JP6654766B2 - 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 low resistance between power generating elements and excellent power generation performance.

  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 the electrode which is not enough. Therefore, there is a possibility that the ceramic interconnector cannot be formed, and even if the ceramic interconnector can be formed, a sufficient gas sealing property may not be obtained.

  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. 2006-310090 (Patent Literature 1) discloses one fuel cell of one adjacent cell (power generation element) in order to obtain a solid oxide fuel cell having a dense and highly conductive interconnector. An interconnector including a first layer provided to cover the portion and containing a predetermined oxide, and a second layer provided on the first layer and containing an oxide different from the oxide contained in the first layer. Have been. According to FIG. 1 of this document, an interconnector is provided between the solid electrolyte of one adjacent cell and the solid electrolyte of the other cell and on the solid electrolyte of the other cell. Further, the air electrode is provided on the interconnector provided on the solid electrolyte of one cell to the solid electrolyte of the other cell.

  However, Patent Document 1 does not consider the positional relationship between the interconnector and the air electrode of the adjacent power generation element, and the two are separated in FIG. In this case, the distance between the power generation elements becomes longer, and the resistance between the power generation elements increases, so that the power generation performance decreases.

  Therefore, as far as the present inventors know, the manufacture of a solid oxide fuel cell stack comprising a power generating element capable of high power output by reducing the distance between the interconnector and the air electrode of the adjacent power generating element. Has not yet been realized.

JP 2006-310090 A

  The present inventors have recently covered the interconnector with the air electrode of one of the adjacent power generating elements, and further reduced the distance between the interconnector and the air electrode of the other power generating element by reducing the distance therebetween. It has been found that the distance between the power generating elements can be reduced, thereby reducing the resistance between the power generating elements and improving the power generation performance. The present invention is based on such findings.

  Accordingly, an object of the present invention is to provide a solid oxide fuel cell having a small resistance between power generation elements and excellent power generation performance.

And, the solid oxide fuel cell stack according to the present invention,
A support,
On the surface of the support, a fuel electrode, a solid electrolyte and a plurality of power generating elements that are stacked at least sequentially air electrode,
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:
The interconnector is formed between a first interconnector formed on the solid electrolyte of the other power generating element, and the solid electrolyte of one power generating element and the solid electrolyte of the other power generating element. And at least a second interconnector,
An air electrode of the one power generating element covers a surface of the first interconnector and a surface of the second interconnector,
The total length of the joining distance between the air electrode of the one power generating element and the first interconnector and the joining distance between the air electrode of the one power generating element and the second interconnector: A; The length between the solid electrolyte of one power generation element and the solid electrolyte of the other power generation element: A ′ satisfies A / A ′ ≧ 1, and the air electrode side of the solid electrolyte of the other power generation element And the length between the end of the interconnector and the end of the air electrode of the other power generating element on the surface of the first interconnector: L, and the length of the surface on the air electrode side of the first interconnector: L '. Satisfies L / L ′ ≦ 1.

1 is a front view of a horizontal-striped solid oxide fuel cell stack according to the present invention. FIG. 2 is a schematic cross-sectional view of the vicinity of a power generating element constituting a solid oxide fuel cell stack according to the present invention. 1 is a cross-sectional view showing one preferred embodiment of a solid oxide fuel cell stack according to the present invention. 1 is a cross-sectional view showing one preferred embodiment of a solid oxide fuel cell stack according to the present invention. 1 is a cross-sectional view showing one preferred embodiment of a solid oxide fuel cell stack according to the present invention.

The solid oxide fuel cell stack according to the present invention is a solid oxide fuel cell stack according to the present invention, except that the mutual positional relationship between the solid electrolyte, the air electrode, and the interconnector in the adjacent power generation element satisfies the requirements described below. On the surface of the support, a fuel electrode, a plurality of power generating elements in which a solid electrolyte and an air electrode are laminated at least sequentially, among these, the air electrode of one adjacent power generating element, and the fuel electrode of the other power generating element And at least an interconnector for electrically connecting the same to the same as those generally classified or understood in the art as a solid oxide 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 flow paths formed therein.

  The solid oxide fuel cell stack according to the present invention means a so-called horizontal stripe type solid oxide fuel cell stack. In the present invention, a horizontal stripe type solid oxide fuel cell refers to a solid oxide fuel cell in which a plurality of power generating 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 generating element is a laminate 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 has a support. 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 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.

