JP2016042457A - Stack structure of fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stack structure of a fuel battery hard to cause chromium (Cr) volatilized from a surface of a manifold (especially, a support plate) to poison a power generation element part of a cell.SOLUTION: A stack structure of a fuel battery comprises: a manifold 200 made of a stainless steel; cells 100 each having one end on a fuel gas inflow side, which is bonded to and supported by the manifold 200 through a bonding material so that the cells protrude from a top wall 210 of the manifold 200 upward, and being arrayed in a stack; and a coating film 400 formed over the entire surface of the manifold 200, and including (Mn, Co)O. The coating film 400 includes MgO particles serving as a trapping agent (a so-called getter) for chromium (Cr). The coating film 400 is composed of a porous film having a porosity of 10-40%. It is preferable that the content of MgO in the coating film 400 is 3-30 vol.%.SELECTED DRAWING: Figure 15

Description

  The present invention relates to a fuel cell stack structure.

  Conventionally, a stack structure of a solid oxide fuel cell (hereinafter referred to as “SOFC”) including a plurality of fuel cells and a manifold that supports each fuel cell is known (for example, a patent) Reference 1). In addition, a stack structure of SOFC including a plurality of fuel cells and a separator that supports each fuel cell is known.

JP 2005-1000068 A

  The manifold or separator is usually made of stainless steel (a metal material containing iron and chromium, SUS). In addition to the manifold or separator, the SOFC stack structure may have a metal member made of stainless steel. When the SOFC stack structure having a metal member made of stainless steel is operated at an operating temperature (for example, around 800 ° C.), chromium (Cr) is volatilized from the metal member such as a manifold, and the volatilization occurs. The generated power element portion (particularly, the air electrode) of the cell can be poisoned by the chromium. As a result, the performance (characteristics) of the electrode deteriorates and the durability of the SOFC may decrease.

  In order to cope with this problem, the present inventor is considering forming a coating film on the surface of a metal member such as a manifold. Due to the presence of this coating film, chromium volatilized from the surface of a metal member such as a manifold does not easily flow out of the film at the operating temperature of the SOFC, and does not easily reach the power generation element portion of the cell. As a result, the possibility that the power generating element portion of the cell is poisoned by the volatilized chromium can be reduced.

  Incidentally, it is effective to make the coating film dense in order to surely suppress the arrival of volatile chromium from the surface of a metal member such as a manifold to the power generation element part by forming the coating film. This is based on the fact that when the coating film is porous, the volatilized chromium can easily flow out of the film through pores inside the film. However, in general, when a dense film is formed, there is a problem that the manufacturing cost is higher than when a porous film is formed.

  From the above, the present invention is a fuel cell stack structure in which a coating film is formed on the surface of a metal member made of a metal material containing iron and chromium, and the coating film is porous, It is an object of the present invention to provide a material that can reliably suppress chromium volatilized from the surface of the metal member from reaching the power generation element portion of the cell.

  The fuel cell stack structure according to the first aspect of the present invention is characterized in that a porous coating film comprising a ceramic material as a main component and MgO on the surface of a metal member composed of a metal material containing iron and chromium. Is in the formation. Here, the porous means that the porosity is 10% or more. The coating film preferably has a porosity of 10 to 40%. The metal member is preferably made of stainless steel. The support substrate is preferably flat.

  According to the above configuration, MgO functions as a capture agent (so-called getter) that captures chromium (Cr). Therefore, even if the coating film is porous, the metal member (typically, the manifold) Chromium volatilized from the surface can be trapped by MgO present inside the film while passing through the pores inside the film. Therefore, it becomes difficult for the volatilized chromium to flow out of the film. As a result, the volatilized chromium can be reliably suppressed from reaching the power generation element portion of the cell.

  The content of MgO in the coating film is preferably 3 to 30% by volume. The thickness of the coating film is preferably 5 to 100 μm. Moreover, it is preferable that the average value of the diameter of the pore which exists in the said coating film is 0.1-10 micrometers. These points will be described later.

The coating film is preferably composed of conductive ceramics. In particular, when the coating film is made of (Mn, Co) ₃ O ₄ , it is difficult for large thermal stress to act on the coating film, and the possibility that peeling due to the thermal stress occurs in the coating film is reduced. This is because the thermal expansion coefficients of the metal member material (stainless steel) and (Mn, Co) ₃ O ₄ are substantially equal. The coating film can also be made of Co ₃ O ₄ , ZnO, LSCF, or the like.

The fuel cell stack structure according to the second aspect of the present invention includes a plurality of fuel cells and a manifold. Each fuel cell has a longitudinal direction and a support substrate in which a fuel gas flow path along the longitudinal direction is formed, and at least a fuel electrode, a solid electrolyte, and air provided on the surface of the support substrate And a power generation element unit in which the poles are stacked in this order. The manifold has an internal space and includes an introduction portion for introducing fuel gas into the internal space. The manifold is configured so that each cell protrudes upward from the upper wall of the manifold, and the plurality of cells are arranged in a stack, and the internal space and the fuel in the plurality of cells A bonding material is used for one end of the fuel gas inflow side in the longitudinal direction of the support substrate of each cell with respect to the upper wall so as to communicate with one end of the fuel gas inflow side of each gas flow path. To join and support. A coating film made of (Mn, Co) ₃ O ₄ and containing MgO is formed on the surface of a metal member made of a metal material containing iron and chromium among the members constituting the stack structure. .

