JP2002134133A - Cell of solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell of a solid electrolyte fuel cell, capable of enhancing reproducibility by suppressing dispersion of cell performance to a minimum, providing high output density at early stage, and keeping high output density over a long time. SOLUTION: The cell of the solid electrolyte fuel cell is manufactured, in such a way that a solid electrolyte 31 whose main component is ZrO2 and a fuel electrode 33 are stacked in order on the surface of an air electrode 32, comprising a perovskite type composite oxide containing La and Mn, and the air electrode 32, the solid electrolyte 31, and the fuel electrode 33 are sintered simultaneously. The amount of Mn on a surface layer 45 of the solid electrolyte 31 is specified to be 1.5 wt.% or smaller.

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 in which a solid electrolyte and a fuel electrode are stacked on the surface of an air electrode.

[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.

[0003] In general, cylindrical and flat plate types of solid oxide fuel cells are known. Flat fuel cells are
Although it has the feature of high power density per unit volume of power generation, there are problems such as incomplete gas sealing and non-uniformity of temperature distribution in the cell for practical use.

On the other hand, in a cylindrical fuel cell,
Although the power density is low, the cell has high mechanical strength and can maintain uniform temperature in the cell. Both types of solid oxide fuel cells are being actively researched and developed utilizing their respective characteristics.

As shown in FIG. 2, a single cell of a cylindrical fuel cell has a porous cathode support tube 2 made of a LaMnO ₃ -based material having an open porosity of about 30 to 40%, and a Y electrode is formed on the surface thereof.
_A solid electrolyte 3 composed of ₂ O ₃ stabilized ZrO ₂ is coated, and a porous Ni-zirconia fuel electrode 4 is provided on the surface thereof.

In the fuel cell module, each single cell is connected via a LaCrO ₃ -based current collector (interconnector) 5. For power generation, air (oxygen) 6 flows inside the cathode support tube 2 and fuel (hydrogen) 7 flows outside, and 1000
It is performed at a temperature of 1050 ° C.

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 an extrusion method or the like, and then fired to form a cylindrical support. Then, a slurry of an air electrode, a solid electrolyte, a fuel electrode, and a current collector is applied to the outer peripheral surface of the support, and the slurry is sequentially fired and laminated, or an electrochemical vapor deposition method is applied to the surface of the cylindrical support. An air electrode, a solid electrolyte, a fuel electrode, and a current collector are sequentially formed by (EVD method), a plasma spraying method, or the like.

In recent years, a so-called co-sintering method has been proposed in which at least two of the constituent materials are simultaneously fired in order to simplify the manufacturing process of the cell and reduce the manufacturing cost. In this co-sintering method, for example, a solid electrolyte molded body and a current collector molded body are wound in a roll shape around a cylindrical air electrode molded body and simultaneously fired, and then a fuel electrode layer is formed on the surface of the solid electrolyte layer. Is the way. In order to simplify the process, a co-sintering method has been proposed in which a fuel electrode compact is further laminated on the surface of the solid electrolyte compact and fired simultaneously.

This co-sintering method is a very simple process with a small number of manufacturing steps, and is advantageous in improving the yield and cost reduction in manufacturing cells. In such a fuel cell by the co-sintering method, a solid electrolyte composed of Y ₂ O ₃ stabilized or partially stabilized ZrO ₂ is used, and the coefficient of thermal expansion matches the solid electrolyte. , LaMnO
_The perovskite-type composite oxide of No. _{3 in} which a part of La is substituted with Y and Ca is used (see Japanese Patent Application Laid-Open No. 10-162847).

[0010]

However, when a cylindrical fuel cell is manufactured using the above-described co-sintering method,
During co-sintering, Mn element, which is a component of the air electrode, diffuses in the solid phase toward the inside of the fuel electrode via the solid electrolyte. As a result, the amount of Mn in the fuel electrode increases, the polarization value of the fuel electrode site and the actual resistance value of the cell component increase,
As a result, there is a problem that the output density in the initial stage is low.

