JP2006202667A - Manufacturing method of solid electrolyte membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a solid electrolyte membrane having long-term stability, high ionic conductivity, and high strength. <P>SOLUTION: This method is used for manufacturing a solid electrolyte membrane by preparing an alumina-added rare-earth stabilized zirconia solid solution by mixing rare-earth oxide particles each having a specific surface area of 20-30 m<SP>2</SP>/g, zirconia (ZrO<SB>2</SB>) and 0.1-2.0 pts. by mass of alumina (Al<SB>2</SB>O<SB>3</SB>) in the total 100 pts. by mass of the rare-earth oxide particles and ZrO<SB>2</SB>, and thereafter heat-treating them, and by forming the solid solution into a membrane. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a solid electrolyte membrane. The present invention particularly relates to a method for producing a solid electrolyte membrane having long-term stability, high ionic conductivity, and high strength used for a power generation membrane in a solid oxide fuel cell (SOFC) cogeneration system.

A yttria-stabilized zirconia (YSZ) produced by a coprecipitation method is generally used as a solid electrolyte used in a solid oxide fuel cell. YSZ is preferably used because it is stable in the vicinity of the operating temperature of SOFC. However, there is a problem that the price of the powder is relatively high and the ionic conductivity is relatively low. The reason for the high cost of the powder is that it is made by a complicated coprecipitation method. On the other hand, the ionic conductivity is an intrinsic property of the substance and cannot be eliminated when yttria (Y ₂ O ₃ ) is dissolved in zirconia (ZrO ₂ ).

Scandia (Sc ₂ O ₃ ) stabilized zirconia (ScSZ) is known as a rare earth oxide stabilized zirconia having high ionic conductivity. However, ScSZ has a problem in that there is no continuity in thermal expansion compared to normal stabilized zirconia. Further, although LSGM (LaSrGaMg-based) has been proposed, there is a problem in stability such as scattering of gallium (Ga) at high temperature, and it is difficult to put it into practical use.

Patent Document 1 discloses a method for producing a rare earth oxide-stabilized zirconia having relatively high ionic conductivity at a low cost by a solid phase reaction method instead of a coprecipitation method. According to this method, it is possible to obtain a solid electrolyte having a low ion cost and sufficient ionic conductivity for use as a fuel cell as compared with the coprecipitation method, but having a long-term stability and high strength. Obtaining a membrane is required in the practical application of solid oxide fuel cells.
Japanese Patent Laid-Open No. 2003-178771

  An object of this invention is to provide the manufacturing method of the solid electrolyte membrane which has long-term stability, high ionic conductivity, and high intensity | strength.

The present invention is a method of manufacturing a solid electrolyte membrane, and a rare earth oxide particles having a specific surface area of 20 to 30 m ² / g, and ZrO _2, the total of 100 parts by mass of the said rare earth oxide particles and ZrO ₂ Then, 0.1 to 2.0 parts by mass of alumina (Al ₂ O ₃ ) is mixed and then heat-treated to prepare an Al ₂ O ₃ -added rare earth oxide stabilized zirconia solid solution, and the solid solution is formed into a film. To do.

The specific surface area of the Al ₂ O ₃ is preferably 10 to 15 m ² / g.

The specific surface area of the ZrO ₂ is preferably 5 to ²⁰ m ² / g.

The rare earth oxide is preferably one or more selected from lutetia (Lu ₂ O ₃ ), ytterbia (Yb ₂ O ₃ ), and erbia (Er ₂ O ₃ ).

  Moreover, according to another situation, this invention is the solid electrolyte membrane manufactured by the said manufacturing method.

  According to still another aspect of the present invention, there is provided a solid oxide fuel cell, a power generation film in which a fuel electrode, the above-described solid electrolyte film, and an air electrode are sequentially stacked, and an interconnector. And are laminated.

  As an effect of the present invention, it is possible to produce a solid electrolyte membrane having ionic conductivity suitable for use in a fuel cell and having a strength about twice that of the conventional one. Such performance can be maintained over a long period of time, and a durable battery can be obtained when used as a power generation membrane of a solid oxide fuel cell. Furthermore, according to the method for producing a solid electrolyte membrane of the present invention, it is possible to produce a solid electrolyte membrane having high performance at a cost less than half that of the prior art, which is useful for practical application of a solid oxide fuel cell. Conceivable.

