KR101840094B1 - Ceria electrolyte for low temperature sintering and solid oxide fuel cells using the same - Google Patents

Abstract

The present invention relates to a ceria electrolyte for a solid oxide fuel cell, which is a ceria (CeO ₂ ) electrolyte in which samarium (Sm), ether bis (Yb) and bismuth (Bi) To a ceria electrolyte for a solid oxide fuel cell having low-temperature sintering characteristics.

Description

TECHNICAL FIELD [0001] The present invention relates to a ceria electrolyte having low-temperature sintering properties and a solid oxide fuel cell using the ceria electrolyte.

The present invention relates to a ceria electrolyte for low temperature sintering of solid oxide fuel cells (hereinafter referred to as SOFC), and more particularly to a ceria electrolyte for low temperature sintering of solid oxide fuel cells (hereinafter referred to as SOFC) Cerium (CeO ₂ ) electrolyte having a low temperature sintering property at the same time and a solid oxide fuel cell using the same.

2. Description of the Related Art In recent years, high performance materials have been actively applied to a solid oxide fuel cell (hereinafter referred to as "SOFC") in order to prevent a decrease in operating temperature for ensuring high temperature stability and a decrease in output due to a decrease in operating temperature. Currently, zirconia-based electrolytes such as 8YSZ (8 mol% Y ₂ O ₃ stabilized ZrO ₂ ) are the most widely used electrolyte materials for unit cells of SOFC.

Initially, a unit cell using a zirconia-based electrolyte such as 8YSZ was used as a composite material made of a mixture of an LSM (Sr doped LaMnO ₃ ) material and an electrolyte material, which are pure electron conductors as an air electrode material. the mixed conducting (MIEC such as _{LSCF (Sr & Co doped LaFeO 3} ) exhibits excellent catalytic properties for the purpose of high electrical conductivity and oxygen ionization at low temperatures in order to increase the ^{W / cm 2): mixed ionic} and electronic conductor) use of the air electrode material Is rapidly increasing.

However, most mixed conducting cathode materials, such as LSCF, exhibit disadvantages in that they react at the interface with zirconia electrolyte at the heat treatment temperature range of the air electrode to form reaction products of non-conducting properties. Therefore, the high- temperature reaction of mixed conducting cathode such as LSCF and zirconia- Recently, a buffer layer (BL) is additionally introduced between the air electrode and the electrolyte.

Particularly, the ceria electrolyte (Gd or Sm doped CeO ₂ ) in which Gd ₂ O ₃ or Sm ₂ O ₃ is applied to pure CeO ₂ at a concentration of 5 to 10 mol% has high oxygen ion conductivity and does not react with the MIEC air electrodes, And is most widely applied as an anti-reaction film material for preventing the reaction product between the electrolyte and the air electrode, which is formed between the zirconia (ZrO ₂ ) electrolyte membrane of the SOFC and the mixed conducting cathode layer.

The ceria electrolyte, which is applied as a reaction preventive layer, has a characteristic of forming a zirconia electrolyte and a zirconia electrolyte at a high temperature of 1300 ° C or higher. Since the solid solution formed at a high temperature through mutual diffusion has a very low ion conductivity, Which is a cause of lowering the output.

Currently, a method of manufacturing a unit cell using a ceria-based reaction preventive film includes a method of forming a fuel electrode support, a zirconia-based electrolyte, and a ceria electrolyte into a laminated molded body and then performing simultaneous sintering; a method in which only an anode support and a zirconia electrolyte are laminated and sintered Two methods of coating and heat-treating the ceria-containing film on the surface of the electrolyte membrane have been applied.

Therefore, when a unit cell is manufactured through simultaneous sintering of a ceria electrolyte with a zirconia electrolyte, a technique of co-sintering at a temperature of 1300 ° C or less is required, but in order to have a dense microstructure of 95% or more required as an electrolyte, Sintering conditions of 1350 캜 or higher are required.

In addition, when sintering at 1350 DEG C or higher to form a dense electrolyte, and then forming a ceria-based reaction preventive film through coating and heat treatment on the surface of the electrolyte, the already sintered electrolyte membrane does not shrink together and thus it is difficult to form a dense ceria electrolyte And coating and heat treatment processes are added to increase processing time and process cost.

Therefore, if the heat treatment temperature of the ceria-based electrolyte used as the reaction prevention film can be lowered to the heat treatment temperature region of the air electrode, the ceria-based electrolyte and the air electrode can be heat-treated at the same time, shortening the process time and ensuring a dense fine structure even at a low temperature. Can be improved.

As described above, there is a need for a technique capable of lowering the heat treatment temperature of the ceria-based electrolyte to 1150 占 폚, which is the heat treatment temperature region of the air electrode.

1. Korean Patent Publication No. 10-2013-0040640 2. Korean Patent Publication No. 10-2013-0099704

The present invention was conceived in view of the above-mentioned necessity. It is an object of the present invention to provide a method for manufacturing a Sm doped CeO ₂ (SDC) electrolyte by further employing Bi to lower the heat treatment temperature to 1150 ° C, The present invention is to provide a ceria electrolyte having a low sintering temperature compared to conventional ceria electrolytes by simultaneously using a small amount of Yb in order to prevent an increase in total cation radius due to employment and a decrease in ion conductivity.

