JP5732180B1 - Fuel cell - Google Patents

Abstract

The present invention provides a fuel cell having a support substrate having a gas flow path formed therein, in which “a crack from the inner wall of the gas flow path toward the surface of the support substrate” is difficult to be formed. In this fuel cell, a power generating element portion A in which a fuel electrode 20, a solid electrolyte 40, and an air electrode 60 are sequentially laminated is formed on the surface of a support substrate 10 in which a gas flow path 11 is formed. The The porosity of the support substrate is 15 to 55%. As the pores inside the support substrate 10, there are a plurality of first pores having a pore diameter of less than 20 μm and one or a plurality of second pores having a pore diameter of 20 μm or more. When a region having a distance from the inner wall of the gas flow path 11 of the support substrate 10 of 100 μm or less is defined as a “flow path vicinity area”, the porosity of all pores including the first and second pores in the “flow path vicinity area” (Sa) is 25 to 50%, and the porosity (Sb1) of the second pores in the “channel vicinity region” is 6.5% or less. [Selection] Figure 2

Description

  The present invention relates to a fuel cell.

  Conventionally, “a support substrate having a gas flow path formed therein” and “a power generation element portion that is provided on the support substrate and in which a fuel electrode, a solid electrolyte, and an air electrode are stacked in this order” Are known (for example, see Patent Document 1).

  In the fuel cell described in the above document, the fuel gas flowing through the gas flow path formed inside the support substrate moves to the fuel electrode through the pores inside the support substrate, and is consumed for power generation at the fuel electrode. Is done. That is, the support substrate is made of a porous material.

Japanese Patent No. 4888733

  By the way, when the above-described fuel cell is operated under a severe environment in terms of thermal stress, a “crack toward the surface of the support substrate starting from the inner wall of the gas flow path of the support substrate” may occur ( (See the arrow in FIG. 15 described later). This is considered due to the fact that stress tends to concentrate on the inner wall of the gas flow path.

  The present inventor conducted research and experiments every day in order to deal with this problem. As a result, the present inventor has found an effective condition for making the above-described crack difficult to occur.

  As described above, the present invention is a fuel cell having a support substrate in which a gas flow path is formed, and “a crack toward the surface of the support substrate starting from the inner wall of the gas flow path” is unlikely to occur. The purpose is to provide.

  In the fuel cell according to the present invention, the support substrate including the same support substrate as described above and the same power generation element unit as described above may be flat or cylindrical. The porosity of the entire support substrate is 15 to 55%.

  The fuel cell according to the present invention is characterized in that, as the pores inside the support substrate, a plurality of first pores having a pore diameter of less than 20 μm, and one or a plurality of second pores having a pore diameter of 20 μm or more, And the porosity (Sa) of all the pores composed of the first and second pores in a region where the distance from the inner wall of the gas channel in the support substrate is 100 μm or less (region near the channel) is 25-50. And the porosity (Sb1) of the second pores in the vicinity of the flow path is 6.5% or less.

  Usually, in order to produce a porous support substrate (fired body), a method of dispersing and mixing a pore former (powder) in a support body molded body (before firing) is employed. At the time of firing, the pore former is burned away inside the molded body, whereby a large number of pores are formed inside the support substrate (fired body) (that is, the support substrate becomes porous).

  Usually, the particle diameter of the pore former is on the order of several μm. Therefore, when the molded body is fired in a state where the particles of the pore former are surely dispersed in the molded body without agglomeration, only the first pores (diameter of less than 20 μm) are formed inside the support substrate. obtain. However, it is actually very difficult to disperse particles of such a very small pore former in the molded body without agglomeration. Therefore, due to the aggregation of the pore former, not only the first pores but also the second pores (diameter of 20 μm or more) are inevitably formed in the support substrate. For this reason, not only the first pores but also the second pores may exist in the vicinity of the flow path.

  The inventor paid attention to the vicinity of the flow channel, which is a region close to the “inner wall of the gas flow channel”, which is the starting point of the crack. Then, the present inventor said that “the porosity (Sa) of all the pores is 25 to 50% and the porosity (Sb1) of the second pores is 6.5% or less with respect to the flow path vicinity region”. (Or 0.025 to 6.5%) ", the above-described cracking occurs when the above-described fuel cell is operated under a severe environment in terms of thermal stress as compared with the case where it is not. It was found that it is difficult to occur (details will be described later).

  In the fuel cell according to the present invention, for the region near the flow path, “the porosity (Sb2) of the second pore existing so as to be exposed on the inner wall of the gas flow path is 0.3% or less (or 0 0.001 to 0.3%) ".

  The present inventor stated, “The porosity (Sa) of all the pores is 25 to 50%, and the porosity (Sb1) of the second pores is 6.5% or less (or 0.025 to 6.5. 5%) ", the porosity (Sb2) of the second pores present so as to be exposed on the inner wall of the gas flow path is 0.3% or less (or 0.001-0.3%). It has also been found that the above-mentioned cracks are more difficult to occur (details will be described later).

1 is a perspective view showing a fuel cell according to an embodiment of the present invention. FIG. 2 is a cross-sectional view corresponding to line 2-2 of the fuel cell shown in FIG. It is the top view which showed the state of the fuel electrode and interconnector which were embed | buried under the recessed part of the support substrate shown in FIG. It is a figure for demonstrating the operation state of the fuel cell shown in FIG. It is a figure for demonstrating the flow of the electric current in the operating state of the fuel cell shown in FIG. It is a perspective view which shows the support substrate shown in FIG. FIG. 3 is a cross-sectional view corresponding to FIG. 2 in a first stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 3 is a cross-sectional view corresponding to FIG. 2 in a second stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 3 is a cross-sectional view corresponding to FIG. 2 in a third stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 4 is a cross-sectional view corresponding to FIG. 2 in a fourth stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 6 is a cross-sectional view corresponding to FIG. 2 in a fifth stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 7 is a cross-sectional view corresponding to FIG. 2 in a sixth stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 8 is a cross-sectional view corresponding to FIG. 2 in a seventh stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 7 is a cross-sectional view corresponding to FIG. 2 in an eighth stage in the manufacturing process of the fuel cell shown in FIG. 1. It is a figure for demonstrating the mode of the crack which may generate | occur | produce in a support substrate. It is a figure for demonstrating a mode that a 2nd pore exists in the flow path vicinity area | region in a support substrate. It is a figure for demonstrating the flow-path vicinity area | region in a support substrate. It is a figure corresponding to FIG. 2 of the other modification of the fuel cell which concerns on this invention. FIG. 5 is a cutaway perspective view of a solid oxide fuel cell according to another embodiment of the present invention. It is the schematic diagram which showed a mode that the cell and the separator were laminated | stacked alternately about the fuel cell shown in FIG. It is the figure which expanded and showed one cell and its periphery about the fuel cell shown in FIG. It is a figure for demonstrating the mode of the crack which may generate | occur | produce in a fuel electrode. It is a figure for demonstrating a mode that a 2nd pore exists in a fuel electrode. It is a figure for demonstrating the flow-path vicinity area | region in a fuel electrode.

(Constitution)
FIG. 1 shows a structure of a solid oxide fuel cell (SOFC) according to an embodiment of the present invention. This SOFC is electrically connected in series to each of the upper and lower surfaces (main surfaces (planes) on both sides parallel to each other) of the flat support substrate 10 having a longitudinal direction (x-axis direction) (this example). In this case, the four power generation element portions A having the same shape are arranged at predetermined intervals in the longitudinal direction, so-called “horizontal stripe type”.

