JP2015099677A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell with a fuel electrode that is buried in a first recessed part formed on a main surface of a support substrate, in which separation hardly occurs at "a boundary between the fuel electrode and an interconnector buried in a second recessed part formed in the fuel electrode" during reduction treatment.SOLUTION: In a fuel cell, a recessed part 12 is formed at a place where each of power generation element parts A is provided on a main surface of a support substrate 10. In each recessed part 12, a fuel electrode 20 of a respective power generation element part A is buried. A recessed part 21b is formed on the top surface of each fuel electrode 20. An interconnector 30 is buried in each recessed part 21b. The nickel element concentration and the yttrium element concentration at an end part of the interconnector 30 on a side closer to the bottom wall of the recessed part 21b is higher than the nickel element concentration and the yttrium element concentration at an end part of the interconnector 30 on a side further away from the bottom wall of the recessed part 21b.

Description

  The present invention relates to a fuel cell.

  Conventionally, "a support substrate having a gas flow path formed therein" and "a fuel electrode that is provided at a plurality of locations separated from each other on the main surface of the support substrate and includes at least nickel and yttrium," A plurality of power generation element portions in which a solid electrolyte and an air electrode are laminated ”and“ one fuel electrode of each of the adjacent power generation element portions provided between one or a plurality of adjacent power generation element portions ” And one or a plurality of electrical connection portions that electrically connect the other air electrode ”are widely known (see, for example, Patent Document 1). Such a configuration is also called a “horizontal stripe type”.

  In the fuel cell described in the above document, each of the electrical connection portions is composed of a first part (interconnector) including lanthanum chromite and a porous material connected to the first part. It is comprised with the 2nd part (air electrode current collection film | membrane). The first portion has a porosity smaller than the porosity of the second portion to the extent that it has a gas sealing function. The first part is connected to one fuel electrode and the second part of the adjacent power generation element part, and the second part includes the other air electrode and the first part of the adjacent power generation element part. It is connected to the.

  Further, in the fuel cell described in the above document, the first recesses each having a bottom wall made of the material of the support substrate and a side wall made of the material of the support substrate at the plurality of locations on the main surface of the support substrate. Is formed. A corresponding fuel electrode of the power generation element portion is embedded in each of the first recesses. A second wall having a bottom wall made of the material of the fuel electrode and a side wall made of the material of the fuel electrode on a surface opposite to the surface contacting the bottom wall of the first recess in each buried fuel electrode. Recesses are respectively formed. The first portions of the corresponding electrical connection portions are embedded in the second recesses, respectively.

  Each component of the fuel cell described above is usually formed by firing in an oxygen-containing atmosphere. For this reason, in the state after the firing, the nickel component (Ni) in the fuel electrode is nickel oxide (NiO), and the conductivity of the fuel electrode is lowered. Therefore, in order to obtain the conductivity of the fuel electrode, usually, after the firing, reducing fuel gas is allowed to flow from the support substrate side at 800 to 1000 ° C. for 1 to 10 hours to convert NiO in the fuel electrode to Ni. (Reduction process) is performed.

  The lanthanum chromite contained in the first portion (interconnector) of the electrical connection portion has a property of expanding in a reducing atmosphere (thus, during the reduction treatment). Due to this, at the time of the reduction treatment, separation occurs at the boundary between the first portion (interconnector) of the electrical connection portion and the fuel electrode (including nickel and yttrium) embedded therein. A problem sometimes occurred. It has been desired to suppress the occurrence of such problems.

Japanese Patent No. 4824135

  An object of the present invention is a fuel cell in which an inner electrode is embedded in a recess formed in a main surface of a support substrate in which a gas flow path is formed. An object of the present invention is to provide a material that is less likely to be peeled off at the “boundary portion between the embedded interconnector”.

  The fuel cell according to the present invention includes a support substrate, a power generation element portion, and an electrical connection portion, similar to those described in the above-mentioned document, and the electrical connection portion includes the first portion and the second portion. The first recesses are formed in the plurality of locations on the main surface of the support substrate, and the fuel electrodes of the corresponding power generation element units are embedded in the first recesses, respectively. The second recesses are respectively formed on the surfaces of the fuel electrodes opposite to the surfaces contacting the bottom walls of the first recesses, and the first portions of the electrical connection portions corresponding to the second recesses. Are buried.

