KR102109730B1 - Method for fabricating solid oxide fuel cell - Google Patents

Abstract

Provided is a method for manufacturing a solid oxide fuel cell. The manufacturing method includes forming an electrolyte layer by sequentially stacking a yttria stabilized zirconia (YSZ) layer and a rare-earth-doped ceria (RDC) layer on a negative electrode support. The electrolyte layer is isotropically compressed. The isotropically compressed electrolyte layer is sintered. An anode layer is formed on the sintered electrolyte layer.

Description

Manufacturing method of solid oxide fuel cell {Method for fabricating solid oxide fuel cell}

The present invention relates to a fuel cell, and more particularly to a solid oxide fuel cell.

The fuel cell includes an anode provided with fuel, a cathode provided with air, and an electrolyte layer disposed between the anode and the cathode. When hydrogen is used as a fuel, only water is generated as a product, so it is very eco-friendly and has a relatively high energy conversion efficiency compared to a conventional internal combustion engine.

Such a fuel cell includes a solid oxide fuel cell (SOFC) having an oxygen ion conductor in an electrolyte layer. Solid oxide fuel cells generally operate at the highest temperature (700 to 1000 ° C) among fuel cells, and have a simpler structure compared to other fuel cells because all components are made of solids. There is no problem, no precious metal catalyst is required, and fuel supply through direct internal reforming is easy. In addition, it also has the advantage of being capable of thermal combined power generation using waste heat because it discharges hot gases. Due to these advantages, research on solid oxide fuel cells is currently actively conducted.

The electrolyte layer of the solid oxide fuel cell must have a high density because it must block air flowing from the anode and the cathode. For this, there may be a method of increasing the sintering temperature, but a high sintering temperature may cause other problems.

Therefore, the problem to be solved by the present invention is to provide a method for producing a solid oxide fuel cell having an electrolyte layer having an excellent density even when sintering is performed at a low temperature.

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above technical problem, an embodiment of the present invention provides a method for manufacturing a solid oxide fuel cell. The manufacturing method includes forming an electrolyte layer by sequentially stacking a yttria stabilized zirconia (YSZ) layer and a rare-earth-doped ceria (RDC) layer on a negative electrode support. The electrolyte layer is isotropically compressed. The isotropically compressed electrolyte layer is sintered. An anode layer is formed on the sintered electrolyte layer.

The sintering may be performed at a temperature below the temperature at which a reaction product between YSZ and RDC is produced. The sintering may be performed at a temperature of 1220 to 1280 ° C.

The RDC may be gdolinium-doped ceria (GDC). The negative electrode support may include a catalyst metal and YSZ. The anode layer may include a perovskite metal oxide and RDC. The metal oxide of the perovskite structure may be LSCF (La _1-x Sr _x Co _1-y Fe _y O ₃ , where 0 <x <1, 0 <y <1).

The electrolyte layer may not include a sintering aid.

The electrolyte layer may be formed on the pre-sintered negative electrode support.

As described above, a solid oxide fuel cell manufactured according to embodiments of the present invention may exhibit excellent electrical properties by providing an electrolyte layer having excellent density even when sintering is performed at a low temperature.

However, the effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a cross-sectional view showing a cross-section of a solid oxide fuel cell according to an embodiment of the present invention.
2 is a schematic diagram showing an isotropic compressor used in this embodiment.
3 is a schematic diagram showing a process according to Example 1 of the present unit cell.
Figure 4 is an X-ray diffraction graph (X-Ray Diffraction Graph) of the result of heat treatment of the mixture of GDC powder and YSZ powder at 1250 and 1300 degrees, respectively.
5A and 5B are SEM photographs showing the surface and cross-section of the electrolyte layer before isotropic compression (5a) and after isotropic compression (5b) during the course of the unit cell preparation example 1;
6 is a graph showing the IV curve and the output density obtained while operating the unit cells prepared according to the unit cell preparation example 1 and the unit cell preparation example at 600 degrees.
7 is a graph showing the electrochemical impedance characteristics obtained by operating the unit cells prepared according to the unit cell preparation example 1 and the unit cell manufacturing example 2 at 600 degrees.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings in order to describe the present invention in more detail. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. In the drawings, when a layer is said to be "on" another layer or substrate, it may be formed directly on another layer or substrate, or a third layer may be interposed between them.

