KR102270111B1 - Perobskite based cathode material, cathode containing the same, and solid oxide fuel cell containing the same - Google Patents

Abstract

The cathode material according to the present invention is characterized in that it satisfies the following formula (1).
[Formula 1]
LaNi _a Fe _b Cu _c O ₃
In Formula 1, a+b+c=1 is satisfied, a is 0.55 to 0.75, and c is 0.05 to 0.2.

Description

Perovskite-based cathode material, cathode including the same, and solid oxide fuel cell including the same

The present invention relates to a perovskite-based cathode material usable for a solid oxide electrolytic cell or a solid oxide fuel cell.

It relates to a high-conductivity cathode material for a solid oxide electrolysis cell (hereinafter referred to as SOEC), and the ceramic cells for SOEC that are currently under development are solid oxide fuel cells (hereinafter referred to as SOFC). It is generally composed of the same material as the ceramic cell for use.

Therefore, most of the cathode materials for SOFC and SOEC ceramic cells are LSM (La _{1 - x} Sr _x MnO ₃ ) or LSCF (La _1-x Sr _x Co _1-y Fe _y O ₃ ) perovskite cathode materials. is becoming These cathode materials have strontium (Sr) as a key element, and as Sr is substituted into the A-site, it secures electrical and ionic conductivity that can be used as a cathode material.

However, _{LSM (La 1 - x Sr x} MnO 3) , or the case of using the air electrode material, such as _{LSCF (La 1-x Sr x} Co 1-y Fe y O 3), as the cell is driven for a long time in the air electrode and electrolyte interface SrZrO ₃ , the insulator impurity is formed, which causes a significant decrease in conductivity, which causes a decrease in the output of the cell, and further causes a serious phenomenon such as separation of the cathode.

In order to overcome this problem, _{research and development on LNF (LaNi 1 - x} Fe _x O ₃ ) material that does not contain Sr is being conducted, but there is a problem of low electrical conductivity.

Republic of Korea Patent Publication No. 10-2017-0124819

An object of the present invention is to provide a cathode material and cathode having excellent durability when applied to a solid oxide electrolytic cell or a solid oxide fuel cell.

Another object of the present invention is to provide a cathode material capable of preventing generation of non-conductive impurities due to long-time operation of a solid oxide electrolytic cell or a solid oxide fuel cell.

Another object of the present invention is to provide a cathode material having high electrical conductivity.

Another object of the present invention is to provide a cathode material having a high sintering density.

The perovskite-based cathode material according to the present invention satisfies the following formula (1).

[Formula 1]

LaNi _a Fe _b Cu _c O ₃

In Formula 1, a+b+c=1 is satisfied, a is 0.55 to 0.75, and c is 0.05 to 0.2.

In the perovskite-based cathode material according to an embodiment of the present invention, in Formula 1, a is 0.55 to 0.65, and c is 0.1 to 0.2.

The present invention also provides a cathode, the cathode according to the present invention comprises: a cathode current collector layer comprising a perovskite-based cathode material according to an embodiment of the present invention; and

and a cathode functional layer comprising a perovskite cathode material and an ion conductive material according to an embodiment of the present invention.

In the cathode according to an embodiment of the present invention, the ion conductive material may be gadolinium-doped ceria.

In the cathode according to an embodiment of the present invention, the ion conductive material _{satisfies Gd 1 - y} Ce _y O ₂ , and y may be 0.6 to 0.9.

In the cathode according to an embodiment of the present invention, the cathode functional layer may include 50 to 60 wt% of the perovskite compound and the remaining amount of the ion conductive material.

The present invention also provides a unit cell, wherein the unit cell includes an air electrode according to an embodiment of the present invention, an anode, and an electrolyte interposed between the cathode and the anode.

The present invention also provides a solid oxide fuel cell or a solid oxide electrolysis cell including the unit cell.

Since the cathode material according to the present invention contains a composition satisfying the following formula (1), it does not contain strontium, so it can fundamentally block the generation of non-conductive impurities such as _{SrZrO 3 by strontium, thereby significantly improving durability, and the existing LNF (LaNi 1 - x} Fe _x O ₃ ,x = 0.1 to 0.4) Compared to the material, there is an advantage of significantly improved electrical conductivity. In addition, the sintering density can be increased by the substitution of copper as a solid solution, and conversely, the cathode can be heat treated at a low temperature.

