JP3339983B2 - Solid oxide fuel cell and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell, and more particularly, to a solid oxide fuel cell capable of co-firing an air electrode and a current collector, and a method of manufacturing the same. .

[0002]

2. Description of the Related Art Conventionally, since a solid oxide fuel cell has a high operating temperature of 900 to 1050 ° C., it has a high power generation efficiency and is expected as a third generation power generation system. In general, a solid oxide fuel cell includes a cylindrical type and a flat type. The flat fuel cell has the feature that the power density per unit volume of power generation is high, but there are problems such as imperfect gas seal and non-uniformity of the temperature distribution in the cell in practical use. On the other hand, the cylindrical fuel cell has the features that the output density is low, but the mechanical strength of the cell is high and the temperature uniformity in the cell can be maintained. Both types of solid electrolyte fuel cells are being actively researched and developed utilizing their respective features.

As shown in FIG. 1, a single cell of a cylindrical fuel cell has a support tube 1 made of CaO-stabilized ZrO ₂ having an open porosity of about 40%, and a porous air made of a LaMnO ₃ material on the tube. A pole 2 is formed, and Y ₂ O ₃ stabilized Zr is formed on its surface.
A solid electrolyte 3 made of O ₂ is covered, and a porous Ni-zirconia fuel electrode 4 is provided on this surface. In the fuel cell module, each single cell is La
It is connected via a CrO ₃ -based current collector (interconnector) 5. Power generation is performed at a temperature of 1000 to 1050 ° C. by flowing air (oxygen) inside the support tube 1 and fuel (hydrogen) outside.

In recent years, attempts have been made to use a LaMnO ₃ -based material, which is an air electrode material, directly as a porous support tube in order to simplify the process in the cell fabrication process. As a support tube material having the function as an air electrode, La is 20 at% by Ca or 10 to 15 by Sr.
A LaMnO ₃ solid solution material with atomic percent substitution is used.

As a method of manufacturing the above-described fuel cell, for example, an insulating powder made of CaO-stabilized ZrO ₂ is formed into a cylindrical shape by extrusion molding or the like,
This is fired to produce a cylindrical support, and a slurry of an air electrode, a solid electrolyte, a fuel electrode, or a current collector is applied to the outer peripheral surface of the support tube, and this is sequentially fired and laminated, or Electrochemical vapor deposition (EVD) is applied to the surface of a cylindrical support tube.
Electrode, solid electrolyte,
In some cases, a fuel electrode or a current collector is sequentially formed.

Recently, there has been proposed a method of simultaneously firing at least two of the constituent materials in order to simplify the manufacturing process of the cell. This co-firing method is advantageous in improving the yield during cell production and reducing costs since the number of production steps is reduced.

[0007]

SUMMARY OF THE INVENTION The present inventors have attempted simultaneous firing in various combinations, and as a result,
When the air electrode made of aMnO ₃ -based material and the current collector made of LaCrO ₃ -based material are fired simultaneously, the current collector side near the interface between the two is not fired densely, and the electricity between the air electrode and the current collector is It was found that there was a defect that the electrical connection was insufficient and the original power generation performance was not exhibited.

As a result of various studies on the cause, a LaCrO ₃ -based chromite compound was used as an air electrode,
When a LaMnO ₃ -based manganite compound is simultaneously fired as a current collector, when Mn in the air electrode is simultaneously fired with the current collector, Mn in the air electrode diffuses into the current collector, and the diffused Mn Replaces Cr in the current collector, and Cr is released as vapor. The released Cr is condensed and deposited as Cr ₂ O _{3 on} the contact portion (neck portion) of the particles during the sintering process and inhibits sintering. As a result, a dense chromite compound is formed particularly near the interface with the air electrode. It turns out that it is not done.

Therefore, the present invention provides a solid electrolyte fuel cell capable of forming a dense current collector without the above-mentioned problems when the air electrode and the current collector are co-fired. It is an object of the present invention to provide a cell and a method for manufacturing the cell.

