KR20230129789A - Single cell for solid oxide fuel cell including a cathode capable of preventing secondary phase formation and solid oxide fuel cell containing thereof - Google Patents

Abstract

The single cell for a solid oxide fuel cell according to the present invention is characterized by including an air electrode containing a compound of the following formula (1).
[Formula 1]
LaNi _x Fe _y Cu _(1-xy) O ₃
In Formula 1, x is 0.4 to 0.7, y is 0.2 to 0.4, and (1-xy) is greater than 0 and less than or equal to 0.2.

Description

Single cell for solid oxide fuel cell including a cathode capable of preventing secondary phase formation and solid oxide fuel cell containing the same}

The present invention relates to a solid oxide fuel cell that includes a cathode that does not contain Sr and can fundamentally block secondary phase formation by Sr, and a reaction prevention membrane that has an additional electrochemical reaction function.

In the case of solid oxide cells used in high-temperature fuel cells and high-temperature water electrolysis, high-performance mixed ionic & electronic conductors (MIEC: Mixed Ionic & Electronic Conductor) such as LSCF (Sr&Co doped LaFeO ₃ ) are mainly used as air electrode materials.

However, cathode materials containing Sr, such as LSCF, have the disadvantage of reacting with zirconia electrolyte during the coating and heat treatment steps to generate a SrZrO ₃ secondary phase with insulating properties, and this SrZrO ₃ is a non-conducting material that significantly reduces battery performance. there is.

Therefore, to solve this problem, an anti-reaction film (Gd or Sm doped CeO ₂ ) is additionally applied between the mixed conductive air electrode and the electrolyte interface. Applying an anti-reaction film has the effect of preventing the creation of secondary phases, but as additional anti-reaction films are applied, the resistance of the cell increases, which ultimately reduces cell performance. In order to minimize performance degradation, it is necessary to reduce the thickness of the anti-reaction film as much as possible while densifying it. Skills that can do it are required.

The most efficient way to densify the anti-reaction film is to increase the heat treatment temperature, but ceria (CeO ₂ ) and zirconia (ZrO ₂ ) form a solid solution when heat treated above 1250°C, so it is necessary to increase the heat treatment temperature. There is a limit. Accordingly, methods such as applying additives to increase low-temperature sinterability have been proposed, but there are limits to densification of the reaction prevention film.

As a result, due to limitations in densifying the reaction prevention film, there is a problem in that when the solid oxide cell is operated for a long time, the Sr in the air electrode moves the reaction prevention film and creates a SrZrO ₃ secondary phase on the electrolyte surface.

Republic of Korea Patent Publication No. 10-2021-0028416

The purpose of the present invention is to provide an air electrode that can fundamentally prevent the generation of a secondary phase of SrZrO ₃ and a single cell for a solid oxide fuel cell including the same, and thereby prevent the degradation of battery durability due to the generation of a secondary phase of SrZrO ₃ There is an advantage.

The single cell for a solid oxide fuel cell according to the present invention is characterized by including an air electrode containing a compound of the following formula (1).

[Formula 1]

LaNi _x Fe _y Cu _(1-xy) O ₃

In Formula 1, x is 0.4 to 0.7, y is 0.2 to 0.4, and (1-x-y) is greater than 0 and less than or equal to 0.2.

In a single cell for a solid oxide fuel cell according to an embodiment of the present invention, the air electrode may be characterized in that it does not contain Sr.

In the single cell for a solid oxide fuel cell according to an embodiment of the present invention, the single cell for a solid oxide fuel cell may be characterized in that a secondary phase containing Sr is not generated at the interface between the air electrode and the electrolyte.

In a single cell for a solid oxide fuel cell according to an embodiment of the present invention, the air electrode may include an air electrode current collection layer and an air electrode functional layer.

In a single cell for a solid oxide fuel cell according to an embodiment of the present invention, the cathode functional layer is characterized in that it includes a compound of Formula 1 and Re-doped ceria of Formula 2 below.

[Formula 2]

Re _a Ce _(1-a) O _b

In Formula 2, Re=Gd, Sm, Y, a is 0.1 to 0.2, and b is 1.9 or more and less than 1.95.

In a single cell for a solid oxide fuel cell according to an embodiment of the present invention, the single cell for a solid oxide fuel cell may be characterized in that an air electrode current collection layer, an air electrode functional layer, a reaction prevention film, an electrolyte, an anode functional layer, and an anode support are sequentially stacked. You can.

In a single cell for a solid oxide fuel cell according to an embodiment of the present invention, the reaction prevention film may include a compound of the following formula (3) as a sintering additive.