1 shows the results of X-ray diffraction analysis of the perovskite-based cathode material prepared by Preparation Example of the present invention.
2 is a view showing the results of measuring the sintering shrinkage according to the sintering of the perovskite-based cathode material according to the preparation example of the present invention.
3 is a view showing the results of observing the microstructure after sintering according to the sintering of the perovskite-based cathode material according to the preparation example of the present invention.
4 and 5 show the results of measuring the electrical conductivity according to the temperature of the perovskite-based cathode material prepared by the Preparation Example of the present invention.
6 shows the structure of a cell manufactured by applying the perovskite-based cathode material manufactured by Preparation Example of the present invention.
7 is a view showing the results of measuring the power density of the cell according to the embodiment and the comparative example of the present invention.

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 perovskite-based cathode material according to the present invention satisfies the following formula (1).

[Formula 1]

LaNi _a Fe _b Cu _c O ₃

In Formula 1, a+b+c=1 is satisfied, a is 0.55 to 0.75, and c is 0.05 to 0.2.

A _{- (x Sr x MnO 3 La} 1) or _{LSCF (La 1-x Sr x} Co 1-y Fe y O 3) a conventional solid oxide electrolysis cell, or an air electrode material is typically LSM containing strontium in the solid oxide fuel cell was used. However, when such cathode material including strontium is used, _{non-conductive impurities such as SrZrO 3} are generated when used for a long period of time, which causes a significant decrease in ion and electrical conductivity, and causes a decrease in durability.

_{Accordingly, while using the LNF (LaNi 1 - x} Fe _x O ₃ ) material that can fundamentally block the generation of non-conductive impurities by solving the problems of the cathode material containing strontium, LNF (LaNi _{1 - x} Fe _x O) ₃ ) As a result of conducting research to develop a cathode that has excellent electrical conductivity by overcoming the limitations of materials and can exhibit excellent power density when applied to a solid oxide fuel cell, the LNF (LaNi _{1 - x} Fe _x O) ₃ ) It was confirmed that high electrical conductivity and power density were exhibited when a part of iron (Fe) was substituted with copper (Cu) in the material, and accordingly, the present invention provides a perovskite-based cathode material satisfying the following Chemical Formula 1 to provide.

[Formula 1]

LaNi _a Fe _b Cu _c O ₃

In Formula 1, a+b+c=1 is satisfied, a is 0.55 to 0.75, and c is 0.05 to 0.2.

The perovskite-based cathode material according to the present invention can significantly improve electrical conductivity by using a compound satisfying the above formula (1) as the cathode material. Specifically, the perovskite-based compound of Chemical Formula 1 contains the same ratio of nickel and has an advantage of having an electrical conductivity at 600° C. or more that is 1.4 times higher than that of a compound that does not contain copper.

In Chemical Formula 1, if the content of nickel is high, it may cause a significant decrease in electrical conductivity, if the content of nickel is low, it may cause a decrease in durability, and when copper is included in a small amount, to promote the effect of improving the electrical conductivity by adding copper It is difficult, and when copper is included in a large amount, there is a problem that not only the overall electrical conductivity is lowered due to a change in the ratio of iron and nickel, but also the electrical conductivity decreases rapidly due to a rise in temperature.

Furthermore, through the substitutional solid solution of copper, the shrinkage rate of the sintering step during the manufacturing process of the perovskite-based cathode material can be improved and the densification effect can be increased. There is an advantage in that it is possible to manufacture a high perovskite-based cathode material.

More preferably, in the perovskite-based cathode material according to an embodiment of the present invention, in Formula 1, a may be 0.55 to 0.65, and c may be 0.1 to 0.2. By using a perovskite-based cathode material satisfying this range, the electrical conductivity in the range of 600 to 850 ° C. may be 400 S/cm or more, preferably 500 S/cm or more, and more preferably 550 S/cm or more, which It has the same nickel content and is 1.5 times, preferably 1.7 times or more, improved compared to the perovskite cathode material that does not contain copper, and the electrical conductivity of the perovskite cathode material can be significantly improved by the addition of copper As a result, there is an advantage in that the output density can be improved when applied to a solid oxide fuel cell.

Furthermore, in Formula 1, when a is 0.55 to 0.65 and c satisfies 0.1 to 0.2, _{not only the existing LNF (LaNi 1-x} Fe _x O ₃ ) material, but also LSM (La _{1 - x} Sr _x MnO ₃ ) or LSCF (La _{1 - x} Sr _x Co _{1 - y} Fe _y O ₃ ) Compared to the material, it is possible to achieve a significant improvement in power density when applied to a solid oxide electrolytic cell or a solid oxide fuel cell, and specifically, under the same conditions Compared to the case of using the conventionally used LSM (La _{1 - x} Sr _x MnO ₃ ) material as the cathode, there is an advantage that the maximum power density can be improved by more than 1.4 times.

