JP2003173801A - Solid electrolyte fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolyte fuel cell, and its manufacturing method, equipped with an anti-reaction layer for effectively preventing reaction of solid electrolyte and each electrode. <P>SOLUTION: The solid electrolyte fuel cell is provided with a fuel electrode equipped on one side of a planar solid electrolyte and an air electrode equipped on the other side of the solid electrolyte, and an anti-reaction layer fitted between the solid electrolyte and at least either the fuel electrode or the air electrode with a porosity to be not more than 25%. By controlling the porosity at 25% or under, a solid electrolyte fuel cell with a good low electric resistance. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat plate type solid electrolyte fuel cell having a fuel electrode and an air electrode on both sides of a flat plate type solid electrolyte, and introducing a reaction preventive layer at the electrode interface of the solid electrolyte, and its manufacture. It is about the method. More specifically, the present invention relates to a solid oxide fuel cell having a low internal resistance using a reaction preventive layer that effectively prevents a reaction between a solid electrolyte and each electrode, and a method for producing the same.

[0002]

2. Description of the Related Art When manufacturing a solid oxide fuel cell (hereinafter abbreviated as "fuel cell"), the reactivity between the zirconia-based electrolyte and the air electrode material is high. There is a problem that a reaction phase of resistance is generated, the internal resistance of the entire fuel cell increases, and the output of the fuel cell decreases. In addition, since the reactivity of the lanthanum garde-based electrolyte with the fuel electrode material and the air electrode material is also high, there is a problem that a reaction phase is similarly generated at the interface between the solid electrolyte and each electrode, which causes a reduction in the output of the fuel cell. It was To solve the problem, there is a study to prevent the reaction by firing a green sheet for reaction prevention layer containing cerium oxide as a main component on the fired solid electrolyte, and further firing each electrode. Arisaka, and
M. Watanabe, Solid State Ionics, 135, 347 (2000) and HU
chida, S.Arisaka, and M.Watanabe, Erectrochem.Solid-S
Tate. Lett., 2, 428 (1999), etc.

[0003]

However, since the structure of the reaction-preventing layer in the above-mentioned document has pores in places, the electrode material and the solid electrolyte directly contact with each other through the pores to react with each other. A reaction phase may form. Also,
In general, the reaction preventive layer is required to have a low electric resistance, that is, a high oxygen ion conductivity. Therefore, a dense one in which particles are connected to each other is preferable. Therefore, when forming the reaction preventive layer containing cerium oxide as a main component on the surface of the zirconia-based electrolyte, the baking temperature is raised to densify the reaction preventive layer. However, if the baking temperature is unduly raised, the reaction between the electrolyte and the reaction preventive layer may lead to a decrease in ionic conductivity.

Further, the process of baking the reaction preventive layer on the surface of the solid electrolyte after baking is a two-step baking process, so that the cost associated with baking increases. The present invention solves the above problems, and provides a solid oxide fuel cell having a low internal resistance using a reaction preventive layer that effectively prevents a reaction between a solid electrolyte and each electrode, and a method for producing the same. The purpose is to

[0005]

The solid oxide fuel cell of the present invention comprises a flat solid electrolyte, a fuel electrode provided on one surface of the solid electrolyte, and a fuel electrode provided on the other surface of the solid electrolyte. And a reaction prevention layer which is provided between the solid electrolyte and at least one of the fuel electrode and the air electrode, and which is Ce _1-x Ln _x O _2-δ having a porosity of 25% or less. , Are provided. Ln is a rare earth element, and the range of x is 0.05 ≦ x ≦ 0.3. In addition, δ is the amount of oxygen deficiency.

Further, the reaction preventing layer contains Ga element,
The content of the Ga element is 0.05 to 1.5 m in terms of oxide.
can be ol%. The thickness of the reaction preventive layer may be 1 to 20 μm. Furthermore, the thickness of the solid electrolyte can be 10 times or more that of the reaction preventive layer. The solid electrolyte is zirconia (Z) stabilized with Ln ₂ O ₃ (where Ln is a rare earth element).
rO ₂ ), or lanthanum garde (LaGaO ₃ ) doped with at least one of Sr and Mg.

