KR102287531B1 - Single cell for solid oxide fuel cell and solid oxide fuel cell conataining thereof - Google Patents

Abstract

A unit cell for a solid oxide fuel cell according to the present invention comprises: a first cathode active layer including a compound of Formula 1 below and ceria doped with a first rare earth metal; and a second cathode active layer including ceria doped with a compound of Formula 2 and a second rare earth metal.
[Formula 1]
(La _{1 - x} Sr _x ) _z Co _{1 - y} Fe _y O ₃
In Formula 1, x, y, and z satisfy 0.2≤x≤0.5, 0.5≤y≤0.8, and 0.95≤z≤0.98.
[Formula 2]
(Sm _{1 - a} Sr _a ) _b CoO ₃
In Formula 2, a and b satisfy 0.3≤a≤0.5 and 0.95≤b≤0.98.

Description

Single cell for solid oxide fuel cell and solid oxide fuel cell including same

The present invention relates to a single cell for a solid oxide fuel cell including a cathode active layer having two layers.

In a fuel cell, oxygen is supplied to the cathode and fuel gas is supplied to the anode, and an electrochemical reaction in the form of a reverse reaction of electrolysis of water proceeds to generate electricity, heat, and water with high efficiency without causing pollution. do. In particular, the solid oxide fuel cell (SOFC) is a type of fuel cell in which the electrolyte is a solid metal oxide with a dense structure and oxygen ions are transported from the cathode to the anode. It is possible to use various fuels through direct internal reforming without doing so, and since it discharges high-temperature gas, there is an advantage of thermal combined power generation using waste heat.

Currently, studies on SOFCs are being actively conducted, and among them, studies for lowering the operating temperature of SOFCs are also being conducted. When the operating temperature of the SOFC is lowered, the high temperature durability of metal materials can be improved and the application field can be expanded to the transportation field through fast operation. There is a problem that occurs.

In SOFC single cells, as the operating temperature decreases, the oxygen ion conductivity of the electrolyte material decreases rapidly, and the catalytic activity and electrochemical properties of the cathode decrease. Therefore, various new materials have been developed to overcome this. In particular, for cathode materials, various MIEC (Mixed Ionic & Electronic Conductors) have been developed for medium and low temperature operation. However, the biggest disadvantage of the developed materials is that the thermal expansion coefficient is too large, so that it cannot be effectively applied to a single cell.

Republic of Korea Patent Publication No. 10-2017-0088587

An object of the present invention is to use an anode material capable of producing high output at a lower temperature than a conventional solid oxide fuel cell, while preventing defects due to a high coefficient of thermal expansion that occurs when using an existing cathode material, and including the same To provide a single cell for a solid oxide fuel cell and a solid oxide fuel cell including the same.

A unit cell for a solid oxide fuel cell according to the present invention comprises: a first cathode active layer including a compound of Formula 1 below and ceria doped with a first rare earth metal; and a second cathode active layer including ceria doped with a compound of Formula 2 and a second rare earth metal.

[Formula 1]

(La _1-x Sr _x ) _z Co _1-y Fe _y O ₃

In Formula 1, x, y, and z satisfy 0.2≤x≤0.5, 0.5≤y≤0.8, and 0.95≤z≤1.

[Formula 2]

(Sm _1-a Sr _a ) _b CoO ₃

In Formula 2, a and b satisfy 0.3≤a≤0.5 and 0.95≤b≤1.

In the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, the unit cell for a solid oxide fuel cell includes an anode support; anode active layer; electrolyte; reaction prevention film; a first cathode active layer; a second cathode active layer; and a cathode current collector layer; it may be characterized in that these are sequentially stacked.

In the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, a coefficient of thermal expansion of the second cathode active layer may be greater than a coefficient of thermal expansion of the first cathode active layer.

In the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, in the ceria doped with the first rare earth metal or the ceria doped with the second rare earth metal, the rare earth metal may be Y, Sc metal, or a lanthanide metal.

The ceria electrolyte applied as a composite material to the first cathode active layer and the second cathode active layer in the unit cell for a solid oxide fuel cell according to an embodiment of the present invention may satisfy Formula 3 below.

[Formula 3]

Re _A Ce _1-A O _2-(A/2)

In Formula 3, Re is one or two or more selected from Gd, Sm, Y, Er, Yb and Sc, and A is 0.1 to 0.2.