1 is a cross-sectional view showing a cross-section of a solid oxide fuel cell according to an embodiment of the present invention.

Referring to FIG. 1, a negative electrode support 10 or an air electrode support may be provided. The negative electrode support 10 may include a catalytic metal and an oxygen ion conductor, and may also be a cermet of the catalyst metal and an oxygen ion conductor. A cathode layer 20 or an anode layer may be formed on the cathode support 10. The cathode layer 20 may also include a catalytic metal and an oxygen ion conductor, and further may be a cermet of the catalyst metal and an oxygen ion conductor.

The catalytic metal in the cathode support 10 and the cathode layer 20 may serve to improve electron conductivity and also to generate protons and electrons from fuel (eg, hydrogen). The catalytic metal may be a transition metal, for example, Ni, Cu, Pt, Pd, or a combination of two or more of them. The negative electrode support 10 and the oxygen ion conductor in the negative electrode layer 20 are oxygen ion conductive metal oxides having a fluorite structure, and rare-earth-doped ceria (RDC) work. Examples include: neodymium-doped ceria (NDC), gadolinium-doped ceria (GDC), and samarium-doped ceria (SDC); YSZ (yttria stabilized zirconia, ZrO ₂ / Y ₂ O ₃ ); And ScSZ (scandia stabilized zirconia, ZrO ₂ / Sc ₂ O ₃ ). Specifically, the oxygen support in the negative electrode support 10 and the negative electrode layer 20 may be YSZ, and the catalyst metal may be Ni.

The negative electrode support 10 casts a slurry or dispersion comprising NiO as an example of an oxide of a catalyst metal, YSZ as an example of an oxygen ion conductor, a dispersant, a plasticizer, and a binder, compresses, and compresses a temperature of about 800 to 900 degrees. It can be obtained by pre-sintering. Pre-sintering means that the negative electrode support 10 is sintered to have a stable state so as not to be broken for handling. Thereafter, the negative electrode layer 20 may be formed on the negative electrode support 10. The cathode layer 20 may be formed using a wet method, specifically a dipping method, a coating method, a printing method, or the like. As an example, after attaching a release film (not shown) on the lower surface of the negative electrode support 10, an oxide of the catalyst metal as an example NiO, an oxygen ion conductor as an example YSZ, a dispersing agent, and a binder comprising The negative electrode layer 20 may be formed by dipping a negative electrode support 10 to which the release film is attached in a slurry or dispersion, and then dipping up.

Electrolyte layers 30a and 30b may be formed on the cathode layer 20. The electrolyte layers 30a and 30b may be a double layer of the YSZ layer 30a and the RDC layer 30b as an oxygen ion conductor layer. The RDC may be, for example, NDC, GDC, or SDC. The electrolyte layers 30a and 30b may increase the sintering density, but may not contain a sintering aid capable of increasing resistance by acting as an impurity.

The electrolyte layers 30a and 30b may be formed using a wet method, specifically a dipping method, a coating method, or a printing method. When the electrolyte layers 30a and 30b are formed using a wet method, the thickness of the electrolyte layers 30a and 30b can be lowered to improve ion conductivity. As an example, the YSZ layer 30a is formed using a dipping method in which the negative electrode support 10 on which the negative electrode layer 20 is formed is immersed in a slurry or dispersion liquid containing YSZ powder, dispersant, and binder, and then raised. Then, the cathode layer 20 and the YSZ layer 30a, the anode support 10 formed in turn, is immersed in a slurry or dispersion containing RDC powder, a dispersant, and a binder, and then using the dipping method to raise the RDC. Layer 30b may be formed.

