horizontal stripe type solid oxide fuel cell stack. 5, the intermediate layer 203 covers the side surface of the fuel electrode 202 as compared to FIG.

  FIG. 6 is a schematic diagram showing one embodiment of the solid oxide fuel cell stack according to the present invention, and shows the vicinity of one of the adjacent power generating elements in the horizontal stripe type solid oxide fuel cell stack. 6, a solid electrolyte 204 is provided between the intermediate layer 203 and the interconnector 205 in FIG.

  FIG. 7 is a schematic diagram showing one embodiment of the solid oxide fuel cell stack according to the present invention, and shows the vicinity of one of the power generating elements adjacent to each other in the horizontal stripe type solid oxide fuel cell stack. 7, a solid electrolyte 204 is provided between the intermediate layer 203 and the interconnector 205 as compared to FIG. The solid electrolyte 204 is in contact with a part of the surface of the fuel electrode 202.

  Since the solid electrolyte 204 is dense, by providing the solid electrolyte 204 between the intermediate layer 203 and the interconnector 205, the gas sealing property can be further improved.

  FIG. 8 is a schematic view showing one embodiment of the solid oxide fuel cell stack according to the present invention, and shows the vicinity of one of the power generating elements adjacent to each other in the horizontal stripe type solid oxide fuel cell stack. 8, an intermediate layer 203 covers the side surface of the fuel electrode 202 and a solid electrolyte 204 is provided between the intermediate layer 203 and the interconnector 205 in FIG.

  FIG. 9 is a schematic diagram showing one embodiment of the solid oxide fuel cell stack according to the present invention, and shows the vicinity of one of the power generating elements adjacent to each other in the horizontal stripe type solid oxide fuel cell stack. 9, both the intermediate layer 203 and the solid electrolyte 204 are provided between the fuel electrode 202 and the interconnector 205 in FIG.

  FIG. 10 is a schematic diagram showing one embodiment of the solid oxide fuel cell stack according to the present invention, and shows the vicinity of one of the power generating elements adjacent to each other in the vertical stripe type solid oxide fuel cell stack. In FIG. 10, a solid electrolyte 204 and an air electrode 206 are sequentially laminated on the surface of a fuel electrode 202 also serving as a support. An intermediate layer 203 is provided between the fuel electrode 202 and the interconnector 205.

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

  The support can be produced, for example, as follows. First, a solvent (water, alcohol, etc.) is added to the raw material powder to produce a clay. At this time, a dispersant, a binder, an antifoaming agent, a pore-forming agent, a combination thereof, or the like may be added as an optional component. For forming the kneaded material, a sheet forming method, a press forming method, an extrusion forming method, or the like is used. When a support having a gas flow path formed therein is formed, it is preferable to use the extrusion forming method. In the case of forming a multi-layered support, a method of forming the upper layer by coating or printing may be used in addition to the multilayer extrusion molding in which the multi-layer is integrally extruded. Specific examples of the coating method include a slurry coating method of 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 clay is formed and dried to obtain a support precursor. This support precursor is then preferably calcined (800 ° C. or more and less than 1100 ° C.) to obtain a calcined body of a porous support, and then calcined the calcined body of the support alone. A 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 from 1100 ° C to less than 1400 ° C.

  The intermediate layer and the interconnector can be manufactured, for example, as follows. First, each raw material powder is prepared. The production of the raw material powder can be performed, for example, by a solid phase method. That is, the powder of the metal oxide as a raw material is weighed so as to have a desired composition ratio, mixed in a solution, and then the solvent is removed. Make powder. A solvent (water, alcohol, etc.) and, if necessary, a molding aid such as a dispersant and a binder are added to the 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), and then dried (1100 ° C. or more and less than 1400 ° C., preferably 1250 ° C.). C. or higher and lower than 1400 ° C.) to obtain an intermediate layer and an interconnector. For the coating, the same method as described above can be used. Alternatively, each dried film may be formed in advance as a transfer sheet, and the transfer film may be provided by attaching the transfer film to a laminate.

