JPH0652869A - Solid electrolyte film of fuel cell and manufacture thereof - Google Patents

Abstract

PURPOSE:To efficiently manufacture a compact film of solid electrolyte required to a solid electrolyte fuel cell (SOFC). CONSTITUTION:A compact film 2 of electrolyte for blocking pores in an electrode base 1 and a frame-sprayed film 3 of electrolyte formed by frame spraying method are sequentially provided on the electrode base 1. A slurry of particles of stabilized zirconia (YSZ) is previously applied to the surface of an electrode serving as a cell base and is sintered to block the pores, and the film of electrolyte is formed thereafter by frame spraying, whereby a compact film of solid electrolyte can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte membrane for a fuel cell and a method for producing the same, and more particularly to an electrolyte membrane for a single cell of a solid oxide fuel cell and a method for producing the same.

[0002]

2. Description of the Related Art Solid oxide fuel cells (hereinafter referred to as SOFC
Is an abbreviation) is a solid electrolyte having selective permeability of ions,
Two electrodes (an oxidizer electrode and a fuel electrode) arranged with this pinched in between
It is configured with as a basic element. Then, by flowing oxygen to the oxidizer electrode and hydrogen to the fuel electrode, the chemical reaction proceeds,
Power is generated.

As the electrolyte, a material that allows either oxygen ions or hydrogen ions to pass therethrough may be used, but normally a material having oxygen ion permeability is used in view of material restrictions. As the electrolyte material, stabilized zirconia (YSZ) is used in which yttria oxide is added to zirconia to stabilize the structure. The oxidizer electrode has a perovskite structure and a part of lanthanum is alkaline earth metal. Replaced Lantern Manganite (La
_1-x (M) _x ) _y MnO ₃ (M: alkaline earth metal), and a nickel zirconia cermet prepared by mixing YSZ with a predetermined amount of Ni is used as the fuel electrode.

As a structure of the SOFC, for example, as shown in FIG. 4, a unit cell 40 having an oxidant electrode 42 and a fuel electrode 43 on both surfaces of a solid electrolyte 41 is an interconnector having a fuel passage 47 and an oxidant passage 48. A structure in which the electrolyte has mechanical strength is known, which has a structure in which the electrolyte is laminated via 44. Further, as shown in FIG. 5, a solid electrolyte 41 and an oxidizer electrode 42 are formed on a fuel electrode substrate 46 having a fuel passage 47.
There is also known an SOFC having a structure in which a plurality of single cells 40 having a plurality of stacked layers are stacked with an oxidizer electrode substrate 45 in which an interconnector 34 is stacked and an oxidizer passage 48 is formed. In this case, one electrode is provided with mechanical strength, and the electrolyte and the other electrode are formed on the surface thereof.

[0005]

However, each member in the SOFC is a ceramic produced by subjecting the above-mentioned materials to high temperature treatment, and the electrolyte in each material is SO.
The electrical conductivity is small even at 900 to 1000 ° C., which is the operating temperature of FC. Therefore, in order to prevent the output shortage of the single cell due to the voltage drop in the electrolyte part, it is necessary to reduce the thickness of the electrolyte. However, in the former structure, it is necessary to impart mechanical strength to the electrolyte itself so as to support the entire cell, an extremely thin film cannot be used, and the thickness is 300 to 5
It is about 00 μm.

On the other hand, in the latter structure, one of the electrodes serves as a support for the cell, and the conductivity of the electrode material is 1000 to 10000 times as large as that of the electrolyte material, so that the thickness of the support can be omitted. As a result, the electrolyte may be as thin as the manufacturing allowance, and extremely high performance as a single cell is expected. However, in reality, there are restrictions due to the manufacturing method of the electrode support and the structure and shape, and as the method of manufacturing the cell having such a structure, a method of stacking electrodes and electrolyte sheets and co-sintering, or plasma A method of forming an electrolyte membrane by thermal spraying or laser spraying has been adopted.

