KR102459438B1 - Solid oxide fuel cell having co-ionic conductor electrolyte with improved durability and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a solid oxide fuel cell including a co-ionic conductor electrolyte having improved durability and a manufacturing method thereof, which comprises: a negative electrode support layer; a negative electrode functional layer; a BCY-GDC electrolyte layer including yttria-doped barium cerates (BCY) and gadolinium-doped ceria (GDC); a BZY-NDC electrolyte layer including a yttria-doped barium zirconate (BZY) and a neodymium-doped ceria (NDC); and a positive electrode functional layer, wherein the above-mentioned layers are sequentially stacked. The solid oxide fuel cell according to the present invention has the co-ionic conductor electrolyte layer in a bilayer structure, which includes the BCY-GDC layer in contact with the negative electrode and the BZY-NDC layer in contact with the positive electrode, thereby realizing the co-ionic conductor electrolyte fuel cell having high durability, which keeps advantages of the co-ionic conductor electrolyte, such as prevention of fuel dilution and degradation at high temperature intact and prevents the electrode from being separated from the electrolyte even under a condition of a reverse voltage operation.

Description

Solid oxide fuel cell including mixed ion conductor electrolyte with improved durability and manufacturing method thereof

The present invention relates to a solid oxide fuel cell and a method for manufacturing the same, and more particularly, to a solid oxide containing a mixed ion conductor electrolyte having excellent durability in which interfacial delamination between an electrode and an electrolyte does not occur even under a negative cell voltage operating condition. It relates to a fuel cell and a method for manufacturing the same.

The third-generation solid oxide fuel cell (SOFC) has advantages such as variety of fuels and high efficiency. Recently, research on a low-temperature solid oxide fuel cell capable of preventing high-temperature degradation, which is the biggest problem of a high-temperature solid oxide fuel cell, is being actively conducted.

Low-temperature solid oxide fuel cell electrolytes are mainly composed of ceria-based electrolytes [Gd _0.2 Ce _0.2 O _2-d (GDC) or Nd _0.1 Ce _0.9 O _2-d (NCD)], which are ionic conductors, and perovsky, which are proton (hydrogen ions) conductors. It can be divided into perovskite oxide, BaCe _0.85 Y _0.15 O _3-d (BCY) or BaZr _0.85 Y _0.15 O _3-d (BZY)]. While GDC and NDC show excellent conductivity at low temperature, they are having difficulties in practical stack application due to leakage current caused by ceria reduction problem, open circuit voltage (OCV) lowering, and chemical stability problems. In the case of proton conductors, BCY is chemically unstable in water vapor and carbon dioxide atmosphere, and while BZY has excellent chemical stability, it has problems such as increased grain boundary resistance due to poor sinterability.

Recently, a co-ionic conductor electrolyte that combines an oxygen ion conductive electrolyte and a proton conductive electrolyte that can compensate for these shortcomings is attracting attention. By composing the two types of electrolytes as a composite, the chemical stability of the ceria system can be increased and high OCV can be secured, and the problem of sinterability of the perovskite oxide system can be solved. In addition, since both oxygen ions and hydrogen ions can be transferred, water vapor, a fuel cell by-product, is formed at both the anode and the cathode, thereby solving the fuel dilution problem at the anode ( FIG. 1 ).

Meanwhile, since the electromotive force of the fuel cell is at most 1V per unit cell, a step of stacking several cells in series is required to obtain a desired output. If one cell in the stack exhibits a large performance deviation, the cell with low performance operates with a negative cell voltage above the critical current value and the oxygen partial pressure increases, leading to electrode/electrolyte delamination and operation of the entire stack This stops (FIG. 2). Therefore, it is possible to secure the durability of the unit cell when the stack is applied by sufficiently considering such operating conditions and environment when developing the unit cell.

In the case of the aforementioned mixed ion conductor electrolytes (BCY-GDC, BZY-NDC, etc.), it has been reported that the cell voltage drop significantly occurs under reverse voltage operating conditions and exhibits unstable behavior.

Therefore, in order to secure the durability of the mixed ion conductor electrolyte fuel cell in preparation for reverse voltage operation, a new electrolyte design is required.

International Patent Publication WO 2010-078356 (published on: March 17, 2005) Korean Patent Publication No. 10-2015-0081928 (published on: July 15, 2015)

The technical problem to be solved by the present invention is a low-temperature solid oxide fuel cell including a mixed ion conductor electrolyte layer of a new structure that can effectively prevent both delamination between anode/electrolyte and anode/electrolyte under reverse voltage operation conditions, and manufacturing thereof to provide a way

In order for the solid oxide fuel cell to stably maintain its performance under reverse voltage operation conditions, it is necessary to suppress the partial pressure of oxygen/hydrogen inside the electrolyte, and for this, high electron conductivity is required in the electrolyte region adjacent to the electrode.

