KR100793155B1 - Fabrication method for unit cell of solid oxide fuel cell - Google Patents

Abstract

A method for manufacturing a unit cell of a solid oxide fuel cell is provided to produce the unit cell having high reaction activity, high thermal cycle stability, increased production yield, excellent performances, and improved economic efficiency. A method for manufacturing a unit cell of a solid oxide fuel cell includes the steps of: forming a negative electrode supporter(10) having a composition comprising 40-60wt% of nickel oxide and 40-60wt% of stabilized zirconia; forming a first functional layer(11) on the negative electrode supporter using a mixture having a composition comprising 30-45wt% of nickel oxide and 55-70wt% of stabilized zirconia; forming a second functional layer(12) beneath the negative electrode supporter using a mixture having a composition comprising 55-70wt% of nickel oxide and 30-45wt% of stabilized zirconia; forming an electrolyte layer(13) on the first functional layer using poreless, compact stabilized zirconia; forming a third functional layer(14) beneath the second functional layer, wherein the third functional layer has the same composition as the electrolyte layer and comprises many pores; and forming a positive electrode layer(15) on the electrolyte layer, wherein the positive electrode layer is formed of any one selected from lanthanum-strontium-manganese oxide or lanthanum-strontium-cobalt-iron oxide.

Description

Fabrication Method for Unit Cell of Solid Oxide Fuel Cell}

1 is a schematic diagram showing the structure of a unit cell of the present invention.

※ Explanation of symbols on main parts of drawing ※

10: cathode support 11: first functional layer

12 second functional layer 13 electrolyte layer

14: third functional layer 15: anode layer

The present invention relates to a method for manufacturing a unit cell for a solid oxide fuel cell, and has a high activity and thermal cycle stability, as well as prevents warpage during cooling after sintering and shows better performance while improving the production yield of a solid oxide fuel cell ( The present invention relates to a method for manufacturing a unit cell for an SOFC.

In general, a fuel cell is meant to generate electricity by reacting a fuel such as hydrogen or natural gas with oxygen, and is recognized as one of the main energy technologies of the future due to characteristics such as high efficiency, pollution-free, and noise.

There are several types of fuel cells. The double solid oxide fuel cell (SOFC) uses zirconia ceramics (ZrO ₂ ) or ceria (CeO ₂ ) or lanthanum-strontium-gadolinium-magnesium oxide (LSGM) as solid electrolytes. Refers to. The solid oxides are generally yttria (Y ₂ O ₃ ), ceria (CeO ₂ ), scandia (Sc ₂ O ₃ ) gadolinium oxide (Gd ₂ ) for the purpose of improving thermal stability and ionic conductivity at high temperature. O ₃₎ and it contains an appropriate amount of stabilizing jereul etc.)

A unit cell of a solid oxide fuel cell (SOFC) is formed in the form of a cathode material on one side and a cathode material on the other side with the solid electrolytes in the center. As a conventional cathode material, a mixture of nickel oxide (NiO) and stabilized zirconia is used, and lanthanum-strontium-manganese oxide (LSM), lanthanum-strontium-cobalt-iron oxide (LSCF), or the like is used as the anode material.

In the conventional method of manufacturing a unit cell of a solid oxide fuel cell (SOFC), a dense electrolyte sintered body having a thickness of 200 μm and 10 μm is first sintered in a furnace, followed by heat treatment by coating a cathode material on one side and an anode material on the other side. By producing (electrolyte support type).

As another method, first, the negative electrode material (mixture of NiO and zirconia powder) is molded into 1mm ± 10㎛ according to the conventional ceramic molding process, and firstly sintered at a relatively low temperature (1300-1400 ℃) to make a pre-sintered body. On the other hand, the electrolyte, which is a solid oxide, is coated on a surface of 5 to 20㎛ by a conventional ceramic coating method (slurry coating or spray coating, etc.), and then maintained at a temperature range of 1400-1500 ^o C in a sintering furnace for 1 to 5 hours. A method of producing a sintered body by performing secondary sintering, coating an anode material (LSM, LSCF, etc.) on the upper surface of the electrolyte layer again, and tertiary sintering by a method similar to the above is known (cathode supported type).

The negative electrode material used in the anode-supported solid oxide fuel cell has a moderate strength to support the unit cell structure, and high porosity and gas permeability so that the fuel gas (mainly hydrogen or natural gas, etc.) can sufficiently penetrate and react. Must have

The manufacturing method of the negative electrode material mainly follows the conventional ceramic manufacturing method, that is, by adding an additive (pore former mainly carbon or starch, etc.) to the mixture of NiO and stabilized zirconia powder to prevent the densification phenomenon during the sintering to leave pores. A method of sintering after molding is known.