Further, when a cylindrical fuel cell having an effective length of 40 cm contributing to power generation is manufactured by using the above-described co-sintering method, the inside of the solid electrolyte and the inside of the solid electrolyte and between a plurality of cells can be obtained. The amount of diffusion of the Mn component from the air electrode inside the fuel electrode is different, and therefore, the dispersion of the polarization value of the fuel electrode site and the actual resistance value of the cell component is large, and the characteristic reproducibility of the manufactured cell is poor. However, there was a problem of lack of reliability.

According to the present invention, there is provided a solid material capable of minimizing variations in cell performance and improving reproducibility, obtaining a high output density at an initial stage, and maintaining a high output density for a long period of time. An object of the present invention is to provide an electrolyte fuel cell.

[0013]

According to the present invention, there is provided a solid oxide fuel cell according to the present invention, in which a surface of an air electrode made of a perovskite-type composite oxide containing at least La and Mn is coated with Z
In a solid electrolyte fuel cell in which a solid electrolyte containing rO ₂ as a main component and a fuel electrode are sequentially laminated, and the air electrode and the solid electrolyte are simultaneously sintered, a surface of the solid electrolyte on the air electrode side is provided. From the surface layer having a thickness of 30 μm to 1.5 μ% by weight or less. The fuel electrode is desirably sintered at the same time as the air electrode and the solid electrolyte because the process can be simplified.

In such a solid oxide fuel cell, a diffusion preventing layer containing CeO ₂ as a main component, for example, Ce in which Y and Zr are dissolved, is provided between the solid electrolyte and the air electrode.
By forming a diffusion prevention layer containing O ₂ as a main component,
Mn, which tends to diffuse from the air electrode to the fuel electrode via the solid electrolyte, can be blocked or suppressed by the diffusion preventing layer, and the Mn content in the surface layer having a thickness of 30 μm from the air electrode side surface of the solid electrolyte is 1.5 wt. % Or less, and the Mn content in the anode can be reduced, whereby the polarization value of the anode site and the actual resistance value of the cell component can be reduced, the power density can be increased, and the power density can be increased. Can be maintained over a long period of time.

This is because, when the amount of Mn present in the fuel electrode is large, the sinterability of the fuel electrode is excessively promoted, the grain growth of the metal particles in the fuel electrode becomes excessive, and the metal particles and the solid electrolyte This is because the contact area with the anode decreases, and the polarization value of the fuel electrode site increases. Further, since Mn is precipitated between the metal particles, the conductivity decreases, and the actual resistance value of the cell component increases. .

Then, a thickness of 30 μm formed from the surface of the solid electrolyte on the diffusion prevention layer side toward the fuel electrode of the solid electrolyte.
Is not more than 1.5% by weight in the surface layer of
In addition to the effect of reducing the amount of Mn in the fuel electrode, the actual resistance of the cell component (solid electrolyte) can be further reduced.
Within a cell having the same specifications, a difference in performance between cells can be suppressed. In particular, since the variation in performance inside the cell is reduced, the effective length (air electrode,
The length of the portion where the solid electrolyte and the fuel electrode are overlapped and laminated) is 4
In the power generation of a cylindrical cell (sometimes called a long cell) of 0 cm or more, cell destruction due to electrical local damage can be prevented.

In the present invention, it is desirable that the diffusion preventing layer contains CeO _{2 in} which Y and Zr are dissolved as a main component. CeO ₂ in which Y is dissolved (sometimes called YDC)
Is used as a starting material, and CeO in which Y and Zr are dissolved
₂ , or CeO _{2 in} which Y and Zr are dissolved, and Ce, Y
Because There is formed a diffusion barrier layer made of a mixture of ZrO ₂ were dissolved, the thermal expansion coefficient of the diffusion preventing layer can be brought closer by the cell components, and the diffusion preventing layer, the interfacial peeling between the solid electrolyte and the air electrode It is possible to suppress breakage due to heating and cooling during manufacturing or during power generation, thereby improving the cell manufacturing yield.