  The fuel cell according to the present invention is characterized in that, with respect to the first portion of each embedded electrical connection portion, the first portion on the side closer to the bottom wall of the second recess in the depth direction of the second recess. The concentration (Xn2) of the nickel element at the end is greater than the concentration (Xn1) of the nickel element at the end of the first portion farther from the bottom wall of the second recess in the depth direction of the second recess; There is.

  Here, the concentration (Xy2) of the yttrium element at the end of the first portion on the side close to the bottom wall of the second recess in the depth direction of the second recess is the depth in the depth direction of the second recess. It is preferable that the concentration be higher than the concentration (Xy1) of the yttrium element at the end of the first portion far from the bottom wall of the second recess.

  By adopting the above feature, the present inventor has established that “the concentration of nickel element and yttrium element in the first portion (interconnector) of the electrical connection portion embedded in the second recess of the fuel electrode is uniform in the depth direction. The reason is unclear compared to “a mode that is,” but at the time of the reduction treatment, the “boundary portion between the fuel electrode and the first portion (interconnector) of the electrical connection portion embedded in the fuel electrode” It was found that exfoliation hardly occurs.

  In addition, the present inventor, when the concentration ratio of nickel element (Xn2 / Xn1) is 1.3 to 3.5, or when the concentration ratio of yttrium element (Xy2 / Xy1) is 2 to 10, It has also been found that cracks are less likely to occur in the first portion (interconnector) of the electrical connection portion after a thermal cycle test that is severe in terms of thermal stress as compared to the case where this is not the case.

1 is a perspective view showing a fuel cell according to the present invention. FIG. 2 is a cross-sectional view corresponding to line 2-2 of the fuel cell shown in FIG. It is the top view which showed the state of the fuel electrode and interconnector which were embed | buried under the recessed part of the support substrate shown in FIG. It is a figure for demonstrating the operation state of the fuel cell shown in FIG. It is a figure for demonstrating the flow of the electric current in the operating state of the fuel cell shown in FIG. It is a perspective view which shows the support substrate shown in FIG. FIG. 3 is a cross-sectional view corresponding to FIG. 2 in a first stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 3 is a cross-sectional view corresponding to FIG. 2 in a second stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 3 is a cross-sectional view corresponding to FIG. 2 in a third stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 4 is a cross-sectional view corresponding to FIG. 2 in a fourth stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 6 is a cross-sectional view corresponding to FIG. 2 in a fifth stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 7 is a cross-sectional view corresponding to FIG. 2 in a sixth stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 8 is a cross-sectional view corresponding to FIG. 2 in a seventh stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 7 is a cross-sectional view corresponding to FIG. 2 in an eighth stage in the manufacturing process of the fuel cell shown in FIG. 1. FIG. 10 is a cross-sectional view corresponding to FIG. 2 in a ninth stage in the manufacturing process of the fuel cell shown in FIG. 1. In the comparative example, it is the schematic diagram which showed the path | route at the time of an electric current passing between an interconnector and a fuel electrode. In the fuel cell shown in FIG. 1, it is the schematic diagram which showed the path | route at the time of an electric current passing between an interconnector and a fuel electrode. It is a figure for demonstrating element distribution in an interconnector. It is a figure which shows an example of element distribution in an interconnector. It is sectional drawing corresponding to FIG. 2 of the 1st modification of the fuel cell which concerns on this invention. It is sectional drawing corresponding to FIG. 2 of the 2nd modification of the fuel cell which concerns on this invention.

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

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

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

The support substrate 10 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. The porosity of the support substrate 10 is 20 to 60% after “reduction treatment” described later. Hereinafter, the porosity values of the other members are also values after the reduction treatment. The porosity was measured by polishing the cross section of the resin-embedded sample (after the reduction treatment) and analyzing the image (secondary electron image) of the cross section by SEM (scanning electron microscope). . The acceleration voltage of SEM was set to 5 kV, and the magnification of SEM was set to 5000 times or 7500 times. The measurement of the porosity was performed on arbitrary 10 cross-sections of the sample, and the average value thereof was adopted as the porosity value.

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

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

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

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

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

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

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

The fuel electrode active part 22 can 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. The porosity of the fuel electrode current collector 21 is 25 to 50%, and the porosity of the fuel electrode active part 22 is also 25 to 50%.