  The fuel electrode, solid electrolyte and air electrode can be produced, for example, as follows. 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. to 1100 ° C., preferably 300 ° C. to 1100 ° C.) to form a dried film, which is then fired (1100 ° C. to less than 1400 ° C., preferably 1250 ° C.). By performing the above operation, the fuel electrode, the solid electrolyte and the air electrode can be obtained. For the coating, the same method as described above can be used. Alternatively, each dried film may be formed in advance as a transfer sheet, and the transfer film may be provided by attaching the transfer film to a laminate.

  According to a preferred embodiment of the production method of the present invention, it is preferable to perform the firing each time each layer is formed. That is, according to this aspect, after forming a dried film of the fuel electrode on the surface of the support or the calcined body thereof, baking to form the fuel electrode, and forming and baking a dried film of the solid electrolyte. A step of forming a solid electrolyte, a step of forming a dry film of the intermediate layer and baking to form an intermediate layer, a step of forming a dry film of the interconnector and then firing to form an interconnector, Forming a dried film and then firing to form an air electrode. The current collecting layer is formed after the formation of the air electrode.

  According to another preferred embodiment of the production method of the present invention, a support or a calcined body thereof is produced, a dry film of the fuel electrode is formed on the surface of the support or the calcined body thereof, and a dry film of the intermediate layer is formed. Forming a dried film of the solid electrolyte, co-firing (1250 ° C. or more and less than 1400 ° C.) the laminated molded body composed of the support, the fuel electrode, the intermediate layer and the dried film of the solid electrolyte, and then drying the interconnector And baking the interconnector (1100 ° C. or more and less than 1400 ° C., preferably 1250 ° C. or more and less than 1400 ° C.) to form a dry film of the air electrode, and baking the whole.

  In the above-described embodiment of the production method according to the present invention, the co-firing is carried out in such a manner that after forming the dried film of the fuel electrode, the intermediate layer and the solid electrolyte on the support or the calcined body thereof, the laminated molded body composed of these is fired at once. It is carried out. In this embodiment, baking is preferably performed in an oxidizing atmosphere so that the solid electrolyte and the intermediate layer are not denatured by diffusion of the dopant. More preferably, baking is performed in an atmosphere in which a mixed gas of air and oxygen has an oxygen concentration of 20% by mass or more and 30% by mass or less.

  In the above embodiment of the production method according to the present invention, it is preferable that at least the intermediate layer and the solid electrolyte are obtained by co-firing. At the time of firing, the elements contained in the intermediate layer and the elements contained in the solid electrolyte diffuse into each other. That is, when the element contained in the intermediate layer and the element contained in the solid electrolyte are the same, they diffuse into each other. Such elements include strontium and lanthanum. Thereby, the adhesion between the intermediate layer and the solid electrolyte can be improved.

  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 Clay A for Support)
High-purity forsterite (Mg ₂ SiO ₄ raw material containing 0.05% by mass of CaO) powder was adjusted to have an average particle size of 0.7 μm. 100 parts by weight of this powder, 20 parts by weight of a solvent (water), 8 parts by weight of a binder (methyl cellulose), 0.5 parts by weight of a lubricant, and 15 parts by weight of a pore-forming agent (acrylic resin particles having an average particle diameter of 5 μm) After mixing with a high-speed mixer, the mixture was kneaded with a kneader (kneader), deaerated with a vacuum kneading device, and a kneaded material for extrusion molding was prepared. Here, the average particle diameter is a value measured in accordance with JIS R1629 and indicated as a 50% diameter (the same applies hereinafter).

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

(Preparation of slurry for anode catalyst layer)
After a mixture of NiO powder and GDC10 (10 mol% GdO _1.5 -90 mol% CeO ₂ ) powder was prepared by a coprecipitation method, heat treatment was performed to obtain a powder for a fuel electrode catalyst layer. The mixing ratio between the NiO powder and the GDC10 powder was 50/50 by weight. The average particle diameter of the obtained fuel electrode catalyst layer powder was adjusted to be 0.5 μm. 100 parts by weight of this powder, 100 parts by weight of a solvent (carbitol), 5 parts by weight of a binder (soluble polymer), 2 parts by weight of a dispersant (nonionic surfactant), and 2 parts of an antifoaming agent (organic polymer) After that, the slurry was prepared by sufficiently stirring the mixture.

