JP6524756B2 - 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 with excellent conductivity and gas sealability.

  Fuel cells, unlike heat engines that go through thermal energy and kinetic energy processes, react fuels such as natural gas and hydrogen with oxygen in the air through a solid electrolyte and continue from the chemical energy possessed by the fuel Energy converter that directly obtains electrical energy. Among them, the solid oxide fuel cell is a fuel cell operating as a cell using a solid oxide (ceramic) as a solid electrolyte, a fuel electrode as a negative electrode, and an air electrode as a positive electrode. Solid oxide fuel cells are also known to have the advantage of high energy conversion efficiency.

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

  Generally, ceramic interconnectors can not achieve sufficient conductivity unless they have a small thickness (for example, about 100 μm or less). However, if the thickness of the ceramic interconnector is reduced in order to obtain sufficient conductivity, and such a thin ceramic interconnector is to be formed on the surface of the porous electrode (fuel electrode or air electrode), There is a possibility that the ceramic interconnector may be taken into the electrode. As a result, there is a fear that the ceramic interconnector can not be formed, or even if it can be formed, there is a possibility that a sufficient gas sealability can not be obtained since the ceramic interconnector can be formed 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 this is undesirable because it mixes with air. In order to improve the gas sealability of the ceramic interconnector, it is necessary to increase the compactness of the ceramic interconnector, and compact sintering of the ceramic interconnector is required. In addition, when the conductivity of the ceramic interconnector is low, the resistance of the ceramic interconnector is increased, and the output of the fuel cell is reduced. Furthermore, if the oxide ion insulation of the ceramic interconnector is low, oxide ions will leak from the air electrode side of the ceramic interconnector to the fuel electrode side, and the efficiency of the fuel cell will be 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 the fuel gas leaks from the gap.

As a material of a ceramic interconnector, a lanthanum chromite (LaCrO ₃ ) based interconnector is widely used. Although this LaCrO ₃ -based interconnector is generally highly conductive, it is known that sintering is difficult. In addition, since chromium (Cr) is contained, so-called Cr poisoning may occur.

In addition, as a material of the ceramic interconnector, an SLT-based interconnector represented by SrLaTiO _3-δ is widely used. The SLT system interconnector, compared with LaCrO ₃ system interconnector, although low conductivity, sinterability is known to be good. In the SLT-based interconnector, for example, SrLaTiO _3-δ (SLT) is obtained by substituting Sr sites in the crystal lattice of SrTiO ₃ which is an insulator with lanthanum (La) to form SrLaTiO _3-δ (SLT). The conductivity is expressed by partially changing Ti ⁴⁺ of the Ti site in the crystal lattice to Ti ³⁺ . Note that δ is a value determined to satisfy the charge neutral condition.

  JP 2008-270203 A (Patent Document 1) aims to provide an SLT-based interconnector which simultaneously realizes the improvement of the conductivity and the improvement of the adhesion with the solid electrolyte while maintaining the airtightness well. In order to realize this object, the ceramic interconnector is composed of an airtightness-oriented portion formed on the fuel electrode side and a conductivity-oriented portion formed on the air electrode side and higher in conductivity than the airtightness-oriented portion. It is described to be a two-layer structure. Further, according to FIG. 2 of this document, the solid electrolyte of one power generation element is formed so that the fuel electrode of one power generation element and the air electrode of the other power generation element adjacent to each other are in contact under the ceramic interconnector. The described embodiments are described.

  Moreover, in the patent 5244264 (patent document 2), in order to lower the electrical resistivity of the laminated body of a chromite-based interconnector and a conductive support member (fuel electrode), a chromite-based interconnector and a conductive property are used. It is described to control the amount of iron contained in each of the support members. As a result, the resistance between the two is reduced, the connectivity is improved, and densification during co-sintering is synergistically promoted. Also, according to FIG. 2 of this document, an embodiment is described in which the solid electrolyte is formed so as to partially cover the chromite-based interconnector disposed in contact with the fuel electrode.

  However, none of the above documents takes into consideration the improvement of the gas sealability of the interconnector by bringing the interconnector and the solid electrolyte into contact with each other. Therefore, none of the above documents can realize the manufacture of a solid oxide fuel cell stack having a ceramic interconnector having excellent conductivity and gas sealability.

