KR20200072002A - Electrolyte for solid oxide fuel cell, solid oxide fuel cell and method of preparing solid oxide fuel cell - Google Patents

Abstract

Provided is a solid electrolyte for a solid oxide fuel cell, capable of implementing excellent electrical and ionic conductivity while improving durability. The solid electrolyte includes a ceramic solid oxide layer; and a reaction inhibitory layer including a compound expressed by chemical formula 1, Ce_aM_bBi_cSc_dO_2, where M is one selected from the group consisting of Gd, Sm, Pr, Y and a combination thereof, a + b + c + d = 1, 0 < a <= 0.80, 0 < b <= 0.2, 0 < c <= 0.03, 0 < d <= 0.03, and 0 < b + c + d <= 0.20.

Description

Solid electrolyte for solid oxide fuel cells, solid oxide fuel cells and a method for manufacturing the same {ELECTROLYTE FOR SOLID OXIDE FUEL CELL, SOLID OXIDE FUEL CELL AND METHOD OF PREPARING SOLID OXIDE FUEL CELL}

The present invention relates to a solid electrolyte for a solid oxide fuel cell, a solid oxide fuel cell and a method for manufacturing the same, and more specifically, a solid oxide fuel capable of realizing excellent electrical conductivity and ion conductivity while increasing durability by operating in a medium temperature region The present invention relates to a material for developing a solid electrolyte for a battery, a solid oxide fuel cell using the same, and a method for manufacturing the same.

A fuel cell generates electric energy by reacting a fuel and an oxidizing agent with an electrochemical reduction reaction. The redox reaction is carried out by a catalyst, and generally can continuously produce electricity by continuously supplying fuel.

As one type of fuel cell, a solid oxide fuel cell (SOFC) is a fuel cell that uses solid oxide as an electrolyte and operates at the highest temperature of 700 to 1000°C among existing fuel cells. The solid oxide fuel cell has a simple structure compared to other fuel cells because each component is made of a solid, and there is no problem of electrolyte loss and replenishment and corrosion.

A typical solid oxide fuel cell is composed of an oxygen ion conductive electrolyte and cathodes (cathode) and anodes (anode, cathode) located on both sides. The oxygen ions generated by the reduction reaction of oxygen at the cathode move to the anode through the electrolyte, and then react with hydrogen supplied to the anode to produce water, and at this time, the anode (anode) Electrons are generated in ), and electrons are consumed in the cathode, so the basic operation principle is to connect two electrodes to each other to generate a current.

A solid oxide fuel cell (SOFC) capable of diversifying fuels with advantages of high energy efficiency has been actively developed for large-scale distributed power generation in addition to a building fuel cell.

SOFC for distributed power generation is being developed as a combined power generation system that drives gas turbines and microturbines using high-temperature waste heat discharged from SOFCs.

The fuel cell for distributed power generation has an advantage of obtaining high energy efficiency by operating at a high temperature of about 800°C or higher and recovering high-temperature waste heat. On the other hand, a fuel cell for distributed power generation operating at such a high temperature has a problem in that output decreases from a single cell when operated at a high temperature for a long time. One of the causes of the deterioration is that an insulating material such as Mn and Sr oxide is deposited on the electrolyte/electrode interface from the anode material to delay the electrochemical reaction. Another cause is contamination from peripheral piping parts, which are mainly metal due to high temperature action.

When a low-temperature active electrode material is used, the operating temperature can be lowered, thereby solving the problem of power deterioration and durability, which are problems of the fuel cell operating in the above-described high temperature region.

In order to fabricate a fuel cell operating in a medium temperature region, a positive electrode material having high activity at a low temperature may be used. Representative examples of such a positive electrode material include a new material having a cobalt and iron-based perovskite such as LSCF or a Ruddlesden-Popp structure such as La ₂ NiO ₄ .

However, the highly active positive electrode material has a problem of generating an insulating secondary phase by reacting with a zirconia-based electrolyte material.

In addition, ceria oxide-based electrolytes have a problem of lowering the ionic conductivity by generating a zirconia-based electrolyte and a solid solution in the co-sintering process.

An object of the present invention is to solve the above-mentioned problems, and the high-active positive electrode material is to develop a low-temperature sinterable ceria-based material that does not generate an insulating secondary phase by reacting with a zirconia-based electrolyte material as a coating material of the electrolyte.

