JP5646785B1 - Fuel cell - Google Patents

Abstract

A fuel cell in which a dense coating film is formed at an end of a gas discharge side of a porous support substrate having a gas flow path formed therein, and cracks are generated on the surface of the dense coating film. Provide something that can control the situation. This fuel cell is provided with a flat porous support substrate 10 in which a plurality of gas flow paths 11 are formed along the longitudinal direction, and a main surface of the support substrate 10, and at least a fuel electrode. , A solid electrolyte, and a power generation element unit in which an air electrode is laminated in this order. A dense coating film having a porosity smaller than that of the support substrate 10 is formed on the end portion on the gas discharge side of the inner wall surface of each gas flow path 11 and on the end surface on the gas discharge side in the longitudinal direction of the support substrate 10. A porous coating film having a larger porosity than the dense coating film is further formed on the dense coating film. [Selection] Figure 1

Description

  The present invention relates to a fuel cell.

  Conventionally, “a porous support substrate that is a flat plate having a longitudinal direction and in which one or a plurality of gas flow paths are formed along the longitudinal direction” and “the main surface of the support substrate” And a solid oxide fuel cell that is a fired body provided with at least a fuel electrode, a solid electrolyte, and an air electrode stacked in this order. Reference 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 discharge 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 discharge side end of the support substrate, and the excess gas described above and the air inside 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. Secondly, when the air in the external space enters the inside of the gas discharge side end of the support substrate, 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 There is known a configuration in which a dense coating film (first coating film) having a lower porosity than a support substrate is formed on the side end face (see, for example, Patent Document 1). Formation of the first coating film makes it difficult for air in the external space to enter the gas discharge side end portion of the support substrate, and as a result, generation of cracks in the support substrate can be suppressed.

JP 2012-9228 A

  Incidentally, it has been found that in the configuration in which the first coating film is formed as described above, a new problem that a crack occurs on the surface of the first coating film is likely to occur. This is considered based on the following reasons. That is, the first coating film is exposed to the external space in the vicinity of the gas discharge port of each gas flow path. Therefore, as described above, when the surplus gas burns by reacting with air (oxygen) in the external space in the vicinity of the gas discharge port, the heat (combustion heat) resulting from the combustion is the first. Easy to be transmitted to the surface of the coating film. In other words, the degree of change in the surface temperature of the first coating film is very large. On the other hand, since the first coating film is a dense film, the Young's modulus of the first coating film is large. Therefore, in the first coating film, the stress generated with respect to the strain is relatively large. From the above, the thermal stress generated on the surface of the first coating film tends to be particularly excessive. As a result, it is considered that cracks are likely to occur on the surface of the first coating film.

  When cracks occur on the surface of the first coating film, the air in the external space can easily enter the inside of the gas discharge side end portion of the support substrate, and the above-described “ The problem of “crack generation inside the support substrate” is likely to occur again. It is desired to suppress the occurrence of cracks on the surface of the first coating film.

  An object of the present invention is a fuel cell in which a dense coating film is formed on the gas discharge side end portion of a porous support substrate having a gas flow path formed therein, and the surface of the dense coating film is cracked. It is in providing the thing which can suppress the situation where this occurs.

  The fuel cell according to the present invention includes the same support substrate and power generation element unit as 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. A (dense) first coating film is formed.

  The fuel cell is characterized in that a second coating film having a porosity (porous) larger than that of the first coating film is formed on the first coating film. Here, the porosity of the support substrate is 20 to 60%, the porosity of the first coating film is 0.5 to 10%, and the porosity of the second coating film is 20 to 60%. % Is preferred. The second coating film is preferably formed over the entire surface of the first coating film.

  According to the above configuration, since the second coating film is formed on the surface of the first coating film, the first coating film is not exposed to the external space in the vicinity of the gas discharge port of each gas flow path. Accordingly, as compared with an embodiment in which the second coating film is not formed, the combustion heat of the surplus gas is not easily transmitted to the surface of the first coating film, and the degree of change in the surface temperature of the first coating film is reduced. As a result, excessive stress is less likely to occur on the surface of the first coating film, and cracks are less likely to occur on the surface of the first coating film.