It is a perspective view which shows one cell used for the stack structure of the fuel cell which concerns on embodiment of this invention. It is sectional drawing corresponding to the 2-2 line of the 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 cell shown in FIG. It is a figure for demonstrating the flow of the electric current in the operating state of the 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 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 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 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 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 cell shown in FIG. 1. FIG. 6 is a cross-sectional view corresponding to FIG. 2 in a sixth stage in the manufacturing process of the cell shown in FIG. 1. FIG. 8 is a cross-sectional view corresponding to FIG. 2 in a seventh stage in the process of manufacturing the cell shown in FIG. 1. FIG. 8 is a cross-sectional view corresponding to FIG. 2 in an eighth stage in the manufacturing process of the cell shown in FIG. 1. 1 is an overall perspective view of a stack structure of a fuel cell according to an embodiment of the present invention. FIG. 16 is an overall perspective view of the fuel gas manifold shown in FIG. 15. It is an enlarged view of the insertion hole formed in the support plate shown in FIG. It is the longitudinal cross-sectional view which showed the mode of the junction part of an insertion hole and the one end part of a cell, and the mode that the coating film was formed in the support plate. It is the cross-sectional view which showed the mode of the junction part of an insertion hole and the one end part of a cell, and the mode that the coating film was formed in the support plate. It is the longitudinal cross-sectional view which showed a mode that MgO particle | grains were contained inside the coating film. It is the figure which showed a mode that fuel gas and air were supplied / discharged with respect to the stack | stuck structure shown in FIG. FIG. 20 is a view corresponding to FIG. 19 in the case where one end portions of a plurality of cells are inserted into one insertion hole. It is a figure corresponding to FIG. 18 in the case where a cell is arrange | positioned with respect to a support plate so that the one end part of a cell may not enter into the hole of a support plate. It is sectional drawing which shows the stack structure of the fuel cell which concerns on a modification.

(Example of cell configuration used for stack structure)
First, a cell 100 used in a stack structure of a solid oxide fuel cell (SOFC) according to an embodiment of the present invention will be described.

(Constitution)
As shown in FIG. 1, the 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). A plurality of (in this example, four) identical power generation element portions A connected to each other have a so-called “horizontal stripe type” configuration in which they are arranged at predetermined intervals in the longitudinal direction.

The shape of the entire cell 100 as viewed from above is, for example, a side length L1 in the longitudinal direction (x-axis direction) of 50 to 500 mm and a length L2 in the width direction (y-axis direction) orthogonal to the longitudinal direction is 10. It is a rectangle of ˜100 mm (L1> L2). The total thickness L3 of the cell 100 is 1 to 5 mm (L2> L3). The entire 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, details of the cell 100 will be described with reference to FIG. 2, which is a partial cross-sectional view of the cell 100 corresponding to line 2-2 shown in FIG. 1. FIG. 2 is a partial cross-sectional view showing a configuration (part of) each of a typical pair of adjacent power generation element portions A and A and a configuration between the power generation element portions A and A. The configuration between the other power generation element portions A and A in other sets is the same as the configuration shown in FIG.

  The support substrate 10 is a flat plate-like fired body made of a porous material having no electronic conductivity. As shown in FIG. 6 to be described later, a plurality of (six in this example) fuel gas passages 11 (through holes) extending in the longitudinal direction are provided in the support substrate 10 at predetermined intervals in the width direction. Is formed. In this example, each recess 12 includes a bottom wall made of the material of the support substrate 10 and side walls closed in the circumferential direction made of the material of the support substrate 10 over the entire circumference (two side walls along the longitudinal direction and the width direction). A rectangular parallelepiped depression defined by two side walls).

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 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.

  The thickness of the support substrate 10 is 1 to 5 mm. 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 “electrical connection portions”.

  The interconnector 30 corresponds to the “first portion made of a dense material” in the “electrical connection portion” and has a porosity of less than 10%. 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 with respect to the “horizontal stripe type” cell 100 shown in FIG. 10 by exposing the upper and lower surfaces (in particular, each air electrode current collecting film 70) to “gas containing oxygen” (air or the like) (or flowing a gas containing oxygen along the upper and lower surfaces of the support substrate 10), An electromotive force is generated by an oxygen partial pressure difference generated between both side surfaces of the solid electrolyte membrane 40. Furthermore, when this structure is connected to an external load, chemical reactions shown in the following formulas (1) and (2) occur, and current flows (power generation state).
(1/2) · O ₂ + 2e ⁻ → O ₂ ⁻ (at the 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 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) The power is removed.

(Production method)
Next, an example of a manufacturing method of the “horizontal stripe type” cell 100 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 using, for example, a printing method or the like using a slurry obtained by adding a binder or the like to the powder of the material of the interconnector 30 (for example, LaCrO3).

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

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

  Then, 10 g of the support substrate molded body in which various molded films are thus formed is fired in air at 1500 ° C. for 3 hours. Thereby, the structure of the state in which the air electrode 60 and the air electrode current collection film | membrane 70 are not formed in the 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 cell 100 shown in FIG. 1 is obtained. At this point, the Ni component in the fuel electrode 20 (current collector 21 + active portion 22) is NiO due to firing in an oxygen-containing atmosphere. Therefore, in order to acquire the electron conductivity of the fuel electrode 20 (current collector 21 + active part 22), a reducing fuel gas is then flowed from the support substrate 10 side, and NiO is heated at 800 to 1000 ° C. for 1 to 10 hours. The reduction treatment is performed over a period of time. This reduction process may be performed during power generation. In the above, an example of the manufacturing method of the cell 100 shown in FIG. 1 was demonstrated.