Another object of the present invention is to solve the other problems described above, and to develop a low temperature sinterable ceria-based material that does not generate a zirconia-based electrolyte and a solid solution in a co-sintering process of a solid oxide fuel cell as a coating material of an electrolyte. do.

Since the solid electrolyte for a solid oxide fuel cell according to the present invention is a ceria-based material capable of low-temperature sintering, the electrolyte material of the ceramic solid oxide layer is coated, so that the highly active anode material reacts with the ceramic solid oxide layer to not produce an insulating secondary phase. This can solve the problem of reduction in electrical conductivity.

Since the solid electrolyte for a solid oxide fuel cell according to the present invention is formed by including a reaction inhibiting layer of a ceria-based material capable of low-temperature sintering, the temperature of the solid oxide fuel cell during sintering can be lowered. The problem of reducing the ion conductivity can be solved by preventing the formation of a reaction inhibiting layer, a zirconia-based electrolyte, and a solid solution phase.

The solid electrolyte for a solid oxide fuel cell according to the present invention is excellent in a solid oxide fuel cell using a positive electrode material exhibiting activity in a medium temperature region by preventing the highly active positive electrode material from reacting with the ceramic solid oxide layer to form an insulating secondary phase. Implement electrical conductivity.

The solid electrolyte for a solid oxide fuel cell according to the present invention is capable of lowering the temperature during co-sintering of the solid oxide fuel cell. Even in a solid oxide fuel cell using a positive electrode material exhibiting activity in a medium temperature region, excellent ionic conductivity is realized.

1 is a schematic cross-sectional view of the structure of a solid electrolyte for a solid oxide fuel cell according to an embodiment of the present invention.
2 is a schematic cross-sectional view of the structure of a solid oxide fuel cell according to another embodiment of the present invention.
3 to 6 are SEM images of the reaction inhibiting layers prepared in Example 1, Example 3, Comparative Example 1 and Comparative Example 3, respectively.
7 is a graph showing porosity of the reaction inhibiting layers formed in Examples 1 to 3 and Comparative Examples 1 to 3, respectively.
8 is a graph showing the electrical conductivity of the reaction inhibiting layers formed in Examples 1, 3-5 and Comparative Examples 1 and 3, respectively.
FIG. 9 is a graph of the results of electrical conductivity with respect to the sintering density of the results of FIG. 8.

The terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. Based on the principle that it can be, it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention. In addition, the embodiments shown in the embodiments and the drawings shown in the present specification are only one of the most preferred embodiments of the present invention, and do not represent all of the technical spirit of the present invention, and can be replaced at the time of application. It should be understood that there may be various equivalents and variations.

In one embodiment of the invention,

Ceramic solid oxide layer; And

Reaction inhibiting layer comprising a compound represented by the formula (1);

It provides a solid electrolyte for a solid oxide fuel cell comprising a.

<Formula 1>

Ce _a M _b Bi _c Sc _d O ₂

In the above formula,

M represents one selected from the group consisting of Gd, Sm, Pr, Y and combinations thereof,

a+b+c+d=1, 0<a≤0.80, 0<b≤0.2, 0<c≤0.03, 0<d≤0.03, 0<b+c+d≤0.20.

1 is a schematic cross-sectional view of the structure of a solid electrolyte for a solid oxide fuel cell according to an embodiment of the present invention. In FIG. 1, the solid electrolyte 10 for a solid oxide fuel cell is formed by sequentially stacking a ceramic solid oxide layer 1 and a reaction inhibiting layer 2.

A solid oxide fuel cell is composed of an oxygen ion conductive electrolyte and cathodes (cathode) and anodes (anode, cathode) located on both sides. The oxygen ions generated by the reduction reaction of oxygen at the cathode move to the anode through the electrolyte, and then react with hydrogen supplied to the anode to produce water, and at this time, the anode (anode) Electrons are generated in ), and electrons are consumed in the cathode, so the basic operation principle is to connect two electrodes to each other to generate a current.

The solid electrolyte for the solid oxide fuel cell may be interposed between the cathode and the anode.

A solid oxide fuel cell operating at a high temperature of about 800° C. or higher has an advantage of obtaining high energy efficiency by recovering high-temperature waste heat. On the other hand, a solid oxide fuel cell operating at such a high temperature has a problem in that output decreases from a single cell when operating at a high temperature for a long time. One of the causes of the deterioration is that an insulating material such as Mn and Sr oxide is deposited on the electrolyte/electrode interface from the anode material to delay the electrochemical reaction. Another cause is contamination from peripheral piping parts, which are mainly metal due to high temperature action.