  In addition, the second coating film is exposed to the external space in the vicinity of the gas discharge port of each gas flow path. Accordingly, the combustion heat of the surplus gas is easily transmitted to the surface of the second coating film. In other words, the degree of change in the surface temperature of the second coating film is relatively large. However, since the second coating film is a porous film, the Young's modulus is small. Therefore, since excessive stress is unlikely to occur on the surface of the second coating film, cracks are unlikely to occur on the surface of the second coating film.

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. 3 of the 2nd 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. 18 is an overall perspective view of the fuel gas manifold shown in FIG. 17. It is sectional drawing which shows the flow of the gas inside the stack structure shown in FIG. FIG. 18 is a perspective view showing how fuel gas and air are supplied to and discharged from the stack structure shown in FIG. 17.

(Constitution)
FIG. 1 shows an embodiment of a solid oxide fuel cell (SOFC) cell 100 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 SOFC cell 100 of this embodiment viewed from above is, for example, a length L1 of the side in the longitudinal direction of 50 to 500 mm and a length L2 in the width direction (y-axis direction) perpendicular to the longitudinal direction of 10 to 10. It is a 100 mm rectangle. The total thickness L3 of the SOFC cell 100 is 1 to 5 mm. The entire SOFC cell 100 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 cell 100 will be described with reference to FIG. 2, which is a partial cross-sectional view of the SOFC cell 100 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 channel 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 can be made of, for example, CSZ (calcia stabilized zirconia). Alternatively, it may be composed of NiO (nickel oxide) and YSZ (8YSZ) (yttria stabilized zirconia), NiO (nickel oxide) and Y ₂ O ₃ (yttria), or MgO. (Magnesium oxide) and MgAl ₂ O ₄ (magnesia alumina spinel) may be used. The porosity of the support substrate 10 is 20 to 60%.

  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.

  The support substrate 10 may be configured to include “transition metal oxide or transition metal” and insulating ceramics. 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).

Further, as the insulating ceramic, MgO (magnesium oxide) or “mixture of MgAl ₂ O ₄ (magnesia alumina spinel) and MgO (magnesium oxide)” is preferable. Further, CSZ (calcia stabilized zirconia), YSZ (8YSZ) (yttria stabilized zirconia), Y ₂ O ₃ (yttria) may be used as the insulating ceramic.

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, the insulating property of the support substrate 10 can be ensured by the support substrate 10 containing insulating ceramics. As a result, insulation between adjacent fuel electrodes can be ensured. On the other hand, the support substrate 10 may be made of only an insulating ceramic material that does not contain Ni elements, for example, MgO—Y ₂ O ₃ or MgO—MgAl ₂ O ₄ .

  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 oxygen ion 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 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, as shown in FIG. 4, the fuel gas (hydrogen gas or the like) flows through the fuel gas flow path 11 of the support substrate 10 to the “horizontal stripe type” SOFC cell 100 described above, and By exposing the lower surface (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), the solid electrolyte membrane An electromotive force is generated by a difference in oxygen partial pressure generated between both side surfaces of 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 the entire SOFC cell 100 (specifically, in FIG. 4, the interconnector 30 of the power generating element part A on the foremost side and the air electrode 60 of the power generating element part A on the farthest side in FIG. And power is extracted.

(Production method)
Next, an example of a manufacturing method of the “horizontal stripe type” SOFC cell 100 shown in FIG. 6 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 coating film 500 and a molding film of a coating film 600 (see FIG. 19), which will be described later, are formed on the gas discharge side end of the molded body 10g of the support substrate in this state, It is formed using a dipping 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. Thereby, the structure in which the air electrode 60 and the air electrode current collector film 70 are not formed in the SOFC cell 100 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 the SOFC cell 100 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 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 and the circumferential direction. 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. 16, the recess 21b 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 plurality of cells 100 described above will be described with reference to FIGS. As shown in FIG. 17, 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. The gas discharge 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. 18, 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. 19, the bonding material 300 is formed between the inner wall of the insertion hole 211 and the outer wall of the gas inflow side end of the cell 100 at each of the joints between the insertion hole 211 and the gas inflow side end 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 11 of each cell 100 communicates with the internal space of the manifold 200.