(Example of overall structure of stack structure)
Next, a stack structure of a solid oxide fuel cell (SOFC) according to an embodiment of the present invention using the above-described cell 100 will be described. As shown in FIG. 15, the stack structure includes a plurality of cells 100 and a fuel gas manifold (an example of a metal member) 200 for supplying fuel gas to each of the plurality of cells 100. . The manifold 200 is a rectangular parallelepiped housing having a longitudinal direction (z-axis direction). The entire manifold 200 is made of a material (such as stainless steel) containing iron and chromium such as stainless steel.

  The upper wall of the manifold 200 (in other words, the top plate (flat plate) of the gas tank) also serves as a flat plate-like support plate 210 for supporting a large number of cells 100. Therefore, the support plate 210 is also made of stainless steel or the like. 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. Each cell 100 is supported by a support plate 210. Specifically, the end (one end) on the fuel gas inflow side in the longitudinal direction (x-axis direction) of the support substrate 10 in each cell 100 is bonded and supported to the support plate 210 using a bonding material. (Details of the bonding structure will be described later). Each cell 100 protrudes upward (in the positive x-axis direction) from the support plate 210. In addition, in each cell 100, a plurality of cells 100 are arranged in a stack along the longitudinal direction (z-axis direction) of the manifold 200. The end (other end) on the fuel gas discharge side in the longitudinal direction (x-axis direction) of the support substrate 10 in each cell 100 is a free end. Therefore, this stack structure can be expressed as a “cantilever stack structure”.

  As shown in FIG. 16, a large number of insertion holes 211 communicating with the internal space of the manifold 200 are formed on the surface (upper surface) of the support plate 210 (the upper wall of the manifold 200). The one end of the corresponding cell 100 is inserted into each insertion hole 211. Therefore, the internal space of the manifold 200 communicates with one end portion of each of the gas flow paths 11 of the plurality of cells 100 on the fuel gas inflow side.

  As shown in FIG. 17, the shape of each insertion hole 211 is an oval shape (L4> L5) having a length L4 and a width L5, and the direction of the symmetry axis with respect to line symmetry (second longitudinal direction, y-axis direction). Have The length L4 of the insertion hole 211 is 0.2 to 3 mm longer than the length L2 (see FIG. 1) of the side surface of one end of the cell 100. Similarly, the width L5 of the insertion hole 211 is 0.2 to 3 mm larger than the width L3 (see FIG. 1) of the side surface of one end of the cell 100. That is, as shown in FIGS. 18 and 19, when the one end of the cell 100 is inserted into the insertion hole 211, a gap is formed between the inner wall of the insertion hole 211 and the outer wall of the one end of the cell 100. Is done. In other words, the one end of the cell 100 is loosely fitted into the insertion hole 211. In FIG. 18 and FIG. 19 (particularly FIG. 19), the gap is exaggerated.

  As shown in FIGS. 18 and 19, solidified bonding material 300 is provided to fill the gap in each of the bonding portions between the insertion hole 211 and the one end of the cell 100. Thereby, each insertion hole 211 and the said one end part of the cell 100 corresponding are each joined and fixed. As shown in FIG. 18, the one end of the gas flow path 11 of each cell 100 communicates with the internal space of the manifold 200.

  Further, as shown in FIG. 18 (and FIG. 15), in this example, “the entire area of the outer wall surface of the manifold 200 (the entire area of the surface (upper surface) of the support plate 210, the side surface and the bottom surface of the outer wall of the manifold 200). The coating film 400 is continuously formed over “the entire area)”, “the entire area of the inner wall surface of each insertion hole 211”, and “the entire area of the inner wall surface that defines the internal space of the manifold 200”. As a result, the bonding material 300 covers the entire circumference of the side surface of the one end of each cell 100 so as to cover “the part corresponding to the entire circumference of the peripheral edge of each insertion hole 211” on the surface of the coating film 400. It is provided so that it may contact. The coating film 400 may not be formed on the “surface other than the entire surface (upper surface) of the support plate 210” of the manifold 200. For example, the coating film 400 is formed only on the upper surface and the lower surface of the manifold 200, and may not be formed on the inner wall surface of each insertion hole 211.

The bonding material 300 is made of crystallized glass. As the crystallized glass, for example, a SiO ₂ —B ₂ O ₃ system, a SiO ₂ —CaO system, or a MgO—B ₂ O ₃ system can be adopted, but a SiO ₂ —MgO system is most preferable. In this specification, crystallized glass means that the ratio (crystallinity) of “volume occupied by crystal phase” to the total volume is 60% or more, and “volume occupied by amorphous phase and impurities relative to the total volume”. "Refers to glass (ceramics) having a ratio of less than 40%. The crystallinity of the crystallized glass is specifically determined by, for example, “the crystal phase and the composition after the crystal phase is identified by using XRD or the like and crystallized by using SEM and EDS or SEM and EPMA. The volume ratio of the crystal phase region is calculated based on the result of observing the distribution. The porosity of the bonding material 300 is less than 10%. In other words, the bonding material 300 is dense.