Thereafter, the electrolyte layers 30a and 30b may be isostatically compressed. This isotropic compression means that the pressure on the electrolyte layers 30a and 30b is almost the same in all directions. In this case, the gaps or voids between the oxygen ion conductor particles in the electrolyte layers 30a and 30b can be reduced in all directions, so that the overall density of the electrolyte layers 30a and 30b can be improved.

2 is a schematic diagram showing an isotropic compressor used in this embodiment.

1 and 2, when the negative electrode layer 20 and the negative electrode support 10 in which the electrolyte layers 30a and 30b are sequentially formed are sealed, placed in a pressure chamber filled with a pressure medium, and when pressure is applied to the pressure medium, An isotropic pressure may be applied to the electrolyte layers 30a and 30b including the cathode layer 20. The pressure medium may be water, and the isotropic compression may proceed at room temperature.

Referring back to FIG. 1, the isotropically compressed product can be sintered. At this time, the cathode layer 20, the electrolyte layers 30a, 30b, and the cathode support 10 may be co-sintered. Such co-sintering can improve the adhesion between each layer and reduce the manufacturing cost. When the electrolyte layer (30a, 30b) is a double layer of the YSZ layer (30a) and RDC layer (30b), the co-sintering is an example of the reaction product of YSZ and RDC between the YSZ layer (30a) and RDC layer (30b) As, it can be carried out at a temperature lower than the temperature at which (Ce, Zr) O ₂ is formed. In this case, it is possible to improve the ionic conductivity of the electrolyte layers 30a and 30b by suppressing the production of a reaction product of YSZ and RDC having low ionic conductivity.

The temperature at which the reaction products of YSZ and RDC are formed is about 1300 ° C. or higher, and in this embodiment, the co-sintering may be performed at a temperature of 1250 ° C., for example, a temperature of less than 1300 ° C., for example, 1220 to 1280 ° C. have. In addition, the air sintering may be performed in an air atmosphere, and may be performed for about 3 to 5 hours.

Since the electrolyte layers 30a and 30b are sufficiently compressed and compacted in all directions through the isostatic compression described above, the co-sintering proceeds at a temperature below the temperature at which the reaction products of YSZ and RDC are formed and the electrolyte layer 30a , Even if the sintering aid is not included in 30b), and the densification according to sintering is performed less, the sufficiently dense electrolyte layers 30a and 30b can be obtained. As described above, sintering proceeds at a relatively low temperature while being sufficiently high in density, so that the production of reaction products of YSZ and RDC is suppressed, and the electrolyte layers 30a and 30b that do not contain impurities as sintering aids greatly improve ion conductivity. It can also be greatly suppressed the gas permeability, it is possible to lower the open circuit voltage, output density and resistance of the battery.

Thereafter, an anode layer 40 or a fuel electrode layer may be formed on the electrolyte layers 30a and 30b. The anode layer 40 may include an electron-conducting metal oxide having a perovskite structure as an electron conductor and an oxygen-ion conducting metal oxide having a fluorite structure as an oxygen ion conductor. The electron-conductive metal oxide of the perovskite structure is LSCF (La _1-x Sr _x Co _1-y Fe _y O ₃ , where 0 <x <1, 0 <y <1), LSC (La _1-x Sr _x CoO ₃ , where 0 <x <1), LSF (La _1-x Sr _x FeO ₃ , where 0 <x <1), or BSCF (Ba _1-x Sr _x Co _1-y Fe _y O ₃ , where It may be 0 <x <1, 0 <y <1). The oxygen ion conductor may include RDC, as an example, NDC, GDC, and SDC as described above; YSZ; And it may include one or more selected from the group consisting of ScSZ. As an example, the anode layer is LSCF (La _1-x Sr _x Co _1-y Fe _y O ₃ , where 0 <x <1, 0 <y <1) and RDC exhibit good electron conduction properties even at low temperatures. It can be provided. When the electrolyte layer (30a, 30b) is a double layer of the YSZ layer (30a) and the RDC layer (30b), the RDC layer (30b) is located between the anode layer 40 and the YSZ layer (30a), The chemical reaction between the electron conductor of the perovskite structure in the anode layer 40 and YSZ can be suppressed.

