JP4736068B2 - Solid oxide fuel cell - Google Patents

Description

  The present invention relates to a solid oxide fuel cell.

  As a solid electrolyte used in a solid oxide fuel cell, it is important to stably maintain high oxygen ion conductivity and high strength for a long period of time, at least 40,000 hours, in addition to high oxygen ion conductivity and high strength.

  Conventionally, zirconia-based materials, lanthanum gallate-based materials, and ceria-based materials are generally used as solid electrolytes in solid oxide fuel cells. For example, in Patent Document 1, a solid electrolyte having no gas permeability and high oxygen ion conductivity is obtained by using zirconia in which yttria and scandia are dissolved.

JP 2004-87490 A

  However, as a result of experiments by the present inventors, there is a problem that the solid electrolyte exposed between the fuel electrode and the interconnector may be pulverized during long-term power generation of 100 hours or more, resulting in a decrease in power generation performance or cell damage. I understood that. An object of the present invention is to suppress pulverization of a solid electrolyte.

In the present invention, has an air electrode which functions as a support as well as have a gas permeability, and a solid electrolyte provided with a tightness that is disposed so as to cover the one side surface of the air electrode, a gas-permeable, said A fuel electrode disposed so as to cover a surface opposite to a surface in contact with the air electrode, a solid electrolyte disposed adjacent to the one side surface of the air electrode, and the air electrode; A solid oxide fuel cell comprising an interconnector electrically connected to the air electrode and having airtightness so that the oxidizing atmosphere on the side and the reducing atmosphere on the fuel electrode side can be shut off, The fuel electrode is arranged to provide an exposed portion where the solid electrolyte is exposed so as not to be electrically connected to the air electrode via the interconnector, and corresponds to the exposed portion where the solid electrolyte is exposed. Place As the air electrode present inside than the exposed portion is not in contact with the solid electrolyte in was placed a shielding body made of non-oxygen ion conductor so as to cover the entire area of the air electrode that faces the exposed portion It is characterized by that. In the present invention, an air electrode having gas permeability, a solid electrolyte having airtightness arranged so as to cover one side surface of the air electrode, gas permeability, and the solid electrolyte being the air electrode A fuel electrode disposed so as to cover a surface opposite to the surface in contact with the surface, a support that contacts the other side of the air electrode, and a surface of the support that contacts the air electrode adjacent to the solid electrolyte And an interconnector electrically connected to the air electrode and having airtightness so that the oxidizing atmosphere on the air electrode side and the reducing atmosphere on the fuel electrode side can be blocked. The exposed portion where the solid electrolyte is exposed is provided so that the fuel electrode as the outer electrode is not electrically connected to the air electrode via the interconnector. Arranged as Serial at a position where the solid electrolyte corresponding to the exposed portion exposed the interconnector enters the air electrode is characterized by comprising configured to be formed only in a region corresponding to the fuel electrode.

In the solid oxide fuel cell thus configured, oxygen ions are generated at the contact portion between the solid electrolyte and the air electrode during power generation, but the path through which oxygen ions reach the surface of the solid electrolyte exposed to the outside is shielded. Since it is blocked by the body, it is possible to prevent a phenomenon in which oxygen ions become excessive on the surface of the solid electrolyte exposed to the outside and cause powdering. Therefore, the airtightness of the solid electrolyte can be maintained for a long time, and a solid oxide fuel cell with higher durability can be provided more reliably.
The term “non-oxygen ion conductor” as used herein refers to a material having a lower oxygen ion conductivity than that of the solid electrolyte at least at the cell temperature during power generation.

  In the present invention, preferably, the shield is a part of the interconnector.

  In the solid oxide fuel cell configured as described above, a shield can be easily configured simply by changing the shape of an existing interconnector, and a path through which oxygen ions reach the surface of the solid electrolyte exposed to the outside. Can be cut off.