The coating film 400 is made of a conductive ceramic material. Preferably, the coating film 400 is made of (Mn, Co) ₃ O ₄ . The thermal expansion coefficient of (Mn, Co) ₃ O ₄ is substantially equal to the thermal expansion coefficient of the material of the manifold 200 (stainless steel). Therefore, a large thermal stress hardly acts on the coating film 400 between the manifold 200 and the manifold 200. As a result, the possibility that peeling due to thermal stress occurs in the coating film 400 is reduced. The porosity of the coating film 400 is preferably 10 to 40%. Thereby, compared with the case where the coating film 400 is dense, the manufacturing cost of the coating film 400 becomes low.

As shown in FIG. 20, MgO particles are included in the coating film 400. The MgO particles are scattered (scattered) substantially uniformly throughout the coating film 400. As described above, with regard to the action and effect due to the inclusion of MgO particles, the content of MgO in the coating film 400, the thickness of the coating film 400, and the average value of the diameters of pores existing inside the coating film 400, It will be described later. As shown in FIG. 20, a chromia (Cr ₂ O ₃ ) film is interposed between the manifold 200 and the coating film 400. This chromia film is inevitably generated at the time of heat treatment to be described later performed on the coating film 400. The thickness of the chromia film is 2 to 15 μm.

  Also, as shown in FIG. 18, between adjacent cells 100, 100, between adjacent cells 100, 100 (more specifically, the fuel electrode 20 of one cell 100 and the air electrode of the other cell 100). A current collecting member 500 for electrically connecting 60) in series is interposed. The current collecting member 500 is made of, for example, a metal mesh. In addition, a current collecting member 600 for electrically connecting the front side and the back side of each cell 100 in series is also provided.

  When the cantilever stack structure of the fuel cell described above is operated, as shown in FIG. 21, fuel gas (eg, hydrogen) at a high temperature (eg, 600 to 800 ° C.) and “gas containing oxygen (eg, air) ) ". 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 other 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.

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 “entire area of the outer wall surface of the manifold 200”, “the entire area of the inner wall surface of each insertion hole 211”, and “the entire area of the inner wall surface that defines the internal space of the manifold 200” are coated for the coating film 400. A paste film of (Mn, Co) ₃ O ₄ is continuously formed. This paste contains MgO particles in addition to (Mn, Co) ₃ O ₄ powder. The particle size of (Mn, Co) ₃ O ₄ powder is 2 to 30 μm, and the particle size of MgO particles is 0.5 to 5 μm.

  This paste film is formed by, for example, coating or dipping. In this way, when the paste film is formed over the entire inner and outer wall surfaces of the manifold 200 and the inner wall surfaces of the respective insertion holes 211, masking is not necessary, and therefore the man-hour and cost required for coating are reduced. Can be done.

  Next, the plurality of cells 100 are aligned and fixed in a stack using a predetermined jig or the like. Next, while maintaining the state in which the plurality of cells 100 are aligned and fixed in a stack, each end of each of the plurality of cells 100 is inserted into the corresponding insertion hole of the support plate 210 (where the paste film is formed). 211 is inserted at a time. Next, a paste of an amorphous material (amorphous glass) for the bonding material 300 is filled in each gap of the bonding portion between the insertion hole 211 and one end portion of the cell 100. At that time, as shown in FIG. 18, the paste may be supplied to the joint to the extent that it protrudes upward from the surface of the support plate 210. In other words, the paste for the bonding material 300 covers the “part corresponding to the entire circumference of the peripheral edge of each insertion hole 211” on the surface of the paste film for the coating film 400, and the one end of each cell 100. It may be provided so as to be in contact with the entire circumference of the side surface.

Next, the amorphous material paste for the bonding material 300 filled as described above and the (Mn, Co) ₃ O ₄ paste film for the coating film 400 formed as described above are subjected to heat treatment (crystal Processing) is added. When the temperature of the amorphous material reaches its crystallization temperature by this heat treatment, a crystal phase is generated inside the material at the crystallization temperature, and crystallization proceeds. As a result, the amorphous material is solidified and ceramicized to become crystallized glass. Thereby, the bonding material 300 made of crystallized glass exhibits a function, and one end of each cell is bonded and fixed to the corresponding insertion hole 211. In other words, one end of each cell 100 is joined and supported by the support plate 210 using the joining material 300. Further, the coating film 400 can exhibit a coating function described later. Thereafter, the predetermined jig is removed from the plurality of cells 100 to complete the above-described cantilever stack structure.

  Hereinafter, the above-mentioned “paste of amorphous material (amorphous glass) for the bonding material 300” will be additionally described.

  One of poisoning elements that degrade the SOFC cell is boron B. When B of a certain concentration or more is supplied to the fuel electrode, Ni particles constituting the fuel electrode are enlarged, and as a result, the reaction resistance of the fuel electrode is increased and the SOFC cell is deteriorated. In addition, the strength of the solid electrolyte membrane is reduced by the solid solution of boron B with the solid electrolyte membrane, and as a result, the boron B may be scattered to the air electrode side. Glass is suspected as one source of B to the fuel and air electrodes. From such a viewpoint, it has been desired to reduce the B content in the bonding material 300. Based on the above knowledge, the content of boron B in the paste (and hence in the bonding material 300 as crystallized glass) (in particular, in the surface layer region of 30 μm or less from the surface of the bonding material 300) is 10 mol% or less. It is preferable that

  Similarly, impurities such as alkali metals, phosphorus P, sulfur S, and chlorine Cl are known as poisoning elements that degrade the SOFC cell. Similar to the above B, it is desired to reduce the content of the impurities in the bonding material 300 from the viewpoint of suppressing poisoning deterioration of the SOFC cell. Based on the above viewpoint, each content of alkali metal, P, S, and Cl in the paste (and thus in the bonding material 300 as crystallized glass) is preferably 0.5 mol% or less. .