  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 porosity of the interconnector 30 is 10% or less.

As shown in FIG. 2, only the boundary between the bottom surface of the interconnector 30 and the fuel electrode 20 (current collector 21) among the boundary between the interconnector 30 and the fuel electrode 20 (current collector 21). The intermediate film 35 is interposed. The intermediate film 35 is composed of, for example, a mixed powder of NiO and Y ₂ O ₃ (yttria), a mixed powder of NiO and GDC (gadolinia doped ceria), and a mixed powder of NiO and LaCrO ₃ .

  The conductivity of the fuel electrode current collector 21 is 100 to 1000 S / cm, the conductivity of the interconnector 30 is 0.5 to 30 S / cm, and the conductivity of the intermediate film 35 is 200 to 2000 S / cm. That is, the conductivity of the intermediate film 35 is greater than the conductivity of the interconnector 30. The conductivity of the intermediate film 35 may be larger or smaller than the conductivity of the fuel electrode current collector 21, but is preferably larger than the conductivity of the fuel electrode current collector 21. The thickness of the intermediate film 35 is 2 to 20 μm. The porosity of the intermediate film 35 is 10 to 60%. The intermediate film 35 may exist over the entire bottom surface of the interconnector 30 or may exist only over a portion of the bottom surface of the interconnector 30.

  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. The porosity of the solid electrolyte membrane 40 is 10% or less.

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

  As shown in FIG. 2, in this example, the solid electrolyte membrane 40 includes the upper surface of the fuel electrode 20 (current collector 21 + active portion 22), both end portions in the longitudinal direction on the upper surface of the interconnector 30, and the support substrate. 10 main surfaces are covered. 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 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%.

In contrast to the “horizontal stripe” SOFC described above, as shown in FIG. 4, fuel gas (hydrogen gas or the like) in one direction (same direction) in the longitudinal direction in each fuel gas channel 11 of the support substrate 10. ) And the upper and lower surfaces of the support substrate 10 (in particular, the air electrode current collector films 70) are exposed to “gas containing oxygen” (air or the like) (or oxygen is included along the upper and lower surfaces of the support substrate 10). By flowing gas), an electromotive force is generated by a difference in oxygen partial pressure 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⁻ (where: air electrode 60) (1)
H ₂ + O ²⁻ → H ₂ O + 2e ⁻
(At: Fuel electrode 20) (2)

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

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

  First, a support substrate molded body 10g having the shape shown in FIG. 6 is produced. The 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 15 showing partial cross sections corresponding to the line 7-7 shown in FIG.

  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. First, an intermediate film molded body 35g is embedded and formed. The molded body 35g of each intermediate film is embedded, for example, using a slurry obtained by adding a binder or the like to the material of the intermediate film 35 (mixed powder of NiO and Y ₂ O ₃ ) using a printing method or the like. It is formed.

  Next, as shown in FIG. 11, an interconnector molded body 30 g is embedded and formed in each of the recesses where the intermediate film 35 is embedded and formed. The formation of the interconnector molded body 30g will be described later.

  Next, as shown in FIG. 12, a plurality of fuel electrode molded bodies (21g + 22g), a plurality of interconnector molded bodies 30g, and a plurality of intermediate film molded bodies 35g are 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 on the outer peripheral surface extending in the longitudinal direction of the substrate molded body 10g. . 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. 13, a reaction preventing film forming film 50 g is formed on the outer surface of the solid electrolyte film forming body 40 g in contact with the fuel electrode forming body 22 g. The molded film 50g of each reaction preventing film is formed using a slurry obtained by adding a binder or the like to the powder of the material (for example, GDC) of the reaction preventing film 50, using a printing method or the like.

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

  Next, as shown in FIG. 14, 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. 15, for each pair of adjacent power generation element portions, air is formed so as to straddle the air electrode molding film 60 g of one power generation element portion and the interconnector 30 of the other power generation element portion. On the outer surface of the electrode forming film 60 g, the solid electrolyte film 40, and the interconnector 30, the air electrode current collecting film forming film 70 g is formed. The forming film 70g of each air electrode current collector film is obtained by using a slurry obtained by adding a binder or the like to the powder of the material of the air electrode current collector film 70 (for example, LSCF), using a printing method or the like. It is formed.