Above, it has been described that the cathode layer 20 is formed on the cathode support 10, but is not limited thereto, and the formation of the cathode layer 20 may be omitted, and in this case, the cathode support 10 serves as a cathode layer. It can be done. In addition, a negative electrode current collector (not shown) may be formed under the negative electrode support 10, and a positive electrode current collector (not shown) may be formed over the positive electrode layer 40. The current collector is a conductor containing a plurality of pores, and may be a metal mesh, a metal foam, or a porous carbon structure. In the case of a metal mesh or metal foam, it may be made of Ni, Co, Mn, or alloys thereof, or stainless steel coated on the surface with Ni, Co, Mn, or alloys of these.

In the fuel cell, oxygen supplied from the outside in the cathode layer 20 is converted into oxygen ions while consuming electrons supplied through an external circuit, and the oxygen ions are converted into the anode through the electrolyte layers 30a and 30b. It is transferred to the layer 40, and in the anode layer 40, the oxygen ion and hydrogen, which is a fuel supplied from the outside, meet to operate on the principle of generating electrons and water. Such a fuel cell may be operable at 600 degrees to 800 degrees.

Hereinafter, a preferred experimental example (example) is presented to help understanding of the present invention. However, the following experimental examples are only to help understanding of the present invention, and the present invention is not limited by the following experimental examples.

<Unit cell manufacturing example 1>

3 is a schematic diagram showing a process according to Example 1 of the present unit cell.

Preparation of negative electrode support : 110 g of NiO powder, 90 g of YSZ powder, and 1 g of fish oil as a dispersant were added into a mixed solvent of 32.5 g of ethanol and 32.5 g of toluene to perform ball milling for 24 hours. 10 g of a plasticizer of butyl benzyl phthalate and 13.5 g of a polyvinyl butyral binder were added to the ball milled product, followed by ball milling again for 24 hours to obtain a slurry. The slurry was stirred in vacuo for about 9 hours to remove air bubbles and gases. The slurry from which bubbles and gases were removed was tape-cast to a thickness of 1 mm on a substrate, dried at 60 degrees, and separated from the substrate to obtain a negative electrode support tape. After cutting the negative electrode support tape to an appropriate size, two cut negative electrode support tapes were stacked, and a pressure of 5 MPa was applied over the laminated negative electrode support tape for 6 hours to obtain a negative electrode support having a final thickness of 1 mm.

Pre-sintering the negative electrode support: The negative electrode support was pre-sintered for 2 hours at a high temperature furnace in an air atmosphere at 850 ° C. to obtain a negative electrode support having appropriate strength. Parafilm was attached on the lower surface of the pre-sintered negative electrode support at a temperature of 60 ° C.

NiO / YSZ cathode layer formation : NiO powder 50g, YSZ powder 50g, and dispersant 1.5 g of fish oil were added in 200g of ethanol and ball milled for 24 hours. To the ball milled product, 7 g of 10 wt% polyvinyl butyral ethanol solution and 40 g of a binder solution (Kceracell) were added and ball milled again for 24 hours to obtain a NiO / YSZ dispersion. The negative electrode support having the parafilm attached to the lower surface was immersed in the NiO / YSZ dispersion for 1 minute, then raised at a constant rate and dried at room temperature for about 5 minutes. At this time, a NiO / YSZ negative electrode layer was formed to a thickness of 10 μm on the upper surface of the negative electrode support without parafilm attached.

