JP5455266B1 - Fuel cell - Google Patents

Abstract

A fuel cell in which a coating film is formed at a gas outflow side end of a porous support substrate having a gas flow path formed therein, which can suppress the occurrence of cracks in the coating film. To provide.
The fuel cell is composed of a porous insulating ceramic material containing no Ni element, and a flat porous support substrate having a plurality of gas flow paths formed therein along the longitudinal direction. 10 and a power generating element portion provided on the main surface of the support substrate 10 and having at least a fuel electrode, a solid electrolyte, and an air electrode laminated in this order. The gas discharge side end of the inner wall surface of each gas flow path 11 and the gas discharge side end face in the longitudinal direction of the support substrate 10 are made of zirconia having a porosity smaller than that of the support substrate and containing rare earth elements. A coating film is formed.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell.

  Conventionally, “a porous support which has a flat plate shape having a longitudinal direction and is composed of an insulating porous material containing Ni element and in which one or a plurality of gas flow paths are formed along the longitudinal direction. A "substrate", and "a plurality of power generating element portions that are provided at a plurality of positions apart from each other on the main surface of the support substrate, and at least a fuel electrode, a solid electrolyte, and an air electrode are stacked in this order", and "1 One or a plurality of electrical connection portions that are respectively provided between a pair or a plurality of adjacent power generation element portions and electrically connect one fuel electrode and the other air electrode of the adjacent power generation element portions And so-called “horizontal stripe type” solid oxide fuel cells are widely known (see, for example, Patent Document 1).

  In the fuel cell which is such a fired body, heat treatment is performed to supply a reducing gas to the fuel cell at a high temperature (for example, about 800 ° C.) before operating the fuel cell in order to obtain conductivity of the fuel electrode and the like. (Hereinafter referred to as “reduction treatment”) is performed, and the fuel cell is transferred from the non-reduced form to the reduced form.

  In such a fuel cell, “the gas (fuel gas) flows in one direction (same direction) in the longitudinal direction in each gas flow path, and excess gas discharged from the gas discharge port of each gas flow path to the external space is In the vicinity of the gas discharge port, a configuration in which it reacts with air (oxygen) in the external space and is burned can be employed.

  When this configuration is employed, cracks are likely to occur at the gas outflow side end of the support substrate. This is considered based on the following reasons. First, due to the support substrate being porous, the air in the external space enters the inside of the gas outflow side end of the support substrate, and the excess gas described above and the air It reacts and burns. As a result, excessive thermal stress due to heat generation due to combustion is locally generated in the inside, and cracks are generated. Second, the air inside the external space enters the inside of the gas outflow side end of the support substrate, so that the inside which is a reductant is reoxidized. As a result, an excessive stress accompanying a dimensional change (oxidation expansion or contraction) due to re-oxidation is locally generated in the inside, and a crack is generated.

  In order to suppress the occurrence of such cracks, the gas discharge side end of the support substrate, specifically, the gas discharge side end of the inner wall surface of each gas flow path, and the gas discharge in the longitudinal direction of the support substrate A configuration is known in which a coating film made of zirconia (typically yttria-stabilized zirconia YSZ) containing a rare earth element and having a porosity smaller than that of the support substrate is formed on the side end face (for example, , See Patent Document 1). Formation of this coating film makes it difficult for air in the external space to enter the inside of the gas outflow side end portion of the support substrate, and as a result, the occurrence of cracks can be suppressed.

JP 2012-9226 A

  By the way, as described above, a fuel cell having a configuration in which a “coating film composed of YSZ” is formed at the end portion on the gas outflow side of “a support substrate composed of an insulating porous material containing Ni element” ( When the above reduction treatment is performed on the fired body, cracks may occur in the coating film depending on the conditions of the reduction treatment.

  The present invention has been made to cope with the above-described problems, and its purpose is to provide “a rare earth element-containing zirconia at a gas outflow side end of a“ porous support substrate having a gas flow path formed therein ”. It is an object of the present invention to provide a fuel cell in which a coating film composed of the above is formed, which can suppress the occurrence of cracks in the coating film.

  The fuel cell according to the present invention is a “horizontal stripe type” fuel cell including a support substrate, a power generation element portion, and an electrical connection portion similar to those described above. One end side and the other end side in the longitudinal direction of each gas flow path correspond to a gas inflow side and a gas discharge side, respectively. In this fuel cell, at least the gas discharge side end portion of the inner wall surface of each gas flow path and the gas discharge side end surface of the support substrate in the longitudinal direction have a lower porosity than the support substrate. In addition, a coating film made of zirconia containing a rare earth element is formed.

  This fuel cell is characterized in that the support substrate is made of a porous insulating ceramic material that does not contain Ni element. Here, it is preferable that the support substrate has a porosity of 20 to 60%, and the coating film has a porosity of 0 to 10%.

As described above, the present inventor has a configuration in which the “coating film made of YSZ” is formed at the end of the gas outflow side of the “support substrate made of a porous insulating ceramic material not containing Ni element”. It has been found that no cracks are generated in the coating film when the above reduction treatment is performed on the completed fuel cell (fired body). Hereinafter, Electrochimica Acta 54 (2009) 927-934 (Non-Patent Document 1), J. Am. Ceram. Soc., 84 [11] 2652-56, about this result.
54 (2001) (Non-Patent Document 2).