(Preparation of slurry for reaction suppression layer)
50 parts by weight of a powder of cerium-based composite oxide LDC40 (40 mol% LaO _1.5 -60 mol% CeO ₂ ) was used as a material for the reaction suppression layer. To this material powder, 0.04 parts by weight of Ga ₂ O ₃ powder as a sintering aid was mixed, and further 100 parts by weight of a solvent (carbitol), 4 parts by weight of a binder (soluble polymer), and a dispersant (nonionic interface). After mixing 1 part by weight of an activator) and 1 part by weight of an antifoaming agent (organic polymer), the mixture was sufficiently stirred to prepare a slurry.

(Preparation of slurry for solid electrolyte)
LSGM powder having a composition of La _0.9 Sr _0.1 Ga _0.8 Mg _0.2 O ₃ was used as a material for the solid electrolyte. 50 parts by weight of the LSGM powder were mixed with 100 parts by weight of a solvent (carbitol), 4 parts by weight of a binder (soluble polymer), 1 part by weight of a dispersant (nonionic surfactant), and an antifoaming agent (organic polymer). 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 _was used a powder having the composition of _{La 0.6 Sr 0.4 Co 0.2 Fe 0.8} O 3. 40 parts by weight of this powder were mixed with 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 part by weight of an antifoaming agent (organic polymer). After mixing with parts by weight, the mixture was sufficiently stirred to prepare a slurry.

(Preparation of raw material powder for intermediate layer)
The production of the raw material powder for the intermediate layer was performed by a solid phase method. Strontium, lanthanum, titanium, niobium, and iron have a composition ratio of a perovskite-type oxide represented by Sr _0.37 La _0.52 Ti _0.50 Nb _0.10 Fe _0.40 O _3-δ . The powder of the metal oxide of each element as a raw material was weighed and mixed in a solution. Thereafter, the powder obtained by removing the solvent was fired at 1150 ° C. and pulverized to prepare a raw material powder for an intermediate layer.

(Preparation of slurry for intermediate layer)
As a material for the intermediate layer, a powder having a composition of Sr _0.37 La _0.52 Ti _0.50 Nb _0.10 Fe _0.40 O _3-δ was used. 40 parts by weight of this powder were mixed with 100 parts by weight of a solvent (carbitol), 4 parts by weight of a binder (soluble polymer), 1 part by weight of a dispersant (nonionic surfactant), and 1 part by weight of an antifoaming agent (organic polymer). After mixing with parts by weight, the mixture was sufficiently stirred to prepare a slurry.

(Preparation of raw material powder for interconnectors)
The production of the interconnector raw material powder was performed by a solid phase method. The metal oxide powder of each element as a raw material was weighed so that strontium, lanthanum, and titanium had a composition ratio of a perovskite-type oxide represented by Sr _0.90 La _0.04 TiO _3-δ , and the solution was dissolved. Mixed in. Thereafter, the powder obtained by removing the solvent was fired at 1150 ° C. and pulverized to prepare an interconnector raw material powder.

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

(Production of solid oxide fuel cell stack)
Using the clay and the respective slurries obtained as described above, a solid oxide fuel cell stack was produced by the following method.

  A cylindrical molded body was produced from the porous support body clay A by an extrusion molding method. After drying at room temperature, heat treatment was performed at 1100 ° C. for 2 hours to prepare a calcined body of the support. On the surface of this support, a fuel electrode, a fuel electrode catalyst layer, an intermediate layer, a reaction suppression layer, and a solid electrolyte were formed in this order by a slurry coating method, and dried to obtain a laminated molded body in which a dried film was laminated. The laminate was co-fired at 1300 ° C. for 2 hours.

  Next, an interconnector was formed on the obtained fired body by a slurry coating method. These were fired at 1250 ° C. for 2 hours.