The bonding material used when bonding the SOFC cell to another member is required to have a high coefficient of thermal expansion (10 × 10 ⁻⁶ / K or more at 50 to 850 ° C.). Generally, the glass composition in the paste is adjusted so that a crystal phase having a high thermal expansion coefficient is precipitated after the paste is crystallized by heat treatment. Here, in order to obtain a crystallized glass having a low B content and a high thermal expansion coefficient of 11.0 × 10 ⁻⁶ / K or more at 50 to 850 ° C., the glass in the paste is used. It has been found that adding barium Ba is important. Based on the above viewpoint, the content of Ba in the glass in the paste for the bonding material 300 is preferably 5 to 40 mol% as BaO.

  By the way, crystallized glass (crystallinity of 60% or more) obtained by crystallizing the paste by heat treatment includes a plurality of types of crystal phases. This is based on the following reason. That is, in general, during the heat treatment, the temperature rise pattern varies depending on the location in the space in the furnace used for the heat treatment. Accordingly, during the heat treatment, the temperature rise pattern of the paste also varies depending on the portion of the paste. As a result, the crystal phase to be deposited may vary depending on the portion of the paste. From the above, the crystallized glass obtained by crystallizing the paste can contain a plurality of types of crystal phases.

(Operations and effects due to MgO contained in coating film 400)
As described above, the coating film 400 made of (Mn, Co) ₃ O ₄ contains MgO particles. Here, since MgO functions as a capture agent (so-called getter) that captures chromium (Cr), even if the coating film 400 is porous, chromium volatilized from the surface of the manifold 200 made of stainless steel. Can be trapped by MgO existing inside the film while passing through the pores inside the coating film. Accordingly, the volatilized chromium is less likely to flow out of the coating film 400. As a result, it is possible to reliably suppress the volatilized chromium from reaching the power generation element portion of the cell 100 and poisoning the power generation element portion (particularly, the air electrode 60).

  Hereinafter, the test A performed for confirming the above-described action and effect due to the MgO contained in the porous coating film 400 will be described.

(Test A)
In the test A, a plurality of samples having different contents (volume%) of MgO particles contained in the coating film 400 made of (Mn, Co) ₃ O ₄ were prepared for the SOFC stack structure shown in FIG. It was done. Specifically, as shown in Table 1, seven types of levels were prepared. One sample (stack structure) was made for each level. Levels 2 to 7 contain MgO particles (MgO content> 0%), but only Level 1 does not contain MgO particles (MgO content = 0%). The content of MgO was adjusted by adjusting the amount of MgO particles included in the paste for the coating film 400. The particle size of (Mn, Co) ₃ O ₄ powder contained in this paste was 2 to ₃₀ μm, and the particle size of MgO particles was 0.5 to 5 μm.

  For each sample (stack structure) after the heat treatment, the number of stacks (number of cells 100) was 5. The cell 100 had a thin plate shape with a length (x-axis direction) of 50 to 500 mm, a width (y-axis direction) of 10 to 100 mm, and a thickness (z-axis direction) of 1 to 5 mm. The manifold 200 had a rectangular parallelepiped shape with a length (z-axis direction) of 20 to 40 mm, a width (y-axis direction) of 50 to 150 mm, and a height (x-axis direction) of 10 to 50 mm. The entire manifold 200 was made of stainless steel.

  About each sample after the said heat processing, the thickness of the coating film 400 was 20-50 micrometers. The porosity of the coating film 400 was 10 to 40%. That is, the coating film 400 was a porous film. The average value of the diameters of the pores existing inside the coating film 400 was 0.1 to 10 μm. The coating film 400 was formed over the entire surface of the manifold 200 as in the above embodiment (see FIG. 18). The said heat processing about a coating film was performed over 1 to 10 hours at 800-1050 degreeC. The porosity and the pore diameter of the coating film 400 were adjusted by adjusting the particle diameter of the powder in the paste, the added amount of the pore former, and the like. The thickness of the coating film 400 was adjusted by adjusting the thickness of the paste film.

  As the “thickness” of the coating film 400, an average value of thicknesses at predetermined ten locations in the coating film 400 was used. In addition, in the outer edge portion of the coating film 400 (region corresponding to the outer edge portion of the support plate 210), in consideration of the fact that the thickness of the coating film 400 is difficult to stabilize, portions other than the outer edge portion of the coating film 400 (the center portion, The “predetermined 10 places” were selected and adopted from the flat portion.

