JP4883954B2 - Solid oxide fuel cell and method for producing the same - Google Patents

Description

  The present invention relates to a solid oxide fuel cell (SOFC) and a method for producing the same.

  SOFC is being developed as a third generation fuel cell for power generation. The SOFC has a structure in which a solid electrolyte is sandwiched between an air electrode and a fuel electrode, supplies oxygen to the air electrode, supplies fuel gas such as hydrogen and carbon monoxide to the fuel electrode, and so on. An electromotive force is obtained by an oxidation-reduction reaction via an electrolyte.

  In order to improve the power generation performance of SOFC, it is important to employ a material having high oxide ion conductivity as the solid electrolyte. Conventionally, for example, gallate-based oxides (particularly lanthanum gallate-based oxides) are known as materials having high oxide ion conductivity (see Patent Document 1).

  On the other hand, it is desired to reduce the thickness of the solid electrolyte from the viewpoint of improving the battery performance by reducing the internal resistance of the SOFC, the viewpoint of cost reduction, and the like. However, gallate-based oxides have a limited mechanical strength due to their low mechanical strength. In general, in the case of a gallate-based oxide electrolyte, a thickness of about 200 to 300 μm is required to ensure mechanical strength. For example, Patent Document 2 discloses an SOFC including a lanthanum gallate solid electrolyte. In the example, the thickness of the solid electrolyte is set to 200 μm.

  In order to reduce the thickness of the gallate oxide electrolyte, for example, it has been proposed to increase the thickness of the fuel electrode excessively to support the electrolyte strength. This is a so-called fuel electrode supported SOFC. However, the fuel electrode supported SOFC has the following drawbacks. That is, 1) the mechanical strength of the electrolyte is still insufficient, and 2) the thickness of the SOFC becomes larger than necessary because the fuel electrode needs to be thicker than necessary.

From the above, in SOFCs using gallate-based oxide electrolytes, it is desired to develop a technology that can sufficiently ensure the performance and mechanical strength of the solid electrolyte and further reduce the thickness of the solid electrolyte.
JP 2003-197219 A JP 2003-263993 A

  The main object of the present invention is to provide a technique capable of sufficiently securing the performance and mechanical strength of a solid electrolyte and further reducing the thickness of the solid electrolyte in an SOFC using a gallate oxide electrolyte.

  As a result of intensive studies to achieve the above object, the present inventor found that the SOFC using a gallate-based oxide electrolyte can achieve the above object when the solid electrolyte has a specific multilayer structure. The present invention has been completed.

  That is, this invention relates to the following SOFC and its manufacturing method.

  1. A solid oxide fuel cell having a solid electrolyte, a fuel electrode, and an air electrode, wherein the solid electrolyte has a laminated structure of 1) a support electrolyte having a through-hole in the thickness direction and 2) a gallate oxide electrolyte A solid oxide fuel cell.

  2. Item 2. The solid oxide fuel cell according to Item 1, wherein the support electrolyte is a fluorite-type compound.

3. The support electrolyte has the following general composition formula (1)
Ln _1-x A _x MO _p (1)
[In the formula, Ln represents a rare earth element. A represents an alkaline earth metal element. M represents a transition metal element. x represents 0 <x ≦ 0.4. p represents the number of oxygen atoms. ]
Item 2. The solid oxide fuel cell according to Item 1, which is an electron conductive perovskite oxide represented by:

4). The gallate oxide electrolyte has the following general composition formula (2)
_{Ln 1-x A x Ga 1} -y-z B y E z O p (2)
[Wherein, Ln represents at least one of La, Ce, Pr, Nd and Sm. A represents at least one of Sr, Ca, and Ba. B represents at least one of Mg and Al. E represents at least one of Co, Fe, Ni, and Cu. x represents 0.05 ≦ x ≦ 0.3. y represents 0 <y ≦ 0.29. z represents 0 ≦ z ≦ 0.3. p represents the number of oxygen atoms. ]
Item 4. The solid oxide fuel cell according to any one of Items 1 to 3, which is a gallate-based oxide.

  5. Item 5. The solid oxide fuel cell according to any one of Items 1 to 4, wherein the gallate oxide electrolyte has a thickness of 30 to 250 µm.

