JP6678042B2 - Solid oxide fuel cell single cell and solid oxide fuel cell stack - Google Patents

Description

  The present invention relates to a solid oxide fuel cell unit cell having a solid electrolyte layer, an air electrode layer, and a fuel electrode layer, and a solid oxide fuel cell stack provided with the solid oxide fuel cell unit cell.

Conventionally, as a fuel cell, for example, a solid oxide fuel cell (hereinafter, also referred to as SOFC) using a solid electrolyte (solid oxide) is known.
In this SOFC, for example, a porous fuel electrode layer in contact with a fuel gas is provided on one side of a solid electrolyte layer, and a porous oxidant electrode layer (air electrode) in contact with an oxidant gas (for example, air) is provided on the other side. Layer) is used.

  In recent years, various techniques have been proposed in which the porosity (open porosity) in the thickness direction of a fuel electrode layer is set to a predetermined value in order to improve the performance of a fuel cell and the like (Patent Documents). 1-3).

  For example, Patent Literature 3 discloses a technique for improving the power generation performance by reducing the porosity of the fuel electrode layer toward the solid electrolyte layer, thereby reducing the polarization during the electrode reaction.

JP-A-9-50812 Japanese Patent No. 5179718 JP-A-2004-55194

  However, in the above-described prior art, the porosity inside the fuel electrode layer (on the side of the solid electrolyte layer) is smaller than that outside, so that the water vapor generated by the power generation reaction tends to stay near the solid electrolyte layer of the fuel electrode layer. Become. As a result, there is a problem in that the supply of the fuel gas to the three-phase interface, which is a reaction field where the solid electrolyte layer, the fuel electrode layer, and the reaction gas (fuel gas) are in contact with each other, is reduced, and the power generation performance is reduced.

  As a countermeasure, for example, if the porosity of the fuel electrode layer (particularly, the porosity near the solid electrolyte) is increased, contaminants (for example, S, Cl, Si, B, and P) in the fuel gas supplied from the outside become three-phase. There is a problem in that it easily adheres to the interface and the durability is reduced.

  The present invention has been made in view of such a problem, and provides a solid oxide fuel cell single cell and a solid oxide fuel cell stack that can enhance power generation performance and also increase durability. The purpose is to provide.

  (1) The solid oxide fuel cell unit cell according to the first aspect of the present invention includes an air electrode layer, a fuel electrode layer, and a solid electrolyte layer disposed between the air electrode layer and the fuel electrode layer. Wherein the fuel electrode layer comprises an active layer, an intermediate layer, and a diffusion layer from the solid electrolyte layer side, and the active layer, the intermediate layer, and the diffusion layer. Has open porosity, wherein the open porosity of the intermediate layer is smaller than the open porosity of the active layer, and the open porosity of the active layer is smaller than the open porosity of the diffusion layer. .

  In the first aspect, the fuel electrode layer includes, from the solid electrolyte layer side, an active layer, an intermediate layer, and a diffusion layer. The open porosity of the intermediate layer is smaller than the open porosity of the active layer. Is smaller than the open porosity of the diffusion layer. That is, in the fuel electrode layer, from the solid electrolyte layer side, an active layer having a medium open porosity, an intermediate layer having the smallest open porosity, and a diffusion layer having the largest open porosity are arranged in this order. I have.

  As described above, in the first embodiment, the open porosity of the active layer is larger than the open porosity of the intermediate layer, so that the steam generated by the power generation reaction hardly stays in the active layer (that is, the steam concentration is low). As a result, the fuel gas is easily supplied to the three-phase interface, so that there is an effect that the power generation performance is high.

  In the first embodiment, the open porosity of the intermediate layer is smaller than that of the active layer and the diffusion layer. Therefore, the contaminants in the fuel gas supplied from the outside are trapped in the intermediate layer and hardly enter the active layer. Therefore, the contaminants are less likely to adhere to the three-phase interface, resulting in an effect of high durability.

(2) In the solid oxide fuel cell unit cell according to the second aspect of the present invention, the thickness of the intermediate layer is smaller than the thickness of the active layer, and the thickness of the active layer is smaller than the thickness of the diffusion layer.
In the second aspect, the fuel electrode layer is arranged in the order of the active layer having a medium thickness, the intermediate layer having the smallest thickness, and the diffusion layer having the largest thickness from the solid electrolyte layer side.