  According to the present invention, it has become possible to provide a solid oxide fuel cell that does not cause pulverization in long-term power generation, and thereby has high power generation performance and durability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged cross-sectional view of a portion in the vicinity of an interconnector 2 of a cylindrical vertical stripe solid oxide fuel cell according to an embodiment of the present invention, and is a diagram illustrating a form of Example 1; FIG. 3 is an enlarged cross-sectional view of a portion in the vicinity of an interconnector 2 of a cylindrical vertical stripe type solid oxide fuel cell according to an embodiment of the present invention, and is a diagram showing a form of Example 2. FIG. 5 is an enlarged cross-sectional view of a portion in the vicinity of an interconnector 2 of a cylindrical vertical stripe type solid oxide fuel cell according to an embodiment of the present invention, and is a diagram showing a form of Example 3. FIG. 5 is an enlarged cross-sectional view of a portion in the vicinity of an interconnector 2 of a cylindrical vertical stripe type solid oxide fuel cell according to an embodiment of the present invention, and is a diagram showing a form of Example 4; FIG. 6 is an enlarged cross-sectional view of a portion in the vicinity of an interconnector 2 of a cylindrical vertical stripe type solid oxide fuel cell according to an embodiment of the present invention, and is a diagram showing a form of Example 5. It is a figure which shows the cross section of the cylindrical vertical stripe type solid oxide fuel cell based on the conventional embodiment. It is a figure which shows the cross section of the solid oxide fuel cell of a cylindrical horizontal stripe type based on the conventional embodiment. It is a figure which shows the cross section of the flat cylinder type solid oxide fuel cell based on conventional embodiment. It is sectional drawing which expanded the part of the vicinity of the interconnector 2 of the cylindrical vertical stripe type solid oxide fuel cell which concerns on conventional embodiment, and is a figure which shows the form of the comparative example 1. FIG. It is sectional drawing to which the part of the interconnector 2 vicinity of the cylindrical vertical stripe type solid oxide fuel cell which concerns on conventional embodiment was expanded, and is a figure which shows the form of the comparative example 2. FIG.

  The best mode for carrying out the present invention will be described below.

  The solid electrolyte 3 that can be used in the present invention is preferably a zirconia-based material whose crystal structure includes cubic or rhombohedral. As the zirconia-based material containing cubic crystals, for example, zirconia stabilized with yttria, zirconia stabilized with scandia, zirconia stabilized with calcia can be preferably used. For example, zirconia stabilized with scandia can be preferably used as the zirconia-based material including rhombohedral.

  A zirconia-based material containing a cubic or rhombohedron is preferable because it has excellent chemical stability and high oxygen ion conductivity.

  The solid electrolyte 3 usable in the present invention is most preferably a zirconia-based material stabilized with yttria and / or scandia.

  Since the zirconia-based material stabilized with yttria and / or scandia has particularly high oxygen ion conductivity, it becomes possible to provide a solid oxide fuel cell with particularly high power generation performance.

  The solid oxide fuel cell that can be used in the present invention will be described below.

A conventional cylindrical vertical stripe type solid oxide fuel cell, which is a solid oxide fuel cell, is shown in FIG. A fuel electrode 4 is configured so as not to contact the interconnector 2 on the solid electrolyte 3 and further on the solid electrolyte 3 on the air electrode 1. During power generation, electrons flowing inside the air electrode 1 react with oxygen outside at the interface between the air electrode 1 and the solid electrolyte 3 to generate oxygen ions as shown in the formula (1). The oxygen ions pass through the solid electrolyte 3 and reach the fuel electrode 4, and hydrogen or carbon monoxide in the fuel reacts with oxygen ions to generate water or carbon dioxide and electrons. These reactions are represented by formulas (2) and (3).
_{^{O 2 + 4e - → 2O 2-}} ... (1)
H ₂ + O ²⁻ → H ₂ O + 2e ⁻ (2)
_{^{CO + O 2- → CO 2 +}} 2e - ... (3)

  Examples of the solid oxide fuel cell that can be used in the present invention include a cylindrical vertical stripe type as shown in FIG. 6, a cylindrical horizontal stripe type as shown in FIG. 7, a flat cylindrical type as shown in FIG. it can.