In the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, the first cathode active layer comprises the compound of Formula 1 : ceria doped with the first rare earth metal in a weight ratio of 60: 40 to 50: 50. can

In the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, the second cathode active layer may include the compound of Formula 2: ceria doped with the second rare earth metal in a weight ratio of 60:40 to 50:50.

The present invention also provides a solid oxide fuel cell, and the solid oxide fuel cell according to the present invention may include a single cell for a solid oxide fuel cell according to an embodiment of the present invention.

A unit cell for a solid oxide fuel cell according to the present invention comprises: a first cathode active layer including a compound of Formula 1 below and ceria doped with a first rare earth metal; and a second cathode active layer comprising ceria doped with a compound of Formula 2 and a second rare earth metal, thereby preventing defects due to a high coefficient of thermal expansion and exhibiting high output in a solid oxide fuel cell. there is.

[Formula 1]

(La _{1 - x} Sr _x ) _z Co _{1 - y} Fe _y O ₃

In Formula 1, x, y, and z satisfy 0.2≤x≤0.5, 0.5≤y≤0.8, and 0.95≤z≤1.

[Formula 2]

(Sm _{1 - a} Sr _a ) _b CoO ₃

In Formula 2, a and b satisfy 0.3≤a≤0.5 and 0.95≤b≤1.

1 is a cross-sectional view of a single cell for a solid oxide fuel cell according to an embodiment of the present invention.
2 to 4 show voltage and output densities according to driving temperature and current density of single cells for solid oxide fuel cells according to Examples and Comparative Examples of the present invention.
5 shows the results of driving the unit cells for solid oxide fuel cells of Examples and Comparative Examples at 750°C.
6 to 9 are observations of microstructures of single cells for solid oxide fuel cells according to Examples and Comparative Examples of the present invention.
10 and 11 show the power density at the maximum power density and a specific current density of the embodiment and the comparative example of the present invention.
12 is a diagram illustrating the output in comparison with the case where hydrogen is used as the single cell fuel of Examples and Comparative Examples of the present invention and when biosyngas containing hydrogen is used.

Advantages and features of embodiments of the present invention, and methods of achieving them, will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the art to which the present invention pertains It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

In describing the embodiments of the present invention, if it is determined that a detailed description of a well-known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, the terms to be described later are terms defined in consideration of functions in an embodiment of the present invention, which may vary according to intentions or customs of users and operators. Therefore, the definition should be made based on the content throughout this specification.

The conventional solid oxide fuel cell is driven at a high temperature, so it is difficult to apply it in a field requiring fast operation, and when the driving temperature is lowered, there is a problem in that the output is significantly reduced. In order to overcome this problem, research is being conducted to manufacture a solid oxide fuel cell that exhibits high output even at low temperatures by adding cobalt to materials such as cathodes included in single cells for solid oxide fuel cells or by increasing the cobalt content. However, there is a problem in that the coefficient of thermal expansion increases when the cobalt content is increased. Accordingly, when heating to the driving temperature, problems such as cracks or peeling may occur at the interface due to the difference in the thermal expansion coefficients of the electrolyte, the reaction prevention film, the cathode active layer, and the cathode current collecting layer. There may be problems with degradation.

Specifically, the coefficient of thermal expansion of the zirconia electrolyte is about 10-11×10 ^-6 K ^-1 _{, and Gd-doped CeO 2} (GDC) widely used as a reaction prevention film is 12-13×10 ^-6 K ^-1 . LSCF which normally is used as a _{(La 0. 6 Sr 0.} 4 Co 0. 2 Fe 0. 8 O 3) air electrode is 14 ~ 15 × 10 ^-6 K ^-1 in the coefficient of thermal expansion of the thermal expansion coefficient of the electrolyte film or reaction Similar to that, there is no problem of peeling when heated. However, in the case of changing the air electrode material for the low-temperature driving to the cobalt is a relatively large amount containing material, such as _{LSC (La 0. 6 Sr 0} . 4 CoO 3) or _{SSC (Sm 0.5 Sr 0.5 CoO 3} ), the respective coefficient of thermal expansion 22-26×10 ^-6 K ^-1 , 19-22×10 ^-6 K ^{-1 , which} is relatively high, and thus the above-described problems such as peeling may occur.