  Then, the support substrate 10 in which the molded films 60g and 70g are thus formed is baked in air at 1050 ° C. for 3 hours. Thereby, the SOFC shown in FIG. 1 is obtained. In the above, an example of the manufacturing method of SOFC shown in FIG. 1 was demonstrated.

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

(Intermediate membrane)
In the above embodiment, as described above, the intermediate film 35 having higher conductivity than the interconnector 30 is interposed at the boundary between the bottom surface of the interconnector 30 and the fuel electrode 20 (the current collector 21). Hereinafter, the operation and effect of this will be described. First, as a preparation for explaining this operation and effect, as shown in FIG. 16, a comparative example is assumed in which only the intermediate film 35 is not interposed with respect to the above embodiment.

  In this comparative example, each interconnector 30 is connected to the support electrode 10 from the “part constituting the power generation element part A (that is, the part where the solid electrolyte 40 and the air electrode 60 are laminated) in the corresponding fuel electrode current collector 21. It is embedded in the outer surface of the “part extending in the plane direction”. In general, the conductivity of the air electrode current collector film 70 and the fuel electrode current collector 21 is about 1 to 2 digits greater than the conductivity of the interconnector 30. Furthermore, since the interface between the interconnector 30 and the fuel electrode current collector 21 is a region where different materials are joined, there is an interface resistance. Under these conditions, in this comparative example, current flows in the interconnector 30 so that the path in the interconnector 30 is the shortest. That is, as indicated by the black arrow in FIG. 16, the current flowing through the air electrode current collector film 70 is “at the interface between the side surface of the interconnector 30 and the fuel electrode current collector 21” (see Z in the figure). After entering the interconnector 30 from a close position and passing through the interconnector 30 through the shortest path, it passes through the “interface between the side surface of the interconnector 30 and the fuel electrode current collector 21” (see Z in the figure). Thus, it tends to flow to the fuel electrode current collector 21 (as a result, the “part constituting the power generation element portion A” in the fuel electrode current collector 21, rightward in the drawing).

  As described above, in the configuration in which the current passes through the interface between the side surface of the interconnector 30 and the fuel electrode current collector 21, when the fuel cell is operated for a long time, the interface sometimes peels off. . This is considered based on the following reasons. That is, as described above, in this example, each interconnector 30 has a very thin plate shape (a shape having a large planar shape and a small thickness), and has an extremely small side surface area. Therefore, when the current passes through the interface between the side surface of the interconnector 30 and the fuel electrode current collector 21, the current is excessively concentrated and a lot of Joule heat is likely to be generated. This Joule heat generates a local temperature distribution in the vicinity of the interface, and as a result, it is considered that peeling is likely to occur at the interface.

  On the other hand, in the above embodiment, as shown in FIG. 17, the intermediate film 35 having higher conductivity than the interconnector 30 is provided on the bottom surface of the interconnector 30. By inserting this layer, the interface resistance existing between the interconnector 30 and the fuel electrode current collector 21 can be greatly reduced. Therefore, the current path can be controlled so that the current passes through “the bottom surface of the interconnector 30 having a large area” instead of “the side surface of the interconnector 30 having a small area” (see the black arrow in FIG. 17). . As a result, the occurrence of peeling of the interface due to the generation of Joule heat when the current passes through the interface between the “side surface of the interconnector 30 having a small area” and the fuel electrode current collector 21 can be suppressed.

(Element distribution in the interconnector)
In the above embodiment, the element concentrations of nickel Ni and yttrium Y are not uniform inside each interconnector 30. More specifically, as shown in FIG. 18, the interconnector 30 has a side closer to the upper surface of the interconnector 30 (from the bottom wall of the recess 21 b) in the thickness direction of the interconnector 30 (depth direction of the recess 21 b). In order from the far side), it is composed of five layers of a layer, b layer, c layer, d layer, and e layer.

  FIG. 19 shows an example of the distribution of elemental concentrations of nickel Ni and yttrium Y inside the interconnector 30. As shown in FIG. 19, the Ni element concentration and the Y element concentration in the interconnector 30 are smaller as it is closer to the a layer and larger as it is closer to the e layer. In other words, the Ni element concentration in the interconnector 30 on the side close to the bottom wall of the recess 21b is larger than the Ni element concentration in the interconnector 30 on the side far from the bottom wall of the recess 21b, and the bottom wall of the recess 21b. The Y element concentration in the interconnector 30 on the near side is higher than the Y element concentration in the interconnector 30 on the far side from the bottom wall of the recess 21b.