Unexamined-Japanese-Patent No. 2010-212036 Patent No. 5244264 gazette

  The present inventors have now found that the gas sealability of the interconnector can be improved by joining the interconnector and the solid electrolyte. The present invention is based on such findings.

  Accordingly, an object of the present invention is to provide a solid oxide fuel cell stack comprising a ceramic interconnector having excellent conductivity and gas sealability.

And, the solid oxide fuel cell stack according to the present invention is
A support,
A plurality of power generation elements in which a fuel electrode, a solid electrolyte and an air electrode are at least sequentially stacked on the surface of the support;
At least an interconnector that electrically connects the air electrode of one of the plurality of power generation elements adjacent to the other power generation element and the fuel electrode of the other power generation element, and the plurality of power generation elements are connected in series A solid oxide fuel cell stack formed by
Under the interconnector provided under the air electrode of one power generating element, the solid electrolyte of one power generating element is provided to be joined to the interconnector, and on the fuel electrode of the other power generating element A solid electrolyte of the other power generation element is provided on the provided interconnector so as to be joined to the interconnector.

FIG. 1 is a front view of a horizontal stripe solid oxide fuel cell stack according to the present invention. It is a cross-sectional schematic diagram of the electric power generation element vicinity which comprises the solid oxide fuel cell stack by this invention. It is a cross-sectional schematic diagram which shows the preferable aspect containing two adjacent electric power generation elements which comprise the solid oxide fuel cell stack by this invention. It is a cross-sectional schematic diagram which shows another preferable aspect including two adjacent electric power generation elements which comprise the solid oxide fuel cell stack by this invention. The manufacturing method of the solid oxide fuel cell stack by this invention WHEREIN: The process of forming the interconnector by the side of a fuel electrode as L in a junction distance with a solid electrolyte is shown. The manufacturing method of the solid oxide fuel cell stack by this invention WHEREIN: The process of forming the interconnector by the side of an air electrode as L 'with a junction distance with a solid electrolyte is shown. It is a cross-sectional schematic diagram of the solid oxide fuel cell stack produced by the comparative example.

Definition The solid oxide fuel cell stack according to the present invention means that at least the fuel electrode, the solid electrolyte, and the air electrode are sequentially stacked, except that the structure of the interconnector and the solid electrolyte satisfy the requirements described later. In the industry, which comprises at least a plurality of power generation elements, and the interconnector electrically connecting the air electrode of one of the adjacent power generation elements and the fuel electrode of the other power generation element. It means the same one as classified or understood as a solid oxide fuel cell stack. In addition, the shape of the solid oxide fuel cell stack according to the present invention is not limited either, and may be, for example, a cylindrical shape, or a hollow plate having a plurality of gas flow paths formed therein.

  The solid oxide fuel cell stack according to the invention means a so-called horizontal stripe solid oxide fuel cell. In the present invention, the horizontal stripe type solid oxide fuel cell means a solid oxide fuel cell in which a plurality of power generation elements are formed on the surface of one support.

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

  The solid oxide fuel cell system using the solid oxide fuel cell stack according to the present invention is not limited to a specific one, and its manufacturing method and other materials constituting the same are all known. It can be used.

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

Support The solid oxide fuel cell stack according to the present invention has a support. 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, gas permeable, has mechanical strength for supporting the power generation element, and has electrical insulation. It can be used without As a material of the support, one or more selected from the group consisting of MgO, calcia stabilized zirconia (CSZ), and forsterite can be used. The preferred thickness of the support is 0.5 to 2 mm.

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

  According to a preferred embodiment of the 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 with good gas permeability. The support needs to maintain the structure of the power generating element. As a result, the support is thicker than the current collecting layer, which only requires conductivity. That is, the support tends to have a lower gas permeability than the current collecting layer. Also, comparing the diffusion rates of oxygen gas and hydrogen gas, hydrogen gas is generally several times faster than oxygen gas. From these facts, when the inner electrode is an air electrode, oxygen which is less likely to permeate through the support passes through the support, and therefore, the gas diffusion overvoltage is higher than when the inner electrode is a fuel electrode. growing. As a result, power generation performance tends to decrease. Therefore, the power generation performance is better when the inner electrode is a fuel electrode. 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 passing fuel gas, catalytic activity (electrode activity) for adsorbing hydrogen, conductivity, and oxide ion conductivity. The porosity of the anode may be less than that of the support.