In the case of the former method of co-sintering the sheet,
Since a large amount of operation is required for sheet production using an organic solvent and an organic binder, and pressure bonding and sintering of the sheet, the thermal spraying method, which has a high deposition rate regardless of the shape and size of the sample, is an industrial method. It is preferable from the viewpoint. However, when an SOFC electrolyte membrane is manufactured by the thermal spraying method, YSZ
However, there was a problem because its melting point was as high as about 2700 ° C. That is, in the thermal spraying method, YSZ powder is supplied into a high-temperature thermal spraying flame to bring it into a molten state, and the molten YSZ is fused on the substrate before it solidifies. Solidified YSZ particles may be generated, and not all YSZ reach the substrate in a sufficiently melted state. Therefore, the produced YSZ film is not a perfect dense body, and therefore, there is a phenomenon that some amount of gas (especially hydrogen having a small molecular diameter) is transmitted. To prevent this, it is conceivable to increase the thickness of the electrolyte, but in that case the voltage drop in the electrolyte increases. Therefore, even if a single cell is produced using such a non-compact electrolyte, the electromotive force of the cell will be lower than the theoretical value, or the voltage drop when the current is taken out becomes large. Then, the power generation characteristics were not always sufficient.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a solid electrolyte of SOFC having a structure in which a cell itself is mechanically supported by an electrode material and a method for producing the same, in which a slurry of solid electrolyte powder is first applied and sintered on an electrode substrate. The present invention provides a solid electrolyte membrane in which a sprayed electrolyte membrane is formed again on the formed sintered electrolyte membrane by a thermal spraying method, and a method for producing the solid electrolyte membrane. By this, the dense solid electrolyte membrane required for SOFC can be efficiently produced. The purpose is to manufacture well.

[0009]

In order to solve the above problems, the solid electrolyte membrane of the fuel cell according to the present invention is an electrolyte dense thin film for closing pores of the electrode substrate on an electrode substrate, and a thermal spraying method. It is characterized in that the electrolytic sprayed film formed by is sequentially provided.

Further, in the method for producing a solid electrolyte membrane for a fuel cell of the present invention, a slurry of solid electrolyte powder is applied onto an electrode substrate and sintered, and then the surface of the sintered electrolyte dense thin film is sprayed with an electrolyte. It is characterized in that a sprayed film is formed.

A feature of the present invention is that when an electrolyte membrane is formed on an electrode substrate by using a thermal spraying method, first, a slurry of an electrolyte is applied and sintered to close fine pores on the substrate surface. After that, an electrolyte sprayed film having a predetermined thickness is formed by using a spraying method which is advantageous in terms of film production rate and the like, whereby a dense film suitable for SOFC is efficiently produced.

Conventionally, a solid electrolyte membrane has been produced only by the thermal spraying method, but the denseness of the membrane is low and SOFC of sufficient performance cannot be realized only by this method.

[0013]

EXAMPLE FIG. 1 shows the concept of the method for producing a solid electrolyte membrane according to the present invention. 1 is a porous electrode substrate, 2 is an electrolyte dense thin film, and 3 is an electrolyte sprayed film sprayed. In the manufacturing method according to the present invention, first of all, on the substrate 1 (see FIG. 1).
Solid electrolyte powder slurry is applied and sintered to form a dense and gas impermeable electrolyte dense thin film 2 (see FIG. 2),
Then, an electrolyte sprayed film 3 is formed by spraying an electrolyte on the surface of the dense thin film 2 to form a solid electrolyte film necessary for producing a fuel cell (see FIG. 3). Even if the microcracks 4 are formed on the electrolyte sprayed film 3, since the dense electrolyte dense thin film 2 is formed, gas permeation can be prevented.

The manufacturing method and the like of the above-mentioned electrolyte dense thin film 2 is basically not limited as long as it closes the pores of the electrode substrate 1. Further, the thickness may be a sufficient thickness to close the pores of the electrode substrate 1 as described above. Preferably 2-10
μm. If the thickness is less than 2 μm, the pores may not be sufficiently closed, and if the thickness exceeds 10 μm, cracks may occur in the electrolyte dense thin film 2.