The interconnector 2 that can be used in the present invention is preferably electrically connected to the air electrode 1, stable in both an oxidizing atmosphere and a reducing atmosphere, having high electron conductivity, and excellent airtightness. For the interconnector 2 material, for example, (La, A) CrO ₃ , (A: alkali metal), La (Cr, Mg) O ₃ , (B, Ca) TiO ₃ , (B: rare earth element) are used. It is done.

  The fuel electrode 4 that can be used in the present invention preferably has high gas permeability and high electron conductivity. From this point of view, Ni alloy, Co alloy, Ni—Co alloy, Ni / yttria stabilized zirconia, Ni / scandia stabilized zirconia, Ni / calcia stabilized zirconia, Ni / ceria-based material, and the like are used. The fuel electrode 4 may be formed of a plurality of layers. For example, an inclined composite material such as Ni / yttria-stabilized zirconia can be used. By making the fuel electrode 4 an inclined structure, higher power generation performance can be obtained.

  The air electrode 1 that can be used in the present invention may be formed of a single layer having both a catalytic function and a support function, or may be formed on a support 12 having a support function. Furthermore, it may be formed of a plurality of layers.

When the air electrode 1 is composed of one layer having both a catalytic function and a support function, there is an advantage that the power generation efficiency is excellent. In this case, the air electrode 1, the gas permeability is high, preferably has a high electron conductivity and oxygen ion _{conductivity, (La 1-x Sr x} ) electronic conductors such as _y MnO ₃ and zirconia-based material or ceria composite and the oxygen ion conductor, such as a system materials or lanthanum gallate-based _material, mixed conducting material such as _{(La 1-x Sr x)} y (Co 1-z Fe z) O 3 is used. Moreover, when the air electrode 1 is formed on the support body 12, since it is not necessary to give the air electrode 1 a support function, there exists an advantage that manufacture is easy. In this case, the support 12 preferably has good gas permeability and a thermal expansion coefficient close to that of the air electrode 1. A porous body such as (CaO) _x (ZrO ₂ ) _1-x or (La _1-x Sr _x ) _y MnO ₃ can be used. The air electrode 1 formed on the support 12 is preferably one having high gas permeability and high electron conductivity and oxygen ion conductivity. From this viewpoint, a composite of an electron conductor such as (La _1-x Sr _x ) _y MnO ₃ and an oxygen ion conductor such as a zirconia-based material, a ceria-based material, or a lanthanum gallate-based material, or (La _1-x Sr mixed conductor such as _{x) y (Co 1-z} Fe z) O 3 is used. Furthermore, higher power generation performance can be obtained by forming the air electrode 1 from a plurality of layers. For example, an example in which the ratio of the composite of (La _1-x Sr _x ) _y MnO ₃ and zirconia-based material is inclined can be given.

  The solid electrolyte 3 that can be used in the present invention preferably has high oxygen ion conductivity, excellent airtightness, excellent mechanical strength, and excellent material stability. A zirconia material, a lanthanum gallate material, a ceria material, or the like is used. The solid electrolyte 3 may be formed of a plurality of layers. For example, two layers of yttria-stabilized zirconia and scandia-stabilized zirconia, scandia-stabilized zirconia, yttria-stabilized zirconia, and scandia-stabilized zirconia 3 A layer structure can be mentioned. By using a multi-layer structure, high power generation performance and sinterability can be improved.

In order to improve oxygen ion conductivity and / or sinterability, zirconia-based materials include CeO ₂ , Pr ₂ O ₃ , Nd ₂ O ₃ , Pm ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ , PbO, Bi ₂ O ₃ , MnO ₂ , Fe ₂ O ₃ or the like may be dissolved. Two or more types may be dissolved.