  6). Item 6. The solid oxide fuel cell according to any one of Items 1 to 5, wherein the solid electrolyte has a thickness of 130 to 450 µm.

  7). 7. The flat plate type solid oxide fuel cell according to any one of Items 1 to 6, wherein the solid electrolyte, the fuel electrode, and the air electrode are all flat.

  8). Item 7. The cylindrical solid oxide fuel cell according to any one of Items 1 to 6, wherein the solid electrolyte, the fuel electrode, and the air electrode are all cylindrical.

9. A method for producing a solid oxide fuel cell comprising the following steps in order:
(1) Step 1 for obtaining a support electrolyte having a through-hole in the thickness direction and a gallate oxide electrolyte,
(2) Step 2 of laminating one of the support electrolyte and the gallate oxide electrolyte and the fuel electrode,
(3) Step 3 of laminating the other one of the support electrolyte and the gallate oxide electrolyte and the air electrode.

Hereinafter, the SOFC of the present invention and the manufacturing method thereof will be described in detail.

1. SOFC of the present invention
The SOFC of the present invention is a SOFC having a solid electrolyte, a fuel electrode, and an air electrode, wherein the solid electrolyte layer has a laminated structure of 1) a support electrolyte having through holes in the thickness direction and 2) a gallate oxide electrolyte. It is characterized by having.

  In the SOFC of the present invention having the above characteristics, the solid electrolyte has a laminated structure of a support electrolyte and a gallate oxide electrolyte, so that the performance and mechanical strength of the solid electrolyte are sufficiently secured, and the solid electrolyte is made thin. it can. In a preferred embodiment of the present invention, the thickness and thickness of the gallate oxide electrolyte can be reduced to about 30 μm while sufficiently ensuring the performance and mechanical strength of the solid electrolyte. Further, the thickness of the solid electrolyte (laminated body) can be reduced to about 130 μm. The reduction in the thickness of the solid electrolyte leads to an effect of reducing IR loss, and as a result, the power generation efficiency of the SOFC can be increased. In addition, since the SOFC of the present invention has a gallate oxide electrolyte, the oxide ion conduction of the solid electrolyte is good.

  Hereinafter, the configuration of the SOFC of the present invention will be specifically described.

  The solid electrolyte has a laminated structure of 1) a support electrolyte having through-holes in the thickness direction and 2) a gallate oxide electrolyte.

  As the support electrolyte, one having a through hole in the thickness direction is used. The material of the support electrolyte is preferably a material that has high mechanical strength, can sufficiently exhibit the mechanical strength required for the solid electrolyte, and can contribute to thinning of the solid electrolyte. In addition, a material having good oxide ion conductivity, electronic conductivity, high temperature stability, and the like is more preferable.

  Examples of the material for the support electrolyte include those shown in (a) to (c) below.

(I) Fluorite-type compound Examples of the fluorite-type compound include yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), and ceria (including stabilized ceria).

As YSZ, for example, (Y ₂ O ₃ ) _x (ZrO ₂ ) _1-x (where x is 0 <x ≦ 0.12) is preferable, and so-called 8YSZ where x is 0.08 is preferable. More preferred.

As ScSZ, for example, (Sc ₂ O ₃ ) _x (ZrO ₂ ) _1-x (where x is 0 <x ≦ 0.12) is preferable.

As the ceria, for example, Ce _1-x M _x O _p (where M is a rare earth element such as Sm, Gd, Y, Nd, La, Pr, Yb, Eu, or an alkaline earth metal element such as Ca, Sr). At least one type, x is 0 ≦ x ≦ 0.5, and p is the number of oxygen atoms.

(B) Electron conductive perovskite type compound As the electron conductive perovskite type compound, for example, the following general composition formula (1)
Ln _1-x A _x MO _p (1)
[In the formula, Ln represents a rare earth element. A represents an alkaline earth metal element. M represents a transition metal element. x represents 0 <x ≦ 0.4. p represents the number of oxygen atoms. ]
Is preferred.

(C) Other materials As other materials, for example, materials other than the above (A) and (B), and generally known materials can be used as insulating materials. Examples of such a material include at least one of Al ₂ O ₃ , SiC, and Si ₃ N ₄ .