Formation of YSZ electrolyte layer : 100 g of YSZ powder and 1.2 g of fish oil as a dispersant were added into 300 g of ethanol and ball milled for 24 hours. To the ball milled product, 11 g of 10 wt% polyvinyl butyral ethanol solution and 40 g of a binder solution (Kceracell) were added and ball milled again for 24 hours to obtain an YSZ dispersion. The negative electrode support on which the NiO / YSZ negative electrode layer was formed was immersed in the YSZ dispersion for 2 seconds, dried at a constant rate, and dried at room temperature for about 5 minutes. At this time, an YSZ electrolyte layer was formed on the NiO / YSZ cathode layer to a thickness of 2 μm.

Formation of GDC electrolyte layer : 100 g of GDC powder and 1.3 g of fish oil as a dispersant were added into 300 g of ethanol to perform ball milling for 24 hours. 10 g of a 10 wt% polyvinyl butyral ethanol solution and 20 g of a binder solution (Kceracell) were added to the ball milled result, and then ball milled again for 24 hours to obtain a GDC dispersion. The negative electrode support in which the NiO / YSZ negative electrode layer and the YSZ electrolyte layer were sequentially formed was immersed in the GDC dispersion for 2 seconds, dried at a constant rate, and dried at room temperature for about 5 minutes. At this time, a GDC electrolyte layer was formed on the YSZ electrolyte layer to a thickness of 5 μm.

Isotropic compression : A sample in which NiO / YSZ anode layer, YSZ electrolyte layer, and GDC electrolyte layer were sequentially formed on the anode support was sealed in a vacuum, then placed in an isotropic compressor, and a pressure of 300 MPa was applied for 5 minutes. Thereafter, the latex tube was removed and heat treatment was performed for 1 hour at 850 degrees in an air atmosphere to remove organic substances such as a binder.

Co-sintering : NiO / YSZ negative electrode layer, YSZ electrolyte layer, and GDC electrolyte layer were sequentially formed on the negative electrode support, and isotropically compressed samples were sintered in a high temperature furnace at 1250 ° C. for 4 hours to complete a half cell.

Formation of anode layer : 12 g of GDC powder and 12 g of LSCF (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ) powder were added into 12 g of ethanol and ball milled for 24 hours. 4 g of 10 wt% polyvinyl butyral ethanol solution and 20 g of a binder solution (Kceracell) were added to the ball milled product, followed by ball milling for 24 hours to obtain a GDC / LSCF slurry. The GDC / LSCF slurry was screen printed on the GDC electrolyte layer of the sintered half-cell, and then dried in an oven at 60 degrees for 3 hours to form a GDC / LSCF anode layer with a thickness of 15 μm. Thereafter, the unit cell was completed by heat treatment for 2 hours in a high-temperature furnace at an air atmosphere of 1050 degrees.

<Unit cell manufacturing example 2>

A unit cell was prepared using the same method as in unit cell preparation example 1, except that the isotropic compression step was not performed.

Figure 4 is an X-ray diffraction graph (X-Ray Diffraction Graph) of the result of heat treatment of the mixture of GDC powder and YSZ powder at 1250 and 1300 degrees, respectively. At this time, the heat treatment was performed for 4 hours in the furnace of the air atmosphere, similar to this co-sintering process in Preparation Example 1.

Referring to FIG. 4, when the mixture of GDC powder and YSZ powder is heat-treated at 1250 ° C, peaks representing GDC and peaks representing YSZ are separated from each other and appear sharp.

However, when the mixture of the GDC powder and the YSZ powder is heat-treated at 1300 degrees, it can be confirmed that the peaks representing the adjacent GDCs and the peaks representing the YSZs are not separated and combined. From this, it can be estimated that (Ce, Zr) O ₂ phase was formed due to the reaction of GDC and YSZ during the 1300 degree heat treatment.