Therefore, in the case of a fuel cell operating in a medium temperature region with a lower operating temperature, there is an advantage of increasing durability.

A positive electrode material having high activity at low temperature may be used to manufacture a fuel cell operating in a medium temperature region of about 500 to about 750°C. Representative examples of such a positive electrode material include a new material having a cobalt and iron-based perovskite such as LSCF or a Ruddlesden-Popp structure such as La ₂ NiO ₄ .

The highly active positive electrode material has a problem of generating an insulating secondary phase by reacting with a zirconia-based electrolyte material.

In the reaction inhibiting layer 2 of the solid electrolyte for the solid oxide fuel cell, when the cathode is used as the above-described high-active material, the ceramic solid oxide layer 1 of the solid electrolyte reacts with the cathode to generate an insulating secondary phase. It serves to prevent it.

The compound represented by Chemical Formula 1 may be formed by doping a dopant with a ceria-based oxide at a relatively low sintering temperature. The compound represented by Chemical Formula 1 is heat treated at a relatively low sintering temperature, but the sinterability is improved, so that the reaction inhibiting layer 2 is more densely formed, and accordingly, electrical conductivity can be improved.

In addition, by forming the reaction inhibiting layer 2 densely, it is possible to effectively prevent diffusion of elements (eg, Sr, Mn) of the cathode and maintain performance for a long time.

In addition, since the compound represented by Formula 1 is formed by doping a dopant with ceria oxide at a relatively low sintering temperature, the ceria-based oxide is the ceramic solid oxide layer (1) during the co-sintering process of a solid oxide fuel cell. It is possible to improve the ionic conductivity by preventing the formation of a super solid solution.

For example, when a zirconia-based electrolyte material is used as the ceramic solid oxide layer 1, during the high-temperature heat treatment process of the solid oxide fuel cell, the ceria oxide is the same as the zirconia-based electrolyte material and (Zr, Ce)O ₂ This is because when a solid solution phase is generated, there may be a problem of lowering the ionic conductivity.

The ceramic solid oxide layer (1) is a fluorite-based oxide such as Bi ₂ O _3, YSZ (Yttria-stabilized zirconia), a perovskite-based oxide such as LSGM ((La,Sr)(Ga,Mg)O ₃ ) And combinations thereof.

In another embodiment of the invention,

Sequentially sintering (1300 to 1400°C) by sequentially laminating a cathode layer (NiO-YSZ) and a ceramic solid oxide layer (electrolyte layer); Applying a metal-doped ceria oxide on the ceramic solid oxide layer to form a reaction inhibiting layer, followed by heat treatment at a lower temperature (1100 to 1250°C); And it provides a method for manufacturing a solid oxide fuel cell comprising a heat treatment (800 to 1000 ℃) step of the anode layer (such as LSCF).

In another embodiment of the invention,

Cathode layer (NiO-YSZ) / ceramic solid oxide layer (electrolyte layer) / metal-doped ceria oxide layer (reaction inhibiting layer) by sequentially laminating (sintering 1200 to 1250 ℃); It provides a method for manufacturing a solid oxide fuel cell comprising a heat treatment (800 to 1000 ℃) step of the anode layer (such as LSCF).

The ceramic solid oxide layer is the same as the ceramic solid oxide layer 1 described above, and may be formed of an electrolyte material, and specific examples are as described above.

The ceramic solid oxide layer has already been sintered.

The detailed description of the reaction inhibiting layer 2 formed in the method for manufacturing the solid oxide fuel cell is as described above.

The laminate may be co-sintered at 1200°C to 1250°C. As described above, since the sintering temperature is relatively low, it is possible to prevent the metal-doped ceria oxide layer and the ceramic solid oxide layer from generating a solid solution phase.

The reaction inhibiting layer 2 obtained after sintering is formed by doping Bi and Si together with the metal-doped ceria oxide layer, thereby reducing the sintering temperature and improving the sintering property, thereby increasing the sintering density.

The reaction inhibiting layer 2 obtained after sintering has a low porosity. Specifically, the porosity of the reaction inhibiting layer 2 may be 1 to 20% by volume.

In another embodiment of the invention,

Cathode layer; A solid electrolyte for the solid oxide fuel cell; And an anode layer; provides a solid oxide fuel cell comprising a.