As a material which comprises such a fuel electrode, a NiO / zirconium containing oxide, a NiO / cerium containing oxide etc. are mentioned, for example, It contains at least any one of these. Here, the NiO / zirconium-containing oxide means one in which NiO and a zirconium-containing oxide are uniformly mixed at a predetermined ratio. Further, the NiO / cerium-containing oxide means one in which NiO and a cerium-containing oxide are uniformly mixed at a predetermined ratio. Examples of the zirconium-containing oxide of the NiO / zirconium-containing oxide include, for example, zirconium-containing oxides doped with one or more of CaO, Y ₂ O ₃ , and Sc ₂ O ₃ . As a cerium-containing oxide of NiO / cerium-containing oxide, a 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 any one or more combinations selected from the group consisting of 0.05 ≦ y ≦ 0.50) and the like. In addition, since NiO is reduced in a fuel atmosphere to become Ni, 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 multiple layers. As an example where the inner electrode is a multi-layered fuel electrode, Ni / YSZ (yttria stabilized zirconia) is used on the support side, and Ni / GDC (Gd ₂ O ₃ -CeO ₂ ) (ie, on the solid electrolyte side). The anode catalyst layer is used. The preferred thickness of the fuel electrode is 10 to 200 μm. The preferred thickness of the anode catalyst layer is 0 to 30 μm.

Air electrode In the present invention, the air electrode has porosity for transmitting oxygen, catalytic activity (electrode activity) for adsorbing or ionizing oxygen, conductivity, and oxide ion conductivity. The porosity and conductivity of the cathode may be smaller than that of the current collecting layer.

As a material constituting such a cathode, 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 Lanthanum cobalt oxide such as フ ェ ラ イ ト 0.6), and lanthanum ferrite oxide (La _1−m Sr _m Co _1−n Fe _n O ₃ (where 0.05), which is a solid solution of LaSrFeO ₃ system and LaSrCoO ₃ system. <M <0.50, 0 <n <1)) and the like can be mentioned. The cathode may be a single layer or multiple layers. As an example of the case where the outer electrode is a multilayer air electrode, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ (ie, 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 preferred thickness of the air electrode is 0.2 to 30 μm.

Solid Electrolyte In the present invention, the solid electrolyte has oxide ion conductivity, gas sealability, and electrical insulation. As a material constituting such a solid electrolyte, a lanthanum gallate-based oxide, a stabilized zirconia in which one or more selected from Y, Ca, and Sc as a solid solution species are dissolved is mentioned. 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, δ is a value determined to satisfy the charge neutral condition) It is a system 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 multiple layers. When the solid electrolyte is a multilayer, for example, a reaction suppression layer can be provided between the fuel electrode and the solid electrolyte made 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. Moreover, the preferable thickness of a reaction suppression layer is 0-20 micrometers.

Current Collection Layer The solid oxide fuel cell stack according to the present invention comprises a current collection layer electrically connecting the outer electrode and the interconnector. The current collection layer has gas (oxygen) permeability and conductivity for smoothly circulating electrons generated from the air electrode. In the present invention, when the outer electrode is an air electrode, the current collection layer is formed of a conductive paste containing 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 addition, when the outer electrode is a fuel electrode, the current collection layer can be formed by baking a paste containing a metal oxide such as NiO or Ni or a metal which can be reduced to obtain conductivity. In addition, the current collection layer is preferably a porous or mesh structure or the like 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, in the present invention, the interconnector means a ceramic interconnector. The ceramic material, the general formula _{Sr x La y TiO 3-δ} ( here, x and y is a positive real number satisfying 0.8 ≦ x + y ≦ 1.0, and 0.01 <y ≦ 0.1 It is preferable that it consists of a perovskite type oxide represented by.). 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, the embodiment does not exclude an embodiment in which the interconnector includes other components, 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%. Preferably 90 mol% or more, more preferably 95 mol% or more is contained. Still more preferably, the interconnector consists only of the perovskite oxide. When the main component of the interconnector is an oxide having such a composition ratio, it is possible to simultaneously achieve sufficient compactness and conductivity. The interconnector is made conductive by replacing La with SrTiO ₃ as a base. According to a more preferable aspect of the present invention, the composition ratio of Sr and La satisfies the relationship of 0.8 ≦ x + y ≦ 0.9 and 0.01 <y ≦ 0.1. This can further enhance the compactness. Alternatively, Ti may be replaced by Nb. Thereby, the conductivity can be further enhanced. 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 contain, as an unavoidable component, an element diffused to the interconnector from other members, ie, the fuel electrode, the air electrode, the solid electrolyte, etc., for example, at the time of firing. 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 changes in accordance with 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.

