KR102128941B1 - Method for manufacturing solid oxide fuel cell having durable electrolyte under negative voltage condition - Google Patents

Abstract

The present invention is a negative electrode (anode) layer formed on one surface containing a ceria (CeO ₂ ); An electrolyte layer formed on a layer containing the ceria, and comprising YSZ (Yttria-stabilized zirconia); And manufacturing a solid oxide fuel cell unit cell stacked in the order of the anode layer. And (b) sintering the solid oxide fuel cell unit cell, comprising a method for manufacturing a solid oxide fuel cell in which reverse voltage deterioration is prevented, of the solid oxide fuel cell (SOFC) according to the present invention. According to the manufacturing method, the cerium concentration decreases as the cerium concentration decreases from the anode/electrolyte interface toward the center of the electrolyte layer by diffusing cerium ions from the layer containing ceria provided on the cathode side into the electrolyte layer through the sintering process. A cathode/electrolyte (Gradient anode/electrolyte) structured solid oxide fuel cell can be manufactured, and the solid oxide fuel cell has an electron conductivity (N-type) locally only in the electrolyte section close to the cathode/electrolyte interface. In the situation, it is possible to effectively prevent the cathode/electrolyte peeling, and since only a part of the inside of the electrolyte has electronic conductivity, leakage current can also be prevented.

Description

Manufacturing Method of Solid Oxide Fuel Cell with Prevention of Reverse Voltage Deterioration {METHOD FOR MANUFACTURING SOLID OXIDE FUEL CELL HAVING DURABLE ELECTROLYTE UNDER NEGATIVE VOLTAGE CONDITION}

The present invention relates to a method for manufacturing a solid oxide fuel cell, and more particularly, to a solid oxide fuel cell including an electrolyte layer having a structure capable of preventing deterioration of an SOFC cell stack under a negative cell voltage. It is about a manufacturing method.

Due to future energy and pollution problems, interest in eco-friendly energy resources is increasing. As one of eco-friendly energy technologies, a solid oxide fuel cell that converts chemical energy into electrical energy by chemical reaction between hydrogen and oxygen and does not emit pollution such as carbon dioxide through non-combustion electrochemical reaction has attracted attention as renewable energy. have.

However, the electromotive force of the fuel cell requires a step of stacking multiple cells in series in order to obtain a desired output of about 1 V per unit cell. At this time, if one cell in the stack exhibits a large performance deviation, the cell exhibiting low performance operates at a negative cell voltage above a threshold current value, causing physical destruction due to rapid deterioration, thereby stopping the entire stack operation. (Figure 1). These phenomena are actually common in electrochemical devices connected in series. In order to ensure stability and commercialization of batteries, it is necessary to minimize the performance difference between cells.

Currently, the most widely used electrolyte for solid oxide fuel cells is zirconia (YSZ) doped with 8 mol% yttria. YSZ is a material in which oxygen ion conductivity is dominant due to oxygen vacancies generated by the addition of yttria, and has little advantage in electronic conductivity, and has the advantage of being chemically stable regardless of the oxidation/reduction atmosphere.

Here, the fact that the oxygen ion conductivity is different depending on the difference in perspective. From a performance point of view, pure oxygen ion conductivity benefits from a high open circuit voltage and hence high output. However, from the viewpoint of durability, pure oxygen ion conductivity is no longer an advantage.

Operation at the above-mentioned reverse voltage may cause an abnormally high oxygen chemical potential inside the solid electrolyte to cause separation between the electrode and the electrolyte interface. That is, in order to continue operating the fuel cell stack, a technology capable of operating without deterioration even at a reverse voltage is required.

In this regard, in Korean Patent Registration No. 10-1180182 (a solid oxide fuel cell having excellent peel resistance), a leakage current is provided by including a ceria component only in an electrolyte layer close to an anode using a triple layer electrolyte to impart electronic conductivity. And prevented deterioration of reverse voltage. However, such a multi-layered electrolyte structure complicates the manufacturing process, and has a number of disadvantages, such as resistance to increase due to a thick electrolyte and interfacial resistance between layers.