  The “porosity”, “average pore diameter”, and “MgO particle content” of the coating film 400 were calculated as follows. First, a so-called “resin filling” process was performed on the film so that the resin entered the pores of the coating film. The surface of the coating film treated with “resin filling” was mechanically polished. By performing image processing on the image obtained by observing the microstructure of the mechanically polished surface using a scanning electron microscope, the area of each pore portion (portion where the resin enters) is reduced. Calculated. From the area of each pore portion, the equivalent diameter of each pore was calculated. The average value of the equivalent diameters was defined as the “average value of pore diameter” (μm) of the coating film. Further, the ratio of the “total area of the pores” to the “total area of the mechanically polished surface” was set as the “porosity” (volume%) of the coating film 400. In addition, the total area of the portion occupied by the MgO particles was calculated by the image processing. The ratio of “total area of portions occupied by MgO particles” to “total area of the mechanically polished surface” was the MgO particle content (% by volume). The “porosity”, “average pore diameter”, and “MgO particle content” of the coating film 400 are respectively measured from a plurality of mechanically polished surfaces (for example, 10 locations). It is preferable to employ an average value of the obtained values.

  In this test A, an endurance test on the stability of the output voltage of the stack structure was performed on each of the samples after the heat treatment in a high temperature atmosphere of 800 ° C. while maintaining a constant current. Specifically, the reduction rate (deterioration rate) of the output voltage at the time when 1000 hours passed was calculated. The evaluation results are shown in Table 1.

  As is clear from Table 1, when the MgO particles are included in the coating film 400 (see levels 2 to 7), the deterioration rate of the output voltage is lower than when the MgO particles are not included (see level 1). small. This is considered based on the following reasons. That is, if MgO is not contained in the coating film 400, chromium volatilized from the surface of the manifold 200 made of stainless steel during the durability test causes pores inside the porous coating film 400 to be formed. It continues to flow out of the coating film 400. Therefore, when the outflowed chromium continues to reach the power generation element portion of the cell 100, poisoning of the power generation element portion (particularly, the fuel electrode 20 and the air electrode 60) proceeds, and the performance (characteristics) of the electrode deteriorates. proceed. As a result, the deterioration rate of the output voltage is increased after the endurance test.

  On the other hand, if the coating film 400 contains MgO particles, chromium volatilized from the surface of the manifold 200 is trapped by MgO existing inside the film while passing through the pores inside the porous coating film 400. Can be done. Accordingly, the volatilized chromium is less likely to flow out of the coating film 400. As a result, the power generation element portion (particularly, the air electrode 60) is not easily poisoned by the volatilized chromium, and thus the deterioration rate of the output voltage is reduced after the durability test.

In addition, when the content of MgO exceeded 30% by volume (see level 7), the coating film 400 was peeled off. This is considered based on the following reasons. That is, the thermal expansion coefficient of MgO is larger than that of (Mn, Co) ₃ O ₄ . Therefore, if the content of MgO in the coating film 400 is too large, the thermal expansion coefficient of the coating film 400 becomes too large, and the thermal expansion coefficient of the coating film 400 and the thermal expansion coefficient of the material of the manifold 200 (stainless steel). The difference increases. As a result, a large thermal stress acts on the coating film 400 between the manifold 200 and the coating film 400 is easily peeled off due to the thermal stress. Moreover, the test was not performed when the MgO content was less than 3% by volume. From the above, when the MgO content is 3 to 30% by volume (see Levels 2 to 6), after the durability test, the deterioration rate of the output voltage is reduced, and the coating film 400 is peeled off. It can be said that it becomes difficult to generate.

(Range of film thickness to suppress the occurrence of cracks in the coating film)

  In the SOFC stack structure shown in FIG. 15, cracks (or peeling) do not occur in the coating film 400 when operated in a normal environment. However, when the SOFC stack structure is operated under severe thermal stress, cracks may occur in the coating film 400. The inventor has found that the occurrence of such cracks has a strong correlation with the thickness of the coating film 400. Hereinafter, test B in which this has been confirmed will be described.

(Test B)
In Test B, a plurality of samples having different thicknesses of the coating film 400 made of (Mn, Co) ₃ O ₄ were fabricated for the SOFC stack structure shown in FIG. Specifically, as shown in Table 2, 10 types of levels were prepared. Ten samples (N = 10) were made for each level. For each sample, as in Test A above, the “thickness” of the coating film 400 was the average value of the thicknesses at the predetermined ten locations in the coating film 400. The thickness values listed in Table 2 are the values after the heat treatment (N = 10 average value).

  The basic form (size, number of stacks, materials, etc.), heat treatment conditions, etc. of each sample (SOFC stack structure shown in FIG. 15) were the same as in Test A above. In each sample, after the heat treatment, the porosity of the coating film 400 is 10 to 40%, and the content of MgO particles in the coating film 400 is 3 to 30% by volume. The average value of the diameter was set to 0.1 to 10 μm. The calculation method of “thickness”, “porosity”, “average value of pore diameter”, and “content ratio of MgO particles” of the coating film 400 is the same as in the above test A (about test C described later) The same).

  For each sample after the heat treatment, “a pattern in which the ambient temperature is raised from room temperature to 750 ° C. in 2 hours and then lowered from 750 ° C. to room temperature in 4 hours while reducing fuel gas is passed through the fuel electrode 20”. A heat cycle test was repeated 100 times. And about each sample, the presence or absence of the generation | occurrence | production of the crack (or peeling) in the surface of the coating film 400 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 seen from Table 2, after the thermal cycle test, which is severe in terms of thermal stress, if the thickness of the coating film 400 is greater than 100 μm, cracks are likely to occur on the surface of the coating film 400. It is considered that when the thickness of the coating film 400 is 100 μm or more, a slight crack may be observed at the stage of drying the coated paste, and the crack is generated starting from the minute crack. Moreover, the sample which has the coating film | membrane 400 with a thickness of less than 5 micrometers was not produced for the convenience of the test. As mentioned above, it can be said that the said crack is hard to generate | occur | produce as the thickness of the coating film 400 exists in the range of 5-100 micrometers.