  Non-Patent Documents 1 and 2 include that “when YSZ and NiO are co-sintered, NiO will be dissolved in YSZ” and “YSZ in which NiO is dissolved is exposed to a reducing atmosphere. , Reduced Ni is precipitated ". On the other hand, the above-described conventional fuel cell, that is, a configuration in which a “coating film composed of YSZ” is formed at the gas outflow side end of “a support substrate composed of an insulating porous material containing Ni element”. In the fuel cell having, the support substrate and the coating film are usually fired at the same time. As a result, NiO in the support substrate can move into the coating film composed of YSZ by diffusion, and YSZ and NiO can be co-sintered. In addition, the fired body is then exposed to a reducing atmosphere by the reduction treatment or the like.

  As described above, in the conventional fuel cell described above, the phenomenon described in Non-Patent Documents 1 and 2, that is, “a phenomenon in which NiO is dissolved in YSZ by co-sintering of YSZ and NiO”, and “ It can be inferred that the phenomenon that “reduced Ni precipitates when YSZ in which NiO is dissolved is exposed to a reducing atmosphere” occurs. Even when the support substrate and the coating film are not fired at the same time, “NiO in the support substrate moves into the coating film composed of YSZ due to diffusion, and NiO is dissolved in YSZ. When YSZ in which NiO is dissolved is exposed to a reducing atmosphere, a phenomenon in which reduced Ni precipitates may occur.

  On the other hand, it is considered that cracks may occur in the coating film composed of YSZ due to precipitation of reduced Ni in the coating film composed of YSZ. From the above, in the conventional fuel cell described above, it can be estimated that cracks may occur in the coating film made of YSZ due to the fact that the material constituting the support substrate contains Ni element.

  On the other hand, in the fuel cell according to the present invention, the material constituting the support substrate does not contain Ni element. Therefore, the above-described “phenomenon in which reduced Ni is precipitated by exposing YSZ in which NiO is dissolved to a solid atmosphere” is not possible. As a result, it is considered that cracks do not occur in the coating film even if the above-described reduction treatment is performed on the completed fuel cell (fired body).

  When the fuel cell according to the present invention is operated under a normal environment, the coating film does not crack. However, when the fuel cell is operated under a severe environment in terms of thermal stress, cracks may occur in the coating film.

  When the surface roughness of the portion formed on the inner wall surface of each gas flow path in the coating film is 0.13 to 5.2 μm in terms of arithmetic average roughness Ra, In comparison, it was found that cracks are less likely to occur in the same part. Furthermore, when the thickness of the portion formed on the inner wall surface of each gas flow path in the coating film is 3 to 45 μm, cracks are more unlikely to occur in the same portion than when the thickness is not. I also found out. Details of these points will be described later.

1 is a perspective view showing a fuel battery cell according to an embodiment of the present invention. It is sectional drawing corresponding to the 2-2 line of the fuel battery 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 battery cell shown in FIG. It is a figure for demonstrating the flow of the electric current in the operating state of the fuel battery 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 sectional drawing corresponding to FIG. 2 of the 1st modification of the fuel battery cell shown in FIG. It is sectional drawing corresponding to FIG. 2 of the 2nd modification of the fuel battery cell shown in FIG. It is sectional drawing corresponding to FIG. 2 of the 3rd modification of the fuel battery cell shown in FIG. It is sectional drawing corresponding to FIG. 3 of the 4th modification of the fuel battery cell shown in FIG. FIG. 2 is an overall perspective view of a stack structure including a plurality of fuel cells shown in FIG. 1. FIG. 20 is an overall perspective view of the fuel gas manifold shown in FIG. 19. FIG. 20 is a cross-sectional view showing a gas flow inside the stack structure shown in FIG. 19. It is the perspective view which showed a mode that fuel gas and air were supplied / discharged with respect to the stack | stuck structure shown in FIG.

(Constitution)
FIG. 1 shows an embodiment of a solid oxide fuel cell (SOFC) cell according to the present invention. This SOFC cell 100 is electrically connected in series to 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). In this example, four (4) identically shaped power generation element portions A are arranged at predetermined intervals in the longitudinal direction and have a so-called “horizontal stripe type” configuration.

  The shape of the entire cell 100 as viewed from above is, for example, that the length L1 (<L1) in the width direction (y-axis direction) perpendicular to the longitudinal direction is 1 to 5 cm and the length L1 of the side in the longitudinal direction is 1 to 1. It is a 10 cm rectangle. The total thickness L3 (<L2) of the SOFC is 1 to 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. The cross-sectional shape of each fuel gas channel 11 is a circle having a diameter D of 0.5 to 3 mm. The space | interval (pitch) P in the width direction of the adjacent fuel gas flow paths 11 and 11 is 1-5 mm. In addition, the cross-sectional shape of each fuel gas flow path 11 may be an ellipse, a long hole, a quadrangle having arcs at four corners, or the like. Further, in this example, each recess 12 includes a bottom wall made of the material of the support substrate 10 and a side wall made of the material of the support substrate 10 over the entire circumference (two side walls and a width along the longitudinal direction). Two side walls extending in the direction), and a rectangular parallelepiped-shaped depression.