When forming a dense electrolyte thin film by a sintering method using the slurry according to the present invention as described above, the average particle size of the solid electrolyte powder is preferably 0.1 to 1 μm. If it is less than 0.1 μm, it is difficult to produce a solid electrolyte powder, which is not practical. On the other hand, if it exceeds 1 μm, the sintering temperature becomes high and the electrode substrate may be damaged.

As specific examples, first, examples in which a solid electrolyte membrane is formed by the method of the present invention on a porous electrode substrate made of a fuel electrode material will be shown.

As the material for the fuel electrode, nickel zirconia cermet, which is widely used here, was used. The material used to prepare the cermet was nickel oxide powder and yttria-stabilized zirconia powder (with 8 mol% yttria oxide added: Tosoh TZ-8Y).
And nickel oxide is 40 vol% in volume ratio.
It was weighed and mixed so as to be included above. PVA in the mixture
A system binder was added in an amount of 2 to 5% by weight and then press-molded, and this was sintered at 1300 ° C. for 2 hours. The porosity of the sintered body is about 20 to 30%, though it varies slightly depending on the amount of the binder added. This is subjected to a reduction treatment at 900 to 1000 ° C. in an H 2 atmosphere, whereby reduction of NiO proceeds,
The porosity could be about 40%. The pores of the sintered body after this reduction treatment were distributed around 0.2 to 3 μm with 1 μm as the center. Therefore, when the electrolyte is directly sprayed onto the substrate 1, microcracks 4 are generated in the sprayed electrolyte sprayed film 3 as shown in FIG. 6, so that the fuel gas easily permeates to the oxygen electrode 1 side. Will result in poor power generation characteristics.

Therefore, in the present invention, the dense thin film 2 of the electrolyte is formed on the surface of the fuel electrode 1 as shown in FIG. 3, but the slurry coating method was used for the formation. For the preparation of the slurry, water was used as a medium, a dispersant was added thereto, and YSZ and water were mixed at a volume ratio of about 3: 1 to obtain a slurry. The composition of YSZ used for preparing the slurry is the same stabilized zirconia as that used for the electrode and the thermal spraying material (adding 8 mol% of yttria oxide) from the viewpoint of conductivity. However, in order to improve the sinterability of the applied slurry, a powder having a small particle size was used. It was possible to sinter the coating film at a low temperature by using a powder having a small particle size. TZ-8 manufactured by Tosoh of YSZ, which has been widely used as an electrolyte so far.
In the case of Y, the sintering temperature for densification has a lower limit of 1300 ° C., but the crystallite diameter is reduced to 200 to 250 Å and the grain size is reduced to an average of about 0.5 μm to obtain 1200.
Sintering could be performed at a temperature of about ° C.

One of the advantages of reducing the particle size is that the sintering temperature becomes low and the electrode substrate 1 becomes a base of the electrolyte sprayed film 3 without applying thermal stress, and the fineness of the porous electrode substrate 1 is obtained. The point is that the dense electrolyte thin film 2 that closes the pores can be produced. Further, not only this but also a good effect in closing the pores of the electrode could be obtained. If it is difficult to enter the pores, a better effect can be obtained by reducing the pressure on the side opposite to the coated surface. By the way, since the hydrogen gas is supplied to the fuel electrode substrate 1 in a reducing state when power is generated by forming a cell, the pores are larger than those immediately after sintering in an oxidizing atmosphere.

Even in such a state, since the YSZ fine particles in the applied slurry need to effectively close the pores on the electrode surface, a reduction treatment was performed before applying the slurry. After applying the slurry in this manner, the electrode substrate was heat-treated at a temperature of 1200 to 1250 ° C. for about 2 hours to form a thin dense electrolyte dense film 2.