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

(conductivity)
In the present invention, the conductivity of the interconnector is preferably 0.01 S / cm or more, more preferably 0.02 S / cm or more, in an air atmosphere at 700 ° C. Also, the higher the conductivity, the better, and there is no upper limit, but it is preferably 0.16 S / cm or less. As a result, 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 produced by uniaxially pressing the raw material powder of the interconnector at a load of 900 kgf / cm ² and firing at 1300 ° C. for 2 hours in the air. The electrical conductivity of the test piece is measured at 700 ° C. in the atmosphere according to the direct current four-terminal method based on the specification 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. Moreover, it is preferable that it is 0% or more. As a result, the gas sealability 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 fabricated solid oxide fuel cell stack is cut out so as to include an interconnector, and this interconnector is accelerated by a scanning electron microscope (for example, S-4100 manufactured by Hitachi, Ltd.) at an acceleration voltage of 15 kV and a secondary electron image at a magnification of 100 to It observes by 10000 times and obtains a SEM image. This SEM image is evaluated by image processing software (for example, Winroofver 6.5.1, manufactured by MITANI CORPORATION). As a result, a histogram is obtained in which the horizontal axis is luminance and the vertical axis is appearance frequency. In this histogram, a region where the luminance is lower than the average value of the minimum value and the maximum value of luminance is a low luminance region, and a region where the luminance is higher than the average value is a high luminance region. The low luminance region is determined to be pores, and the high luminance region other than the pores is determined to be an interconnector to perform binarization processing. Thereafter, the porosity can be obtained from the following equation.
Porosity (%) = Integral value of low luminance region ÷ Integral value of appearance frequency of whole × 100

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

<Method obtained by measurement by Archimedes method>
A raw material powder of an interconnector is uniaxially pressed at a load of 900 kgf / cm ² , and fired at 1300 ° C. for 2 hours in an air atmosphere to obtain a test piece. This test piece is measured by the Archimedes method based on the definition of JIS R 1634 to obtain the porosity.

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

The interconnector preferably contains 30 mol% or more and 50 mol% or less of strontium in the composition in terms of elements 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 an amount of 15 mol% or less, more preferably 2.5 mol% or more and 15 mol% or less, in terms of element excluding oxygen. That is, the solid electrolyte is represented by 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 It is preferable to include a lanthanum gallate oxide (LSGM) represented by ≦ c ≦ 0.15, where δ is a value determined so as to satisfy the charge neutral condition.

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

  FIG. 2 is a schematic view showing one embodiment of the solid oxide fuel cell stack 210 according to the present invention, showing 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. The solid oxide fuel cell stack 210 includes a support 201, (first / second) fuel electrode 202 (i.e., fuel electrode layer 202a and fuel electrode catalyst layer 202b), and (first / second) solid The 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 are included. Here, (first / second) means a single layer or two layers, and in the case of two layers, it has a first layer and a second layer.

  FIG. 3 is a schematic cross-sectional view showing a preferred embodiment including two adjacent power generation elements constituting the solid oxide fuel cell stack according to the present invention. In FIG. 3, a support 301, two power generation elements in which a fuel electrode 302, a solid electrolyte 304 and an air electrode 305 are sequentially laminated on the surface of the support 301, and two power generation elements adjacent to each other Solid oxide comprising at least an air electrode 305 of one power generation element and an interconnector 303 electrically connecting a fuel electrode 302 of the other power generation element, and two adjacent power generation elements are connected in series Type fuel cell stack.

  Under the interconnector 303 provided under the air electrode 305 of one power generation element, a solid electrolyte 304 of one power generation element is provided in contact with the interconnector 303. Furthermore, on the interconnector 303 provided on the fuel electrode 302 of the other power generation element, the solid electrolyte 304 of the other power generation element is provided in contact with the interconnector 303. As seen from FIG. 3 from the air electrode 305 side of one of the power generation elements, a dense solid electrolyte 304 is formed under the interconnector 303. As viewed from the fuel electrode 302 side of the other power generation element, a dense solid electrolyte 304 is formed on the interconnector 303. Therefore, the gas sealability of the interconnector 303 can be favorably maintained.

