KR101808387B1 - 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 gadolinium (Gd), erbium (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 for low temperature sintering, and a solid oxide fuel cell using the ceria electrolyte. BACKGROUND ART < RTI ID = 0.0 >

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 Cerium (CeO ₂ ) electrolyte having a low temperature sintering property at the same time and a solid oxide fuel cell using the same.

Currently, a zirconia-based electrolyte such as 8YSZ (8 mol% Y ₂ O ₃ stabilized ZrO ₂ ) is the most widely used electrolyte material for a unit cell for a solid oxide fuel cell (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. (MIEC) air electrode material such as LSCF (Sr & Co doped LaFeO ₃ ) is used in order to increase the W / cm ² .

Most mixed conducting cathode materials, such as LSCF, react at the interface with the zirconia electrolyte at the heat treatment temperature range of the cathode to form reaction products of non-conducting properties. Therefore, the high temperature reaction of mixed conducting cathode such as LSCF and zirconia electrolyte In recent years, an anti-reaction film is additionally introduced between the air electrode and the electrolyte.

In particular, the ceria electrolyte (Gd or Sm-doped CeO ₂ ) is most widely applied as an anti-reaction film material for preventing the reaction products between the electrolyte and the air electrode, which is formed between the zirconia (ZrO ₂ ) electrolyte membrane and the mixed conducting cathode layer of the SOFC have.

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, A sintering condition of 1300 DEG C or more is required.

In addition, in the case of forming a dense electrolyte by sintering at 1300 ° C. or higher, and then forming a ceria-based reaction preventive film through coating and heat treatment on the surface of the electrolyte membrane, the already sintered electrolyte membrane does not shrink together and is difficult to form a dense ceria electrolyte There is a drawback that the 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 has been devised in view of the above-mentioned needs. It is an object of the present invention to provide a method for manufacturing a Gd doped CeO ₂ (GDC) electrolyte, which further comprises a step of 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 achieve the above object, the ceria electrolyte for low temperature sintering according to the present invention is characterized in that gadolinium (Gd), ytterbium (Yb) and bismuth (Bi) ₂ ) As the electrolyte, it may have a composition represented by the following formula (1).

[Chemical Formula 1]

Gd _x Yb _y Bi _z Ce _{1- xy z} O _{2 -?}

- 0.05? X? 0.15, 0.005? Y? 0.05, 0.005? Z? 0.05, 0.06? X + Y + Z? 0.25,? = (X + Y + Z) / 2

The total cation radius of the ceria (CeO ₂ ) electrolyte in which the gadolinium (Gd), erbium (Yb) and bismuth (Bi) are solubilized at the same time may 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

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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]

Gd _x Yb _y Bi _z Ce _{1- xy z} O _{2 -?}

- 0.05? X? 0.15, 0.005? Y? 0.05, 0.005? Z? 0.05, 0.06? X + Y + Z? 0.25,? = (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 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 gadolinium (Gd), erbium (Yb) and bismuth (Bi) It shows a similar total cation radius and can exhibit a high sintered density of 95% or more even at a sintering temperature of 1200 ° C while maintaining a high oxygen ion conductivity of a conventional GDC electrolyte.