In particular, in the case of a mixed ion conductor electrolyte, since both hydrogen ions and oxygen ions move, high electronic conductivity is required for both the electrolyte region adjacent to the anode and the electrolyte region adjacent to the cathode. Since a single layer made of only ion conductors (BCY-GDC, BZY-NDC, etc.) is included as the electrolyte, delamination between the anode or cathode and the electrolyte may occur under reverse voltage operation conditions, which may adversely affect the durability of the SOFC cell stack.

That is, in the case of the SOFC cell with the BCY-GDC single-layer electrolyte, high N-type electron and ion mixed conductivity exists in the electrolyte region adjacent to the cathode, but the electron conductivity in the electrolyte region adjacent to the anode is insufficient (by pure ionic conductivity). Delamination of the anode/electrolyte interface may occur. On the other hand, in the case of the SOFC cell containing the BZY-NDC single-layer electrolyte, high P-type electron and ion mixed conductivity exists in the electrolyte region adjacent to the anode, but the electron conductivity in the electrolyte region adjacent to the cathode is insufficient, resulting in separation of the cathode/electrolyte interface. can happen

Accordingly, in the present invention, the mixed ion conductor electrolyte layer has a bilayer structure, and the electrolyte layer in contact with the anode side of the bilayer is made of a mixed ion conductor having high electronic conductivity in the electrolyte region close to the anode, and the cathode side The electrolyte layer in contact with the anode is made of a mixed ion conductor with high electronic conductivity in the electrolyte region close to the cathode, so that it is possible to prevent delamination at both the anode/electrolyte interface and the cathode/electrolyte interface even under reverse voltage operation conditions. An object of the present invention is to provide a conductive solid oxide fuel cell.

Specifically, in order to achieve the above-described technical problem, the present invention is an anode support layer; anode functional layer; a BCY-GDC electrolyte layer comprising barium cerates (BCY) doped with yttria and ceria doped with gadolinium (Gd); BZY-NDC electrolyte layer comprising yttria-doped barium zirconate (BZY) and neodymium-doped ceria (NDC) doped with neodymium (Nd); and a positive electrode functional layer; provides a solid oxide fuel cell in which the sequentially stacked solid oxide fuel cell is stacked.

Among the bilayer electrolyte layer composed of the BCY-GDC electrolyte layer and the BZY-NDC electrolyte layer, the BCY-GDC electrolyte layer adjacent to the negative electrode has an N-type electron conductivity by reducing ceria by low oxygen partial pressure. In the BZY-NDC electrolyte layer adjacent to the anode side, the oxygen vacancies are partially filled with oxygen due to the high oxygen partial pressure, thereby increasing the P-type conductivity. As a result, electron conductivity can be secured in both the electrolyte region adjacent to the anode and cathode interface, and leakage current can be prevented because the intermediate region has very low electron conductivity. With such a double-layer structure, it is possible to realize a highly durable mixed ion conductor electrolyte fuel cell that does not delaminate even under reverse voltage conditions.

Meanwhile, the negative electrode support layer may be formed of a mixture including nickel oxide (NiO) and a BaCeO ₃ -BaZrO ₃ solid mixture (BZCYYb) doped with yttrium (Y) and ytterbium (Yb).

In addition, the anode functional layer may be formed of a mixture including nickel oxide (NiO) and BCY-GDC.

Nickel oxide (NiO) in the negative electrode support layer and the negative electrode functional layer is reduced to nickel (Ni) by hydrogen during operation of the fuel cell.

In addition, the anode functional layer may be formed of a mixture including lanthanum-strontium-cobalt-iron oxide (LSCF) and NDC.

And, in another aspect of the present invention, there is provided a method for manufacturing the solid oxide fuel cell, comprising the steps of: (a) forming an anode support layer; (b) forming a negative electrode functional layer on the upper surface of the negative electrode support layer; (c) a mixture containing barium cerates (BCY) doped with yttria and ceria doped with gadolinium (Gd) on the upper surface of the negative electrode functional layer (gadolinium-doped ceria, GDC) forming a BCY-GDC electrolyte layer using; (d) on the upper surface of the BCY-GDC electrolyte layer, a mixture comprising yttria-doped barium zirconate (BZY) and neodymium (Nd) doped ceria (neodymium-doped ceria, NDC) preparing a laminate by forming a BZY-NDC electrolyte layer using; (e) sintering the laminate at a temperature of 1450 to 1550° C. for 1 to 10 hours; and (f) forming a positive electrode functional layer on the upper surface of the BZY-NDC electrolyte layer of the laminate sintered in step (e).