[0010]

Means for Solving the Problems The present inventors have repeatedly studied the composition of the air electrode and the current collector with respect to the above object, and as a result, the air electrode was changed from the group 3a element of the periodic table. A perovskite-type composite oxide containing at least one selected from the group consisting of at least one selected from the group consisting of Ca, Sr, and Ba; Mn; and at least one selected from the group consisting of Co, Ni, and Fe; As well as Periodic Table No. 3a
When co-firing was performed using a composition in which a second phase consisting of an oxide containing a group-group element was precipitated, it was found that the presence of the second phase prevented the diffusion of Mn, thereby densifying the current collector. It has been found that a good junction between the air electrode and the current collector can be formed without hindering the formation of the air electrode and the present invention.

That is, the solid electrolyte fuel cell of the present invention has a current collector in which an air electrode is formed on one surface of the solid electrolyte and a fuel electrode is formed on the other surface, and is electrically connected to the solid electrolyte and the air electrode. In the solid electrolyte fuel cell having a body, the air electrode is formed of at least one element selected from Group 3a elements of the periodic table, at least one element selected from the group consisting of Ca, Sr, and Ba; Mn; , Ni, and a perovskite-type composite oxide containing at least one selected from the group consisting of Fe as a main crystal phase, and a composite oxide containing a second phase composed of an oxide containing a Group 3a element of the periodic table, in particular, The overall composition of the air electrode is shown below.

[0012]

Embedded image

When expressed as: 0.1 ≦ x ≦ 0.6, 0 <y
≦ 0.2, 0 ≦ z ≦ 0.3, wherein the current collector comprises at least one element selected from Group 3a elements of the periodic table, and Ca, Sr, Ba, Mg And a composite oxide having a main crystal phase of a perovskite crystal containing at least one selected from the group consisting of Cr and Cr.

According to the method for manufacturing a solid oxide fuel cell of the present invention, when the overall composition is represented by the above formula,
0.1 ≦ x ≦ 0.6, 0 <y ≦ 0.2, 0 ≦ z ≦ 0.3
An air electrode molded body comprising a composition satisfying the following conditions, at least one element selected from Group 3a elements of the periodic table, and Ca, S
at least one selected from the group consisting of r, Ba and Mg, and C
and laminating a current collector molded body made of an oxide composition containing r and simultaneously firing the same in an oxidizing atmosphere.

Hereinafter, the present invention will be described in detail. The air electrode in the solid oxide fuel cell of the present invention is structurally composed of at least one element selected from Group 3a elements of the periodic table, Ca,
At least one selected from the group consisting of Sr and Ba;
And a perovskite-type composite oxide containing at least one member selected from the group consisting of Co, Ni, and Fe;
It is composed of a composite oxide containing a second phase composed of an oxide containing a group element. Therefore, in the composition of the whole air electrode, the element of Group 3a of the periodic table is contained in excess of the perovskite type composition.

[0016]

Embedded image

When expressed as: 0.1 ≦ x ≦ 0.6, 0 <y
≦ 0.2 and 0 ≦ z ≦ 0.3.

Here, in the composition of the air electrode, Ca, S
The addition of r or Ba serves to increase the electrical conductivity of the air electrode and to match the coefficient of thermal expansion with other solid electrolytes and current collectors. However, if the amount is large, a phase other than the perovskite-type crystal is generated, and the air electrode is densified, and a porous electrode is not formed.
≦ 0.6. Preferably, 0.1 ≦ x ≦ 0.
3.

Further, in the perovskite type crystal represented by ABO ₃ , by making the amount of the A site larger than the amount of the B site, an oxide phase containing a Group 3a element of the periodic table is precipitated, whereby the Mn content is reduced. Diffusion can be suppressed. However, if the excess is excessive, that is, if the y value in the above chemical formula 1 is too large, the sinterability deteriorates. In addition, since the electric conductivity also decreases and the matching of the thermal expansion coefficient between the solid electrolyte and the current collector deteriorates, the y value is set to 0 <y ≦ 0.2. Desirably, 0 <y ≦ 0.1. In addition, La, as an element of Group 3a of the periodic table of the air electrode constituent component, La,
Y, Yb, Sc, Sm, Er, Nd, Gd, Dy and the like. Among them, La, Y, Yb, and Nd are particularly effective.

The addition of Co, Ni or Fe also
It acts to prevent the diffusion of Mn into the solid electrolyte or the current collector that will be in direct contact with the air electrode, but if the amount is too large, a phase other than the perovskite crystal is generated, and the air electrode becomes denser. From the above, the z value was set in the range of 0 ≦ z ≦ 0.3. Desirably, 0 ≦ z ≦ 0.1.