  The shape of the entire SOFC as viewed from above is, for example, a rectangle whose length in the longitudinal direction is 50 to 500 mm and whose length in the width direction (y-axis direction) perpendicular to the longitudinal direction is 10 to 100 mm. The total thickness of this SOFC is 1-5 mm. The entire SOFC has a vertically symmetrical shape with respect to a plane passing through the center in the thickness direction and parallel to the main surface of the support substrate 10. Hereinafter, in addition to FIG. 1, the details of the SOFC will be described with reference to FIG. 2, which is a partial cross-sectional view of the SOFC corresponding to line 2-2 shown in FIG. FIG. 2 is a partial cross-sectional view showing a configuration (part of) each of a typical pair of adjacent power generation element portions A and A and a configuration between the power generation element portions A and A. The configuration between the other power generation element portions A and A in other sets is the same as the configuration shown in FIG.

  The support substrate 10 is a flat plate-like fired body made of a porous material having no electronic conductivity. As shown in FIG. 6 to be described later, a plurality of (six in this example) fuel gas passages 11 (through holes) extending in the longitudinal direction are provided in the support substrate 10 at predetermined intervals in the width direction. Is formed. In this example, the recesses 12 are respectively formed at positions corresponding to the plurality of power generation element portions A on the upper and lower surfaces of the support substrate 10. Each recess 12 has a bottom wall made of the material of the support substrate 10 and side walls closed in the circumferential direction made of the material of the support substrate 10 (two side walls along the longitudinal direction and two side walls along the width direction). ) And a rectangular parallelepiped depression defined by Each recess 12 has a length (dimension in the x-axis direction) of 5 to 50 mm, a width (dimension in the y-axis direction) of 2 to 95 mm, and a depth (dimension in the z-axis direction) of 0.03 to 1. .5 mm.

The support substrate 10 includes MgO (magnesium oxide) and a first oxide ceramic. The support substrate 10 contains the first oxide ceramic because the thermal expansion coefficient of MgO alone (about 14 ppm / K) is compared with the thermal expansion coefficient of normal electrode material (10-13 ppm / K). This is because the equivalent thermal expansion coefficient of the support substrate 10 is brought close to the thermal expansion coefficient of a normal electrode material due to the large size. Therefore, as the first oxide ceramic, those having a smaller thermal expansion coefficient than that of a normal electrode material (10 to 13 ppm / K) are preferable. Specifically, as the “first oxide ceramic”, Y ₂ O ₃ (yttria), YSZ (8YSZ) (yttria stabilized zirconia), CSZ (calcia stabilized zirconia) and the like are suitable. The support substrate 10 may contain “transition metal oxide or transition metal”. As the “transition metal oxide or transition metal”, NiO (nickel oxide) or Ni (nickel) is suitable. The transition metal can function as a catalyst for promoting a reforming reaction of the fuel gas (hydrocarbon-based gas reforming catalyst).

  As described above, since the support substrate 10 contains “transition metal oxide or transition metal”, the gas containing the residual gas component before the reforming is supplied to the fuel through the numerous pores inside the porous support substrate 10. In the process of being supplied from the gas flow path 11 to the fuel electrode, the catalytic action can promote the reforming of the residual gas component before the reforming. In addition, when the support substrate 10 contains insulating oxide ceramics, the insulation of the support substrate 10 can be ensured. As a result, insulation between adjacent fuel electrodes can be ensured.

  The thickness of the support substrate 10 is 1 to 5 mm. The porosity of the entire support substrate 10 is 15 to 55%. In addition, the value of porosity is a value after the reduction process described later (the same applies to other porosity values). The porosity was measured by polishing the cross section of the resin-embedded sample (after the reduction treatment) and analyzing the image (secondary electron image) of the cross section by SEM (scanning electron microscope). . Specifically, the ratio of the “total area of portions corresponding to the resin-filled region on the cross section” to the “total area of the cross section” was defined as the “porosity” of the cross section. The acceleration voltage of SEM was set to 5 kV, and the magnification of SEM was set to 5000 times or 7500 times. The measurement of the porosity was performed on arbitrary 10 cross-sections of the sample, and the average value thereof was adopted as the porosity value.

  Hereinafter, only the configuration on the upper surface side of the support substrate 10 will be described in consideration of the fact that the shape of the structure is vertically symmetrical. The same applies to the configuration of the lower surface side of the support substrate 10.

  As shown in FIGS. 2 and 3, the entire fuel electrode current collector 21 is embedded (filled) in each recess 12 formed in the upper surface (upper main surface) of the support substrate 10. Therefore, each fuel electrode current collector 21 has a rectangular parallelepiped shape.

  A recess 21 a is formed on the upper surface (outer surface) of each fuel electrode current collector 21. Each recess 21a includes a bottom wall made of the material of the fuel electrode current collector 21 and a side wall (two side walls along the longitudinal direction) closed in the circumferential direction made of the material of the fuel electrode current collector 21 over the entire circumference. And two side walls along the width direction).

  The entire anode active portion 22 is embedded (filled) in each recess 21a. Accordingly, each fuel electrode active portion 22 has a rectangular parallelepiped shape. A fuel electrode 20 is configured by the fuel electrode current collector 21 and the fuel electrode active unit 22. The fuel electrode 20 (fuel electrode current collector 21 + fuel electrode active part 22) is a fired body made of a porous material having electron conductivity. The four side surfaces and the bottom surface of each anode active portion 22 are in contact with the anode current collecting portion 21 in the recess 21a.

  A recess 21b is formed in a portion of the upper surface (outer surface) of each fuel electrode current collector 21 excluding the recess 21a. Each recess 21b includes a bottom wall made of a material of the fuel electrode current collector 21 and a circumferentially closed side wall made of the material of the fuel electrode current collector 21 (two side walls along the longitudinal direction). And two side walls along the width direction).

  An interconnector 30 is embedded (filled) in each recess 21b. Accordingly, each interconnector 30 has a rectangular parallelepiped shape. The interconnector 30 is a fired body made of a dense material having electronic conductivity. The four side surfaces and the bottom surface of each interconnector 30 are in contact with the fuel electrode current collector 21 in the recess 21b.

  The upper surface (outer surface) of the fuel electrode 20 (the fuel electrode current collector 21 and the fuel electrode active unit 22), the upper surface (outer surface) of the interconnector 30, and the main surface of the support substrate 10 form one plane (recessed portion). The same plane as the main surface of the support substrate 10 when 12 is not formed) is formed. That is, no step is formed between the upper surface of the fuel electrode 20, the upper surface of the interconnector 30, and the main surface of the support substrate 10.

The fuel electrode current collector 21 includes NiO (nickel oxide) and a second oxide ceramic. The anode current collector 21 contains the second oxide ceramic because the thermal expansion coefficient of NiO alone (about 14 ppm / K) is the thermal expansion coefficient of normal electrode materials (10-13 ppm / K). This is because the equivalent thermal expansion coefficient of the fuel electrode current collector 21 is brought close to the thermal expansion coefficient of a normal electrode material due to the fact that it is larger than. Therefore, as the second oxide ceramic, those having a smaller thermal expansion coefficient than that of a normal electrode material (10 to 13 ppm / K) are preferable. Specifically, as the “second oxide ceramic”, Y ₂ O ₃ (yttria), YSZ (8YSZ) (yttria stabilized zirconia), CSZ (calcia stabilized zirconia) and the like are suitable. The thickness of the fuel electrode current collector 21 (that is, the depth of the recess 12) is 50 to 500 μm. The porosity of the fuel electrode current collector 21 is 15 to 55%.

  The anode active part 22 includes a substance having electron conductivity and a substance having oxygen ion conductivity. As the “substance having electron conductivity”, NiO (nickel oxide) is suitable. As the “substance having oxygen ion conductivity”, YSZ (8YSZ) (yttria stabilized zirconia), GDC (gadolinium doped ceria) and the like are suitable. The thickness of the fuel electrode active part 22 is 5 to 30 μm. The porosity of the anode active portion 22 is 15 to 55%.