Accordingly, the present applicant conducted research to overcome the limitations of the low-temperature driving cathode, and as a result, developed a single cell for a solid oxide fuel cell including a first cathode active layer and a second cathode active layer, which will be described later.

A unit cell for a solid oxide fuel cell according to the present invention comprises: a first cathode active layer including a compound of Formula 1 below and ceria doped with a first rare earth metal; and

and a second cathode active layer including ceria doped with a compound of Formula 2 and a second rare earth metal.

[Formula 1]

(La _{1 - x} Sr _x ) _z Co _{1 - y} Fe _y O ₃

In Formula 1, x, y, and z satisfy 0.2≤x≤0.5, 0.5≤y≤0.8, and 0.95≤z≤1.

[Formula 2]

(Sm _{1 - a} Sr _a ) _b CoO ₃

In Formula 2, a and b satisfy 0.3≤a≤0.5 and 0.95≤b≤1.

The unit cell for a solid oxide fuel cell according to the present invention has a structure in which the first cathode active layer and the second cathode active layer are stacked, thereby overcoming the above-described problem caused by the increase in the cobalt content, and exhibiting excellent output at medium and low temperatures, and the coefficient of thermal expansion Problems such as cracks due to differences can be prevented. At this time, in the present invention, the medium and low temperature may be a temperature lower than the operating temperature of a typical solid oxide fuel cell, and specifically may be 500 to 750 °C.

Preferably, the unit cell for a solid oxide fuel cell according to an embodiment of the present invention includes an anode support; anode active layer; electrolyte; reaction prevention film; a first cathode active layer; a second cathode active layer; and a cathode current collecting layer; may be sequentially stacked, that is, the first cathode active layer may be in contact with the reaction preventing layer, and the second cathode active layer may be in contact with the cathode current collecting layer.

Furthermore, in the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, the thermal expansion coefficient of the second cathode active layer may be greater than that of the first cathode active layer. In addition, the electrolyte and the reaction prevention membrane , the first cathode active layer, the second cathode active layer, and the cathode current collecting layer may be characterized in that the coefficient of thermal expansion is the same or greater. That is, the coefficient of thermal expansion of the reaction prevention film is equal to or greater than the coefficient of thermal expansion of the electrolyte, the coefficient of thermal expansion of the first cathode active layer is equal to or greater than that of the reaction prevention film, and the coefficient of thermal expansion of the second cathode active layer is higher than that of the first cathode active layer. The same or greater than the second cathode active layer, the cathode current collecting layer may have the same or greater coefficient of thermal expansion.

The unit cell for a solid oxide fuel cell according to an embodiment of the present invention minimizes interfacial stress during heating for driving by exhibiting the above-described coefficient of thermal expansion of each layer included therein, thereby preventing the problem of cracking or peeling at the interlayer interface. there is.

Preferably, in Formula 1, x, y and z may satisfy 0.3≤x≤0.5, 0.6≤y≤0.8, 0.95≤z≤0.98, and in Formula 2, a and b are 0.4≤a≤0.5, 0.95≤b≤0.98 may be satisfied. That is, in Formula 1, the sum of the molar ratios of La and Sr may be 1 or less, and in Formula 2, the sum of the molar ratios of Sm and Sr may be 1 or less. When Chemical Formulas 1 and 2 satisfy the above range, there is an advantage in that a higher output of the cathode may be exhibited. In addition, when the sum of the molar ratios of La and Sr is 1 or less, the _{formation of impurities such as SrZrO 3} due to the reaction of Sr and the electrolyte occurring during long-term operation can be prevented and the reactivity can be lowered.

In the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, in the ceria doped with the first rare earth metal and the ceria doped with the second rare earth metal, the rare earth metal may be Y, Sc metal or a lanthanide metal, More preferably, the following formula (3) may be satisfied.

[Formula 3]

Re _A Ce _{1 -A} O _2-(A/2)

In Formula 3, Re is one or two or more selected from Gd, Sm, Y, Er, Yb and Sc, and A is 0.1 to 0.2.