Further, by using YDC, Y is converted to Ce.
All can be dissolved in O ₂ or ZrO ₂ , and the precipitation of a Y ₂ O ₃ phase having a low coefficient of thermal expansion can be prevented in the diffusion prevention layer, and as a result, local unbonded portions are eliminated. Peeling can be prevented.

In the solid oxide fuel cell according to the present invention, the Mn content in the fuel electrode is desirably 0.2% by weight or less. By doing so, the polarization value of the fuel electrode site and the actual resistance value of the cell component can be further reduced.

Further, in the solid oxide fuel cell of the present invention, it is desirable that the solid electrolyte is ZrO ₂ containing Y ₂ O ₃ . Further, the diffusion prevention layer is made of CeO ₂ ,
Desirably, Zr and Y are dissolved. It is desirable that the diffusion preventing layer does not contain Sm.

Further, the solid oxide fuel cell of the present invention comprises, for example, ZrO ₂ in which Y is dissolved and CeO _{2 in} which Y is dissolved on the surface of an air electrode molded body containing at least La and Mn. After forming a coating film by applying the paste containing the solid electrolyte formed body and the fuel electrode formed body containing ZrO ₂ on the surface of the coating film, a stacked formed body is formed. It is formed by firing the body.

For example, when a cell is co-fired using a cylindrical air electrode material made of a perovskite-type composite oxide containing La, Ca, Y and Mn, each component element constituting the air electrode during co-sintering is obtained. Among them, the diffusion (evaporation and diffusion in the solid phase) of the Mn element is particularly fast. That is, during firing, Mn in the air electrode molded body tends to diffuse from the air electrode molded body to the fuel electrode molded body via the solid electrolyte molded body.

Therefore, according to the present invention, a paste containing ZrO ₂ in which Y is dissolved and CeO _{2 in} which Y is dissolved is applied to the surface of the air electrode molded body (including the calcined body). A solid electrolyte molded body (a concept including a calcined body) and a fuel electrode molded body are sequentially laminated and fired, so that CeO ₂ in which Y and Zr are dissolved as a solid solution, or Y and Zr is formed between the solid electrolyte and the air electrode. Zr is made of a mixture of ZrO ₂ to CeO ₂ and Y and Ce forms a solid solution in which a solid solution, Y and Zr diffusion preventing layer of CeO ₂ principal components solid solution is formed. The diffusion preventing layer can block or suppress Mn from diffusing from the air electrode molded body to the fuel electrode molded body via the solid electrolyte molded body, and reduce the amount of Mn diffusion in the solid electrolyte and the fuel electrode. As a paste, Y is ZrO ₂ or Ce
Without solid solution in O _2, it may be added as Y ₂ O _3.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid oxide fuel cell according to the present invention comprises a cylindrical solid electrolyte 31 having an air electrode 32 formed on the inner surface and a fuel electrode 33 formed on the outer surface, as shown in FIG.
The current collector (interconnector) 35 is electrically connected to the air electrode 32.

That is, the notch 36 is formed in a part of the solid electrolyte 31.
Is formed, a part of the air electrode 32 formed on the inner surface of the solid electrolyte 31 is exposed, and the surface of the solid electrolyte 31 near the exposed surface 37 and the notch 36 is covered with the current collector 35, Current collectors 35 are joined to the surfaces of both ends of the solid electrolyte 31 and the surface of the air electrode 32 exposed from the notch 36 of the solid electrolyte 31.

Current collector 35 electrically connected to air electrode 32
Are formed on the outer surface of the cell body 34 so as to cover the continuous same surface 39 having almost no level difference.
And are not electrically connected.

When connecting between the cells, the current collector 35 is electrically connected to the fuel electrode of another cell via Ni felt, thereby forming a fuel cell module. The continuous same surface 39 is formed by polishing the both ends of the solid electrolyte until both ends of the solid electrolyte and a part of the air electrode become continuous and substantially the same surface.

