JP2017183209A - Fuel cell and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell in which occurrence of breakdown due to volume expansion of a fuel electrode or a substrate can be suppressed, and to provide a manufacturing method thereof.SOLUTION: A fuel cell includes multiple cells 105 each including a fuel electrode 109, an air electrode 113 and a solid electrolyte 111, at least one interconnector 107 interconnecting the cells 105 electrically, and a dense membrane 120 provided on the fuel electrode 109 side or air electrode 113 side for overlapping part, so as to cover the overlapping part of the interconnector 107 and solid electrolyte 111.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a fuel cell and a manufacturing method thereof.

Conventionally, a fuel cell in which a plurality of cells including a fuel electrode, an air electrode, and an electrolyte are electrically connected by an interconnector is known.
For example, Patent Documents 1 to 6 disclose a horizontal stripe fuel cell in which a plurality of cells are arranged on a base body along a specific direction and adjacent cells are connected by an interconnector.

Japanese Patent No. 4368850 JP 2011-181412 A Japanese Patent Laid-Open No. 4-355058 JP-A-7-114932 Japanese Patent Laid-Open No. 10-79259 Japanese Utility Model Publication No. 6-77161

In the fuel cell, the electrolyte and the interconnector are formed as a dense film, and separate the gas on the air electrode side and the gas on the fuel electrode side. However, in the overlapping portion of the electrolyte and the interconnector, a defect may occur due to, for example, a shrinkage difference during integral sintering of the electrolyte and the interconnector. If there is a defect in the electrolyte or interconnector, the gas separation property of the fuel cell is impaired. If oxygen leaks to the fuel electrode side through defects in the electrolyte or interconnector, volume expansion may occur due to oxidation of the material constituting the fuel electrode or the substrate. The volume expansion of the fuel electrode or the substrate can cause damage to the fuel cell.
In this regard, Patent Documents 1 to 6 do not disclose a specific configuration for suppressing damage to the fuel cell due to a defect in the overlapping portion of the electrolyte and the interconnector.

  An object of at least some embodiments of the present invention is to provide a fuel cell capable of suppressing the occurrence of damage due to volume expansion of a fuel electrode and a substrate, and a method for manufacturing the same.

(1) A fuel cell according to at least some embodiments of the present invention includes:
A plurality of cells each including a fuel electrode, an air electrode and a solid electrolyte;
At least one interconnector for electrically connecting the cells;
A dense membrane provided on the fuel electrode side or the air electrode side with respect to the overlapping portion so as to cover the overlapping portion of the interconnector and the solid electrolyte;
Is provided.

According to the configuration of (1) above, even if a defect occurs in the overlapping portion of the interconnector and the solid electrolyte, the overlapping portion is not defective by the dense film provided on the fuel electrode side or the air electrode side with respect to the overlapping portion. Oxygen leakage to the fuel electrode side can be prevented. Thereby, the volume expansion resulting from the oxidation of the material which comprises a fuel electrode or a base | substrate can be suppressed, and the reliability of a fuel cell can be improved.
In addition, the formation of the dense film increases the strength of the fuel cell, and increases the likelihood of the stress generated due to the volume expansion of the fuel electrode or the substrate, thereby improving the reliability of the fuel cell. it can.

(2) In some embodiments, in the configuration of (1) above,
At least one of the fuel electrode or the substrate supporting the plurality of cells contains Ni.

When at least one of the substrate and the fuel electrode contains Ni as in the configuration of (2) above, when oxygen leaks from the air electrode side, the volume expansion associated with the oxidation of the substrate or fuel electrode containing Ni occurs. There is a possibility of damaging the fuel cell.
In this regard, as described in (1) above, even if the substrate or the fuel electrode contains Ni by providing a dense film so as to cover the overlapping portion of the interconnector and the solid electrolyte that are likely to cause defects. A highly reliable fuel cell can be realized.

(3) In some embodiments, in the above configuration (1) or (2),
The dense film has a porosity of 10% or less.
In this specification, the “porosity” of a member means the ratio of the pore volume to the total volume of the member.

  According to the configuration of (3) above, even if a defect occurs in the overlapping portion of the interconnector and the solid electrolyte by setting the porosity of the dense film covering the overlapping portion of the interconnector and the solid electrolyte to 10% or less. Thus, leakage of oxygen to the fuel electrode side through the defect can be effectively prevented. Therefore, the volume expansion resulting from the oxidation of the material which comprises a fuel electrode or a base | substrate can be suppressed effectively, and the reliability of a fuel cell can be improved further.

(4) In some embodiments, in any one of the above configurations (1) to (3),
The protruding area S of the dense film to the area where the air electrode and the fuel electrode face each other with the solid electrolyte or the interconnector interposed therebetween is the total area of the area where the dense film is formed as S _total Then, the relationship S / S _total ≦ 0.5 is satisfied.

The reaction in the fuel cell occurs as follows. Oxygen-containing gas (for example, air) supplied to the air electrode during the operation of the fuel cell is dissociated at the interface between the air electrode and the solid electrolyte, and oxygen ions are generated. Oxygen ions that have moved through the solid electrolyte from the air electrode side toward the fuel electrode side react with fuel (for example, hydrogen or carbon monoxide) at the interface between the fuel electrode and the solid electrolyte. Thus, the reaction at the interface between the solid electrolyte and the fuel electrode is realized by the solid electrolyte moving oxygen ions to the fuel electrode side.
According to the configuration of (4) above, the protruding rate (S / S _total ) of the dense membrane to the region where the air electrode and the fuel electrode face each other across the solid electrolyte or interconnector is 0.5 or less. The dense film is unlikely to hinder the movement of electrons and oxygen ions. Therefore, while suppressing the power generation performance degradation of the fuel cell due to the dense membrane, the dense membrane suppresses oxygen leakage through defects in the overlapping portion between the interconnector and the solid electrolyte, thereby improving the reliability of the fuel cell. Can be secured.

(5) In some embodiments, in any one of the above configurations (1) to (4),
The dense film includes at least one of a material that is a main component of the interconnector, zirconia, or alumina.

  According to the configuration of (5) above, a dense film excellent in heat resistance, stability in the fuel cell (no reactivity with peripheral materials), and denseness can be realized, and the reliability of the fuel cell The sex can be further enhanced.

(6) In some embodiments, in any one of the above configurations (1) to (5),
The dense film includes a first material having a lower melting point in a reduced state than in an oxidized state,
The dense film is provided on the air electrode side with respect to the overlapping portion so as to cover the overlapping portion.