  FIG. 4 is a schematic cross-sectional view showing another preferred embodiment including two adjacent power generation elements constituting the solid oxide fuel cell stack according to the present invention. In FIG. 4, under the solid electrolyte 304 of one power generation element provided under the air pole 305 of one power generation element and under the interconnector 303, the solid electrolyte 304 of the one power generation element is joined to A connector 303 is further provided. Furthermore, on the solid electrolyte 304 of the other power generation element provided on the fuel electrode 302 of the other power generation element and on the interconnector 303, it is joined with the solid electrolyte 304 of the other power generation element to connect the interconnector 303. Are further provided. When FIG. 4 is viewed from the air electrode 305 side of one of the power generation elements, a dense solid electrolyte 304 is formed between the interconnectors 303. Further, when viewed from the fuel electrode 302 side of the other power generation element, a dense solid electrolyte 304 is formed between the interconnectors 303. Therefore, the gas sealability of the interconnector 303 can be favorably maintained. In FIG. 4, since the bonding distance between the interconnector 303 and the solid electrolyte 304 is longer than that in FIG. 3, a better gas sealability can be obtained.

  In the present invention, the longer the bonding distance between the solid electrolyte 304 of one power generating element and the solid electrolyte 304 of the other power generating element and the interconnector 303, the better. The bonding distance is at least twice the thickness of the solid electrolyte 304. Is preferred. Thereby, the adhesion between the solid electrolyte 304 and the interconnector 303 and the gas sealability of the interconnector 303 can be obtained. Here, the bonding distance between the solid electrolyte and the interconnector means the length of the portion where the solid electrolyte 304 and the interconnector 303 are bonded. That is, the length of the portion where solid electrolyte 304 and interconnector 303 of one adjacent power generation element are joined, and the length of the portion where solid electrolyte 304 and interconnector 303 of the other adjacent power generation element are joined Satoshi is added. Bonding means that there is no gap, and they are in contact and in close contact. The bonding distance and thickness can be determined by the following method. First, the manufactured solid oxide fuel cell stack is cut so as to include one adjacent power generation element and the other power generation element. Then, this cut surface is observed three times with a scanning electron microscope (SEM) at an arbitrary magnification of 1 to 100 times, and the maximum value and the minimum value of the obtained bonding distance are added and divided by 2 to obtain Can. The thickness can also be determined in the same manner.

According to a preferred embodiment of the present invention, in the solid oxide fuel cell stack, each of the solid electrolyte 304 of one power generation element and the solid electrolyte 304 of the other power generation element and the interconnector 303 both contain strontium, and each solid The amount of strontium contained in the interconnector 303 is larger than the amount of strontium contained in the electrolyte 304. When both the solid electrolyte 304 and the interconnector 303 contain strontium, diffusion of strontium occurs at the time of firing, and the compactness and adhesion become high. Specifically, Sr _x La _y TiO _{3 -δ} containing solid electrolyte 304 and more Sr than that, and having high reactivity with solid electrolyte 304 (where x and y satisfy 0.8 ≦ x + y ≦ 1. 0) and the positive inter-connector 303 satisfying 0.01 <y ≦ 0.1 is joined, so that both react at the time of firing, and between the solid electrolyte 304 and the interconnector 303. Adhesion can be improved. Preferably, solid electrolyte 304 is a lanthanum gallate oxide doped with Sr. As a result, the gas sealability between the solid electrolyte 304 and the interconnector 303 can be improved.

Method of Manufacturing Solid Oxide Fuel Cell Stack The method of manufacturing a solid oxide fuel cell stack according to the present invention is not limited to a specific one. The solid oxide fuel cell stack according to the present invention is manufactured, for example, as follows. In the following description, the case where the inner electrode is 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 make a clay. At this time, as an optional component, a dispersant, a binder, an antifoamer or a pore forming agent, or a combination thereof may be added. A sheet forming method, a press forming method, an extrusion forming method or the like is used for forming the clay, but in the case of forming a support having a gas flow path formed therein, the extrusion forming method is preferably used. In the case of forming a multilayer support, a method of forming the upper layer by coating or printing can also be used in addition to multilayer extrusion in which the multilayer 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, a transfer method and the like. Examples of the printing method include a screen printing method and an inkjet printing method. Then, the prepared clay is shaped 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 the porous support, and then the calcined body of the support is calcined alone. The support may be obtained, or may be fired at least with the fuel electrode or the like to obtain the support. The firing temperature is preferably 1100 ° C. or more and less than 1400 ° C.