  Next, an air electrode was formed on the surface of the solid electrolyte and baked at 1100 ° C. for 2 hours to produce a solid oxide fuel cell stack. The support had dimensions after co-firing and an outer diameter of 10 mm and a thickness of 1 mm. The prepared 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. And the thickness of the air electrode was 20 μm. The outside diameter of the support was measured by a micrometer at a portion where no film was formed. The thickness of each layer was determined by cutting the produced solid oxide fuel cell stack, observing the cross section with an SEM at an arbitrary magnification of 30 to 2000 times, and adding the maximum value and the minimum value of the obtained thickness to 2 Divided by The cut position was the center of the portion where the air electrode was formed. The following evaluations were performed on the obtained solid oxide fuel cell stack.

Examples 2 to 13
A solid oxide fuel cell stack was obtained in the same manner as in Example 1, except that powders having the compositions shown in Table 1 were used as materials for the intermediate layer and the interconnector. The following evaluations were performed for the obtained solid oxide fuel cell stack.

Comparative Example 1
A solid oxide fuel was prepared in the same manner as in Example 1 except that a powder having a composition of Sr _0.40 La _0.55 Ti _0.60 Fe _0.40 O _3-δ was used as a material for the intermediate layer. A battery cell stack was obtained. The following evaluations were performed for the obtained solid oxide fuel cell stack. In Comparative Example 1, the porosity was high, and a dense pressed body and fuel cell could not be produced. This is because a stable perovskite structure cannot be maintained because the amount of oxygen exceeds 3.00, an impurity phase such as La ₂ Ti ₂ O ₇ is generated, and poor denseness due to sintering inhibition occurs. It is thought that it was.

Comparative Example 2
A solid was prepared in the same manner as in Example 1, except that a powder having a composition of Sr _0.77 La _0.09 Ti _0.90 Nb _0.05 Fe _0.05 O _3-δ was used as a material for the intermediate layer. An oxide fuel cell stack was obtained. The following evaluations were performed for the obtained solid oxide fuel cell stack. In Comparative Example 2, the porosity was high, and a dense pressed body and fuel cell could not be produced. It is considered that this is because a stable perovskite structure could not be maintained due to a low oxygen content, and an impurity phase such as TiO ₂ was generated, resulting in poor denseness due to inhibition of sintering.

Comparative Example 3
Example 1 was _repeated in the same manner as in Example 1 except that a powder having a composition of Sr _0.30 La _0.55 Ti _0.90 Nb _0.05 Fe _0.05 O _3-δ was used as the material of the intermediate layer. A solid oxide fuel cell stack was obtained. The following evaluations were performed for the obtained solid oxide fuel cell stack.

Comparative Example 4
The procedure of Example 1 was _repeated except that a powder having a composition of Sr _0.40 La _0.55 Ti _0.30 Fe _0.70 O _3-δ was used as the material of the intermediate layer. A fuel cell stack was obtained. The following evaluations were performed for the obtained solid oxide fuel cell stack.

Comparative Example 5
A solid oxide fuel was prepared in the same manner as in Example 1 except that an intermediate layer was not formed and a powder having a composition of Sr _0.55 La _0.30 TiO _3-δ was used as a material for the interconnector. A battery cell stack was obtained. Regarding the obtained solid oxide fuel cell stack, in Comparative Example 5, an interconnector could not be formed in the production of the fuel cell. This is probably because the interconnector was taken into the fuel electrode during firing.

Evaluation (analysis of composition)
Regarding the composition of the intermediate layer and the interconnector, the intermediate layer and the interconnector were 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. The thin film was evaluated by STEM-EDX to obtain element mapping. The composition ratio was analyzed by quantitatively analyzing the element mapping using a thin film approximation method. As a result, it was confirmed that the main components of the composition of the intermediate layer and the interconnector were the same as the composition of the raw material powder.

(Calculation of the oxygen content of the middle layer)
As the oxygen content of the intermediate layer, in each composition of the manufactured solid oxide fuel cell stack, the sum of the valences of the cations of each element and the sum of the valences of the oxide ions that are divalent anions are equal. The amount of oxygen at the time was determined. As the valence of the cation of each element, Sr was calculated as divalent, La and Fe as trivalent, Ti and Co as tetravalent, and Nb, V and Ta as pentavalent. Table 2 shows the results.

(Measurement of porosity 1)
The porosity of the intermediate layer and the interconnector was measured by the following method. Each raw material powder was uniaxially pressed under a load of 900 kgf / cm ² and fired at 1300 ° C. for 2 hours in an air atmosphere to prepare a test piece. The porosity of this test piece was measured by the Archimedes method based on the provisions of JIS R 1634. Table 2 shows the results.