However, there are some unresolved problems in the method of manufacturing a unit cell for an anode-supported solid oxide fuel cell (SOFC). The remaining problem is the lack of gas reaction activity due to the coarse particles in the anode layer. This is due to the low stability against thermal cycles that are indispensable in the operation of fuel cells and high failure rates due to warpage due to the shrinkage difference between the electrolyte layer and the cathode layer.

The reason for the lack of activity of the negative electrode material is that in order to secure sufficient porosity during the production of the negative electrode material, that is, to delay the densification during sintering, the starting material NiO and stabilized zirconia must be used as coarse particles. This is because a triple phase boundary (TPB) in which a gas reaction occurs inside is not sufficiently formed.

As a solution for the lack of the active material of the negative electrode material, the functional layer (FL) having a finer particle size (less than 1 μm) having the same composition as the negative electrode support between the negative electrode support (the main body occupying most of the negative electrode layer) and the electrolyte layer; It is known to insert a functional layer as thin as several tens of micrometers.

Second, the reason why the thermal cycle stability of the negative electrode material (or the negative electrode material and the electrolyte interface) is low is explained by two reasons. First, in the solid oxide fuel cell, the negative electrode material is a mixture of NiO and stabilized zirconia (typically 5: 5 composition). On the other hand, since the electrolyte layer in contact with the negative electrode material is made of stabilized zirconia alone, thermal stress occurs during the thermal cycle (heating and cooling) due to the difference in thermal expansion coefficient between the two layers, causing cracks at the interface between the negative electrode material and the electrolyte. It is one cause.

Another is the oxidation / reduction reaction of Ni during fuel cell operation (inert power is generated in an inert atmosphere such as hydrogen or methane gas on the cathode side during power generation operation, but during cooling, the Ni in the cathode layer causes the oxidation / reduction reaction to occur. Due to the change in volume accompanied by), the crack is generated inside the negative electrode material.

In order to solve this problem, some researchers use a method of suppressing the oxidation / reduction reaction of Ni by continuously injecting hydrogen or methane gas to the cathode after the operation of the solid oxide fuel cell is finished. Because of the increase in the operating cost of the economical disadvantages are present.

Third, the reason why the defect rate is high during the production of the unit cell for the solid oxide fuel cell is that the electrolyte layer is coated on the upper surface of the anode material and the degree of shrinkage of the electrolyte layer during the sintering and the cooling period after the sintering and Since the degree of shrinkage is different, it is known that the warpage phenomenon occurs in either direction.

The present invention has been invented to solve the above problems, when manufacturing a unit cell for a solid oxide fuel cell (SOFC), by coating a plurality of functional layers of different compositions on the upper and lower sides of the negative electrode material, high reaction activity and heat It is an object of the present invention to provide a method for manufacturing a unit cell for a solid oxide fuel cell having better performance and improved economic efficiency by enabling cycle stability and improving yield at the same time.

The present invention for achieving the above object is a step of forming a negative electrode support having a composition ratio of 40-60% by weight nickel oxide: stabilized zirconia 40-60% by weight

Forming a first functional layer of a mixture having a composition ratio of nickel oxide 30-45% by weight: stabilized zirconia 55-70% by weight on the upper surface of the negative electrode support

Forming a second functional layer from a mixture having a composition ratio of nickel oxide 55 to 70 wt%: stabilized zirconia 30 to 45 wt% on the lower surface of the anode support;

Forming an electrolyte layer with dense stabilized zirconia having almost no pores on the upper surface of the first functional layer

Forming a third functional layer on the bottom surface of the second functional layer and having the same composition as the electrolyte layer and including a plurality of holes;

Forming an anode layer of either lanthanum-strontium-manganese oxide or lanthanum-strontium-cobalt-iron oxide on the upper surface of the electrolyte layer.

Referring to the method of manufacturing a unit cell for a solid oxide fuel cell of the present invention having the above configuration in detail as follows.

Nickel oxide (NiO) 40-60% by weight as a raw material of the negative electrode support (10): Stabilized Zirconia (SZ: Stabilized Zirconia) 40-60% by weight of the composition and the pore forming agent (carbon or starch, etc.) and organic binder (Binder) and the dispersant (dispersant) is added and mixed, followed by molding and sintering according to a conventional manufacturing process to prepare a negative electrode support. At this time, the thickness of the negative electrode support is preferably 0.5 ~ 1mm.