The method for producing a solid oxide fuel cell is characterized in that a laminated body in which a green sheet for a reaction preventing layer is laminated is formed on the surface of a green sheet for a solid electrolyte, and then the laminated body is simultaneously fired. . The firing can be performed under the condition that the shrinkage rate when the green sheet for solid electrolyte is fired alone is smaller than the shrinkage rate when the green sheet for reaction prevention layer is fired alone. Furthermore, the firing temperature of the laminate is 1250 to 155.
It can be 0 ° C. Further, the average particle size of the raw material powder of the green sheet for reaction prevention layer can be 0.3 to 3 μm.

[0008]

EFFECTS OF THE INVENTION According to the solid oxide fuel cell of the present invention, by using a dense reaction preventing layer having a porosity of 25% or less, the solid electrolyte can be provided between at least one of the fuel electrode and the air electrode and the solid electrolyte. The reaction can be effectively prevented, and a solid oxide fuel cell having a small internal resistance can be obtained. In particular, when the reaction preventive layer is made of Ce _1-x Ln _x O _2-δ , the ionic conductivity is high and the reactivity between the solid electrolyte and each electrode can be lowered. Furthermore, by containing Ga element in a predetermined ratio, a densified reaction preventing layer can be easily obtained.

The thickness of the reaction preventive layer is 1 to 20 μm.
By setting m, the reaction between the solid electrolyte and the reaction preventive layer can be effectively prevented, and the electric resistance can be made low. Further, by making the thickness of the solid electrolyte 10 times or more that of the reaction preventive layer, it is possible to prevent warpage of the solid oxide fuel cell due to the difference in shrinkage ratio between the reaction preventive layer and the solid electrolyte during sintering. You can

According to the method for producing a solid oxide fuel cell of the present invention, the solid electrolyte green sheet and the reaction preventive layer green sheet are simultaneously fired, so that the solid electrolyte green sheet shrinks during sintering. The reaction preventing layer green sheet can be forcibly shrunk, the reaction preventing layer can be densified, and the porosity can be controlled. In particular, by setting the shrinkage ratio when the solid electrolyte green sheet is fired alone to be smaller than the shrinkage ratio when the reaction prevention layer green sheet is fired alone, the reaction prevention layer green sheet. It is possible to reduce the shrinkage rate and to make it more compact. Further, by simultaneously firing the solid electrolyte green sheet and the reaction prevention layer green sheet at a firing temperature within a predetermined range, while preventing the reaction between the solid electrolyte and the reaction prevention layer while densifying the reaction prevention layer. You can Further, by limiting the average particle size of the raw material powder of the reaction preventive layer, the reaction between the solid electrolyte and the reaction preventive layer can be prevented and the porosity can be controlled.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
Reveal The solid oxide fuel cell of the present invention comprises electrodes
Direct contact between the material and the solid electrolyte
For the reaction prevention layer to be introduced to prevent the
The porosity of the reaction-prevention layer should be
The feature is that the reaction prevention layer is made finer.
It The present inventors have controlled the porosity by various methods.
As a result, the porosity was 25% or less (preferably 24).
% Or less, more preferably 23% or less),
It is possible to effectively prevent the reaction between each electrode and the solid electrolyte.
I found out that In addition, in the grain boundary of the reaction prevention layer
Electric resistance also decreases, and porosity exceeds 25%
In comparison, the performance improvement becomes clear. Above "porosity" is
Note: Take a cross-section of the "reaction prevention layer" and make sure that the entire
The ratio of the area occupied by the created pores. Also, the porosity is 2
Within 5% is more than 25%,
This is because the performance improvement of the output density becomes clear. Above "C
e_1-xLn_xO_2-δIs a rare earth element
Elementary, that is, at least selected from the group consisting of Sc and Y
Both are a kind. Of these rare earth elements, Sm and
And Gd are preferred. Further, as a specific example, Ce_0.8S
m_0.2O _1.9(Hereinafter referred to as SDC) and Ce_0.8Gd_0.2O
_1.9(Hereinafter referred to as GDC).

Further, in the reaction preventing layer, the Ga element is converted into an oxide in an amount of 0.05 to 1.5 mol% (preferably, 0.1.
1-1 mol%, more preferably 0.3-1 mol
%) Is preferably contained. By containing the Ga element, the reaction preventing layer can be easily densified, the porosity can be lowered, and the electric resistance can be further reduced. Further, if the content of Ga element is less than 0.05 mol%, the effect is not clearly recognized. On the other hand, 1.5m
If it is added in excess of ol%, the electric resistance of the reaction-preventing layer tends to increase, which is not preferable. The reaction-preventing layer may contain various components and additives for other purposes as long as it does not impair the ionic conductivity and does not impair the effect of preventing the reaction.