In order to accomplish the above object, the ceria electrolyte for low temperature sintering according to the present invention is characterized in that cerium (CeO) having low-temperature sintering condition is prepared by substituting samarium (Yb) and bismuth (Bi) ₂ ) As the electrolyte, it may have a composition represented by the following formula (1).

[Chemical Formula 1]

Sm _x Yb _y Bi _z Ce _{1 -xy- z} O _{2 -δ}

- 0.17? 0.005? Y? 0.05, 0.005? Z? 0.05, 0.11? X + Y + Z? 0.27,? = (X + Y + Z) / 2

The total cation radius of the ceria (CeO ₂ ) electrolyte in which samarium (Sm), erbium (Yb) and bismuth (Bi) are simultaneously solubilized can be 0.98-0.99 Å.

According to an aspect of the present invention, there is provided a solid oxide fuel cell including a fuel electrode, a zirconia electrolyte formed by sintering at the same time as the fuel electrode, a ceria electrolyte for low temperature sintering on the surface of the zirconia electrolyte, And then heat-treated at a temperature ranging from 1100 ° C to 1200 ° C, and an air electrode prepared by coating and heat-treating the surface of the ceria reaction prevention film.

The zirconia electrolyte is a zirconia-based electrolyte having a fluorite structure, and may have a composition represented by the following formula (2).

(2)

(Re ₂ O ₃ ) _x (ZrO ₂ ) _1-x

- Re = at least one element selected from Y, Sc, Yb, Ce, Gd and Sm, 0.04? X?

The air electrode is a mixed conductor of a perovskite (ABO ₃ ) crystal structure having both electron and oxygen ion conductivity, and may have a composition represented by the following formula (3).

(3)

ABO ₃

- At least one element selected from among La, Sm, Pr, Ba, Sr and Ca

- B = at least one element selected from Fe, Co, Ni and Cu

- the content ratio of A and B is 0.95? A / B? 1

The air electrode is a mixed conductor having a double layer perovskite (ABC ₂ O _{5 + delta} ) crystal structure having both electron and oxygen ion conductivity, and may have a composition represented by the following formula (4).

[Chemical Formula 4]

ABC ₂ O _{5 + 隆}

- one or more elements selected from A = La, Sm, Nd and Pr

- B = at least one element selected from Ba, Sr and Ca

- at least one element selected from C = Co, Fe, Ni, Cu, Mn
- δ represents oxygen excess or oxygen deficiency.

Wherein the cathode comprises a mixed conductor of 50 to 70 wt% of a double layer perovskite (ABC ₂ O _{5 + delta} ) crystal structure and 30 to 50 wt% of a ceria electrolyte, wherein the ceria electrolyte has a composition represented by the following formula .

[Chemical Formula 1]

Sm _x Yb _y Bi _z Ce _1-xyz O _{2 -?}

- 0.17? 0.005? Y? 0.05, 0.005? Z? 0.05, 0.11? X + Y + Z? 0.27,? = (X + Y + Z) / 2

Wherein the cathode comprises a mixed conductor of 50 to 70 wt% of a double layer perovskite (ABC ₂ O _{5 + δ} ) crystal structure and 30 to 50 wt% of a ceria electrolyte, wherein the ceria electrolyte has a composition represented by the following formula .

[Chemical Formula 5]

Re _x Ce _1-x O _2-隆

- Re = at least one element selected from Gd, Sm, Y, Nd and Pr, 0.05? X? 0.2,? = X / 2

The fuel electrode may be composed of 30 to 50 wt% of a zirconia-based electrolyte having a fluorite structure and 50 to 70 wt% of NiO.

The solid oxide fuel cell may be an anode supported cell (ASC), an electrolyte supported cell (ESC), or a metal supported cell (MSC) structure.

The unit cell may be in the form of a planer-type, a tubular-type, or a flat-tube type.

The ceria electrolyte for low temperature sintering according to the present invention is a ceria (CeO ₂ ) electrolyte having a low temperature sintering property by simultaneously substituting samarium (Sm), erbium (Yb) and bismuth (Bi) It exhibits a similar total cation radius and can exhibit high sintered density of 95% or more even at a sintering temperature of 1150 ° C while maintaining the high oxygen ion conductivity of conventional SDC electrolytes.

In the solid oxide fuel cell using the ceria electrolyte for low temperature sintering according to the present invention, the heat treatment temperature of the ceria electrolyte is lowered to 1150 ° C or less, which is the heat treatment temperature of the air electrode, on the dense electrolyte membrane sintered at 1350 ° C or higher to secure a firm adhesion with the electrolyte membrane can do.

In addition, the ceria reaction preventive film and the mixed conducting cathode such as LSCF are continuously coated and then simultaneously heat-treated to shorten the processing time, and a unit cell having a high output density can be manufactured.

The effects of the present invention described above are exemplarily described, and the scope of the present invention is not limited by these effects.