After that, an electrolyte layer 3 necessary for forming SOFC was formed on this surface by a plasma spraying device. Then, an SOFC single cell was produced by forming an electrode layer of an oxidizer electrode on the electrolyte layer. Here, the formation of the oxidizer electrode layer was performed by a slurry coating method. That is, lanthanum manganite was mixed with polyethylene glycol and ethanol to prepare a slurry, which was applied to the surface of the electrolyte, and then 1100 to 1300 ° C.
And heat-treated at a temperature within the range.

In forming the electrolyte membrane by thermal spraying, atmospheric spraying was used and the thickness was 50 μm to 100 μm. Of course, vacuum spraying does not cause any problems in the present invention. Conventionally, in order to form a YSZ film by a thermal spraying method, the reduced pressure thermal spraying was more suitable from the viewpoint of improving the denseness. Since it is in a blocked state,
There is no problem with atmospheric spraying. Further, in YSZ formation by the thermal spraying method, the film thickness is increased to about 200 to 300 μm in order to cope with gas permeation due to generation of microcracks. However, according to the present invention, the permeation of gas can be prevented on the electrode surface, so that there is no need to increase the thickness of the sprayed film 3. In thermal spraying, the film is usually formed by scanning the surface of the sample several times with the thermal spray flame, but the film thickness per scanning is about 10 μm. Therefore, in order to form a thick film, the number of times of scanning of the flame is inevitably increased, but in this case, not only the time required for film formation increases and the manufacturing cost increases, but also the sample is sprayed at high temperature. Since the time exposed to the flame becomes long, the sample temperature rises, which may cause problems such as breakage of the sample and change of the material of the substrate. However, according to the present invention, since the time required for thermal spraying is shortened, not only the manufacturing cost can be reduced, but also the manufacturing yield can be remarkably improved.

Next, examples of the present invention carried out using an oxidizer electrode substrate will be described. The basic process is similar to that described so far when an oxidizer electrode is used,
The production is simplified by the fact that the process of reduction treatment before closing the pores by slurry coating is unnecessary.
Here, LA _0.8 Sr _0.2 MnO ₃ , which is commonly used in SOFC, was used as the material powder. In addition, the powder was appropriately selected and used from several kinds of particles having an average particle size within the range of 2 to 10 μm. Regarding the sintering characteristics of these powders, the smaller the average particle size, the easier the sintering proceeds and the denser the powder becomes. Therefore, the sintering conditions were determined according to the particle size of each powder, and the oxidizer electrode substrate was prepared. . The manufactured substrate was press-molded by adding a PVA-based binder like the fuel electrode substrate. Regarding the physical properties of the produced oxidant electrode substrate, the porosity was 20 to 40%, and the average pore diameter was approximately 1 to 2 μm.

A YSZ slurry prepared by the same method as that used for the fuel electrode was applied to such a sample substrate and sintered to close the pores on the surface. At this time,
The powder used for the YSZ slurry is a fine powder, and as described above, a dense sintered product can be obtained at about 1200 ° C. On the other hand, if the oxidizer electrode is sintered at an excessively high temperature, it will become densified, and the porosity required for the electrode will be lost. The upper limit of the sintering temperature of the raw material is 1200
˜1250 ° C. However, since the YSZ applied to the surface can be sintered at the same temperature as this, it was possible to close the pores on the surface without exposing the oxidizer electrode substrate to an unnecessary high temperature. Following such a process, a sprayed film was produced by a plasma spraying device. Then, a fuel cell layer made of nickel zirconia cermet was formed on the electrolyte membrane to obtain a single cell. When forming the fuel electrode, the cermet slurry coating / sintering method cannot be applied because the heat resistance temperature of the oxidizer electrode substrate (lanthanum manganite) is about 1300 ° C., which is lower than the sintering temperature of nickel zirconia cermet. Therefore, the cermet layer was formed by the plasma spraying method without heat stress on the substrate.

As described above, according to the present invention, a SOFC cell having a higher performance than ever can be obtained by a method according to the process for producing an electrolyte by the thermal spraying method that has been performed so far. In addition, the yield of products can be improved by shortening the thermal spraying process, without changing the conventional thermal spraying process itself.