  If a defect exists in the solid electrolyte or interconnector, the fuel supplied to the air electrode side through the defect reacts with oxygen, and the temperature rises locally in the vicinity of the defect. In the configuration of (6) above, the dense film containing the first material is provided on the air electrode side so as to cover the overlapping portion of the solid electrolyte and the interconnector. The dense film on the air electrode side exposed to (under the condition) has a lower melting point due to the characteristics of the first material. For this reason, the local temperature increase in the vicinity of the defect and the decrease in the melting point of the first material constituting the dense film combine to soften or melt the first material in the vicinity of the defect of the solid electrolyte or interconnector. One material can block a gas leakage path. When the defect of the solid electrolyte or the interconnector is closed, the reaction between the fuel and oxygen is suppressed, the temperature is lowered, and the first material returns to the solid. Thus, defects in the solid electrolyte or interconnector can be automatically repaired, and a self-healing function of the fuel cell can be realized.

(7) In one embodiment, in the configuration of (6) above,
The first material is an Fe—Si—Al-based compound.

According to the configuration of (7), the first material is an Fe—Si—Al-based compound having a property that the melting point is 1400 ° C. or higher in the oxidized state but has a melting point of about 1100 ° C. (minimum 1086 ° C.) in the reduced state. By using, the defect of a solid electrolyte or an interconnector can be repaired effectively.
That is, when the first material (Fe-Si-Al compound) is exposed to a fuel atmosphere (reducing conditions) due to the presence of defects in the solid electrolyte or interconnector, the melting point is about 1100 ° C (at least 1086 ° C). descend. Even if the normal operating temperature of the fuel cell is about 900 ° C., the temperature in the vicinity of the defect reaches the melting point in the reduced state of the first material (Fe—Si—Al-based compound) due to a local temperature increase in the vicinity of the defect. It is possible. When the temperature in the vicinity of the defect exceeds the melting point of the first material in the reduced state, the first material is melted and the gas leakage path (defect) is closed. When the defect of the solid electrolyte or the interconnector is closed, the reaction between the fuel and oxygen is suppressed, the temperature is lowered, and the first material returns to the solid. In this process, since the melt of the first material is solidified by liquid phase sintering, the first material becomes a very dense gas tight layer, and the gas leakage path (defect) is effectively blocked.

(8) In some embodiments, in any one of the above configurations (1) to (5),
The dense film includes a second material having a lower melting point in the oxidized state than in the reduced state,
The dense film is provided on the fuel electrode side with respect to the overlapping portion so as to cover the overlapping portion.

  According to the configuration of (8) above, the dense film containing the second material is provided on the fuel electrode side so as to cover the surface of the solid electrolyte or the interconnector, and the dense film containing the second material is exposed to the oxidizing atmosphere due to the presence of the defect. The dense film on the fuel electrode side has a lower melting point due to the characteristics of the second material. For this reason, the local temperature increase in the vicinity of the defect and the decrease in the melting point of the second material constituting the dense film combine to soften or melt the second material in the vicinity of the defect in the solid electrolyte or interconnector. The gas leakage path can be blocked by the two materials. When the defect of the solid electrolyte or the interconnector is closed, the reaction between the fuel and oxygen is suppressed, the temperature is lowered, and the second material returns to a solid. Thus, defects in the solid electrolyte or interconnector can be automatically repaired, and a self-healing function of the fuel cell can be realized.

(9) In one embodiment, in the configuration of (8) above,
The second material is vanadium oxide.

According to the configuration of the above (9), vanadium oxide having a property that the melting point is about 1450 ° C. in the reduced state (V ₂ O ₄ ) but the melting point becomes about 680 ° C. when the oxidized state (V ₂ O ₅ ) is obtained. By using it as the second material, it is possible to effectively repair defects in the solid electrolyte or interconnector.
That is, when the second material (vanadium oxide) is exposed to oxidizing conditions due to the presence of defects in the solid electrolyte or interconnector, the melting point is lowered to about 680 ° C. Thus, when the temperature in the vicinity of the defect exceeds the melting point of the second material in the oxidized state, the second material is melted and the gas leakage path (defect) is closed. When the defect of the solid electrolyte or the interconnector is closed, the reaction between the fuel and oxygen is suppressed, the temperature is lowered, and the second material returns to a solid. In this process, since the melt of the second material is solidified by liquid phase sintering, the second material becomes a very dense gas tight layer, and the gas leakage path (defect) is effectively blocked.

(10) A method of manufacturing a fuel cell according to at least some embodiments of the present invention includes:
Forming a plurality of cells each including a fuel electrode, an air electrode and a solid electrolyte;
Forming at least one interconnector for electrically connecting adjacent cells;
Forming a dense film on the fuel electrode side or the air electrode side with respect to the overlapping portion so as to cover the overlapping portion of the interconnector and the solid electrolyte;
Is provided.

According to the method of (10) above, since the dense film covering the overlapping portion of the interconnector and the solid electrolyte is provided on the fuel electrode side or the air electrode side with respect to the overlapping portion, a highly reliable fuel cell can be obtained. it can.
That is, in the fuel cell obtained by the method of (10) above, even if a defect occurs in the overlapping portion of the interconnector and the solid electrolyte, a dense membrane provided on the fuel electrode side or air electrode side with respect to the overlapping portion. , Leakage of oxygen to the fuel electrode side through defects in the overlapping portion can be prevented. Thereby, the volume expansion resulting from the oxidation of the material which comprises a fuel electrode or a base | substrate can be suppressed, and the reliability of a fuel cell can be improved. In addition, the formation of the dense film increases the strength of the fuel cell and increases the likelihood of the stress generated due to the volume expansion of the fuel electrode or the substrate, thereby improving the reliability of the fuel cell.

(11) In some embodiments, in the method of (10) above,
Depositing one of the fuel electrode or the air electrode;
Forming the solid electrolyte and the interconnector on the one of the fuel electrode or the air electrode, and firing the solid electrolyte and the interconnector integrally,
The dense film is formed.

According to the method of (11) above, even if a defect occurs in the overlapping portion due to the difference in shrinkage when the solid electrolyte and the interconnector are integrally fired, a dense film is formed later so as to cover the overlapping portion. The reliability of the fuel cell can be effectively improved.
In addition, since the dense film is formed after the integral firing of the solid electrolyte and the interconnector, there is no restriction on the shrinkage rate during the integral firing, so the degree of freedom in setting the film thickness of the dense film is improved.

