JP5455271B1 - Fuel cell - Google Patents

Abstract

A fuel cell in which a coating film is formed at a gas discharge side end of a porous support substrate having a gas flow path formed therein, which can suppress the occurrence of cracks in the coating film. To provide.
The fuel cell is provided with a flat porous support substrate 11 in which a plurality of gas flow paths 18 are formed along the longitudinal direction, and a main surface of the support substrate 11, and at least a fuel electrode. 12, a solid electrolyte 13 and an air electrode 14 are stacked in this order. A coating film having a porosity smaller than that of the support substrate is formed on the end portion on the gas discharge side in the inner wall surface of each gas flow path 18 and on the end surface on the gas discharge side in the longitudinal direction of the support substrate 11. The surface roughness of the portion of the coating film formed on the end surface of the support substrate 11 on the gas discharge side is 0.13 to 5.2 μm in terms of arithmetic average roughness Ra.
[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 coating film having a porosity smaller than that of a support substrate is formed on the side end face (see, for example, Patent Document 1). Formation of this coating film makes it difficult for air in the external space to enter the inside of the gas discharge side end portion of the support substrate, and as a result, generation of the cracks can be suppressed.

JP 2012-9226 A

  By the way, in the configuration in which the coating film is formed as described above, a crack may occur in the coating film depending on the operating environment of the fuel cell. The present inventor has conducted various experiments in order to deal with such problems. As a result, the present inventors have found that the occurrence of such cracks has a strong correlation with the “surface roughness of the coating film”.

  An object of the present invention is a fuel cell in which a coating film is formed at a gas discharge side end of a porous support substrate in which a gas flow path is formed, and a situation in which a crack occurs in the coating film is suppressed. It is to provide what you get.

  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 coating film is formed.

  This fuel cell is characterized in that the surface roughness of the portion of the coating film formed on the end surface on the gas discharge side of the support substrate is 0.13 to 5.2 μm in terms of arithmetic average roughness Ra. . Here, it is preferable that the support substrate has a porosity of 20 to 60%, and the coating film has a porosity of 0 to 10%.

  This inventor is not so when the surface roughness of the part formed in the end surface of the said support substrate in the said gas exhaust side in the said coating film is 0.13-5.2 micrometers by arithmetic mean roughness Ra. It has been found that cracks are less likely to occur in the same part than in the case. Furthermore, when the thickness of the portion of the coating film formed on the end surface on the gas discharge side of the support substrate is 3 to 45 μm, more cracks are generated in the same portion than in the case where the thickness is not so. I also found it difficult. Details of these points will be described later.

1 is a perspective view showing a fuel battery cell according to a first embodiment of the present invention. FIG. 2 is an overall perspective view of a stack structure including a plurality of fuel cells shown in FIG. 1. FIG. 3 is a perspective view of the entire fuel gas manifold shown in FIG. 2. It is sectional drawing which shows the flow of the gas in the inside of the stack structure shown in FIG. FIG. 3 is a perspective view showing how fuel gas and air are supplied to and discharged from the stack structure shown in FIG. 2. It is a perspective view which shows the fuel battery cell which concerns on 2nd Embodiment of this invention. It is sectional drawing corresponding to the 7-7 line | wire 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. 8 is a cross-sectional view corresponding to FIG. 7 in a first stage in the manufacturing process of the fuel cell shown in FIG. 6. FIG. 8 is a cross-sectional view corresponding to FIG. 7 in a second stage in the manufacturing process of the fuel cell shown in FIG. 6. FIG. 8 is a cross-sectional view corresponding to FIG. 7 in a third stage in the manufacturing process of the fuel cell shown in FIG. 6. FIG. 8 is a cross-sectional view corresponding to FIG. 7 in a fourth stage in the manufacturing process of the fuel cell shown in FIG. 6. FIG. 8 is a cross-sectional view corresponding to FIG. 7 in a fifth stage in the manufacturing process of the fuel cell shown in FIG. 6. FIG. 8 is a cross-sectional view corresponding to FIG. 7 in a sixth stage in the manufacturing process of the fuel cell shown in FIG. 6. FIG. 7 is a cross-sectional view corresponding to FIG. 7 in a seventh stage in the manufacturing process of the fuel cell shown in FIG. 6. FIG. 8 is a cross-sectional view corresponding to FIG. 7 in an eighth stage in the manufacturing process of the fuel cell shown in FIG. 6. It is sectional drawing corresponding to FIG. 7 of the 1st modification of the fuel cell shown in FIG. It is sectional drawing corresponding to FIG. 7 of the 2nd modification of the fuel battery cell shown in FIG. It is sectional drawing corresponding to FIG. 7 of the 3rd modification of the fuel battery cell shown in FIG. It is sectional drawing corresponding to FIG. 8 of the 4th modification of the fuel battery cell shown in FIG. FIG. 7 is an overall perspective view of a stack structure including a plurality of fuel cells shown in FIG. 6. It is a perspective view of the whole fuel gas manifold shown in FIG. FIG. 25 is a cross-sectional view showing a gas flow inside the stack structure shown in FIG. 24. It is the perspective view which showed a mode that fuel gas and air were supplied / discharged with respect to the stack | stuck structure shown in FIG.

(First embodiment)
As shown in FIG. 1, in the solid oxide fuel cell (SOFC) cell 100 according to the first embodiment of the present invention, a porous surface on one main surface of a flat porous conductive support 11 is porous. The fuel electrode 12, the dense solid electrolyte 13, and the air electrode 14 made of porous conductive ceramics are sequentially laminated. Further, an intermediate film 15, an interconnector 16 made of a lanthanum-chromium oxide material, and a current collecting film 17 made of a P-type semiconductor material are sequentially formed on the main surface of the conductive support 11 opposite to the air electrode 14. Has been.