  Zirconia has a monoclinic structure in which fluorite-type face-centered cubic crystals are distorted at room temperature, but it transforms into tetragonal crystals at about 1170 ° C and to cubic crystals at about 2370 ° C, and the volume changes with the phase transformation. Therefore, when used in a solid oxide fuel cell, cracks may occur in the solid electrolyte 3 due to the thermal cycle. Therefore, in the solid electrolyte 3 of the solid oxide fuel cell, an oxide of a metal having a valence of 2+ or a metal having a valence of 3+ was dissolved, and a tetragonal crystal or a cubic crystal was stably present up to room temperature. Something is used. Stabilized zirconia having a crystal structure such as tetragonal, cubic or rhombohedral can be obtained depending on the amount of oxide dissolved. Generally, zirconia in which yttria is dissolved or zirconia in which scandia is dissolved is used.

  The present inventors have observed that a cubic or rhombohedral zirconia-based material that is a material constituting the solid electrolyte 3 and has been conventionally stabilized is powdered by long-term power generation. Further detailed investigations result in a structure in which there is no contact surface between the solid electrolyte 3 and the air electrode 1 below the exposed portion 5 of the solid electrolyte 3 formed between the interconnector 2 and the fuel electrode 4. Thus, it was found that powdering can be suppressed.

  The following can be considered as reasons why powdering can be suppressed by adopting a structure having no contact surface between the solid electrolyte 3 and the air electrode 1 below the exposed portion 5.

FIG. 9 is an enlarged cross-sectional view of a portion in the vicinity of the interconnector 2 of the cylindrical vertical stripe solid oxide fuel cell shown in FIG. 6, and is a view showing a conventional structure in which the air electrode 1 is composed of one layer.
FIG. 10 is a conventional example different from FIG. 9, and is an enlarged cross-sectional view of a portion in the vicinity of the interconnector 2 of a cylindrical vertical stripe type solid oxide fuel cell, and the air electrode 1 is a conductive support. 1 is a diagram showing a conventional structure formed on a substrate 12.

The zirconia-based material used as the solid electrolyte 3 causes oxygen ions to be lost by dissolving yttria and scandia in zirconia, thereby improving oxygen ion conductivity and stabilizing the cubic crystal to room temperature. Here, as shown in FIG. 9 or 10, when a contact surface between the solid electrolyte 3 and the air electrode 1 exists below the exposed portion 5, oxygen ions generated on the contact surface are in the solid electrolyte 3. Although it moves, the oxygen ion is not consumed and remains in the solid electrolyte 3 because the upper part of the exposed portion 5 is not in contact with the fuel electrode 4. As a result, it is considered that the surface of the solid electrolyte 3 in the exposed portion 5 becomes oxygen ion excess and the crystal structure becomes unstable. Further, the adsorption of water vapor contained in the fuel gas or water vapor generated during power generation to the surface of the solid electrolyte 3 in the exposed portion 5 is considered as one of the factors destabilizing the crystal structure. As a result of overlapping of these factors, it is considered that the crystal structure of the solid electrolyte 3 changes and powdering occurs. Therefore, by making the contact surface between the solid electrolyte 3 and the air electrode 1 below the exposed portion 5, that is, the structure having no oxygen ion generation source, oxygen ions are not supplied to the exposed portion 5. It is thought that it can be suppressed. Although the present inventors have observed such a phenomenon with the solid electrolyte 3 made of a zirconia-based material, it is considered that the same phenomenon occurs in the solid electrolyte 3 made of another material.

  When the solid electrolyte 3 is pulverized, the solid electrolyte 3 is thinned or pores are formed to reduce the airtightness and strength. As a result of the decrease in airtightness, the air electrode 1 and the fuel gas react to cause reductive expansion of the air electrode 1, and in the worst case, the solid oxide fuel cell is damaged. In the experiments by the present inventors, it was observed that the solid oxide fuel cell was damaged when the thickness of the solid electrolyte 3 became several μm or less. As a result of analysis by scanning electron microscope observation, it was found that the microstructure of the air electrode 1 was changed and reductive expansion occurred. Further, it is presumed that oxygen ion conductivity decreases due to powdering, and the output of the solid oxide fuel cell decreases.