(Measurement of conductivity)
The conductivity of the intermediate layer and the interconnector was measured by the following method. Each raw material powder was uniaxially pressed under a load of 900 kgf / cm ² and fired at 1300 ° C. for 2 hours in an air atmosphere to prepare a test piece. The conductivity of this test piece was measured at 700 ° C. in an air atmosphere by a direct current four-terminal method based on the provisions of JIS R 1650-2. Table 2 shows the results.

(Identification of impurity phase)
The impurity phase in the crystal phase was identified by the following method. A test piece was prepared by uniaxially pressing the raw material powder of the intermediate layer under a load of 900 kgf / cm ² and firing at 1300 ° C. for 2 hours. This test piece was ground in a mortar until the BET reached ¹ m ² / g to 3 m ² / g. After measuring the diffraction intensity of the obtained pulverized product at 2θ = 20 ° to 90 ° using a powder X-ray diffractometer (XRD: manufactured by PANalytical), a peak remaining when a main peak due to a perovskite structure is removed is obtained. It was determined as an impurity peak. The impurity peaks were collated with an ICDD card, and it was identified that the impurity phases were TiO ₂ , La ₂ Ti ₂ O ₇ , and Fe ₂ TiO ₄ . Table 2 shows the results.

(Measurement of thickness of intermediate layer and interconnector)
Each thickness was measured by the following method. The manufactured solid oxide fuel cell stack was cut so as to include the intermediate layer and the interconnector. This cross section was observed three times with an SEM at an arbitrary magnification of 30 to 2000 times, and the maximum value and the minimum value of the obtained values were added and divided by 2 to obtain the thickness. Table 2 shows the results.

(Measurement of porosity 2)
From the produced solid oxide fuel cell stack, the porosity of the intermediate layer and the interconnector was determined as follows. First, the prepared solid oxide fuel cell was cut out so as to include an intermediate layer, and the intermediate layer was subjected to a scanning electron microscope (S-4100 manufactured by Hitachi, Ltd.) at an acceleration voltage of 15 kV, a secondary electron image, and a magnification of 100 to 10,000 times. And an SEM image was obtained. The SEM image was evaluated using image processing software (Winroofver 6.5.1, manufactured by MITANI CORPORATION). As a result, a histogram was obtained in which the horizontal axis was luminance and the vertical axis was appearance frequency. In this histogram, an area where the luminance is lower than the average of the minimum and maximum values of the luminance is a low luminance area, and an area where the luminance is higher than the average is a high luminance area. The low-luminance area was determined to be a pore, and the high-luminance area other than the pore was determined to be an intermediate layer, thereby performing a binarization process. Then, the porosity of the intermediate layer was obtained by the following equation. The porosity of the interconnector was determined by the same method as that for the intermediate layer. Table 2 shows the results.
Porosity (%) = Integral value of low-luminance area / Integral value of overall appearance frequency × 100

(Measurement of OCV)
A power generation test was performed using the obtained solid oxide fuel cell stack. For current collection on the fuel electrode side, a current collector metal was adhered to an exposed portion of the fuel electrode with a silver paste and baked. For current collection on the air electrode side, a current collector metal was adhered to the exposed portion of the adjacent fuel electrode with silver paste and baked.

A power generation test was performed under the following power generation conditions, and an electromotive force 0 hours after the operation: OCV (V) was measured. Table 2 shows the results.
Fuel gas: a mixed gas of (H ₂ + 3% H ₂ O) and N ₂ (mixing ratio is H ₂ : N ₂ = 7: 4 (vol: vol))
Oxidizing gas: air Operating temperature: 700 ° C

(Measurement of terminal voltage)
Under the following power generation conditions, a voltage between 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. Table 2 shows the results.
Fuel gas: mixed gas of (H ₂ + 3% H ₂ O) and N ₂ (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