As shown in FIG. 19, the interconnector 30 including five layers is formed as follows, for example. First, using a slurry obtained by adding NiO powder, Y ₂ O ₃ powder, a binder, etc. to the powder of the interconnector 30 (for example, LaCrO ₃ ), using a printing method, dipping, etc., “ The “molded body corresponding to the e layer” is embedded and formed in the bottom of the recess 21b. Next, on the upper surface of the “molded body corresponding to the e layer” in the recess 21b, a slurry having a smaller content ratio of the NiO powder and the Y ₂ O ₃ powder than the slurry for the “molded body corresponding to the e layer” is used. The “molded body corresponding to the d layer” is embedded and formed using a printing method, dipping, or the like. Next, on the upper surface of the “molded body corresponding to the d layer” in the recess 21b, a slurry having a smaller content ratio of the NiO powder and the Y ₂ O ₃ powder than the slurry for the “molded body corresponding to the d layer” is used. The “molded body corresponding to the c layer” is embedded and formed using a printing method, dipping, or the like. Next, on the upper surface of the “molded body corresponding to the c layer” in the concave portion 21b, a slurry having a smaller content ratio of the NiO powder and the Y ₂ O ₃ powder than the slurry for the “molded body corresponding to the c layer” is used. The “molded body corresponding to the b layer” is embedded and formed by using a printing method, dipping, or the like. Finally, on the upper surface of the “molded body corresponding to the b layer” in the recess 21b, a slurry having a smaller content ratio of the NiO powder and the Y ₂ O ₃ powder than the slurry for the “molded body corresponding to the b layer” is used. Using the printing method, dipping, etc., the “molded product corresponding to the layer a” is embedded and formed. As a result, an interconnector molded body 30g (see FIG. 11) consisting of five layers is formed.

  Thereafter, the interconnector molded body 30g having five layers is co-fired with the support substrate molded body 10g, the fuel electrode molded body (21g + 22g), and the intermediate film molded body 35g (FIG. 13 → FIG. 14). See). As a result, an interconnector 30 (fired body) consisting of five layers shown in FIG. 19 is obtained.

  The interconnector 30 shown in FIG. 19 is configured such that the Ni element concentration and the Y element concentration in the interconnector 30 decrease in five steps from the side closer to the bottom wall of the recess 21b to the side farther. However, the Ni element concentration and the Y element concentration in the interconnector 30 may be gradually reduced steplessly from the side closer to the bottom wall of the recess 21b toward the far side.

  By adopting a configuration in which the element concentrations of nickel Ni and yttrium Y are distributed as described above in the interconnector 30, the present inventor “in the interconnector 30 embedded in the recess 21 b of the fuel electrode 20. The reason is unknown as compared with “a mode in which the concentrations of elements of nickel Ni and yttrium Y are uniform in the depth direction”, but at the time of the reduction treatment, the “boundary portion between the fuel electrode 20 and the interconnector 30” It was found that exfoliation hardly occurs.

(Proper range of element distribution in the interconnector)
In the SOFC according to the above-described embodiment, cracks do not occur in the interconnector 30 when operated in a normal environment. However, when this SOFC is operated in a severe environment due to thermal stress, the interconnector 30 may crack.

  Hereinafter, as shown in FIG. 19, the Ni element concentration of the a layer in the interconnector 30 (that is, the end near the bottom wall of the recess 21b) is Xn1, and the e layer in the interconnector 30 (that is, the recess 21b). The Ni element concentration at the end far from the bottom wall is Xn2. The present inventor has found that the occurrence of such cracks has a strong correlation with the value “Xn2 / Xn1”. Hereinafter, test A in which this has been confirmed will be described.