1 is a graph showing the total cation radius of a commercially available SDC electrolyte.
2 is a graph showing the total cation radii of SDC electrolytes in which Bi is additionally substituted and solubilized
3 is a graph showing the total cation radii of SDC electrolytes in which Yb is additionally substituted and solubilized.
FIG. 4 is a graph showing the sintered density of the SBC electrolyte according to the increase of the high capacity of Bi and the increase of the sintering temperature according to the solid state reaction method according to the embodiment of the present invention.
FIG. 5 is a graph showing the increase of the Bi capacity by the solid-phase reaction method and the shrinkage ratio of the SBC electrolyte according to the sintering temperature increase according to the embodiment of the present invention.
FIG. 6 is a graph showing sintering shrinkage ratios according to sintering temperatures after molding the common SDC electrolyte and SYBC electrolyte synthesized by the citric acid method in the embodiment of the present invention by the same method.
FIG. 7 is a graph showing the porosity of a conventional SDC electrolyte synthesized by a citric acid method and a SYBC electrolyte according to an embodiment of the present invention after molding according to the sintering temperature.
8 is a graph showing sintering densities of conventional SDC electrolytes synthesized by the citric acid method and SYBC electrolytes in accordance with the sintering temperature after molding according to the same method.
FIG. 9 is a photograph of a microstructure of a conventional SDC electrolyte synthesized by a citric acid method and a SYBC electrolyte formed by the same method and analyzing the microstructure according to a sintering temperature through a scanning electron microscope.
10 is a graph showing the crystal structure of a general SDC electrolyte synthesized by a citric acid method and a SYBC electrolyte by sieving the same at 1100 ° C and X-ray diffraction analysis.
FIG. 11 is a graph showing the comparison of the ionic conductivities of the general SDC electrolytes prepared by the citric acid method and sintered at 1100.degree. C. to 1400.degree. C. by the direct current four-terminal method according to the embodiment of the present invention.
12 is a graph showing ion conductivity of SYBC electrolytes sintered at 1100 ° C. to 1400 ° C. by a citric acid method through an embodiment of the present invention and comparing the ionic conductivities of the SYBC electrolytes at different operating temperatures using a DC four terminal method.
13 is a graph comparing ionic conductivities of SDC and SYBC electrolytes synthesized by a citric acid method and sintered at 1100 ° C to 1400 ° C at 750 ° C according to an embodiment of the present invention.
FIG. 14 is a graph comparing the ionic conductivities of SDC and SYBC electrolytes sintered at 1100 ° C. and 1200 ° C., which are synthesized by the citric acid method through the embodiments of the present invention and which are low temperature sintering sections.
FIG. 15 is a photograph showing a comparison of the microstructures of ESC applied with LSM air electrode and ESC applied with SYBC electrolyte as LSCF air electrode and reaction preventive membrane in the embodiment of the present invention.
FIG. 16 is a graph illustrating the output density of an embodiment of the present invention by driving an ESC applying LSM air electrode at 750 ° C, 800 ° C, and 850 ° C.
17 is a graph illustrating ESD performance by driving an ESC using SYBC electrolyte as an LSCF air electrode and an anti-reaction membrane at 750 DEG C, 800 DEG C, and 850 DEG C in the embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. The scope of technical thought is not limited to the following examples. Rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items. The same reference numerals denote the same elements at all times. Further, the various elements and regions in the drawings are schematically drawn. Accordingly, the technical spirit of the present invention is not limited by the relative size or spacing depicted in the accompanying drawings.

The ceria electrolyte for low temperature sintering according to the present invention is a ceria (CeO ₂ ) electrolyte having low temperature sintering conditions by simultaneously substituting samarium (Sm), erbium (Yb) and bismuth (Bi) Lt; / RTI >

[Chemical Formula 1]

Sm _x Yb _y Bi _z Ce _1-xyz O _{2 -?}

- 0.17? 0.005? Y? 0.05, 0.005? Z? 0.05, 0.11? X + Y + Z? 0.27,? = (X + Y + Z) / 2

Sm _x Ce _1-x O _2-δ , which is one of the currently commercialized ceria electrolytes, and has a formula of Sm ³⁺ substituted with a part of Ce ^{4+ which} is the main lattice ion, vacancy ) Is formed, and this oxygen vacancy becomes a diffusion path of oxygen ions. Sm-substituted ceria electrolyte is named Sm-doped ceria (hereinafter SDC) electrolyte.

The ceria electrolyte for low-temperature sintering according to the present invention is used for securing the low-temperature sintering property of the SDC electrolyte and maintaining high ion conductivity and introducing bismuth (Bi) as an additional substituting solid element for low temperature sintering characteristics, It is possible to introduce Yb as an additional substituting element. The cation radii of Sm ³⁺ , Bi ³⁺ , Ce ⁴⁺ and Yb ³⁺ are 1.079 Å, 1.17 Å, 0.97 Å and 0.985 Å, respectively.