In addition, in Formula 1, when a is 0.55 to 0.65 and c satisfies 0.1 to 0.2, a sintering shrinkage rate of 20% or more may be exhibited during sintering, and accordingly, a cathode having a dense structure can be manufactured.

In the method for manufacturing a perovskite-based cathode material according to an embodiment of the present invention, an oxide powder of a metal such as La, Ni, Fe, Cu, etc. is weighed according to a desired composition, mixed through a ball mill to prepare a slurry, and this It is possible to manufacture the perovskite cathode material according to an embodiment of the present invention by heat-treating and pulverizing it after drying.

The present invention also provides a cathode, the cathode according to the present invention comprises: a cathode current collector layer comprising a perovskite-based cathode material according to an embodiment of the present invention; and a cathode functional layer comprising a perovskite cathode material and an ion conductive material according to an embodiment of the present invention. That is, the cathode according to the present invention has a layered structure, and preferably, the cathode functional layer may have a structure in contact with the electrolyte through the reaction preventing film.

The cathode according to the present invention can overcome the low ionic conductivity of the perovskite cathode material by including the layered structure of the cathode current collector layer and the cathode functional layer, and maximize the effect due to the high electrical conductivity of the perovskite cathode material. There are advantages that can be

The ion-conducting material in the air electrode in accordance with one embodiment of the present invention may be a gadolinium-doped ceria, more specifically, the ion conductive material is Gd _{1 -} satisfies the formulas of _y Ce _y O _2, y is from 0.6 to 0.9. By mixing the ion conductive material that satisfies these conditions with the perovskite-based cathode material, it has the advantage of exhibiting high power density by preventing a decrease in power density with high ion conductivity.

More specifically, the cathode current collecting layer may be made of a perovskite-based cathode material, and the cathode functional layer may include 50 to 60% by weight of the perovskite-based cathode material and the remaining amount of the ion conductive material. When a small amount of the perovskite-based cathode material is included in the cathode functional layer, it may cause a decrease in electrical conductivity of the entire cathode, and if a large amount of the perovskite-based cathode material is included, there may be a problem of causing a decrease in ionic conductivity. .

The cathode according to an embodiment of the present invention may be manufactured by applying a paste for a cathode functional layer and a paste for a cathode current collector layer on an electrolyte or a reaction preventing film formed on the electrolyte, and then performing heat treatment. The application may be used without limitation in the case of a conventional paste application method, and screen printing may be preferably used, but the present invention is not limited thereto. In addition, the heat treatment may be performed at 950 to 1100° C. for 1 to 4 hours, and the heat treatment temperature and time may vary depending on the thickness of the cathode functional layer paste and the cathode current collector layer paste.

The cathode according to an embodiment of the present invention can be applied to a solid oxide electrolysis cell or a solid oxide fuel cell, and when applied to such a solid oxide electrolysis cell or a solid oxide fuel cell, it can be used without a decrease in output for a long period of time. have.

The present invention also provides a unit cell for a solid oxide fuel cell or a solid oxide electrolytic cell, the unit cell according to an embodiment of the present invention comprising: the cathode according to an embodiment of the present invention; anode; and an electrolyte interposed between the cathode and the anode. In this case, the anode and the electrolyte may be manufactured using a commonly used material, but the present invention is not limited thereto. In addition, the unit cell according to an embodiment of the present invention may include a reaction preventing film interposed between the cathode and the electrolyte in order to prevent a reaction between the cathode and the electrolyte, but the present invention is not limited thereto.

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.

1. Confirmation of physical properties of perovskite-based cathode materials

As a starting material for preparing the cathode specimen, oxide raw materials La ₂ O ₃ , NiO, Fe ₂ O ₃ , and CuO were applied, and the oxide powders were weighed to match the composition shown in Tables 1 and 2, followed by an ethanol solvent and zirconia (ZrO _{2 ).} ) was mixed through a ball mill process using balls. After drying, the mixed slurry was first calcined at 950° C. in the air for 3 hours, and then pulverized again by a wet ball mill process. After drying, secondary calcination was performed at 1200° C. in the air for 3 hours, and then pulverized again by a wet ball mill process and dried to complete powder synthesis. Synthetic powders were prepared into compacts having dimensions of 40 mm × 40 mm × 4 mm in width, length, and thickness, respectively, using a uniaxial pressure molding process.