The upper surface of the negative electrode support prepared as described above (the surface in contact with the electrolyte) was coated with a mixture prepared by mixing a mixture of nickel oxide 30-45% by weight: stabilized zirconia 55-70% by weight with a thickness of 5-50 μm. The first functional layer 11 is formed.

On the lower surface of the negative electrode support (the side opposite to the surface in contact with the electrolyte), a mixture prepared by mixing 55-70% by weight of nickel oxide: 45-30% by weight of stabilized zirconia was coated with a thickness of 5-50 μm. The bifunctional layer 12 is formed.

At this time, the coating method of the first functional layer and the second functional layer is selected by any one of the method of dip coating, spray coating or screen printing.

In addition, the functional layers may be coated with a single layer having a thickness of 5-50 μm. In the case of the first functional layer, the amount of nickel oxide decreases from the cathode support side to the electrolyte side, and in the case of the cathode support in the second functional layer. It may be coated with a plurality of layers having a composition gradient in a direction in which the nickel oxide content increases as the distance increases.

For example, the first functional layer is inclined by sequentially coating a layer having a composition ratio of nickel oxide and zirconia 40: 60% by weight, a layer 35: 65% by weight and a layer 30: 70% by weight on the cathode support. A functional layer having a composition may be prepared, and in the case of the second functional layer, a coating layer of nickel oxide and zirconia having a composition ratio of 60: 40% by weight, a layer of 65: 35% by weight, and a layer of 70: 30% by weight is sequentially coated. It is also possible to produce a functional layer having a gradient composition.

The first functional layer of the upper surface of the negative electrode support prepared as described above has a smaller nickel oxide content and a higher content of stabilized zirconia than the conventional negative electrode material, so that the coefficient of thermal expansion of the negative electrode material and the electrolyte layer is consistent. This results in the effect of suppressing the occurrence of cracking due to thermal stress during the thermal cycle.

Also, when the first functional layer is formed, nickel oxide and stabilized zirconia powders used for manufacturing the functional layer are finer than those used for the production of the negative electrode support, as in the conventional method for manufacturing a functional layer for a solid oxide fuel cell. It is also possible to improve the gas reaction activity by increasing the three-phase contact at the interface with the electrolyte.

In addition, the second functional layer has a higher content of acidic nickel than its conventional negative electrode material, and the reason for doing this is as follows.

First, when the solid oxide fuel cell is operated at high temperature, nickel oxide in the negative electrode material is reduced by the fuel gas (hydrogen or methane, etc.) to exist in the state of metal nickel (Ni). As it is interrupted, the surrounding air causes oxidation reaction. At this time, the oxidation reaction of nickel is accompanied by a large volume expansion, which is known as a major factor causing the degradation and destruction of the unit cell by causing cracks in the negative electrode material or the interface between the negative electrode material and the electrolyte.

However, as in the present invention, if the functional layer having the nickel oxide content increased to 55-70% by weight is placed on the lower surface of the negative electrode material, that is, the fuel gas is injected, the injection of fuel gas is stopped after the operation of the fuel cell is stopped. When is added, the nickel particles in the functional layer are first oxidized to expand the volume and block the air inlet, so that the fuel cell can sufficiently oxidize the nickel particles in the anode material, especially at the interface between the anode material and the electrolyte. The cooling is delayed until the time when no further oxidation reaction occurs, thereby bringing about the effect of suppressing the occurrence of cracks in the negative electrode material or the interface between the negative electrode material and the electrolyte.

On the other hand, the reason for limiting the thickness of each functional layer on the upper and lower surfaces of the negative electrode material of the present invention manufactured as described above is 5-50 μm, when the thickness of the functional layer is 5 μm or less, the thickness is too thin. If the thickness of the functional layer is not larger than 50 µm, the thickness of the functional layer is too thick, which hinders the flow of fuel gas or due to the difference in the coefficient of thermal expansion due to the difference in composition with the cathode support. It is preferable that the thickness of the upper and lower functional layers is about 5-50 μm because there is a risk of not being able to withstand thermal stress and peeling off and not functioning.

In addition, the reason for limiting the composition ratio of nickel oxide: stabilized zirconia on the upper surface, that is, the first functional layer, in the negative electrode material of the present invention is in the range of 30-45: 55-70% by weight. The purpose of the first functional layer to reduce the content of nickel and increase the amount of stabilizing zirconia to increase the coherence of the coefficient of thermal expansion is not achieved. It is preferable that the content of nickel oxide in the first functional layer is 30-45% by weight because the amount of nickel acting as a catalyst is insufficient, that is, the lack of three-phase contact results in deterioration of battery activity. Do.