The composition of the SDC electrolyte, which is currently used as a composition having the highest ionic conductivity, is Sm _x Ce _1-x O _{2- (x / 2)} and X = 0.1 to 0.2. The average ion radius of all cations As shown in FIG. As can be seen from the above calculation results, the size of the cation radius of the commercialized SDC electrolytes is about 0.98 to 0.99 (Å).

In the case of replacing a part of Sm with Bi, that is, in the case of an SDC electrolyte (Sm _0.15 Bi _x Ce _0.85-x O _{2- (0.15 + x) / 2} ) in which Bi is additionally substituted and solved for ensuring low temperature sinterability of the SDC electrolyte The change in the cation radius is shown in Fig. 2, and it can be confirmed by calculating that the larger the ion radius of the Bi than that of Sm and Ce, the higher the substitution solubility, the larger the total cation radius. When the content of Bi, that is, X is 0.02 or more, the total cation radius increases to 0.99 (Å) or more.

In order to secure the low-temperature sintering property of the existing SDC electrolyte, the effect of increasing the total radius of the cation in the case of additionally substituting Bi is effective. ) To narrow the conduction of oxygen ions.

Conversely, the change in the cation radius with respect to the SDC electrolyte (Sm _{2 -x} Yb _x Ce _0.8 O _1.9 ) in which Yb is additionally substituted and solved is the same as that in FIG. 3, and a part of Sm is replaced with Yb having a relatively small ionic radius, The calculation shows that the total cation radius decreases with increasing substitutional solubility.

Therefore, in the present invention, Yb having an ionic radius smaller than that of Sm can be substituted at the same time in order to suppress the increase of the total cation radius due to substitution employment of Bi having a relatively larger ionic radius than Sm.

The total cation radius of the ceria (CeO ₂ ) electrolyte in which samarium (Sm), erbium (Yb) and bismuth (Bi) are simultaneously solubilized can be 0.98-0.99 Å.

The solid oxide fuel cell using the ceria electrolyte for low temperature sintering according to the present invention includes a fuel electrode, a zirconia electrolyte, a ceria reaction prevention film, and an air electrode.

The fuel electrode may be composed of 30 to 50 wt% of a zirconia-based electrolyte having a fluorite structure and 50 to 70 wt% of NiO.

The zirconia electrolyte may be formed by sintering simultaneously with the fuel electrode. The zirconia electrolyte may have a composition of the following formula (2).

(2)

(Re ₂ O ₃ ) _x (ZrO ₂ ) _1-x

- Re = at least one element selected from Y, Sc, Yb, Ce, Gd and Sm, 0.04? X?

The ceria reaction prevention film may be formed by coating the surface of the zirconia electrolyte with the ceria electrolyte for low-temperature sintering and then heat-treating the ceria electrolyte at a temperature ranging from 1100 ° C to 1200 ° C.

The air electrode may be prepared by coating and heat-treating the surface of the ceria reaction prevention film. The cathode may be a mixed conductor of a perovskite (ABO ₃ ) crystal structure having both electron and oxygen ion conductivity.

(3)

ABO ₃

- At least one element selected from among La, Sm, Pr, Ba, Sr and Ca

- B = at least one element selected from Fe, Co, Ni and Cu

- the content ratio of A and B is 0.95? A / B? 1

Also, the cathode is a mixed conductor having a double layer perovskite (ABC ₂ O _{5 + δ} ) crystal structure having both electrons and oxygen ion conductivity, and may have a composition represented by the following formula (4).

[Chemical Formula 4]

ABC ₂ O _{5 + 隆}

- one or more elements selected from A = La, Sm, Nd and Pr

- B = at least one element selected from Ba, Sr and Ca

- at least one element selected from C = Co, Fe, Ni, Cu, Mn
- δ represents oxygen excess or oxygen deficiency.

In addition, the air electrode is composed of a mixed conductor of 50 to 70 wt% of a double layered perovskite (ABC ₂ O _{5 + δ} ) crystal structure and 30 to 50 wt% of a ceria electrolyte, wherein the ceria- Lt; / RTI >

[Chemical Formula 1]

Sm _x Yb _y Bi _z Ce _1-xyz O _{2 -?}

- 0.17? 0.005? Y? 0.05, 0.005? Z? 0.05, 0.11? X + Y + Z? 0.27,? = (X + Y + Z) / 2

As described above, when the ceria electrolyte contained in the air electrode of the solid oxide fuel cell is used in the same composition as the ceria electrolyte used in the reaction prevention film, the time for the heat treatment process can be shortened and the fine structure can be secured even at a low temperature. There is an advantage that the output characteristic of the battery can be improved.

The air electrode is composed of 50 to 70 wt% of a mixed conductor having a double layer perovskite (ABC ₂ O _{5 + δ} ) crystal structure and 30 to 50 wt% of a ceria electrolyte, wherein the ceria electrolyte has a composition represented by the following formula Lt; / RTI >

[Chemical Formula 5]

Re _x Ce _1-x O _2-隆

- Re = at least one element selected from Gd, Sm, Y, Nd and Pr, 0.05? X? 0.2,? = X / 2

The solid oxide fuel cell may be an anode supported cell (ASC), an electrolyte supported cell (ESC), or a metal supported cell (MSC) structure, The unit cell may be in the form of a planer-type, a tubular-type, or a flat-tube type.