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

The solid oxide fuel cell according to the present invention is provided with a mixed ion conductor electrolyte layer having a bilayer structure including a BCY-GDC layer in contact with the negative electrode side and a BZY-NDC layer in contact with the positive electrode side. It is possible to realize a highly durable mixed ion conductor electrolyte fuel cell that not only maintains its advantages (prevention of fuel dilution and high temperature degradation), but also does not delaminate at the anode/electrolyte interface and at the cathode/electrolyte interface even under reverse voltage operation conditions.

1 is a schematic cross-sectional view of a SOFC cell having a mixed ion conductor electrolyte consisting of a single layer according to the prior art.
2 is an IV (current-voltage) graph for each of a cell stack including a normal cell stack and a defective cell.
3 is a schematic cross-sectional view of an SOFC cell including a mixed ion conductor electrolyte having a bilayer structure in which each layer is composed of a mixed ion conductor electrolyte having a different composition according to the present invention.
4 is a flowchart showing each step of the process of manufacturing the solid oxide fuel cell including the mixed ion conductor electrolyte in the present embodiment.
5(a) and 5(b) are XRD analysis results for each of the BCY-GDC electrolyte layer and the BZY-NDC electrolyte layer among the mixed ion conductor electrolyte double layers of the SOFC cell prepared in Examples of the present application.
6 is an SEM/EDS analysis result of a cross-section of a mixed ion conductor electrolyte double layer of the SOFC cell prepared in Example of the present application.
7 (a) is the result of measuring the voltage of the SOFC cell manufactured in the present Example in an open circuit state, FIG. 7 (b) is the (+) voltage constant current test result for the SOFC cell manufactured in the present Example , FIG. 7(c) is a negative voltage constant current test result for the SOFC cell manufactured in Example of the present application.
FIG. 8(a) is a constant current test result for an SOFC cell including a BCY-GDC single layer as an electrolyte, and FIG. 8(b) is a constant current test result for an SOFC cell including a BZY-NDC single layer as an electrolyte.
9 is a scanning electron microscope (SEM) photograph showing the cell cross-sectional microstructure after driving the stack including the SOFC cell prepared in Example of the present application for ~ 90 hours.

In describing the present invention, if it is determined that a detailed description of a related well-known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Since the embodiment according to the concept of the present invention may have various changes and may have various forms, a specific embodiment 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 with respect to a specific disclosed form, and should be understood to include all changes, equivalents or substitutes included in the spirit and scope of the present invention.

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as “comprise” or “have” are intended to designate that the described feature, number, step, operation, component, part, or combination thereof exists, and includes one or more other features or numbers. , it is to be understood that it does not preclude the possibility of the presence or addition of steps, operations, components, parts, or combinations thereof.

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

<Example>

As shown in FIG. 4, the following steps (1) to (6) were sequentially performed to prepare a co-ionic conductor electrolyte SOFC unit cell having a schematic cross-sectional view shown in FIG. 3 .

(1) After die-pressing a mixed powder composed of 65 wt% NiO and 35 wt% BZCYYb (BaZr _0.1 Ce _0.7 Y _0.1 Yb _0.1 O _2.9 ), heat treatment at 900° C. for 1 hour to prepare an anode support layer (AS).

(2) NiO and BCY (65 wt%)-GCD (35 wt%) were mixed in a ratio of 60 wt% : 40 wt%, respectively, for the preparation of the anode functional layer (AFL), and added using a planetary ball mill for particle refinement A grinding process was performed.

(3) After grinding, a slurry was prepared using a butanol solvent, and the AS layer prepared above was drop-coated and heat-treated at 950° C. for 1 hour.

(4) BCY (65 wt%)-GCD (35 wt%) slurry was drop-coated on the heat-treated AS/AFL substrate and heat-treated at 1000°C for 1 hour.

(5) BZY (25 wt%)-NDC (75 wt%) slurry was drop-coated on the heat-treated BCY-GDC layer and sintered at 1550° C. for 4 hours.

(6) A positive electrode functional layer (CFL) in which LSCF (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ) and NDC were mixed in a ratio of 60 wt% : 40 wt%, respectively, was coated and then heat treated at 950°C for 2 hours.