(Test A)
In this test A, a plurality of samples having different combinations of Xn1 and Xn2 (that is, different values “Xn2 / Xn1”) were produced for the SOFC shown in FIG. Specifically, as shown in Table 1, seven kinds of levels (combinations) were prepared. Ten samples (N = 10) were made for each level. For each sample, the values of Xn1 and Xn2 were calculated by measuring and quantifying the content of each element for the cross section of the sample using EPMA (Electron Probe Micro Analyzer) and calculating the composition ratio thereof. . The values of Xn1 and Xn2 described in Table 1 are values after the reduction treatment (average value of N = 10).

In each sample (SOFC stack structure shown in FIG. 1), the interconnector 30 has five layers as shown in FIG. The fuel electrode current collector 21 is composed of “NiO (nickel oxide) and YSZ (8YSZ) (yttria-stabilized zirconia)” or “NiO (nickel oxide) and Y ₂ O ₃ (yttria)”. The intermediate film 35 is composed of “NiO and Y ₂ O ₃ (yttria)”. The intermediate film 35 was present over the entire bottom surface of the interconnector 30. The fuel electrode 20 (current collector 21 + active part 22), the interconnector 30, and the intermediate film 35 were formed by co-firing and then subjecting the fired body to a reduction treatment. The adjustment of the value Xn1 is made by adjusting the content ratio of the NiO powder added to the slurry for the “formed product corresponding to the a layer”, and the adjustment of the value Xn2 is for the “formed product corresponding to the e layer”. The content ratio of NiO powder added to the slurry was adjusted.

  For each sample after the reduction 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 circulated through the fuel electrode 20. The 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 interconnector 30 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 seen from Table 1, after the thermal cycle test, which is severe in terms of thermal stress, if the value “Xn2 / Xn1” is less than 1.3 or greater than 3.5, the reason is unknown. However, cracks are likely to occur in the interconnector 30, and if “Xn2 / Xn1” is within the range of 1.3 to 3.5, the reason is unknown, but cracks are unlikely to occur in the interconnector 30. From the above, it can be said that when the value “Xn2 / Xn1” is within the range of 1.3 to 3.5, the crack is hardly generated.

  In addition, the present inventor has values 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 if “Xn2 / Xn1” is out of the range of 1.3 to 3.5, it is separately confirmed that no crack occurs in the interconnector 30.

  Hereinafter, as shown in FIG. 19, the Y element concentration in the a layer in the interconnector 30 (that is, the end near the bottom wall of the recess 21b) is Xy1, and the e layer in the interconnector 30 (that is, the recess 21b). The Y element concentration at the end far from the bottom wall is Xy2. The inventor has also found that the occurrence of cracks in the interconnector 30 described above has a strong correlation with the value “Xy2 / Xy1”. Hereinafter, test B in which this has been confirmed will be described.

(Test B)
In this test B, a plurality of samples having different combinations of Xy1 and Xy2 (that is, different values “Xy2 / Xy1”) were produced for the SOFC shown in FIG. Specifically, as shown in Table 2, eight levels (combinations) were prepared. Ten samples (N = 10) were made for each level. For each sample, the values of Xy1 and Xy2 are calculated by measuring and quantifying the content of each element for the cross section of the sample using EPMA, and calculating their composition ratio, like Xn1 and Xn2 described above. It was done. The values of Xy1 and Xy2 described in Table 2 are values after the reduction treatment (average value of N = 10).

In each sample (SOFC stack structure shown in FIG. 1), the interconnector 30 has five layers as shown in FIG. The fuel electrode current collector 21 is composed of “NiO (nickel oxide) and YSZ (8YSZ) (yttria-stabilized zirconia)” or “NiO (nickel oxide) and Y ₂ O ₃ (yttria)”. The intermediate film 35 is composed of “NiO and Y ₂ O ₃ (yttria)”. The intermediate film 35 was present over the entire bottom surface of the interconnector 30. The fuel electrode 20 (current collector 21 + active part 22), the interconnector 30, and the intermediate film 35 were formed by co-firing and then subjecting the fired body to a reduction treatment. The adjustment of the value Xy1 is made by adjusting the content ratio of the Y ₂ O ₃ powder added to the slurry for the “molded body corresponding to the a layer”, and the adjustment of the value Xy2 is made by adjusting “the molding corresponding to the e layer”. This was done by adjusting the content of Y ₂ O ₃ powder added to the “body” slurry.