In the air electrode, the perovskite-type crystal phase constituting the main crystal phase has an average crystal grain size of 3 to 20.
μm, particularly preferably 5 to 15 μm. This is because if the particle diameter of the main crystal phase is smaller than 3 μm, the gas permeability is low although the strength is high, and if it exceeds 20 μm, the gas permeability is high but the strength is insufficient. The open porosity of the air electrode is 20 to 45 in terms of gas permeability.
%, Especially 30 to 40%, is suitable. The average pore diameter in the range of 1.0 to 5.0 μm is excellent in gas permeability.

On the other hand, the current collector in the solid oxide fuel cell of the present invention is at least one selected from the group 3a elements of the periodic table and at least one selected from the group consisting of Ca, Sr, Ba and Mg. And a perovskite-type composite oxide containing Cr as a main crystal phase. More specifically, the composition is represented by the following chemical formula 2.

[0023]

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In the formula, a, b, c and p in the chemical formula (2)
It is desirable that the following satisfies a + b + c + p = 20 <a, 0 <c, 0 <p 0.002 ≦ b ≦ 0.9 0.001 ≦ bc ≦ 0.8.

The reason why the composition of the current collector is limited to the above range is that when the amount (b) of the D element such as Mg or Ca is smaller than 0.002, the electric conductivity becomes small, and the essence of the conductive ceramic is reduced. Characteristics cannot be obtained, and it cannot be used as a fuel cell separator, interconnector, or heating element.
Conversely, if it is larger than 0.9, the electric conductivity is reduced and the sinterability is also deteriorated. Further, when the difference (bc) between the b value and the amount of the E element (c) is smaller than 0.001, the electric conductivity is small, and when it exceeds 0.8, the sinterability decreases.

In the conductive ceramic constituting the current collector, a part of Cr can be replaced with Mn, Fe, or Co at a ratio of 30 atomic% or less based on Cr.

The current collector has a perovskite type crystal phase as a main phase, and has an average crystal grain size of 50 μm.
Below, it is particularly desirable that it is 20 μm or less. In addition,
The open porosity of the current collector is preferably a dense body of 1% or less, particularly 0.5% or less from the viewpoint of preventing gas permeability.

The solid electrolyte in the fuel cell of the present invention is stabilized by a known stabilizer such as CaO or MgO in addition to rare earth element oxides such as Y ₂ O ₃ , CeO ₂ and Yb ₂ O _3. ZrO ₂ is used the coefficient of thermal expansion 9 to 12 × 10 ^- is desirably about ⁶ / ° C.. It as the fuel electrode remainder containing 30 to 80 wt% of Ni composed of porous cermet consisting of stabilized ZrO ₂ (including a stabilizer such as Y ₂ O ₃₎ is desirable.

The structure of the fuel cell according to the present invention is similar to that of the cylindrical fuel cell shown in FIG.
It may be a well-known flat-type fuel cell structure in which a solid electrolyte, a fuel electrode, and a current collector are laminated.

Next, a method for manufacturing a solid oxide fuel cell according to the present invention will be described with reference to the cylindrical fuel cell shown in FIG. 1 as an example. A major feature of the manufacturing method of the present invention is that the air electrode and the current collector are sintered by simultaneous firing.

First, a cylindrical support tube is prepared. This cylindrical support tube is made of, for example, Y ₂ O ₃ or CaO-stabilized ZrO.
It is obtained by forming by extrusion molding or the like using a porous material such as ₂ , and then firing it.

Next, on the surface of the cylindrical support tube, a molded layer made of the composition constituting the air electrode is formed. First, the air electrode molded body layer is made of a Group 3a element oxide of the periodic table, an alkaline earth element oxide, a Mn oxide, Co, Ni, Fe, or the like so as to have a composition represented by Chemical Formula 1 described above. After preparing powders of the metal oxides or carbonates, nitrates, acetates, and the like of the respective metals capable of forming oxides by heat treatment, these are calcined at 1400 to 1600 ° C. to form a solid solution. Thereafter, the solid solution is pulverized to obtain a solid solution powder.

Then, a slurry is prepared using the solid solution powder, and the slurry is applied to the surface of the cylindrical support tube and dried, or a green sheet is prepared using the solid solution powder by a doctor blade method or the like. The air electrode molding layer is formed by winding around the support tube surface.