The solid electrolyte 31 is, for example, 3 to 15 mol%.
Partially stabilized or stabilized ZrO ₂ containing Y ₂ O ₃ is used. Further, as the air electrode 32, for example, La
Used is LaMnO _{3 in} which Ca or Sr is substituted by 10 to 30 atomic% and Y is substituted by 5 to 20 atomic%. As the current collector 35, for example, L in which Cr is substituted by Mg by 10 to 30 atomic% is used.
aCrO ₃ is used.

As the fuel electrode 33, 50 to 80% by weight N
A ZrO ₂ (containing Y ₂ O ₃ ) cermet containing i is used. The solid electrolyte 31, the current collector 35, and the fuel electrode 33 are not limited to the above examples, and may be made of known materials. The air electrode 32 may be made of a perovskite-type composite oxide containing at least La and Mn.

In the solid oxide fuel cell of the present invention, CeO is placed between the solid electrolyte 31 and the air electrode 32.
A diffusion prevention layer 41 containing ₂ as a main component is formed. This diffusion prevention layer 41 is made of CeO ₂ in which Y and Zr are dissolved.
As a main component, and desirably contains 70% by weight or more of CeO _{2 in} which Y and Zr are dissolved.
In particular, the CeO ₂ which CeO ₂ or Y and Zr, Y and Zr in solid solution is a solid solution, Ce, Y was dissolved Zr
It preferably comprises a mixture of O ₂ .

The diffusion preventing layer 41 has a composition formula of 1-z
{(CeO ₂ ) 1 -x (Y ₂ O ₃ ) x} · z} (ZrO ₂ )
1−y (Y ₂ O ₃ ) y}, where 0.2 ≦ x ≦
0.4, 0.05 ≦ y ≦ 0.08, 0.03 ≦ z ≦ 0.
It is desirable to satisfy Condition 3.

When x is less than 20 mol%, the thermal expansion coefficient of the diffusion preventing layer 41 tends to be higher than that of other cell components, and when x is more than 40 mol%, Y ₂
This is because O ₃ cannot be completely dissolved in CeO ₂ or ZrO ₂ and tends to precipitate as Y ₂ O ₃ .

By setting y to 5 to 8 mol%, the coefficient of thermal expansion of the diffusion preventing layer 41 can be made closer to that of other cell components. Further, when z is less than 3% by weight, a thermal expansion mismatch with the cell constituting member tends to occur as in the above case, and when z is more than 30% by weight, ZrO ₂ which easily diffuses Mn increases. This is because the effect of suppressing Mn diffusion is reduced.

The diffusion preventing layer 41 may further contain Ca and Y as air cathode components by diffusion, and the thickness of the diffusion preventing layer 41 is set at 2 from the viewpoint of matching thermal expansion coefficients between members. １５15 μm is desirable. In particular, the thickness is preferably 10 to 15 μm from the viewpoint of suppressing the difference in performance between cells and between cells.

Further, in order to suppress the difference in performance between cells and between cells, it is possible to adjust the ratio of the A site and the B site of the LaMnO ₃ -based composite oxide constituting the air electrode 32. is there. That is, the composition is preferably as close to the stoichiometric composition as possible so that the A site is less than the stoichiometric composition so as to be less than 1, and so as not to decompose the perovskite oxide. In particular, it is preferably 0.97 to 0.99.

The Mn content in the fuel electrode 33 is set to 0.2% by weight or less. Thus, the amount of Mn in the fuel electrode 33 is reduced to 0.1.
By setting the content to 2% by weight or less, the polarization value of the fuel electrode site and the actual resistance value of the cell component can be further reduced.

In the present invention, the Mn in the 30 μm thick surface layer 45 formed from the surface of the solid electrolyte 31 on the side of the diffusion preventing layer 41 toward the fuel electrode 33 of the solid electrolyte 31.
The amount is not more than 1.5% by weight.