  That is, in the fuel electrode layer, since the thickness of the intermediate layer is smaller than that of the active layer and the diffusion layer, the resistance of the active layer at the time of discharging steam and introducing fuel gas is small. Thereby, the steam generated by the power generation reaction can be efficiently discharged, and the fuel gas can also be efficiently introduced, so that there is an effect that the power generation performance is high.

(3) A solid oxide fuel cell stack according to a third aspect of the present invention includes the solid oxide fuel cell unit cell according to the first or second aspect.
In the third aspect, since one or more single cells of the solid oxide fuel cell having the above-described configuration are provided, high power generation performance is achieved.

<Each configuration of the present invention will be described below>
The solid oxide fuel cell single cell and the solid oxide fuel cell stack are devices that generate power using a fuel gas and an oxidizing gas. Here, the fuel gas refers to a gas containing a reducing agent (eg, hydrogen) serving as a fuel, and the oxidizing gas refers to a gas (eg, air) containing an oxidizing agent (eg, oxygen).

When power generation is performed using a single cell of a solid oxide fuel cell and a solid oxide fuel cell stack, a fuel gas is introduced into the fuel electrode side, and an oxidant gas is introduced into the air electrode side.
Various shapes such as a flat plate shape, a cylindrical shape, and a flat shape can be adopted as a single cell of a solid oxide fuel cell.

  When a plurality of solid oxide fuel cell single cells are used as the solid oxide fuel cell stack, all the solid oxide fuel cell single cells described above may be used, or some of the solid oxide fuel cell single cells may be used. A single cell of a solid oxide fuel cell may be used.

  In the solid oxide fuel cell stack, the solid oxide fuel cell single cells can be arranged so as to be continuous in a predetermined direction. In the case of using, for example, a plate-shaped solid oxide fuel cell single cell, they can be stacked and arranged.

-A porous layer can be adopted as the air electrode layer and the fuel electrode layer (accordingly, the active layer, the intermediate layer, and the diffusion layer).
-The open porosity is the ratio of open pores in each of the porous components (active layer, intermediate layer, diffusion layer). In addition, normally, the open pores indicate pores that communicate with each other (in a gas path) so as to reach the surface directly from the inside or through another pore or the like in each configuration.

In the solid oxide fuel cell unit cell according to the present invention, the pores observed in the cross section of each layer are regarded as substantially open pores.
As the fuel gas, hydrogen, a hydrocarbon serving as a hydrogen source, a mixed gas of hydrogen and a hydrocarbon, and a fuel gas humidified by passing these gases through water at a predetermined temperature, and a vapor mixed with these gases were used. Fuel gas and the like.

  The hydrocarbon is not particularly limited, and examples thereof include natural gas, naphtha, and coal gasification gas. Furthermore, methane, ethane, propane, butane, pentane and the like have 1 to 10, preferably 1 to 7, more preferably 1 to 4 saturated hydrocarbons, and unsaturated hydrocarbons such as ethylene and propylene as main components. Are preferable, and those containing a saturated hydrocarbon as a main component are more preferable. One of these fuel gases may be used alone, or two or more thereof may be used in combination. Further, an inert gas such as nitrogen and argon may be contained.

  -Examples of the oxidizing gas include a mixed gas of oxygen and another gas. Further, the mixed gas may contain 80% by volume or less of an inert gas such as nitrogen and argon. Of these oxidizing gases, air (containing about 80% by volume of nitrogen) is preferred because it is safe and inexpensive.

It is sectional drawing which shows typically the state which fractured the fuel cell single cell of embodiment in the thickness direction. It is sectional drawing which fractures | ruptures the fuel cell single cell of embodiment in thickness direction, and expands and shows a principal part typically. It is a perspective view showing typically the fuel cell stack of an embodiment. FIG. 4 is a cross-sectional view schematically illustrating a state in which the fuel cell stack of the embodiment is broken in a stacking direction (cross-section taken along line AA in FIG. 3).

Hereinafter, embodiments of the present invention will be described.
[Embodiment]
a) First, a solid oxide fuel cell single cell (hereinafter, also simply referred to as “single cell”), which is a basic configuration of a solid oxide fuel cell, will be described.