(12) In some embodiments, in the above method (10) or (11),
In the step of forming the dense film,
After applying the constituent material of the dense film,
The dense film is fired together with the fuel electrode or the air electrode.

  According to the above method (12), since the dense film is fired together with the fuel electrode or the air electrode, an increase in the steps for forming the dense film can be suppressed. As a result, it is possible to obtain a fuel cell with improved reliability by forming a dense film while suppressing an increase in manufacturing cost.

According to at least some embodiments of the present invention, even if a defect occurs in the overlapping portion of the interconnector and the solid electrolyte, the overlapping portion is formed by the dense film provided on the fuel electrode side or the air electrode side with respect to the overlapping portion. Oxygen leakage to the fuel electrode side through the defects can be prevented. Thereby, the volume expansion resulting from the oxidation of the material which comprises a fuel electrode or a base | substrate can be suppressed, and the reliability of a fuel cell can be improved.
In addition, the formation of the dense film increases the strength of the fuel cell, and increases the likelihood of the stress generated due to the volume expansion of the fuel electrode or the substrate, thereby improving the reliability of the fuel cell. it can.

It is sectional drawing of the fuel cell which concerns on one Embodiment. It is a figure which shows a mode that Ni of the base | substrate was reoxidized. It is a figure for demonstrating an example of the formation range of a dense film. It is sectional drawing which shows the structure which used the functional film which has the defect repair function which concerns on one Embodiment as a dense film. FIG. 5 is a ternary phase diagram in an oxidation state of an Fe—Al—Si based compound as an example of a constituent material of the functional film illustrated in FIG. 4. FIG. 5 is a ternary phase diagram in a reduced state of an Fe—Al—Si based compound as an example of a constituent material of the functional film illustrated in FIG. 4. It is sectional drawing which shows the structure which used the functional film which has the defect repair function which concerns on other embodiment as a dense film. It is a flowchart which shows the manufacturing method of the fuel cell which concerns on one Embodiment. It is a flowchart which shows the manufacturing method of the fuel cell which concerns on one Embodiment.

  Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Absent.

FIG. 1 is a cross-sectional view of a fuel cell 100 according to an embodiment.
As shown in FIG. 1, in some embodiments, the fuel cell 100 includes a base 103, a plurality of cells (fuel cell) 105 provided on the base 103, and an electrical connection between adjacent cells 105. And an interconnector 107 to be connected.

The substrate 103 may be a cylindrical substrate tube or a flat substrate plate.
The base 103 may be made of a porous material. Examples of the material of the substrate 103 include CaO stabilized ZrO ₂ (CSZ), Y ₂ O ₃ stabilized ZrO ₂ (YSZ), or MgAl ₂ O ₄ .

Each cell 105 formed on the substrate 103 includes a fuel electrode 109, an air electrode 113, and a solid electrolyte 111.
In the exemplary embodiment shown in FIG. 1, in the cell 105, a fuel electrode 109, a solid electrolyte 111, and an air electrode 113 are stacked in this order on a base body 103. In this case, the fuel gas is supplied to the space 1 on the opposite side of the cell 105 across the base 103, while oxygen or the like is contained in the space 2 on the opposite side of the space 1 across the cell 105 and the base 103. Gas is supplied. Then, the fuel gas diffuses in the base 103 and the fuel gas is supplied to the fuel electrode 109. In the example shown in FIG. 1, the fuel gas and the oxygen-containing gas are opposed to each other, but the fuel gas and the oxygen-containing gas may flow in the same direction.
In another embodiment, the cell 105 is stacked on the substrate 103 in the order of the air electrode 113, the solid electrolyte 111, and the fuel electrode 109. In this case, unlike the embodiment shown in FIG. 1, the oxygen-containing gas is supplied to the space 1 on the opposite side of the cell 105 across the substrate 103, while the space 1 is sandwiched between the cell 105 and the substrate 103. The fuel gas is supplied to the space 2 on the opposite side. Then, the oxygen-containing gas diffuses in the base 103 and the oxygen-containing gas is supplied to the air electrode 113.

The reaction in the fuel cell 100 occurs as follows.
That is, the oxygen-containing gas supplied to the air electrode 113 side during the operation of the fuel cell 100 is dissociated at the interface between the air electrode 113 and the solid electrolyte 111 to generate oxygen ions (O ²⁻ ). Oxygen ions that have moved through the solid electrolyte 111 from the air electrode 113 side toward the fuel electrode 109 side react with fuel (for example, hydrogen or carbon monoxide) at the interface between the fuel electrode 109 and the solid electrolyte 111.

As the material of the fuel electrode 109, for example, it is composed of an oxide of a composite material of Ni and a zirconia-based electrolyte material. For example, Ni / YSZ is used. In this case, Ni contained in the fuel electrode 109 has a catalytic action on the fuel gas.
This catalytic action is to react a fuel gas supplied to the fuel electrode 109, for example, a mixed gas of methane (CH ₄ ) and water vapor, and reform it into hydrogen (H ₂ ) and carbon monoxide (CO). is there. Further, the fuel electrode 109 has an interface between the solid electrolyte 111 and hydrogen (H ₂ ) and carbon monoxide (CO) obtained by reforming and oxygen ions (O ²⁻ ) supplied via the solid electrolyte 111. It reacts electrochemically in the vicinity to produce water (H ₂ O) and carbon dioxide (CO ₂ ).

The air electrode 113 is made of, for example, a LaSrMnO ₃ oxide or a LaCoO ₃ oxide. The air electrode 113 generates oxygen ions (O ²⁻ ) by dissociating oxygen in an oxygen-containing gas such as air supplied near the interface with the solid electrolyte 111. An electromotive force is generated in the fuel battery cell 105 by the electrons released from oxygen.

The solid electrolyte 111 is provided between the fuel electrode 109 and the air electrode 113, and is formed as a dense film having airtightness that prevents gas from passing therethrough. The material of the solid electrolyte 111 is, for example, YSZ having high oxygen ion conductivity at a high temperature. The solid electrolyte 111 is airtight so as to move oxygen ions (O ²⁻ ) generated at the air electrode 113 to the fuel electrode 109 while preventing the fuel gas and oxygen-containing gas from permeating.