5A and 5B are SEM photographs showing the surface and cross-section of the electrolyte layer before isotropic compression (5a) and after isotropic compression (5b) during the course of the unit cell preparation example 1;

Referring to FIGS. 5A and 5B, it can be seen that the pores in the surface and the cross-section are almost eliminated in the electrolyte layer after isotropic compression (5b) compared to before isotropic compression (5a). From this, it can be seen that the electrolyte layer was contracted in all directions such as the side direction as well as the upper and lower directions by isotropic compression to be densified.

6 is a graph showing the I-V curve and the power density obtained while operating the unit cells prepared according to the unit cell preparation example 1 and the unit cell manufacturing example 2 at 600 degrees.

Referring to FIG. 6, it can be seen that the unit cell obtained in the unit cell manufacturing example 1 has a higher open circuit volatge (OCR) than the unit cell obtained in the unit cell manufacturing example 2, and a maximum output density is very high. It is possible to obtain an electrolyte layer having a sufficiently high density even after air sintering at a relatively low temperature of 1250 ° C by isotropic compression after forming the YSZ electrolyte layer and the GDC electrolyte layer, as described in Production Example 1 of the unit cell. It can be seen that the open circuit voltage seems to increase as the permeation of gases flowing through the cathode is suppressed, and the density of the pores in the electrolyte layer decreases as the density improves, resulting in an increase in output density as the resistance decreases.

On the other hand, when the YSZ electrolyte layer and the GDC electrolyte layer are formed and then sintered at 1250 ° C, which is a relatively low temperature, after forming the YSZ electrolyte layer and the GDC electrolyte layer, as described in Preparation Example 2, it is difficult to obtain an electrolyte layer having a sufficiently high density, and the opening is low. It can be seen as indicating the furnace voltage and output density.

7 is a graph showing the electrochemical impedance characteristics obtained by operating the unit cells prepared according to the unit cell preparation example 1 and the unit cell manufacturing example 2 at 600 degrees.

Referring to FIG. 7, the unit cell obtained in Example 1 of the unit cell in which the YSZ electrolyte layer and the GDC electrolyte layer were sequentially formed and then isotropically compressed and subjected to co-sintering, Unit Cell Production Example 2 in which the isotropic compression step was not performed It can be seen that the resistance is smaller than the unit cell obtained in. This may mean that the contact between the YSZ electrolyte layer and the GDC electrolyte layer is better in the unit cell obtained in the unit cell preparation example 1.

As described above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications and alterations by those skilled in the art within the technical spirit and scope of the present invention This is possible.

Claims (9)

After forming the negative electrode support, the step of pre-sintering to 800 to 900 degrees;
Forming an electrolyte layer by sequentially stacking a layer of yttria stabilized zirconia (YSZ) and a rare-earth-doped ceria (RDC) layer on the pre-sintered negative electrode support using a wet method;
Isotropically compressing the electrolyte layer;
Co-sintering the negative electrode support and the isotropically compressed electrolyte layer at a temperature of at least 1220 ° C. and below a temperature at which a reaction product between the YSZ layer and the RDC layer is produced; And
And forming an anode layer on the sintered electrolyte layer. delete The method according to claim 1,
The sintering is performed at a temperature of 1220 to 1280 ℃ solid oxide fuel cell manufacturing method. The method according to claim 1,
The RDC is a solid oxide fuel cell manufacturing method that is GDC (gadolinium-doped ceria). The method according to claim 1,
The anode support is a solid oxide fuel cell manufacturing method comprising a catalyst metal and YSZ. The method according to claim 1,
The anode layer is a method of manufacturing a solid oxide fuel cell having a perovskite structure metal oxide and RDC. The method according to claim 6,
The metal oxide of the perovskite structure is LSCF (La _1-x Sr _x Co _1-y Fe _y O ₃ , wherein 0 <x <1, 0 <y <1). The method according to claim 1,
The electrolyte layer is a solid oxide fuel cell manufacturing method that does not include a sintering aid. delete

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