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 total cation radii of commercial GDC electrolytes.
2 is a graph showing total cation radii of GDC electrolytes in which Yb is further substituted and solubilized.
3 is a graph showing the total cation radii of the GDC electrolyte in which Bi is additionally substituted and solubilized.
4 is a graph showing the total cation radii according to the composition of the substituted solid solution of ceria electrolyte according to the embodiment of the present invention.
5 is a graph showing the sintered density of the GDC 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. 6 is a graph showing the increase in the Bi content by the solid-phase reaction method and the shrinkage ratio of the GDC electrolyte according to the sintering temperature increase according to the embodiment of the present invention.
FIG. 7 is a graph showing sintering shrinkage ratios of selenium electrolyte compositions in which Bi and Yb are co-solved according to an embodiment of the present invention, after sintering at 1200 ° C. for 5 hours through a solid phase reaction method.
FIG. 8 is a graph showing selenium electrolyte compositions according to an embodiment of the present invention by sintering at 1200 ° C. for 5 hours through a solid-phase reaction method, and measuring ion conductivity according to operating temperature using a DC four-terminal method.
FIG. 9 is a graph showing sintering shrinkage ratios according to sintering temperatures after forming the electrolyte of the CE-3 composition synthesized by the co-precipitation method in the embodiment of the present invention by the same method as that of the commercial GDC electrolyte.
10 is a graph showing sintered density according to sintering temperature after forming the electrolyte of the CE-3 composition synthesized by coprecipitation in the embodiment of the present invention by the same method as that of the commercial GDC electrolyte.
FIG. 11 is a photograph of a microstructure according to a sintering temperature of a CE-3 electrolyte synthesized by coprecipitation in the same manner as a conventional GDC electrolyte and analyzed by a scanning electron microscope.
12 is a graph showing the comparison of the crystal structure of the electrolyte of the CE-3 composition synthesized by coprecipitation in the embodiment of the present invention by sintering at 1200 DEG C after sintering in the same manner as the commercial GDC electrolyte and by X-ray diffraction analysis .
FIG. 13 is a graph showing the comparison of ionic conductivities at operating temperatures by sintering the electrolyte of the CE-3 composition synthesized by the coprecipitation method at 1200 ° C., 1300 ° C., and 1400 ° C., respectively, Graph.
FIG. 14 is a graph comparing the ionic conductivities at operating temperatures of the electrolyte of the CE-3 composition synthesized by coprecipitation according to the present invention and the commercial GDC electrolyte at 1150 ° C. and 1300 ° C., respectively, Fig.
FIG. 15 is a photograph of a microstructure of a fractured surface of an ESC-1 and ESC-2 unit cell manufactured through an embodiment of the present invention, using a scanning electron microscope.
16 is a graph showing the voltage and power density according to current density when the ESC-1 and ESC-2 unit cells manufactured through the embodiment of the present invention are driven at 850 ° C.

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 gadolinium (Gd), erbium (Yb) and bismuth (Bi) Lt; / RTI >

[Chemical Formula 1]

Gd _x Yb _y Bi _z Ce _{1- xy z} O _{2 -?}

- 0.05? X? 0.15, 0.005? Y? 0.05, 0.005? Z? 0.05, 0.06? X + Y + Z? 0.25,? = (X + Y + Z) / 2

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

In GDC electrolytes, the ionic conductivity increases with increasing substitutional amount of Gd, but when it is dissolved in excess, the ionic conductivity decreases due to the bonding of oxygen vacancies. Generally, the amount of Gd dissolved in the ceria (CeO ₂ ) electrolyte is 10 to 20 mol% or less, and the highest ionic conductivity is shown in this range.

The ceria electrolyte for low-temperature sintering according to the present invention is used for securing the low-temperature sintering property of the GDC electrolyte and for maintaining high ion conductivity, and introducing bismuth (Bi) as an additional substituting solid element for low temperature sintering property, It is possible to introduce Yb as an additional substituting element. The cation radii of Gd ³⁺ , Bi ³⁺ , Ce ⁴⁺ and Yb ³⁺ are 1.053 Å, 1.17 Å, 0.97 Å and 0.985 Å, respectively.

The composition of the GDC electrolyte, which is currently used as a composition with the highest ionic conductivity, is Gd _x Ce _1-x O _{2- (x / 2)} and X = 0.1-0.2. The average ion radius of all the cations As shown in Fig. As can be seen from the above calculation results, the size of the cation radius of the commercialized GDC electrolytes is about 0.978 to 0.987 (Å).

The change in the cation radius with respect to the GDC electrolyte (Gd _2-x Yb _x Ce _0.8 O _1.9 ) in which Yb is further substituted and solved is the same as the result in Fig. 2, and a part of Gd is replaced with Yb having a relatively small ionic radius, Calculations show that the total cation radius decreases with increasing solubility.

On the other hand, the change in cation radius for the case of a GDC electrolyte (Gd _0.15 Bi _x Ce _0.85-x O _{2- (0.15 + x) / 2} ) It can be confirmed by calculating that the total ion radius increases as the substitution solubility increases with the relative solubility of Bi having a large ion radius.

In order to secure the low-temperature sintering property of the existing GDC electrolyte, the effect of increasing the total radius of the cation is increased when the substitution of Bi is further carried out. ) To narrow the conduction of oxygen ions.

Therefore, in the present invention, Yb having an ionic radius smaller than that of Gd can be simultaneously substituted to suppress the increase of the total cation radius due to substitution of Bi having a relatively larger ionic radius than Gd.