The support substrate 10 is made of an insulating ceramic material that does not contain Ni element. Examples of this material include “MgO (magnesium oxide) and Y ₂ O ₃ (yttrium oxide) mixture (MgO—Y ₂ O ₃ )” or “MgAl ₂ O ₄ (magnesia alumina spinel) and MgO (oxidation). A mixture of magnesium) (MgO—MgAl ₂ O ₄ ) ”. Further, CSZ (calcia stabilized zirconia), YSZ (8YSZ) (yttria stabilized zirconia), Y ₂ O ₃ (yttria) may be included. As described above, the insulating property of the supporting substrate 10 can be ensured by configuring the supporting substrate 10 with insulating ceramics. As a result, insulation between adjacent fuel electrodes can be ensured. The porosity of the support substrate 10 is 20 to 60%.

  The width of the support substrate 10 is 10 to 100 mm, and the thickness is 1 to 5 mm. The aspect ratio (width / thickness) of the support substrate 10 is 5 to 100. 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 has a rectangular parallelepiped shape defined by a bottom wall made of the material of the fuel electrode current collector 21 and side walls closed in the circumferential direction (two side walls along the longitudinal direction and two side walls along the width direction). It is a depression. Of the side walls closed in the circumferential direction, two side walls along the longitudinal direction are made of the material of the support substrate 10, and two side walls along the width direction are made of the material of the fuel electrode current collector 21.

  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 two side surfaces and the bottom surface along the width direction 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 has a rectangular parallelepiped shape defined by a bottom wall made of the material of the fuel electrode current collector 21 and side walls closed in the circumferential direction (two side walls along the longitudinal direction and two side walls along the width direction). It is a depression. Of the side walls closed in the circumferential direction, two side walls along the longitudinal direction are made of the material of the support substrate 10, and two side walls along the width direction are made of the material of the fuel electrode current collector 21.

  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 two side surfaces and the bottom surface along the width direction 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 active part 22 may be composed of, for example, NiO (nickel oxide) and YSZ (8YSZ) (yttria stabilized zirconia). Or you may comprise from NiO (nickel oxide) and GDC (gadolinium dope ceria). The fuel electrode current collector 21 can be composed of, for example, NiO (nickel oxide) and YSZ (8YSZ) (yttria stabilized zirconia). Alternatively, it may be composed of NiO (nickel oxide) and Y ₂ O ₃ (yttria), or may be composed of NiO (nickel oxide) and CSZ (calcia stabilized zirconia). The thickness of the anode active portion 22 is 5 to 30 μm, and the thickness of the anode current collecting portion 21 (that is, the depth of the recess 12) is 50 to 500 μm.

  As described above, the fuel electrode current collector 21 includes a substance having electronic conductivity. The fuel electrode active part 22 includes a substance having electron conductivity and a substance having oxidative ion (oxygen ion) conductivity. The “volume ratio of the substance having oxidative ion conductivity relative to the total volume excluding the pore portion” in the anode active portion 22 is “the oxidative ion conductivity relative to the entire volume excluding the pore portion” in the anode current collecting portion 21. Greater than the volume fraction of the substance having

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 ionic conductivity and not electron 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.

  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 to suppress the occurrence of a phenomenon in which a reaction layer having a large electric resistance is formed at the interface with the substrate 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 the “electrical connection part”.

  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 fuel gas (hydrogen gas or the like) flows through the fuel gas flow path 11 of the support substrate 10 and the upper and lower surfaces of the support substrate 10 (see FIG. 4) with respect to the “horizontal stripe type” SOFC described above. In particular, by exposing each air electrode current collector film 70) to “a gas containing oxygen” (air or the like) (or flowing a gas containing oxygen along the upper and lower surfaces of the support substrate 10), the solid electrolyte membrane 40 An electromotive force is generated by a difference in oxygen partial pressure generated between the two side surfaces. 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 ⁻
(At: 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 14, “g” at the end of the reference numeral of each member represents that the member is “before firing”.

  First, a support substrate molded body 10g having the shape shown in FIG. 6 is produced. The molded body 10g of the support substrate is manufactured by using a method such as extrusion molding or cutting using a slurry obtained by adding a binder or the like to the material of the support substrate 10 (for example, CSZ). obtain. Hereinafter, the description will be continued with reference to FIGS. 7 to 14 showing partial cross sections corresponding to line 7-7 shown in FIG. 6.

  When the support substrate molded body 10g is manufactured as shown in FIG. 7, the fuel electrode current collector is then placed in each recess formed in the upper and lower surfaces of the support substrate molded body 10g as shown in FIG. Each of the molded parts 21g is embedded and formed. 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 of the fuel electrode active parts 22g use, for example, a slurry obtained by adding a binder or the like to the powder of the material of the fuel electrode 20 (for example, Ni and YSZ), It is embedded and formed using printing methods.

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. Although not shown in FIG. 12, a molding film of a coating film 500 (see FIG. 21), which will be described later, is also applied to the gas outflow side end of the support substrate molding 10g in this state using a dipping method or the like. Formed.

  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 molded film 60g of each air electrode is formed using a slurry obtained by adding a binder or the like to the powder of the material of the air electrode 60 (for example, LSCF), using a printing method or the like.

  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 obtained by using a slurry obtained by adding a binder or the like to the powder of the material of the air electrode current collector film 70 (for example, LSCF), using a printing method or the like. It is formed.