Next, the solid oxide fuel cell of the present invention is
By providing the reaction preventive layer of the present invention between the solid electrolyte and the fuel electrode and / or the air electrode, it is possible to effectively prevent the reaction between each electrode and the solid electrolyte,
Generation of a high resistance reaction phase is suppressed. As a result, the solid oxide fuel cell of the present invention has extremely low electric resistance and improved performance. The reaction preventing layer of the present invention can be provided between the solid electrolyte and the air electrode, between the solid electrolyte and the fuel electrode, or both. In particular, it can be provided at the electrode interface of the solid electrolyte where the reaction easily occurs.

The thickness of the reaction preventive layer is 1 to 20 μm (preferably 1 to 10 μm, more preferably 1 to 5 μm).
m, particularly preferably 2 to 5 μm). When it is less than 1 μm, the front and back are easily communicated with each other due to pores, and the reaction between the solid electrolyte and each electrode tends to occur at that portion, which is not preferable. In addition, a reaction occurs at the interface between the solid electrolyte and the reaction preventive layer during the heat treatment for fixing the reaction preventive layer on the solid electrolyte, and a high resistance reaction phase is easily formed, which is not preferable. On the other hand, if it exceeds 20 μm, the ion migration resistance in the reaction preventive layer tends to increase, which is not preferable. Therefore, it is preferable that the thickness of the reaction preventing layer is as thin as possible.

The thickness of the solid electrolyte is 10 times or more that of the reaction preventive layer. When the thickness of the solid electrolyte is 10 times or more that of the reaction preventive layer, the warp of the fuel cell due to the difference in shrinkage rate between the reaction preventive layer and the solid electrolyte during sintering can be prevented. That is, by making the solid electrolyte thicker than the reaction prevention layer, the fuel cell can be fired almost without being affected by the reaction prevention layer.

As the solid electrolyte, any conventionally known solid electrolyte may be used. In addition, Ln (however,
Ln is a rare earth element stabilized zirconia (Zr
O ₂ ), or lanthanum garade (LaGaO ₃ ) doped with either or both of Sr and Mg, for example, zirconia-based oxide, LaGaO ₃ -based oxide, B
Examples thereof include aCeO ₃ based oxide. This is because these are materials that can be stably used as solid electrolytes for fuel cells and have excellent ionic conductivity. Zirconia-based electrolyte, since the reaction with the air electrode is likely to occur, it is preferable to introduce the reaction preventive layer of the present invention at the interface between the solid electrolyte and the air electrode, by using the reaction preventive layer of the present invention, The fuel cell characteristics are effectively improved. Also,
In the lanthanum garde-based electrolyte, the constituent elements are easily diffused at both the interface between the fuel electrode and the solid electrolyte and the interface between the air electrode and the solid electrolyte. Therefore, it is preferable to introduce the reaction preventive layer into both interfaces.

As the fuel electrode, any conventionally known material may be used. For example, a metal such as Au, Pd, Ni and Fe, or the above metal and a metal oxide such as ZrO ₂ , CeO ₂ or MnO ₂ may be used. Can be mentioned. Also,
The air electrode may be any conventionally known material, for example, platinum, or a metal oxide such as lanthanum oxide, strontium oxide, cerium oxide, cobalt oxide, manganese oxide, iron oxide or a combination thereof. Examples thereof include oxides.

Further, according to the method for producing a solid oxide fuel cell of the present invention, the solid electrolyte green sheet and the reaction preventive layer green sheet are simultaneously fired,
Due to the shrinkage of the solid electrolyte during sintering, the reaction-preventing layer can be forcibly contracted, the reaction-preventing layer can be densified, and the porosity can be controlled. Then, the fuel electrode and the air electrode are formed simultaneously or one at a time on the solid electrolyte on which the reaction prevention layer is formed. Either the fuel electrode or the air electrode may be formed first. Each of the above-mentioned "green sheets" is a sheet that includes not only the unfired body but also the calcined body.

In particular, the shrinkage factor when the green sheet for solid electrolyte is fired alone is set to be smaller than the shrinkage factor when the reaction preventive layer is fired alone, so that the reaction preventive layer is further shrunk. It is possible to further densify (reduce the shrinkage rate). This "contraction rate"
Is a value obtained by dividing the width Y of the sintered body by the width X of the green sheet by sintering the corresponding portion alone. (Shrinkage rate = Y ÷
X) The difference in shrinkage may be any, but it is preferable that the shrinkage A of the green sheet for the solid electrolyte and the shrinkage of the green sheet for the reaction preventive layer be such that the shrinkage is effective and there is no warpage. The ratio of B (the value of A ÷ B) is 0.80 to 0.98 times the shrinkage of the solid electrolyte, and more preferably 0.85.
It is preferably about 0.95 times.