Cylindrical unit cells are easy to gas-seal and have excellent mechanical characteristics of the structure itself, so large stacks of several tens kW to several hundred kW class can be manufactured, but the output density per unit volume is low. The flat plate type cell has a high output density per unit volume but has a disadvantage in that it has high stack sealability and mutual reactivity between the components and low mechanical stability of the cell. This type is advantageous for households with a power density of less than 1 kW, buildings with a capacity of 10 kW or higher, and APUs with several kW for transportation. The cylindrical unit cell is applied to the fuel electrode support body and the air electrode support body, and the plate body can be manufactured by the anode support body, the electrolyte support body and the metal support body. The flat tubular unit cell is based on the anode support type and is currently being applied to the domestic or multi-cell type of power generation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, details of the present invention will be described with reference to examples and experimental examples.

1. Confirmation of Bi substitution employment effect

1-1. Composition design

(Sm _x Ce _1-x O _{2-x / 2} , X = 0.1, 0.2) as shown in the following Table 1 and an electrolyte (Sm _0.1 designed _{Bi x Ce 0.9-x O 1.95} -x / 2, X = 0.025, 0.05, the composition having the formula of 0.075, 0.1, or less SBC).

Sample   Composition 1: SDC-19 Sm _0.1 Ce _0.9 O _1.95 2: SDC-28 Sm _0.2 Ce _0.8 O _1.9 3: X = 0.025 Sm _0.1 Bi _0.025 Ce _0.875 O _1.9375 4: X = 0.05 Sm _0.1 Bi _0.05 Ce _0.85 O _1.925 5: X = 0.075 Sm _0.1 Bi _0.075 Ce _0.825 O _1.9125 6: X = 0.1 Sm _0.1 Bi _0.1 Ce _0.8 O _1.9

1-2. Electrolyte Specimen Manufacturing

Sm ₂ O ₃ , Bi ₂ O _3, and CeO ₂ were used as raw materials for the synthesis of the electrolyte of Table 1 by the solid-phase reaction method. After weighing according to the composition, ethanol was used as a solvent and zirconia balls having a diameter of 5 mm were milled And the wet ball mill was mixed.

The wet mixed electrolyte slurries were dried and uniaxially compacted into flat and disk-shaped green compacts.

- Flat-plate shaped body Size: 40mm width, 40mm length, 4mm thickness

- Disc-shaped molded body Size: Diameter 27mm, Thickness 3mm

The formed electrolyte specimens were sintered in air at 1100 ~ 1400 ℃ for 5 hours.

1-3. Confirmation of sintering shrinkage, porosity and sintering density

Figure 4 is Table 1, using a powder synthesized by the solid phase synthesis of the composition 1100 ℃, 1200 ℃, 1300 ℃ and Sm _x (SDC one at 1400 ℃ sintered for 5 hours, _{Ce 1-x O 2-x} / 2, X (SBC: Sm _0.1 Bi _x Ce _0.9-x O _1.95 (= 0.1, X = 2) electrolyte, SDC-19 (X = 0.1) and SDC-28 _{-x / 2} , X = 0.025, 0.05, 0.075, 0.1).

The results of FIG. 4 indicate that when the target sintering temperature is 1100 ° C. and 1200 ° C., the sintering density increases as the Bi content increases. At a high temperature sintering temperature of 1300 ° C., = 0.075, 0.1), it can be confirmed that the sintered density is lowered or the effect is no more than 1200 ° C.

FIG. 5 is a graph showing shrinkage ratios of electrolyte specimens sintered at 1200.degree. C. and 1300.degree. C., which correspond to the results of FIG. 4, calculated by the following equation.

The results of Fig. 5 show that the sintered electrolyte specimens sintered at 1200 ℃ show an increase in shrinkage as the Bi content increases, and that the decrease in the volume of the electrolyte is responsible for the increase in sintered density of the electrolyte. On the other hand, the electrolyte specimens sintered at 1300 ℃ showed the increase of the shrinkage ratio with the increase of Bi content, and the maximum shrinkage ratio at the composition of X = 0.05 and 0.075, respectively. That is, the increase in the shrinkage ratio is a volume expansion due to over-molding, and it can be judged that the sintering density shown in FIG. 4 is reduced due to the volume expansion.

Therefore, the substitution effect of Bi contributes to the low-temperature sintering of the SDC electrolyte. However, it can be confirmed that the effect of substitution is excessive when applied in an excess amount. Specifically, it is preferable that the substitution effect does not exceed 5 mol% (X = 0.05) have.

2. Simultaneous substitution of Bi and Yb

2-1. Design of ceria electrolyte composition

First, in order to confirm the effect of substitution with Bi for general electrolyte SDC and the electrolyte (hereinafter, referred to as SYBC) in which Bi and Yb were simultaneously substituted and solubilized, a composition having the following chemical formula was designed.