  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. In the above, an example of the manufacturing method of SOFC shown in FIG. 1 was demonstrated.

  At this time, the Ni component in the support substrate 10 and the fuel electrode 20 is NiO by firing in an oxygen-containing atmosphere. Therefore, in order to acquire the conductivity of the fuel electrode 20, thereafter, reducing fuel gas is flowed from the support substrate 10 side, and NiO is reduced at 800 to 1000 ° C. for 1 to 10 hours. This reduction process may be performed during power generation.

  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. For example, it may be a square, a circle, an ellipse, a long hole shape, or the like.

  In the above embodiment, the entire interconnector 30 is embedded in each recess 12, but only a part of the interconnector 30 is embedded in each recess 12, and the remaining portion of the interconnector 30 is recessed 12. May protrude outside (that is, protrude from the main surface of the support substrate 10).

  Moreover, in the said embodiment, although the angle (theta) which the bottom wall and side wall in the recessed part 12 make is 90 degrees, as shown in FIG. 15, angle (theta) may be 90-135 degrees. Moreover, in the said embodiment, as shown in FIG. 16, the part where the bottom wall and side wall in the recessed part 12 cross | intersect is the circular arc shape of the radius R, and the ratio of the radius R with respect to the depth of the recessed part 12 is 0. .01 to 1 may be used.

  Moreover, in the said embodiment, although the several recessed part 12 is formed in each of the upper and lower surfaces of the flat support substrate 10, and the several electric power generation element part A is provided, as shown in FIG. A plurality of recesses 12 may be formed only on one side of the ten and a plurality of power generation element portions A may be provided.

  Further, in the above embodiment, the fuel electrode 20 is composed of two layers of the fuel electrode current collector 21 and the fuel electrode active portion 22, but the fuel electrode 20 is a single layer corresponding to the fuel electrode active portion 22. It may be configured. In the above embodiment, the support substrate 10 has a flat plate shape, but may have a cylindrical shape.

  In addition, in the above embodiment, as shown in FIG. 3, the recess 21 b formed on the outer surface of the anode current collector 21 has a bottom wall made of the material of the anode current collector 21, It is a rectangular parallelepiped depression defined by closed side walls (two side walls along the longitudinal direction made of the material of the support substrate 10 and two side walls along the width direction made of the material of the fuel electrode current collector 21). ing. As a result, the two side surfaces and the bottom surface along the width direction of the interconnector 30 embedded in the recess 21b are in contact with the fuel electrode current collector 21 in the recess 21b.

  On the other hand, as shown in FIG. 18, the recess 21 b formed on the outer surface of the fuel electrode current collector 21 has a bottom wall made of the material of the fuel electrode current collector 21 and the fuel electrode current collector over the entire circumference. It may be a rectangular parallelepiped recess defined by circumferentially closed side walls (two side walls along the longitudinal direction and two side walls along the width direction) made of the material of the electric part 21. According to this, all four side surfaces and the bottom surface of the interconnector 30 embedded in the recess 21b are in contact with the fuel electrode current collector 21 in the recess 21b. Therefore, the area of the interface between the fuel electrode current collector 21 and the interconnector 30 can be further increased. Therefore, the electronic conductivity between the fuel electrode current collector 21 and the interconnector 30 can be further increased, and as a result, the power generation output of the fuel cell can be further increased.

(Example of stack structure)
Next, an example of a stack structure using the above-described plurality of cells 100 will be described with reference to FIGS. As shown in FIG. 19, the stack structure includes a large number of cells 100 and a fuel gas manifold 200 for supplying a fuel gas to each of the large number of cells 100. The entire manifold 200 is made of a material such as stainless steel.

  The top plate of the manifold 200 (in other words, the top plate (flat plate) of the gas tank) also serves as a support plate 210 for supporting a large number of cells 100. The manifold 200 is provided with an introduction passage 220 for introducing fuel gas from the outside into the internal space of the manifold 200. The gas inflow side of each cell 100 in the first longitudinal direction so that each cell 100 protrudes from the surface of the support plate 210 along the first longitudinal direction (x-axis direction) and the plurality of cells 100 are arranged in a stack. The end is joined and supported by the support plate 210. A gas outflow side end in the first longitudinal direction of each cell 100 is a free end. Therefore, this stack structure can be expressed as a “cantilever stack structure”.

  As shown in FIG. 20, a large number of insertion holes 211 communicating with the internal space of the manifold 200 are formed on the surface of the support plate 210 (the top plate of the manifold 200). Into each insertion hole 211, the gas inflow side end of the corresponding cell 100 is inserted (freely fitted).

  As shown in FIG. 21, in each of the joint portions between the insertion hole 211 and the gas inflow side end portion of the cell 100, the joining material 300 is formed between the inner wall of the insertion hole 211 and the outer wall of the gas inflow side end portion of the cell 100. The gaps between them are filled. Thereby, each insertion hole 211 and the gas inflow side edge part of the corresponding cell 100 are joined and fixed, respectively. As the bonding material 300, amorphous glass, crystallized glass, or the like can be used. The gas inflow side end of the gas flow path 18 of each cell 100 communicates with the internal space of the manifold 200.