Next, a current collector molded layer is laminated on part of the surface of the air electrode molded layer. Similarly to the air electrode molded body layer, the current collector molded body layer has a composition represented by Chemical Formula 2 described above, so that an oxide of an element belonging to Group 3a of the periodic table, an oxide of an alkaline earth element, an oxide of Cr, an oxide of Mn, After preparing powders of oxides, metal oxides such as oxides of Zr and Hf, or carbonates, nitrates, acetates and the like of the above metals capable of forming oxides by heat treatment, these are temporarily heated to 1400 to 1600 ° C. A baking treatment is performed to form a solid solution. Thereafter, the solid solution is pulverized to obtain a solid solution powder.

Then, a slurry is prepared using the solid solution powder, and the slurry is applied to a predetermined portion of the air electrode forming layer and dried, or a green sheet is prepared using the solid solution powder by a doctor blade method or the like. This is adhered to a part of the surface of the air electrode molded body layer using an organic adhesive or the like to form a current collector molded body layer.

Next, the laminate is fired at a temperature of 1300 to 1600 ° C. for about 3 to 15 hours in an oxidizing atmosphere such as the atmosphere, so that the air electrode molded layer and the current collector molded layer are simultaneously formed. Sinter.

Further, the solid electrolyte and the fuel electrode are formed by sintering by sequentially forming their layers at predetermined positions of a laminated sintered body obtained by simultaneously sintering the air electrode and the current collector, respectively, or After the formation of the electrode molded body layer and the current collector molded body layer, the solid electrolyte molded body layer and / or the fuel electrode molded body layer can be further laminated and fired simultaneously.

The manufacturing method in the present invention is not limited to the case having the cylindrical support tube, and when the air electrode also serves as the cylindrical support tube, it is replaced with the air electrode molded body layer by extrusion molding or cold isostatic pressing. Except for molding into a cylindrical air electrode molded body by a method or the like, each component may be laminated and produced in the same manner as described above.

In the case of a flat fuel cell, a plate-like molded body of each component is prepared, and at least an air electrode molded body layer and a current collector molded body layer are laminated and fired simultaneously. In some cases, the solid electrolyte molded body layer and the fuel electrode molded body layer may be laminated and fired simultaneously.

[0040]

In the past, when an air electrode made of a manganite compound such as LaMnO ₃ and a current collector made of a chromite compound such as LaCrO ₃ were simultaneously fired, Mn in the air electrode diffused into the current collector. The diffused Mn substitutes for Cr in the current collector, and Cr is released as vapor. The released Cr becomes Cr ₂ O _{3 at} the contact portion (neck portion) of the particles during the sintering process and condenses and deposits to inhibit sintering. As a result, a dense chromite compound is formed particularly near the interface with the air electrode. Not formed.

According to the fuel cell of the present invention, the air electrode comprises at least one element selected from the group 3a elements of the periodic table, at least one element selected from the group consisting of Ca, Sr and Ba, and Mn; A perovskite-type composite oxide containing at least one selected from the group consisting of Co, Ni, and Fe is used as a main crystal phase, and a perovskite-type composite oxide containing an element belonging to Group 3a of the periodic table.
2 phase is precipitated, and the current collector is formed of at least one element selected from Group 3a elements of the periodic table, Ca, Sr, Ba, and Mg.
And a perovskite-type composite oxide containing Cr and Mn.

According to this structure, the oxide of the Group 3a element of the periodic table in the air electrode suppresses the diffusion of Mn, and Co, Ni, and Fe also have the function of reducing the diffusion of Mn. It functions to prevent evaporation of Cr in the current collector due to diffusion of Mn in the electrode to the current collector.

As a result, even when the air electrode and the current collector are fired at the same time, insufficient densification near the interface between the air electrode and the current collector is obtained without hindering the sintering of the Mn current collector. And the current collector can be sintered densely.

Therefore, since the air electrode and the current collector can be simultaneously fired without any hindrance to manufacture the fuel cell, the cell manufacturing process can be simplified, and the yield at the time of manufacturing the cell can be reduced. And cost can be reduced.

Further, as a fuel cell, the electrical connection between the air electrode and the current collector is improved and the current collecting performance is improved, so that the power generated from the cell can be efficiently collected, and The power generation performance of the battery cell can also be improved.