2 is a schematic cross-sectional view of the structure of a solid oxide fuel cell according to another embodiment of the present invention. In FIG. 2, the solid oxide fuel cell 100 is formed by sequentially stacking the cathode layer 20, the solid electrolyte layer 10, and the anode layer 30.

The detailed description of the solid electrolyte 10 is as described above.

The anode layer 30 is LSM (La _1-x Sr _x MnO ₃ , where x=0.1∼0.3), La _1-x Sr _x FeO ₃ ,(such as x=0.3), La _1-x Sr _x Co _y Fe _1-y O ₃ (such as La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ) and/or Pr _1-x Sr _x MnO ₃ (such as Pr _0.8 Sr _0.2 MnO ₃ ) may be formed, but the present invention Other materials may be used as long as it does not deviate from the range of. For example, alternatively Ruddlesden-Popper nickelate and La _1-x Ca _x MnO ₃ (such as La _0.8 Ca _0.2 MnO ₃ ) materials can be used.

The cathode layer 20 may be made of a material similar to the electrolyte material (the material of the ceramic solid oxide layer). Specifically, the cathode layer 20 may be made of a porous YSZ layer, but is not limited thereto.

The solid oxide fuel cell may be manufactured according to various known structures such as an anode support type, an anode support type, and an electrolyte support type.

Hereinafter, examples and comparative examples of the present invention will be described. The following examples are only examples of the present invention, and the present invention is not limited to the examples below.

(Example)

Example 1-5 was prepared so that the content of Gd ₂ O ₃ , Bi ₂ O ₃ and Sc ₂ O ₃ dopant in CeO ₂ is 15at% as shown in Table 1 below.

Comparative Example 1-3 was prepared so that the content of Gd ₂ O ₃ and Bi ₂ O ₃ dopant in CeO ₂ is 15at% as shown in Table 1 below.

division Dopant content ratio in specimen (atomic%) 15at% in total Example 1 Gd:Bi:Sc=12:1:2 Example 2 Gd:Bi:Sc=11:2:2 Example 3 Gd:Bi:Sc=10:3:2 Example 4 Gd:Bi:Sc=11:3:1 Example 5 Gd:Bi:Sc=13:1:1 Comparative Example 1 Gd:Bi=14:1 Comparative Example 2 Gd:Bi=13:2 Comparative Example 3 Gd:Bi=12:3

Experimental Example 1

Scanning electron microscope (SEM) analysis of the reaction inhibiting layers prepared in Example 1, Example 3, Comparative Example 1 and Comparative Example 3 was performed.

3 to 6 are SEM images of the reaction inhibiting layers prepared in Example 1, Example 3, Comparative Example 1 and Comparative Example 3, respectively.

3 to 6, the reaction suppressing layers of Examples 1 and 3 of FIGS. 3 and 4 have the same Bi doping amount, respectively, and the reaction inhibition of Comparative Examples 1 and 3 of FIGS. 5 and 6 is suppressed. It can be seen that the sintered density is increased because it is more densely formed than the layer. In addition, although the sum of the doping concentrations of Bi and Sc in the reaction suppressing layer of Example 1 in FIG. 3 and the doping concentrations of Bi in the reaction suppressing layer in Comparative Example 3 in FIG. 6 are all equal to 3 at%, the embodiment of FIG. 3 is performed. It can be seen that the reaction inhibitory layer of Example 1 is formed more densely, so that the sintering density increases.

Experimental Example 2

The porosity of the reaction inhibiting layers formed in Examples 1 to 3 and Comparative Examples 1 to 3, respectively, was evaluated.

7 is a graph showing porosity of the reaction inhibiting layers formed in Examples 1 to 3 and Comparative Examples 1 to 3, respectively.

In Examples 1-3 and Comparative Examples 1-3, the porosity decreased as the amount of Bi doping increased, but in Examples 1 to 3, the porosity decreased in comparison with Comparative Examples having the same amount of Bi doping, respectively.

Experimental Example 3

The electrical conductivity of the reaction inhibiting layers formed in Examples 1, 3-5 and Comparative Examples 1 and 3, respectively, was evaluated.

Electrical conductivity was measured using a Source-Measure Unit (K2400, Keithley).

8 is a graph showing electrical conductivity measured at 750° C. by flowing air synthesized in an electric furnace with respect to the reaction inhibiting layers formed in Examples 1, 3-5 and Comparative Examples 1 and 3, respectively. 8,% in parentheses is a record of the measured sinter density.