In addition, the interconnector 107 is formed as a dense film having an air tightness that prevents gas from passing, like the solid electrolyte 111. The interconnector 107 electrically connects the air electrode 113 of one fuel battery cell 105 and the fuel electrode 109 of the other fuel battery cell 105 in adjacent fuel battery cells 105, and connects the adjacent fuel battery cells 105 to each other. Connect in series.
The material of the interconnector 107 may be used those having a stable electric conductivity under both atmosphere of a reducing atmosphere and an oxidizing atmosphere, for _{example, M 1-x L x TiO} 3 , such as SrTiO ₃ system (M A conductive perovskite type oxide represented by an alkaline earth metal element and L is a lanthanoid element can be used.

In this way, in each fuel cell 105, the oxygen-containing gas and the fuel gas are separated by the solid electrolyte 111 and the interconnector 107 as a dense membrane.
However, in the overlapping portion 108 of the solid electrolyte 111 and the interconnector 107, a defect may occur when the fuel cell is manufactured. If a defect exists in the solid electrolyte 111 or the interconnector 107, the gas separation property of the fuel cell 105 is impaired. In this case, the oxygen-containing gas leaks to the fuel electrode 109 side through defects in the solid electrolyte 111 and the interconnector 107 during operation or stop of the fuel cell. Then, Ni contained in the fuel electrode 109 and the substrate 103 is reoxidized by the oxygen-containing gas, and volume expansion occurs. Volume expansion of the fuel electrode 109 and the base 103 may cause damage to the fuel cell 105.

FIG. 2 is a diagram illustrating a state in which Ni of the base 103 is reoxidized.
As shown in the figure, a defect 115 exists in the overlapping portion 108 between the solid electrolyte 111 and the interconnector 107. The defect 115 is generated due to, for example, a difference in shrinkage when the solid electrolyte 111 and the interconnector 107 are integrally sintered. That is, since the solid electrolyte 111 and the interconnector 107 have different shrinkage rates at the time of integral sintering, a defect 115 occurs in the overlapping portion 108 due to the shrinkage difference at the time of integral sintering.
The defect 115 generated in the overlapping portion 108 during the manufacture of the fuel cell is that oxygen diffuses due to the difference in oxygen concentration between the base body 103 (or the fuel electrode 109) side and the air electrode 113 side during operation and stop of the fuel cell. Thus, it can be a leakage path for oxygen to enter the base 103 (or the fuel electrode 109) side. Oxygen that has entered the substrate 103 (or the fuel electrode 109) reacts with Ni contained in the substrate 103 (or the fuel electrode 109) and changes to NiO (Ni reoxidation). For this reason, the substrate 103 (or the fuel electrode 109) partially expands in volume. In FIG. 2, a region where Ni is reoxidized (reoxidation region) is schematically indicated by reference numeral 117. In the example shown in FIG. 2, the reoxidation region 117 is formed in the base 103, but the reoxidation region 117 can also be formed in the fuel electrode 109.
When the reoxidation region 117 is formed on the substrate 103 (or the fuel electrode 109), stress is generated in each part of the fuel cell 105 due to partial volume expansion of the substrate 103 (or the fuel electrode 109), and the defect 115 grows. However, the amount of oxygen leakage to the substrate 103 (or the fuel electrode 109) increases, and Ni reoxidation is promoted. The volume expansion of the substrate 103 (or the fuel electrode 109) due to Ni reoxidation becomes significant, and the fuel cell 100 is damaged when the stress due to the volume expansion reaches the fracture stress of the fuel cell 100. End up.

Therefore, in some embodiments, as illustrated in FIG. 1, the fuel cell 100 includes a fuel electrode 109 side or an air electrode 113 with respect to the overlapping portion 108 so as to cover the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111. It further includes a dense film (oxygen intrusion suppression film) 120 provided on the side.
Thereby, even if a defect 115 (see FIG. 2) occurs in the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111, the dense film 120 provided on the fuel electrode 109 side or the air electrode 113 side with respect to the overlapping portion 108. Thus, leakage of oxygen to the fuel electrode 109 side through the defect 115 (see FIG. 2) of the overlapping portion 108 can be prevented. Therefore, the volume expansion resulting from the oxidation of the component (for example, Ni) contained in the fuel electrode 109 or the base body 103 can be suppressed, and the reliability of the fuel cell 105 can be improved.
In addition, the formation of the dense film 120 increases the strength of the fuel cell 100 and increases the likelihood of the stress generated due to the volume expansion of the fuel electrode 109 or the base body 103. Can increase the sex.

In the exemplary embodiment shown in FIG. 1, the dense membrane 120 is on the air electrode 113 side (that is, on the opposite side of the base body 103 across the overlapping portion 108) with respect to the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111. ). In another embodiment, unlike FIG. 1, the air electrode 113, the solid electrolyte 111, and the fuel electrode 109 are stacked in this order on the base 103, and the dense film 120 covering the overlapping portion 108 is formed on the fuel electrode 109 side ( That is, it is provided on the opposite side of the base body 103 with the overlapping portion 108 in between.
Thus, by providing the dense film 120 on the opposite side of the base body 103 with the overlapping portion 108 interposed therebetween, the dense film 120 is formed after the interconnector 107 and the solid electrolyte 111 are sintered in the manufacturing process of the fuel cell 100. It becomes possible. In this case, the dense film 120 is integrally fired together with an electrode (air electrode 113 in the example shown in FIG. 1) located on the opposite side of the substrate 103 with the interconnector 107 and the solid electrolyte 111 interposed therebetween, thereby complicating the manufacturing process. Without this, the dense film 120 can be formed. In addition, after the interconnector 107 and the solid electrolyte 111 are integrally fired, the constituent material of the dense film 120 is applied and fired so that the shrinkage rate is not restricted when the interconnector 107 and the solid electrolyte 111 are integrally fired. Therefore, the degree of freedom in setting the film thickness of the dense film 120 is improved.

  As described above, when the substrate 103 or the fuel electrode 109 contains Ni by providing the dense film 120 so as to cover the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111 in which the defect 115 (see FIG. 2) is likely to occur. Even so, a highly reliable fuel cell 105 can be realized.

The dense film 120 may have a porosity of 10% or less.
By setting the porosity of the dense film 120 covering the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111 to 10% or less, a defect 115 (see FIG. 2) is temporarily generated in the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111. However, oxygen leakage to the fuel electrode 109 side through the defect 115 can be effectively prevented. Therefore, the volume expansion resulting from the oxidation of the material (for example, Ni) which comprises the fuel electrode 109 and the base | substrate 103 can be suppressed effectively, and the reliability of the fuel cell 105 can be improved further.