  The cell 100 has a flat plate shape having a first longitudinal direction (x-axis direction), the length L1 (length in the first longitudinal direction) of the cell 100 is 50 to 500 mm, and the width L2 is 10 to 100 mm. The thickness L3 is 1 to 5 mm (L1> L2). The shape of the side surface (length L2, oval shape of width L3, L2> L3) of one end portion of the cell 100 in the first longitudinal direction (x-axis direction) has the second longitudinal direction (y-axis direction).

  A plurality of gas flow paths 18 parallel to each other are formed in the conductive support 11 at intervals in the width direction (y direction) along the longitudinal direction (x axis direction). The cross-sectional shape of each gas flow path 18 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 gas flow paths 18 and 18 is 1-5 mm. In addition, the cross-sectional shape of each gas flow path 18 may be an ellipse, a long hole, a quadrangle having arcs at four corners, or the like.

  The cell 100 includes side end portions B and B provided on both sides in the width direction (direction perpendicular to the longitudinal direction) and a pair of flat portions A and A connecting the side end portions B and B, respectively. ing. The pair of flat portions A and A are flat and substantially parallel. On one of the flat portions A and A, the fuel electrode 12, the solid electrolyte 13, and the air electrode 14 are formed in this order on one main surface of the conductive support 11, and on the other of the flat portions A and A, On the other main surface of the conductive support 11, an intermediate film 15, an interconnector 16, and a current collecting film 17 are formed in this order.

  The width of the conductive support 11 is preferably 10 to 100 mm, and the thickness is preferably 1 to 5 mm. The aspect ratio (width / thickness) of the conductive support 11 is 5 to 100. The shape of the conductive support 11 is expressed as “thin plate shape”, but depending on the combination of the dimension in the width direction and the dimension in the thickness direction, it may be referred to as “ellipsoidal column shape” or “flat shape”. Can be expressed. The shape of the conductive support 11 may be cylindrical.

  The conductive support 11 is composed mainly of a rare earth element oxide composed of one or more selected from Y, Lu, Yb, Tm, Er, Ho, Dy, Gd, Sm and Pr and Ni and / or NiO. It is desirable to be composed of the material In addition to Ni, Fe, Cu, or the like may be included.

The conductive support 11 can also be described as including “NiO (nickel oxide) or Ni (nickel)” and “insulating ceramics”. Insulating ceramics include CSZ (calcia stabilized zirconia), YSZ (8YSZ) (yttria stabilized zirconia), Y ₂ O ₃ (yttria), MgO (magnesium oxide), or “MgAl ₂ O ₄ (magnesia alumina spinel). ) And MgO (magnesium oxide) "or the like. The conductivity of the conductive support 11 is 10 to 2000 S / cm at 800 ° C. The porosity of the conductive support 11 is 20 to 60%.

The intermediate film 15 formed between the conductive support 11 and the interconnector 16 is made of a material mainly containing ZrO ₂ containing Ni and / or NiO and a rare earth element, or a rare earth oxide (for example, Y ₂ O ₃ ). The Ni conversion amount of the Ni compound in the intermediate film 15 is preferably 35 to 80% by volume, and more preferably 50 to 70% by volume in the total amount. When the Ni conversion amount is 35% by volume or more, the conductive path by Ni is increased, and the conductivity of the intermediate film 15 is improved. As a result, the voltage drop caused by the intermediate film 15 is reduced. Moreover, when the Ni conversion amount is 80% by volume or less, the difference in thermal expansion coefficient between the conductive support 11 and the interconnector 16 can be reduced, and the occurrence of cracks at the interface between the two can be suppressed.

  Further, from the viewpoint of reducing the voltage drop, the thickness of the intermediate film 15 is preferably 20 μm or less, and more preferably 10 μm or less.

The thermal expansion coefficient of the middle rare earth element or heavy rare earth element oxide is smaller than that of “ZrO ₂ containing Y ₂ O ₃ ” in the solid electrolyte 13. Therefore, the thermal expansion coefficient of the conductive support 11 as a cermet material with Ni can be made closer to the thermal expansion coefficient of the solid electrolyte 13. As a result, cracks in the solid electrolyte 13 and separation of the solid electrolyte 13 from the fuel electrode 12 can be suppressed. Furthermore, by using a heavy rare earth element oxide having a small thermal expansion coefficient, Ni in the conductive support 11 can be increased, and the electrical conductivity of the conductive support 11 can be increased. From this viewpoint, it is desirable to use heavy rare earth element oxides.

  If the sum of the thermal expansion coefficients of the rare earth element oxide is less than the thermal expansion coefficient of the solid electrolyte 13, the light rare earth elements La, Ce, Pr, and Nd oxides are added to the medium rare earth element and heavy rare earth element. There is no problem even if it is contained.

  Moreover, the raw material cost can be significantly reduced by using a complex rare earth element oxide containing a plurality of inexpensive rare earth elements in the course of purification. Also in this case, it is desirable that the thermal expansion coefficient of the complex rare earth element oxide is less than the thermal expansion coefficient of the solid electrolyte 13.

  Further, it is desirable to provide a current collector film 17 made of a P-type semiconductor, for example, a transition metal perovskite oxide, on the surface of the interconnector 16. When a current collecting member made of metal is disposed directly on the surface of the interconnector 16, the potential drop increases due to non-ohmic contact. In order to secure ohmic contact and reduce the potential drop, it is necessary to connect the current collector film 17 made of a P-type semiconductor to the interconnector 16. As the P-type semiconductor, it is desirable to use a transition metal perovskite oxide. As the transition metal perovskite oxide, it is desirable to use at least one of a lanthanum-manganese oxide, a lanthanum-iron oxide, a lanthanum-cobalt oxide, or a composite oxide thereof.