(Measurement of conductivity of conductive part)
Under the following evaluation conditions, a potential line and a current line are connected to the fuel electrode of one power generation element adjacent to the interconnector, and the potential difference between the fuel electrode terminal of the one power generation element adjacent to the interconnector while the current is flowing. A was measured. Thereafter, a through-hole was provided so as to penetrate the interconnector and the intermediate layer and reach the fuel electrode of one of the adjacent power generating elements, and the potential line and the current line were connected to the fuel electrode below the through-hole via the Ag paste. . A potential line and a current line were also connected to the fuel electrode of the other adjacent power generating element. The electric potential difference B between the terminal of the fuel electrode of the other adjacent power generating element below the through hole of the interconnector and the terminal of the other adjacent fuel electrode was measured while applying a current.
Fuel gas: mixed gas of (H ₂ + 3% H ₂ O) and N ₂ (mixing ratio is H ₂ : N ₂ = 7: 4 (vol: vol))
Oxidizing gas: air Operating temperature: 700 ° C
Current: 1A

The conductivity of the conductive portion was calculated from the following equation.
Conductivity = current ÷ (potential difference A−potential difference B) × (film thickness of interconnect + film thickness of intermediate layer) ÷ conductive area of interconnect The conductive area of the interconnect is sandwiched between the air electrode and the intermediate layer. The area of the interconnector is measured using a caliper. Table 2 shows the results.

(Measurement of critical fuel utilization)
Under the conditions of the power generation test described above, the power generation test was performed by supplying electricity at a current density of 0.4 A / cm ² . Thereafter, the supply amount of the fuel gas was gradually reduced, the supply amount of hydrogen immediately before the potential dropped sharply was measured, and the limit fuel utilization was calculated from the following equation. Table 2 shows the results.
Limit fuel utilization rate = (amount of hydrogen used for power generation) / (amount of hydrogen supply immediately before potential drops rapidly) × 100
The amount of hydrogen used for power generation is the amount of current (C / s) × 60 (s) × 22.4 (L / mol) ｍｏｌFaraday constant (C / mol) ×） (valence) × It can be obtained by the number of power generating elements.

10: power generation element, 210: solid oxide fuel cell stack, 201: support, 202: fuel electrode, 203: intermediate layer, 204: solid electrolyte, 205: interconnector, 206: air electrode

Claims (6)

Fuel electrodes, solid electrolyte and a plurality of power generating elements formed by laminating the air electrode at least sequentially,
The air electrode of one adjacent power generation element of the plurality of power generation elements is electrically connected to the fuel electrode of the other power generation element , and Sr _0.90 La _0.04 TiO _3-δ , Sr _{0. At} least an interconnect made of a perovskite oxide represented by ₈₀ La _0.10 TiO _3-δ or Sr _0.95 La _0.02 TiO _3-δ , wherein the plurality of power generating elements are connected in series A solid oxide fuel cell stack comprising:
Between the fuel electrode of the interconnector and the other power generating element, and a porosity of 1% or less state, and are the conductivity of the temperature of 700 ℃ in air atmosphere 0.05 S / cm or _more, Sr a _La b Ti _{1-c-d Nb c Fe} d O 3-δ ( However, a, b, c and d are, 0.29 ≦ a ≦ 0.4,0.5 ≦ b ≦ 0.6,0.1 ≦ c ≦ 0.25, and 0.3 ≦ d ≦ 0.6 and meet positive real number a is) the intermediate layer ing a perovskite oxide represented by is formed, the solid oxide fuel cell stack .   The electrical conductivity of claim 1, wherein the conductivity of the intermediate layer is substantially equal to or higher than the electrical conductivity of the interconnector, and the porosity of the intermediate layer is lower than the porosity of the interconnector. Solid oxide fuel cell stack.   3. The solid oxide fuel cell stack according to claim 1, wherein the thickness of the intermediate layer is larger than the thickness of the interconnector.   The solid oxide fuel cell stack according to claim 1, wherein a thickness of the intermediate layer is 10 μm or more and 100 μm or less.   The solid oxide fuel cell stack according to any one of claims 1 to 4, wherein a solid electrolyte is formed between the interconnector and the intermediate layer. The solid oxide fuel cell stack according to any one of claims 1 to 5 , wherein the amount of oxygen (3-δ) in the intermediate layer is 3.00 or less.

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