4 is a graph showing the total cation radii according to the composition of the substituted solid solution of ceria electrolyte according to the embodiment of the present invention. The total cation radius of the ceria (CeO ₂ ) electrolyte in which the gadolinium (Gd), erbium (Yb) and bismuth (Bi) are solubilized at the same time may 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

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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]

Gd _x Yb _y Bi _z Ce _{1- xy z} O _{2 -?}

- 0.05? X? 0.15, 0.005? Y? 0.05, 0.005? Z? 0.05, 0.06? X + Y + Z? 0.25,? = (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 cell can be fabricated as an anode support type, an air cathode support type, and a segment-type, and the plate type can be manufactured as an anode support body, an electrolyte support body, and a 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

(Gd _x Ce _1-x O _{2-x / 2} , X = 0.1, 0.2) as shown in the following Table 1 and an electrolyte (Gd _0.1 Bi _x Ce _0.9-x O _{1.95-x / 2} , X = 0.025, 0.05, 0.075, 0.1).

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

1-2. Electrolyte Specimen Manufacturing

Gd ₂ O ₃ , Bi ₂ O ₃ and CeO ₂ were used as raw materials for the synthesis of the electrolytes of the above Table 1, and after weighing according to the composition, ethanol was used as a solvent and zirconia balls having a diameter of 5 mm were used as milling media, Followed by ball milling.

The wet mixed electrolyte slurries were dried at 75 ℃ and then compacted into flat and disk-shaped green compacts by 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 air at 1100 ℃ to 1400 ℃ for 5 hours.

1-3. Determination of density and shrinkage of sintered body

FIG. 5 is a graph showing the relationship between GDC (GdxCe1 _- xO2 _{-x / 2} , X ( _{x)) obtained} by sintering at 1100 DEG C, 1200 DEG C, 1300 DEG C and 1400 DEG C for 5 hours using the powder synthesized by the solid- = 0.1, x = 2) electrolyte, GDC-19 (x = 0.1 ), GDC-28 (x = 0.2) electrolyte and Gd and Bi substituted employed at the same time the electrolyte _{(Gd 0.1 Bi x Ce 0.9-} x O 1.95-x _{/ 2} , X = 0.025, 0.05, 0.075, 0.1).

The results of FIG. 5 indicate that when the target sintering temperature is 1100 ° C. and 1200 ° C., the sintering density increases as the content of Bi increases. At a high temperature sintering temperature of 1300 ° C., = 0.075, 0.1), it can be confirmed that the sintered density is lower than 1200 ° C.

FIG. 6 is a graph showing the shrinkage ratios of electrolyte specimens sintered at 1200 ° C. and 1300 ° C., which correspond to the results of FIG. 5, calculated by the following equation.

The results of FIG. 6 indicate that the sintered electrolyte specimens sintered at 1200 ° C increase shrinkage as the Bi content increases, and that the reduction 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 ℃ show an increase in the shrinkage ratio with increasing Bi content, a maximum shrinkage ratio at the X = 0.05 composition, and a contraction rate lower as the Bi content increases. That is, the increase in the shrinkage ratio is a volume expansion due to the over-molding, and it can be judged that the sintering density shown in FIG. 5 is reduced due to the volume expansion.

Therefore, the substitution effect of Bi contributes to the low-temperature sintering of the GDC 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 Bi substitution on the electrolyte in which Bi and Yb are simultaneously substituted in Gd doped ceria (GDC), a composition having the following chemical formula was designed.

Sample   Composition CE-1 (Gd _0.9 Yb _0.1 ) _0.15 Ce _0.85 O _1.925 Gd _0.135 Yb _0.015 Ce _0.85 O _1.925 CE-2 (Gd _0.9 Yb _0.1 ) _0.15 Bi _0.01 Ce _0.84 O _1.92 Gd _0.135 Yb _0.015 Bi _0.01 Ce _0.84 O _1.92 CE-3 (Gd _0.9 Yb _0.1 ) _0.15 Bi _0.02 Ce _0.83 O _1.915 Gd _0.135 Yb _0.015 Bi _0.02 Ce _0.83 O _1.915 CE-4 (Gd _0.9 Yb _0.1 ) _0.15 Bi _0.03 Ce _0.82 O _1.91 Gd _0.135 Yb _0.015 Bi _0.03 Ce _0.82 O _1.91 CE-5 (Gd _0.9 Yb _0.1 ) _0.15 Bi _0.04 Ce _0.81 O _1.905 Gd _0.135 Yb _0.015 Bi _0.04 Ce _0.81 O _1.905 CE-6 (Gd _0.9 Yb _0.1 ) _0.15 Bi _0.05 Ce _0.8 O _1.9 Gd _0.135 Yb _0.015 Bi _0.05 Ce _0.8 O _1.9