  Note that NiO in the fuel electrode current collector 21 and in the fuel electrode active part 22 is changed to Ni by a reduction process, which will be described later, to acquire electron conductivity. The “volume ratio of the substance having oxygen ion conductivity with respect to the entire volume excluding the pore portion” in the anode active portion 22 is “having oxygen ion conductivity with respect to the entire volume excluding the pore portion” in the anode current collecting portion 21. It is larger than the “volume ratio of the substance”.

The interconnector 30 can be composed of, for example, LaCrO ₃ (lanthanum chromite). Alternatively, it may be composed of (Sr, La) TiO ₃ (strontium titanate). The thickness of the interconnector 30 is 10 to 100 μm.

  The entire surface excluding the central portion in the longitudinal direction of each portion where the plurality of interconnectors 30 are formed on the outer peripheral surface extending in the longitudinal direction of the support substrate 10 in a state where the fuel electrode 20 and the interconnector 30 are embedded in the respective recesses 12. Is covered with a solid electrolyte membrane 40. The solid electrolyte membrane 40 is a fired body made of a dense material having ion conductivity. The solid electrolyte membrane 40 can be made of, for example, YSZ (8YSZ) (yttria stabilized zirconia). Or you may comprise from LSGM (lantern gallate). The thickness of the solid electrolyte membrane 40 is 3 to 50 μm.

  That is, the entire outer peripheral surface extending in the longitudinal direction of the support substrate 10 in a state where the fuel electrode 20 is embedded in each recess 12 is covered with a dense layer composed of the interconnector 30 and the solid electrolyte membrane 40. This dense layer exhibits a gas sealing function that prevents mixing of the fuel gas flowing in the space inside the dense layer and the air flowing in the space outside the dense layer. In the present application, “dense” means “high density so that gas does not pass”, and specifically means “porosity is 10% or less”.

  As shown in FIG. 2, in this example, the solid electrolyte membrane 40 covers the upper surface of the fuel electrode 20, both end portions in the longitudinal direction on the upper surface of the interconnector 30, and the main surface of the support substrate 10. Here, as described above, no step is formed between the upper surface of the fuel electrode 20, the upper surface of the interconnector 30, and the main surface of the support substrate 10. Therefore, the solid electrolyte membrane 40 is flattened. As a result, compared with the case where a step is formed in the solid electrolyte membrane 40, the generation of cracks in the solid electrolyte membrane 40 due to stress concentration can be suppressed, and the gas sealing function of the solid electrolyte membrane 40 is reduced. Can be suppressed.

  An air electrode 60 is formed on the upper surface of a portion in contact with each fuel electrode active part 22 in the solid electrolyte membrane 40 via a reaction preventing film 50. The reaction preventing film 50 is a fired body made of a dense material, and the air electrode 60 is a fired body made of a porous material having electron conductivity. The shape of the reaction preventing film 50 and the air electrode 60 viewed from above is substantially the same rectangle as the fuel electrode active part 22.

The reaction preventing film 50 can be made of, for example, GDC = (Ce, Gd) O ₂ (gadolinium-doped ceria). The thickness of the reaction preventing film 50 is 3 to 50 μm. The air electrode 60 can be made of, for example, LSCF = (La, Sr) (Co, Fe) O ₃ (lanthanum strontium cobalt ferrite). Alternatively, from LSF = (La, Sr) FeO ₃ (lanthanum strontium ferrite), LNF = La (Ni, Fe) O ₃ (lanthanum nickel ferrite), LSC = (La, Sr) CoO ₃ (lanthanum strontium cobaltite), etc. It may be configured. Further, the air electrode 60 may be configured by two layers of a first layer (inner layer) made of LSCF and a second layer (outer layer) made of LSC. The thickness of the air electrode 60 is 10 to 100 μm.

  The reaction preventing film 50 is interposed because the YSZ in the solid electrolyte film 40 and the Sr in the air electrode 60 react with each other in the SOFC during the production or operation of the SOFC, and the solid electrolyte film 40 and the air electrode. This is in order to suppress the occurrence of a phenomenon in which a reaction layer having a large electric resistance is formed at the boundary portion with 60.

  Here, the laminated body formed by laminating the fuel electrode 20, the solid electrolyte membrane 40, the reaction preventing membrane 50, and the air electrode 60 corresponds to the “power generation element portion A” (see FIG. 2). In other words, a plurality (four in this example) of power generating element portions A are arranged on the upper surface of the support substrate 10 at a predetermined interval in the longitudinal direction.

  For each pair of adjacent power generation element portions A and A, the air electrode 60 of one power generation element portion A (on the left side in FIG. 2) and the interconnector of the other power generation element portion A (on the right side in FIG. 2). The air electrode current collecting film 70 is formed on the upper surfaces of the air electrode 60, the solid electrolyte film 40, and the interconnector 30. The air electrode current collector film 70 is a fired body made of a porous material having electron conductivity. The shape of the air electrode current collector film 70 as viewed from above is a rectangle.

The air electrode current collector film 70 can be made of, for example, LSCF = (La, Sr) (Co, Fe) O ₃ (lanthanum strontium cobalt ferrite). Alternatively, LSC = (La, Sr) CoO ₃ (lanthanum strontium cobaltite) may be used. Or you may comprise from Ag (silver) and Ag-Pd (silver palladium alloy). The thickness of the air electrode current collector film 70 is 50 to 500 μm.

  By forming each air electrode current collecting film 70 in this way, for each pair of adjacent power generation element portions A and A, the air electrode 60 of one power generation element portion A (on the left side in FIG. 2), The other fuel electrode 20 (particularly, the fuel electrode current collector 21) of the power generating element part A (on the right side in FIG. 2) passes through the “air electrode current collector film 70 and interconnector 30” having electronic conductivity. Are electrically connected. As a result, a plurality (four in this example) of power generation element portions A arranged on the upper surface of the support substrate 10 are electrically connected in series. Here, the “air electrode current collector film 70 and the interconnector 30” having electronic conductivity correspond to “electrical connection portions”.

  The interconnector 30 corresponds to the “first portion made of a dense material” in the “electrical connection portion” and has a porosity of 10% or less. The air electrode current collecting film 70 corresponds to the “second portion made of a porous material” in the “electrical connection portion”, and has a porosity of 20 to 60%.

As described above, the reformed fuel gas (hydrogen gas or the like) flows through the fuel gas flow path 11 of the support substrate 10 as shown in FIG. By exposing the upper and lower surfaces (in particular, each air electrode current collecting film 70) to “gas containing oxygen” (air or the like) (or flowing a gas containing oxygen along the upper and lower surfaces of the support substrate 10), a solid is obtained. An electromotive force is generated by an oxygen partial pressure difference generated between both side surfaces of the electrolyte membrane 40. Furthermore, when this structure is connected to an external load, chemical reactions shown in the following formulas (1) and (2) occur, and current flows (power generation state).
(1/2) · O ₂ + 2e ⁻ → O ²⁻ (where: air electrode 60) (1)
H ₂ + O ²⁻ → H ₂ O + 2e ⁻ (in the fuel electrode 20) (2)

  In the power generation state, as shown in FIG. 5, a current flows as indicated by an arrow in each pair of adjacent power generation element portions A and A. As a result, as shown in FIG. 4, from this entire SOFC (specifically, the interconnector 30 of the power generating element part A on the frontmost side in FIG. 4 and the air electrode 60 of the power generating element part A on the innermost side in FIG. Power).

(Production method)
Next, an example of a method for manufacturing the “horizontal stripe type” SOFC shown in FIG. 1 will be briefly described with reference to FIGS. 6 to 15, “g” at the end of the reference numeral of each member indicates that the member is “before firing”.