The fuel electrode 12 provided on the main surface of the conductive support 11 is composed of Ni and ZrO _{2 in} which a rare earth element is dissolved. The thickness of the fuel electrode 12 is desirably 1 to 30 μm. When the thickness of the fuel electrode 12 is 1 μm or more, a three-layer interface as the fuel electrode 12 is sufficiently formed. Further, when the thickness of the fuel electrode 12 is 30 μm or less, interfacial peeling due to a difference in thermal expansion from the solid electrolyte 13 can be prevented.

The solid electrolyte 13 provided on the main surface of the fuel electrode 12 is made of yttria-stabilized zirconia YSZ (dense ceramic) containing yttria (Y ₂ O ₃ ). The thickness of the solid electrolyte 13 is desirably 0.5 to 100 μm. Gas permeation can be prevented when the thickness of the solid electrolyte 13 is 0.5 μm or more. Moreover, the increase in a resistance component can be suppressed because the thickness of the solid electrolyte 13 is 100 micrometers or less.

The air electrode 14 is a lanthanum-manganese oxide, lanthanum-iron oxide, lanthanum-cobalt oxide of a transition metal perovskite oxide, or at least one porous conductive material of a composite oxide thereof. Made of ceramics. The air electrode 14 is preferably a (La, Sr) (Fe, Co) O ₃ system from the viewpoint of high electrical conductivity in the middle temperature range of about 800 ° C. The thickness of the air electrode 14 is preferably 10 to 100 μm from the viewpoint of current collection.

  The interconnector 16 is a dense body in order to prevent leakage of fuel gas and oxygen-containing gas between the inside and outside of the conductive support 11. Moreover, since the inner and outer surfaces of the interconnector 16 are in contact with the fuel gas and the oxygen-containing gas, respectively, they have reduction resistance and oxidation resistance.

  The thickness of the interconnector 16 is desirably 30 to 200 μm. When the thickness of the interconnector 16 is 30 μm or more, gas permeation can be completely prevented, and when it is 200 μm or less, an increase in resistance component can be suppressed.

For example, a bonding layer made of Ni and ZrO ₂ or Y ₂ O ₃ may be interposed between the end portion of the interconnector 16 and the end portion of the solid electrolyte 13 in order to improve the sealing performance.

  In this cell 100, the dense solid electrolyte 13 is not only on one main surface of the conductive support 11 but also on the side of the interconnector 16 on the other main surface via the side end of the conductive support 11. It is formed to the end face. That is, the solid electrolyte 13 is extended to the other main surface of the conductive support 11 so as to form the side ends B, B on both sides, and is joined to the interconnector 16. Note that the side ends B and B (side ends of the conductive support 11) have curved shapes that protrude outward in the width direction in order to relieve the thermal stress that occurs due to heating and cooling associated with power generation. It is desirable.

  Next, a method for manufacturing the cell 100 as described above will be described. First, rare earth element oxide powder excluding La, Ce, Pr, and Nd elements and Ni and / or NiO powder are mixed. A conductive support material in which an organic binder and a solvent are mixed is extruded into this mixed powder to produce a plate-shaped conductive support molded body. This molded body is dried and degreased.

In addition, a sheet-like solid electrolyte molded body is produced using a solid electrolyte material in which a ZrO ₂ powder in which a rare earth element (Y) is dissolved, an organic binder, and a solvent are mixed.

Next, a slurry to be the fuel electrode 12 prepared by mixing Ni and / or NiO powder, ZrO ₂ powder in which a rare earth element is solid-solved, an organic binder, and a solvent is formed into the solid electrolyte molded body. Applied to one side. Thereby, a fuel electrode molded body is formed on one surface of the solid electrolyte molded body.

  Next, the conductive support body is formed such that a laminate of the sheet-like solid electrolyte formed body and the fuel electrode body is in contact with the conductive electrode body. It is wound around the compact.

  Next, several layers of the sheet-like solid electrolyte molded body are laminated on the solid electrolyte molded body at the position where the side end portions B and B of the laminated molded body are formed, and dried. Moreover, the slurry used as the solid electrolyte 13 may be screen-printed on the solid electrolyte molded body. In addition, degreasing may be performed at this time.

  Next, a sheet-like interconnector molded body is produced using an interconnector material in which a lanthanum-chromium oxide powder, an organic binder, and a solvent are mixed.

Moreover, a sheet-like intermediate film molded body is produced using a slurry in which Ni and / or NiO powder, a ZrO ₂ powder in which a rare earth element is dissolved, an organic binder, and a solvent are mixed.

  Next, the interconnector molded body and the intermediate film molded body are laminated. The laminate is laminated on the conductive support molded body so that the intermediate film molded body side of the laminate is in contact with the exposed conductive support molded body side.

  Thereby, the fuel electrode molded body and the solid electrolyte molded body are sequentially laminated on one main surface of the conductive support molded body, and the intermediate film molded body and the interconnector molded body are laminated on the other main surface. A body is made. Each molded body can be produced by sheet molding by a doctor blade, printing, slurry dip, spraying by spraying, and the like. Moreover, each molded object can be produced by these combinations. Note that a molded film of a coating film 500 (see FIG. 4), which will be described later, is also formed on the gas discharge side end of the support molded body in this state using a dipping method or the like.

  Next, the laminated molded body is degreased and cofired at 1300 to 1600 ° C. in an oxygen-containing atmosphere.