  The present invention is described in detail below. The following description does not limit the invention.

According to the method for manufacturing a solid electrolyte membrane according to one embodiment of the present invention, after adding rare earth oxide particles, ZrO ₂ , and Al ₂ O ₃ , heat treatment is performed to stabilize the alumina-added rare earth oxide. A zirconia solid solution is prepared, and the solid solution is formed into a film.

As the rare earth oxide particles, it is preferable to use fine powder having a specific surface area of 20 to 30 m ² / g and a particle size of 0.1 to 0.5 μm. If the specific surface area is less than 20 m ² / g, it is difficult to form a solid solution, and if it is greater than 30 m ² / g, the cohesive force between the fine powders exceeds the dispersion force, making it difficult to sufficiently disperse and mix. Examples of the rare earth oxide, europia (Eu ₂ O _3), Gadoria (Gd ₂ O _3), dysprosia (Dy ₂ O _3), 378 holmia (Ho ₂ O _3), erbia (Er ₂ O _3), Tsuria (Tm ₂ O ₃ ), Yb ₂ O ₃ , Lu ₂ O _{3 and the} like can be used, but are not limited thereto. From the viewpoint of performance and cost, Lu ₂ O ₃ , Yb ₂ O ₃ , and Er ₂ O ₃ can be preferably used.

Generally, as ZrO ₂ , a fine powder having a specific surface area of 5 to 30 m ² / g, preferably 5 to ²⁰ m ² / g and a particle size of about 0.3 to 1.0 μm can be used. This is because when the specific surface areas of the rare earth oxide and ZrO ₂ are uniform, uniform mixing is possible.

Al ₂ O ₃ can be added to the solid solution to function as a binder. Alumina melts at the time of sintering and promotes the sintering, but does not dissolve in zirconia after the sintering and precipitates at the grain boundary, so that the conductivity is not lowered. Al ₂ O ₃ may be a fine powder having a specific surface area of 10 to 15 m ² / g and a particle size of about 0.3 to 0.5 μm. The reason for setting such a specific surface area is that the rare earth oxide and ZrO ₂ have the same particle size and can be mixed uniformly.

In the mixing of rare earth oxide, ZrO ₂ and Al ₂ O ₃ , Al ₂ O ₃ , a surfactant and water as a solvent are added to the rare earth oxide fine powder and ZrO ₂ fine powder, To prepare.

Surfactants can be used to improve the dispersibility of rare earth oxides, ZrO ₂ and Al ₂ O ₃ . Examples of such surfactants include, but are not limited to, polycarboxylic acid ammonium and polyethyleneimine. As a solvent for preparing the dispersion, water and ethanol can be used. The solvent can be appropriately selected depending on the combination with the surfactant used as a dispersant. Preferably, water and ammonium polycarboxylate are used in combination with ethanol and polyethyleneimine, respectively.

ZrO ₂ and the rare earth oxide are preferably mixed so that ZrO ₂ is about 88 to 92 mol% and the rare earth oxide is about 8 to 12 mol%. If the rare earth oxide is less than 8 mol%, the obtained solid solution contains a large amount of monoclinic crystals, so that the stability is low and the conductivity is insufficient. If the rare earth oxide is more than 12 mol%, the resulting solid solution This is because although the stability is high, the ionic conductivity is lowered. More preferably, the rare earth oxide is mixed so as to be about 8 to 10 mol%, and most preferably mixed so as to be about 10 mol%. The rare earth oxide to be mixed may be one kind or two or more kinds.

The amount of Al ₂ O ₃ added is preferably 0.1 to 2.0 parts by mass, with the total mass of rare earth oxide particles and ZrO ₂ being 100 parts by mass. If the added amount of Al ₂ O ₃ is less than 0.1 parts by mass, sufficient strength cannot be imparted to the solid solution, and if it is more than 2.0 parts by mass, it can act as an impurity in the solid solution and the conductivity can be lowered. It is because there is sex. The addition amount of Al ₂ O ₃ is more preferably 0.25 to 1.0 part by mass, and most preferably 0.5 part by mass.

  Surfactant can be prepared so that it may become about 1 mass% with an active ingredient. Moreover, a solvent can be mixed so that it may become 30-300 mass% with respect to solid content.