As described above, in order to reduce the diffusion of the Mn component from the air electrode as compared with the prior art, it is necessary to increase the Mn diffusion preventing ability. For that purpose, the ZrO ₂ of the diffusion prevention layer 41 is used.
The amount must be reduced and the ceria (CeO ₂ ) content must be increased. On the other hand, simply increasing the content of ceria (CeO ₂ ) causes a mismatch in the coefficient of thermal expansion between the cell components (the solid electrolyte 31 and the air electrode 32), and as a result, the solid electrolyte 31 and the diffusion prevention layer 41 In this case, the cell yield is reduced due to the interface separation. From the above, it is better to use Y as the solid solution species in CeO ₂ than in Sm.
Is more preferable in that the content of CeO ₂ in the above can be increased.
As described above, by providing the diffusion preventing layer 41 and reducing the Mn content in the surface layer 45 to 1.5% by weight or less, in addition to the effect of reducing the Mn content in the fuel electrode 33, the actual resistance value of the cell component is further reduced. Can be lowered, and as a result,
Variations in performance between cells can be suppressed.

In the method for manufacturing the solid oxide fuel cell constructed as described above, first, a cylindrical air electrode molded body is formed. The cylindrical air electrode molded body is made of, for example, La ₂ O ₃ , Y ₂ O ₃ , CaCO ₃ and Mn ₂ O in accordance with a predetermined composition.
Weigh and mix ₃ raw materials.

Thereafter, for example, the mixture is calcined at a temperature of about 1500 ° C. for 2 to 10 hours, and then pulverized to a particle size of 4 to 8 μm. A binder is mixed and kneaded with the prepared powder to produce a cylindrical air electrode molded body by an extrusion molding method, further debindered, and calcined at 1200 to 1250 ° C. to form a cylindrical air electrode temporary body. Prepare a fired body. Since the diffusion of Mn is remarkable at 1400 ° C. or higher, Mn hardly diffuses at the calcining temperature of the air electrode compact.

Further, for example, a ZrO ₂ powder in which at least one of Y ₂ O ₃ and CaO is dissolved as a solid solution and a composition formula of (CeO ₂ )
CeO ₂ in which Y represented by 1-x (Y ₂ O ₃ ) x is dissolved
The powder is mixed and calcined, and then toluene is added as a solvent to the mixed powder whose particle size has been adjusted to prepare a paste. The paste is applied to the surface of a cylindrical air electrode calcined body to form a Mn diffusion preventing layer 41. Form a coating film. Y _{2 in the} paste
O ₃ may be present, but after firing. It is desirable that all be dissolved in ZrO ₂ or CeO ₂ . In addition, Mn
The diffusion prevention layer 41 may be prepared by temporarily forming a sheet using a paste and laminating the sheet on the surface of the air electrode calcined body. By doing so, the thickness variation of the Mn diffusion prevention layer 41 can be prevented.

As the sheet-like first solid electrolyte molded body,
Toluene, a binder, a slurry obtained by adding a commercially available dispersant to a predetermined powder, by a method such as a doctor blade, for example, using a molded thing to a thickness of 100 ~ 120μm, the cylindrical air electrode calcined body The first solid electrolyte molded body is adhered to the surface of the coating film of the diffusion preventing layer 41 formed on the surface and calcined to form the first solid electrolyte calcined body on the surface of the air electrode calcined body. In addition, although the first solid electrolyte molded body was calcined, it does not have to be calcined.

Next, a sheet-shaped fuel electrode molded body is manufactured. First, for example, a slurry prepared by adding toluene and a binder to a Ni / YSZ mixed powder prepared at a predetermined ratio is prepared. Similarly to the production of the first solid electrolyte molded body, the molded body is dried and formed into a sheet-shaped second solid electrolyte molded body having a thickness of, for example, 15 μm.