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 of the 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, the fuel electrode catalyst layer) is used on the solid electrolyte side. Used. 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.

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.

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.

Interconnector (composition)
In the present invention, the interconnector is made of ceramic. That is, the interconnector of the present invention 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. 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, and a solid electrolyte 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.

(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 since the higher the conductivity, the better, but it is preferably 0.16 S / cm or less. Thereby, the conductivity of the interconnector can be improved, and the power generation output of the solid oxide fuel cell stack can be improved.

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 interconnector under a load of 900 kgf / cm ² and firing at 1300 ° C. for 2 hours in the 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.

(Porosity)
In the present invention, the porosity of the interconnector is preferably 1% or less, more preferably 0.1% or less. Further, it is preferably 0% or more. Thereby, the gas sealing property of the interconnector can be secured, and the power generation efficiency of the solid oxide fuel cell stack can be improved. The porosity can be measured using the following method.

<Method to obtain from SEM image>
The manufactured solid oxide fuel cell stack is cut out so as to include an interconnector, and the interconnector is accelerated by 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 100 μm. Observe at 10000x and obtain SEM image. The SEM image is evaluated using image processing software (for example, Winroofver 6.5.1, manufactured by MITANI 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 interconnector, 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, the porosity obtained by the following method can be used as one index in order to confirm that the interconnector has a desired porosity obtained by the above method.

<Method obtained by Archimedes method>
The test piece is obtained by uniaxially pressing the raw material powder of the interconnector 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.

  In the present invention, it is preferable that both the solid electrolyte and the interconnector contain strontium. In the present invention, the amount of strontium contained in the interconnector is more preferably 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.

The interconnector preferably contains strontium in a composition of 30 mol% or more and 50 mol% or less in terms of an element excluding oxygen. _{That, Sr x La y TiO 3-} δ ( here, x and y, 0.8 ≦ x + y ≦ 1.0 , and a positive real number satisfying 0.01 <y ≦ 0.1.) In further It is preferable to satisfy 0.3 ≦ x / (x + y + 1) ≦ 0.5. 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 has the 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).

(Thickness)
In the present invention, the preferred thickness of the interconnector is 5 μm or more and 50 μm or less.

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 schematic diagram showing one embodiment of the solid oxide fuel cell stack 210 according to the present invention, and shows the vicinity of the power generating element 10 in the solid oxide fuel cell stack. FIG. 2 shows a type in which the inner electrode is a fuel electrode. As shown in FIG. 2, the solid oxide fuel cell stack 210 includes a support 201, a (first / second) anode 202 (that is, an anode layer 202a and an anode catalyst layer 202b), The first / second) solid electrolyte 203 (that is, the reaction suppression layer 203 a and the solid electrolyte layer 203 b), the air electrode 204, the current collecting layer 205, and the interconnector 206. Here, (first / second) means a single layer or two layers, and in the case of two layers, means having a first layer and a second layer.

  FIG. 3 shows one preferred embodiment of the solid oxide fuel cell stack according to the present invention. The fuel electrode 302 is formed on the surface of the support 301. A solid electrolyte 304 is formed between adjacent fuel electrodes and on the surface of the fuel electrode. The interconnector 303 is formed between the first interconnector 306 formed on the solid electrolyte 304 of the other power generating element and the solid electrolyte 304 of one adjacent power generating element and the solid electrolyte 304 of the other power generating element. And at least a second interconnector 307 formed therein. The air electrode 305 of one power generation element covers the surface of the second interconnector 307. At this time, the entire surface of the second interconnector is covered. The air electrode 305 of one power generation element covers a part of the surface of the first interconnector 306.

  The total length of the junction distance between the air electrode 305 of one power generation element and the first interconnector 306 and the junction distance between the air electrode 305 of one power generation element and the second interconnector 307: A The length between the solid electrolyte 304 of the power generation element of the first power generation element and the solid electrolyte 304 of the other power generation element: A ′ is such that the surface of the interconnector 303 has the surface of one of the power generation elements so that A / A ′ ≧ 1. It is covered with an air electrode 305. With such a configuration, the conductive area of the interconnector 303 can be increased, and the conductivity can be increased. The length between the solid electrolyte 304 of one power generation element and the solid electrolyte 304 of the other power generation element: A ′ is the length between the solid electrolyte 304 of one power generation element and the solid electrolyte 304 of the other power generation element. The shortest length between them.