Korean Patent Publication No. 10-2015-0128715 (Publication date: 2015. 11. 18) : Korean Registered Patent No. 10-1180182 (Registration Date: 2010. 08. 30) International Publication Patent WO 2010-078356 (Publication date: 2010. 07. 08)

The technical problem to be solved by the present invention is a solid oxide that can effectively prevent the separation between the negative electrode layer and the electrolyte layer in a reverse voltage situation without causing problems such as increased complexity and resistance of the electrolyte layer manufacturing process of the prior art. It is to provide a fuel cell manufacturing method.

According to a paper that studies the deterioration of cells using electrolytes containing Yttria-stabilized zirconia (YSZ) due to reverse voltage, cells using YSZ electrolytes not only reduce the voltage per hour, but also after operation, open circuit voltage and power density It showed a decrease, and as a result of post-analysis, it was found that peeling was observed at the anode and electrolyte interfaces.

The cause of the peeling phenomenon between the negative electrode and the electrolyte interface is due to the high oxygen partial pressure at the negative electrode/electrolyte interface due to the reverse voltage, and the key is to reduce the oxygen partial pressure at the interface to prevent peeling.

When YSZ added with a dopant such as ceria, which exhibits electronic conductivity, is used as an electrolyte, electron conductivity by the dopant decreases the high oxygen partial pressure at the negative electrode/electrolyte interface that occurs during reverse voltage operation and does not cause peeling. . However, when ceria is added to all regions of the single-layer YSZ electrolyte, leakage current may occur.

On the other hand, as described in the background art, if a multi-layered electrolyte is constructed, leakage current can be prevented, but problems such as complexity of the manufacturing process, increased electrolyte thickness, and interface resistance may occur.

Therefore, the present invention is a method of not adding ceria directly into the electrolyte, and a cathode layer containing ceria having electronic conductivity is formed on one surface during the cell manufacturing process, and the cell is sintered to high temperature. A method of manufacturing a cell employing a gradient anode/electrolyte, in which cerium ions are dissolved in an electrolyte layer containing YSZ (Yttria-stabilized zirconia) through diffusion to make local electronic conductivity to provide.

Specifically, in order to achieve the above technical problem, the present invention (a) a layer comprising a ceria (CeO ₂ ) A cathode (anode) layer formed on one surface; An electrolyte layer formed on a layer containing the ceria, and comprising YSZ (Yttria-stabilized zirconia); And manufacturing a solid oxide fuel cell unit cell stacked in the order of the anode layer. And (b) sintering the solid oxide fuel cell unit cell. The present invention provides a method of manufacturing a solid oxide fuel cell having a reverse voltage deterioration phenomenon.

In manufacturing the unit cell stack in the step (a), the negative electrode layer is an anode functional layer (Anode Functional Layer) formed on the negative electrode support layer (Anode Support, AS) and a layer comprising the ceria. AFL).

At this time, the negative electrode support layer and the negative electrode functional layer may be made of a nickel (Ni)-based material, furthermore, the negative electrode support layer may include nickel and YSZ, and the negative electrode functional layer may include nickel, YSZ, and ceria.

In addition, the positive electrode layer may include a positive electrode functional layer (CFL) formed on the electrolyte layer and a positive electrode current collector layer (Current Collector, CC) formed on the positive electrode functional layer, for example, The positive electrode functional layer includes Sr-doped LaMnO ₃ (LSM) and YSZ, and the positive electrode current collector layer may include LSM.

In the step (b), the unit cell prepared in the step (a) is sintered, and cerium (cerium) ions are diffused into the electrolyte layer from the layer containing ceria provided on the negative electrode side through sintering to the negative electrode/ From the interface of the electrolyte layer toward the center of the electrolyte layer, a gradient structure in which cerium concentration decreases is formed.

At this time, the sintering condition in the step (b) is a predetermined thickness (however, it should be smaller than the total thickness of the electrolyte layer) in the direction of the electrolyte layer from the interface between the cathode layer and the electrolyte layer. Is not particularly limited, and for example, may be performed at a temperature of 1410 to 1510°C for 1 to 11 hours.

And, the present invention, in another aspect of the invention, provides a solid oxide fuel cell unit cell manufactured by the above manufacturing method.

Furthermore, the present invention, in another aspect of the invention, provides a solid oxide fuel cell stack including a plurality of the unit cells.