  In addition, when the above embodiment is used under 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 when the thickness of the film 400 is outside the range of 5 to 100 μm, it has been separately confirmed that no cracks are generated on the surface of the coating film 400.

(Range of pore diameter in the film to suppress the occurrence of cracks in the coating film)
The present inventor has found that the occurrence of the cracks generated when the SOFC stack structure shown in FIG. 15 is operated under a severe thermal stress environment is “the average value of the diameters of the pores in the coating film 400. And found a strong correlation. Hereinafter, test C in which this has been confirmed will be described.

(Test C)
In Test C, for the SOFC stack structure shown in FIG. 15, a plurality of samples having different average diameters of pores in the coating film 400 made of (Mn, Co) ₃ O ₄ were produced. Specifically, as shown in Table 3, ten types of levels were prepared. Ten samples (N = 10) were made for each level. The average value of the pore diameters described in Table 3 is the value after the heat treatment (crystallization treatment) (the average value of N = 10).

  The basic form (size, number of stacks, materials, etc.), heat treatment conditions, etc. of each sample (SOFC stack structure shown in FIG. 15) were the same as in Test A above. In each sample, after the heat treatment, the porosity of the coating film 400 is 10 to 40%, the content of MgO particles in the coating film 400 is 3 to 30% by volume, and the thickness of the coating film 400 is 20 to 20%. 50 μm.

  For each sample after the above heat treatment (after the crystallization treatment), “From the 750 ° C. to the normal temperature after raising the ambient temperature from room temperature to 750 ° C. in 2 hours while supplying the reducing fuel gas to the fuel electrode 20 The thermal cycle test was repeated 100 times for the “pattern to be lowered in 4 hours”. And about each sample, the presence or absence of the generation | occurrence | production of the crack (or peeling) in the surface of the coating film 400 was confirmed. This confirmation was made by visual observation as well as observation using a microscope. The results are as shown in Table 3.

  As can be seen from Table 3, after the thermal cycle test, which is severe in terms of thermal stress, if the average pore diameter in the coating film 400 is larger than 10 μm, cracks are generated on the surface of the coating film 400. Easy to do. This is considered that when the average value of the pore diameter is larger than 10 μm, stress concentration occurs on the inner wall surface of the pore, which is caused by the occurrence of cracks. Moreover, the sample which has the coating film 400 whose average value of the diameter of a pore is less than 0.1 micrometer was not produced for the convenience of the test. As mentioned above, it can be said that the said crack is hard to generate | occur | produce as the average value of the diameter of the pore in the coating film 400 exists in the range of 0.1-10 micrometers.

  In addition, when the above embodiment is used under 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), It has been separately confirmed that cracks do not occur on the surface of the coating film 400 even if the average value of the pore diameters in the film 400 is outside the range of 0.1 to 10 μm.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, in the above-described embodiment, a so-called “horizontal stripe type” cell in which adjacent power generating element portions are electrically connected is employed, but only one power generating element portion is provided on the surface of the support substrate. A cell may be employed.

  Moreover, in the said embodiment, although the said one end part of one cell is inserted in one insertion hole formed in the support plate, as shown in FIG. 22, one insertion hole 211 formed in the support plate The one end portions of two or more cells 100 may be inserted into the two. In FIG. 22, the interval between adjacent cells 100 is exaggerated. Further, all of the one end portions of the plurality of cells may be inserted into one (only) insertion hole formed in the support plate.

  In the above embodiment, the one end of the cell 100 is inserted into the insertion hole 211 (that is, the one end of the cell 100 enters the internal space of the insertion hole 211) (see FIG. 23, the one end of the cell 100 may not be inserted into the hole 211 (that is, the one end of the cell 100 may not enter the internal space of the hole 211). ). In this case, the bonding material 300 is provided so as to fill a space existing between the hole 211 and the one end of the cell 100 in each of the bonding portions between the holes 211 and the corresponding one end of the cell 100. It is done.

  Furthermore, in the above embodiment, the top plate of the manifold 200 also serves as the support plate 210 for supporting a large number of cells 100 (that is, the support plate 210 is configured integrally with the manifold 200). As long as the internal space of the manifold and the gas flow paths of the plurality of cells communicate with each other, the support plate may be configured separately from the manifold.

  In the above embodiment, a plurality of recesses 12 are formed on each of the upper and lower surfaces of the flat support substrate 10 and a plurality of power generation element portions A are provided. The recessed part 12 may be formed and the several electric power generation element part A may be provided. In the above embodiment, the support substrate 10 has a flat plate shape, but the support substrate may have a cylindrical shape. In this case, the inner space of the cylindrical support substrate functions as a gas flow path.

Moreover, in the said embodiment, although the coating film 400 is formed only on the surface of the manifold 200, the current collection member 500 and / or the current collection member 600 (refer FIG. 18, FIG. 23) contain iron and chromium. When made of a metal material (stainless steel or the like), the coating film 400 (film made of (Mn, Co) ₃ O ₄ and containing MgO) is also formed on the surface of the current collecting member 500 and / or the current collecting member 600. Is preferably formed. Thereby, it is possible to prevent chromium volatilized not only from the manifold 200 but also from the surface of the current collecting member 500 and / or the current collecting member 600 from reaching the power generating element portion of the cell 100.