Sample       Composition SDC Sm _0.2 Ce _0.8 O _1.9 SYBC Sm _0.16 Yb _0.02 Bi _0.02 Ce _0.8 O _1.9

2-2. Electrolyte Specimen Manufacturing

The SDC and SYBC of Table 2 were prepared by dissolving the metal nitrate raw material in pure water to the composition ratio and then dissolving the citric acid again. The mixed aqueous solution was stirred and heated at 250 ° C. to prepare a concentrate Respectively.

The concentrate was burned at 500 ℃. The burned SDC and SYBC powders were pulverized and dispersed through a wet ball mill process. After drying, they were heat treated at 1000 ℃ and then pulverized by a wet ball mill process.

The final synthesized SDC and SYBC powders were molded into flat and disk-shaped green compacts through uniaxial pressing.

- Flat-plate shaped body Size: 40mm width, 40mm length, 4mm thickness

- Disc-shaped molded body Size: Diameter 27mm, Thickness 3mm

The formed electrolyte specimens were sintered in the air at 1100 ~ 1400 ℃ for 3 hours.

2-3. Confirmation of sintering shrinkage, porosity and sintering density

6 shows the results of evaluating the shrinkage ratio of SDC and SYBC sintered bodies produced by the citric acid method and sintered in the air at 1100 ° C to 1400 ° C for 3 hours.

As a result of the shrinkage evaluation, the SDC electrolyte exhibited a typical ceramic sintering behavior in which the slope of the shrinkage gradually decreased with increasing sintering temperature, whereas the SYBC electrolyte showed the maximum shrinkage at the sintering temperature of 1200 ° C. And a decrease in shrinkage due to condensation.

7 and 8 are results of evaluating the porosity and sintering density of SDC and SYBC sintered bodies produced by the citric acid method and sintered in air at 1100 ° C to 1400 ° C for 3 hours using the Archimedes gravity method.

In the evaluation of the porosity, the SDC electrolyte showed a sharp decrease in porosity due to sintering densification in the range of 1100 ° C to 1300 ° C and a low porosity decrease in the high temperature range of 1300 ° C to 1400 ° C. The SYBC electrolyte was sintered at a low temperature of 1100 ° C to 1200 ° C The sintering densities of the sintered ceramics decreased rapidly due to the sintering densification and the low porosity decreased at the mid - temperature sintering temperature of 1200 ℃ ~ 1300 ℃ and the porosity increased due to the under - sintering at the high temperature range of 1300 ℃ ~ 1400 ℃. In particular, it is more preferable that the SYBC electrolyte has a porosity of 10% or less in the sample sintered at 1200 ° C for 3 hours, and it can be confirmed that the target low-temperature sintering property can be sufficiently secured.

The sintered density of SDC and SYBC showed similar results to the shrinkage behavior and showed the opposite behavior to porosity. As a result, the sintered density of SYBC electrolyte sintered at 1200 ° C and sintered at 1400 ° C was equivalent to that of SYBC The sintering characteristics at low temperature were remarkably high.

2-4. Confirmation of microstructure of sintered body

FIG. 9 is a microstructure photograph of a sintered compact of SDC and SYBC sintered at 1100 ° C and 1300 ° C using a scanning electron microscope. The SDC sintered at 1100 ° C showed sintering at the same temperature It can be seen that the SYBC electrolyte has already undergone significant densification. In SDC sintered at 1300 ℃, densification and crystal grain growth are progressing, and most of the grain size is fine to less than 0.5um. On the other hand, the SYBC electrolyte sintered at the same temperature has already undergone sufficient grain growth, .

10 is a graph showing the crystal structure of a general SDC electrolyte and a SYBC electrolyte formed by the same method, sintering at 1100 ° C and X-ray diffraction analysis, in an embodiment of the present invention. The crystal structure of sintered SDC and SYBC sintered at 1100 ° C was analyzed. As shown in Fig. 10, both of the electrolytes showed a fluorite crystal structure without any impurity phase or secondary phase, but the crystallinity of SYBC under densification was relatively high Respectively.

2-5. Ion conductivity checking

In order to evaluate ionic conductivity of sintered SDC and SYBC electrolytes at each temperature range, flat plate type electrolytic specimens were processed into bars of 2 mm in length, 2 mm in length and 20 mm in length, The change of ionic conductivity according to temperature was compared and analyzed.

The ionic conductivity of the cerium and zirconium type electrolytes having a fluorite structure is generally such that the higher the concentration of oxygen vacancies, the higher the sintered density, and the ionic radius of the cation exchanged for oxygen vacancy formation, Or Zr4 +) radii.

FIG. 11 is a graph showing ion conductivity of a general SDC electrolyte sintered at 1100 ° C. to 1400 ° C. according to an embodiment of the present invention by comparing the ionic conductivities of the SDC electrolytes at different operating temperatures using a DC four-terminal method. This indicates that the ionic conductivity of the SDC electrolyte is directly related to the sintering density. That is, the increase rate of the sintering density and the increase rate of the ionic conductivity with the sintering temperature increase are almost the same.