According to a method for manufacturing a solid oxide fuel cell (SOFC) according to the present invention, cerium (cerium) ions are diffused into the electrolyte layer from a layer containing ceria provided on the negative electrode side through a sintering process, from the negative electrode/electrolyte layer interface. It is possible to manufacture a solid anode fuel cell having a gradient anode/electrolyte structure in which cerium concentration decreases toward the center of the electrolyte layer, and the solid oxide fuel cell localizes only the electrolyte section close to the cathode/electrolyte interface. Since it has electronic conductivity (N-type), it is possible to effectively prevent cathodic/electrolyte peeling in reverse voltage situations, and leakage current can also be prevented because only a part of the electrolyte has electronic conductivity.

In other words, the cerium (cerium) ion is diffused into the electrolyte layer composed of a single layer through the sintering process to impart local electronic conductivity inside the electrolyte layer, thereby eliminating the need to form a multi-layer electrolyte structure requiring a complicated manufacturing process as in the prior art. It is possible to manufacture a solid oxide fuel cell that can secure voltage durability and prevent leakage current.

1 is an IV (current-voltage) graph for each of a cell stack including a normal cell stack and a bad cell.
2 is a flowchart showing each step of a method of manufacturing a solid oxide fuel cell in which reverse voltage degradation is prevented according to the present invention.
3 is a flow chart showing each step of the SOFC cell manufacturing process having a gradient anode/electrolyte structure according to an embodiment of the present application.
4 is a schematic cross-sectional view of an SOFC cell having a gradient anode/electrolyte structure manufactured according to an embodiment of the present application.
5 is an EDS line analysis results for the SOFC cell prepared according to the present example.
FIG. 6(a) is a graph showing a voltage change over time when a constant current (CC) is applied to a SOFC cell including a conventional YSZ electrolyte layer, and FIG. 6(b) is a graph showing the results of the corresponding constant current test IV measurement, FIG. 6(c) is a scanning electron microscope (SEM) photograph showing the microstructure of the cell cross section after the corresponding constant current test.
Figure 7 (a) is a graph showing the voltage change over time when the constant current (CC) is applied to the SOFC cell prepared in the present embodiment, Figure 7 (b) is a graph showing the results of the corresponding constant current test IV measurement, Figure 7(c) is a scanning electron microscope (SEM) photograph showing the microstructure of the cell cross section after the corresponding constant current test.

In the description of the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

Embodiments according to the concept of the present invention may be applied to various changes and may have various forms, and thus specific embodiments will be illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiment according to the concept of the present invention to a specific disclosure form, and it should be understood to include all modifications, equivalents, or substitutes included in the spirit and scope of the present invention.

The terms used herein are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms "include" or "have" are intended to indicate that a feature, number, step, action, component, part, or combination thereof described is present, and one or more other features or numbers. It should be understood that it does not preclude the existence or addition possibilities of, steps, actions, components, parts or combinations thereof.

Hereinafter, the present invention will be described in more detail through examples.

<Example>

As shown in FIG. 3, steps (1) to (6) below were sequentially performed to prepare SOFC unit cells having a gradient anode/electrolyte structure having a schematic cross-sectional view shown in FIG. 4.

(1) After the anode powder composed of NiO and YSZ was die-pressed, heat treatment was performed at 900°C for 1 hour to prepare a cathode support layer (AS).

(2) NiO, YSZ, and ceria were mixed at a ratio of 60 wt%: 20 wt%: 20 wt%, respectively, for the preparation of the negative electrode functional layer (AFL), and additional grinding was performed using a planetary ball mill for particle refinement.

(3) After grinding, it was prepared as a slurry using a butanol solvent, and was coated with a drop on the previously prepared AS layer, followed by heat treatment at 900°C for 1 hour.

(4) The YSZ slurry was drop coated on the heat-treated AS/AFL substrate and sintered at 1460°C for 6 hours.

(5) An anode functional layer mixed with LSM and YSZ was screen-printed on a sintered cell and heat-treated at 1170°C for 1 hour.

(6) An anode made of LSM was screen-printed on the anode functional layer and heat treated at 1160°C for 1 hour.

<Experimental Example>

1. Ceria diffusion distance analysis after sintering

For the unit cell prepared in the above example, EDS analysis was performed to analyze how much ceria diffused into the electrolyte during sintering.