Although any conventionally known method may be used as the firing method, the solid electrolyte and the reaction-preventing layer may be 1250 to 1550 ° C. (preferably 1250 to 1550 ° C.).
The firing temperature can be 1550 ° C., more preferably 1300 to 1500 ° C., and particularly preferably 1350 to 1500 ° C.). When the temperature is lower than 1250 ° C, it is difficult for the solid electrolyte and the reaction preventing layer to be sufficiently densified, and it is difficult to use as a fuel cell. Also, 1
If the temperature exceeds 550 ° C, a reaction occurs at the interface between the solid electrolyte and the reaction preventive layer during sintering to form a high resistance reaction phase, which tends to deteriorate the fuel cell performance.

The average particle diameter of the raw material powder for the reaction prevention layer is 0.3 to 3 μm (preferably 0.5 to 2.5 μm).
m, and more preferably 0.5 to 1.5 μm).
When the average particle size of the raw material of the reaction preventive layer is less than 0.3 μm, a reaction is likely to occur at the interface between the solid electrolyte and the reaction preventive layer at the time of sintering, and a high resistance reaction phase is generated to deteriorate the performance of the fuel cell. Tend to do. On the other hand, if the average particle size exceeds 3 μm, the powder packing density of the reaction-preventing layer compact becomes low when the green sheet for the reaction-preventing layer is formed on the solid electrolyte compact or the calcined body. Porosity tends to remain in the reaction preventive layer even after firing, and it is difficult to control the porosity.

[0022]

EXAMPLES The present invention will be specifically described below with reference to examples. 1. Sample preparation Yttria-stabilized zirconia (8mo
1% Y ₂ O ₃ -92 mol% ZrO ₂ , hereinafter abbreviated as 8YSZ), and ceria (Sm _0.2 Ce _0.8 O _1.9 , hereinafter abbreviated as SDC) doped with Samaria as a reaction-preventing layer was used to perform each test. It was In addition, YSZ powder is molded into a disk shape and subjected to cold isostatic pressing (CIP) for 150
A pressure of 0 kg / cm ² was applied to obtain a molded body substrate. Further, SDC of the reaction preventing layer material was obtained by mixing samarium oxide and cerium oxide in a predetermined amount in ethanol and then calcining at 1400 ° C. for 6 hours to obtain SDC powder. Then, it was crushed in ethanol to obtain a powder having a controlled particle size and made into a paste. The SDC paste was screen-printed on the YSZ compact and co-fired at the temperatures shown in Table 1 below to obtain a sample. In addition, this time, although an example is shown with the powder obtained by the solid phase method, it has been confirmed that the SDC powder obtained by the coprecipitation method has the same effect.

2. Example 1 (1) Measuring method In Example 1, the following measurements were performed. The details are shown below. Measurement of thickness of reaction-preventing layer, measurement of porosity The thickness of reaction-preventing layer and porosity of reaction-preventing layer were measured from a photograph obtained by a field emission electron microscope (hereinafter abbreviated as FE-SEM). . The obtained disk-shaped sample was cut in half, embedded with an epoxy resin, and then polished into a mirror surface so that a cross section could be seen. With respect to the mirror-polished cross section, a photograph was taken with a FE-SEM in a field of view of 500 times, and the thickness of the reaction-preventing layer was determined from the dimension on the photograph. The porosity of the reaction preventive layer is F
Using E-SEM, the width of the short side of the image is 8 times the thickness of the reaction prevention layer
After obtaining an SEM photograph so that the entire image would be the structure of the reaction-preventing layer in the field of view corresponding to 0%, the pores of the obtained electron microscope were colored white and the SDC texture was colored black, and image analysis on a computer was performed. The area ratio of the pores (white parts) was determined by software, and the ratio was defined as the porosity.