  As schematically shown in FIG. 1, the single cell 1 is a flat plate-shaped fuel electrode layer 3 in contact with a fuel gas (eg, hydrogen), a solid electrolyte layer 5 having oxygen ion conductivity, A reaction prevention layer 7 for preventing a reaction between the electrolyte layer 5 and the air electrode layer 9 and a porous air electrode layer 9 that is in contact with an oxidizing gas (for example, oxygen in air) are stacked in this order.

The unit cell 1 is a unit cell 1 of a so-called fuel electrode support type in which the fuel electrode layer 3 serves as a support base.
Specifically, as schematically shown in FIG. 2, the fuel electrode layer 3 is laminated in the order of the active layer 11, the intermediate layer (trap layer) 13, and the diffusion layer (substrate layer) 15 from the solid electrolyte layer 5 side. It is a thing.

  In particular, in the present embodiment, the active layer 11, the intermediate layer 13, and the diffusion layer 15 are porous layers having pores (open pores), and the open porosity of the intermediate layer 13 is larger than the open porosity of the active layer 11. It is small, and the open porosity of the active layer 11 is smaller than the open porosity of the diffusion layer 15.

The thickness of the intermediate layer 13 is smaller than the thickness of the active layer 11, and the thickness of the active layer 11 is smaller than the thickness of the diffusion layer 15.
Hereinafter, each configuration will be described in detail.

<Air electrode layer 9>
The air electrode layer 9 contacts an oxidizing gas serving as an oxygen source and functions as a cathode in the single cell 1.

  The material of the air electrode layer 9 can be appropriately selected depending on the use conditions of the fuel cell and the like. As this material, for example, a metal, a metal oxide, a metal composite oxide, or the like can be used. Examples of the metal include a metal such as Pt, Au, Ag, Pd, Ir, Ru, and Ru, or an alloy containing two or more metals.

Further, as the metal oxide, for example, oxides such as La, Sr, Ce, Co, Mn, and Fe (for example, La ₂ O ₃ , SrO, Ce ₂ O ₃ , Co ₂ O ₃ , MnO ₂ , FeO) Etc.). Examples of the complex oxide include various complex oxides containing at least one of La, Pr, Sm, Sr, Ba, Co, Fe, Mn and the like (for example, La _1-x Sr _x CoO ₃ -based). composite _{oxides, La 1-x Sr x FeO} 3 -based composite _{oxide, La 1-x Sr x Co} 1-y Fe y O 3 composite _{oxide, La 1-x Sr x MnO} 3 composite oxide, Pr _1-x Ba _x CoO ₃ composite _{oxide, Sm 1-x Sr x CoO} 3 -based composite oxide and the like).

<Reaction prevention layer 7>
As the reaction prevention layer 7, a material containing CeO and a rare earth element as main components can be adopted. Note that the entire material may be composed of CeO and rare earth elements.

<Solid electrolyte layer 5>
The solid electrolyte layer 5 is made of a solid electrolyte material having oxygen ion conductivity. Examples of the material of the solid electrolyte layer 5 include YSZ (yttria-stabilized zirconia), ScSZ (scandia-stabilized zirconia), SDC (samarium-doped ceria), GDC (gadria-doped ceria), and perovskite-based oxides. No. These may be a single film or a multilayer film in which two or more compositions have a laminated structure. Examples of the multilayer film include a YSZ + SDC film and a YSZ + GDC film.

  The thickness of the solid electrolyte layer 5 is preferably 3 to 20 μm. If the thickness is less than 3 μm, it is difficult to reduce the thickness, and it is difficult to obtain a cell without defects.

<Fuel electrode layer 3 (whole)>
The fuel electrode layer 3 comes into contact with a fuel gas serving as a hydrogen source, and functions as an anode in the single cell 1.

As the fuel electrode layer 3, a cermet composed of metal (particularly Ni) particles and ceramic particles can be employed.
As the metal, other than Ni, Cu, Fe, Co, Ag, Pt, Pd, W, Mo, and alloys thereof can be used.

  Examples of the ceramic include zirconia, YSZ, ScSZ, SDC, GDC, alumina, silica, titania and the like. In particular, YSZ, ScSZ, SDC, and GDC are desirable. This is because they have oxygen ion conductivity and enhance the electrochemical activity of the fuel electrode layer 3. The electrochemical activity is a power generation reaction.