  The interconnector can be produced, for example, as follows. First, a raw material powder is produced. The raw material powder can be produced, for example, by a solid phase method. That is, the powder of the metal oxide as the raw material is weighed to obtain a desired composition ratio, mixed in the solution and then the solvent is removed, and the powder obtained is calcined, for example, at 1150 ° C., and pulverized to obtain the raw material. Make a powder. A solvent (water, alcohol, etc.) and, if necessary, a forming aid such as a dispersing agent or a binder are added to the raw material powder to prepare a slurry or paste. The slurry or paste is coated and dried to form a dried film obtained by drying (80 ° C. to 1100 ° C., preferably 300 ° C. to 1100 ° C.), and then firing (1100 ° C. to less than 1400 ° C., preferably 1250) The interconnector can be obtained by setting the temperature in the range of from 0.degree. The coating can be performed by the same method as described above. Alternatively, each dry film may be formed in advance as a transfer sheet, and may be provided by sticking a transfer film to a laminate.

  The fuel electrode, the solid electrolyte and the air electrode can be produced, for example, as follows. A solvent (water, alcohol, etc.) and, if necessary, a forming aid such as a dispersing agent or a binder are added to each raw material powder to prepare a slurry or paste. The slurry or paste is coated and dried to form a dried film obtained by drying (80 ° C. to 1100 ° C., preferably 300 ° C. to 1100 ° C.), and then firing (1100 ° C. to less than 1400 ° C., preferably 1250) The fuel electrode, the solid electrolyte, and the air electrode can be obtained by setting the temperature to °° C or more and less than 1400 ° C. The coating can be performed by the same method as described above. Alternatively, each dry film may be formed in advance as a transfer sheet, and may be provided by sticking a transfer film to a laminate.

  According to a preferred embodiment of the production method of the present invention, the firing is preferably performed each time each layer is formed. That is, according to this aspect, after forming a dry film of the fuel electrode on the surface of the support or the calcined body thereof, baking is performed to form the fuel electrode, and a dry film of the solid electrolyte is formed and then baked. Of forming a solid electrolyte, forming a dry film of the interconnector, baking it to form the interconnector, and forming a dry film of the air electrode and baking it to form the air electrode It contains. Also, the formation of the current collection layer is performed 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 dried film of a fuel electrode is formed on the surface of the support or the calcined body, and a dried film of an interconnector Forming a dry film of the solid electrolyte, then co-firing (at least 1250 ° C. and less than 1400 ° C.) the laminated molded product comprising the support, the fuel electrode, the interconnector and the dry film of the solid electrolyte, and then drying the air electrode Forming a coating and baking the whole.

  In the above embodiment of the manufacturing method according to the present invention, co-firing is performed in which the laminated molded body made of these is formed at one time after forming dry films of the fuel electrode, the interconnector and the solid electrolyte on the support or the calcined body thereof. It is carried out. In this embodiment, the firing is preferably performed in an oxidizing atmosphere so that the solid electrolyte or the interconnector is not modified by the diffusion of the dopant. More preferably, firing is performed using a mixed gas of air and oxygen in an atmosphere having an oxygen concentration of 20% by mass to 30% by mass.

  In the above aspect of the production method according to the present invention, it is preferable that at least the interconnector and the solid electrolyte be obtained by co-firing (1250 ° C. or more and less than 1400 ° C.). At the time of firing, the element contained in the interconnector and the element contained in the solid electrolyte mutually diffuse. That is, when the element contained in the interconnector and the element contained in the solid electrolyte are the same, they mutually diffuse. Such elements include strontium and lanthanum. Thereby, the adhesiveness of an interconnector and a solid electrolyte can be improved.

  In the manufacturing method according to the present invention, the interconnector can be appropriately formed in plural times according to the structure of the interconnector. In this case, the dry film of each interconnector may be fired to obtain the interconnector, or the dry film may be co-fired integrally to obtain the interconnector. For example, as shown in FIGS. 5 and 6, when the interconnector is formed separately on the interconnector on the fuel electrode side and on the air electrode side, the following method can be used. The fuel electrode side interconnector refers to an interconnect formed on the fuel electrode of the other adjacent power generation element and provided to be joined to the solid electrolyte of the other adjacent power generation element. Further, the interconnector on the air electrode side refers to an interconnector provided below the air electrode of one of the adjacent power generation elements so as to be joined to the solid electrolyte of the adjacent one power generation element. Specifically, a step of forming a dry film of the interconnector on the fuel electrode side on the surface of the fuel electrode, a step of forming a dry film of the solid electrolyte, and a dry film of the interconnector on the air electrode side The process and the dry film of the interconnector on both the fuel electrode side and the air electrode side and the dry film of the solid electrolyte are co-fired together to form an interconnector and a solid electrolyte.