That is, in the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, the ceria doped with the first rare earth metal or the ceria doped with the second rare earth metal is selected from gadolinium, samarium, yttrium, europium, ytterbium and scandium. One or two or more selected may be a doped ceria electrolyte. By applying the rare-earth metal-doped ceria satisfying Chemical Formula 3 to the first cathode active layer or the second cathode active layer, exfoliation at the interface between the first cathode active layer and the second cathode active layer is prevented, and the reaction preventing film and the first Peeling of the cathode active layer can be prevented.

In the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, the first cathode active layer may include the compound of Formula 1: ceria doped with the first rare earth metal in a weight ratio of 60: 40 to 50: 50, The second cathode active layer may include the compound of Formula 2: ceria doped with the second rare earth metal in a weight ratio of 60:40 to 50:50. That is, in the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, the first cathode active layer or the second cathode active layer may each contain 40 to 50 wt% of ceria doped with a rare earth metal, and the remaining amount of Formula 1 or Formula 2 may be included. By satisfying the above range, it is possible to properly secure a triple phase boundary (TPB) while minimizing the deviation of the coefficient of thermal expansion between the first cathode active layer and the second cathode active layer, thereby activating the electrochemical reaction of the cathode.

In the unit cell for a solid oxide fuel cell according to an embodiment of the present invention, the first cathode active layer and the second cathode active layer may be coated by screen printing, respectively, and may be coated by performing screen printing once, respectively, but the present invention This is not limited thereto.

In the single cell for a solid oxide fuel cell according to an embodiment of the present invention, the electrolyte can be used without limitation in the case of a commonly known solid oxide fuel cell. In a specific and non-limiting example, the electrolyte is a zirconia (ZrO ₂ )-based oxide, a ceria (CeO ₂ )-based oxide, a lanthanum-strontium-gadolinium-magnesium oxide (LSGM), etc., in which a rare earth metal oxide is substituted and dissolved in solid solution for stabilization. It may be a zirconia electrolyte in which yttrium oxide or the like is preferably dissolved as a stabilizer.

The anode support and the anode active layer may also use materials commonly used in solid oxide fuel cells without limitation, and as a specific and non-limiting example, the anode support and the anode active layer may each contain nickel oxide and yttrium oxide as a stabilizer. It may be a mixture of zirconia, and it is evident that the specific composition may vary depending on the place of use of the unit cell for solid oxide fuel cells, required output and operating temperature, and the like.

The reaction prevention film may also be made of a material commonly used in a solid oxide fuel cell. As a specific and non-limiting example, the reaction prevention layer may be ceria in which gadolinium, ytterbium, bismuth, and the like are substituted, but the present invention is not limited thereto.

The unit cell for a solid oxide fuel cell according to an embodiment of the present invention is an electrolyte supported cell (ESC), an anode supported cell (ASC), and a cathode supported cell (CSC: Cathode supported cell). Cell) or a multi-cell type single cell (Segment-type), but the present invention is not limited thereto.

The present invention also provides a solid oxide fuel cell including the single cell for a solid oxide fuel cell according to an embodiment of the present invention. As described above, the solid oxide fuel cell according to the present invention is characterized in that it prevents peeling or cracking due to a rise in temperature to secure durability and excellent output.

Hereinafter, the present invention will be specifically described by way of Examples and Comparative Examples. The examples below are only for helping understanding of the present invention, and the scope of the present invention is not limited by the examples below.

[Example 1]

Simultaneous sintered body for cathode application is 8YSZ (8mol% Y ₂ O ₃ stabilized ZrO ₂ ) electrolyte, anode active layer (AFL: Anode Functional Layer, NiO:8YSZ=57:43wt%), anode support (AS: Anode Supporter, NiO: _{3YSZ = 60:....} 40wt%) have been produced is 5 sintered at 1350 ℃ the electrolyte surface GYBC (Yb Gd _{0 135 0 0 015} Bi ₀₂ O ₈₃ Ce _{0 1 .915)} reaction film 1250 after the screen printing It was heat-treated at ℃ for 2 hours.

The first cathode active layer and the second cathode active layer were screen-printed on the surface of the GYBC reaction prevention film once, respectively, and the cathode current collector layer was screen-printed one more time, and then heat-treated at 1050° C. for 1.5 hours to complete a single cell for a solid oxide fuel cell. In this case, specific compositions of the first cathode active layer, the second cathode active layer, and the cathode current collecting layer are shown in Table 1.