[Formula 3]

(La _(1-m) Sr _m ) _n MnO ₃

In Formula 3, m is 0.1 to 0.5, and n is greater than 0 and less than or equal to 0.98.

A single cell for a solid oxide fuel cell according to the present invention includes an air electrode containing a compound of the following formula (1). The single cell for a solid oxide fuel cell according to the present invention includes an air electrode of the following formula _{(1), and since the air electrode does not contain Sr, it has the advantage of fundamentally preventing the creation of a secondary phase of SrZrO 3 ,} and thus the It has the advantage of preventing degradation of battery durability due to secondary phase generation.

[Formula 1]

LaNi _x Fe _y Cu _(1-xy) O ₃

In Formula 1, x is 0.4 to 0.7, y is 0.2 to 0.4, and (1-x-y) is greater than 0 and less than or equal to 0.2.

Figure 1 shows a comparison of cell voltage and power density according to current density of cells manufactured according to an example.
Figure 2 shows a comparison of cell voltage and output density under a current density condition of 0.4 A/cm2.
Figure 3 illustrates a cross-section of a cell manufactured according to an example after operation, observed through a scanning electron microscope.

Advantages and features of the embodiments of the present invention and methods for achieving them will become clear by referring to the embodiments described in detail below along with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various different forms. The present embodiments are merely provided to ensure that the disclosure of the present invention is complete and to be understood by those skilled in the art. 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 the specification.

In describing embodiments of the present invention, if a detailed description of a known function or configuration is judged to unnecessarily obscure the gist of the present invention, the detailed description will be omitted. The terms described below are terms defined in consideration of functions in the embodiments of the present invention, and may vary depending on the intention or custom of the user or operator. Therefore, the definition should be made based on the contents throughout this specification.

The single cell for a solid oxide fuel cell according to the present invention is characterized by including an air electrode containing a compound of the following formula (1).

[Formula 1]

LaNi _x Fe _y Cu _(1-xy) O ₃

In Formula 1, x is 0.4 to 0.7, y is 0.2 to 0.4, and (1-x-y) is greater than 0 and less than or equal to 0.2.

Specifically, in Formula 1, x may be 0.5 to 0.68, preferably 0.55 to 0.65, and y may be 0.22 to 0.38, preferably 0.25 to 0.35. If the values of x and y are outside the above-mentioned range, there is a possibility that the crystal phase may become unstable.

The single cell for a solid oxide fuel cell according to the present invention can also be characterized as not containing Sr, and by not containing Sr, it has the advantage of preventing the creation of a secondary phase due to the reaction of Sr and Zr and the resulting decrease in battery output. There is.

Conventionally, in order to prevent secondary phase formation due to the reaction between Sr and Zr, a technology was developed to add a reaction prevention film to prevent direct contact between the electrolyte and the air electrode. However, when adding such a reaction prevention film, there is a problem that the cell resistance inevitably increases, thereby causing a decrease in the output density of the cell.

In order to solve this problem, an attempt was made to minimize the increase in resistance by increasing the density of the reaction prevention film. However, when heat treatment is performed at a high temperature to increase the density of the reaction prevention film, the ceria contained in the reaction prevention film and the zirconia in the electrolyte form an electric solid solution. This happens.

In addition, even if a reaction prevention film is introduced, there is a problem in that when the fuel cell is operated for a long time, Sr passes through the reaction prevention film and forms a secondary phase due to a reaction between Sr and Zr on the electrolyte surface.

Accordingly, in order to fundamentally prevent this problem, the present applicant continued research to produce an air electrode with excellent electrochemical reaction without containing Sr. As a result, an air electrode containing the composition of Formula 1 above and not containing Sr was produced. The above-mentioned secondary phase formation problem was fundamentally solved by using .

That is, the single cell for a solid oxide fuel cell according to the present invention is characterized by not containing Sr, thereby preventing the generation of a secondary phase containing Sr at the interface of the electrolyte.

A single cell for a solid oxide fuel cell according to an embodiment of the present invention includes an air cathode current collection layer and an air cathode functional layer. Specifically, the air electrode current collection layer may include the compound of Formula 1, and preferably may be a layer composed of the compound of Formula 1. The air cathode functional layer may be a mixed layer of the compound of Formula 1 and the compound of Formula 2.

[Formula 2]

Re _a Ce _(1-a) O _b

In Formula 2, Re=Gd, one or two or more selected from Sm and Y, a is 0.1 to 0.2, and b is 1.9 or more and less than 1.95. In Formula 2, if the a value is less than 0.1 or more than 0.2, a problem may occur where ionic conductivity is lowered.