  As shown in FIG. 19, between adjacent cells 100, 100, between adjacent cells 100, 100 (more specifically, fuel electrode 12 of one cell 100 and air electrode 14 of the other cell 100). Current collecting member 400 for electrically connecting the two in series. The current collecting member 400 is made of, for example, a metal mesh.

  Further, as shown in FIG. 19, a dense coating film 500 having a porosity smaller than that of the support substrate 10 is formed at the gas discharge side end (free end) of each cell 100. As shown in the enlarged view of the Z portion in FIG. 19, specifically, the coating film 500 is a portion (hereinafter referred to as an “end face coating film”) formed over the entire end face on the gas discharge side in the longitudinal direction of the cell 100. 501 and a portion (hereinafter referred to as “channel inner wall surface coating film”) 502 formed at the end portion on the gas discharge side of the inner wall surface of each gas channel. In other words, the coating film 500 is formed at least on the end surface on the gas discharge side in the longitudinal direction of the support substrate 10 and on the end portion on the gas discharge side in the inner wall surface of each gas flow path 11. The end face coating film 501 is continuous with each flow path inner wall surface coating film 502. In the example shown in FIG. 19, the coating film 500 is also formed on the gas discharge side end of the side surface of the cell 100. This portion 503 of the coating film 500 is continuous with the end face coating film 501.

  The length H1 in the longitudinal direction of each channel inner wall surface coating film 502 (see the enlarged view of the Z portion in FIG. 19) is preferably 10 mm or more. The end portion in the longitudinal direction of the coating film portion 503 is continuous with the end portion so as to cover the outer surface of the end portion in the longitudinal direction of the solid electrolyte membrane 40 formed on the outer periphery of the support substrate 10.

  The coating film 500 is made of, for example, zirconia (3YSZ, 8YSZ, 10YSZ) containing rare earth elements, or glass. The coating film 500 may be made of the same material as the solid electrolyte film 40 (for example, yttria-stabilized zirconia YSZ), or may be made of the same material as the support substrate 10. 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 0.5 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).

  As shown in FIG. 19, a porous coating film 600 having a larger porosity than the coating film 500 is formed on the entire surface of the coating film 500. As shown in the enlarged view of the Z portion in FIG. 19, specifically, the coating film 600 is a portion (hereinafter referred to as “end face coating film”) 601 formed over the entire surface of the end face coating film 501; And a portion (hereinafter, referred to as “channel inner wall surface coating film”) 602 formed over the entire surface of each channel inner wall surface coating film 502. In other words, the coating film 600 is formed at least on the end surface on the gas discharge side in the longitudinal direction of the support substrate 10 and on the end portion on the gas discharge side in the inner wall surface of each gas flow path 11. The end surface coating film 601 is continuous with each flow path inner wall surface coating film 602. In the example shown in FIG. 19, the coating film 600 is also formed over the entire surface of the portion 503 of the coating film 500. This portion 603 of the coating film 600 is continuous with the end face coating film 601.

  The length H2 in the longitudinal direction of each channel inner wall surface coating film 602 (see the enlarged view of the Z portion in FIG. 19) is preferably 5 mm or more. The end portion in the longitudinal direction of the coating film portion 603 is continuous with the end portion so as to cover the outer surface of the end portion in the longitudinal direction of the solid electrolyte membrane 40 formed on the outer periphery of the support substrate 10.

  The coating film 600 is made of, for example, zirconia (3YSZ, 8YSZ, 10YSZ) or glass. The porosity of the porous coating film 600 is 20 to 60%. As described above, the coating film 600 may be formed by co-firing with the support substrate 10, the fuel electrode 20, the solid electrolyte film 40, and the coating film 500, or the support film 10, the fuel electrode 20, the solid electrolyte film. 40 and after the coating film 500 is baked, it may be formed by a vacuum film forming process (such as a CVD method (chemical vapor deposition)).

  The thickness T1 of the coating film 500 and the thickness T2 of the coating film 600 (see the enlarged view of the Z part in FIG. 19) are 3 to 100 μm and 3 to 100 μm, respectively. The surface roughness of the coating film 500 and the surface roughness of the coating film 600 are an arithmetic average roughness Ra, which are 0.1 to 10 μm and 1 to 50 μm, respectively.