First, a support substrate molded body 10g having the shape shown in FIG. 6 is produced. The support substrate molded body 10g is extruded using, for example, a slurry obtained by adding a binder, a pore former, a dispersing agent, or the like to the powder of the material of the support substrate 10 (for example, MgO and Y ₂ O ₃ ). It can be produced using techniques such as molding and cutting. Hereinafter, the description will be continued with reference to FIGS. 7 to 15 showing partial cross sections corresponding to the line 7-7 shown in FIG.

As shown in FIG. 7, when the support substrate molded body 10g is manufactured, next, as shown in FIG. 8, in each recess 12 formed on the upper and lower surfaces of the support substrate molded body 10g, the fuel electrode assembly is formed. The molded part 21g of the electric part is embedded and formed respectively. Next, as shown in FIG. 9, a molded body 22g of the fuel electrode active portion is embedded and formed in each recess formed in the outer surface of the molded body 21g of each fuel electrode current collector. The molded body 21g of each fuel electrode current collector and each fuel electrode active part 22g are made of, for example, a powder of the material of the fuel electrode 20 (for example, Ni and Y ₂ O ₃ ) with a binder, a pore former, a dispersing material, and the like. Using the slurry obtained by addition, it is embedded and formed using a printing method or the like.

Subsequently, as shown in FIG. 10, in each concave portion formed in “the portion excluding the portion where the molded body 22 g of the fuel electrode active portion is embedded” on the outer surface of the molded body 21 g of each fuel electrode current collector. The interconnector molded bodies 30g are respectively embedded and formed. The molded body 30g of each interconnector is embedded and formed by using a slurry obtained by adding a binder or the like to the material of the interconnector 30 (for example, LaCrO ₃ ), using a printing method or the like. .

  Next, as shown in FIG. 11, the outer periphery extending in the longitudinal direction of the molded body 10g of the support substrate in a state in which the molded body (21g + 22g) of the plurality of fuel electrodes and the molded body 30g of the plurality of interconnectors are respectively embedded and formed. A solid electrolyte membrane molded film 40g is formed on the entire surface excluding the central portion in the longitudinal direction of each portion where the plurality of interconnector molded bodies 30g are formed. The molded membrane 40g of the solid electrolyte membrane is formed using, for example, a printing method, a dipping method, etc., using a slurry obtained by adding a binder or the like to the powder of the material of the solid electrolyte membrane 40 (for example, YSZ). The

  Next, as shown in FIG. 12, a reaction prevention film molding film 50g is formed on the outer surface of the solid electrolyte membrane molding body 40g in contact with the fuel electrode molding body 22g. The molded film 50g of each reaction preventing film is formed using a slurry obtained by adding a binder or the like to the powder of the material (for example, GDC) of the reaction preventing film 50, using a printing method or the like.

  Then, 10 g of the support substrate molded body in which various molded films are thus formed is fired in air at 1500 ° C. for 3 hours. As a result, a structure in which the air electrode 60 and the air electrode current collector film 70 are not formed in the SOFC shown in FIG. 1 is obtained.

  Next, as shown in FIG. 13, an air electrode forming film 60 g is formed on the outer surface of each reaction preventing film 50. The forming film 60g of each air electrode uses, for example, a printing method or the like using a slurry obtained by adding a binder, a pore former, a dispersing material, or the like to the powder of the material of the air electrode 60 (for example, LSCF). Formed.

  Next, as shown in FIG. 14, for each pair of adjacent power generation element portions, air is formed so as to straddle the air electrode molding film 60 g of one power generation element portion and the interconnector 30 of the other power generation element portion. On the outer surface of the electrode forming film 60 g, the solid electrolyte film 40, and the interconnector 30, the air electrode current collecting film forming film 70 g is formed. The forming film 70g of each air electrode current collector film is, for example, using a slurry obtained by adding a binder, a pore former, a dispersing material, etc. to the powder of the material of the air electrode current collector film 70 (for example, LSCF), It is formed using a printing method or the like.

  Then, the support substrate 10 in which the molded films 60g and 70g are thus formed is baked in air at 1050 ° C. for 3 hours. Thereby, the SOFC shown in FIG. 1 is obtained. At this point, the Ni component in the fuel electrode 20 (current collector 21 + active portion 22) is NiO due to firing in an oxygen-containing atmosphere. Therefore, in order to acquire the electron conductivity of the fuel electrode 20 (current collector 21 + active part 22), a reducing fuel gas is then flowed from the support substrate 10 side, and NiO is heated at 800 to 1000 ° C. for 1 to 10 hours. The reduction treatment is performed over a period of time. This reduction process may be performed during power generation. In the above, an example of the manufacturing method of SOFC shown in FIG. 1 was demonstrated.

(Preventing cracks)
When the SOFC according to the above embodiment is operated under a severe thermal stress environment unlike a normal environment, as shown in FIG. 15, “the inner wall of the gas flow path 11 of the support substrate 10 is a starting point. May occur ”(see the arrow in FIG. 15). This phenomenon is considered to be caused by the fact that stress tends to concentrate on the inner wall of the gas flow path 11. It is important to reduce the possibility of such cracks.

  Hereinafter, with respect to the pores formed in the support substrate 10, pores having a pore diameter of less than 20 μm are referred to as “first pores”, and pores having a pore diameter of 20 μm or more are referred to as “second pores”. The diameter of pores existing on a certain cross section is defined as “the diameter of an equivalent circle having the same area as the area occupied by the pores on the cross section”.

  In the manufacturing process of the above-described embodiment, in order to produce the porous support substrate 10 (fired body), the pore former (powder) is dispersed and mixed in the support substrate molded body 10g (before firing). The particle diameter of the pore former to be mixed is on the order of several μm. Therefore, when the molded body 10g is baked in a state where the particles of the pore former are surely dispersed in the molded body 10g without agglomerating, the “first pores” are formed inside the support substrate 10 (baked body). Only (diameter less than 20 μm) can be formed. However, it is actually very difficult to disperse particles of such a very small pore former in the molded body 10g without agglomerating.

  Therefore, in the above embodiment, due to the aggregation of the pore former, not only the first pores but also the “second pores” (diameter of 20 μm or more) are inevitably formed in the support substrate 10. (See FIG. 16). In FIG. 16, only the second pores are shown, and the first pores (smaller than the second pores) are not shown. The maximum diameter of the second pores was 200 μm. In addition, the first and second pores are distributed substantially uniformly throughout the support substrate 10.

  The inventor of the present invention paid attention to a “channel vicinity region” that is a region close to the “inner wall of the gas flow channel 11” that is the starting point of the crack. As shown in FIG. 17, the “region near the flow path” refers to a “area where the distance from the inner wall of the gas flow path 11 in the support substrate 10 is 100 μm or less” (area indicated by fine dots in FIG. 17). See). That is, in the above-described embodiment, each “channel vicinity region” corresponds to a cylindrical region having a thickness of 100 μm. The first pores and the second pores can also exist in the vicinity of the flow path.

  Hereinafter, as shown in FIG. 16, among “second pores existing in the vicinity of the flow channel”, “second pores present so as to be exposed on the inner wall of the gas flow channel 11”, particularly “surface second pores”. The “second pores existing so as not to be exposed on the inner wall of the gas flow path 11” are particularly called “internal second pores”. The “surface second pores” and the “internal second pores” are also collectively referred to as “total second pores”. The “first pores existing in the vicinity of the flow path” and the “second pores existing in the vicinity of the flow path” are collectively referred to as “all pores”.

  The porosity of all pores in the region near the flow path (ratio of the total volume of all pores to the total volume in the region near the flow path) is referred to as “the porosity Sa of all pores”, and the entire second pore in the region near the flow path The porosity (the ratio of the total volume of the entire second pores to the total volume in the vicinity of the flow path) is referred to as “the porosity Sb1 of the entire second pores”.