<Experimental example>

1. Phase/microstructure/elemental analysis of co-ionic conductor electrolytes

As a result of performing XRD analysis on the unit cell prepared in the above example, as shown in FIG. 5 , both electrolytes (BCY-GDC and BZY-NDC) constituting the double-layer electrolyte were formed without a secondary phase. This was confirmed.

6 is a SEM/EDS analysis result of a cross-section of a double-layer electrolyte. A high Zr concentration was observed from the cathode interface to about 10 μm (BZY-NDC region), and it can be seen that the Zr concentration sharply decreased in the region after that. (BCY-GDC region).

2. Reverse voltage endurance test

The open circuit voltage of the fuel cell based on the double-layer structure electrolyte prepared in the above example exhibited a normal value of 1.0 to 1.1 V (FIG. 7(a)).

To confirm the durability under reverse voltage operation, the (+) voltage (~ 0.2 V, 227 mA/cm ² ) test was performed for 3 to 4 hours (Fig. 7(b)), and then the (-) voltage test was performed at -0.05 V , (227 mA/cm ² ), -0.05 V, (227 mA/cm ² ), -0.05 V, (227 mA/cm ² ) was carried out stepwise in the order ( FIG. 7( c )). Unlike the BCY-GDC single-layer cell test results (FIG. 8(a)) and the BZY-NDC single-layer cell (FIG. 8(b)) test results, the double-layer electrolyte cell prepared in this example shows a stable voltage even under reverse voltage conditions. It can be seen that the value is maintained.

In addition, as a result of post-mortem analysis, no physical damage (delamination) was observed at both the anode/electrolyte interface and the cathode/electrolyte interface ( FIG. 9 ).

Combining the above results, it can be seen that the mixed ion conductor electrolyte having a double layer structure is a very effective cell design for preventing electrode delamination of a mixed ion conductor based fuel cell.

As mentioned above, although embodiments of the present invention have been described with reference to the accompanying drawings, 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 (7)

anode support layer;
anode functional layer;
Formed using a mixture containing yttria-doped barium cerates (BCY) and gadolinium-doped ceria (GDC) doped, so that yttria is doped BCY-GDC electrolyte layer comprising barium cerates (BCY) and gadolinium-doped ceria (GDC) doped;
Yttria-doped barium zirconate (BZY) and neodymium (Nd) doped barium zirconate formed by using a mixture containing ceria (neodymium-doped ceria, NDC) doped barium zirconate (BZY), BZY-NDC electrolyte layer including (barium zirconate, BZY) and neodymium (Nd) doped ceria (neodymium-doped ceria, NDC); and
A solid oxide fuel cell in which a positive electrode functional layer is sequentially stacked. According to claim 1,
The negative electrode support layer,
A solid oxide fuel cell comprising nickel oxide (NiO) and a mixture containing a BaCeO ₃ -BaZrO ₃ solid mixture (BZCYYb) doped with yttrium (Y) and ytterbium (Yb). According to claim 1,
The anode functional layer,
A solid oxide fuel cell, characterized in that it is formed of a mixture containing nickel oxide (NiO) and BCY-GDC. The method of claim 1,
The anode functional layer,
A solid oxide fuel cell, characterized in that it is formed of a mixture containing lanthanum-strontium-cobalt-iron oxide (LSCF) and NDC. (a) forming a negative electrode support layer;
(b) forming a negative electrode functional layer on the upper surface of the negative electrode support layer;
(c) a mixture containing barium cerates (BCY) doped with yttria and ceria doped with gadolinium (Gd) on the upper surface of the negative electrode functional layer (gadolinium-doped ceria, GDC) forming a BCY-GDC electrolyte layer using;
(d) on the upper surface of the BCY-GDC electrolyte layer, a mixture comprising yttria-doped barium zirconate (BZY) and neodymium (Nd) doped ceria (neodymium-doped ceria, NDC) preparing a laminate by forming a BZY-NDC electrolyte layer using;
(e) sintering the laminate; and
(f) forming a positive electrode functional layer on the upper surface of the BZY-NDC electrolyte layer of the laminate sintered in step (e); 6. The method of claim 5,
A method for manufacturing a solid oxide fuel cell, characterized in that in step (e), sintering is performed at a temperature of 1450 to 1550° C. for 1 to 10 hours. A solid oxide fuel cell stack comprising a plurality of solid oxide fuel cell unit cells according to any one of claims 1 to 4.

Images