  Next, a transition metal perovskite oxide powder, which is a P-type semiconductor, and a solvent are mixed to produce a paste. The laminate is immersed in this paste. An air electrode molded body and a current collector film molded body are formed on the surfaces of the solid electrolyte 13 and the interconnector 16 by dipping or direct spray application, respectively. These molded bodies are baked at 1000 to 1300 ° C., whereby the fuel cell according to the present invention is manufactured.

  At this time, the Ni component in the conductive support 11, the fuel electrode 12, and the intermediate film 15 is NiO by firing in an oxygen-containing atmosphere. Therefore, in order to acquire these electroconductivity, after that, reducing fuel gas is flowed from the electroconductive support body 11 side, and NiO is reduced at 800-1000 degreeC over 1 to 10 hours. This reduction process may be performed during power generation.

(Example of stack structure)
Next, an example of a stack structure using the above-described plurality of cells 100 will be described with reference to FIGS. As shown in FIG. 2, 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. 3, 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. 4, 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 18 of each cell 100 communicates with the internal space of the manifold 200.

  As shown in FIG. 4, 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.

  As shown in FIG. 4, a coating film 500 having a porosity smaller than that of the conductive support 11 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. 4, 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 conductive support 11 and on the end portion on the gas discharge side in the inner wall surface of each gas flow path 18. The end face coating film 501 is continuous with each flow path inner wall surface coating film 502. In the example shown in FIG. 4, 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 H in the longitudinal direction of each channel inner wall surface coating film 502 (see the enlarged view of the Z portion in FIG. 4) 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 13 formed on the outer periphery of the conductive support 11.

  The coating film 500 is made of, for example, zirconia containing a rare earth element. The coating film 500 may be made of the same material as the solid electrolyte 13 (for example, yttria-stabilized zirconia YSZ), or may be made of the same material as the conductive support 11. The coating film 500 is dense enough to prevent air from entering the conductive support 11 from the external space, and its porosity is 0 to 10%. As described above, the coating film 500 may be formed by co-firing the conductive support 11, the fuel electrode 12, and the solid electrolyte 13, or firing the conductive support 11, the fuel electrode 12, and the solid electrolyte 13. Later, it may be formed by a vacuum film forming process method (evaporation method, CVD method (Chemical Vapor Deposition) or the like).

  When operating the stack structure described above, as shown in FIG. 5, 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 to the internal space of the manifold 200 and is then introduced into the gas flow path 18 of the corresponding cell 100 via each insertion hole 211. The fuel gas that has passed through each gas flow path 18 is then discharged from the gas discharge side end (free end) of each gas flow path 18. 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 18 to the external space reacts with air (oxygen) in the external space near the gas discharge port and is burned. Here, since the coating film 500 is formed on the gas discharge side end (free end) of each cell 100, the inside of the gas discharge side end of the porous conductive support 11 is placed in the external space. The entry of certain air can be suppressed. As a result, it is possible to suppress the occurrence of a situation in which a crack is generated at the gas discharge side end portion of the conductive support 11 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.

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

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

  When the fuel cell (stack structure) according to the first embodiment that has been reduced by the reduction treatment is operated in a normal environment, no cracks are generated in the coating film 500. However, when the fuel cell (stack structure) is operated under a severe thermal stress environment, cracks may occur in the coating film 500 (particularly, the end face coating film 501). The present inventor has found that the occurrence of such cracks has a strong correlation with the “surface roughness of the coating film 500 (end surface coating film 501)”. Hereinafter, test A in which this has been confirmed will be described.

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

  As the conductive support 11 used in each sample (the fuel cell shown in FIG. 1), the porosity of the material is 20 to 60%, and the thickness and width are 2.5 mm and 50 mm, respectively (that is, The aspect ratio was 20), the cross-sectional shape of the gas flow path 18 was a circle having a diameter of 1.5 mm, and the pitch P between the adjacent gas flow paths 18 and 18 was 5.0 mm. In each sample, as described above, the laminated molded body (a molded body in which at least a fuel electrode molded body and a solid electrolyte molded body are laminated on a conductive support molded body) and a molded body of a coating film are co-fired. It was done. Thereafter, a reduction process was performed on each sample. In each sample, the thickness of the coating film 500 (in particular, the end face coating film 501) was 5 to 10 μm.

  Adjustment of the “surface roughness of the coating film” was achieved by adjusting the surface roughness of the conductive support 11, the average particle diameter of the coating material, the slurry viscosity, the pulling speed during dip coating, and the like. Specifically, the surface roughness (Ra) of the support is 0.25 to 2.5 μm, the average particle size of the coating material is 0.3 to 1.2 μm, the slurry viscosity is 1 to 10,000 mPa · s, and the lifting speed is It adjusted within the range of 0.1-30 mm / sec. The firing temperature was adjusted within the range of 1300 to 1600 ° C. The firing time was adjusted within a range of 1 to 20 hours. The reduction treatment temperature was adjusted within the range of 800 to 1000 ° C. The reduction treatment time was adjusted within a range of 1 to 10 hours.

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

  For each sample in the stage after the reduction treatment (reduced state), “the ambient temperature was raised from room temperature to 750 ° C. in 2 hours while reducing fuel gas was circulated through the fuel electrode 12 and then from 750 ° C. to room temperature. The thermal cycle test was repeated 100 times. And about each sample, the presence or absence of the generation | occurrence | production of the crack in the end surface coating film 501 was confirmed. This confirmation was made by visual observation as well as observation using a microscope. The results are as shown in Table 1.

  As can be understood from Table 1, after the thermal cycle test, which is severe in terms of thermal stress, if the surface roughness of the end face coating film 501 exceeds 5.2 μm in arithmetic average roughness Ra, the reason is unknown. However, cracks are likely to occur in the end face coating film 501. On the other hand, when the surface roughness of the end face coating film 501 is not more than 5.2 μm in terms of arithmetic average roughness Ra, it can be said that the cracks are hardly generated.