FIG. 12 is a graph showing ion conductivity of SYBC electrolytes sintered at 1100 ° C. to 1400 ° C. according to an embodiment of the present invention by comparing their ionic conductivities at operating temperatures using a DC four-terminal method. In the case of the SYBC electrolyte, all electrolytes except the sintered electrolyte at 1100 ° C exhibit equivalent ion conductivity due to the low-temperature sintering property. As a result, the ionic conductivity is equivalent to that of SDC already sintered at a low temperature.

FIG. 13 is a graph comparing ionic conductivities of SDC and SYBC electrolytes sintered at 1100 ° C. to 1400 ° C. at 750 ° C. according to an embodiment of the present invention, and shows the same result as the shrinkage ratio comparison result of FIG. 6. As shown in FIG. 13, the SYBC electrolyte of the present invention has an ionic conductivity of at least 0.02 S / cm at 750 ° C when sintered at 1100 ° C and has an ionic conductivity of at least 0.045 S / cm at 750 ° C when sintered at 1200 ° C. .

FIG. 14 is a graph comparing the ionic conductivities of SDC and SYBC electrolytes sintered at 1100 ° C. and 1200 ° C., which are low temperature sintering sections, according to an embodiment of the present invention. Due to the low temperature sintering property, the ionic conductivity of SYBC is relatively high, and thus it can be utilized as an anti-reaction film through low temperature sintering.

As a result, since the oxygen vacancies (O ₂ -δ, δ = 0.1) of SDC and SYBC are the same, the high ionic conductivity of SYBC through low temperature sintering can be judged as a result of substitution and employment of Bi and Yb, And shows the same pattern as the shrinkage ratio comparison result shown in the figure.

In particular, as shown in FIG. 14, the SYBC electrolyte sintered at 1100 deg. C and 1200 deg. C, which is a low temperature sintering section, has ionic conductivity of at least 0.02 S / cm at 750 deg. C, which is the most widely used SOFC driving temperature. Can be secured.

2-6. Unit cell production

In this embodiment, an output characteristic of a unit cell in which a SYBC electrolyte material is introduced as a reaction prevention film of a unit cell is analyzed.

 The electrolyte layer is formed by uniaxial pressing → electrolyte support sintering (1450 ℃ for 5 hours) → anode coating and heat treatment (1300 ℃ for 3 hours) → reaction coating SYBC coating and heat treatment (1200 ℃ for 3 hours) → LSCF cathode Coating and heat treatment (1050 占 폚, 3 hours).

Electrolytic support molding: 10Sc1CeSZ (10 mol% Sc ₂ O ₃ & 1 mol% CeO ₂ stabilized ZrO ₂ ) The electrolyte powder is uniaxially pressed using a 27 mm diameter mold.

  Electrolytic Support Sintering: Uniaxially pressed 27 mm disk-shaped electrolytic shaped body is sintered at 1450 ℃ for 5 hours in the atmosphere and mechanically processed to make an electrolyte support with a diameter of 20mm and a thickness of 300um.

Anode coating and heat treatment: A composite powder (NiO: 10Sc1CeSZ = 58: 42 wt%) having a controlled specific surface area (BET) of 8-10 m ² / g was prepared as a paste and screen- Is coated and then heat-treated at 1300 ° C for 3 hours in the air.

  SYBC reaction prevention film coating and heat treatment: SYBC electrolyte powder is made into a paste, then SYBC of 8 mm in diameter is coated through a screen printing process, followed by heat treatment at 1200 ° C. for 3 hours in the air.

Air electrode coating and heat treatment: A fine composite powder (LSCF: SYBC = 60: 40 wt%) with a controlled specific surface area (BET) of 8 to 10 m ² / g and a controlled specific surface area (BET) of 4 to 6 m ² / g Coarse LSCF powders were each prepared as a paste, and a CFF (cathode functional layer) and a cathode current collector (CCC) cathode having a diameter of 8 mm were coated through a continuous screen printing process and then heat-treated at 1050 ° C. for 3 hours in the air.

  The SYBC anti-reaction film is not formed for comparative evaluation, and the LSM air electrode (CFL = LSM (60): 10Sc1CeSZ (40), CCC = LSM) is applied.

2-7. Confirmation of unit cell output characteristics

FIG. 15 is a photograph showing a comparison of the microstructures of ESC applied with LSM air electrode and ESC applied with SYBC electrolyte as LSCF air electrode and reaction preventive membrane in the embodiment of the present invention. It can be seen that both of the prepared single cells were applied with the same electrolyte thickness of 300 μm.

FIG. 16 is a graph showing output densities obtained by driving ESC at 750 ° C., 800 ° C., and 850 ° C. using an LSM air electrode in an embodiment of the present invention. FIG. The ESC with the electrolyte was operated at 750 ° C, 800 ° C and 850 ° C to evaluate the power density.

For LSM cathode-based single cells, the maximum power density was 0.65 W / cm ² at a current density of about 1.6 A / cm ² at 850 ° C, and about 0.55 W / cm ² at a rated voltage of 0.7 V .

LSCF air electrodes, while the unit cells and the case of SYBC film is composed of the reaction, the maximum power density is the rated voltage conditions of about 1.8A / cm ² current density 0.95W / cm ^2, and at 0.7V at 850 ℃ about 0.85W / cm < ^{2 &} gt ;, which is about 45% when comparing the maximum power density.