Specifically, the air cathode functional layer may include 50 to 55% by weight of the compound of Formula 1 and the balance of the compound of Formula 2. LNFC is an electronic conductor and Re-doped ceria is an ion conductor, so these two materials must be mixed most evenly to secure the triple phase boundary (TPB), which is the actual electrochemical reaction point. From this perspective, the ratio of the compound in Formula 2 is If it is outside the above-described range, it is disadvantageous in securing a three-phase interface, which may lead to a decrease in battery output.

A single cell for a solid oxide fuel cell according to an embodiment of the present invention may be one in which an air electrode current collection layer, an air electrode functional layer, a reaction prevention film, an electrolyte, an anode functional layer, and an anode support are sequentially laminated, preferably having the above-described laminated structure. It may be a fuel electrode support type single cell.

In terms of manufacturing method, a single cell for a solid oxide fuel cell according to an embodiment of the present invention manufactures an anode-electrolyte sintered body by stacking an electrolyte, an anode functional layer, and an anode support, and then reacts on the electrolyte surface of the anode-electrolyte sintered body. The anti-reaction film is coated and then sintered to form an anti-reaction film layer, and the air electrode functional layer and the air electrode current collection layer are continuously coated on the anti-reaction film layer and heat treated to finally manufacture a single cell for a solid oxide fuel cell.

The anode-electrolyte sintered body is manufactured by separately manufacturing an electrolyte molded sheet, an anode functional layer molded sheet, and an anode support molded sheet, which are then fabricated into a laminated bonded sheet, and then sintered at 1300 to 1400° C. for 3 to 10 hours. It can be manufactured, and in this case, sintering can be performed in air, and unless specifically limited in the present invention, sintering is considered to have been performed in air.

In a single cell for a solid oxide fuel cell according to an embodiment of the present invention, the anode functional layer and the anode support may include NiO and yttria-stabilized zirconia (hereinafter referred to as YSZ). In this case, yttria-stabilized zirconia is It may contain 3 to 10 mol% of tria.

Specifically, the anode support may include 55 to 70% by weight of NiO and the balance of YSZ, and the anode functional layer may include 50 to 65% by weight of NiO and the balance of YSZ.

Additionally, the electrolyte may use the yttria-stabilized zirconia, and specifically, yttria-stabilized zirconia containing 8 to 10 mol% of yttria may be used.

The reaction prevention film can be manufactured by applying a reaction prevention film paste on the electrolyte of the fuel electrode-electrolyte sintered body and then sintering. Specifically, the reaction prevention film is characterized by including a compound of the following formula (3) as a sintering additive.

[Formula 3]

(La _(1-m) Sr _m ) _n MnO ₃

In Formula 3, m is 0.1 to 0.5, and n may be greater than 0 and 0.98 or less, preferably 0.95 to 0.98. When an anti-reaction film is formed by adding a sintering additive that satisfies Formula 3 above, an electrochemical reaction occurs in the anti-reaction film, which has the advantage of further increasing the output of the battery.

In detail, the paste for the reaction prevention film may be based on a ceria-based composite oxide and may include the compound of Formula 3 as a sintering additive. At this time, the ceria-based composite oxide may satisfy the following Chemical Formula 4.

[Formula 4]

R _z Ce _(1-z) O _(2-z/2)

In Formula 4, R is one or more selected from Gd, Sm, Y, Yb and Bi, and z is 0.1 to 0.2.

In a single cell for a solid oxide fuel cell according to an embodiment of the present invention, the reaction prevention film may include ceria-based composite oxide: a sintering additive of Chemical Formula 3 in a weight ratio of 100:7 to 15, preferably 8 to 12, and Chemical Formula 3 When the sintering additive content of Formula 3 increases, the reaction prevention film becomes denser and, conversely, it becomes difficult to secure a three-phase interface. Conversely, when the sintering additive content of Formula 3 decreases, it is difficult to secure a three-phase interface, so the electrochemical reaction does not occur in the reaction prevention film, so the battery The output may be lowered. Therefore, it is very important to secure process conditions that can ensure an appropriate amount of addition and appropriate microstructure.

The paste for the reaction prevention film can be manufactured by sintering at a sintering temperature of 1050 to 1180 ° C for 30 to 180 minutes. If the sintering temperature is too high, it is difficult to secure a three-phase interface, and the electrochemical reaction deteriorates, resulting in a solid oxide fuel cell. may cause a decrease in output. Conversely, if the sintering temperature is low below 1050°C, there is a problem in securing the interfacial bonding strength between the electrolyte and the anti-reaction film, and considering that the final cathode heat treatment temperature is 1050°C, a higher sintering temperature is required.