  The total thickness of the fuel electrode layer 3 is preferably in the range of about 500 to 2000 μm. If it is less than 500 μm, it is difficult to obtain sufficient strength in the cell, and if it is more than 2000 μm, the permeability of the fuel gas becomes poor and the power generation efficiency may be reduced.

<Active layer 11>
The active layer 11 is a porous layer of the fuel electrode layer 3 disposed in contact with the solid electrolyte layer 5, and has higher electrochemical activity than the intermediate layer 13 and the diffusion layer 15.

  That is, as will be described later, the active layer 11 has a large amount of oxygen ions adjacent to the solid electrolyte layer 5 and has a high level of electrochemical activity as compared with the intermediate layer 13 and the diffusion layer 15. 15, a structure in which hydrogen (ions) are supplied from the intermediate layer 13, and a structure (arrangement) in which an electrochemical reaction proceeds most in the fuel electrode layer 3.

  As the active layer 11, a cermet composed of metal (for example, Ni) particles and ceramic particles as shown in the fuel electrode layer 3 (entire) can be employed. As the metal and the ceramic, the materials shown in the fuel electrode layer 3 (entire) can be employed.

In order to form pores (open pores) in the active layer 11, for example, organic beads can be used as described later.
Further, the content of the metal (especially Ni) in the cermet is desirably 20 to 45% by volume (especially 30 to 35% by volume) when the total amount of the cermet is 100% by volume, for example, 30% by volume can be adopted. . Here, if it is less than 20% by volume, the conductivity (conductivity) decreases, and if it exceeds 45% by volume, it is difficult to obtain a permeable structure.

  The active layer 11 has a higher electrochemical activity than the intermediate layer 13 and the diffusion layer 15. That is, in order to make the conductivity of the active layer 11 higher than that of the intermediate layer 13 and the diffusion layer 15, for example, the content of the metal such as Ni in the cermet should be larger in the active layer 11 than in the intermediate layer 13 and the diffusion layer 15. Is preferred.

  As the thickness of the active layer 11, for example, a range of 5 to 50 μm (for example, 10 μm) can be adopted. Here, when the thickness of the active layer 11 is less than 5 μm, holes are easily formed in the solid electrolyte layer 5, and when the thickness is more than 50 μm, the air permeability of the active layer 11 is deteriorated (accordingly, water vapor is easily retained. ), The power generation performance decreases.

  As the open porosity of the active layer 11, for example, a range of 10 to 25% by volume (for example, 15% by volume) can be adopted. Here, when the open porosity of the active layer 11 is less than 10% by volume, the air permeability deteriorates, and when it exceeds 25% by volume, the power generation reaction field (three-phase interface) decreases, and the power generation efficiency deteriorates. Become.

<Intermediate layer 13>
The intermediate layer 13 is a porous layer disposed between the active layer 11 and the diffusion layer 15, and mainly collects pollutants (for example, S, Cl, Si, B, and P) contained in fuel gas and the like. (Trap) function.

  As the intermediate layer 13, a cermet composed of metal (for example, Ni) particles and ceramic particles as shown in the fuel electrode layer 3 (entire) can be employed. As the metal and the ceramic, the materials shown in the fuel electrode layer 3 (entire) can be employed.

  Further, the content of the metal (especially Ni) in the cermet is desirably 20 to 45% by volume (especially 30 to 35% by volume) when the total amount of the cermet is 100% by volume, for example, 30% by volume can be adopted. . Here, when the content is less than 20% by volume, the conductivity is reduced. When the content is more than 45% by volume, it is difficult to obtain a permeable tissue.

  As the thickness of the intermediate layer 13, for example, a range of 1 to 5 μm (for example, 3 μm) can be adopted. Here, if the thickness of the intermediate layer 13 is less than 1 μm, the function of collecting contaminants becomes small, and it becomes difficult to sufficiently collect contaminants. On the other hand, if the thickness of the intermediate layer 13 exceeds 5 μm, the air permeability of the water vapor and the fuel gas in the fuel electrode layer 3 deteriorates, and the power generation performance decreases.

  As the open porosity of the intermediate layer 13, for example, a range of 5 to 10% by volume (for example, 9% by volume) can be adopted. Here, if the open porosity of the intermediate layer 13 is less than 5% by volume, the air permeability deteriorates, and if it exceeds 10% by volume, the function of collecting contaminants is reduced.