Further, as described above, the coating film 500 formed in each sample is formed by co-firing with the conductive support 11, the fuel electrode 12, and the solid electrolyte 13. In this case, the surface roughness of the end face coating film 501 could not be less than 0.13 μm in terms of arithmetic average roughness Ra. From the above, when the surface roughness of the end surface coating film 501 is within the range of 0.13 to 5.2 μm in terms of arithmetic average roughness Ra, cracks are less likely to occur in the end surface coating film 501 than in the case where it is not. It can be said.
It is preferable.

  The inventor uses the first embodiment 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 if the surface roughness of the end face coating film 501 is outside the range of 0.13 to 5.2 μm in terms of arithmetic average roughness Ra, it is separately confirmed that the coating film 500 (end face coating film 501) does not crack. ing.

  The above results correspond to the case where the cross-sectional shape of each gas flow path 18 is circular. Has already been confirmed. This result corresponds to the case where the aspect ratio of the conductive support is 20, but it has already been confirmed that the same result can be obtained if the aspect ratio of the conductive support is in the range of 5 to 100. ing. Further, it is desirable that the surface roughness of the coating film 500 is uniform over the entire area of the coating film 500. Therefore, the surface roughness of the coating film 500 excluding the end surface coating film 501 is also the same as that of the end surface coating film 501. Similarly, the arithmetic average roughness Ra is preferably in the range of 0.13 to 5.2 μm.

(Thickness of coating film)
Further, the inventor of the present invention has a thickness T1 of the end face coating film 501 (refer to an enlarged view of the Z portion in FIG. 4) of 3 when the surface roughness of the end face coating film 501 is 0.13 to 5.2 μm. It has also been found that cracks are less likely to occur in the end face coating film 501 when the thickness is ˜45 μm. Hereinafter, test B in which this has been confirmed will be described.

(Test B)
In test B, for the fuel cell according to the first embodiment, the material of the conductive support 11, the material of the end face coating film 501, the surface roughness of the end face coating film 501, and the thickness T1 of the end face coating film 501 are Several samples with different combinations were made. Specifically, as shown in Table 2, eleven kinds of levels (combinations) were prepared. Ten samples (N = 10) were made for each level. The surface roughness of the end face coating film 501 of each sample is in the range of 0.3 to 0.8 μm.

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

  Then, for each sample in the stage after the reduction treatment (reduced state), a thermal cycle test that is severer in terms of thermal stress than the thermal cycle test performed in test A, that is, “reducing a reducing fuel gas to the fuel electrode 12. While circulating, the thermal cycle test was repeated 100 times. “Pattern of raising the ambient temperature from room temperature to 750 ° C. over 1 hour and then lowering from 750 ° C. to room temperature over 2 hours”. And about each sample, the presence or absence of the generation | occurrence | production of the crack in the end surface coating film 501 was confirmed. This confirmation was made by visual observation as well as observation using a microscope. The results are as shown in Table 2.

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

  The above results correspond to the case where the cross-sectional shape of each gas flow path 18 is circular. Has already been confirmed. This result corresponds to the case where the aspect ratio of the conductive support is 20, but it has already been confirmed that the same result can be obtained if the aspect ratio of the conductive support is in the range of 5 to 100. ing. Further, it is desirable that the thickness of the coating film 500 is uniform over the entire area of the coating film 500. Therefore, the thickness of the coating film 500 excluding the end face coating film 501 is also the same as that of the end face coating film 501. It is desirable to be within the range of 3 to 45 μm.

  As described above, from the results of Tables 1 and 2, when the surface roughness of the end face coating film 501 is within the range of 0.13 to 5.2 μm in terms of arithmetic average roughness Ra, the end face coating film 501 is hardly cracked. Furthermore, it can be said that when the thickness T1 of the end surface coating film 501 is in the range of 3 to 45 μm, the cracks are more difficult to occur.

(Second Embodiment)
FIG. 6 shows a second embodiment of a solid oxide fuel cell (SOFC) according to the present invention. This SOFC is electrically connected in series to each of the upper and lower surfaces (main surfaces (planes) on both sides parallel to each other) of the flat support substrate 10 having a longitudinal direction (x-axis direction) (this example). In this case, the four power generation element portions A having the same shape are arranged at predetermined intervals in the longitudinal direction, so-called “horizontal stripe type”. In this respect, a so-called “vertical stripe type” in which a plurality of cells each provided with only one “power generation element portion in which a fuel electrode, a solid electrolyte, and an air electrode are laminated in this order” are laminated on the surface of the conductive support. This is different from the first embodiment in which the configuration is adopted.

  The shape of the entire SOFC of the second embodiment viewed from above is, for example, that the length of the side in the longitudinal direction is 5 to 50 cm and the length in the width direction (y-axis direction) perpendicular to the longitudinal direction is 1 to 10 cm. It is a rectangle. The total thickness of this SOFC is 1-5 mm. The entire SOFC has a vertically symmetrical shape with respect to a plane passing through the center in the thickness direction and parallel to the main surface of the support substrate 10. Hereinafter, in addition to FIG. 6, the details of the SOFC will be described with reference to FIG. 7 which is a partial sectional view corresponding to the line 7-7 shown in FIG. 6 of the SOFC. FIG. 7 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. 11 to be described later, a plurality (six in this example) of fuel gas passages 11 (through holes) extending in the longitudinal direction are provided in the support substrate 10 at predetermined intervals in the width direction. Is formed. The cross-sectional shape of each fuel gas channel 11 is a circle having a diameter D of 0.5 to 3 mm. The space | interval (pitch) P in the width direction of the adjacent fuel gas flow paths 11 and 11 is 1-5 mm. In addition, the cross-sectional shape of each fuel gas flow path 11 may be an ellipse, a long hole, a quadrangle having arcs at four corners, or the like. Further, in this example, each recess 12 includes a bottom wall made of the material of the support substrate 10 and a side wall made of the material of the support substrate 10 over the entire circumference (two side walls and a width along the longitudinal direction). Two side walls extending in the direction), and a rectangular parallelepiped-shaped depression.