In addition, the reason for limiting the composition ratio of nickel oxide: stabilized zirconia of the second functional layer to the range of 55-70% by weight: 30-45% by weight in the negative electrode material of the present invention is that when the content of nickel oxide is less than 55% by weight By increasing the content of nickel oxide, the second functional layer intended to form an anti-oxidation layer during cooling of the fuel cell does not achieve its original purpose, and when the content of nickel oxide is more than 70% by weight, the second function occurs during initial oxidation. The nickel oxide content in the second functional layer is preferably 55-70% by weight because the volume expansion of the nickel particles in the layer is excessive and there is a risk of causing destruction of the second functional layer itself.

On the upper surface of the anode material prepared as described above, the stabilized zirconia is coated with a thickness of 5-20 μm according to a conventional coating method to form an electrolyte layer 13, wherein the electrolyte layer 13 has a conventional sintering temperature (1400). When the sintered at ~ 1500 ℃) is coated to form a dense layer with little pores.

In addition, the lower surface of the negative electrode material is coated with a stabilizing zirconia in the same thickness as the electrolyte layer on the upper surface according to a conventional coating method to form a third functional layer 14, wherein the third functional layer is a cathode through the fuel gas sufficiently passes through The coating should be in the form of a lattice, with 50-70% of the pores in an area ratio to reach the ash.

The reason for forming the third functional layer composed of stabilizing zirconia only on the lower surface of the negative electrode material is a difference in shrinkage due to the difference in composition between the electrolyte layer and the negative electrode layer in the simultaneous sintering process formed after the coating of the electrolyte layer. Since the third functional layer having the same composition and thickness is present on the opposite side of the electrolyte layer, the stress due to the difference in shrinkage acts on both the upper and lower sides, thereby obtaining an effect of preventing warpage in the sintering process.

On the other hand, the reason for limiting the area ratio of the holes included in the third functional layer to 50-70% is that when the ratio of the holes is 50% or less, there is not enough area for the fuel gas to pass through, which lowers the performance of the fuel cell. This is because when the area ratio of the holes is 70% or more, that is, when the amount of stabilizing zirconia of the third functional layer is 30% or less, there is a high possibility that the solid fraction in the functional layer is insufficient to transmit even stress over the entire area. .

The upper surface of the negative electrode material in which the electrolyte layer has been formed as described above—that is, the upper surface of the dense electrolyte layer—is lanthanum-strontium-manganese oxide (LSM) or lanthanum-strontium-cobalt-iron oxide (LSCF) or the like according to a conventional method. The cathode material is coated and heat treated to complete a unit cell for a solid oxide fuel cell.

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

EXAMPLE

In the experiment of the present invention, in order to prepare a negative electrode material for a solid oxide fuel cell, 3% of PVB (Polyvinyl-butiral) and a pore-forming agent were first used as an organic binder in a 50:50 mixture of commercial nickel oxide powder and stabilized zirconia powder. 25 v / o of commercially available carbon black was added, followed by wet mixing in a ball mill for 24 hours in a conventional ceramic mixing process using ethanol as a mixed medium.

After the mixing, the dried powders were molded and sintered according to a conventional ceramic manufacturing process to produce a cathode support having a side of 50 mm and a thickness of 1 mm.

On the lower surface of the fabricated anode support, a paste prepared at 60:40 and 70:30 in nickel oxide and stabilized zirconia composition ratios was sequentially coated by a 10 μm thickness using a screen printer to form a second functional layer. On the other side (top), a paste prepared at 40:60 and 35:65 of nickel oxide and stabilized zirconia, respectively, was sequentially coated by 10 μm thickness using a screen printer to form a first functional layer. .

In addition, on the upper surface of the dried first functional layer, a paste made of only stabilized zirconia was again coated with a screen printer to a thickness of 20 μm to form an electrolyte layer, and on the other side (bottom), a paste made of only stabilized zirconia was screened. Printing formed a third functional layer of 20 탆 thickness.

At this time, in the coating process of the electrolyte layer, the electrolyte paste is uniformly coated on all areas of the coating by using a general screen having a uniformly formed micropore (200mesh). In the coating process of the third functional layer, a screen having a lattice pattern is used. The area ratio of the holes between the lattice coated with the electrolyte layer was about 60%.

The molded products manufactured as described above were put into a conventional sintering furnace and sintered at 1450 ° C. for 3 hours according to a conventional ceramic sintering method. After sintering, the molded bodies were subjected to a coating process of a conventional cathode layer and then to the sintering furnace. The sample was re-sintered at 1150 ° C. for 2 hours to produce a final unit cell for a solid oxide fuel cell.