Referring to Example 1, the coefficient of thermal expansion of the electrolyte is about 10-11×10 ^-6 K ^-1, and the coefficient of thermal expansion of the reaction barrier is 12-13×10 ^-6 K ^{-1, which} is higher than the coefficient of thermal expansion of the electrolyte. It can be confirmed that the coefficient of thermal expansion is large. Also look at the first cathode active layer, about ^{12 ~ 13 × 10 -6 K ~} 15 -1 GYBC and 14 having a coefficient of thermal expansion ^{× 10 -6 K -1 LSCF (La} 0 having a coefficient of thermal _{expansion. 6} Sr _{0. 4 Co 0. 2 Fe 0.} 8 O 3) is to check that the mixture, a second look at the air electrode active layer GYBC having a thermal expansion coefficient of about 12 ~ 13 × 10 ^-6 K ^-1 and about 19 ~ 22 × 10 ^It can be seen that SSC (Sm _0.5 Sr _0.5 CoO ₃ ) having a thermal expansion coefficient of -6 K ^-1 is mixed, and as a result, the thermal expansion coefficient of the entire first cathode active layer is greater than that of the reaction prevention film, and the second cathode It can be seen that it is logically justified that the thermal expansion coefficient of the entire active layer is greater than that of the first cathode active layer.

[Comparative Examples 1 and 2]

A single cell for a solid oxide fuel cell was manufactured in the same manner as in Example 1, except that the compositions of the first cathode active layer and the second cathode active layer were changed as shown in Table 1 below.

cathode configuration Comparative Example 1 (C1) Example 1 (C2) Comparative Example 2 (C3) cathode current collector LSCF LSCF LSCF second cathode active layer LSCF 53wt% +GDC 47wt% SSC 53wt%
+GDC 47wt% SSC 53wt%
+GDC 47wt% first cathode active layer LSCF 53wt%
+GDC 47wt% LSCF 53wt%
+GDC 47wt% SSC 53wt%
+GDC 47wt% - LSCF : La _{0 . 6} Sr _{0 . 4} Co _{0 . 2} Fe _{0 . 8} O ₃ , - SSC : Sm _{0 . 5} Sr _{0 . 5} CoO ₃ , - GDC : Gd _{0 . 2} Ce _{0 . 8} O _{1 .9}

output check

The single cells for solid oxide fuel cells prepared in Examples and Comparative Examples were driven using hydrogen fuel, and voltage and power densities according to driving temperature and current density are shown in Table 2 and FIGS. 2 to 4 below. Figure 2 is Comparative Example 1, Figure 3 is Example 1, Figure 4 is the output when the cell of Comparative Example 2 is used.

cathode configuration operating temperature Cell voltage (@0.4A/cm ² ) Maximum power density Comparative Example 1 650℃ 0.866V 0.604 W/cm ² 700℃ 0.908V 0.785 W/cm ² 750℃ 0.928V 0.928 W/cm ² Example 1 650℃ 0.889V 0.683 W/cm ² 700℃ 0.931V 0.912 W/cm ² 750℃ 0.948V 1.097 W/cm ²

Referring to FIG. 4, the single cell for the solid oxide fuel cell to which Comparative Example 2 was applied showed a similar value of OCV (Open Circuit Voltage) to about 1.2V compared to Comparative Example 1 or Example 2, but a sharp voltage drop due to increase in current density was observed. It can be seen that the maximum power density is ^{remarkably low as 0.1 W/cm 2 .}

Comparing Comparative Example 1 and Example 1 in Table 2, it can be seen that Example 1 in which the composition of the first cathode active layer and the second cathode active layer is different shows a high maximum power density at the entire temperature, 650 to 750 It can be confirmed that the output density is improved by at least 13% and at most 18% in the ℃ temperature range.

5 is a comparison of the maximum power densities of the single cells for solid oxide fuel cells according to Examples and Comparative Examples at 750° C., and it can be seen that the single cells for solid oxide fuel cells according to the Examples exhibit remarkably high maximum power densities.

Section check after operation

After confirming the power density, the microstructure of the cross section was observed and shown in FIGS. 6 to 8 . 6 is a cross-sectional view of the solid oxide unit cell of Comparative Example 1, FIG. 7 is Example 1, and FIG. 8 is Comparative Example 2.