Measurement of Average Particle Size The powder was dispersed in an aqueous solution of sodium hexametaphosphate, and the particle size distribution was measured by a laser diffraction type particle size distribution measuring device. The average particle size obtained from the results is shown as the measurement result. Shrinkage of the solid electrolyte green sheet, and shrinkage of the reaction-prevention layer green sheet Shrinkage of the solid electrolyte green sheet, and shrinkage of the reaction-prevention layer green sheet The shrinkage alone is calculated from the following formula: It was (Shrinkage rate) = (Sintered body diameter) / (Green sheet diameter)

Evaluation of electrical characteristics 0.5 mm of the sample prepared by the procedure of “1. Preparation of sample”
A porous platinum electrode is baked as a counter electrode on the surface having no reaction prevention layer, and La _0.6 Sr _0.4 CoO is formed on the other surface.
_3-δ (hereinafter abbreviated as LSC) was baked as an air electrode, and the reference electrode was taken out to a portion of the sample where the reaction-preventing layer was present, which could be directly fixed to the electrolyte. Here, the electrode area of the counter electrode and the air electrode was 0.785 cm ² , and a current of 200 mA was applied between the counter electrode and the air electrode under the atmospheric pressure of 800 ° C., and the change in the voltage between the reference electrode and the air electrode that was dropping at that time was measured. did.
This evaluation method is an evaluation by a half cell of a solid oxide fuel cell, but the evaluation of the fuel cell by improving the performance of the reaction preventive layer formed on the air electrode side is sufficiently possible by this method.

(2) Measurement Results For the sample obtained by co-firing the solid electrolyte (8YSZ) and the reaction preventive layer (SDC), the porosity and the electrical characteristics were evaluated by the methods shown in the above Tables 1 and 2. Shown in.

[0027]

[Table 1]

From the results shown in Table 1, it can be seen that Samples 1, 6, 7 and 14 which are comparative examples having a porosity of more than 25% have poor electrical characteristics. Sample 1 was co-fired at 1200 ° C., but the reaction preventive layer had a porosity of 32% and was not sufficiently densified, and accordingly, it was found that the voltage drop was large and the electric resistance was large. . Sample 5 is a sample prepared by co-firing at a firing temperature of 1600 ° C. and a porosity of 3%.
However, as a result of electrical characteristics evaluation by the DC method, it was found that the voltage drop was very large and the electric resistance was large. When the interface between the solid electrolyte and the reaction preventive layer of Sample 5 was examined with an energy dispersive X-ray detector (hereinafter abbreviated as EDS), it was confirmed that a high resistance reaction phase was formed. From this, it was found that the optimum co-firing temperature was 1250 to 1550 ° C. Sample 6 is a sample obtained by baking SDC as a reaction-preventing layer on the solid electrolyte sintered body and firing twice, but the porosity is 36% and the sample is not sufficiently densified.
As a result, the voltage drop increased and the electrical resistance was found to be high.

Samples 7 to 9 are the results of investigating the influence of the thickness of the solid electrolyte on the production of fuel cells. As a result, in the sample 7, the solid electrolyte was thinner than the reaction preventive layer (100: 15), so that the fuel cell was warped. It was found that as the thickness of the solid electrolyte became thinner, the stress forcibly contracting the reaction-preventing layer tended to become smaller, and the porosity of the reaction-preventing layer was not sufficiently obtained. Therefore, in sample 7, the porosity is 28%,
The electric resistance was not good. Good results were obtained for sample 8 (200: 15) and sample 9 (300: 15). Therefore, the thickness of the solid electrolyte is optimally 10 times or more that of the reaction preventive layer.

Sample 10 has a reaction preventive layer having a thickness of 25 μm.
Since it was made thicker, it could not be sufficiently shrunk, and it was found that even though the simultaneous firing was performed, only the electrical characteristics comparable to those of the sample 6 of the conventional method fired twice were obtained. For this reason,
It can be seen that the optimum thickness of the reaction prevention layer is 20 μm or less. Samples 11 to 14 are the results of examining the average particle size of the reaction preventive layer SDC powder. From the results, sample 11
It was found that when powder having an average particle size of less than 0.3 μm was used, the porosity was 4% and the density was high, but the electrical characteristics had a large voltage drop and the performance was poor. When the cause of this was investigated at the solid electrolyte-reaction prevention layer interface using EDS, it was confirmed that a high resistance reaction phase was formed. Further, since the sample 14 had an average particle size of more than 3 μm, the porosity was 42%. It is considered that the powder packing density was low at the time of forming the reaction preventing layer green sheet. Therefore, the reaction prevention layer SDC
The optimum average particle diameter of the powder is 0.3 to 3 μm.