FIG. 4 shows the results of calculation of the total cation radii of the electrolytes of the above composition, which are in the range of 0.98 to 0.99 (Å), and are well controlled by the total cation size of conventional commercial GDC electrolytes.

2-2. Electrolyte Specimen Manufacturing

In order to synthesize the ceria electrolyte of Table 2, Gd ₂ O ₃ , Yb ₂ O ₃ , Bi ₂ O ₃ and CeO ₂ were used as raw materials, and after weighing according to the composition, ethanol was used as a solvent and zirconia balls Was mixed with a wet ball mill using a milling media.

The wet mixed electrolyte slurries were dried at 75 ℃ and then compacted into flat and disk-shaped green compacts by uniaxial pressing.

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

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

The electrolyte specimens were sintered at 1200 ℃ for 5 hours in air. For comparative evaluation, electrolyte specimens were prepared using commercial GDC (Gd _0.1 Ce _0.9 O _1.95 , LN grade of Anan Kasei Co., Japan) powder.

2-3. Determination of density and shrinkage of sintered body

FIG. 7 is a graph showing the shrinkage ratio for ceria electrolytes sintered at 1200 ° C. for 5 hours at the same time as Yb and Bi shown in Table 2 are substituted at the same time, and the same tendency as the shrinkage rate behavior of sintered electrolytes at 1200 ° C. As a result, it can be confirmed that the target low-temperature sintering characteristics can be secured even if Bi is applied at 5 mol% or less.

Particularly, when Bi is added in an amount of 2 mol% or more as in Examples CE-3 to CE-6 having a shrinkage ratio of 10% or more in a sample synthesized by a solid-phase reaction method and sintered at 1200 ° C for 5 hours as shown in FIG. 7, .

2-4. Ion conductivity checking

FIG. 8 is a graph showing the results of processing of CE-1 to 6 flat electrolyte specimens sintered at 1200 ° C for 5 hours in a bar shape of 2 mm in width, 2 mm in length and 20 mm in length, This is the result of comparative analysis of changes in ionic conductivity.

The ionic conductivities of ceria and zirconia type electrolytes having a fluorite structure are generally as follows: the higher the oxygen vacancy concentration, the higher the sintering density, and the larger the ion radius of the cation exchanged for oxygen vacancy formation, ⁴⁺ or Zr ⁴⁺ ) radii.

The results of FIG. 8 show that as the substitutional amount of Bi increases from CE-1 to CE-4, the ionic conductivity increases and the ionic conductivity of commercial GDC electrolyte sintered at 1400 ° C. is close to that of main electrode As a result, the sintering density and oxygen vacancy increase with increasing Bi content can be explained. Bi, like Gd ³⁺ and Yb ³⁺ , is present in the electrolyte lattice as Bi ³⁺ and thus forms oxygen vacancies.

Particularly, as shown in Fig. 8, 2mol% to 4mol% of Bi is applied as in Examples CE-3 to CE-5 having ionic conductivities of 0.02S / cm or more at 700 ° C to 800 ° C, .

2-5. Comparison with commercial GDC electrolytes

The ceria electrolyte of CE-3 was synthesized by the wet coprecipitation method which is a commercial synthesis process. The water-soluble Gd nitrate (Gd (NO ₃ ) ₃ · 6H ₂ O), Yb nitrate (Yb (NO ₃ ) ₃ · 6H ₂ O ), Bi nitrate (Bi (NO ₃ ) ₃ · 5H ₂ O) and Ce nitrate (Ce (NO ₃ ) ₃ · 6H ₂ O) were dissolved in pure water to prepare a 0.25M mixed nitrate solution.