The present invention relates to a ceria-based electrolyte for a ceria-based reaction preventive membrane for preventing interfacial reaction between a mixed conducting cathode and a zirconia-based electrolyte among components for a high-power solid oxide fuel cell (SOFC) Sintered at a lower temperature than that of the Sm-doped CeO ₂ (SDC) material, which is a ceria-based reaction preventive material, and provides a ceria-based electrolyte composition ensuring ion conductivity equal to that of a conventional SDC electrolyte material by controlling the total cation radius.

The ceria electrolyte according to the present invention is characterized in that Bi and Yb are simultaneously substituted with Sm to ensure low-temperature sintering characteristics upon introduction of Bi and control the total cation radius for ensuring oxygen ion conductivity by introduction of Yb.

It is possible to prevent diffusion and employment of zirconia-based electrolyte and ceria-based electrolyte due to high-temperature sintering, and to stably form an anti-reaction film through low-temperature sintering. Through the introduction of a new ceria- A solid oxide fuel cell having a high output density of 0.85 W / cm < ² > under the condition of a rated voltage can be manufactured.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. And will be apparent to those skilled in the art.

Claims (11)

A ceria (CeO ₂ ) electrolyte in which samarium (Sm), erbium (Yb) and bismuth (Bi) are simultaneously substituted and solubilized,
The total cation radius of the ceria (CeO ₂ ) electrolyte in which samarium (Sm), erbium (Yb) and bismuth (Bi) are solubilized at the same time is 0.98-0.99 Å,
The ceria electrolyte (CeO ₂ ) is produced by sintering at 1100 ° C to 1200 ° C,
When sintered at 1150 ° C, it has a sintered density of 95% or more,
When sintered at 1100 ° C, it has an ionic conductivity of at least 0.02 S / cm at 750 ° C,
When sintered at 1200 ° C, a ceria electrolyte having ionic conductivity of at least 0.045 S / cm at 750 ° C
[Chemical Formula 1]
Sm _x Yb _y Bi _z Ce _1-xyz O _{2 -?}
Y = 0.05, 0.02? Z? 0.05, 0.11? X + Y + Z? 0.27,? = (X + Y + Z) / 2
delete Fuel electrode;
A zirconia electrolyte formed by sintering simultaneously with the anode;
A ceria reaction prevention film formed by coating the ceria electrolyte of claim 1 on the surface of the zirconia electrolyte and then heat-treating the ceria electrolyte at a temperature ranging from 1100 ° C to 1200 ° C; And
A solid oxide fuel cell including an air electrode prepared by coating and heat-treating the surface of the ceria-
The method of claim 3,
Wherein the zirconia electrolyte is a zirconia-based electrolyte having a fluorite structure, the solid oxide fuel cell having a composition represented by the following formula (2)
(2)
(Re ₂ O ₃ ) _x (ZrO ₂ ) _1-x
- Re = at least one element selected from Y, Sc, Yb, Ce, Gd and Sm, 0.04? X?
The method of claim 3,
The air electrode is a mixed conductor of a perovskite (ABO ₃ ) crystal structure having both electron and oxygen ion conductivity, and is a solid oxide fuel cell having a composition represented by the following formula
(3)
ABO ₃
- At least one element selected from among La, Sm, Pr, Ba, Sr and Ca
- B = at least one element selected from Fe, Co, Ni and Cu
- the content ratio of A and B is 0.95? A / B? 1
delete The method of claim 3,
Wherein the cathode comprises a mixture conductor of 50 to 70 wt% of a perovskite (ABO ₃ ) crystal structure and 30 to 50 wt% of a ceria electrolyte, wherein the ceria electrolyte is a solid oxide fuel cell
[Chemical Formula 1]
Sm _x Yb _y Bi _z Ce _1-xyz O _{2 -?}
- 0.17? 0.005? Y? 0.05, 0.005? Z? 0.05, 0.11? X + Y + Z? 0.27,? = (X + Y + Z) / 2
The method of claim 3,
Wherein the cathode comprises a mixture conductor of 50 to 70 wt% of a perovskite (ABO ₃ ) crystal structure and 30 to 50 wt% of a ceria electrolyte, wherein the ceria electrolyte comprises a solid oxide fuel cell
[Chemical Formula 5]
Re _x Ce _1-x O _2-隆
- Re = at least one element selected from Gd, Sm, Y, Nd and Pr, 0.05? X? 0.2,? = X / 2
The method of claim 3,
Wherein the fuel electrode comprises a solid oxide fuel cell comprising a zirconia-based electrolyte having a fluorite structure of 30 to 50 wt% and NiO of 50 to 70 wt%
The method of claim 3,
The solid oxide fuel cell includes an anode supported cell (ASC), an electrolyte supported cell (ESC), or a solid oxide fuel (MSC) structure having a metal supported cell (MSC) battery
11. The method of claim 10,
The unit cell may be a solid oxide fuel cell, such as a planer-type, a tubular-type, or a flat-tube type,

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