  As shown in FIG. 21, a current collecting member 400 for electrically connecting adjacent cells 100, 100 in series is interposed between adjacent cells 100, 100. The current collecting member 400 is made of, for example, a metal mesh.

  Further, as shown in FIG. 21, a coating film 500 having a lower porosity than the support substrate 10 is formed at the gas outflow side end (free end) of each cell 100. As shown in the enlarged view of the Z portion in FIG. 21, specifically, the coating film 500 is a portion (hereinafter referred to as “channel inner wall surface”) formed at the end portion on the gas discharge side of the inner wall surface of each gas channel. 501 and a portion (hereinafter referred to as an “end face coating film”) 502 formed over the entire end face on the gas discharge side in the longitudinal direction of the cell 100. In other words, the coating film 500 is formed on at least the end portion on the gas discharge side of the inner wall surface of each gas flow path 11 and the end surface on the gas discharge side in the longitudinal direction of the support substrate 10. The end surface coating film 502 is continuous with each flow path inner wall surface coating film 501. In the example shown in FIG. 21, the coating film 500 is also formed on the gas discharge side end of the side surface of the cell 100. This part of the coating film 500 is continuous with the end face coating film 502.

  The coating film 500 is made of zirconia (for example, YSZ) containing a rare earth element. The coating film 500 is dense enough to prevent air from entering the support substrate 10 from the external space, and has a porosity of 0 to 10%. As described above, the coating film 500 may be formed by co-firing the support substrate 10, the fuel electrode 20, and the solid electrolyte film 40, or after firing the support substrate 10, the fuel electrode 20, and the solid electrolyte film 40, It may be formed by a vacuum film forming process method (evaporation method, CVD method (Chemical Vapor Deposition) or the like).

  When operating the stack structure described above, as shown in FIG. 22, a high-temperature (for example, 600 to 800 ° C.) fuel gas (such as hydrogen) and “a gas containing oxygen (such as air)” are circulated. . The fuel gas introduced from the introduction passage 220 moves into the internal space of the manifold 200 and is then introduced into the gas flow path 11 of the corresponding cell 100 via each insertion hole 211. The fuel gas that has passed through each gas flow path 11 is then discharged from the gas outflow side end (free end) of each gas flow path 11 to the outside. Air flows in the width direction (y-axis direction) of the cells 100 along the gaps between the adjacent cells 100 in the stack structure.

  Excess gas discharged from the gas discharge port of each gas flow path 11 to the external space reacts with air (oxygen) in the external space near the gas discharge port and burns. Here, since the coating film 500 is formed at the gas outflow side end (free end) of each cell 100, the air in the external space inside the gas outflow side end of the porous support substrate 10. Can be prevented from entering. As a result, it is possible to suppress occurrence of a situation in which a crack is generated at the gas outflow side end portion of the support substrate 10 due to the ingress of air into the inside.

  The above-mentioned cantilever stack structure is assembled by the following procedure, for example. First, a required number of completed cells 100 and a completed manifold 200 are prepared. Next, the plurality of cells 100 are aligned and fixed in a stack using a predetermined jig or the like. Next, one end of each of the plurality of cells 100 is inserted into the corresponding insertion hole 211 of the support plate 210 at a time while maintaining the state in which the plurality of cells 100 are aligned and fixed in a stack. Next, the paste for the bonding material 300 is filled in each gap of the bonding portion between the insertion hole 211 and one end of the cell 100.

  Next, heat treatment is applied to the paste filled as described above. Thereby, when the paste is dried and solidified, the function as the bonding material 300 is exhibited, and the gas inflow end of each cell is bonded and fixed to the corresponding insertion hole 211 (accordingly, the support plate 210). The Thereafter, the predetermined jig is removed from the plurality of cells 100 to complete the above-described cantilever stack structure.

(Action / Effect)
In the embodiment described above, the material constituting the support substrate 10 does not contain Ni element. Therefore, the phenomenon described in Non-Patent Documents 1 and 2 listed in the summary of the invention, that is, “a phenomenon in which NiO is dissolved in YSZ by co-sintering of YSZ and NiO”, and “NiO The phenomenon that reduced Ni precipitates when YSZ in which YSZ is dissolved is exposed to a reducing atmosphere cannot occur. As a result, it is considered that cracks are unlikely to occur in the coating film 500 even if the above-described reduction treatment is performed on the completed fuel cell (fired body).

  “The support substrate 10 is made of a material not containing Ni element” not only means “the whole support substrate 10 is made of a material not containing Ni element” but also “coating on the support substrate 10. Most of the support substrate 10 (at least half of the support substrate 10) including at least a region in the vicinity of the interface with the film 500 (for example, a region having a distance of 5 mm or less from the interface) is made of a material that does not contain Ni element, and the rest It is a concept that also includes an embodiment in which “a portion is made of a material containing Ni element”. Examples of the latter include, for example, “the interface between the support substrate 10 and the fuel electrode 20 due to the diffusion of Ni in the fuel electrode 20 into the support substrate 10 by diffusion during co-firing of the support substrate 10 and the fuel electrode 20. In a mode in which only the region in the vicinity of Ni is included, or in order to electrically connect the power generating element portions A on the upper and lower surfaces of the flat support substrate 10, only a part of the support substrate 10 is conductive. An embodiment in which a Ni element having a property is included ”is considered.