<Diffusion layer 15>
The diffusion layer 15 is an outermost porous layer disposed in contact with the intermediate layer 13 and mainly has a function of introducing fuel gas into the intermediate layer 13 and the active layer 11 and supporting the entire unit cell 1. .

  As the diffusion layer 15, a cermet composed of metal (for example, Ni) particles and ceramic particles as shown in the fuel electrode layer 3 (entire) can be employed. As the metal and the ceramic, the materials shown in the fuel electrode layer 3 (entire) can be employed.

In order to form pores (open pores) of the diffusion layer 15, for example, organic beads can be used as described later.
Further, the content of the metal (especially Ni) in the cermet is desirably 20 to 45% by volume (especially 30 to 35% by volume) when the total amount of the cermet is 100% by volume, for example, 30% by volume can be adopted. . Here, when the content is less than 20% by volume, the conductivity is reduced. When the content is more than 45% by volume, it is difficult to obtain a permeable tissue.

  As the thickness of the diffusion layer 15, for example, a range of 500 to 2000 μm (for example, 800 μm) can be adopted. Here, if the thickness of the diffusion layer is less than 500 μm, the function as a support decreases, and if it exceeds 2000 μm, the air permeability deteriorates and the power generation performance decreases.

  As the open porosity of the diffusion layer 15, for example, a range of 20 to 45% by volume (for example, 31% by volume) can be adopted. Here, if the open porosity of the diffusion layer 15 is less than 20% by volume, the air permeability deteriorates, and if it exceeds 45% by volume, the strength of the diffusion layer 15 is reduced and the function as a support is reduced. .

  As described above, in the present embodiment, the magnitude relationship of the open porosity in the active layer 11, the intermediate layer 13, and the diffusion layer 15, which is a porous layer, is such that the intermediate layer 13 <the active layer 11 <the diffusion layer 15. The magnitude relation of the thicknesses of the layers 11 to 15 is as follows: the intermediate layer 13 <the active layer 11 <the diffusion layer 15. Further, for example, the relationship of the size of each layer of the metal content in the cermet is as follows: active layer 11> intermediate layer 13 and diffusion layer 15.

b) Next, a fuel cell stack including the single cell 1 will be described.
3 and 4, the number of the single cells 1 used in the fuel cell stack 21 is schematically shown as being smaller than the actual number.

As schematically shown in FIGS. 3 and 4, the fuel cell stack 21 includes one or more single cells 1 having the above-described configuration.
Specifically, as shown in FIG. 4, in the fuel cell stack 21, a plurality of power generation units 23 each including the single cell 1 as a main part are continuously stacked in the vertical direction (stacking direction) in FIG.

In this embodiment, for convenience of explanation, directions such as “up” and “down” are described based on the directions of the drawings, but do not specify the actual direction of the fuel cell stack.
Specifically, the power generation unit 23 includes the single cell 1, the cathode current collector 27, the anode current collector 29, the cathode-side insulating frame 31, the separator 33, the anode-side frame 35, The interconnector 25 on one side (upper side in FIG. 4) (the end plate 37 at the upper end of the fuel cell stack 21) and the interconnector 25 on the other side (the end plate 39 at the lower end of the fuel cell stack 21) And Note that adjacent power generation units 23 are configured to share one interconnector 25.

  Here, the air electrode current collector 27 is joined to the adjacent interconnector 25 by a brazing material (not shown). The air electrode side insulating frame 31 is a mica frame made of soft mica.

  The above-described members are stacked and integrated to form a fuel cell stack 21. In addition, for integration of each member, a bolt penetrating in the laminating direction may be used, or may be integrated by a known method.

Hereinafter, each configuration of the fuel cell stack 21 will be described.
<Air electrode current collector 27>
As the material of the air electrode current collector 27, metal or conductive ceramic can be used.

The cathode current collector 27 is in contact with the cathode layer 9 on one side, and is joined to the interconnector 25 (or end plate 37) by brazing on the other side.
<Fuel electrode current collector 29>
The material of the anode current collector 29 is preferably a metal, and can be formed of, for example, Ni or a Ni-based alloy.

The anode current collector 29 is in contact with the anode layer 3 on one side and is joined to the interconnector 25 (or end plate 39) on the other side.
<Separator 33>
The separator 33 is a plate member that is joined to the outer periphery of the unit cell 1 and has a frame shape in a plan view. Examples of the material of the separator 33 include metals such as stainless steel.