  Among the materials (a) to (c), a fluorite type compound is preferable from the viewpoint of mechanical strength, and among the fluorite type compounds, YSZ (particularly 8YSZ) is preferable. The bending strength of gallate oxide is about 170 MPa, whereas the bending strength of 8YSZ is as large as about 300 MPa. Therefore, by combining 8YSZ, the strength of the solid electrolyte can be effectively increased.

  The support electrolyte has through holes in the thickness direction. The shape, size, arrangement mode and the like of the through holes are not limited. Examples of the shape of the through hole include a circle, a triangle, a quadrangle, and other polygons. The size of the through hole can be appropriately set in consideration of the mechanical strength of the support electrolyte. The arrangement mode of the through holes may be regular or irregular, and examples of the regular arrangement mode include a honeycomb shape. FIG. 3 shows a specific example of the support electrolyte, the shape of the through holes, and the arrangement of the through holes.

  The thickness of the support electrolyte is not limited, and can be selected from a range of about 100 to 350 μm depending on the mechanical strength of the support electrolyte, the demand for thinning the solid electrolyte, and the like. Among these, about 100-250 micrometers is preferable. When 8YSZ having excellent mechanical strength is used as the support electrolyte, it is easy to meet the demand for thinning the solid electrolyte.

The material of the gallate oxide electrolyte is not particularly limited as long as it has good oxide ion conductivity and is suitable for a solid electrolyte. For example, the following general composition formula (2)
_{Ln 1-x A x Ga 1} -y-z B y E z O p (2)
[Wherein, Ln represents at least one of La, Ce, Pr, Nd and Sm. A represents at least one of Sr, Ca, and Ba. B represents at least one of Mg and Al. E represents at least one of Co, Fe, Ni, and Cu. x represents 0.05 ≦ x ≦ 0.3. y represents 0 <y ≦ 0.29. z represents 0 ≦ z ≦ 0.3. p represents the number of oxygen atoms. ]
A gallate oxide represented by the formula is preferred.

Among the gallate oxides represented by the general composition formula (2), the following composition formula (3)
_{La x Sr 1-x Ga y} Mg 1-y O p (3)
[However, 0.8 <x <1, 0.65 <y <0.95, p represents the number of oxygen atoms]
The lanthanum gallate oxide shown by these is preferable.

Further, among the lanthanum gallate oxides, the following composition formula (4)
_{La 0.9 Sr 0.1 Ga 0.8 Mg 0.2} O p (4)
[Wherein p represents the number of oxygen atoms]
So-called LSGM1020 shown by these is more preferable.

  The thickness of the gallate oxide electrolyte is not limited, but can be widely selected from about 30 to 250 μm. Among these, about 30-100 micrometers is more preferable. When 8YSZ is used as the support electrolyte, the thickness of the gallate oxide electrolyte can be reduced to about 30 μm while ensuring the performance and mechanical strength required for the solid electrolyte.

  The thickness of the solid electrolyte (laminated body of both electrolytes) can be widely selected from the range of about 130 to 450 μm. Among these, about 130-300 micrometers is preferable.

  As the SOFC of the present invention, known components can be used as other components (fuel electrode, air electrode, etc.) other than the solid electrolyte.

  Examples of the fuel electrode include NiO / YSZ composite particles, NiO / SDC (SDC: Samaria doped ceria) composite particles, NiO / ScSZ composite particles, NiO / YDC (YDC: yttria doped ceria) composite particles, NiO / LSGM. Examples thereof include sintered bodies such as (LSGM: lanthanum strontium gallium magnesium oxide) composite particles.

  The thickness of the fuel electrode is not limited, but is preferably about 10 to 100 μm, more preferably about 15 to 50 μm.

The air electrode, for example, L Acoo ₃ based oxides, sintered bodies such as SmCoO ₃ based oxide. Examples of the SmCoO ₃ oxide include Sm _0.5 Sr _0.5 CoO ₃ (SSC).

  Although the thickness of an air electrode is not limited, About 10-100 micrometers is preferable and about 15-50 micrometers is more preferable.