  In the above embodiment, the manifold 200 has been described as corresponding to the metal member of the present invention. However, a metal member that is not a manifold corresponds to the metal member of the present invention, and the surface of the metal member is coated with MgO. A film 400 may be formed. For example, in the above embodiment, the manifold 200 supports each cell 100 (a so-called cylindrical plate stack structure, but as shown in FIG. 24, the separator supports each cell 100 as shown in FIG. In this case, a separator corresponds to the metal member of the present invention.

  Specifically, the stack structure of the fuel cell includes a cell 100 and a plurality of separators 201. Each separator 201 is electrically connected to the cell 100 via the mesh 301. The mesh 301 is nickel, for example. Each separator 201 is bonded to the cell 100 via a seal glass 401.

  The cell 100 includes a fuel electrode 101, a solid electrolyte 102, and an air electrode 103. A fuel electrode 101 is disposed on one surface of the electrolyte 102, and an air electrode 103 is disposed on the other surface of the electrolyte 102. Each separator 201 is configured to supply air or fuel gas to the cell 100. Each separator 201 supplies, for example, fuel gas or air to the fuel electrode 101 or the air electrode 103 through the through hole TH.

  A coating film 400 containing MgO is formed on the surface of each separator 201. The coating film 400 is also formed on the inner wall surface of the through hole TH. The coating film 400 is the same as that in the above embodiment, and a detailed description thereof is omitted. The coating film 400 may be formed only on the surface of each separator 201 on the air electrode side.

In the above embodiment, the coating film 400, (Mn, _Co) are constituted by 3 _{O 4,} the base material of the coating film 400 is not particularly limited thereto. For example, the base material of the coating film 400 is Co ₃ O ₄ , ZnO, (La, Sr) (Co, Fe) O ₃ , (La, Sr) FeO ₃ , La (Ni, Fe, Cu) O ₃ , or (Sm, Sr) CoO ₃ may be used. This coating film 400 may be applied to the mesh 301.

  DESCRIPTION OF SYMBOLS 10 ... Support substrate, 11 ... Fuel gas flow path, 20 ... Fuel electrode, 40 ... Solid electrolyte membrane, 60 ... Air electrode, 100 ... Cell, 200 ... Manifold, 210 ... Support plate, 211 ... Insertion hole, 300 ... Bonding material , 400 ... coating film, A ... power generation element part

Claims (12)

A plurality of fuel cells having a fuel electrode, a solid electrolyte, and an air electrode;
A metal member composed of a metal material containing iron and chromium;
A fuel cell stack structure comprising: a porous coating film formed on a surface of the metal member and containing a ceramic material as a main component and containing MgO. The fuel cell stack structure according to claim 1,
The coating film is a stack structure of a fuel cell made of a conductive ceramic material. A fuel cell stack structure according to claim 2,
The stack structure of a fuel cell, wherein the conductive ceramic material is (Mn, Co) ₃ O ₄ . The fuel cell stack structure according to any one of claims 1 to 3,
A stack structure of a fuel cell, wherein the coating film has a porosity of 10 to 40%. The fuel cell stack structure according to any one of claims 1 to 4,
The stack structure of the fuel cell, wherein the content of MgO in the coating film is 3 to 30% by volume. The fuel cell stack structure according to any one of claims 1 to 5,
The stack structure of the fuel cell, wherein the coating film has a thickness of 5 to 100 μm. The fuel cell stack structure according to any one of claims 1 to 6,
A fuel cell stack structure, wherein an average value of pore diameters present in the coating film is 0.1 to 10 μm. The stack structure of the fuel cell according to any one of claims 1 to 7,
The metal member is a manifold that supports the fuel cells.
The fuel cell includes a power generation element unit having the fuel electrode, the solid electrolyte, and the air electrode, and a support substrate that supports the power generation element unit,
A stack structure of a fuel cell, wherein the support substrate has a longitudinal direction, and a fuel gas passage along the longitudinal direction is formed inside. The fuel cell stack structure according to claim 8,
The manifold has an upper wall made of a metal material containing the iron and chromium,
The coding membrane is a fuel cell stack structure formed over the entire surface of the upper wall of the manifold. The fuel cell stack structure according to claim 9, wherein
The entire manifold is made of a metal material containing the iron and chromium,
In the upper wall of the manifold, one or a plurality of through-holes for communicating the internal space of the manifold and one end portion on the fuel gas inflow side of the plurality of cells are formed,
The one end of each cell is positioned corresponding to the corresponding hole;
The entire circumference of the side surface of the one end of each cell is such that the gas in the internal space of the manifold does not leak outside through a gap between each hole and the corresponding one end of the cell. It is bonded and fixed to the upper wall of the manifold via the bonding material,
The coating film is a fuel cell stack structure formed continuously on the inner wall surface of each hole and the entire surface of the manifold in addition to the entire surface of the upper wall of the manifold. The fuel cell stack structure according to claim 10,
The bonding material is provided so as to cover a portion of the surface of the coating film corresponding to the entire circumference of the peripheral edge of each hole and to be in contact with the entire circumference of the side surface of the one end of each cell. A fuel cell stack structure. In the fuel cell stack structure according to any one of claims 1 to 7,
The metal member is a separator disposed between the fuel cells.
Fuel cell stack structure.