[0046]

EXAMPLES A cylindrical air electrode molded body, a solid electrolyte molded body, a fuel electrode molded body, and a current collector molded body were produced as components of a solid oxide fuel cell in the following manner.

(Cylindrical air electrode molding) Commercial purity
9% or more of oxides of Group 3a elements of the periodic table, oxides of alkaline earth metals, Mn ₂ O ₃ , CoO, NiO, Fe ₂
O ₃ was used as a starting material, and this was weighed and mixed so that each metal element had a predetermined composition shown in Table 1, and then mixed at 1500 ° C. for 3 hours.
The mixture was calcined for a period of time and pulverized to obtain a solid solution powder having an average particle size of 5 to 8 μm. Next, a binder is added to the solid solution powder,
A cylindrical air electrode molded body was produced by an extrusion molding method.

(Solid Electrolyte Molded Product) Y ₂ O ₃ obtained by the coprecipitation method has an average particle diameter of 1 mol% containing 8 mol%.
A slurry was prepared by adding water and a binder to a ZrO ₂ powder having a thickness of 200 μm, and a thickness of 200 μm was obtained by a doctor blade method.
m of the solid electrolyte compact was prepared.

(Fuel electrode compact) NiO powder and ZrO
₂ (containing 10 mol% Y ₂ O ₃ ) powder in a weight ratio of 70:
Water was added as a solvent to the mixed powder mixed at a ratio of 30 to prepare a slurry, and the slurry was formed to a thickness of 70 by a doctor blade method.
A μm fuel electrode compact was produced.

(Current Collector Molded Product) La ₂ O ₃ , CaCO ₃ , ZrO ₂ , Cr ₂ O ₃ , Mg having a purity of 99.9% commercially available
O was used as a starting material, which was weighed and mixed to a predetermined composition, calcined at 1500 ° C. for 3 hours and pulverized to obtain a solid solution powder having an average particle size of 1 to 3 μm. Next, a slurry was prepared by adding a binder to the solid solution powder, and a current collector molded body having a thickness of 100 μm was prepared by a doctor blade method.

Subsequently, the following experiments were performed using each of the above molded bodies. Experiment 1 First, La (Zr _0.05 Mg _0.1 Cr _0.85 ) was applied to the surface of the cylindrical air electrode molded body having the composition shown in Tables 1 and 2 by using an adhesion liquid.
After winding a current collector formed of a composition of _0.99 O ₃ and La _0.8 Ca _0.22 CrO ₃ into a roll,
Co-firing was performed at 00 ° C. for 6 hours. The thickness of the porous region on the current collector side was measured by observing the structure near the air electrode / current collector interface of the fired laminated sintered body. The porosity was also measured at the same time, and the results are shown in Tables 1 and 2. In each sample, comprehensive evaluation was performed based on the porosity of the air electrode as a cell, the denseness of the current collector, and the thickness of the porous layer of the current collector.

[0052]

[Table 1]

[0053]

[Table 2]

As shown in Tables 1 and 2, Sample No. 1 in which the A-site / B-site ratio was 1.0 and no second phase was precipitated,
In 6, 30, and 35, as a result of elemental analysis, diffusion of Mn into the current collector was observed, and as a result, the thickness of the porous layer of the current collector exceeded 30 μm. On the other hand, the samples other than the above in which the second phase composed of the Group 3a element oxide of the periodic table was deposited could suppress the diffusion of Mn, and as a result, the porous layer had an excellent thickness of 30 μm or less. In the case where the overall composition of the air electrode satisfies the above-mentioned composition, the porosity of the air electrode is 27% to 33%, the porosity of the current collector is 0.5% or less, The thickness of the material layer is 3
It was excellent at 0 μm or less.

However, Samples Nos. 10 and 39 in which the substitution amount of Ni to Mn was excessive, and Sample No. 1 in which the ratio of Ca was excessive.
In Nos. 6 and 45, the porosity of the air electrode decreased, and the gas permeability was poor. In Samples Nos. 6 and 35 in which the A-site / B-site ratio was 1.0 and Mn was replaced with Ni, the thickness of the porous layer was changed to Sample N
O.1 and 30, but the effect was insufficient, and the porosity of the current collector was slightly higher than 0.5%.
Further, in Samples Nos. 5 and 34 having an excessive amount of A sites, the porosity of the air electrode was increased due to poor sinterability, and the strength was low. Moreover, the sample was decomposed in a short time.