After printing and drying the fuel electrode layer molded body on the second solid electrolyte molded body, the fuel electrode layer molded body is printed on the first solid electrolyte calcined body.
The second solid electrolyte molded body on which the fuel electrode layer molded body is formed,
The first solid electrolyte calcined body is wound and laminated so that the second solid electrolyte molded body is in contact with the first solid electrolyte calcined body.

Next, as in the preparation of the solid electrolyte compact, 10
A current collector molded body having a thickness of 0 to 120 μm is attached to a predetermined location.

Thereafter, a laminated body of the cylindrical air electrode calcined body, the coating film of the diffusion preventing layer 41, the first solid electrolyte calcined body, the second solid electrolyte molded body, the fuel electrode molded body and the current collector molded body Is
For example, four layers are co-fired simultaneously at a temperature of 1400 to 1550 ° C. in the atmosphere.

Since the diffusion of Mn affects the firing temperature and the holding time, the Mn content can be further reduced by lowering the firing temperature as much as possible and shortening the firing time as much as possible.

In such a production method, ZrO containing Y as a solid solution
₂ , and a paste containing CeO _{2 in} which Y forms a solid solution,
Diffusion prevention layer 41 applied to the surface of a cylindrical air electrode calcined body
Is formed, and the solid electrolyte molded body and the fuel electrode molded body are sequentially laminated and then fired at the same time, so that the diffusion preventing layer 41 containing Y, Zr and Ce is provided between the solid electrolyte and the air electrode. Is formed, and the diffusion preventing layer 41 can suppress the diffusion of Mn from the air electrode to the solid electrolyte, and can reduce the amount of Mn diffusion in the fuel electrode.

Further, since the diffusion preventing layer of the present invention uses in advance ZrO ₂ in which Y having the same composition as that of the solid electrolyte layer and YDC whose coefficient of thermal expansion is close to the cell constituting member,
It is possible to prevent breakage of the cell during manufacturing and damage caused by heating and cooling during power generation.

Also, in the case of a cylindrical solid electrolyte fuel cell, the air electrode may be formed on one side of the solid electrolyte and the fuel electrode may be formed on the other side, and the structure is not limited to FIG. .

Further, in the above example, the calcined cathode electrode, the first
Although the example in which the solid electrolyte calcined body is formed has been described, these may be an air electrode molded body or a first solid electrolyte molded body.

[0052]

EXAMPLE In order to produce a cylindrical solid oxide fuel cell by a co-sintering method, first, a cylindrical air electrode calcined body was produced by the following procedure. La with commercial purity of 99.9% or more
Starting from ₂ O ₃ , Y ₂ O ₃ , CaCO ₃ , Mn ₂ O ₃ and calcining at 1500 ° C., (La _0.56 Y _0.14 Ca _0.3 )
_0.97 MnO ₃ and (La _0.56 Y _0.14 Ca _0.3 ) _0.98 M
nO ₃ was prepared and then crushed and adjusted to a particle size of 5 μm,
Using this, after extrusion molding, debubbling and calcination were performed under the conditions of 1250 ° C. to prepare a cathode calcined body. At this time, in order to confirm the effect of reducing the Mn diffusion on suppressing the performance variation, as described above, two types of air electrode calcined bodies having A / B site ratios of 0.97 and 0.98 were prepared.

Next, a slurry was prepared using ZrO ₂ powder containing Y ₂ O ₃ at a rate of 8 mol% and having an average particle size of 1 to ₂ μm, and was then 100 μm thick and 15 μm thick by a doctor blade method. Sheets as first and second solid electrolyte molded bodies were prepared.

Next, the production of the fuel electrode molded body will be described. Zr containing 8 mol% of Y ₂ O ₃ having an average particle diameter of 0.6 μm with respect to Ni powder having an average particle diameter of 0.4 μm.
O ₂ powder was prepared and the Ni / YSZ ratio (weight fraction) was 6
The mixture was prepared to be 5/35, crushed and mixed, and slurried.

Thereafter, the prepared slurry was printed on the entire surface of the second solid electrolyte molded body so as to have a thickness of 30 μm.