[0026]

As described above, according to the present invention, SOF is used.
When the electrolyte membrane of the C cell is formed by the thermal spraying method, YSZ fine powder slurry is applied and sintered on the surface of the electrode serving as the cell substrate in advance to close the pores,
After that, the electrolyte sprayed film is formed by spraying. Conventionally, the thermal spraying method has been focused on the advantages that the film production rate is higher than that of the EVD method or the sputtering method, and that the size and shape of the sample surface to be formed is not restricted.
It has been studied as a method for forming an electrolyte thin film of FC. However, the melting point of zirconia, which is the electrolyte material, is 27.
Since the temperature is as high as 00 ° C., a dense film cannot always be formed, and microcracks and the like are present in the film, which causes poor power generation characteristics due to gas permeation. In a sprayed coating, increasing the thickness of the coating can be considered as a measure for preventing such gas permeation. However, if the film thickness is excessively increased by focusing only on the gas permeation, there is a problem that the voltage effect in the electrolyte is increased and the cell performance is deteriorated. However, in the method of the present invention, since the surface of the sample is sprayed with an electrolyte slurry of fine powder that can close the pores before the thermal spraying and the sintering is performed, the surface of the sample is sprayed. In the paragraph before it is done, the elaborateness is enhanced. Therefore, by spraying such a surface, it is possible to prevent the denseness of the entire electrolyte membrane from being greatly affected even if microcracks occur in the electrolyte sprayed membrane. In addition, as an effect of the present invention, the thickness of the electrolyte sprayed film can be made thinner than that of the conventional method, whereby the manufacturing cost can be reduced and the manufacturing yield can be improved.

As a method of manufacturing the electrolyte thin film, it is possible to use only the slurry coating and sintering processes performed in the first step of the present invention. However, in the case of this method, if the thickness of the slurry applied at one time is increased, numerous cracks will be generated on the surface during sintering. Need to repeat times. For this reason, not only the work efficiency is deteriorated, but also the sintering causes a thermal stress on the electrode substrate, which may deteriorate the electrode performance. In the present invention, such a problem does not occur, a large film formation rate by the thermal spraying method can be effectively used, an electrolyte thin film required for SOFC can be obtained, and industrially great advantage can be obtained. .

[Brief description of drawings]

FIG. 1 is an explanatory view of a method for producing a solid electrolyte membrane for a fuel cell of the present invention.

FIG. 2 is an explanatory view of a method for producing a solid electrolyte membrane for a fuel cell of the present invention.

FIG. 3 is a sectional view of a solid electrolyte membrane of a fuel cell of the present invention.

FIG. 4 is an explanatory view showing the structure of a fuel cell.

FIG. 5 is an explanatory view showing the structure of a fuel cell.

FIG. 6 is a cross-sectional view of a solid electrolyte membrane of a conventional fuel cell.

[Explanation of symbols]

 1 Electrode Substrate 2 Electrolyte Thin Film 3 Electrolyte Sprayed Film 4 Microcrack 40 Single Cell 41 Solid Electrolyte 42 Oxidizer Electrode 43 Fuel Electrode 44 In Connector 45 Oxidizer Electrode Substrate 46 Fuel Electrode Substrate 47 Fuel Passage 48 Oxidant Passage

Claims (2)

[Claims] 1. A solid electrolyte membrane for a fuel cell, wherein an electrolyte dense thin film for closing pores of the electrode substrate and an electrolyte sprayed film formed by a spraying method are sequentially provided on the electrode substrate. 2. A solid electrolyte sprayed film is formed by applying a slurry of a solid electrolyte powder on an electrode substrate and sintering the slurry to form an electrolyte dense thin film, and then forming a solid electrolyte sprayed film on the surface of the electrolyte dense thin film by a spraying method. Method for producing solid electrolyte membrane of fuel cell for manufacturing.