  In the above-described embodiment, the circumferential direction in which each of the plurality of recesses 12 for embedding the fuel electrode 20 formed on the upper and lower surfaces of the support substrate 10 is made of the material of the support substrate 10 over the entire circumference. Have closed side walls. In other words, the support body 10 is formed with a frame surrounding each recess 12. Therefore, this structure is not easily deformed when the support substrate 10 receives an external force.

  Further, the support substrate 10 and the embedded member are co-sintered in a state in which the members such as the fuel electrode 20 and the interconnector 30 are filled and embedded in the recesses 12 of the support substrate 10 without gaps. Therefore, a sintered body having high bondability between members and high reliability can be obtained.

  The interconnector 30 is embedded in a recess 21b formed on the outer surface of the fuel electrode current collector 21, and as a result, two side surfaces and a bottom surface along the width direction (y-axis direction) of the rectangular interconnector 30 Are in contact with the anode current collector 21 in the recess 21b. Therefore, the fuel electrode 20 (the current collector 21) and the interconnector 30 are compared to the case where a configuration in which the rectangular parallelepiped interconnector 30 is laminated (contacted) on the outer plane of the fuel electrode current collector 21 is employed. The area of the interface with can be increased. Therefore, the electronic conductivity between the fuel electrode 20 and the interconnector 30 can be increased, and as a result, the power generation output of the fuel cell can be increased.

  Further, in the above-described embodiment, a plurality of power generation element portions A are provided on each of the upper and lower surfaces of the flat support substrate 10. Thereby, compared with the case where a plurality of power generation element portions are provided only on one side surface of the support substrate, the number of power generation element portions in the structure can be increased, and the power generation output of the fuel cell can be increased.

  In the above embodiment, the solid electrolyte membrane 40 covers the outer surface of the fuel electrode 20, both end portions in the longitudinal direction of the outer surface of the interconnector 30, and the main surface of the support substrate 10. Here, no step is formed between the outer surface of the fuel electrode 20, the outer 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.

(Surface roughness of coating film)
In general, in a solid oxide fuel cell (SOFC), in order to obtain the conductivity of the fuel electrode, before operating the SOFC, the SOFC (fuel electrode) as a fired body is subjected to a high temperature (for example, 800 ° C.). It is necessary to reduce the NiO constituting the fuel electrode to Ni by performing a heat treatment (hereinafter referred to as “reduction treatment”) for supplying a reducing gas at a certain degree. That is, it is necessary to transfer the SOFC (the fuel electrode) from the non-reduced form to the reduced form.

  If the SOFC (reduced electrode) is continuously exposed to the reducing atmosphere until the temperature is lowered to around 400 ° C. in the process of lowering the SOFC that has been reduced by the reduction treatment from about 800 ° C. to room temperature, The SOFC (fuel electrode) is maintained in the reductant even at room temperature. On the other hand, when the SOFC (fuel electrode) is exposed to an oxidizing atmosphere before the SOFC that has been reduced by the reduction treatment is cooled down to around 400 ° C., the fuel electrode is re-oxidized and then at room temperature thereafter. The SOFC can be maintained in a non-reduced form. That is, the SOFC (the fuel electrode) can return from the reductant to the non-reducer. Further, the SOFC (the fuel electrode) is removed from the non-reduced material by performing the reduction treatment again at about 800 ° C. with respect to the SOFC in a state where the SOFC (the fuel electrode) becomes a non-reduced material by the reoxidation. It can move again to the reductant. As described above, the state of the SOFC (after production) that is a fired body can be either a reduced form or a non-reduced form depending on the subsequent use conditions.

  When the fuel cell (stack structure) according to the embodiment that has been reduced by the reduction treatment is operated under a normal environment, the coating film 500 does not crack. However, when the fuel cell (stack structure) is operated in a severe environment due to thermal stress, cracks may occur in the coating film 500 (particularly, the inner wall surface coating film 501). The present inventor has found that the occurrence of such cracks has a strong correlation with the “surface roughness of the coating film 500 (channel inner wall surface coating film 501)”. Hereinafter, test A in which this has been confirmed will be described.

(Test A)
In test A, a plurality of samples having different combinations of the material of the support substrate 10, the material of the inner wall surface coating film 501 and the surface roughness of the inner wall surface coating film 501 of the fuel cell according to the above embodiment are obtained. It was made. Specifically, as shown in Table 1, 14 kinds of levels (combinations) were prepared. Ten samples (N = 10) were made for each level. As surface roughness, JIS
“Arithmetic mean roughness Ra” defined in B 0601: 2001 was adopted. The value of the surface roughness described in Table 1 is a value (average value of N = 10) at the stage after completion of the above-described embodiment which is a fired body and after the reduction treatment. The surface roughness was measured along the longitudinal direction of the gas flow path 11. The surface roughness meter used for this measurement is TAYLOR
It is Form Tally Surf Plus manufactured by HOBSON. The radius of curvature of the stylus is 2 μm.