As shown in FIG. 5, which shows the results of the EDS analysis, it was found that about 3 microns of cerium diffused into the 15 micron thick electrolyte. Through this, it can be seen that there is a local electron conductive region inside the YSZ electrolyte.

2. Reverse voltage durability test

In order to check the durability under reverse voltage operation, a constant current test is performed in the order of high voltage (0.6V to 0.7V), low voltage (0.2V to 0.4V), and reverse voltage (-0.3V to -0.4V) in the reverse voltage situation. It was checked whether a voltage drop occurred, and the output density was measured before and after the constant current test. Through this, voltage drop and performance comparison with the existing YSZ electrolyte cell were performed.

As a result of the reverse voltage test of the YSZ electrolyte cell, a voltage drop phenomenon not seen at high voltage and low voltage was observed (Fig. 6(a)), and an output reduction phenomenon was also observed after the reverse voltage test (Fig. 6(b). )). After the test, peeling between the cathode and the electrolyte interface was observed, as can be seen in the image through SEM analysis (FIG. 6(c)).

On the other hand, it can be seen that the cell to which the gradient anode/electrolyte prepared in the present example is applied maintains the voltage under high voltage and low voltage as well as in reverse voltage (FIG. 7(a)). The performance was also not significantly different from that of the existing YSZ cell (FIG. 7(b)), and post analysis revealed that no physical damage occurred between the negative electrode and the electrolyte interface (FIG. 7(c)).

According to the method of manufacturing a solid oxide fuel cell (SOFC) according to the present invention described in detail above, the cerium (cerium) ions are diffused into the electrolyte layer from the layer containing ceria provided on the cathode side through the high temperature sintering process to the cathode/ It is possible to manufacture a solid oxide fuel cell having a gradient anode/electrolyte structure in which cerium concentration decreases from the electrolyte layer interface toward the center of the electrolyte layer, and the solid oxide fuel cell is an electrolyte close to the cathode/electrolyte interface. Since only the section has a local electronic conductivity (N-type), it is possible to effectively prevent cathode/electrolyte delamination in a reverse voltage situation, and only a part of the inside of the electrolyte has electronic conductivity, thereby preventing leakage current.

That is, cerium (cerium) ions are diffused into the electrolyte layer composed of a single layer through the sintering process, and electron conductivity is locally provided inside the electrolyte layer, thereby eliminating the need to form a multi-layer electrolyte structure requiring a complicated manufacturing process as in the prior art. A solid oxide fuel cell having durability against reverse voltage and preventing leakage current can also be manufactured.

The embodiments of the present invention have been described above with reference to the accompanying drawings, but those of ordinary skill in the art to which the present invention pertains can implement the present invention in other specific forms without changing its technical spirit or essential features. You will understand that there is. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (10)

(a) a layer comprising a ceria (CeO ₂ ) formed on one surface (anode) layer; An electrolyte layer formed on a layer containing the ceria, and comprising YSZ (Yttria-stabilized zirconia); And manufacturing a solid oxide fuel cell unit cell stacked in the order of the anode layer. And
(b) sintering the solid oxide fuel cell unit cell;
The cathode layer,
A cathode support layer comprising NiO and YSZ (Anode Support, AS); And
It is formed on the negative electrode support layer and includes a negative electrode functional layer (AFL) comprising NiO, YSZ and ceria in a ratio of 60 wt%: 20 wt%: 20 wt%, respectively,
The anode layer,
A cathode functional layer (CFL) formed on the electrolyte layer and comprising LSM (Sr-doped LaMnO ₃ ) and YSZ; And
It is formed on the anode functional layer and includes an anode current collector layer (CC) including LSM,
A method of manufacturing a solid oxide fuel cell having a reverse voltage deterioration phenomenon, characterized in that sintering is performed at a temperature of 1460° C. for 6 hours in step (b). delete delete delete delete delete According to claim 1,
In the step (b), the cerium concentration decreases as the cerium concentration decreases from the interface between the anode and the electrolyte layer toward the center of the electrolyte layer by diffusing cerium ions from the layer containing ceria provided on the cathode side into the electrolyte layer by sintering A method of manufacturing a solid oxide fuel cell in which reverse voltage degradation is prevented, characterized in that a structure is formed. delete A solid oxide fuel cell unit cell manufactured by the method of claim 1 or 7. A solid oxide fuel cell stack comprising a plurality of unit cells of claim 9.

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