Further, the dense film 120 may be configured to include at least one of a material that is a main component of the interconnector 107, zirconia, or alumina.
In this case, it is possible to realize a dense film 120 having excellent heat resistance, stability in the fuel battery cell 105 (no reactivity with peripheral materials), and denseness, and further improving the reliability of the fuel battery cell 105. Can be increased.

  Here, the formation range of the dense film 120 will be described with reference to FIG. FIG. 3 is a diagram for explaining an example of the formation range of the dense film 120.

As shown in FIG. 3, the dense film 120 may be provided so as to cover at least the entire overlapping portion 108 of the interconnector 107 and the solid electrolyte 111.
Thereby, the defect 115 (see FIG. 2) generated in the overlapping portion 108 between the interconnector 107 and the solid electrolyte 111 can be reliably closed by the dense film 120.

By the way, in the fuel cell 100, the solid electrolyte 111 moves oxygen ions (O ²⁻ ) to the fuel electrode side, whereby a reaction at the interface between the solid electrolyte 111 and the fuel electrode 109 is realized. For this reason, the formation range of the dense film 120 is excessive. For example, when the dense film 120 protrudes greatly in the region 200 where the air electrode 113 and the fuel electrode 109 face each other with the solid electrolyte 111 interposed therebetween, the dense film 120 is This may hinder the movement of oxygen ions through the solid electrolyte 111, and the power generation performance of the fuel cell 100 may deteriorate.
Therefore, in some embodiments, the dense film 120 is formed in a region 300 where the air electrode 113 and the fuel electrode 109 are opposed to each other with the solid electrolyte 111 sandwiched between the region 200 and the dense film 120 are formed. , And the total area S of the region 300 ^{* where} the region where the air electrode 113 and the fuel electrode 109 face each other with the interconnector 107 interposed therebetween and the formation range of the dense film 120 overlap (= the dense film into the above two regions) 120 is set so as to satisfy the relationship of S / S _total ≦ 0.5. Here, S _total is the total area of the region 400 where the dense film 120 is formed.
Further, the dense film 120 is formed in a range where the protruding area S of the dense film 120 is S / S, where S ^* is the total area of the region 200 where the air electrode 113 and the fuel electrode 109 face each other with the solid electrolyte 111 interposed therebetween. ^{* It} may be set so as to satisfy the relationship of ≦ 0.2.

As described above, by setting the formation range of the dense film 120 so as to satisfy at least one of the relationship of S / S _total ≦ 0.5 or the relationship of S / S ^* ≦ 0.2, the air electrode 113 and the fuel Excessive protrusion of the dense film 120 to a region where the electrode 109 faces the solid electrolyte 111 or the interconnector 107 can be suppressed. For this reason, the dense film 120 is unlikely to hinder the movement of electrons and oxygen ions. Therefore, while suppressing a decrease in power generation performance of the fuel cell 100 due to the dense film 120, the dense film 120 causes oxygen to pass through the defect 115 (see FIG. 2) in the overlapping portion 108 between the interconnector 107 and the solid electrolyte 111. Leakage can be suppressed and the reliability of the fuel cell 105 can be ensured.

Next, a configuration using a functional film having a defect repair function as the dense film 120 will be described with reference to FIGS.
FIG. 4 is a cross-sectional view illustrating a configuration in which a functional film having a defect repair function according to an embodiment is used as the dense film 120. FIG. 5 is a ternary phase diagram in the oxidation state of the Fe—Al—Si based compound as an example of the constituent material of the functional film shown in FIG. FIG. 6 is a ternary phase diagram in the reduced state of the Fe—Al—Si compound as an example of the constituent material of the functional film shown in FIG. FIG. 7 is a cross-sectional view illustrating a configuration in which a functional film having a defect repair function according to another embodiment is used as the dense film 120.

  In some embodiments, as shown in FIG. 4A, the dense film 120A having a defect repairing function is formed on the overlapping portion 108 so as to cover the overlapping portion 108 between the interconnector 107 and the solid electrolyte 111. Provided on the air electrode 113 side. In this case, the dense film 120A includes a first material that has a lower melting point in the reduced state than in the oxidized state.

  According to the embodiment shown in FIG. 4A, when the defect 115 exists in the solid electrolyte 111 and / or the interconnector 107 in the overlapping portion 108, the fuel supplied to the air electrode 113 side through the defect 115 Oxygen reacts and the temperature rises locally near the defect 115. In addition, a dense film 120A containing the first material is provided on the air electrode 113 side so as to cover the overlapping portion 108 of the solid electrolyte 111 and the interconnector 107. The exposed dense film 120A on the air electrode 113 side has a lower melting point due to the characteristics of the first material. For this reason, the local temperature increase in the vicinity of the defect 115 and the decrease in the melting point of the first material constituting the dense film 120A are combined, and the first material is in the vicinity of the defect 115 of the solid electrolyte 111 and / or the interconnector 107. Is softened or melted, and as shown in FIG. 4B, a closed region 122A in which the gas leakage path is closed by the first material is formed. When the defect 115 of the solid electrolyte 111 and / or the interconnector 107 is closed in the closed region 122A, the reaction between the fuel and oxygen is suppressed, the temperature is lowered, and the first material returns to a solid. In this way, the defect of the solid electrolyte 111 and / or the interconnector 107 can be automatically repaired, and the self-healing function of the fuel cell 105 can be realized.

In one embodiment, the first material included in the dense film 120A shown in FIG. 4 is an Fe—Si—Al-based compound.
As shown in FIG. 5, the Fe—Si—Al-based compound has a minimum melting point of 1387 ° C. (≈1660 K) in the oxidation state (Fe ₂ O ₃ —SiO ₂ —Al ₂ O ₃ ), Most compositions have a melting point of 1400 ° C. (≈1673 K) or higher. For example, the composition example at point A has a melting point of about 1400 ° C. (≈1673 K). Here, the composition example of the point A, as mass _{fraction, Fe 2 O 3 = 50%} , SiO 2 = 39%, a Al ₂ O 3 = 11%.
On the other hand, as shown in FIG. 6, in the reduced state, in the Fe—Si—Al-based compound (FeO—SiO ₂ —Al ₂ O ₃ ), a low melting point compound is formed according to the ratio of each component. For example, the composition example (point B shown in FIG. 6) corresponding to the point A in FIG. 5 has a melting point of 1083 ° C. Here, the composition example B point, as mass _{fraction, FeO = 47%, SiO 2} = 41%, a Al ₂ O 3 = 12%. Note that even if the composition is other than point B shown in FIG. 6, for example, an Fe—SiO 2 compound formed when the Al content is extremely low also exhibits a low melting point of about 1083 to 1140 ° C. (FeO. In SiO ₂ mp 1140 ° C., in 2FeO · SiO ₂ mp 1083 ° C.). Also, in the case of 3FeO.3SiO ₂ .Al ₂ O ₃ , a low melting point of 1086 ° C. is exhibited.
Thus, since the Fe—Si—Al-based compound has a property that the melting point is lower in the reduced state than in the oxidized state, it can be used as the first material of the dense film 120A having a defect repair function.