  As the support substrate 10 used in each sample (fuel cell shown in FIG. 1), the porosity of the material is 20 to 60%, and the thickness and width are 2.5 mm and 50 mm, respectively (that is, the aspect ratio). 20), the gas channel 11 has a circular cross-sectional shape with a diameter of 1.5 mm, and the pitch P between the adjacent gas channels 11 and 11 is 5.0 mm. In each sample, as described above, the laminated molded body (a molded body in which at least a fuel electrode molded body and a solid electrolyte membrane molded body are laminated on a support substrate molded body) and a molded body of a coating film are co-fired. It was. Thereafter, a reduction process was performed on each sample. In each sample, the thickness of the coating film 500 (in particular, the flow path inner wall surface coating film 501) was 5 to 10 μm.

  Adjustment of the “surface roughness of the coating film” was achieved by adjusting the surface roughness of the support substrate 10, the average particle diameter of the coating material, the slurry viscosity, the pulling speed during dip coating, and the like. Specifically, the surface roughness (Ra) of the support substrate is 0.25 to 2.5 μm, the average particle size of the coating material is 0.3 to 1.2 μm, the slurry viscosity is 1 to 10,000 mPa · s, and the lifting speed is It adjusted within the range of 0.1-30 mm / sec. The firing temperature was adjusted within the range of 1300 to 1600 ° C. The firing time was adjusted within a range of 1 to 20 hours. The reduction treatment temperature was adjusted within the range of 800 to 1000 ° C. The reduction treatment time was adjusted within a range of 1 to 10 hours.

  In this test (the same applies to test B described later), the porosity of the support (support substrate) was measured as follows. First, a so-called “resin filling” process was performed on the support (support substrate) so that the resin entered the pores of the support (support substrate). The surface of the support (support substrate) treated with “resin filling” was mechanically polished. By performing image processing on the image obtained by observing the microstructure of the mechanically polished surface with a scanning electron microscope, the pore portion (the portion where the resin enters) and the non-pore portion ( The area of the portion where the resin did not enter was calculated. The ratio of the “area of the pore portion” to the “total area (the area of the pore portion and the area of the non-pore portion)” was defined as the “porosity” of the support (support substrate).

  For each sample in the stage after the reduction treatment (reduced state), “the ambient temperature was raised from room temperature to 750 ° C. in 2 hours while reducing fuel gas was circulated through the fuel electrode 20 and then from 750 ° C. to room temperature. The thermal cycle test was repeated 100 times. And about each sample, the presence or absence of the generation | occurrence | production of the crack in the flow-path inner wall surface coating film 501 was confirmed. This confirmation was made by visual observation as well as observation using a microscope. The results are as shown in Table 1.

  As can be understood from Table 1, after the thermal cycle test severe in terms of thermal stress, the surface roughness of the channel inner wall surface coating film 501 exceeds 5.2 μm in arithmetic average roughness Ra. Although it is unknown, cracks are likely to occur in the flow channel inner wall surface coating film 501. On the other hand, when the surface roughness of the inner wall surface coating film 501 is 5.2 μm or less in terms of arithmetic average roughness Ra, it can be said that the cracks are hardly generated.

Further, as described above, the coating film 500 formed in each sample is formed by co-firing with the support substrate 10, the fuel electrode 20, and the solid electrolyte film 40. In this case, the surface roughness of the channel inner wall surface coating film 501 could not be less than 0.13 μm in terms of arithmetic average roughness Ra. From the above, when the surface roughness of the channel inner wall surface coating film 501 is within the range of 0.13 to 5.2 μm in terms of arithmetic average roughness Ra, the channel inner wall surface coating film 501 is compared with the case where the surface roughness is not so. It can be said that cracks hardly occur.
It is preferable.

  In addition, the present inventor, when the above embodiment is used under normal conditions / environment (for example, a pattern in which the temperature is raised from room temperature to 750 ° C. in 4 hours and then lowered from 750 ° C. to room temperature in 12 hours). Even if the surface roughness of the road inner wall surface coating film 501 is outside the range of 0.13 to 5.2 μm in terms of arithmetic average roughness Ra, the coating film 500 (channel inner wall surface coating film 501) should not crack. Is confirmed separately.

  The above results correspond to the case where the cross-sectional shape of each gas flow path 11 is circular, but the same result is obtained even if the cross-sectional shape of each gas flow path 11 is an ellipse, a long hole, a quadrangle having arcs at four corners, or the like. Has already been confirmed. This result corresponds to the case where the aspect ratio of the support substrate is 20, but it has already been confirmed that the same result can be obtained if the aspect ratio of the support substrate is in the range of 5 to 100. Further, it is desirable that the surface roughness of the coating film 500 is uniform over the entire area of the coating film 500. Therefore, the surface roughness of the portion of the coating film 500 excluding the inner wall surface coating film 501 of the coating film 500 is also the flow path. Similar to the inner wall surface coating film 501, the arithmetic average roughness Ra is preferably in the range of 0.13 to 5.2 μm.

(Thickness of coating film)
In addition, the present inventor, when the surface roughness of the flow path inner wall surface coating film 501 is 0.13 to 5.2 μm, the thickness T1 of the flow path inner wall surface coating film 501 (enlargement of the Z portion in FIG. 21). It was also found that cracks are less likely to occur in the flow path inner wall surface coating film 501 when the thickness is 3 to 45 μm. Hereinafter, test B in which this has been confirmed will be described.