That is, when the paste for the anti-reaction film is sintered at a sintering temperature of 1050 to 1180 ° C. for 30 to 180 minutes, a three-phase interface is secured, and some electrochemical reaction occurs in the anti-reaction film, which increases the overall output of the unit cell. It can lead to However, when the sintering temperature of the anti-reaction film paste is high, there is a limit in which it is difficult for the effect of this electrochemical reaction to occur, and as a result, there is a limit in which it is difficult to achieve the effect of increasing output due to the electrochemical reaction.

After forming a reaction prevention film on the anode-electrolyte sintered body as described above, the above-mentioned air electrode functional layer and air electrode current collection layer are successively coated and heat treated at 1000 to 1100° C. for 60 to 120 minutes to finally produce a single cell for a solid oxide fuel cell. It can be manufactured.

As described above, the unit cell for a solid oxide fuel cell according to an embodiment of the present invention does not contain Sr in the air electrode, thereby fundamentally blocking the creation of secondary phases due to the reaction between Sr contained in the air electrode and Zr contained in the electrolyte. This has the advantage of preventing a decrease in output due to secondary phase generation. Furthermore, an additional electrochemical reaction occurs in the reaction prevention film due to the sintering additive included in the reaction prevention film, so that the single cell for a solid oxide fuel cell according to an embodiment of the present invention has the characteristic of having excellent power density.

Specifically, the single cell for a solid oxide fuel cell according to an embodiment of the present invention can exhibit a voltage of 0.860 V or more, preferably 0.860 to 0.900 V, under a current density condition of 0.4 A/cm2, and has a power density of 0.350 W. It has the characteristic of exhibiting a power density of more than /cm ² , preferably 0.350 to 0.370 W/cm ² .

The present invention also provides a solid oxide fuel cell, and the solid oxide fuel cell according to the present invention may be manufactured by stacking a single cell for a solid oxide fuel cell according to an embodiment of the present invention. Since the single cell for the solid oxide fuel cell exhibits high output, when applied to a commercial solid oxide fuel cell, a relatively small number of single cells can be used, which can lead to a significant reduction in the production cost when producing a solid oxide fuel cell. there is.

Hereinafter, the present invention will be described in detail by examples and comparative examples. The examples below are only intended to aid understanding of the present invention, and the scope of the present invention is not limited by the examples below.

[Example 1]

It was manufactured as an anode supported cell (ASC) containing the components and materials shown in Table 1 below.

cell ASC-1 ASC-2 ASC-3 Air cathode current collection layer LNFC (LaNi _0.6 Fe _0.3 Cu _0.1 O ₃ ) Air cathode functional layer LNFC: GDC20 = 53:47 (wt%) anti-reaction film GYBC+Co GYBC+LSM electrolyte 8YSZ (8mol% Y ₂ O ₃ stabilized ZrO ₂ ) Fuel electrode functional layer NiO: 8YSZ = 57:43 (wt%) Fuel electrode support NiO: 8YSZ = 60:40 (wt%)

The electrolyte, anode functional layer, and anode support molded sheets in Table 1 were manufactured into laminated bonded sheets, which were then sintered in air at 1350°C for 6 hours to produce a co-sintered body, which was then processed into a disk-shaped specimen with a diameter of 20 mm. .

Two types of materials were used for the reaction prevention film, and ASC-1 was mixed uniformly with GYBC (Gd _0.135 Yb _0.015 Bi _0.02 Ce _0.83 O _1.915 ) and Cobalt nitrate at a weight ratio of 100:1 and then heat treated at 600 ° C for 30 minutes. The composite powder prepared was used, and ASC-2~3 used a composite powder in which GYBC:LSM ((La _0.7 Sr _0.3 ) _0.95 MnO ₃ ) was mixed at a weight ratio of 100:10.

The two types of reaction prevention films prepared were each made with screen printing paste and then coated on the electrolyte surface. ASC-1 was heat treated in air at 1250 ℃ for 2 hours, ASC-2 was heat treated at 1100 ℃, and ASC-3 was heat treated at 1250 ℃ for 2 hours. Each was heat treated in air at 1200°C for 2 hours.