Thus, by using as the first material an Fe—Si—Al-based compound having a property that the melting point is approximately 1400 ° C. or higher in the oxidized state but has a melting point of about 1100 ° C. (at least 1086 ° C.) in the reduced state. The defect of the solid electrolyte 111 or the interconnector 107 can be effectively repaired.
That is, when the first material (Fe—Si—Al-based compound) is exposed to a fuel atmosphere (reducing conditions) due to the presence of the solid electrolyte 111 and / or the defect 115 of the interconnector 107, the melting point is about 1100 ° C. The temperature drops to a minimum of 1086 ° C. Even if the normal operating temperature of the fuel cell is about 900 ° C., the temperature in the vicinity of the defect 115 is reduced to the melting point in the reduced state of the first material (Fe—Si—Al-based compound) due to a local temperature increase in the vicinity of the defect 115. It is possible to reach. When the temperature in the vicinity of the defect 115 exceeds the melting point of the first material in the reduced state, the first material is melted, and the gas leakage path (defect) is blocked in the blocking region 122A. When the defect 115 of the solid electrolyte 111 and / or the interconnector 107 is closed, the reaction between the fuel and oxygen is suppressed, the temperature is lowered, and the first material returns to a solid. In this process, since the melt of the first material is solidified by liquid phase sintering, the first material becomes a very dense gas tight layer, and the gas leakage path (defect) is effectively blocked by the blocking region 122A. Is done.

In another embodiment, as shown in FIG. 7A, the dense film 120B having a defect repairing function provides fuel to the overlapping portion 108 so as to cover the overlapping portion 108 between the interconnector 107 and the solid electrolyte 111. Provided on the pole 109 side. In this case, the dense film 120B includes a second material that has a lower melting point in the oxidized state than in the reduced state.
In the exemplary embodiment shown in FIG. 7, the air electrode 113 is provided on the base 103 side, and the fuel electrode 109 is provided on the opposite side of the base 103 with the interconnector 107 and the solid electrolyte 111 interposed therebetween. Yes. Accordingly, the dense film 120B can be formed after the interconnector 107 and the solid electrolyte 111 are integrally fired, and the dense film 120B can be integrally fired together with the fuel electrode 109. A method for manufacturing the fuel cell 100 having the cell stack structure shown in FIG. 7 will be described in detail later with reference to FIG.

  According to the embodiment shown in FIG. 7A, the dense film 120B containing the second material is provided on the fuel electrode 109 side so as to cover the surface of the solid electrolyte 111 and / or the interconnector 107, and the defect 115 Due to the characteristics of the second material, the melting point of the dense film 120B on the side of the fuel electrode 109 exposed to the oxidizing atmosphere due to the presence thereof is lowered. For this reason, the local temperature increase in the vicinity of the defect 115 and the decrease in the melting point of the second material constituting the dense film 120B are combined, and the second material is formed in the vicinity of the defect in the solid electrolyte 111 and / or the interconnector 107. Softened or melted, the closed region 122B in which the gas leakage path is closed by the second material is formed. When the defect 115 of the solid electrolyte 111 and / or the interconnector 107 is blocked in the blocking region 122B, the reaction between the fuel and oxygen is suppressed, the temperature is lowered, and the second material returns to a solid. Thus, the defect 115 of the solid electrolyte 111 and / or the interconnector 107 can be automatically repaired, and the self-healing function of the fuel cell 105 can be realized.

  In one embodiment, the second material included in the dense film 120B illustrated in FIG. 7 is vanadium oxide.

As described above, vanadium oxide having a property of having a melting point of about 1450 ° C. in the reduced state (V ₂ O ₄ ) but having a melting point of about 680 ° C. in the oxidized state (V ₂ O ₅ ) is used as the second material. Thus, the defect 115 of the solid electrolyte 111 and / or the interconnector 107 can be effectively repaired.
That is, when the second material (vanadium oxide) is exposed to oxidizing conditions due to the presence of the defect 115 of the solid electrolyte 111 and / or the interconnector 107, the melting point is lowered to about 680 ° C. Thus, when the temperature in the vicinity of the defect 115 exceeds the melting point in the oxidation state of the second material, the second material is melted, and the gas leakage path (defect) is blocked in the blocking region 122B. When the defects of the solid electrolyte 111 and / or the interconnector 107 are closed, the reaction between the fuel and oxygen is suppressed, so that the temperature decreases and the second material returns to a solid. In this process, since the melt of the second material is solidified by liquid phase sintering, the second material becomes a very dense gas tight layer, and the gas leakage path (defect) is effectively blocked by the blocking region 122B. Is done.

  Then, with reference to FIGS. 8-9, the manufacturing method of the fuel cell 100 which concerns on some embodiment is demonstrated. FIG. 8 is a flowchart showing a method for manufacturing a fuel cell according to an embodiment. FIG. 9 is a flowchart showing a method of manufacturing a fuel cell according to another embodiment.

As shown in FIG. 8, first, the base body 103 is manufactured (step S10). The substrate 103 may be a cylindrical substrate tube or a flat substrate plate. The base 103 may be made of a porous material. Examples of the material of the substrate 103 include CaO stabilized ZrO ₂ (CSZ), Y ₂ O ₃ stabilized ZrO ₂ (YSZ), or MgAl ₂ O ₄ .

Subsequently, the fuel electrode 109, the solid electrolyte 111, and the interconnector 107 are formed on the substrate 103 (step S12). At this time, after the fuel electrode 109 is formed on the substrate 103, the solid electrolyte 111 and the interconnector 107 are formed. The film formation of each member may be performed by applying a paste-like constituent material onto the substrate 103 by printing.
As a constituent material of the fuel electrode 109, an oxide (for example, Ni / YSZ) of a composite material of Ni and a zirconia-based electrolyte material can be given. As a constituent material of the solid electrolyte 111, YSZ having high oxygen ion conductivity at a high temperature can be used. The interconnector 107 is made of a conductive perovskite oxide represented by M _1-x L _x TiO ₃ such as SrTiO ₃ (M is an alkaline earth metal element and L is a lanthanoid element). Can do.