(Test B)
In test B, for the fuel cell according to the above embodiment, the material of the support substrate 10, the material of the channel inner wall surface coating film 501, the surface roughness of the channel inner wall surface coating film 501, and the channel inner wall surface coating film 501. A plurality of samples having different thickness T1 combinations were produced. Specifically, as shown in Table 2, eleven kinds of levels (combinations) were prepared. Ten samples (N = 10) were made for each level. The surface roughness of the channel inner wall surface coating film 501 of each sample is in the range of 0.3 to 0.8 μm.

  Other dimensions of each sample are the same as those of Test A. The adjustment of the “thickness of the coating film” can be achieved by adjusting the film thickness of the molded body (state before firing) of the coating film.

  Then, for each sample in the stage after the reduction treatment (reduced state), a thermal cycle test that is more severe in terms of thermal stress than the thermal cycle test performed in test A, that is, “reducing fuel gas to the fuel electrode 20. While circulating, the thermal cycle test was repeated 100 times. “Pattern of raising the ambient temperature from room temperature to 750 ° C. over 1 hour and then lowering from 750 ° C. to room temperature over 2 hours”. And about each sample, the presence or absence of the generation | occurrence | production of the crack in the flow-path inner wall surface coating film 501 was confirmed. This confirmation was made by visual observation as well as observation using a microscope. The results are as shown in Table 2.

  As can be understood from Table 2, when the thickness T1 of the inner wall surface coating film 501 is outside the range of 3 to 45 μm, the reason is unknown, but cracks are likely to occur in the inner wall surface coating film 501. On the other hand, when the thickness T1 of the inner wall surface coating film 501 is in the range of 3 to 45 μm, it can be said that the crack is hardly generated.

  The above results correspond to the case where the cross-sectional shape of each gas flow path 11 is circular, but the same result is obtained even if the cross-sectional shape of each gas flow path 11 is an ellipse, a long hole, a quadrangle having arcs at four corners, or the like. Has already been confirmed. This result corresponds to the case where the aspect ratio of the support substrate 10 is 20, but it has already been confirmed that the same result can be obtained if the aspect ratio of the support substrate 10 is in the range of 5 to 100. . The thickness of the coating film 500 is desirably uniform over the entire area of the coating film 500. Therefore, the thickness of the coating film 500 excluding the channel inner wall surface coating film 501 is also equal to the channel inner wall surface. Like the coating film 501, it is desirable to be in the range of 3 to 45 μm.

  As described above, when the surface roughness of the channel inner wall surface coating film 501 is within the range of 0.13 to 5.2 μm in terms of arithmetic average roughness Ra based on the results of Tables 1 and 2, the channel inner wall surface coating film 501. In addition, it can be said that cracks are less likely to occur when the thickness T1 of the inner wall surface coating film 501 is in the range of 3 to 45 μm.

  For the purpose of protecting the coating film 500, a coating layer made of a glass material or the like may be further formed on the surface of the coating film 500. Even in this case, “when the surface roughness of the channel inner wall surface coating film 501 is within the range of 0.13 to 5.2 μm in terms of arithmetic average roughness Ra, compared to the case where it is not, There is no change in the content that “the wall coating film 501 is hardly cracked”.

  DESCRIPTION OF SYMBOLS 10 ... Support substrate, 11 ... Fuel gas flow path, 12 ... Recess, 20 ... Fuel electrode, 40 ... Solid electrolyte membrane, 60 ... Air electrode, 500 ... Coating membrane, A ... Power generation element part

Claims (4)

A support substrate having a longitudinal direction and made of a porous insulating ceramic material not containing Ni element, and one or a plurality of gas flow paths formed along the longitudinal direction;
A plurality of power generating element portions each provided at a plurality of locations apart from each other on the main surface of the support substrate, wherein at least a fuel electrode, a solid electrolyte, and an air electrode are stacked in this order;
One or a plurality of electrical connections that are respectively provided between one or a plurality of adjacent power generation element portions and electrically connect one fuel electrode and the other air electrode of the adjacent power generation element portions. And
A fuel cell that is a fired body comprising:
One end side and the other end side in the longitudinal direction of each gas flow path correspond to a gas inflow side and a gas discharge side, respectively.
At least at the gas discharge side end of the inner wall surface of each gas flow path and at the gas discharge side end surface of the support substrate in the longitudinal direction, the porosity is smaller than that of the support substrate, and a rare earth element A coating film composed of zirconia containing is formed ,
A fuel cell in which the surface roughness of the portion formed on the inner wall surface of each gas flow path in the coating film made of zirconia containing the rare earth element is 0.13 to 5.2 μm in terms of arithmetic average roughness Ra . The fuel cell according to claim 1 , wherein
The fuel cell, wherein a thickness of a portion formed on an inner wall surface of each gas flow path in the coating film made of zirconia containing the rare earth element is 3 to 45 μm. The fuel cell according to claim 1 or 2 ,
The fuel cell according to claim 1, wherein the support substrate has a porosity of 20 to 60%, and the coating film has a porosity of 0 to 10%. The fuel cell according to any one of claims 1 to 3 , wherein
The support substrate has a flat plate shape,
Recesses having a bottom wall made of the material of the support substrate and a circumferentially closed side wall made of the material of the support substrate are formed in the plurality of locations on the main surface of the support substrate,
A fuel cell in which a corresponding fuel electrode of the power generation element portion is embedded in each of the recesses.