Next, commercially available La _{2 having} a purity of 99.9% or more is used.
Starting from O ₃ , Cr ₂ O ₃ , and MgO, this
(Mg _0.3 Cr _0.7 ) After weighing and mixing to a composition of _0.97 O ₃ , the mixture was calcined and pulverized at 1500 ° C. for 3 hours, a slurry was prepared using the solid solution powder, and a 100 μm-thick current collector was obtained by a doctor blade method. A molded body was produced.

ZrO containing 8 mol% of Y ₂ O ₃
And ₂ powder (8YSZ), formula _{(CeO 2) 1-x (} Y 2
O ₃₎ when expressed as x, i.e., Y ₂ O ₃ ZrO ₂ powder dissolved 8 mol% of, Y ₂ O ₃ was dissolved x mol% Ce
O ₂ powder was mixed so as to have the ratio shown in Table 1, and toluene was added as a solvent to the mixed powder to prepare a paste for a diffusion preventing layer. Further, a paste was prepared, and a sheet of a diffusion preventing layer was prepared by the doctor blade method.

First, a sheet of a diffusion prevention layer is laminated on the calcined body of the cathode, and the first solid electrolyte molded body is wound on the sheet in a roll shape so that both ends thereof are opened, and is heated at 1150 ° C. Calcination was performed for 5 hours. After calcination, the first
The solid electrolyte calcined body was polished flat between both ends so as to expose the air electrode calcined body, and worked so as to form a continuous same surface.

Next, the second solid electrolyte molded body having the fuel electrode molded body formed on the surface of the first solid electrolyte calcined body is brought into contact with the first solid electrolyte calcined body and the second solid electrolyte molded body. After drying, a current collector molded body was adhered to the same continuous surface, and then fired at 1550 ° C. for 3 hours in the atmosphere to produce a co-sintered body.

As a comparative sample, a ZrO ₂ powder containing 8 mol% of Y ₂ O ₃ was 20 wt%, and a molar ratio (Ce
O ₂ ) 0.8 (Sm ₂ O ₃ ) 0.2
8 mol of Y ₂ O ₃ paste prepared by mixing 0 wt%
% Of a ZrO ₂ powder was applied to the air electrode calcined body to prepare a co-sintered body in the same manner as described above.

Next, using the above-mentioned co-sintered body, the amount of Mn diffusion in the surface layer having a thickness of 30 μm from the inside of the fuel electrode and from the interface between the solid electrolyte and the diffusion preventing layer to the inside of the solid electrolyte was evaluated. did. Evaluation first, length 50cm
The upper, middle and lower parts of the co-sintered body were cut out to a length of about 10 mm. The components were quantified. Next, the concentration of the Mn component with respect to all the components was calculated. Table 1 shows the results.

Next, a power generation length of 50 cm (effective length of 4 cm) is used.
(0 cm), a sealing member was joined to one end of the co-sintered body. The joining of the sealing member was performed in the following procedure. A slurry is prepared by adding water as a solvent to ZrO ₂ powder having an average particle diameter of 1 μm and containing Y ₂ O ₃ at a ratio of 8 mol%, and one end of the co-sintered body is immersed in the slurry to obtain a slurry. It was applied to the outer peripheral surface at one end so as to have a thickness of 100 μm, and dried.

A molded article having a cap shape as a sealing member was subjected to isostatic pressing (rubber pressing) using a powder having the same composition as the above slurry composition, followed by cutting. afterwards,
One end of the co-sintered body coated with the slurry was inserted into a molding for a sealing member, and baked at 1300 ° C. for 1 hour in the atmosphere.