  Due to the separator 33, the air flow path 41 (which is a flow path of the oxidizing gas) on the side of the air electrode layer 9 and the fuel flow path 43 (which is a flow path of the fuel gas) on the side of the fuel electrode layer 3 are both gaseous. Are separated so that they do not mix.

<Interconnector 25, end plates 37 and 49>
The material of the interconnector 25 and the end plates 37 and 49 is formed of a metal, particularly a heat-resistant alloy such as stainless steel, a nickel-based alloy, and a chromium-based alloy.

c) Next, a method for manufacturing the single fuel cell 1 will be described.
<Preparation of green sheet for diffusion layer>
To a mixed powder (100 parts by weight) of NiO powder (60 parts by weight) and YSZ powder (40 parts by weight), organic beads (10% by weight based on the mixed powder) as a pore former, and butyral resin Then, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol were added and mixed by a ball mill to prepare a slurry. A green sheet for a diffusion layer having a thickness of 250 μm was prepared from the obtained slurry by a doctor blade method.

<Preparation of green sheet for intermediate layer>
To a mixed powder (100 parts by weight) of NiO powder (60 parts by weight) and YSZ powder (40 parts by weight), butyral resin, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol were used. In addition, the mixture was mixed with a ball mill to prepare a slurry. A green sheet for an intermediate layer having a thickness of 4 μm was prepared from the obtained slurry by a doctor blade method.

<Preparation of green sheet for active layer>
To a mixed powder (100 parts by weight) of NiO powder (60 parts by weight) and YSZ powder (40 parts by weight), organic beads (10% by weight based on the mixed powder) as a pore former, and butyral resin Then, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol were added and mixed by a ball mill to prepare a slurry. The obtained slurry was used as a green sheet for an active layer having a thickness of 12 μm by a doctor blade method.

<Preparation of green sheet for solid electrolyte layer>
A butyral resin, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol were added to YSZ powder (100 parts by weight), and mixed with a ball mill to prepare a slurry. A green sheet for a solid electrolyte layer having a thickness of 10 μm was prepared from the obtained slurry by a doctor blade method.

<Preparation of laminated molded body>
Next, four green sheets for the diffusion layer, one green sheet for the intermediate layer, one green sheet for the active layer, and one green sheet for the solid electrolyte layer are laminated and cut into a 150 × 150 mm square. A laminated molded body was produced.

After degreased at 250 ° C., the laminated molded body was fired at 1200 to 1500 ° C. for 1 to 10 hours to produce a laminated fired body.
<Preparation of reaction prevention layer 7>
As a material for the reaction preventing layer 7, a reaction preventing layer paste was prepared using a material composed of GDC (gadolinium-added ceria) and a binder solution.

Next, a reaction prevention layer paste was printed on the surface of the solid electrolyte layer 5 in the laminated fired body.
<Preparation of air electrode layer 9>
Preparation as the material of the air electrode layer 9, for example, a _{La 1-x Sr x Co 1} -y Fe y O 3 powder having an average particle size of 1 to 4 [mu] m, using a material comprising a binder solution, an air electrode layer paste did.

Next, the air electrode layer paste was printed on the reaction prevention layer paste.
Then, the printed reaction preventing layer paste and the air electrode layer paste are fired at 900 to 1200 ° C. for 1 to 5 hours so as not to be dense by firing to form the reaction preventing layer 7 and the air electrode layer 9. did.

Thus, the single cell 1 was completed. In addition, the separator 33 was brazed to the single cell 1.
Further, the above-described members are combined with the single cell 1 as shown in FIG. 4 and the interconnector 25, the respective frames 31, 35, the separator 33, the end plates 37, 39 and the like are formed by a known method such as brazing. By joining, the fuel cell stack 21 can be manufactured.

  Further, when the fuel cell stack 21 manufactured as described above is exposed to a reducing atmosphere such as hydrogen during power generation, for example, NiO in the fuel electrode layer 3 is reduced to Ni, and thus the intermediate layer 13 is formed. Fine pores are formed in the fuel electrode layer 3. Since the active layer 11 and the diffusion layer 15 include a pore-forming material of organic beads at the time of manufacturing, pores (open pores) are formed in the portions where the pore-forming material has disappeared by the above-described firing.

d) Next, a method for distinguishing the active layer 11, the intermediate layer 13, and the diffusion layer 15 will be described.
First, the boundary between the solid electrolyte layer 5 and the fuel electrode layer 3 is imaged with respect to the fuel electrode layer 3 at a magnification centering on the intermediate layer 13 and at least the entire thickness of the layer presumed to be the active layer 11. From the upper end of the image, it is reflected in a region of 1/10 of the length from the top to the bottom of the image. An image (SEM image) is obtained by taking an image so as to appear in a region from 1/5 to 3/5 of the image.