In order to prepare a final sintered body, each cathode compact was sintered for 3 hours at a temperature of 1250° C. in an atmospheric atmosphere at normal pressure.

For the specimens for the analysis of the crystal structure of the cathode sintered bodies, the cathode specimens with a polished surface were used, and the electrolyte specimens for the evaluation of electrical conductivity were mechanically processed to have a size of 2mm × 2mm × 25mm in width, length and length respectively. Conductivity specimens was processed with

The electrical conductivity of the cathode specimens was measured using the DC 4-terminal method. The voltage according to the application of current was measured, and the resistance and conductivity were calculated by applying the cross-sectional area and length of the specimen. The measurement atmosphere was measured in an air atmosphere, and the measurement temperature was measured in a temperature range of 600-850°C, which is the driving temperature range of SOEC.

manufacturing example denomination chemical formula 1-0 LNF-73-0 LaNi _{0 . 7} Fe _{0 . 3} O ₃ 1-1 LNF-73-1 LaNi _0.7 Fe _0.25 Cu _0.05 O ₃ 1-2 LNF-73-2 LaNi _{0 . 7} Fe _{0 . 2} Cu _{0 . 1} O ₃ 1-3 LNF-73-3 LaNi _0.7 Fe _0.15 Cu _0.15 O ₃ 1-4 LNF-73-4 LaNi _{0 . 7} Fe _{0 . 1} Cu _{0 . 2} O ₃

manufacturing example denomination chemical formula 2-0 LNF-64-0 LaNi _{0 . 6} Fe _{0 . 4} O ₃ 2-1 LNF-64-1 LaNi _0.6 Fe _0.35 Cu _0.05 O ₃ 2-2 LNF-64-2 LaNi _{0 . 6} Fe _{0 . 3} Cu _{0 . 1} O ₃ 2-3 LNF-64-3 LaNi _0.6 Fe _0.25 Cu _0.15 O ₃ 2-4 LNF-64-4 LaNi _{0 . 6} Fe _{0 . 2} Cu _{0 . 2} O ₃

of the synthesized powder secondary Confirmation of formation

The synthetic powders prepared in Preparation Examples 1-0 to 2-4 were analyzed through X-ray diffraction, and the results are shown in FIG. 1 .

Looking at the results of X-ray diffraction analysis in FIG. 1, when 0.7 mol of nickel is included in 1 mol of lanthanum, a secondary phase is formed while copper is dissolved in 0.1 mol or more, and when 0.6 mol of nickel is included in 1 mol of lanthanum, copper is It can be confirmed that the secondary phase is formed as more than 0.2 mol is dissolved.

sintering shrinkage Confirm

In Preparation Examples 1-0 to 2-4, the sintering shrinkage according to the sintering heat treatment was measured at a temperature of 1250° C. for 3 hours, and the result is shown in FIG. 2, and the microstructure after sintering of each Preparation Example was observed and shown in FIG. It was.

Referring to FIG. 2 , it can be confirmed that the shrinkage rate due to sintering increases as the ratio of copper increases, and it can be seen that the overall sintering shrinkage rate is high when 0.6 mole of nickel is included compared to 1 mole of lanthanum. In addition, it can be confirmed that 0.6 mol of nickel is included relative to 1 mol of lanthanum, and when 0.05 mol or more of copper is dissolved, a sintering shrinkage rate of 20% or more can be exhibited.

Referring to FIG. 3 , it can be confirmed that the densification effect of the sintered body observed as a microstructure increases as the ratio of copper increases, and when the content of nickel is low, it can be confirmed that the densification effect according to the increase of the copper ratio is more excellent.

Check electrical conductivity

The electrical conductivity of each of the conductive specimens prepared in Preparation Examples 1-0 to 2-4 was measured using the DC 4-terminal method, and the results are shown in FIGS. 4 and 5 .

Referring to FIGS. 4 and 5 , it can be seen that the electrical conductivity when 0.6 mol of nickel is included compared to 1 mol of lanthanum is significantly higher than the electrical conductivity when 0.7 mol of nickel is included. In addition, it can be confirmed that, regardless of the nickel content, when the copper content is 0.15 mol, the highest electrical conductivity is exhibited, and when the copper content is low or high, the electrical conductivity is lowered. In particular, in the case of LNF-73-4 and LNF-64-4, which contain the largest amount of copper, it can be seen that the decrease in electrical conductivity is large as the temperature rises. In addition, it can be seen that the nickel content is 0.6 af, and the copper content exhibits significantly high electrical conductivity of 500 S/cm or more in the range of 0.05 to 0.15, and furthermore, the electrical conductivity of 600 S/cm or more in the range of 0.1 and 0.15 copper content It can be seen that the conductivity is indicated.