  The “porosity Sa of all pores” can also be defined as the ratio of the “total area occupied by all pores existing in the cross section of the channel vicinity region” to the “total area of the cross section of the channel vicinity region”. “The porosity Sb1 of the entire second pores” can also be defined as the ratio of “the total area occupied by the entire second pores existing in the cross section of the channel vicinity region” to “the total area of the cross section of the channel vicinity region”. . Here, the “cross section” refers to a cross section along the yz plane (a plane perpendicular to the longitudinal direction of the support substrate 10) (see FIG. 17).

  The present inventor confirmed that the occurrence of the above-described cracks when the SOFC according to the above embodiment is operated under a severe environment due to thermal stress is “porosity Sa of all pores” and “total second It was found that there is a strong correlation with the porosity Sb1 of the pores. Hereinafter, test A in which these are confirmed will be described.

(Test A)
In this test A, for the SOFC shown in FIG. 1, a plurality of samples having different “porosity Sa (%) of all pores” and “porosity Sb1 (%) of all second pores” were produced. Specifically, as shown in Table 1, eleven kinds of levels (combinations) were prepared. Ten samples (N = 10) were made for each level.

In each sample (SOFC shown in FIG. 1), the support substrate 10 has a length in the longitudinal direction (x-axis direction) of 50 to 500 mm, a length in the width direction (y-axis direction) of 10 to 100 mm, and a thickness. A flat plate shape with a length of 1 to 5 mm was exhibited. The cross section of the gas flow path 11 (specifically, six) of the support substrate 10 was circular, and the diameter was 0.3-4.5 mm. The support substrate 10 was made of MgO and Y ₂ O ₃ , MgO and YSZ, or MgO and CSZ. Regarding the support substrate 10, the porosity Sa of all the pores was adjusted by adjusting the amount and diameter of the pore former contained in the slurry used for producing the molded body 10 g of the support substrate. The porosity Sb1 of the entire second pores was adjusted by adjusting the amount of the dispersing material contained in the slurry. In general, the frequency of occurrence of the above-mentioned “aggregation of pore former” depends on the amount of the dispersing material. Therefore, by adjusting the amount of the dispersing material, the frequency of occurrence of “aggregation of pore forming material particles” (that is, the frequency of occurrence of the second pores, and hence the porosity Sb1 of the entire second pores) can be adjusted. it can.

  The porosity of the entire support substrate 10 was 15 to 55%. The pore diameter of the second pore was in the range of 20 to 200 μm. Firing of the support substrate 10 was performed at 1400 to 1500 ° C. for 1 to 20 hours. The said reduction process performed with respect to each sample was performed over 1-10 hours at 800-1000 degreeC.

  For each sample, the “porosity Sa of all pores” and the “porosity Sb1 of the entire second pore” are measured on arbitrary “cross-sections” (in the x-axis direction) of the support substrate 10. Were adopted as “the porosity Sa of all the pores” and “the porosity Sb1 of the entire second pore”, respectively. The values (%) of “porosity Sa of all pores” and “porosity Sb1 of whole second pores” for each level described in Table 1 are average values of N = 10.

  In this test A, for each sample after the above reduction treatment, “the ambient temperature was raised from room temperature to 750 ° C. over 2 hours while reducing fuel gas was circulated through the fuel electrode 20 and then from 750 ° C. to room temperature for 4 hours. The thermal cycle test was repeated 10 times. And about each sample, the presence or absence of generation | occurrence | production of "the crack which goes to the main surface of the support substrate 10 from the inner wall of the gas flow path 11 of the support substrate 10" was confirmed. This confirmation was made by visual observation and observation of a cross section using a microscope. The results are as shown in Table 1.

  As can be understood from Table 1, when “the porosity Sa of all the pores is 25 to 50% and the porosity Sb1 of the entire second pores is 6.5% or less”, compared to the case where it is not so The cracks described above are unlikely to occur. This is because if there are too many second pores (that is, relatively large pores) in the vicinity of the flow path, the stress tends to concentrate on the inner wall of the gas flow path 11 for some reason, It is thought to be caused by

  As can be understood from Table 1, a sample having a “total porosity Sb1 of the second pore” smaller than 0.025% could not be produced. This is considered to be related to the limitation on the frequency of occurrence of the above-mentioned “aggregation of pore former”.

  As described above, when “the porosity Sa of all the pores is 25 to 50% and the porosity Sb1 of the entire second pores is 6.5% or less (or 0.025 to 6.5%)”. In addition, it can be said that the above-described cracks are less likely to occur even when the above-described SOFC is operated under a severe environment in terms of thermal stress as compared to the case where this is not the case.

  By the way, the present inventor further paid attention to the “second surface pores” (see FIG. 16) exposed on the “inner wall of the gas flow path 11” itself, which is the starting point of the crack. Here, the porosity of the surface second pores in the region near the flow path (the ratio of the total volume of the surface second pores to the total volume of the region near the flow path) is referred to as “the porosity Sb2 of the surface second pores”. “The porosity Sb2 of the surface second pores” can also be defined as the ratio of “the total area occupied by the surface second pores existing in the cross section of the channel vicinity region” to “the total area of the cross section of the channel vicinity region”. . Here, “cross section” refers to a cross section along the yz plane (a plane perpendicular to the longitudinal direction of the support substrate 10), as in “porosity Sa of all pores” and “porosity Sb1 of all second pores”. (See FIG. 17).

  The present inventor stated that “the porosity Sa of all pores is 25 to 50% and the porosity Sb1 of the entire second pores is 6.5% or less (or 0.025 to 6.5%)”. In some cases, when the “porosity Sb2 of the surface second pores” is 0.3% or less (or 0.001 to 0.3%), the above-described cracks are less likely to occur. I also found. Hereinafter, test B in which this has been confirmed will be described.

(Test B)
In the test B, for the SOFC shown in FIG. 1, “the porosity Sa (%) of all pores”, “the porosity Sb1 (%) of the entire second pores”, and “the porosity Sb2 (% of the surface second pores) Samples with different ")" were produced. Specifically, as shown in Table 2, eight levels (combinations) were prepared. Ten samples (N = 10) were made for each level.

  For each sample, the porosity Sa of all the pores is adjusted within a range of 25 to 50%, and the porosity Sb1 of the entire second pores is 6.5% or less (or 0.025 to 6.5%). Adjusted to within the range. About each sample, the dimension of each member other than the item shown in Table 2, a material, a manufacturing process, etc. are the same as that of the test A. The porosity Sb2 of the surface second pores was adjusted by adjusting the porosity of a thin film (fired film) made of the same material as that of the support substrate 10 coated on the inner wall of the gas flow path 11. This thin film (coating film) was co-fired with the support substrate 10.

  In this test B, the thermal cycle test is more severe in terms of thermal stress than the thermal cycle test performed in test A, that is, “the ambient temperature is changed from room temperature to 750 ° C. while reducing fuel gas is circulated through the fuel electrode 20. A heat cycle test was repeated 20 times, in which the pattern was raised from 750 ° C. to room temperature in 2 hours after being raised in 1 hour. And about each sample, the presence or absence of the generation | occurrence | production of the crack mentioned above was confirmed. The results are as shown in Table 2.

  As can be understood from Table 2, when “the porosity Sb2 of the surface second pores” is larger than 0.3%, the above-described cracks are likely to occur. This is considered to be caused by the fact that if the number of surface second pores exposed on the inner wall of the gas flow path 11 is too large, the stress tends to concentrate on the inner wall of the gas flow path 11 for some reason. .