  Further, the length between the end of the interconnector 303 (first interconnector 306) and the end of the air electrode 305 of the other power generating element on the surface of the solid electrolyte 304 on the air electrode side of the other power generating element. : L and the length of the surface on the air electrode side of the first interconnector: L 'satisfy the relationship of L / L' ≤ 1 with the interconnector 303 (first interconnector 306) and the other power generator. The air electrode 305 of the element is brought close. With such a configuration, the distance between the adjacent power generating elements can be reduced, and the resistance between the power generating elements can be reduced.

  As a result, the electrical conductivity of the interconnector can be increased and the electrical resistance between adjacent power generating elements can be reduced, so that the power generation output of the solid oxide fuel cell stack can be increased.

  Each length and joining distance (A, A ', L, L') can be determined as follows. That is, the produced solid oxide fuel cell stack is cut so as to include one adjacent power generation element and the other power generation element. Then, the cut surface is observed three times with a scanning electron microscope (SEM) at an arbitrary magnification of 1 to 100 times, and the obtained maximum value and minimum value of each length are added and divided by two. Each joining distance can be determined in a similar manner.

  FIG. 4 shows another preferred embodiment of the solid oxide fuel cell stack according to the present invention. FIG. 4 can be described similarly to the embodiment shown in FIG.

  According to a preferred embodiment of the present invention, the solid oxide fuel cell stack has A / A ′ ≦ 1.5 or less. According to a preferred embodiment of the present invention, the solid oxide fuel cell stack satisfies 0.5 ≦ L / L ′. As a result, the distance between the power generation elements can be kept within a range where the power generation performance is not impaired, and the output of the solid oxide fuel cell stack can be increased.

  According to a preferred embodiment of the present invention, the solid oxide fuel cell stack satisfies A = A '+ L' (see FIG. 5). That is, it is preferable that the end of the air electrode 305 of one of the power generating elements and the end of the interconnector 303 (first interconnector 306) be flush. In FIG. 5, the air electrode 305 of one power generation element covers the entire surface of the first interconnector 306. That is, in the embodiment shown in FIG. 3, the end of the air electrode 305 of one of the power generation elements and the end of the interconnector 303 (first interconnector 306) are flush with each other, so that The contact area with the contact 303 can be increased. As a result, the conductive area of the interconnector 303 can be increased, so that the conductivity can be increased. Therefore, the power generation output of the power generation element can be improved.

  In these embodiments, the third interconnector 308 may be formed on the solid electrolyte 304 of one power generation element. That is, in this case, the interconnector 303 includes the first interconnector 306, the second interconnector 307, and the third interconnector 308. Accordingly, leakage of oxide ions generated when the air electrode 305 of one adjacent power generation element and the solid electrolyte 304 of one power generation element are in contact with each other can be prevented, so that formation of a reverse battery can be suppressed. Can be. 3 to 5 show an embodiment in which the third interconnector 308 is formed on the solid electrolyte 304 of one of the power generation elements. The entire surface of the third interconnector 308 is covered with the air electrode 305 of one power generation element.

  According to a preferred embodiment of the present invention, the solid oxide fuel cell stack further includes an insulating portion provided between the solid electrolyte 304 of one power generation element and the air electrode 305 of one power generation element. The insulating part is in contact with the interconnector 303 (second interconnector 307). In this case, the insulating section is preferably provided at a location where the third interconnector 308 is formed. With such a configuration, it is possible to prevent leakage of oxide ions generated when the air electrode 305 of one adjacent power generation element and the solid electrolyte 304 of the other power generation element come into contact with each other. As a result, the power generation output of the solid oxide fuel cell stack can be increased.

In the present invention, the insulating portion has an insulating property. Insulating means having electrical insulation and oxide ion insulation. Specifically, it means that the conductivity in an air atmosphere at 700 ° C. is 0.001 S / cm or less and has oxide ion insulating properties. The conductivity can be measured by the method described above. Insulating _{portion, Sr x La y TiO 3-} δ ( here, x and y are real numbers satisfying 0.8 ≦ x + y ≦ 1.0, and 0 ≦ y ≦ 0.01.), TiO 2, folder It preferably contains at least one selected from stellite (Mg ₂ SiO ₄ ), MgO, Al ₂ O ₃ , SiO ₂ and Y ₂ O ₃ . More preferred _{materials, Sr x La y TiO 3-} δ ( here, x and y, 0.8 ≦ x + y ≦ 1.0 , and is a real number satisfying 0 ≦ y ≦ 0.01.) Or forsterite No.