Ammonia water (NH ₄ OH) as a precipitant was added dropwise to the mixed nitrate at a rate of 100 cc / min using a metering pump while the mixed nitrate was continuously stirred, and the precipitated amorphous metal hydrate was washed 5 times, The final CE-3 electrolyte powder was synthesized by wet ball milling and drying after calcination heat treatment at 970 ℃ for 3 hours for grain growth and crystallization of powders.

The CE-3 powders synthesized by coprecipitation method and Lans grade powder of Anan Kasei for comparative evaluation were compacted into flat and disk-shaped green compacts by 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 air at 1100 ~ 1400 ℃ for 5 hours.

FIG. 9 shows the results of comparing shrinkage ratios of CE-3 electrolytes prepared by coprecipitation and commercial sintered Anan kasei GDC electrolytes at the same temperature. The CE-3 electrolyte showed the maximum shrinkage at 1200 ° C, but the shrinkage rate of commercial GDC tends to increase with increasing sintering temperature.

10 shows the results of comparing the sintered densities of the CE-3 electrolytes prepared by the coprecipitation method with those of the commercial Anan kasei GDC electrolyte sintered at the same temperature, In other words, the CE-3 electrolyte can be judged to have undergone shrinkage sintering at 1200 ° C and to undergo grain growth and over-sintering as the sintering temperature becomes higher. Commercial GDC shows continuous shrinkage and sintering until 1400 ° C can do.

The results of the microstructure analysis using the scanning electron microscope of FIG. 11 show that the densification and grain growth of the commercial GDC are progressed at the same time as the sintering temperature is increased, while the CE-3 electrolyte is already densified at 1100 ° C. As the sintering temperature increases, the grain growth only continues.

FIG. 12 shows the crystal structure of CE-3 and commercial GDC electrolyte specimens sintered at 1200 ° C using an X-ray diffractometer, and both specimens showed the same pattern. However, in the relatively low temperature sintered region, CE- The electrolyte shows high crystallinity.

FIG. 13 shows the result of measurement of ion conductivity at 700 ° C to 800 ° C, which is most widely used as a SOFC driving temperature, in CE-3 electrolyte specimens synthesized by coprecipitation and sintered at 1200 ° C, 1300 ° C and 1400 ° C. The ionic conductivity of CE-3 electrolyte specimens sintered at 1200 ℃, which has the highest sintering density and shrinkage ratio, shows the highest ionic conductivity at the same temperature, and the higher the sintering temperature, the lower the ionic conductivity.

The reason for this is that as the sintering temperature increases, the sintering density is lowered due to the undersurface condensation, and the Bi element has a characteristic of volatilizing at high temperature, which can be judged as a pore formation and a reduction effect of oxygen vacancies.

FIG. 14 is a graph comparing the ionic conductivities of the CE-3 electrolyte specimens sintered at 1150 ° C. and the commercial GDC electrolyte specimens sintered at 1300 ° C. according to the coprecipitation method. As the operating temperature increases over 700 ° C., 3, the ionic conductivity of the electrolyte is measured to be higher.

2-6. Unit cell production

In this example, the output characteristics of the unit cell in which the CE-3 electrolyte powder synthesized by the coprecipitation method was introduced as the reaction prevention film of the unit cell was analyzed.

The unit cell is composed of an electrolyte supported cell (ESC). The manufacturing sequence of the unit cell can be fabricated by forming the electrolyte support, sintering the electrolyte support, coating the anode and heat treatment, and coating the cathode and heat treatment.

A unit cell (ESC-1) using LSM (Sr doped LaMnO ₃ ) air electrode was fabricated by the above process and a unit cell (ESC-2) using LSCF (Sr & Co doped LaFeO ₃ ) -3 electrolyte was coated and heat treated.

Electrolytic support forming step:

10Sc1CeSZ (10 mol% Sc ₂ O ₃ + 1 mol% CeO ₂ + 89 mol% ZrO ₂ ) electrolyte powder was uniaxially pressed to produce a disc-shaped molded product having a diameter of 25 mm and a thickness of 2 mm.

Electrolytic support sintering:

The disk-shaped electrolytic shaped body was sintered at 1450 ° C for 5 hours in the atmosphere and processed into an electrolyte support having a diameter of 20 mm and a thickness of 300 μm.

Anode coating and heat treatment:

A fuel electrode composite powder (NiO: 10Sc1CeSZ = 57: 43 wt%) was prepared as a printing paste, coated with a 10 mm diameter anode through a screen printing process, and heat-treated at 1250 ° C for 3 hours in the air.