The support substrate 10 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%.

  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 , 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. 7 and 8, the entire fuel electrode current collector 21 is embedded (filled) in each recess 12 formed in the upper surface (upper main surface) of the support substrate 10. Therefore, each fuel electrode current collector 21 has a rectangular parallelepiped shape. A recess 21 a is formed on the upper surface (outer surface) of each fuel electrode current collector 21. Each recess 21a has a rectangular parallelepiped shape defined by a bottom wall made of the material of the fuel electrode current collector 21 and side walls closed in the circumferential direction (two side walls along the longitudinal direction and two side walls along the width direction). It is a depression. Of the side walls closed in the circumferential direction, two side walls along the longitudinal direction are made of the material of the support substrate 10, and two side walls along the width direction are made of the material of the fuel electrode current collector 21.

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

  A recess 21b is formed in a portion of the upper surface (outer surface) of each fuel electrode current collector 21 excluding the recess 21a. Each recess 21b has a rectangular parallelepiped shape defined by a bottom wall made of the material of the fuel electrode current collector 21 and side walls closed in the circumferential direction (two side walls along the longitudinal direction and two side walls along the width direction). It is a depression. Of the side walls closed in the circumferential direction, two side walls along the longitudinal direction are made of the material of the support substrate 10, and two side walls along the width direction are made of the material of the fuel electrode current collector 21.

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

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

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

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

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

  The entire surface excluding the central portion in the longitudinal direction of each portion where the plurality of interconnectors 30 are formed on the outer peripheral surface extending in the longitudinal direction of the support substrate 10 in a state where the fuel electrode 20 and the interconnector 30 are embedded in the respective recesses 12. Is covered with a solid electrolyte membrane 40. The solid electrolyte membrane 40 is a fired body made of a dense material having ionic conductivity and not electron conductivity. The solid electrolyte membrane 40 can be made of, for example, YSZ (8YSZ) (yttria stabilized zirconia). Or you may comprise from LSGM (lantern gallate). The thickness of the solid electrolyte membrane 40 is 3 to 50 μm.

  That is, the entire outer peripheral surface extending in the longitudinal direction of the support substrate 10 in a state where the fuel electrode 20 is embedded in each recess 12 is covered with a dense layer composed of the interconnector 30 and the solid electrolyte membrane 40. This dense layer exhibits a gas sealing function that prevents mixing of the fuel gas flowing in the space inside the dense layer and the air flowing in the space outside the dense layer.

  As shown in FIG. 7, in this example, the solid electrolyte membrane 40 covers the upper surface of the fuel electrode 20, both side ends 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. 7). 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. 7) and the interconnector of the other power generation element portion A (on the right side in FIG. 7). 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, the air electrode 60 of one power generation element part A (on the left side in FIG. 7) of each pair of adjacent power generation element parts A and A, 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. 7) 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. 9, 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” SOFC described above, and the upper and lower surfaces ( In particular, by exposing each air electrode current collector film 70) to “a gas containing oxygen” (air or the like) (or flowing a gas containing oxygen along the upper and lower surfaces of the support substrate 10), the solid electrolyte membrane 40 An electromotive force is generated by a difference in oxygen partial pressure generated between the two side surfaces. Furthermore, when this structure is connected to an external load, chemical reactions shown in the following formulas (1) and (2) occur, and current flows (power generation state).
(1/2) · O ₂ + 2e ⁻ → O ²⁻ (where: air electrode 60) (1)
H ₂ + O ²⁻ → H ₂ O + 2e ⁻
(At: Fuel electrode 20) (2)

  In the power generation state, as shown in FIG. 10, 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. 9, from the entire SOFC (specifically, the interconnector 30 of the power generating element portion A on the frontmost side in FIG. 9 and the air electrode 60 of the power generating element portion A on the innermost side in FIG. Power).

(Production method)
Next, an example of a method for manufacturing the “horizontal stripe type” SOFC shown in FIG. 6 will be briefly described with reference to FIGS. 11 to 19, “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. 11 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. 12 to 19 showing partial cross sections corresponding to line 12-12 shown in FIG.

  As shown in FIG. 12, when the support substrate molded body 10g is manufactured, as shown in FIG. 13, next, as shown in FIG. Each of the molded parts 21g is embedded and formed. Next, as shown in FIG. 14, a molded body 22g of the fuel electrode active part 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.

Next, as shown in FIG. 15, 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. 16, the outer periphery extending in the longitudinal direction of the molded body 10g of the support substrate in a state where the molded bodies 30g of fuel electrodes (21g + 22g) 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. 17, a molded membrane 50g of the reaction preventing film is formed on the outer surface of the solid electrolyte membrane molded body 40g in contact with the molded body 22g of each fuel electrode. 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. 17, a molding film of a coating film 500 (see FIG. 26), which will be described later, also uses a dipping method or the like at the gas discharge side end of the molded body 10g of the support substrate in this state. Formed.

  Then, 10 g of the support substrate molded body in which various molded films are thus formed is fired in air at 1500 ° C. for 3 hours. As a result, a structure in which the air electrode 60 and the air electrode current collector film 70 are not formed in the SOFC shown in FIG. 6 is obtained.