6 and 7, in the case of Example 1 and Comparative Example 1, it can be seen that each component is tightly bound.

8, it can be seen that in Comparative Example 2, a dense reaction layer is observed at the interface between the reaction prevention film and the electrolyte, and in general, when the LSCF air electrode is operated for a long time, the reaction layer is the electrolyte through the porous reaction prevention film. It is known to diffuse and react to the surface _{to form SrZrO 3 insulators.} However, when SSC is applied to CFL-1, it is interpreted that a reaction layer has already been formed in the ASC fabrication (heat treatment) stage and short-term operation rather than long-term operation, and as this reaction layer increases the resistance of the ASC, low output characteristics appear. can do.

9 is also a cross-section of Comparative Example 2, and it can be seen that peeling was formed at the interface between the reaction prevention film and the first cathode active layer, and transverse cracks were observed throughout the cathode. This appears to be a phenomenon due to the high coefficient of thermal expansion of the SSC cathode material, and such peeling and cracking also seem to have contributed to the low power density of the unit cell of Comparative Example 3.

Output trend analysis

The output trends of Example 1 and Comparative Example 1 were analyzed, and the results are shown in FIGS. 10 and 11 .

10 shows the maximum power density according to the temperature, and referring to FIG. 10 , the difference in the maximum power density may tend to decrease as the driving temperature decreases, which is the interface caused by the difference in the coefficient of thermal expansion as the driving temperature decreases. It is analyzed that the effect of stress is lowered.

^{11 is a comparison of the output densities of the unit cells of Example 1 and Comparative Example 1 based on 0.4 A/cm 2} , which is a low current density region, and in the actual cell/stack driving condition, the unit cell of Example 1 has a high It can be seen that the output is displayed.

biogas to reform output analysis by

The single cells of Examples 1 and 2 were driven at 650° C., and hydrogen and biosynthesis gas were mixed and supplied as fuels. In this case, the specific composition is H ₂ =72%, CO=12%, CO ₂ =14%, CH ₄ =2%.

Referring to FIG. 12 , both Example 1 and Comparative Example 1 show a decrease in voltage and output when hydrogen and biosyngas are used, but it can be confirmed that ^{the difference in output is less than 0.02 W/cm 2 .}

Claims (8)

a first cathode active layer including a compound of Formula 1 and ceria doped with a first rare earth metal; and
a second cathode active layer comprising ceria doped with a compound of Formula 2 and a second rare earth metal; and
anode support; anode active layer; electrolyte; reaction prevention film; a first cathode active layer; a second cathode active layer; and a cathode current collector layer; it is sequentially stacked,
The ceria doped with the first rare earth metal and the ceria doped with the second rare earth metal satisfy Formula 3 below,
The first cathode active layer includes the compound of Formula 1: ceria doped with the first rare earth metal in a weight ratio of 60: 40 to 50: 50,
The second cathode active layer includes the compound of Formula 2: ceria doped with a second rare earth metal in a weight ratio of 60: 40 to 50: 50;
A unit cell for a solid oxide fuel cell, characterized in that the maximum power density is improved by 13% to 18% in the temperature range of 650 to 750° C. compared to the unit cell in which the first cathode active layer and the second cathode active layer are composed of Chemical Formula 1.
[Formula 1]
(La _1-x Sr _x ) _z Co _1-y Fe _y O ₃
(In Formula 1, x, y and z satisfy 0.2≤x≤0.5, 0.5≤y≤0.8, and 0.95≤z≤1.)
[Formula 2]
(Sm _1-a Sr _a ) _b CoO ₃
(In Formula 2, a and b satisfy 0.3≤a≤0.5 and 0.95≤b≤1.)
[Formula 3]
Re _A Ce _1-A O _2-(A/2)
(In Formula 3, Re is one or two or more selected from Gd, Sm, Y, Er, Yb and Sc, and A is 0.1 to 0.2.) delete The method of claim 1,
The unit cell for a solid oxide fuel cell, characterized in that the coefficient of thermal expansion of the second cathode active layer is greater than the coefficient of thermal expansion of the first cathode active layer. delete delete delete delete A solid oxide fuel cell comprising the single cell for a solid oxide fuel cell of any one of claims 1 and 3.

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