Reaction barrier coating and heat treatment:

In the case of the LSCF air electrode unit cell (ESC-2), the CE-3 electrolyte powder synthesized by coprecipitation was coated in the same manner as the fuel electrode and then heat-treated at 1150 ° C. for 3 hours in the air.

Air electrode coating and heat treatment:

LSM (La _0.7 Sr _0.3 MnO ₃ ) air electrode and LSCF (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ) air electrode were used as the cathode material for ESC-1 and ESC-2, : 10Sc1CeSZ = 60: 40 wt%) and LSM air electrode were coated by a continuous process and heat-treated at 1050 ° C for 3 hours.

In the case of ESC-2, the air electrode composite (LSCF: CE-3 = 60: 40 wt%) and the LSCF air electrode were coated by a continuous process and heat-treated at 1050 ° C for 3 hours.

In this embodiment, although the air electrode heat treatment temperature is set to 1050 캜, the air electrode heat treatment temperature may be varied from 1000 캜 to 1200 캜 through particle size control of the air electrode powder.

2-7. Confirmation of unit cell output characteristics

FIG. 15 is a microstructure analysis result of ESC-1 and ESC-2 produced by this embodiment, showing a dense electrolyte and a porous air electrode microstructure. Particularly, ESC-2 and CE- It is possible to confirm that the interfacial adhesion strength to the electrolyte is excellent while being dense through the low temperature heat treatment at 1150 ° C.

The ESC-1 and ESC-2 were used to evaluate the output characteristics at 850 ° C, which is the normal ESC driving temperature. Air and hydrogen were supplied to the air electrode and fuel electrode at 150cc and 50cc per minute, respectively. Figure 16 is the maximum output density of the ESC-1 and is illustrated by comparing the results for the output characteristics of the ESC-2 ESC-1 and the ESC-2 are each 0.61W / cm ² and 0.81W / cm ² was 1A / cm ² by And the output densities were 0.58 W / cm ² and 0.68 W / cm ^{2 at} the current density condition, respectively.

As a result, ESC-2, which is composed of CE-3 reaction barrier and LSCF mixed conductive cathode formed by low-temperature heat treatment, showed 30% higher maximum power density than ESC-1 using LSM air electrode at the same temperature.

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) (GDC), which is a ceria-based reaction preventive material, can be sintered at a lower temperature than that of the GD-doped CeO ₂ (GDC) material and can control the total cation radius to provide a ceria electrolyte composition ensuring ion conductivity equal to that of a conventional GDC electrolyte material.

The ceria electrolyte according to the present invention is characterized in that Bi and Yb are substituted by Gd at the same time to secure the low-temperature sintering property according to the introduction of Bi and control the total cation radius for ensuring oxygen ion conductivity by introduction of Yb.

It is possible to prevent diffuse employment of zirconia-based electrolyte and ceria-based electrolyte due to high-temperature sintering, and to stably form a reaction prevention film through low-temperature sintering. By introducing a new ceria-based reaction prevention film, A solid oxide fuel cell 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)

Gadol Solarium (Gd), data biyum (Yb) and bisseu mousse (Bi) having the same time as replacement of ceria (CeO ₂₎ the electrolytes employed, the composition of the formula,
Wherein the total cation radius of the ceria (CeO ₂ ) electrolyte in which the gadolinium (Gd), erbium (Yb) and bismuth (Bi) are solubilized at the same time is 0.98-0.99 Å,
A ceria electrolyte having a sintered density of 95% or more at a sintering temperature of 1200 캜
[Chemical Formula 1]
Gd _x Yb _y Bi _z Ce _{1- xy z} O _{2 -?}
Y = 0.05, 0.005? Y? 0.05, 0.06? X + Y + Z? 0.25,? = (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]
Gd _x Yb _y Bi _z Ce _{1- xy z} O _{2 -?}
- 0.05? X? 0.15, 0.005? Y? 0.05, 0.005? Z? 0.05, 0.06? X + Y + Z? 0.25,? = (X + Y + Z) / 2
The method of claim 3,
Wherein the cathode comprises a mixed conductor of 50 to 70 wt% of a perovskite (ABO ₃ ) crystal structure and 30 to 50 wt% of a ceria electrolyte, wherein the cathode 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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