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.

  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 interconnector and the insulating part 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.). By performing the above process, the interconnector and the insulating portion 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 then provided by attaching the transfer film to a laminated body.

  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. In other words, according to this aspect, a step of forming a dried film of the fuel electrode on the surface of the support or the calcined body thereof, followed by baking to form the fuel electrode, and a step of forming a dried film of the solid electrolyte, followed by baking. Forming a solid electrolyte, forming a dry film of the interconnector, and then firing to form an interconnector, forming a dry film of the air electrode, and firing to form an air electrode at least. Comprising. The formation of the current collecting layer is performed after the formation of the air electrode.

  When the solid oxide fuel cell has an insulating portion, the following manufacturing method is preferable. That is, a step of forming a dried film of the fuel electrode on the surface of the support or its calcined body, followed by firing to form the fuel electrode, and forming a dried film of the solid electrolyte, followed by firing to form the solid electrolyte. A step of forming a dry film of the interconnector and the insulating part and then firing to form the interconnector and the insulating part, and a step of forming a dry film of the air electrode and firing to form the air electrode at least. Comprising. The formation of the current collecting layer is performed after the formation of the air electrode.

  According to a preferred embodiment of the production method of the present invention, it is preferable that the interconnector and the solid electrolyte are obtained by co-firing (1250 ° C. or more and less than 1400 ° C.). Further, it is more preferable that the interconnector, the solid electrolyte, and the insulating portion are obtained by co-firing (1250 ° C. or higher and lower than 1400 ° C.). At the time of firing, the elements contained in the interconnector, the solid electrolyte, and the insulating portion are mutually diffused. That is, when the elements contained in the interconnector, the solid electrolyte, and the insulating portion are the same, they diffuse with each other. Such elements include strontium and lanthanum. Thereby, the adhesiveness of the interconnector, the solid electrolyte, and the insulating portion can be improved.

  According to another preferred embodiment of the production method of the present invention, a support or a calcined body thereof is produced, a dried film of the fuel electrode is formed on the surface of the support or the calcined body thereof, and a dried film of the solid electrolyte is formed. The laminated molded body composed of the support, the fuel electrode, and the dry film of the solid electrolyte is co-fired (1250 ° C. or more and less than 1400 ° C.), and thereafter, the dry film of the interconnector and the insulating part is formed. And further forming a dry coating of the cathode and firing all of them.

  The formation of the dry film on the cathode is based on the total length of the junction distance between the cathode of one power generation element and the first interconnector and the junction distance between the cathode of one power generation element and the second interconnector. : A, the length between the solid electrolyte of one of the adjacent power generating elements and the solid electrolyte of the other power generating element: A ′ satisfies A / A ′ ≧ 1, and the solid of the other power generating element The length between the end of the interconnector and the end of the cathode of the other power generating element on the cathode side surface of the electrolyte: L, and the length of the cathode side surface of the first interconnector: L ′ is set to satisfy L / L ′ ≦ 1.

  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)
The raw material powder _(Mg 2 SiO ₄ containing from 0.05 wt% CaO) of high purity forsterite average particle size was adjusted to be 0.7 [mu] m. 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) Was mixed in a kneader (kneader), deaerated with a vacuum kneading device, and a kneaded material for extrusion 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 that, the slurry was prepared by sufficiently stirring the mixture.

(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 raw material powder for interconnectors)
The production of the raw material powder for the interconnector was performed by a solid phase method. The metal oxide powder as a raw material is weighed so that strontium, lanthanum, and titanium have a composition ratio of a perovskite oxide represented by Sr _0.90 La _0.04 TiO _3-δ , and the solution Mixed. 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 an interconnector material, an interconnector raw material 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.

(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.

(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 the support, a fuel electrode, a fuel electrode catalyst layer, a reaction suppressing 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, the interconnector was formed into a film by a slurry coating method and baked at 1250 ° C. for 2 hours.