  Next, as shown in FIG. 18, 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. 19, 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. 6 is obtained. In the above, an example of the manufacturing method of SOFC shown in FIG. 6 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 second embodiment, as shown in FIG. 11 and the like, the planar shape of the recess 12 formed in the support substrate 10 (the shape when viewed from the direction perpendicular to the main surface of the support substrate 10) is a rectangle. However, it may be, for example, a square, a circle, an ellipse, or a long hole shape.

  Moreover, in the said 2nd Embodiment, although the whole interconnector 30 is embed | buried under each recessed part 12, only a part of interconnector 30 is embed | buried in each recessed part 12, and the remaining part of the interconnector 30 is You may protrude outside the recessed part 12 (namely, it protrudes from the main surface of the support substrate 10).

  Moreover, in the said 2nd Embodiment, although the angle (theta) which the bottom wall and side wall in the recessed part 12 make is 90 degrees, as shown in FIG. 20, angle (theta) may be 90-135 degrees. . Further, in the second embodiment, as shown in FIG. 21, the portion of the recess 12 where the bottom wall and the side wall intersect each other has an arc shape with a radius R, and the ratio of the radius R to the depth of the recess 12 May be 0.01 to 1.

  Further, in the second embodiment, a plurality of recesses 12 are formed on each of the upper and lower surfaces of the flat support substrate 10 and a plurality of power generation element portions A are provided, but as shown in FIG. A plurality of recesses 12 may be formed only on one side surface of the support substrate 10 and a plurality of power generation element portions A may be provided.

  In the second embodiment, the fuel electrode 20 is composed of two layers of the fuel electrode current collector 21 and the fuel electrode active part 22. The fuel electrode 20 corresponds to the fuel electrode active part 22. It may be composed of layers. In the second embodiment, the support substrate 10 has a flat plate shape, but may have a cylindrical shape.

  In addition, in the second embodiment, as shown in FIG. 8, 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 a peripheral wall. A rectangular parallelepiped recess defined by side walls closed in the direction (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) It has become. 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. 23, 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.

  FIGS. 24 to 27 are diagrams corresponding to FIGS. 2 to 5 in the case where a stack structure using the cell 100 according to the second embodiment is formed, respectively. 24 to 27, members and configurations that are the same as or equivalent to the members and configurations shown in FIGS. 2 to 5 are denoted by the same reference numerals as those used in FIGS.

  As shown in FIG. 26, the gas discharge side end portion (free end portion) of the cell 100 according to the second embodiment used in the stack structure is the same as the cell 100 according to the first embodiment ( 4), a coating film 500 having a porosity smaller than that of the support substrate 10 is formed. The coating film 500 is formed at least 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. The end face coating film 501 is continuous with each flow path inner wall surface coating film 502. In the example shown in FIG. 26, 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 H in the longitudinal direction of each channel inner wall surface coating film 502 (see the enlarged view of the Z portion in FIG. 26) 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 containing a rare earth element. 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 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 the support substrate 10, the fuel electrode 20, and the solid electrolyte film 40 are fired. Further, it may be formed by a vacuum film forming process method (evaporation method, CVD method (Chemical Vapor Deposition) or the like).

(Surface roughness of coating film)
Similarly to the fuel cell according to the first embodiment, the fuel cell (stack structure) according to the second embodiment, which has been reduced by the above-described reduction treatment, is coated when operated in a normal environment. While cracks do not occur in the film 500, cracks may occur in the coating film 500 (particularly, the end face coating film 501) when operated in a severe thermal stress environment. As in the first embodiment, the present inventor has found that the occurrence of such a crack has a strong correlation with the “surface roughness of the coating film 500 (end surface coating film 501)” in the second embodiment as well. It was. Hereinafter, test C in which this has been confirmed will be described.

(Test C)
In test C, as in test A, a plurality of samples with different combinations of the material of the support substrate 10, the material of the end surface coating film 501, and the surface roughness of the end surface coating film 501 for the fuel cell according to the second embodiment. Was made. Specifically, as shown in Table 3, 14 kinds of levels (combinations) were prepared. Ten samples (N = 10) were made for each level. The evaluation method of the surface roughness is the same as in Test A.

  As the support substrate 10 used in each sample (fuel cell shown in FIG. 6), the porosity of the material is 20 to 60%, and the thickness and width are 2.5 mm and 50 mm, respectively (that is, the aspect ratio). 20), the gas channel 11 has a circular cross-sectional shape with a diameter of 1.5 mm, and the pitch P between the adjacent gas channels 11 and 11 is 5.0 mm. In each sample, the support substrate 10, the fuel electrode 20, the solid electrolyte membrane 40, and the coating membrane 500 were co-fired as described above. Thereafter, a reduction process was performed on each sample. In each sample, the thickness of the coating film 500 (in particular, the end face coating film 501) was 5 to 10 μm. The “coating film surface roughness” was adjusted in the same manner as in Test A.

  For each sample in the stage after the reduction treatment (reduced state), “the ambient temperature was raised from room temperature to 750 ° C. in 2 hours while reducing fuel gas was circulated through the fuel electrode 20 and then from 750 ° C. to room temperature. The thermal cycle test was repeated 100 times. And about each sample, the presence or absence of the generation | occurrence | production of the crack in the end surface coating film 501 was confirmed. This confirmation was made by visual observation as well as observation using a microscope. The results are as shown in Table 3.

  As can be understood from Table 3, after the thermal cycle test that is severe in terms of thermal stress, if the surface roughness of the end face coating film 501 exceeds 5.2 μm in arithmetic average roughness Ra, the reason is unknown. However, cracks are likely to occur in the end face coating film 501. On the other hand, when the surface roughness of the end face coating film 501 is not more than 5.2 μm in terms of arithmetic average roughness Ra, it can be said that the cracks are hardly generated.