  The fuel electrode and the air electrode may be disposed so as to sandwich the solid electrolyte. In particular, it is preferable to stack the gallate-based oxide electrolyte and the fuel electrode, and stack the support electrolyte and the air electrode. In this case, it is preferable that the through hole of the support electrolyte is filled with an air electrode. That is, in a preferred embodiment, the air electrode is preferably laminated on one side of the support electrolyte and is in contact with the gallate oxide electrolyte through the through hole.

  As described above, when the air electrode and the gallate oxide electrolyte are in direct contact with each other through the through hole, the oxide ion conduction of the solid electrolyte is good. Assuming that the thicknesses of the fuel electrode and air electrode are the same, the case where the through hole is filled with the air electrode and the volume of the air electrode is secured is larger than the case where the fuel electrode is filled. Therefore, it is easy to improve the power generation efficiency.

  The SOFC of the present invention may be a flat SOFC in which the solid electrolyte, the fuel electrode, and the air electrode are all flat. Further, a cylindrical SOFC in which the solid electrolyte, the fuel electrode, and the air electrode are all cylindrical may be used.

  In the case of a cylindrical SOFC, air (oxygen) is generally circulated inside the cylinder, and fuel gas is circulated outside the cylinder. Therefore, the air electrode, the support electrolyte, the gallate oxide electrolyte, and the fuel electrode are arranged in this order from the inside to the outside of the cylinder, and a part of the air electrode is placed in the through hole of the support electrolyte. Is preferably filled. For example, a lanthanum chromite oxide can be suitably used as an interconnector used for a cylindrical SOFC (particularly, a cylindrical vertical stripe type).

2. SOFC Manufacturing Method The SOFC manufacturing method of the present invention is not limited, but the solid electrolyte, the fuel electrode, and the air electrode can be produced according to the following procedures. That is, in the case of a solid electrolyte, if it is a support electrolyte, for example, a paste obtained by mixing 8YSZ powder with a binder (polyethylene glycol or the like; the same shall apply hereinafter) is applied to a predetermined shape or formed into a green sheet. It can be produced by firing (sintering). The treatment for providing the through-holes in the support electrolyte may be performed on the sintered body, but is preferably performed in a green sheet state in consideration of workability. The gallate oxide electrolyte, the fuel electrode, and the air electrode can also be produced by forming the powder of the material constituting each part into a paste, forming it into a predetermined shape, and then firing (sintering) it.

  However, since the required firing temperature falls in the order of the solid electrolyte, the fuel electrode, and the air electrode, it is necessary to devise the firing order.

Considering the above, the SOFC of the present invention is preferably manufactured by a manufacturing method having the following steps 1 to 3 in order.
(1) Step 1 for obtaining a support electrolyte having a through-hole in the thickness direction and a gallate oxide electrolyte,
(2) Step 2 of laminating one of the support electrolyte and the gallate oxide electrolyte and the fuel electrode,
(3) Step 3 of laminating the other one of the support electrolyte and the gallate oxide electrolyte and the air electrode.

  Hereinafter, each step of the manufacturing method will be described with reference to materials for easy understanding.

[Step 1]
Step 1 obtains a support electrolyte having a through hole in the thickness direction and a gallate oxide electrolyte.

  When both electrolytes are obtained separately, they can be produced as follows.

  For example, the support electrolyte is formed by forming a through-hole after forming a paste containing 8YSZ powder into a green sheet, and then firing at about 1400 to 1500 ° C. in the atmosphere for about 5 to 10 hours (preferably about 5 to 8 hours). To make it. Thereby, the green sheet becomes a sintered body. The means for applying the paste is not particularly limited, but for example, screen printing, doctor blade method and the like are preferable. In addition, the support electrolyte may be formed by providing a through-hole in a commercially available 8YSZ sintered thin film.

  The gallate-based oxide electrolyte is produced by, for example, baking a paste containing LSGM1020 powder into a green sheet and firing at about 1400 to 1500 ° C. in the atmosphere for about 5 to 10 hours (preferably about 5 to 8 hours). Thereby, the green sheet becomes a sintered body.

  As described above, when the sintered bodies of the respective electrolytes are separately manufactured, these electrolytes cannot be directly bonded. A method for indirectly bonding these electrolytes will be described later.