  Note that a binarized image can be adopted as an image (however, if the pores in the image after the binarization processing are significantly different from the actual form due to contrast, the contrast is adjusted or an image not subjected to the binarization processing is used. To adopt). For example, the magnification here can be 2000 times. The magnification of the image is not limited to this.

  Next, virtual lines parallel to the interface between the solid electrolyte layer 5 and the active layer 11 are drawn in order from the solid electrolyte layer 5 side at 0.3 μm intervals, and virtual lines K1, K2, K3,..., Km,. , K (m + 9), K (m + 10),..., Kn.

Next, the ratio (porosity) of the pores existing on each virtual line is measured by a method described later.
Next, among the porosity Ks1, Ks2, Ks3,..., Ksm,..., Ks (m + 9), Ks (m + 10),. Is set for each data group having the porosity of 10 virtual lines, and the average value (Ave) of the 10 porosity values of each data group and the standard deviation (σ) of the porosity of each data group are calculated.

  The data group G1 is composed of Ks1, Ks2,..., Ks10 in order from the solid electrolyte layer 5 side, the data group G2 is composed of Ks2, Ks3,. Ks (m + 1), Ks (m + 2),..., Ks (m + 9), and the data group G (m + 1) includes Ks (m + 1), Ks (m + 2),.

  That is, the data group G (m + 1) includes nine porosity (Ks (m + 1),..., Ks) obtained by removing the porosity Ksm of the first virtual line Km of the data group Gm from the data group Gm. (M + 9)) and a porosity Ks (m + 10) of the virtual line K (m + 10) next to the last virtual line K (m + 9) of the data group.

  For the first time, “the average value of the porosity of G (m + 1)” is “the value obtained by adding twice the standard deviation (σ) of the 10 porosity values of Gm to the average value of the porosity of Gm”. When the value exceeds, or “the average value of the porosity of G (m + 1)” is subtracted from the average value of the porosity of Gm by twice the standard deviation (σ) of the 10 porosity of Gm. The virtual line K (m + 10) corresponding to the tenth porosity Ks (m + 10) of the data group G (m + 1) when the value falls below the “value” for the first time is drawn to the boundary of each layer (between the active layer 11 and the intermediate layer 13). Boundary, the boundary between the intermediate layer 13 and the diffusion layer 15).

  That is, assuming that the average value of the porosity of Gm is GmAve, the average value of the porosity of G (m + 1) is G (m + 1) Ave, and the standard deviation of the porosity of Gm is σm, The virtual line K (m + 10) corresponding to the tenth porosity Ks (m + 10) of the data group G (m + 1) of the data group G (m + 1) is defined by the boundary of each layer (the boundary between the active layer 11 and the intermediate layer 13, the intermediate layer 13 and the diffusion layer). 15).

| (G (m + 1) Ave)-(GmAve) |> 2σm (1)
e) Next, a method for measuring the porosity (open porosity) of the active layer 11, the intermediate layer 13, and the diffusion layer 15 will be described.

  A cross section is formed along the stacking direction of the fuel electrode layer 3 formed by the above-described manufacturing method, and an image (for example, an SEM image) is obtained by imaging the cross section. Note that the magnification of the SEM image is a magnification at which the active layer 11 appears in the thickness direction (here, the photograph was taken at a magnification of 2000, but is not limited to this).

Next, a plurality of straight lines parallel to the direction perpendicular to the stacking direction are drawn at regular intervals (for example, at intervals of 0.3 μm) on the SEM image.
Next, the length of the portion corresponding to the pore on the drawn straight line is measured.

Here, a value obtained by dividing the sum of the lengths of the plurality of pore portions on one straight line by the total straight line length corresponds to the porosity.
Then, an average value of a plurality of (for example, 3 to 30) linear porosity values is obtained, and the average value is defined as each porosity value of the active layer 11, the intermediate layer 13, and the diffusion layer 15. For example, as the number of straight lines, in each layer, ten lines can be used at intervals of 1/10 of the thickness, and the average of the porosity measured by each straight line can be used as the porosity of each layer.