Next, a sample for power generation evaluation was prepared. Using a long cell having a length of 50 cm, three kinds of cut-out cells each having an electrode length of 2.5 cm were prepared as samples of the upper, middle, and lower portions of the cell (abbreviated as cells A, B, and C). For the sample of the present invention, the air electrode was dissolved with hydrochloric acid and the diffusion prevention layer was subjected to x-ray diffraction measurement. As a result, CeO ₂ in which Y and Zr were dissolved in solid form was mainly used, and Y was all CeO 2. ₂ and a Y ₂ O ₃ phase was not present. No peeling of the solid electrolyte or the like was observed.

The power generation is performed by using each of the above-mentioned cut cells for 100 times.
At 0 ° C., air was flowed inside the cell and hydrogen was flown outside, and the performance was measured and evaluated based on the initial value when the output value was stabilized and the value after holding for 1000 hours. These measurement results are shown in Table 1 together with the results of the Mn amount.

[0066]

[Table 1]

According to Table 1, in the sample of the solid oxide fuel cell of the present invention, the Mn content of the fuel electrode portion and the surface layer portion of the solid electrolyte are 0.2% by weight and 1.5% by weight, respectively. The power density at each site in one cell exceeded 0.4 W / cm ² from the beginning,
It can be seen that the output density is almost stable even after a lapse of time.

The variation in the amount of Mn in the surface layer of the present invention was 0.015% by weight or less in A, B and C. The output densities of A, B, and C were almost unchanged.

In the sample of the present invention, the air electrode A / B
It is understood that the closer the site ratio is to the constant ratio, and the more the thickness of the diffusion prevention layer is set to 10 to 15 μm, the more effectively the amount of Mn diffusion can be controlled.

On the other hand, the sample No. In Examples 1 and 8, the amount of Mn in the surface layer of the solid electrolyte varies, and it can be seen that the effect is directly reflected in the variation in the output density. In addition, the sample No. 8, it can be seen that the Mn diffusion amount is large and the initial output density is low.

[0071]

As described in detail above, in the solid oxide fuel cell of the present invention, for example, by forming a diffusion prevention layer containing CeO ₂ as a main component between the solid electrolyte and the air electrode, Mn, which tends to diffuse from the air electrode to the fuel electrode via the solid electrolyte, can be blocked or suppressed by the diffusion preventing layer, and the Mn content in the surface layer of the solid electrolyte can be 1.5% by weight or less. The Mn content in the electrode can be reduced.

As a result, the polarization value of the fuel electrode site and the actual resistance value of the cell components can be reduced, the power density can be increased, and a high power density can be maintained for a long period of time. Variations in performance between cells can be suppressed. In particular, since the variation in performance inside the cell is reduced, it is possible to prevent cell breakage due to electrical local breakage in power generation of a long, for example, cylindrical cell having an effective length of 40 cm.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a cylindrical solid oxide fuel cell according to the present invention, and FIG. 1 (b) is an enlarged cross-sectional view showing a part of FIG.

FIG. 2 is a perspective view showing a conventional cylindrical solid oxide fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 31 ... Solid electrolyte 32 ... Air electrode 33 ... Fuel electrode 35 ... Current collector 41 ... Diffusion prevention layer 45 ... Surface layer

Claims (4)

[Claims] 1. The method according to claim 1, wherein the surface of the air electrode made of a perovskite-type composite oxide containing at least La and Mn is coated with Zr.
In a solid electrolyte fuel cell in which a solid electrolyte containing O ₂ as a main component and a fuel electrode are sequentially laminated, and the air electrode and the solid electrolyte are simultaneously sintered, a surface of the solid electrolyte on the air electrode side is provided. From the surface layer 30 μm thick
A solid oxide fuel cell having an n content of 1.5% by weight or less. 2. The solid oxide fuel cell according to claim 1, wherein a diffusion preventing layer mainly composed of CeO ₂ is formed between the air electrode and the solid electrolyte. 3. The diffusion preventing layer is made of a solid solution of Y and Zr.
3. The solid oxide fuel cell according to claim ₂ , comprising eO ₂ as a main component. 4. The solid oxide fuel cell according to claim 1, wherein the solid electrolyte is ZrO ₂ containing Y ₂ O ₃ .