Looking at the case of Comparative Example 1, Example 1 and Example 5 and Comparative Example 3, Example 4 and Example 5 having the same Bi doping amount, both the Sc content increases, the electrical conductivity tends to increase can confirm. However, the increase in electrical conductivity does not change the electrical conductivity even if the Sc doping amount is increased when the Sc doping amount reaches 1 at%.

The increase in electrical conductivity seen in the Sc doped example of 1 at% or more is considered to be caused by an increase in sintering density.

FIG. 9 is a graph of the results of electrical conductivity with respect to the sintering density of the results of FIG. 8. 9 shows that for each composition, the electrical conductivity is proportional to the sintering density, and that the sintering density increases by doping Sc and Bi simultaneously.

It should be understood that the above-described embodiments are illustrative and non-limiting in all respects, and the scope of the present invention will be indicated by the following claims rather than the above detailed description. And it should be interpreted that the meaning and scope of the claims to be described later, as well as all alterable and deformable forms derived from the equivalent concept, are included in the scope of the present invention.

1: Ceramic solid oxide layer
2: Reaction inhibiting layer
10: solid electrolyte layer
20: cathode layer
30: anode layer
100: solid oxide fuel cell

Claims (7)

Ceramic solid oxide layer; And
Reaction inhibiting layer comprising a compound represented by the formula (1);
Solid electrolyte for a solid oxide fuel cell comprising a.
<Formula 1>
Ce _a M _b Bi _c Sc _d O ₂
In the above formula,
M represents one selected from the group consisting of Gd, Sm, Pr, Y and combinations thereof,
a+b+c+d=1, 0<a≤0.80, 0<b≤0.2, 0<c≤0.03, 0<d≤0.03, 0<b+c+d≤0.20.
According to claim 1,
The ceramic solid oxide layer includes one selected from the group consisting of Bi ₂ O _{3, a} fluorite-based perovskite-based oxide, and combinations thereof.
Solid electrolyte for solid oxide fuel cells:
According to claim 1,
The porosity of the reaction inhibiting layer is 1 to 20% by volume
Solid electrolyte for solid oxide fuel cells.
Cathode layer;
The solid electrolyte according to any one of claims 1 to 3; And
Anode layer;
Solid oxide fuel cell comprising a.
According to claim 4,
The anode layer is La _1-x Sr _x MnO ₃ (here, x=0.1 to 0.3), La _1-x Sr _x FeO ₃ (here, x=0.3), La _1-x Sr _x Co _y Fe _1-y O ₃ (where 0.1≤x≤0.4, 0.1≤y≤0.9) Pr _1-x Sr _x MnO ₃ (where 0.1≤x≤0.3), Ruddlesden-Popper nickelate, La _1-x Ca _x MnO ₃ ( Here, at least one selected from the group consisting of 0.1≤x≤0.4) and combinations thereof
Solid oxide fuel cell.
A step of sequentially sintering the cathode layer and the ceramic solid oxide layer in sequence;
Applying a metal-doped ceria oxide on the ceramic solid oxide layer to form a reaction inhibiting layer, followed by heat treatment at a temperature lower than the co-sintering temperature; And
Heat-treating the anode layer;
Including,
The metal-doped ceria oxide layer is represented by the following formula (1)
Method for manufacturing a solid oxide fuel cell:
<Formula 1>
Ce _a M _b Bi _c Sc _d O ₂
In the above formula,
M represents one selected from the group consisting of Gd, Sm, Pr, Y and combinations thereof,
a+b+c+d=1, 0<a≤0.80, 0<b≤0.2, 0<c≤0.03, 0<d≤0.03, 0<b+c+d≤0.20.
Sequentially sintering by sequentially stacking a cathode layer, a ceramic solid oxide layer, and a metal-doped ceria oxide layer; And heat-treating the anode layer.
The metal-doped ceria oxide layer is represented by the following formula (1)
Method for manufacturing a solid oxide fuel cell:
<Formula 1>
Ce _a M _b Bi _c Sc _d O ₂
In the above formula,
M represents one selected from the group consisting of Gd, Sm, Pr, Y and combinations thereof,
a+b+c+d=1, 0<a≤0.80, 0<b≤0.2, 0<c≤0.03, 0<d≤0.03, 0<b+c+d≤0.20.

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