  Next, an air electrode was formed on the surface of the solid electrolyte so that L / L ′ = 0.7 and A / A ′ = 1.1, and calcined at 1100 ° C. for 2 hours to obtain a solid oxide fuel cell. A cell stack was prepared. 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. The thickness of the interconnector was 15 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 member is determined by cutting the cell of the prepared cell stack, observing the cross section three times with a scanning electron microscope (SEM) at an arbitrary magnification of 30 to 2000 times, and determining the maximum value and the minimum value of the obtained thickness. It is the sum of the values and dividing by two. 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. Table 1 shows the results.

Example 2
A solid oxide fuel cell stack was obtained in the same manner as in Example 1 except that the air electrode layer was formed so that L / L ′ = 0.7 and A / A ′ = 1.0. Was. The following evaluations were performed for the obtained solid oxide fuel cell stack. Table 1 shows the results.

Example 3
A solid oxide fuel cell stack was obtained in the same manner as in Example 1, except that the air electrode layer was formed so that L / L '= 1.0 and A / A' = 1.1. Was. The following evaluations were performed for the obtained solid oxide fuel cell stack. Table 1 shows the results.

Example 4
A solid oxide fuel cell stack was obtained in the same manner as in Example 1, except that the air electrode layer was formed so that L / L '= 1.0 and A / A' = 1.0. Was. The following evaluations were performed for the obtained solid oxide fuel cell stack. Table 1 shows the results.

Example 5
A solid oxidation was performed in the same manner as in Example 1 except that the air electrode layer was formed so that L / L ′ = 0.7 and A / A ′ = 1.5, that is, A = A ′ + L ′. A physical fuel cell stack was obtained. The following evaluations were performed for the obtained solid oxide fuel cell stack. Table 1 shows the results.

Example 6
A solid oxide fuel cell stack was obtained in the same manner as in Example 1, except that the air electrode layer was formed so that L / L '= 0.5 and A / A' = 1.0. Was. The following evaluations were performed for the obtained solid oxide fuel cell stack. Table 1 shows the results.

Comparative Example 1
A solid oxide fuel cell stack was obtained in the same manner as in Example 1, except that the air electrode layer was formed so that L / L '= 0.7 and A / A' = 0.8. Was. The following evaluations were performed for the obtained solid oxide fuel cell stack. Table 1 shows the results.

Comparative Example 2
A solid oxide fuel cell stack was obtained in the same manner as in Example 1, except that the air electrode layer was formed so that L / L '= 1.5 and A / A' = 1.1. Was. The following evaluations were performed for the obtained solid oxide fuel cell stack. Table 1 shows the results.

Evaluation (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 1 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

10: power generation element, 210: solid oxide fuel cell stack, 301: support, 302: fuel electrode, 303: interconnector, 304: solid electrolyte, 305: air electrode, 306: first interconnector, 307 : Second interconnector, 308: third interconnector

Claims (4)

A support,
On the surface of the support, a fuel electrode, a solid electrolyte and a plurality of power generating elements that are stacked at least sequentially air electrode,
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:
The interconnector is formed between a first interconnector formed on the solid electrolyte of the other power generating element, and the solid electrolyte of one power generating element and the solid electrolyte of the other power generating element. And at least a second interconnector,
An air electrode of the one power generating element covers a surface of the first interconnector and a surface of the second interconnector,
The total length of the joining distance between the air electrode of the one power generating element and the first interconnector and the joining distance between the air electrode of the one power generating element and the second interconnector: A; The length between the solid electrolyte of one power generation element and the solid electrolyte of the other power generation element: A ′ satisfies A / A ′ ≧ 1, and the air electrode side of the solid electrolyte of the other power generation element The length between the end of the first interconnector in the same direction as the connection direction of the plurality of power generating elements and the end of the air electrode of the other power generating element on the surface of the first interconnector; Wherein the length of the surface L ′ in the same direction as the connection direction of the plurality of power generating elements on the air electrode side of the interconnector satisfies L / L ′ ≦ 1. Battery cell stack.   The solid oxide fuel cell stack according to claim 1, wherein A = A '+ L' is satisfied.   The insulating part is further provided between the solid electrolyte of the one power generating element and the air electrode of the one power generating element, and the insulating part is in contact with the second interconnector. 3. The solid oxide fuel cell stack according to item 1. The _{interconnector, 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.) The solid oxide fuel cell stack according to any one of claims 1 to 3, comprising a perovskite oxide represented by the following formula:

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