  For each sample after the reduction 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 circulated through the fuel electrode 20. The 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 interconnector 30 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 value “Xy2 / Xy1” is smaller than 2 or larger than 10, the reason is unknown. If the connector 30 is easily cracked and “Xy2 / Xy1” is in the range of 2 to 10, the reason is unknown, but the interconnector 30 is unlikely to crack. From the above, it can be said that when the value “Xy2 / Xy1” is in the range of 2 to 10, the crack is hardly generated.

  In addition, the present inventor has values 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 if “Xy2 / Xy1” is outside the range of 2 to 10, it is separately confirmed that no crack occurs in the interconnector 30.

  In addition, this invention is not limited to the said embodiment, A various modification can be employ | adopted within the scope of the present invention. For example, in the above embodiment, the intermediate film 35 is interposed at the boundary between the bottom surface of the interconnector 30 and the fuel electrode 20 (the current collector 21), but as shown in FIG. The intermediate film 35 may not be interposed.

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

  In addition, in the above-described embodiment, the fuel electrode 20 is configured by two layers of the fuel electrode current collector 21 and the fuel electrode active unit 22, but the fuel electrode 20 is a single layer corresponding to the fuel electrode active unit 22. It may be constituted by.

  DESCRIPTION OF SYMBOLS 10 ... Support substrate, 11 ... Fuel gas flow path, 12 ... Recess, 20 ... Fuel electrode, 21 ... Fuel electrode current collector, 30 ... Interconnector, 40 ... Solid electrolyte membrane, 60 ... Air electrode, A ... Power generation element part

Claims (5)

A support substrate having a gas flow path formed therein;
A plurality of power generating element portions each provided at a plurality of locations separated from each other on the main surface of the support substrate, and a fuel electrode, a solid electrolyte, and an air electrode including at least nickel and yttrium;
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
In a fuel cell comprising
Each of the electrical connection portions includes a first portion including lanthanum chromite, and a second portion connected to the first portion and formed of a porous material, and the first portion includes , Having a porosity smaller than the porosity of the second part to the extent that it has a gas sealing function, the first part is connected to one fuel electrode of the adjacent power generation element part and the second part, The second part is connected to the other air electrode of the adjacent power generation element part and the first part,
First recesses having a bottom wall made of the material of the support substrate and a 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, respectively.
In each of the first recesses, the corresponding fuel electrode of the power generation element unit is embedded,
A second wall having a bottom wall made of the material of the fuel electrode and a side wall made of the material of the fuel electrode on a surface opposite to the surface contacting the bottom wall of the first recess in each buried fuel electrode. Recesses are formed,
In each of the second recesses, the corresponding first portion of the electrical connection portion is embedded,
Concerning the first portion of each of the embedded electrical connection portions, the concentration of nickel element (Xn2) at the end portion of the first portion closer to the bottom wall of the second recess in the depth direction of the second recess Is larger than the concentration (Xn1) of nickel element at the end of the first portion farther from the bottom wall of the second recess in the depth direction of the second recess. The fuel cell according to claim 1, wherein
Concentration of yttrium element (Xy2) at the end of the first portion on the side close to the bottom wall of the second recess in the depth direction of the second recess for the first portion of each embedded electrical connection portion Is higher than the concentration (Xy1) of the yttrium element at the end of the first portion farther from the bottom wall of the second recess in the depth direction of the second recess. The fuel cell according to claim 1 or 2,
The concentration of nickel element at the end of the first portion on the side close to the bottom wall of the second recess with respect to the concentration (Xn1) of the nickel element at the end of the first portion on the side far from the bottom wall of the second recess. A fuel cell having a concentration (Xn2) ratio (Xn2 / Xn1) of 1.3 to 3.5. The fuel cell according to any one of claims 1 to 3, wherein
The concentration of yttrium element at the end of the first portion on the side close to the bottom wall of the second recess with respect to the concentration (Xy1) of the yttrium element at the end of the first portion on the side far from the bottom wall of the second recess. A fuel cell having a concentration (Xy2) ratio (Xy2 / Xy1) of 2 to 10. The fuel cell according to any one of claims 1 to 4, wherein
Only the portion corresponding to the bottom wall of the second recess at the boundary between the first portion of each of the embedded electrical connection portions and the fuel electrode includes nickel and yttrium, and A fuel cell in which a member having a conductivity lower than that of the first portion of the electrical connecting member is interposed.

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