Afterwards, an air electrode functional layer and an air electrode current collection layer having the compositions shown in Table 1 were continuously coated on the sintered ASC and heat treated in air at 1050° C. for 90 minutes to manufacture an anode support type cell. At this time, the composition of GDC20 applied to the air cathode functional layer is Gd _0.2 Ce _0.8 O _1.9 .

Check battery performance

In order to compare and evaluate the battery performance of ASC-1 to ASC-3 prepared in Example 1, the batteries were operated. Specifically, the operating temperature was 750°C, hydrogen was supplied at 100 cc per minute, and air was supplied at 200 cc per minute, and the power density was calculated by measuring the voltage according to the increase in current density.

Figure 1 shows the results of comparing cell voltage and output density according to current density, and Table 2 and Figure 2 below compare and summarize the cell voltage and output density under a current density condition of 0.4 A/cm2.

Sample ASC-1 ASC-2 ASC-3 Voltage (V) 0.862 0.882 0.834 Power density (W/cm ² ) 0.345 0.353 0.333

Referring to Figures 1, 2 and Table 2, it can be seen that ASC-2 shows the highest performance and ASC-3 shows the lowest performance. This can be seen as an additional interfacial reaction occurring in the reaction prevention film of ASC-2, and in the case of ASC-3, it can be seen as a result of a decrease in additional interfacial reaction in the reaction prevention film due to the heat treatment temperature.

Based on the above experimental results, assuming that a 1MW solid oxide fuel cell is manufactured using a stack manufacturing cell with an air electrode area of 100㎠, in the case of ASC-2, the cell output is 35.3W (0.353W/ When manufacturing a 1MW solid oxide fuel cell (cm ² × 100㎠), 28,330 cells are required. In the same way, when manufacturing a 1MW solid oxide fuel cell with ASC-3, the required number of cells is 30,030, which means that about 1,700 more cells are needed compared to ASC-2. Assuming the price per cell is 100,000 won, ASC-2 has the advantage of reducing the manufacturing cost of solid oxide fuel cells by about 170 million won compared to ASC-3.

Figure 3 shows the microstructure of the cross-sections of the three types of cells that were evaluated using a scanning electron microscope. Referring to Figure 3, it can be seen that the air cathode functional layer and electrolyte that were heat treated under the same conditions showed similar microstructures. On the other hand, in the case of the reaction prevention film, it can be seen that the density of ASC-3, which was heat-treated at a higher temperature, is higher than that of ASC-2.

The higher the density of the anti-reaction film, the lower the cell resistance should be, resulting in higher power density. However, in the case of ASC-2 and ASC-3, the opposite result is shown, and in the case of ASC-2, the density of the anti-reaction film is relatively low. It can be seen that it is advantageous to secure a three-phase interface in the anti-reaction film, so additional electrochemical reactions occur in the anti-reaction film, resulting in high power density.

Claims (8)

A single cell for a solid oxide fuel cell including an air electrode containing a compound of the following formula (1).
[Formula 1]
LaNi _x Fe _y Cu _(1-xy) O ₃
(In Formula 1, x is 0.4 to 0.7, y is 0.2 to 0.4, and (1-xy) is greater than 0 and less than or equal to 0.2.) According to clause 1,
A single cell for a solid oxide fuel cell, characterized in that the air electrode does not contain Sr. According to clause 2,
The single cell for a solid oxide fuel cell is characterized in that a secondary phase containing Sr is not generated at the interface between the air electrode and the electrolyte. According to clause 1,
The air electrode is a single cell for a solid oxide fuel cell including an air electrode current collection layer and an air electrode functional layer. According to clause 4,
A single cell for a solid oxide fuel cell, wherein the cathode functional layer includes the compound of Formula 1 and Re-doped ceria of Formula 2 below.
[Formula 2]
Re _a Ce _(1-a) O _b
(In Formula 2, Re=Gd, one or two or more selected from Sm and Y, a is 0.1 to 0.2, and b is 1.9 or more and less than 1.95.) According to clause 4,
The single cell for a solid oxide fuel cell is characterized in that an air electrode current collection layer, an air electrode functional layer, a reaction prevention film, an electrolyte, an anode functional layer, and an anode support are sequentially stacked. According to clause 5,
A single cell for a solid oxide fuel cell, characterized in that the reaction prevention film includes a compound of the following formula (3) as a sintering additive.
[Formula 3]
(La _(1-m) Sr _m ) _n MnO ₃
(In Formula 3, m is 0.1 to 0.5, and n is greater than 0 and less than or equal to 0.98.) A solid oxide fuel cell comprising a single cell for a solid oxide fuel cell according to any one of claims 1 to 6.