2. Application of perovskite cathode material

[Example 1]

LNFC-64-3 cathode material was applied to an anode supported cell (ASC). For the cathode application, a substrate on which an electrolyte (Electrolyte), an anode functional layer (AFL), and an anode supporter (AS) were simultaneously sintered was machined to a diameter of 20 mm and a thickness of 700 μm. LNFC 64-3-material is because the zirconia electrolyte and the _reactivity. As a reaction preventing film (Buffer Layer) material to the electrolyte surface prior to the air electrode coating GYBC (Gd _{0. 135} Yb _{0. 0 015} Bi ₀₂ Ce _{0. 83} O _{1. 915} ) paste was coated with a screen printing process and then heat-treated at 1250° C. for 2 hours to prepare a reaction preventing film.

Functional air electrode layer on a reaction barrier film: LNFC-64-3 to form a (CFL Cathode Functional Layer): ion conductive material, _{GDC (.. Gd 0 2 Ce} 0 8 O 2) of 53: 47 were mixed in a weight ratio of After preparing the paste, it was applied twice by screen printing, and after the screen printing process, pure LNFC-64-3 paste was applied once by screen printing for the production of a cathode current collector (CCC), 1050 ℃ was heat-treated for 2 hours to finally form a cathode functional layer and a cathode current collector layer.

[Comparative Example 1]

_{LSM-73 (La 0.7} Sr _0.3 MnO ₃ ): 8YSZ (8 mol% Y ₂ O ₃ stabilized ZrO ₂ ) as a cathode functional layer was applied to the surface of the same simultaneous sintered body as in Example 1 in a weight ratio of 60: 40, Here, a ceramic cell was manufactured using the same screen printing process and heat treatment using the LSM-73 material as the cathode current collector layer.

Evaluation of power density

The ceramic cells completed in Example 1 and Comparative Example 1 were driven at 650 to 800° C., and the supply amounts of air and hydrogen were controlled at 200 cc/min. Voltage and power density according to operating temperature and current density were evaluated, and the results are shown in FIG. 7 .

7 is a result of driving evaluation at the same 750 ° C. of the ceramic cell to which the cathode material according to the embodiment and the comparative example of the present invention is applied, and the cell to which the LSM-73 cathode as a comparative example is applied is 0.819 at a current density condition ^{of 0.4A/cm 2} It showed a voltage of V, and the resulting power density was calculated to be ^{about 0.33W/cm 2 .} On the other hand, the cell to which the LNFC-64-3 cathode of the embodiment was applied showed a voltage of 0.922V under the current density condition ^{of 0.4A/cm 2 , and the resulting output density was calculated to be about 0.37W/cm 2} , and the GYBC reaction prevention film was introduced. It can be seen that even if the resistance of the cathode is increased, the power density is rather improved as the performance of the cathode is improved. The maximum power density of the cell to which the LSM-73 cathode of the comparative example was applied was about 0.64 W/cm ² , while the maximum power density of the cell to which the cathode of LNFC-64-3 of the example was applied was about 0.93 W/cm ² . It can be seen that there is a large difference in the output density.

Claims (9)

It satisfies the following Chemical Formula 1,
Characterized in that the electrical conductivity is 600 S/cm or more at 600 to 850 ° C.
Perovskite-based cathode material.
[Formula 1]
LaNi _a Fe _b Cu _c O ₃
(In Formula 1, a+b+c=1 is satisfied,
a is 0.55 to 0.65,
c is 0.1 to 0.15.) delete A cathode current collector layer comprising the perovskite cathode material of claim 1; and
A cathode comprising a; cathode functional layer comprising the perovskite cathode material of claim 1 and an ion conductive material. 4. The method of claim 3,
The cathode, characterized in that the ion conductive material is ceria doped with gadolinium. 4. The method of claim 3,
The ion conductive material _{satisfies Gd 1 - y} Ce _y O ₂ , and y is 0.6 to 0.9. 4. The method of claim 3,
The cathode functional layer is a cathode comprising 50 to 60 wt% of a perovskite compound and the remaining amount of an ion conductive material. The cathode of claim 3;
anode; and
A single cell comprising an electrolyte interposed between the cathode and the anode. A solid oxide fuel cell comprising the unit cell of claim 7. A solid oxide electrolytic cell comprising the unit cell of claim 7.

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