  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 high purity forsterite (Mg ₂ SiO ₄ containing 0.05% by mass of CaO) raw material 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 solvent (water), 8 parts by weight of binder (methyl cellulose), 0.5 parts by weight of lubricant, and 15 parts by weight of pore forming agent (acrylic resin particles having an average particle diameter of 5 μm) The mixture was mixed by a high speed mixer, and was kneaded by a kneader (kneader), and deaerated by a vacuum soil kneading apparatus to prepare a clay for extrusion molding. Here, the average particle diameter is a value measured in accordance with JIS R 1629 and indicated by 50% diameter (the same applies hereinafter).

(Preparation of slurry for fuel electrode layer)
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 size of the obtained dry powder was adjusted to be 0.7 μm. 150 parts by weight of this powder, 100 parts by weight of solvent (carbitol), 6 parts by weight of binder (soluble polymer), 2 parts by weight of dispersant (nonionic surfactant), and antifoam (organic polymer system) 2 After mixing with parts by weight, the slurry was prepared by sufficiently stirring.

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

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

(Preparation of slurry for solid electrolyte)
An LSGM powder having a composition of La _0.9 Sr _0.1 Ga _0.8 Mg _0.2 O ₃ was used as a solid electrolyte material. 50 parts by weight of this LSGM powder, 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 antifoamer (organic polymer system) After mixing with 1 part by weight, the slurry was prepared by sufficiently stirring.

(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, 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 an antifoamer (organic polymer system) 1 After mixing with parts by weight, the slurry was prepared by sufficiently stirring.

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

(Preparation of slurry for interconnector)
A powder of a composition of Sr _0.90 La _0.04 TiO _3-δ was used as a material of the interconnector. 40 parts by weight of this powder, 100 parts by weight of a solvent (carbitol), 4 parts by weight of a binder (soluble polymer), 1 part by weight of a dispersing agent (nonionic surfactant), and an antifoamer (organic polymer system) 1 After mixing with parts by weight, the slurry was prepared by sufficiently stirring.

(Fabrication of solid oxide fuel cell stack)
A solid oxide fuel cell stack was produced by the following method using the clay obtained as described above and each slurry. Further, the interconnector is formed on the fuel electrode of the other adjacent power generation element, and the interconnect on the fuel electrode side provided to be joined to the solid electrolyte of the other adjacent power generation element, and the adjacent power generation The element was formed under the air electrode of the element in two steps with the air electrode side interconnector provided to be in contact with the solid electrolyte of one of the adjacent power generation elements.

  A cylindrical molded body was produced from the porous support clay A by extrusion. After drying at room temperature, the support was heat-treated at 1100 ° C. for 2 hours to prepare a calcined support. A laminated molded body in which a fuel electrode, a fuel electrode catalyst layer, an interconnector on the fuel electrode side, a reaction suppression layer, and a solid electrolyte are formed in this order on the surface of a support by a slurry coating method, dried and then dried. I got The laminate was co-fired at 1300 ° C. for 2 hours. As shown in FIG. 5, the bonding distance (L) between the fuel electrode side interconnector and the solid electrolyte was formed to be 200 μm to 220 μm.

  Next, the interconnector on the air electrode side was formed into a film by a slurry coating method, and fired at 1250 ° C. for 2 hours. As shown in FIG. 6, the bonding distance (L ′) between the air electrode side interconnector and the solid electrolyte was formed to be 200 μm to 220 μm.