  As can be understood from Table 2, a sample having a “porosity Sb2 of the surface second pores” of less than 0.001% could not be produced. This is considered to be related to the limitation on the frequency of occurrence of the above-mentioned “aggregation of pore former”.

  As described above, from the results of Table 1 and Table 2, the porosity of the support substrate 10 is 15 to 55%, and “the porosity Sa of all the pores is 25 to 50%, and the entire second porosity is When the porosity Sb1 is 6.5% or less (or 0.025 to 6.5%), the above-described cracks are difficult to occur, and in this case, “the porosity Sb2 of the surface second porosity” Is 0.3% or less (or 0.001 to 0.3%) ", it can be said that the above-described cracks are more difficult to occur.

  In addition, this invention is not limited to the said embodiment, A various modification can be employ | adopted within the scope of the present invention. For example, in the above embodiment, as shown in FIG. 6 and the like, the planar shape of the recess 12 formed in the support substrate 10 (the shape when viewed from the direction perpendicular to the main surface of the support substrate 10) is a rectangle. However, it may be, for example, a square, a circle, an ellipse, or a long hole shape. Further, the support substrate 10 has a flat plate shape, but may have a cylindrical shape.

  Further, in the above embodiment, a plurality of recesses 12 are formed on each of the upper and lower surfaces of the flat support substrate 10 and a plurality of power generation element portions A are provided, but a plurality of recesses 12 are provided only on one side of the support substrate 10. , And a plurality of power generating element portions A may be provided. Further, in the above-described embodiment, a so-called “horizontal stripe type” configuration in which a plurality of power generation element portions A electrically connected in series is disposed on one main surface of the support substrate 10 is employed. However, a configuration in which one power generation element portion A is disposed on one main surface of the support substrate 10 (so-called “vertical stripe type”) may be employed.

  Further, in the above-described embodiment, the fuel electrode 20 is composed of two layers of the fuel electrode current collector 21 and the fuel electrode active unit 22, but the fuel electrode 20 is one layer corresponding to the fuel electrode active unit 22 ( (Ni + oxide ceramics).

  In addition, in the above embodiment, each fuel electrode 20 (current collector 21 and active portion 22) is embedded in the recess 12 formed in the main surface of the support substrate. However, as shown in FIG. The recesses may not be formed on the main surface of the substrate, and each fuel electrode 20 (current collector 21 and active portion 22) may be formed so as to protrude from the main surface of the support substrate.

  In the above, “preventing the occurrence of cracks in the inner wall of the gas flow path of the support substrate” in the fuel cell having the configuration shown in FIG. 1 has been described. The present inventor has found that the same thing as described above can be applied to “preventing generation of cracks on the surface of the fuel electrode” in the fuel cell having the configuration shown in FIGS. 19 to 21. Hereinafter, this point will be described.

(Constitution)
First, the configuration of the fuel cell (solid oxide fuel cell) shown in FIGS. 19 to 21 will be briefly described. This fuel cell has a structure in which cells 100 and separators 200 are alternately stacked. This structure is also called “flat plate stack structure”. As shown in FIG. 20, in this fuel cell, the separator located on the upper side of the uppermost cell 100 is particularly called the upper lid member 300, and the separator located on the lower side of the lowermost cell 100. Is specifically referred to as the lower lid member 400.

  As shown in FIG. 21, the cell 100 includes a flat plate comprising a solid electrolyte layer 120, a fuel electrode 110 stacked on the upper surface of the solid electrolyte layer 120, and an air electrode 130 stacked on the lower surface of the solid electrolyte layer 120. It is a fired body. The planar shape of the cell 100 is, for example, a square having a side length of 10 to 300 mm.

  The thickness of the cell 100 (the length in the z-axis direction) is uniform throughout, for example, 110 to 2100 μm. The thicknesses of the fuel electrode 110, the solid electrolyte layer 120, and the air electrode 130 are, for example, 50 to 2000 μm, 1 to 50 μm, and 50 to 2000 μm, respectively. In the example shown in FIG. 21, the fuel electrode 110 is the thickest among the members constituting the cell 100, and thus the fuel electrode 110 supports the entire cell 100.

The fuel electrode 110 is made of, for example, a porous material containing Ni and YSZ. The solid electrolyte layer 120 is made of a dense material containing YSZ, for example. The air electrode 130 is made of a porous material containing, for example, LSM (La (Sr) MnO ₃ : lanthanum strontium manganite). The porosity of the fuel electrode 110, the solid electrolyte layer 120, and the air electrode 130 is 15 to 55%, 0 to 10%, and 15 to 55%, respectively. The average thermal expansion coefficients of the fuel electrode 110, the solid electrolyte layer 120, and the air electrode 130 from room temperature to 1000 ° C. are approximately 12.5 ppm / K, 10.8 ppm / K, and 11 (10.8), respectively. ppm / K.

  As illustrated in FIGS. 20 and 21, the separator 200 includes a flat plate portion 210 and a frame body portion 220. The planar shape of the separator 200 is the same as the planar shape of the cell 100. The frame body part 220 is located so as to surround the peripheral part of the flat plate part 210 over the entire circumference. The thickness (length in the z-axis direction) of the frame body part 220 is larger than the thickness (length in the z-axis direction) of the flat plate part 210. The frame body part 220 projects both upward and downward with respect to the flat plate part 210.

  The separator 200 is made of a Ni-based heat-resistant alloy (for example, ferrite-based SUS, Inconel 600, Hastelloy, etc.). For example, in the case of SUS430, which is a ferrite SUS, the average thermal expansion coefficient of the separator 200 from room temperature to 1000 ° C. is approximately 12.5 ppm / K. Therefore, the thermal expansion coefficient of the separator 200 is larger than the average thermal expansion coefficient of the cell 100.

  The peripheral part of each cell 100 is sandwiched by the respective frame body parts 220 of the separators 200 adjacent to the upper side and the lower side via a bonding material (glass material or the like). As a result, as shown in FIG. 21, for each cell 100, a fuel flow channel through which fuel gas flows is defined and formed between the cell 100 and the separator 200 adjacent to the upper side of the cell 100. An air flow path through which air flows is defined and formed between the separator 200 adjacent to the lower side of the cell 100. Therefore, the separator 200 functions to prevent mixing of fuel gas and air.

  As described above, with respect to the fuel cell shown in FIGS. 19 to 21, the fuel gas (hydrogen gas or the like) flows through each fuel flow path, and the air flows through each air flow path, and this fuel cell is connected to an external load. By doing so, the power generation based on the above-described chemical reaction formulas (1) and (2) is performed as in the fuel cell shown in FIG.

(Production method)
Next, a method for manufacturing the fuel cell shown in FIGS. 19 to 21 will be briefly described. First, in the cell 100, a ceramic sheet (a layer that becomes the solid electrolyte layer 120) is formed on the lower surface of the sheet (a layer that becomes the fuel electrode 110) by a printing method or the like, and the laminate is fired at 1400 ° C. for 1 hour. The sheet (layer that becomes the air electrode 130) is formed on the lower surface of the fired body by a printing method or the like, and the laminate is fired at 1200 ° C. for 1 hour. The separator 200 is formed by subjecting a Ni-based heat-resistant alloy thin plate material to cutting, pressing, or the like.

  Next, the completed cells 100 and separators 200 are laminated alternately and in a state where a glass material is interposed between the peripheral portion of the adjacent cells 100 and the frame body portion 220 of the separator 200, and this laminate ( The glass material is subjected to heat treatment (830 ° C./1 hr). As a result, the glass material is solidified to integrate the laminate, and the fuel cell shown in FIG. 19 having a flat plate stack structure is completed.