In all of Samples 1 to 14, the shrinkage rate of YSZ which is the solid electrolyte is smaller than that of SDC which is the reaction preventing layer. For this reason, in the sample in which other conditions are favorable, the reaction preventive layer which is effectively shrunk and densified is obtained by the simultaneous firing, and the porosity is controlled.

3. Example 2 The amount of gallium added was x mol%, and Ce _0.8 Sm was used.
_The reaction-preventing layer powder was synthesized so as to have a composition of _(0.2-0.01x) Ga _0.01x O _{2 -δ} , and changes in the characteristics depending on the amount added were investigated. The results are shown in Table 2.

[0033]

[Table 2]

From the results shown in Table 2, the amount of Ga added was 0.05.
It was confirmed that the porosity tends to decrease in the region of mol% or more, and the electrical characteristics are accompanied by a decrease in the voltage drop. It was confirmed that the porosity of the sample added with 2 mol% or more of Ga remained small but the amount of voltage drop increased. Therefore, 0.1 to 1 mo
It was confirmed that by adding 1% of Ga, the shrinkage during sintering of the reaction preventive layer was improved, and more favorable characteristics were obtained.

4. Example 3 The solid electrolyte was La _0.9 Sr _0.1 Ga _0.8 Mg _0.2 O _2.85 (L
The same experiment as in Example 1 was performed as SGM). The results are shown in Table 3.

[0036]

[Table 3]

From Table 3, it can be seen that, as compared with Example 1 in which YSZ is used as the electrolyte under the same conditions, the porosity and the voltage drop are the same or slightly improved. From this result, it is possible to form a dense reaction-preventing layer with LSGM.
It was confirmed that the formation by co-firing is also effective when forming on top. When LSGM is used as a solid electrolyte,
It is conceivable that the reaction prevention layer is applied to both the fuel electrode side and the air electrode side, and the fuel cell performance is improved by using the reaction prevention layer having good electric characteristics.

It should be noted that the present invention is not limited to the above-described embodiments, but various modifications may be made within the scope of the present invention according to the purpose and application. That is, the solid electrolyte is not limited to YSZ and LSGM in the examples, and various known solid electrolytes can be used. Further, the kind of the reaction preventing layer is not limited to the SDC of the above-mentioned examples, and various ceria compounds and the like can be used.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masaaki Hattori             14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi Japan special             Within Toyo Co., Ltd. F term (reference) 5H026 AA06 BB01 BB02 BB08 CX01                       EE12 HH00 HH03 HH04 HH05                       HH08

Claims (9)

[Claims] 1. A flat solid electrolyte, a fuel electrode provided on one surface of the solid electrolyte, an air electrode provided on the other surface of the solid electrolyte, the solid electrolyte, the fuel electrode, and It is provided between at least one of the air electrodes,
A solid oxide fuel cell, comprising: a reaction preventive layer made of Ce _1-x Ln _x O _2-δ having a porosity of 25% or less. However, Ln is a rare earth element, and the range of x is 0.05 ≦ x ≦ 0.3. 2. The reaction preventing layer contains a Ga element,
The content of element a is 0.05 to 1.5 mol in terms of oxide.
%, The solid oxide fuel cell according to claim 1. 3. The solid oxide fuel cell according to claim 1, wherein the reaction prevention layer has a thickness of 1 to 20 μm. 4. The solid oxide fuel cell according to claim 1, wherein the thickness of the solid electrolyte is 10 times or more that of the reaction prevention layer. 5. The solid electrolyte is Ln ₂ O ₃ (where L is
n is a rare earth element) stabilized zirconia (Zr
O _2), or solid oxide fuel cell according to any one of claims 1 to 4 at least one of Sr and Mg is doped lanthanum gallate de (LaGaO _3). 6. The method for producing a solid oxide fuel cell according to claim 1, wherein a green sheet for reaction prevention layer is laminated on a surface of the green sheet for solid electrolyte. A method for producing a solid oxide fuel cell, which comprises forming a laminated body and then simultaneously firing the laminated body. 7. The firing according to claim 6, wherein the shrinkage rate when the green sheet for solid electrolyte is fired alone is smaller than the shrinkage rate when the green sheet for reaction prevention layer is fired alone. Method of manufacturing solid oxide fuel cell. 8. The firing temperature of the laminate is 1250 to 15
It is 50 degreeC, The manufacturing method of the solid oxide fuel cell of Claim 6 or 7. 9. The average particle diameter of the raw material powder of the green sheet for reaction prevention layer is 0.3 to 3 μm.
The method for manufacturing a solid oxide fuel cell according to any one of the above.