  The term “film thickness” as used herein refers to a fracture surface of a solid oxide fuel cell observed with a scanning electron microscope S-4100 manufactured by Hitachi High-Technologies.

  Examples of the present invention will be described below. Of course, the present invention is not limited to the following examples.

Example 1
FIG. 1 is an enlarged cross-sectional view of a portion in the vicinity of an interconnector 2 of a cylindrical vertical stripe type solid oxide fuel cell according to an embodiment of the present invention. A shield 6 made of a non-oxygen ion conductor is disposed on the air electrode 1 below the exposed portion 5 of the solid electrolyte 3. Thereby, since there is no contact surface of the solid electrolyte 3 and the air electrode 1 below the exposed part 5, supply of oxygen ions to the exposed part 5 is suppressed, and generation of powder can be suppressed.

(Example 2)
FIG. 2 is an enlarged cross-sectional view of a portion in the vicinity of the interconnector 2 of the solid oxide fuel cell according to one embodiment of the present invention, and is a diagram showing a form of Example 2. A shield 6 made of a non-oxygen ion conductor is disposed on the air electrode 1 below the exposed portion 5 of the solid electrolyte 3. Unlike FIG. 1, since the coverage is 100% or more, powdering of the solid electrolyte 3 can be surely suppressed, and there is an advantage of higher durability. Here, “coverage” means the ratio of the area of the shield 6 that covers the entire area of the air electrode 1 below the exposed portion 5 to the entire area of the air electrode 1.
In Example 3 shown below, the same effect can be obtained by setting the coverage to 100% or more.

(Example 3)
FIG. 3 is an enlarged cross-sectional view of a portion in the vicinity of the interconnector 2 of the cylindrical vertical stripe type solid oxide fuel cell according to one embodiment of the present invention, and is a diagram showing a form of the third embodiment. A part of the interconnector 2 is disposed below the solid electrolyte 3 having the exposed portion 5 above, and this functions as a shield. By making the shield a part of the interconnector 2, there is an advantage that the shield can be easily manufactured.
Here, examples of the method for forming the interconnector 2 as shown in FIG. 7 include a slurry coating method, a screen printing method, a sheet forming method, and the like.
The interconnector 2 may be formed of a plurality of layers. A structure in which a dense layer 21 wider than the interconnecting portion 22 is provided between the lanthanum chromite as the interconnecting portion 22 and the air electrode 1 can be exemplified. Although the liquid phase is involved in the sintering of the lanthanum chromite, it is possible to prevent the liquid phase from moving to the porous air electrode 1 by providing the dense layer 21. In this case, in the present invention, the interconnecting portion 22 and the dense layer 21 are collectively referred to as an interconnector 2. In the case of the interconnector 2 having the interconnecting portion 22 and the dense layer 21, the material of the interconnecting portion 22 is, for example, (La, A) CrO ₃ , (A: alkali metal), La (Cr, Mg) O ₃ , ( Examples of the material of the dense layer 21 such as B, Ca) TiO ₃ (B: rare earth element) are (La _1-x A _x ) _y MnO ₃ (where A = Ca or Sr). Lantern manga night can be mentioned.

( Reference example )
FIG. 4 is an enlarged cross-sectional view of a portion in the vicinity of the interconnector 2 of a cylindrical vertical stripe type solid oxide fuel cell according to a reference example . The air electrode 1 is provided on the support 12 and is provided only below the fuel electrode 4. Therefore, the air electrode 1 does not exist below the solid electrolyte 3 having the exposed portion 5 above, and there is no contact surface between the solid electrolyte 3 and the air electrode 1, so that oxygen ions are supplied to the exposed portion 5. It is suppressed and it can suppress that powdering arises.