  In the single cell 1 having the configuration as in the present invention, usually, most of the pores communicate with other pores, and thus the porosity corresponds to the open porosity. That is, in the present invention, the porosity obtained by the above-described measurement method can be adopted as the open porosity of the present invention.

  In addition, in this measurement, although the measurement of the open porosity was performed using the SEM image of 2000 times, even if the SEM image of 500 to 20000 times is used, the measurement of the open porosity can be performed by the above measurement method. .

f) Next, the operation and effect of the present embodiment will be described.
In the present embodiment, the fuel electrode layer 3 includes an active layer 11 (which is porous), an intermediate layer 13 and a diffusion layer 15 from the solid electrolyte layer 5 side, and the open porosity of the intermediate layer 13 is active. The open porosity of the active layer 11 is smaller than the open porosity of the diffusion layer 15.

  That is, in the present embodiment, since the open porosity of the active layer 11 is larger than the open porosity of the intermediate layer 13, the steam generated by the power generation reaction of the following formula (2) is unlikely to stay in the active layer 11 (that is, Low concentration). As a result, the supply of the fuel gas to the three-phase interface becomes easy, so that there is an effect that the power generation performance is high.

H ₂ + O ²⁻ → H ₂ O + 2e− (2)
Further, in this embodiment, since the open porosity of the intermediate layer 13 is smaller than that of the active layer 11 and the diffusion layer 15, contaminants in the fuel gas supplied from the outside hardly enter the active layer 11. Therefore, the pollutant is less likely to adhere to the three-phase interface, so that there is an effect that the poisoning durability is high.

  Further, in the present embodiment, the fuel electrode layer 3 includes, from the solid electrolyte layer 5 side, an active layer 11 having a thickness smaller than the diffusion layer 15, an intermediate layer 13 having a thickness smaller than the active layer 11, and a diffusion layer having the largest thickness. 15 are arranged in this order.

  That is, since the thickness of the intermediate layer 13 is the smallest, resistance at the time of discharging steam and introducing fuel gas is small. Also from this point, there is an advantage that the power generation performance is high because the steam generated by the power generation reaction can be efficiently discharged and the fuel gas can be efficiently introduced.

It should be noted that the present invention is not limited to the above embodiments and the like, and it goes without saying that the present invention can be implemented in various modes without departing from the present invention.
(1) For example, in addition to the fuel cell stack in which the plate-shaped fuel cell single cells are stacked as in the above-described embodiment, for example, a plurality of fuel cell single cells having a well-known cylindrical shape or the like are arranged. Things.

  (2) Also, conventionally known forms can be adopted for the fuel electrode current collector and the air electrode current collector. For example, the air electrode current collector may be formed integrally with a part of the interconnector projecting.

DESCRIPTION OF SYMBOLS 1 ... Fuel cell single cell 3 ... Fuel electrode layer 5 ... Solid electrolyte layer 9 ... Air electrode layer 11 ... Active layer 13 ... Intermediate layer 15 ... Diffusion layer 21 ... Fuel cell stack 23 ... Power generation unit 25 ... Interconnectors 37 and 39 ... end plate

Claims (4)

An air electrode layer, a fuel electrode layer, and a solid electrolyte layer disposed between the air electrode layer and the fuel electrode layer, a solid oxide fuel cell single cell having:
The fuel electrode layer includes an active layer, an intermediate layer, and a diffusion layer from the solid electrolyte layer side,
The active layer, the intermediate layer, and the diffusion layer have open pores,
The open porosity of the intermediate layer is smaller than the open porosity of the active layer, open porosity of the active layer is minor than open porosity of the diffusion layer,
The solid oxide fuel cell unit cell, wherein the diffusion layer has conductivity .    The solid oxide fuel cell unit cell according to claim 1, wherein the thickness of the intermediate layer is smaller than the thickness of the active layer, and the thickness of the active layer is smaller than the thickness of the diffusion layer. 3. The solid oxide fuel cell unit cell according to claim 1, wherein the open porosity of the intermediate layer is in the range of 5 to 10% by volume. Solid oxide fuel cell stack comprising the solid oxide fuel cell unit according to any one of claims 1 to 3.

Images