  When both electrolytes are obtained in a laminated state (adhered state), 1) a sintered body and a paste, 2) a sintered body and a green sheet, 3) a green sheet, 4) a state in which the green sheet and the paste are directly joined Utilizing the property that they are directly bonded together by baking. For example, in the case of 1) and 2), the paste and the green sheet are contracted by firing, and at the same time, directly bonded to the other sintered body. In the case of 3) and 4), both directly joined are directly bonded by co-sintering.

  The firing conditions for obtaining both electrolytes in the bonded state can be similarly applied to the firing conditions in cases other than co-sintering. On the other hand, in the case of co-sintering, the firing temperature may be 1300-1400 ° C., and the firing time is the same as above.

  When both electrolytes are obtained in a bonded state, and the gallate oxide electrolyte is formed from a paste, it is necessary to devise measures so that the gallate oxide electrolyte paste does not enter the through hole of the support electrolyte during firing. There is. As such a device, for example, filling through-holes with a material such as wax or resin (a material that is thermally decomposed by firing) can be mentioned.

[Step 2]
In step 2, one of the support electrolyte and the gallate oxide electrolyte is laminated with the fuel electrode.

  In order to produce the fuel electrode, for example, a paste or a green sheet containing NiO / YSZ composite particles is used.

  Specifically, after applying the paste or placing a green sheet on one surface of the support electrolyte and the gallate oxide electrolyte, the temperature is about 1250 to 1350 ° C. in the atmosphere for about 2 to 5 hours (preferably It can be laminated by firing for about 3 to 4 hours. Thereby, the said paste and green sheet become a sintered compact.

  In addition, when laminating | stacking a fuel electrode on a support body electrolyte, it is necessary to use so that a paste may be used and to fill the through-hole of a support body electrolyte. Also, when both electrolytes are produced separately in step 1 (non-adhered state), when applying the fuel electrode paste, both electrolytes are applied in a stacked state, and the fuel electrode paste is gallate-oxidized through the through holes. Handle in contact with the electrolyte. By handling in this way, after firing, the fuel electrode also adheres to the gallate oxide electrolyte through the through-hole, and as a result, both electrolytes are indirectly bonded. At this time, in order to bond both electrolytes more firmly, when applying the fuel electrode paste, it may be applied thinly between both electrolytes and used as a binder for bonding both electrolytes.

[Step 3]
In step 3, the other one of the support electrolyte and the gallate oxide electrolyte is laminated with the air electrode.

In order to produce the air electrode, for example, a paste or a green sheet containing a LaMnO ₃ oxide is used.

  In step 2, when the fuel electrode is laminated with the support electrolyte, the air electrode is laminated with the gallate oxide electrolyte.

  Specifically, after applying the paste or placing a green sheet on the gallate oxide electrolyte, firing at about 1000 to 1150 ° C. for about 2 to 5 hours (preferably about 3 to 4 hours) in the atmosphere. Can be laminated. Thereby, the said paste and green sheet become a sintered compact.

  On the other hand, when the fuel electrode is laminated with the gallate oxide electrolyte in step 2, the air electrode is laminated with the support electrolyte. When the electrolyte laminate in the bonded state is produced in step 1, the air electrode is laminated by applying the air electrode paste in a form that fills the through holes of the support electrolyte, and firing under the above firing conditions. On the other hand, when both electrolytes were produced separately in step 1 (non-adhered state), when applying the air electrode paste, the two electrolytes were applied in a stacked state, and the air electrode paste was gallated through the through-hole. Handle in contact with the system oxide electrolyte. By handling in this way, after firing, the air electrode adheres to the gallate oxide electrolyte through the through-hole, and as a result, both electrolytes are indirectly bonded. At this time, in order to bond the two electrolytes more firmly, when applying the air electrode paste, it may be applied thinly between the two electrolytes and used as a binder for bonding the two electrolytes. Thus, the aspect which fills an air electrode with the through-hole of a support body electrolyte is a suitable embodiment of this invention.