  Next, the fuel electrode 109, the solid electrolyte 111, and the interconnector 107 formed on the substrate 103 are integrally fired (step S14). The firing temperature at this time may be about 1400 ° C., for example.

Subsequently, the constituent material of the dense film 120 is formed by coating so as to cover the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111 (step S16).
The constituent material of the dense film 120 may include a material that is a main component of the interconnector 107, zirconia, and alumina. When the dense film 120 is desired to have a defect repair function, the constituent material of the dense film 120A (see FIG. 4) may include a first material that has a lower melting point in the reduced state than in the oxidized state. In this case, the first material may be an Fe—Si—Al-based compound having a property of having a melting point of 1400 ° C. or higher in the oxidized state but having a melting point of about 1100 ° C. (at least 1086 ° C.) in the reduced state.

After forming the dense film 120, the air electrode 113 is formed (step S18).
As a constituent material of the air electrode 113, for example, a LaSrMnO ₃ -based oxide or a LaCoO ₃ -based oxide can be used. The air electrode 113 may be formed by applying a paste-like constituent material by printing.

Next, the dense film 120 is integrally fired together with the air electrode 113 (step S20). At this time, in the case of the dense film 120A having a defect repair function, the melting point is lower than the relatively high melting point of the first material in the oxidized state (for example, the melting point of 1387 ° C. or more in Fe ₂ O ₃ —SiO ₂ —Al ₂ O ₃ ). You may perform integral baking of step S20 by temperature. Thereby, if baking of step S20 is performed under oxidizing conditions, the first material constituting the dense film 120A will not be in a molten state, so that it can be sintered while maintaining the desired shape of the dense film 120A.
In addition, you may set the integral baking temperature in step S20 within the range of 1000-1300 degreeC, for example.

  Through steps S10 to S20, base 103, a plurality of cells (fuel cell) 105 provided on base 103, interconnector 107 that electrically connects adjacent cells 105, interconnector 107, and solid electrolyte A cell stack including a dense film 120 covering the overlapping portion 108 of 111 is obtained.

  The cell stack thus obtained is reduced (step S22). Finally, when the fuel cell 100 is composed of a set of a plurality of cell stacks, the fuel cell 100 as the final product is obtained by assembling the plurality of cell stacks (step S24).

In the embodiment shown in FIG. 8, a plurality of cells 105 each including a fuel electrode 109, an air electrode 113, and a solid electrolyte 111 are formed on the substrate 103 (steps S <b> 12 to S <b> 14 and steps S <b> 18 to S <b> 20). At least one interconnector 10 is formed to electrically connect the interconnector 107 and the overlapping portion 108 of the solid electrolyte 111 so as to cover the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111. A dense film 120 is formed (steps S16 and S20).
According to this method, since the dense film 120 that covers the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111 is provided on the air electrode 113 side with respect to the overlapping portion 108, a highly reliable fuel cell 100 can be obtained. .
That is, in the fuel cell 100 obtained by the above method, even if a defect occurs in the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111, the dense film 120 provided on the air electrode 113 side with respect to the overlapping portion 108, Leakage of oxygen to the fuel electrode 109 side through the defect 115 of the overlapping portion 108 can be prevented. Thereby, the volume expansion resulting from the oxidation of the material which comprises the fuel electrode 109 and the base | substrate 103 can be suppressed, and the reliability of the fuel cell 105 can be improved. In addition, the formation of the dense film 120 increases the strength of the fuel cell 100 and increases the likelihood of the stress generated due to the volume expansion of the fuel electrode 109 or the base body 103. Improves.

In the embodiment shown in FIG. 8, the fuel electrode 109 is formed on the base 103 (step S12), and the solid electrolyte 111 and the interconnector 107 are formed on the fuel electrode 109 (step S12). After the solid electrolyte 111 and the interconnector 107 are integrally fired (step S14), the dense film 120 is formed (steps S16 and S20).
Thereby, even if the defect 115 occurs in the overlapping portion 108 due to the shrinkage difference when the solid electrolyte 111 and the interconnector 107 are integrally fired, the dense film 120 is formed later so as to cover the overlapping portion 108. The reliability of the fuel cell 100 can be effectively improved.
In addition, since the dense film 120 is formed after the solid electrolyte 111 and the interconnector 107 are integrally fired, there is no restriction on the shrinkage rate at the time of the integral firing, so the degree of freedom in setting the film thickness of the dense film 120 is improved.

Further, in the embodiment shown in FIG. 8, when the dense film 120 is formed, after the constituent material of the dense film 120 is applied, the dense film 120 is baked together with the air electrode 113 (steps S16 and S20). .
Thereby, the dense film 120 can be fired together with the air electrode 113, and an increase in the steps for forming the dense film 120 can be suppressed. Thereby, it is possible to obtain the fuel cell 100 with improved reliability by forming the dense film 120 while suppressing an increase in manufacturing cost.

  In some other embodiments, as shown in FIG. 9, the base 103 is first manufactured (step S110).

  Subsequently, the air electrode 113, the solid electrolyte 111, and the interconnector 107 are formed on the substrate 103 (step S112). At this time, after the air electrode 113 is formed on the substrate 103, the solid electrolyte 111 and the interconnector 107 are formed. The film formation of each member may be performed by applying a paste-like constituent material onto the substrate 103 by printing.

  Next, the air electrode 113, the solid electrolyte 111, and the interconnector 107 formed on the substrate 103 are integrally fired (step S114). The firing temperature at this time may be about 1400 ° C., for example.

Subsequently, the constituent material of the dense film 120 is formed by coating so as to cover the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111 (step S16).
The constituent material of the dense film 120 may include a material that is a main component of the interconnector 107, zirconia, and alumina. When the dense film 120 is desired to have a defect repair function, the constituent material of the dense film 120B (see FIG. 7) may include a second material that has a lower melting point in the oxidized state than in the reduced state. In this case, the second material is vanadium oxide having a property that the melting point is about 1450 ° C. in the reduced state (V ₂ O ₄ ), but the melting point becomes about 680 ° C. in the oxidized state (V ₂ O ₅ ). Also good.

  After the dense film 120 is formed, the fuel electrode 109 is formed (step S118).