(Example 5)
FIG. 5 is an enlarged cross-sectional view of a portion in the vicinity of the interconnector 2 of a cylindrical vertical stripe type solid oxide fuel cell according to an embodiment of the present invention. The air electrode 1 is formed on a support 12, and the support 12 is disposed below the solid electrolyte 3 having the exposed portion 5 above via the interconnector 2.
Also in this structure, since the air electrode 1 exists only below the fuel electrode 4, there is no contact surface between the solid electrolyte 3 and the air electrode 1 below the solid electrolyte 3 having the exposed portion 5 above. Accordingly, supply of oxygen ions to the exposed portion 5 is suppressed, and generation of powder can be suppressed.

  A cylindrical vertical stripe type solid oxide fuel cell having the structure shown in FIGS. 6 and 9 to 9 is formed of an air electrode 1, a solid electrolyte 3 is formed, a fuel electrode 4 is formed, an interconnector 2 is formed, The air electrode 1 is formed by a process including one or more firings, and the forming method of the air electrode 1 includes an extrusion forming method, a cast forming method, and a press forming method, and the solid electrolyte 3 is formed by a slurry coating method. Examples of the method for forming the fuel electrode 4 include a slurry coating method, a screen printing method, and a sheet forming method.

1 ... Air electrode 12 ... Support 2 ... Interconnector
DESCRIPTION OF SYMBOLS 21 ... Dense layer 22 ... Interconnection part 3 ... Solid electrolyte 4 ... Fuel electrode 5 ... Exposed part 6 ... Shield

Claims (3)

An air electrode having gas permeability and functioning as a support;
An airtight solid electrolyte disposed to cover one side of the air electrode;
A fuel electrode having gas permeability and disposed so as to cover a surface opposite to a surface where the solid electrolyte is in contact with the air electrode;
The air electrode is disposed so as to be adjacent to and contacted with the one side surface of the air electrode, and has airtightness so that the oxidizing atmosphere on the air electrode side and the reducing atmosphere on the fuel electrode side can be shut off. An interconnector electrically connected to the air electrode;
A solid oxide fuel cell comprising:
Arranged to provide an exposed portion where the solid electrolyte is exposed so that the fuel electrode is not electrically connected to the air electrode via the interconnector,
Covering the entire area of the air electrode facing the exposed portion so that the air electrode existing inside the exposed portion does not come into contact with the solid electrolyte at a position corresponding to the exposed portion where the solid electrolyte is exposed. A solid oxide fuel cell, characterized in that a shield made of a non-oxygen ion conductor is disposed on the solid oxide fuel cell.   The solid oxide fuel cell according to claim 1, wherein the shield is a part of the interconnector. An air electrode having gas permeability;
An airtight solid electrolyte disposed to cover one side of the air electrode;
A fuel electrode having gas permeability and disposed so as to cover a surface opposite to a surface where the solid electrolyte is in contact with the air electrode;
A support that contacts the other side of the air electrode;
The support is disposed so as to be in contact with the solid electrolyte adjacent to the surface of the support that is in contact with the air electrode, and has airtightness so that the oxidizing atmosphere on the air electrode side and the reducing atmosphere on the fuel electrode side can be shut off. And an interconnector electrically connected to the air electrode,
A solid oxide fuel cell comprising:
The fuel electrode as the outer electrode is disposed so as to provide an exposed portion where the solid electrolyte is exposed so that the fuel electrode is not electrically connected to the air electrode via the interconnector.
The support body at a position corresponding to the exposed portion where the solid electrolyte is exposed, and the interconnector is inserted between the support body and the solid electrolyte so as to face a portion where the exposed portion of the solid electrolyte is formed. A solid oxide fuel cell, characterized in that the air electrode is formed only in a region corresponding to the fuel electrode by covering the entire surface of the interconnector with the interconnector .

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