  At this point, the Ni component in the fuel electrode 110 is NiO due to firing in an oxygen-containing atmosphere. Therefore, in order to acquire the electron conductivity of the fuel electrode 110, thereafter, reducing fuel gas is flowed from the fuel flow path side, and NiO is reduced at 800 to 1000 ° C. for 1 to 10 hours. This reduction process may be performed during power generation.

(Preventing cracks)
When the fuel cell shown in FIG. 19 is operated under a severe thermal stress environment unlike a normal environment, the “surface facing the fuel flow path of the fuel electrode 110 as shown in FIG. May occur ”(see the arrow in FIG. 22). This phenomenon is considered to be caused by the fact that stress tends to concentrate on the surface of the fuel electrode 110. It is important to reduce the possibility of such cracks.

  Hereinafter, as for the pores formed inside the fuel electrode 110, the pores having a pore diameter of less than 20 μm are referred to as “first pores”, and the pores having a pore diameter of 20 μm or more are referred to as “second pores”. Call. Also in the manufacturing process of this fuel cell, in order to produce the porous fuel electrode 110 (fired body), the pore former (powder) is dispersed and mixed in the fuel electrode sheet (before firing). The particle diameter of the pore former to be mixed is on the order of several μm. Therefore, when the sheet is fired in a state where the particles of the pore former are surely dispersed in the sheet without agglomerating, the “first pore” (diameter is 20 μm) is formed inside the fuel electrode 110 (fired body). Less than) can be formed. However, it is actually very difficult to disperse particles of such a very small pore former in the sheet without agglomeration.

  Therefore, in the fuel cell, not only the first pores but also the “second pores” (diameter of 20 μm or more) are inevitably formed inside the fuel electrode 110 due to the aggregation of the pore former. (See FIG. 23). In FIG. 23, only the second pores are shown, and the first pores (smaller than the second pores) are not shown. The maximum diameter of the second pores was 200 μm. In addition, in the entire fuel electrode 110, the first and second pores are substantially uniformly distributed.

  The inventor of the present invention has focused on a “channel vicinity region” that is a region near the “surface facing the fuel flow path of the fuel electrode 110” that is the starting point of the crack described above. As shown in FIG. 24, the “region in the vicinity of the flow path” refers to a “region where the distance from the surface facing the fuel flow path in the fuel electrode 110 is 100 μm or less” (indicated by fine dots in FIG. 24). See area). That is, in this fuel cell, each “region near the flow path” corresponds to a flat plate-like region having a thickness of 100 μm. The first pores and the second pores can also exist in the vicinity of the flow path.

  Hereinafter, as in FIG. 23 described above, as shown in FIG. 23, among “second pores existing in the vicinity of the flow path”, “second pores present so as to be exposed on the surface of the fuel electrode 110” In particular, it is referred to as “surface second pores”, and “second pores present so as not to be exposed on the surface of the fuel electrode 110” are particularly referred to as “internal second pores”. The definitions of “total second pores”, “all pores”, “porosity Sa of all pores”, and “porosity Sb1 of all second pores” are the same as described above.

  The present inventor has determined that the occurrence of cracks in the above-described fuel electrode 110 when the fuel cell is operated under a severe environment due to thermal stress is the “porosity Sa of all the pores” and “total porosity”. It was found that there is a strong correlation with the porosity Sb1 of 2 pores. Hereinafter, test A in which these are confirmed will be described.

(Test C)
In this test C, a plurality of samples having different “porosity Sa (%) of all pores” and “porosity Sb1 (%) of entire second pores” were produced for the fuel cell shown in FIG. Specifically, as shown in Table 3, ten types (combinations) were prepared. Ten samples (N = 10) were made for each level.

  In each sample (SOFC shown in FIG. 19), the cell 100 had a planar shape of a square having a side length of 10 to 300 mm and a thickness of 110 to 2100 μm. The thicknesses of the fuel electrode 110, the solid electrolyte layer 120, and the air electrode 130 were, for example, 50 to 2000 μm, 1 to 50 μm, and 50 to 2000 μm, respectively. Of the members constituting the cell 100, the fuel electrode 110 is the thickest, and thus the fuel electrode 110 supports the entire cell 100.

The fuel electrode 110 was made of a porous material made of Ni and YSZ. The solid electrolyte layer 120 was made of a dense material made of YSZ. The air electrode 130 was made of a porous material made of LSM (La (Sr) MnO ₃ ). The porosity of the fuel electrode 110, the solid electrolyte layer 120, and the air electrode 130 was 15 to 55%, 0 to 10%, and 15 to 55%, respectively.

  Regarding the fuel electrode 110, the porosity Sa of all the pores was adjusted by adjusting the amount and diameter of the pore-forming material contained in the slurry used for producing the fuel electrode sheet. The porosity Sb1 of the entire second pores was adjusted by adjusting the amount of the dispersing material contained in the slurry. In general, the frequency of occurrence of the above-mentioned “aggregation of pore former” depends on the amount of the dispersing material. Therefore, by adjusting the amount of the dispersing material, the frequency of occurrence of “aggregation of pore forming material particles” (that is, the frequency of occurrence of the second pores, and hence the porosity Sb1 of the entire second pores) can be adjusted. it can.

  The porosity of the entire fuel electrode 110 was 15 to 55%. The pore diameter of the second pore was in the range of 20 to 200 μm. Firing of the fuel electrode 110 was performed at 1400 to 1500 ° C. for 1 to 20 hours. The said reduction process performed with respect to each sample was performed over 1-10 hours at 800-1000 degreeC.

  For each sample, the measurement of “porosity Sa of all pores” and “porosity Sb1 of the entire second pore” is performed on arbitrary “cross sections” of the fuel electrode 110 (in the y-axis direction). Were adopted as “the porosity Sa of all the pores” and “the porosity Sb1 of the entire second pore”, respectively. The values (%) of “the porosity Sa of all the pores” and “the porosity Sb1 of the entire second pores” for each level shown in Table 3 are average values of N = 10.

  In this test C, with respect to each sample after the above reduction treatment, “after reducing the ambient temperature from room temperature to 750 ° C. in 2 hours while flowing reducing fuel gas through each fuel flow path, the temperature was increased from 750 ° C. to room temperature 4 The thermal cycle test was repeated 10 times in the “pattern that decreases with time”. For each sample, it was confirmed whether or not “a crack toward the inside of the fuel electrode 110 starting from the surface of the fuel electrode 110 facing the fuel flow path” occurred. This confirmation was made by visual observation and observation of a cross section using a microscope. The results are as shown in Table 3.

  As can be understood from Table 3, when “the porosity Sa of all the pores is 20 to 50% and the porosity Sb1 of the entire second pore is 10% or less”, compared to the case where it is not so, the above-mentioned Cracks are less likely to occur. This is because if there are too many second pores (that is, relatively large pores) in the vicinity of the flow path, stress is likely to be concentrated on the surface of the fuel electrode 110 for some reason. It is thought to be caused.

  As can be understood from Table 3, a sample having a “total porosity of the second pore Sb1” smaller than 0.04% could not be produced. This is considered to be related to the limitation on the frequency of occurrence of the above-mentioned “aggregation of pore former”.

  From the above, when “the porosity Sa of all the pores is 20 to 50% and the porosity Sb1 of the entire second pore is 10% or less (or 0.04 to 10%)”, it is not so. Compared to the case, it can be said that the above-described crack of the fuel electrode is less likely to occur even when the above-described fuel cell is operated under a severe thermal stress environment.

  By the way, the present inventor further paid attention to the “surface second pores” (see FIG. 23) exposed to the “surface of the fuel electrode 110” itself, which is the starting point of the crack of the fuel electrode. Here, the porosity of the surface second pores in the region near the flow path (the ratio of the total volume of the surface second pores to the total volume of the region near the flow path) is referred to as “the porosity Sb2 of the surface second pores”. “The porosity Sb2 of the surface second pores” can also be defined as the ratio of “the total area occupied by the surface second pores existing in the cross section of the channel vicinity region” to “the total area of the cross section of the channel vicinity region”. . Here, the “cross section” refers to a cross section along the xz plane, as in “porosity Sa of all pores” and “porosity Sb1 of all second pores” (see FIG. 24).