  When operating the stack structure described above, as shown in FIG. 20, 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 discharge 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, the coating film 500 and the coating film 600 are formed on the gas discharge side end (free end) of each cell 100, so that the outside of the gas discharge side end of the porous support substrate 10 is externally provided. It is possible to prevent the air in the space from entering. As a result, it is possible to suppress occurrence of a situation in which a crack is generated at the gas discharge side end portion of the support substrate 10 due to the entry 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, as described above, the dense coating film 500 is formed on the gas discharge side end (free end) of the SOFC cell 100, and the porous coating film 600 is formed on the coating film 500. ing. That is, the coating film 500 is not exposed to the external space in the vicinity of the gas outlet of each gas flow path 11. Therefore, as compared with the case where the coating film 600 is not formed, the combustion heat of the surplus gas is not easily transmitted to the surface of the coating film 500, and the degree of change in the surface temperature of the coating film 500 is reduced. As a result, it is difficult for excessive thermal stress to be generated on the surface of the coating film 500, and cracks are hardly generated on the surface of the coating film 500.

  In addition, the coating film 600 is exposed to the external space in the vicinity of the gas discharge port of each gas flow path 11. Accordingly, the combustion heat of the surplus gas is easily transmitted to the surface of the coating film 600. In other words, the degree of change in the surface temperature of the coating film 600 is relatively large. However, since the coating film 600 is a porous film, the Young's modulus is small. Accordingly, since excessive stress is unlikely to occur on the surface of the coating film 600, cracks are unlikely to occur on the surface of the coating film 600.

(Further reduction in the possibility of cracks in the coating film)
In the SOFC shown in FIG. 1 after the above reduction treatment, cracks do not occur on the surface of the coating film 500 and / or the surface of the coating film 600 when operated in a normal environment. However, when the SOFC is operated under a severe thermal stress environment, cracks may occur on the surface of the coating film 500 and / or the surface of the coating film 600. The present inventor has found that the occurrence of such cracks has a strong correlation with the “combination of the porosity of the coating film 500 and the porosity of the coating film 600”. Hereinafter, a test for confirming this will be described. In this specification, “average” refers to “arithmetic average”.

(test)
In this test, a plurality of samples having different combinations of “coating film 500 porosity (%)” and “porosity (%) of coating film 600” were produced for the SOFC shown in FIG. Specifically, as shown in Table 1, 10 types (combinations) were prepared. Ten samples (N = 10) were made for each level. In Level 1, the coating film 600 is not provided.

  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 porosity of the support substrate 10 was 20 to 60%.

  The coating film 500 is formed to include portions 501, 502, and 503 as shown in FIG. 19, and the coating film 600 is formed to include portions 601, 602, and 603 as shown in FIG. 19. . The length H1 in the longitudinal direction of the portion 502 and the length H2 in the longitudinal direction of the portion 602 were 10 to 20 mm and 5 to 30 mm, respectively. The thickness T1 of the coating film 500 and the thickness T2 of the coating film 600 (see the enlarged view of the Z part in FIG. 19) were 3 to 100 μm and 3 to 100 μm, respectively. The surface roughness of the coating film 500 and the surface roughness of the coating film 600 were arithmetic average roughness Ra, and were 0.1 to 10 μm and 1 to 50 μm, respectively. In addition, each said value is a value after the said reduction process.

  The porosity of the coating film 500 and the coating film 600 was adjusted by adjusting the particle size of the powder in the slurry, the added amount of the pore former, and the like. The coating film 500 and the coating film 600 were formed by co-firing with the support substrate 10. This co-firing was performed at 1400-1500 ° C. for 1-3 hours. About each sample, the said reduction process was performed over 1 to 10 hours at 800-1000 degreeC.

  For each sample, measurement of “porosity of coating film 500” and “porosity of coating film 600” is performed at any five “cross-sections” (parallel to the xz plane) of coating films 500 and 600 of two layers. (See the cross section shown in FIG. 19). For each sample, for each coating film, the average of the corresponding five values was adopted as the porosity of the coating film. The value (%) of the “porosity of the coating film 500” and the value (%) of the “porosity of the coating film 600” for each level shown in Table 1 are 10 samples included in the level. It is an average value of the corresponding porosity values (= 10 values) of (N = 10).