The unit cells manufactured as described above were examined for their output characteristics and cracking after operating at 800 to 24 hours using a unit cell operation performance evaluation apparatus. The results are shown in Table 1 below.

TABLE 1

division Cathode support composition (NiO: YSZ) First functional layer composition (NiO: YSZ) Second functional layer composition (NiO: YSZ) 3rd functional layer thickness (㎛) Unit battery output (mW / ㎠) Cracks Bending degree (mm) Comparative Material 1 50:50 - - - 350 Destroyed upon cooling 0.3 Comparative Material 2 50:50 50:50 - - 490 Cracks 0.5 Comparative Material 3 50:50 40:60 60:40 - 510 No crack 0.4 Invention 1 50:50 40:60 60:40 20 500 No crack 0.03 Invention 2 50:50 40:60 + 35:65 60:40 + 70:30 20 500 No crack 0.06

As shown in Table 1 above, when the functional layer was not inserted into the negative electrode material outside of the scope of the present invention, the comparative material 1 showed a result that the unit cell was destroyed during cooling while the output characteristics of the unit cell were low. When the functional layer was inserted but the composition was the same as that of the negative electrode support and the particle size was only fine, the output characteristics of the unit cell were much improved in Comparative Material 2, but the cracks were present in the negative electrode material after the operation was completed.

In addition, if the third functional layer was not inserted regardless of whether the first functional layer and the second functional layer were inserted, the comparative material 1-3 had 0.3mm of both the degree of warpage of the unit cell (the difference between the height of the center and the outside). It was greatly above.

On the other hand, when three functional layers are sequentially inserted on both upper and lower surfaces of the negative electrode material according to the method of the present invention (Invention material 1-2), the output characteristics of the unit cell are excellent and cracks are observed inside the negative electrode material after the operation is finished. The degree of warpage was also 0.06 mm or less, which is much better.

This is because the functional layers inserted on both sides of the anode material improve the gas reaction activity at the anode material and the electrolyte interface, alleviate the possibility of cracking due to thermal stress peroxidation / reduction reaction, and the electrolyte layer and the sintering process. This is because the bending stress due to the difference in shrinkage of the cathode layer is significantly weakened.

As described above, when the unit cell for a solid oxide fuel cell (SOFC) is manufactured, the upper surface of the anode support (the surface in contact with the electrolyte) is coated with a first functional layer having a mixture ratio of nickel oxide reduced to 45 wt% or less. On the lower surface of the negative electrode support (opposite side of the surface in contact with the electrolyte), a second functional layer having an increased mixing ratio of nickel oxide of 55% or more is coated and inserted, and the lower surface of the second functional layer has an electrolyte layer and a composition. By coating the third functional layer of the same thickness has a high reaction activity and thermal cycle stability, while suppressing the warpage phenomenon to provide a method of manufacturing a unit cell for a solid oxide fuel cell with improved performance and high yield of the manufacturing process It works.

Claims (5)

Forming a negative electrode support having a composition ratio of 40-60% by weight of nickel oxide: stabilized zirconia 40-60% by weight Forming a first functional layer of a mixture having a composition ratio of nickel oxide 30-45% by weight: stabilized zirconia 55-70% by weight on the upper surface of the negative electrode support Forming a second functional layer from a mixture having a composition ratio of nickel oxide 55 to 70 wt%: stabilized zirconia 30 to 45 wt% on the lower surface of the anode support; Forming an electrolyte layer with dense stabilized zirconia having almost no pores on the upper surface of the first functional layer Forming a third functional layer on the bottom surface of the second functional layer and having the same composition as the electrolyte layer and including a plurality of holes; Forming an anode layer of any one of lanthanum-strontium-manganese oxide and lanthanum-strontium-cobalt-iron oxide on an upper surface of the electrolyte layer. The method of claim 1, wherein the coating thickness of the first and second functional layers is 5 ~ 50㎛. The method of claim 1, wherein the coating thickness of the electrolyte and the third functional layer is 5 to 20 μm. The solid oxide fuel cell of claim 1, wherein the first functional layer is coated with a plurality of layers having a composition gradient in a direction in which the nickel oxide content decreases from the cathode support side toward the electrolyte side. Method of manufacturing unit cell. The solid oxide fuel cell as claimed in claim 1, wherein the coating of the second functional layer is coated with a plurality of layers having a composition gradient in a direction in which nickel oxide increases as the distance from the cathode support increases. Method of manufacturing unit cell.

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