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

  The inventor uses the second embodiment 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 if the surface roughness of the end face coating film 501 is outside the range of 0.13 to 5.2 μm in terms of arithmetic average roughness Ra, it is separately confirmed that the coating film 500 (end face coating film 501) does not crack. ing.

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

(Thickness of coating film)
In addition, regarding the second embodiment, when the surface roughness of the end surface coating film 501 is 0.13 to 5.2 μm, the present inventor has a thickness T1 of the end surface coating film 501 (in the Z portion in FIG. 26). It has also been found that cracks are less likely to occur in the end face coating film 501 when the thickness is 3 to 45 μm. Hereinafter, Test D in which this is confirmed will be described.

(Test D)
In the test D, for the fuel cell according to the second embodiment, the combination of the material of the support substrate 10, the material of the end surface coating film 501, the surface roughness of the end surface coating film 501, and the thickness T1 of the end surface coating film 501 is Different samples were made. Specifically, as shown in Table 4, 11 kinds of levels (combinations) were prepared. Ten samples (N = 10) were made for each level. The surface roughness of the end face coating film 501 of each sample is in the range of 0.3 to 0.8 μm.

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

  Then, for each sample in the stage after the reduction treatment (reduced state), a thermal cycle test that is more severe in terms of thermal stress than the thermal cycle test performed in test C, that is, “reducing fuel gas to the fuel electrode 12. While circulating, the thermal cycle test was repeated 100 times. “Pattern of raising the ambient temperature from normal temperature to 750 ° C. for 1 hour and then decreasing from 750 ° C. to normal temperature in 2 hours”. And about each sample, the presence or absence of the generation | occurrence | production of the crack in the end surface coating film 501 was confirmed. This confirmation was made by visual observation as well as observation using a microscope. The results are as shown in Table 4.

  As can be understood from Table 4, when the thickness T1 of the end face coating film 501 is outside the range of 3 to 45 μm, the reason is unknown, but cracks are likely to occur in the end face coating film 501. On the other hand, when the thickness T1 of the end face coating film 501 is in the range of 3 to 45 μm, it can be said that the crack is hardly generated.

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

  As described above, from the results of Tables 3 and 4, when the surface roughness of the end face coating film 501 is within the range of 0.13 to 5.2 μm in terms of arithmetic average roughness Ra, the end face coating film is related to the second embodiment. It can be said that cracks hardly occur in 501 and that the crack T is further less likely to occur when the thickness T1 of the end face coating film 501 is in the range of 3 to 45 μm.

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

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

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

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

  In the second embodiment, the solid electrolyte membrane 40 covers the outer surface of the fuel electrode 20, both side ends in the longitudinal direction of the outer surface of the interconnector 30, and the main surface of the support substrate 10. Here, no step is formed between the outer surface of the fuel electrode 20, the outer surface of the interconnector 30, and the main surface of the support substrate 10. Therefore, the solid electrolyte membrane 40 is flattened. As a result, compared with the case where a step is formed in the solid electrolyte membrane 40, the generation of cracks in the solid electrolyte membrane 40 due to stress concentration can be suppressed, and the gas sealing function of the solid electrolyte membrane 40 is reduced. Can be suppressed.

DESCRIPTION OF SYMBOLS 11 ... Electroconductive support body, 12 ... Fuel electrode, 13 ... Solid electrolyte, 14 ... Air electrode,
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 film, 60 ... Air electrode, 70 ... Air electrode current collector film, 500 ... Coating film, A ... Power generation element part

Claims (6)

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 coating film having a porosity smaller than that of the support substrate is formed at least on the end portion on the gas discharge side of 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. And
The fuel cell, wherein a surface roughness of a portion of the coating film formed on the end surface on the gas discharge side of the support substrate is an arithmetic average roughness Ra of 0.13 to 5.2 μm. The fuel cell according to claim 1, wherein
The fuel cell, wherein a thickness of a portion of the coating film formed on an end surface of the support substrate on the gas discharge side is 3 to 45 μm. A porous support substrate having a longitudinal direction and one or more gas flow paths formed therein along the longitudinal direction;
A plurality of power generating element portions each provided at a plurality of locations apart from each other on the main surface of the support substrate, wherein at least a fuel electrode, a solid electrolyte, and an air electrode are stacked in this order;
One or a plurality of electrical connections that are respectively provided between one or a plurality of adjacent power generation element portions and electrically connect one fuel electrode and the other air electrode of the adjacent power generation element portions. And
A fuel cell that is a fired body comprising:
Recesses having a bottom wall made of the material of the support substrate and a circumferentially closed side wall made of the material of the support substrate are formed in the plurality of locations on the main surface of the support substrate,
In each of the recesses, the corresponding fuel electrode of the power generation element portion is embedded,
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 coating film having a porosity smaller than that of the support substrate is formed at least on the end portion on the gas discharge side of 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. And
The fuel cell, wherein a surface roughness of a portion of the coating film formed on the end surface on the gas discharge side of the support substrate is an arithmetic average roughness Ra of 0.13 to 5.2 μm. The fuel cell according to claim 3, wherein
The fuel cell, wherein a thickness of a portion of the coating film formed on an end surface of the support substrate on the gas discharge side is 3 to 45 μm. The fuel cell according to any one of claims 1 to 4, wherein
The fuel cell according to claim 1, wherein the support substrate has a porosity of 20 to 60%, and the coating film has a porosity of 0 to 10%. The fuel cell according to any one of claims 1 to 5, wherein
A fuel cell, wherein a length of the coating film formed at an end of the gas discharge side on an inner wall surface of each gas flow path is 10 mm or more.