Experiment 2 Based on the results of Experiment 1 above, a fuel cell was manufactured and a power generation test was performed.

First, the solid electrolyte molded body, the fuel electrode molded body, and the current collector molded body were wound around the surface of the cylindrical air electrode molded body at predetermined locations using an organic adhesive. The obtained laminated molded body was simultaneously fired in the air at 1500 ° C. for 6 hours to produce a fuel cell. Then, an oxygen gas is supplied inside the cell, and a hydrogen gas is supplied outside the cell.
A power generation test was performed at 0 ° C., and the output density was measured. The results are shown in Table 3.

At this time, as a combination of the composition of the air electrode molded body and the current collector molded body, the combination of the samples No.
1, 3, 14, 16, 29, 34, 54 and 56 were used.

[0059]

[Table 3]

As is evident from the results in Table 3, the product of the present invention had a higher output density and a higher power generation performance of the fuel cell compared to Samples Nos. 1, 16, and 34.

[0061]

As described in detail above, according to the present invention,
Poor sintering of the current collector when the air electrode and the current collector are simultaneously fired can be improved. As a result, it is possible to improve the yield of the cell manufacturing and reduce the cost. In addition, the current collecting performance of the current collector is increased, so that the power generation performance of the fuel cell unit can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a cylindrical fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support pipe 2 Air electrode 3 Solid electrolyte 4 Fuel electrode 5 Current collector

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-8-130029 (JP, A) JP-A-6-44991 (JP, A) JP-A-2-236959 (JP, A) JP-A-1- 200560 (JP, A) JP-A-6-302332 (JP, A) JP-A-7-111157 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 8/12 H01M 4 / 86 H01M 4/88 H01M 8/02

Claims (2)

(57) [Claims] An air electrode is formed on one side of a solid electrolyte, and a fuel electrode is formed on the other side of the solid electrolyte. The solid electrolyte further comprises a current collector electrically connected to the solid electrolyte and the air electrode. In a solid oxide fuel cell unit in which a current collector is sintered simultaneously, the current collector is at least one selected from Group 3a elements of the periodic table, and Ca, Sr, Ba, M
g, and a perovskite-type composite oxide containing Cr, wherein the air electrode comprises at least one selected from Group 3a elements of the periodic table;
at least one selected from the group consisting of a, Sr, and Ba;
n and at least 1 selected from the group consisting of Co, Ni and Fe
And a perovskite-type composite oxide containing a seed as a main crystal phase, and an oxide crystal containing a Group 3a element of the periodic table as a second crystal.
In the formula (A _{1-x + y} B _x ) (Mn _1-z C _z ) O _{3 ± δ} , A is at least one selected from the group 3a elements of the periodic table. Species B is at least one selected from the group consisting of Ca, Sr, and Ba.
Species C is at least one selected from the group consisting of Co, Ni, and Fe.
When expressed as seed, 0.1 ≦ x ≦ 0.6, 0 <y ≦ 0.2, 0
A solid oxide fuel cell which satisfies ≦ z ≦ 0.3. 2. In the formula (A _{1-x + y} B _x ) (Mn _1-z C _z ) O _{3 ± δ} , A is at least one element selected from Group 3a elements of the periodic table. B is at least one selected from the group consisting of Ca, Sr, and Ba.
Species C is at least one selected from the group consisting of Co, Ni, and Fe.
When expressed as seed, 0.1 ≦ x ≦ 0.6, 0 <y ≦ 0.2, 0
An air electrode molded body comprising a composition satisfying ≦ z ≦ 0.3, at least one member selected from Group 3a elements of the periodic table, and at least one member selected from the group consisting of Ca, Sr, Ba, and Mg , And a current collector molded body made of an oxide composition containing Cr, and then fired simultaneously in an oxidizing atmosphere to form, in an air electrode, at least one selected from Group 3a elements of the periodic table. A perovskite-type composite oxide containing one kind, at least one kind selected from the group consisting of Ca, Sr and Ba, and at least one kind selected from the group consisting of Mn and Co, Ni and Fe as a main crystal phase; A method for producing a solid oxide fuel cell, comprising a step of precipitating an oxide crystal containing a Group 3a element as a second phase.