  In the SOFC of the present invention, since the solid electrolyte has a laminated structure of the support electrolyte and the gallate oxide electrolyte, the performance and mechanical strength of the solid electrolyte can be sufficiently secured, and the solid electrolyte can be made into a thin film. In a preferred embodiment of the present invention, the thickness and thickness of the gallate oxide electrolyte can be reduced to about 30 μm while sufficiently ensuring the performance and mechanical strength of the solid electrolyte. Further, the thickness of the solid electrolyte (laminated body) can be reduced to about 130 μm. The reduction in the thickness of the solid electrolyte leads to an effect of reducing IR loss, and as a result, the power generation efficiency of the SOFC can be increased. In addition, since the SOFC of the present invention has a gallate oxide electrolyte, the oxide ion conduction of the solid electrolyte is good.

  According to the SOFC manufacturing method of the present invention, the SOFC of the present invention having the above characteristics can be easily manufactured.

It is a cross-sectional schematic diagram (an example) of the solid electrolyte in the SOFC of the present invention. It is a cross-sectional schematic diagram (an example) which shows the suitable embodiment of SOFC of this invention. It is a figure which shows the specific example of the support body electrolyte in SOFC of this invention, the shape of a through-hole, and the arrangement | sequence of a through-hole.

Explanation of symbols

1. Support electrolyte 2. 2. A through hole formed in the support electrolyte. 3. Galate oxide electrolyte 4. Fuel electrode Air electrode 6. Part of the air electrode filled in the through hole

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the examples.

Example 1
LSGM1020 powder (manufactured by Kyoritsu Material Co., Ltd.) and a binder (polyethylene glycol) were mixed to obtain a gallate-based oxide electrolyte paste (solid content concentration 70% by weight).

  A green sheet was prepared from the paste. A film was formed by a doctor blade method. The gallate oxide electrolyte (thickness: 200 μm, outer diameter: 32 mmφ) was produced by firing the green sheet at 1460 ° C. for 5 hours in the atmosphere.

  In the thickness direction of the 8YSZ sintered thin film (thickness 200 μm, outer diameter 32 mmφ), one 5 mmφ through-hole, six 1 mmφ through-holes and six 4 mmφ through-holes are equally spaced within 16 mmφ from the center. What was arranged and provided was used as a support electrolyte.

  Next, after applying a paste of fuel electrode powder (NiO-SDC composite fine particles (NiO: 60 wt%, SDC: 40 wt%)) to the gallate oxide electrolyte, the coating film is baked at 1280 ° C. for 3 hours in the atmosphere. Thus, a sintered body of the gallate oxide electrolyte and the fuel electrode (the gallate oxide electrolyte and the fuel electrode are bonded) was produced.

  Next, the gallate oxide electrolyte side of the laminate and the support electrolyte were superposed (non-adhered state).

Next, a paste of air electrode powder (SSC (Sm _0.5 Sr _0.5 CoO ₃ )) is applied to the support electrolyte in a manner to fill the through holes, and the coating film is baked at 1100 ° C. in the atmosphere for 3 hours. By doing so, the support electrolyte and the air electrode were laminated while firmly bonding the gallate oxide electrolyte and the support electrolyte.

  The SOFC produced by the above process was an air electrode 230 μm, a support electrolyte 200 μm, a gallate oxide electrolyte 200 μm, and a fuel electrode 30 μm.

Claims (2)

( 1) Step 1 for separately obtaining a support electrolyte having a through-hole in the thickness direction and a gallate oxide electrolyte,
(2) Step 2 of laminating one of the support electrolyte and the gallate oxide electrolyte and the fuel electrode,
(3) Step 3 of laminating the other one of the support electrolyte and the gallate oxide electrolyte and the air electrode
A method for producing a solid oxide fuel cell having:
When laminating the support electrolyte and the fuel electrode in the step 2 or laminating the support electrolyte and the air electrode in the step 3, the two electrolytes are stacked in a non-adhered state, and the fuel electrode paste or the air electrode paste Is applied in such a manner that the through hole of the support electrolyte is filled, the fuel electrode paste or the air electrode paste is brought into contact with the gallate oxide electrolyte through the through hole, and then fired . The manufacturing method according to claim 1, wherein in the step 2 or 3, when the fuel electrode paste or the air electrode paste is applied, it is also applied between both electrolytes.

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