  Next, an air electrode was formed on the surface of the solid electrolyte and fired at 1100 ° C. for 2 hours to produce a solid oxide fuel cell stack. The support had an outer diameter of 10 mm and a thickness of 1 mm as measured after co-firing. The prepared solid oxide fuel cell stack had a fuel electrode thickness of 100 μm, an anode catalyst layer thickness of 10 μm, a reaction suppression layer thickness of 10 μm, and a solid electrolyte thickness of 30 μm. The thickness of the interconnector was 15 μm, and the thickness of the air electrode was 20 μm. Further, the outer diameter of the support was measured with a micrometer at a portion where no film was formed. The thickness of each member is obtained by cutting the prepared cell stack cell and observing the cross section three times with a scanning electron microscope (SEM) at an arbitrary magnification of 30 to 2000 times, and the maximum value and the minimum value of the obtained thickness Add the value and divide by two. The cut portion was at the center of the portion where the air electrode was formed. Moreover, each following evaluation was performed about the obtained solid oxide fuel cell stack. The results are shown in Table 1.

Example 2
The solid oxide fuel cell stack is prepared in the same manner as in Example 1 except that both the fuel electrode side and air electrode side interconnectors are formed so that the bonding distance with the solid electrolyte is 40 μm to 60 μm. Obtained. Each evaluation below was performed about the obtained solid oxide fuel cell stack. The results are shown in Table 1.

Comparative Example 1
For example, as shown in FIG. 7, after forming the inter-connector on the fuel electrode side without forming the film on the fuel electrode side and co-firing the laminated molded body in Example 1, the inter-connector on the air electrode side is formed and formed. The same procedure was followed to obtain a solid oxide fuel cell stack. The bonding distance between the interconnector and the solid electrolyte was formed to be 5 to 10 μm. Each evaluation below was performed about the obtained solid oxide fuel cell stack. The results are shown in Table 1.

Comparative example 2
For example, as shown in FIG. 7, after forming the inter-connector on the fuel electrode side without forming the film on the fuel electrode side and co-firing the laminated molded body in Example 1, the inter-connector on the air electrode side is formed and formed. The same procedure was followed to obtain a solid oxide fuel cell stack. The bonding distance between the interconnector and the solid electrolyte was formed to be 20 to 30 μm. Each evaluation below was performed about the obtained solid oxide fuel cell stack. The results are shown in Table 1.

Evaluation (measurement of OCV)
A power generation test was performed using the obtained solid oxide fuel cell stack. The current collection on the fuel electrode side was performed by bonding a current collection metal to the exposed portion of the fuel electrode with silver paste and baking it. The current collection on the air electrode side was performed by bonding a current collection metal to the exposed part of the adjacent fuel electrode with silver paste and baking it.

A power generation test was conducted under the following power generation conditions, and an electromotive force at 0 hours after operation; OCV (V) was measured. The results are shown in Table 1.
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

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

10: power generation element, 210: solid oxide fuel cell stack, 301: support, 302: fuel electrode, 303: interconnector, 304: solid electrolyte, 305: air electrode

Claims (6)

A support,
A plurality of power generation elements in which a fuel electrode, a solid electrolyte and an air electrode are at least sequentially stacked on the surface of the support;
At least an interconnector that electrically connects the air electrode of one of the plurality of power generation elements adjacent to the other power generation element and the fuel electrode of the other power generation element, and the plurality of power generation elements are connected in series A solid oxide fuel cell stack formed by
Under the interconnector provided under the air electrode of the one power generation element, the solid electrolyte of one power generation element is provided to be joined to the interconnector, and the fuel electrode of the other power generation element A solid oxide fuel cell stack, wherein a solid electrolyte of the other power generation element is provided on the interconnector provided thereon so as to be joined to the interconnector.   The solid oxide type according to claim 1, wherein a bonding distance between each of the solid electrolyte of the one power generation element and the solid electrolyte of the other power generation element and the interconnector is twice or more the thickness of the solid electrolyte. Fuel cell stack.   The interconnector is further coupled to the solid electrolyte of the one power generation element under the air electrode of the one power generation element and the solid electrolyte of the one power generation element provided under the interconnector. The solid oxide fuel cell stack according to claim 1 or 2, which is provided.   Further, on the solid electrolyte of the other power generation element provided on the fuel electrode of the other power generation element and on the interconnector, the interconnector is further joined to be bonded to the solid electrolyte of the other power generation element The solid oxide fuel cell stack according to any one of claims 1 to 3, which is provided.   The solid electrolyte of the one power generation element, the solid electrolyte of the other power generation element, and the interconnector contain strontium, and the amount of strontium contained in the interconnector is more than the amount of strontium contained in each solid electrolyte. The solid oxide fuel cell stack according to any one of claims 1 to 4, wherein 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 5, wherein the solid oxide fuel cell stack comprises a perovskite oxide represented by

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