Next, the dense film 120 is integrally fired together with the fuel electrode 109 (step S120). At this time, in the case of the dense film 120B having a defect repair function, the integral baking in step S120 is performed at a temperature lower than a relatively high melting point of the second material in the reduced state (for example, a melting point of about 1450 ° C. in V ₂ O ₄ ). You may go. Accordingly, if the firing in step S120 is performed under reducing conditions, the second material constituting the dense film 120B does not enter a molten state, and therefore, the dense film 120B can be sintered while maintaining a desired shape.
In addition, you may set the integral baking temperature in step S120 within the range of 1000-1300 degreeC, for example.

  Through steps S110 to S120, base 103, a plurality of cells (fuel cell) 105 provided on base 103, interconnector 107 that electrically connects adjacent cells 105, interconnector 107, and solid electrolyte A cell stack including a dense film 120 covering the overlapping portion 108 of 111 is obtained.

  The cell stack thus obtained is reduced (step S122). Finally, when the fuel cell 100 is composed of a set of a plurality of cell stacks, the fuel cell 100 as the final product is obtained by assembling the plurality of cell stacks (step S124).

In the embodiment shown in FIG. 9, a plurality of cells 105 each including a fuel electrode 109, an air electrode 113, and a solid electrolyte 111 are formed on the base 103 (steps S 112 to S 114, steps S 118 to S 120), and between adjacent cells 105. At least one interconnector 10 is formed to electrically connect the interconnector 107 and the overlapping portion 108 of the solid electrolyte 111 so as to cover the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111. A dense film 120 is formed (steps S116 and S120).
According to this method, since the dense film 120 that covers the overlapping portion 108 of the interconnector 107 and the solid electrolyte 111 is provided on the fuel electrode 109 side with respect to the overlapping portion 108, the highly reliable fuel cell 100 can be obtained. .

In the embodiment shown in FIG. 9, the air electrode 113 is formed on the base 103 (step S112), and the solid electrolyte 111 and the interconnector 107 are formed on the air electrode 113 (step S112). After the solid electrolyte 111 and the interconnector 107 are integrally fired (step S114), the dense film 120 is formed (steps S116 and S120).
Thereby, even if the defect 115 occurs in the overlapping portion 108 due to the shrinkage difference when the solid electrolyte 111 and the interconnector 107 are integrally fired, the dense film 120 is formed later so as to cover the overlapping portion 108. The reliability of the fuel cell 100 can be effectively improved.
In addition, since the dense film 120 is formed after the solid electrolyte 111 and the interconnector 107 are integrally fired, there is no restriction on the shrinkage rate at the time of the integral firing, so the degree of freedom in setting the film thickness of the dense film 120 is improved.

Furthermore, in the embodiment shown in FIG. 9, when forming the dense film 120, after the constituent material of the dense film 120 is applied, the dense film 120 is baked together with the fuel electrode 109 (steps S <b> 116 and S <b> 120).
Thereby, the dense film 120 can be fired together with the fuel electrode 109, and an increase in the steps for forming the dense film 120 can be suppressed. Thereby, it is possible to obtain the fuel cell 100 with improved reliability by forming the dense film 120 while suppressing an increase in manufacturing cost.

  The present invention is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.

For example, an expression indicating that things such as “identical”, “equal”, and “homogeneous” are in an equal state not only represents an exactly equal state, but also has a tolerance or a difference that can provide the same function. It also represents the existing state.
For example, expressions representing shapes such as quadrangular shapes and cylindrical shapes represent not only geometrically strict shapes such as quadrangular shapes and cylindrical shapes, but also irregularities and chamfers as long as the same effects can be obtained. A shape including a part or the like is also expressed.
In addition, the expression “comprising”, “including”, or “having” one constituent element is not an exclusive expression for excluding the existence of another constituent element.

1, 2 Space 100 Fuel cell 103 Base 105 cell (fuel cell)
107 Interconnector 108 Overlapping Portion 109 Fuel Electrode 111 Solid Electrolyte 113 Air Electrode 115 Defect 117 Reoxidation Area 120, 120A, 120B Dense Membrane 122A, 122B Blocking Area

Claims (12)

A plurality of cells each including a fuel electrode, an air electrode and a solid electrolyte;
At least one interconnector for electrically connecting the cells;
A dense membrane provided on the fuel electrode side or the air electrode side with respect to the overlapping portion so as to cover the overlapping portion of the interconnector and the solid electrolyte;
A fuel cell comprising:   2. The fuel cell according to claim 1, wherein at least one of the fuel electrode and the substrate supporting the plurality of cells contains Ni.   The fuel cell according to claim 1, wherein the dense film has a porosity of 10% or less. The protruding area S of the dense film to the area where the air electrode and the fuel electrode face each other with the solid electrolyte or the interconnector interposed therebetween is the total area of the area where the dense film is formed as S _{total 4.} The fuel cell according to claim 1, wherein a relationship of S / S _total ≦ 0.5 is satisfied.   The fuel cell according to any one of claims 1 to 4, wherein the dense film includes at least one of a material that is a main component of the interconnector, zirconia, or alumina. The dense film includes a first material having a lower melting point in a reduced state than in an oxidized state,
The fuel cell according to any one of claims 1 to 5, wherein the dense film is provided on the air electrode side with respect to the overlapping portion so as to cover the overlapping portion.   The fuel cell according to claim 6, wherein the first material is an Fe—Si—Al-based compound. The dense film includes a second material having a lower melting point in the oxidized state than in the reduced state,
The fuel cell according to any one of claims 1 to 5, wherein the dense film is provided on the fuel electrode side with respect to the overlapping portion so as to cover the overlapping portion.   The fuel cell according to claim 8, wherein the second material is vanadium oxide. Forming a plurality of cells each including a fuel electrode, an air electrode and a solid electrolyte;
Forming at least one interconnector for electrically connecting adjacent cells;
Forming a dense film on the fuel electrode side or the air electrode side with respect to the overlapping portion so as to cover the overlapping portion of the interconnector and the solid electrolyte;
A method of manufacturing a fuel cell comprising: Depositing one of the fuel electrode or the air electrode;
Forming the solid electrolyte and the interconnector on the one of the fuel electrode or the air electrode, and firing the solid electrolyte and the interconnector integrally,
The method of manufacturing a fuel cell according to claim 10, wherein the dense film is formed. In the step of forming the dense film,
After applying the constituent material of the dense film,
The method for producing a fuel cell according to claim 10 or 11, wherein the dense film is fired together with the fuel electrode or the air electrode.

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