  In this test, for each sample after the reduction treatment, “with reducing fuel gas flowing through the fuel electrode 20, the ambient temperature was raised from room temperature to 750 ° C. in 2 hours, and then from 750 ° C. to room temperature in 4 hours. The thermal cycle test was repeated 10 times for the “lowering pattern”. For each sample, the presence or absence of occurrence of “cracks on the surface of the coating film 500” and “cracks on the surface of the coating film 600” was confirmed. The presence or absence of the occurrence of “cracks on the surface of the coating film 600” was made by visual observation and observation of a cross section using a microscope. The presence or absence of the occurrence of “cracks on the surface of the coating film 500” was made by observing a cross section using a microscope. The results are as shown in Table 1.

  In Table 1, at level 1, cracks occur on the surface of the coating film 500 (particularly, the surface of the portion 501), and at level 10, cracks occur on the surface of the coating film 600 (particularly, the surface of the portion 601). ing. There are no cracks at other levels.

  As can be seen from Table 1, if the coating film 600 is not provided, cracks are likely to occur on the surface of the coating film 500 (level 1). This is because, as described in the “Summary of the Invention” section above, “the coating film 500 is exposed in the vicinity of the gas discharge port of the gas flow path 11, thereby causing heat generated by the combustion of the excess gas. Is easily transmitted to the surface of the coating film 500, and “the Young's modulus of the coating film 500, which is a dense film, is large”, the thermal stress generated on the surface of the coating film 500 is particularly likely to be excessive. It is considered to be based.

  Further, when “the porosity of the coating film 500 is 0.5 to 10% and the porosity of the coating film 600 is 20 to 60%”, the surface of the coating film 500 and the surface of the coating film 600 It can be said that cracks hardly occur in both cases. On the other hand, if the porosity of the coating film 600 is greater than 60%, cracks are likely to occur on the surface of the coating film 600 (level 10). This is considered to be based on the fact that the strength of the coating film 600 is significantly reduced if the porosity of the coating film 600 is too large.

  As described above, when the porosity of the support substrate 10 is 20 to 60%, “the porosity of the coating film 500 is 0.5 to 10% and the porosity of the coating film 600 is 20 to 60%”. If it is, the surface of the coating film 500 and the surface of the coating film 600 are less likely to be cracked even when the above-described SOFC is operated under a severe thermal stress environment. It can be said.

  In addition, when the above-described embodiment is used under the normal conditions and 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 condition that the porosity of the coating film 500 is 0.5 to 10% and the porosity of the coating film 600 is 20 to 60% is not satisfied, the surface of the coating film 500 and the coating film It has been confirmed separately that cracks hardly occur on the surface of 600.

  DESCRIPTION OF SYMBOLS 10 ... Support substrate, 11 ... Fuel gas flow path, 12 ... Recessed part, 20 ... Fuel electrode, 21 ... Fuel electrode current collecting part, 21a, 21b ... Recessed part, 22 ... Fuel electrode active part, 30 ... Interconnector, 40 ... Solid Electrolyte membrane, 50 ... Reaction prevention membrane, 60 ... Air electrode, 70 ... Air electrode current collector film, 500 ... Coating film, 600 ... Coating film, A ... Power generation element part

Claims (2)

A porous support substrate having a longitudinal direction and one or more gas flow paths formed therein along the longitudinal direction;
A power generation element portion provided on the main surface of the support substrate, wherein at least a fuel electrode, a solid electrolyte, and an air electrode are laminated in this order;
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.
A first coating film having a porosity smaller than that of the support substrate is provided at least on the end portion on the gas discharge side in the inner wall surface of each gas flow path and on the end surface on the gas discharge side in the longitudinal direction of the support substrate. Formed,
A fuel cell, wherein a second coating film having a porosity higher than that of the first coating film is formed on the first coating film. The fuel cell according to claim 1, wherein
The support substrate has a porosity of 20 to 60%, the first coating film has a porosity of 0.5 to 10%, and the second coating film has a porosity of 20 to 60%. ,Fuel cell.