  In the case where the porosity Sa of all the pores is 20 to 50% and the porosity Sb1 of the entire second pores is 10% or less (or 0.04 to 10%), It has also been found that the above-described cracks are less likely to occur when “the porosity Sb2 of the surface second pores” is 0.5% or less (or 0.001 to 0.5%). Hereinafter, Test D in which this is confirmed will be described.

(Test D)
In the test D, with respect to the fuel cell shown in FIG. 19, “the porosity Sa (%) of all pores”, “the porosity Sb1 (%) of the entire second pores”, and “the porosity Sb2 of the surface second pores ( %) ”Were produced. Specifically, as shown in Table 4, eight levels (combinations) were prepared. Ten samples (N = 10) were made for each level.

  For each sample, the porosity Sa of all the pores is adjusted within the range of 20 to 50%, and the porosity Sb1 of the entire second pore is within the range of 10% or less (or 0.04 to 10%). Adjusted. About each sample, the dimension of each member other than the item shown in Table 4, a material, a manufacturing process, etc. are the same as that of the test C. The porosity Sb2 of the surface second pores was adjusted by adjusting the porosity of a thin film (fired film) made of the same material as the fuel electrode 110 coated on the surface of the fuel electrode 110 facing the fuel flow path. . This thin film (coating film) was co-fired with the fuel electrode 110.

  In this test D, a thermal cycle test that is more severe in terms of thermal stress than the thermal cycle test performed in test C, that is, “the ambient temperature is changed from room temperature to 750 ° C. while reducing fuel gas is circulated through each fuel flow path. The heat cycle test was repeated 20 times, “Pattern raised from 750 ° C. to room temperature in 2 hours after being raised in 1 hour”. And about each sample, the presence or absence of the crack of the fuel electrode mentioned above was confirmed. The results are as shown in Table 4.

  As can be understood from Table 4, when “the porosity Sb2 of the surface second pores” is larger than 0.5%, the above-described cracks are likely to occur. This is considered to be caused by the fact that if the number of surface second pores exposed on the surface of the fuel electrode 110 is too large, stress is likely to concentrate on the surface of the fuel electrode 110 for some reason.

  As can be understood from Table 4, a sample having a “porosity Sb2 of the surface second pores” of less than 0.001% could not be produced. This is considered to be related to the limitation on the frequency of occurrence of the above-mentioned “aggregation of pore former”.

  As described above, from the results of Tables 3 and 4, the porosity of the fuel electrode 110 is 15 to 55%, and “the porosity Sa of all the pores is 20 to 50%, and the entire second pore is When the porosity Sb1 is 10% or less (or 0.04 to 10%), cracks of the fuel electrode 110 described above are difficult to occur, and in this case, “the porosity Sb2 of the surface second pores” Is 0.5% or less (or 0.001 to 0.5%) ", it can be said that the above-described cracks of the fuel electrode 110 are more unlikely to occur.

  Even when the fuel electrode 110 is not the thickest structure among the members constituting the cell 100 (for example, when the solid electrolyte membrane 120 is the thickest), Table 3 and Table 4 relate to the adjustment of the pores inside the fuel electrode. It has been found that the exact same result can be obtained.

  Furthermore, the results shown in Test C and Test D (Tables 3 and 4) show that the fuel electrode 110 in the cell 100 has the thickest fuel electrode 110 (therefore, the fuel electrode 110 supports the entire cell 100). It was related to the adjustment of the pores inside. On the other hand, the adjustment of the pores inside the air electrode in the structure in which the air electrode 130 is the thickest in the cell 100 (therefore, the structure in which the air electrode 130 supports the entire cell 100) is the same as in the above test C and test D. As a result of tests, it has been found that the same results as in Tables 3 and 4 are obtained.

  Specifically, regarding the pores in the air electrode 130, the porosity of the air electrode 130 is 15 to 55%, and “the porosity Sa of all the pores is 20 to 50%, and the second When the porosity Sb1 of the pores is 10% or less (or 0.04 to 10%), cracking of the air electrode 130 is difficult to occur, and in this case, “porosity Sb2 of the surface second pores” Is 0.5% or less (or 0.001 to 0.5%) ", the cracks of the air electrode 130 are more unlikely to occur. In this case, the “region in the vicinity of the flow path” refers to a “area where the distance from the surface facing the air flow path in the air electrode 130 is 100 μm or less” (a flat area having a thickness of 100 μm).

  DESCRIPTION OF SYMBOLS 10 ... Support substrate, 11 ... Fuel gas flow path, 12 ... Recess, 15 ... Intermediate layer, 20 ... Fuel electrode, 21 ... Fuel electrode current collector, 21a, 21b ... Recess, 22 ... Fuel electrode active part, 30 ... Inter Connector: 40 ... Solid electrolyte membrane, 50 ... Reaction prevention membrane, 60 ... Air electrode, 70 ... Air electrode current collector membrane, A ... Power generation element part

Claims (6)

A support substrate having a gas flow path formed therein;
A power generation element unit that is provided on the support substrate and in which a fuel electrode, a solid electrolyte, and an air electrode are stacked in this order;
A fuel cell comprising:
The porosity of the entire support substrate is 15 to 55%,
As the pores inside the support substrate, there are a plurality of first pores having a pore diameter of less than 20 μm, and one or a plurality of second pores having a pore diameter of 20 μm or more,
The porosity (Sa) of the total pores composed of the first and second pores in the vicinity of the flow channel in the region where the distance from the inner wall of the gas flow channel in the support substrate is 100 μm or less is 25 to 50%, The fuel cell, wherein a porosity (Sb1) of the second pores in the region near the flow path is 6.5% or less. The fuel cell according to claim 1, wherein
The fuel cell, wherein a porosity (Sb2) of the second pore existing so as to be exposed on an inner wall of the gas flow channel in the flow channel vicinity region is 0.3% or less. A fuel cell comprising a plurality of flat cells and a plurality of separators, wherein the cells and the separators are alternately stacked one by one,
Each cell includes a solid electrolyte layer, a fuel electrode laminated on the first side of the solid electrolyte layer, and an air electrode laminated on the second side of the solid electrolyte layer,
For each cell, a fuel flow path through which fuel gas flows is defined and formed between the cell and the separator adjacent to the first side of the cell, and the cell and the second of the cell. A fuel cell in which an air flow path through which a gas containing oxygen flows between the separator adjacent to the side is formed and formed;
For each cell,
The overall porosity of the first electrode which is one of the fuel electrode and the air electrode is 15 to 55%,
As pores inside the first electrode, there are a plurality of first pores having a pore diameter of less than 20 μm and one or a plurality of second pores having a pore diameter of 20 μm or more,
The porosity (Sa) of the total pores composed of the first and second pores in a region near the flow channel, which is a region having a distance from the surface facing the flow channel corresponding to the first electrode of 100 μm or less, is 20 to 50. %, And the porosity (Sb1) of the second pores in the vicinity of the flow path is 10% or less. The fuel cell according to claim 3, wherein
The fuel cell, wherein a porosity (Sb2) of the second pores existing so as to be exposed on a surface facing the corresponding channel in the region near the channel is 0.5% or less. The fuel cell according to claim 3 or claim 4,
For each cell,
The fuel cell in which the first electrode has the largest thickness among the members constituting each cell. The fuel cell according to any one of claims 3 to 5, wherein
For each cell,
The fuel cell, wherein the first electrode is the fuel electrode.

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