  Next, the prepared dispersion is dispersed by a dispersion apparatus. A ball mill, a vibration mill, an attritor mill, or the like can be used as the dispersing device. It is preferable to use a dispersing device that can obtain a high shearing force. The dispersion time can be appropriately determined depending on the amount of the apparatus and the dispersion. For example, when an attritor mill is used, the dispersion time is preferably about 1 hour.

A dispersion containing the uniformly dispersed rare earth oxide, ZrO ₂ and Al ₂ O ₃ is once dried. Such a drying process is performed for about 0.5 to 20 hours using a dryer, an oven, or the like. After drying, the dispersed powder is heat treated to produce a solid solution of alumina-added rare earth oxide stabilized zirconia. The heat treatment is performed at about 800 to 1300 ° C., preferably 1100 to 1300 ° C. for 1 to 10 hours, preferably 2 to 5 hours using an apparatus such as an oven, an electric furnace, or a gas furnace. If the temperature is too high, the particle growth becomes excessive and it is difficult to perform good film formation in the next step, so it is not preferable to raise the temperature too much. The solid solution of alumina-added rare earth oxide stabilized zirconia produced in this way is a homogeneous cubic solid solution in which rare earth oxide and ZrO ₂ are uniformly mixed, and a monoclinic crystal is partially formed. I have never done it.

  Next, a solid electrolyte membrane is produced using a solid solution of alumina-added rare earth oxide stabilized zirconia. A slurry is prepared by dissolving a solid solution of alumina-added rare earth oxide stabilized zirconia obtained by heat treatment in a solvent. As the solvent, ethanol, water or the like can be used. When manufacturing a sheet of a solid electrolyte membrane, it may be better not to use water as a solvent in relation to the binder used. At this time, although depending on the film forming method, it is preferable to mix a solvent in an amount of 100% by volume with respect to the alumina-added rare earth oxide stabilized zirconia to form a slurry.

  Moreover, it is preferable to mix a binder (binder), a plasticizer, etc. with a slurry. The binder is used to ensure the strength of the manufactured solid electrolyte membrane, and the plasticizer is used to ensure the plasticity of the binder. As such a binder, it is preferable to use polyvinyl butyral. Moreover, it is preferable to use dibutyl phthalate as a plasticizer for softening the binder. These are added in an amount of 2.0 to 20 parts by mass, preferably 8 to 12 parts by mass with respect to 100 parts by mass of the alumina-added rare earth oxide stabilized zirconia in the slurry.

  The prepared slurry is usually subjected to vacuum defoaming and then usually formed at room temperature. As a film forming method, methods such as a doctor blade method and press molding are used, but are not limited thereto. For example, the doctor blade method is a method of forming a slurry into a sheet using a doctor blade. Press molding is a method in which powder is placed in a mold and uniaxially pressed. When producing a solid electrolyte membrane by a doctor blade method, it is preferable to heat-treat at 1400-1500 degreeC after shaping | molding. Alternatively, the slurry can be formed into a sheet shape and then processed into a dimple shape before heat treatment to form a dimple-shaped solid electrolyte membrane.

  The manufactured solid electrolyte membrane can have a thickness of about 100 to 500 μm. The ionic conductivity of the produced solid electrolyte membrane is preferably in the range of 0.2 to 0.3 S / cm at 1000 ° C. because the solid electrolyte membrane is used for a solid oxide fuel cell.

  According to another aspect of the present invention, there is provided a solid oxide formed by laminating a fuel electrode, a solid electrolyte membrane manufactured by the above-described method, a power generation membrane obtained by sequentially laminating an air electrode, and an interconnector. It is a physical fuel cell. Such a solid oxide fuel cell includes, for example, a power generation film obtained by sequentially laminating a fuel electrode, a solid electrolyte membrane, and an air electrode into a dimple shape. Can be stacked and assembled in order. Alternatively, a solid oxide fuel cell according to another embodiment includes a sheet-shaped power generation film obtained by sequentially laminating a fuel electrode, a solid electrolyte membrane, and an air electrode, and an interconnector processed into a dimple shape. It can also be stacked and assembled. However, the solid oxide fuel cell is not limited to a specific form, and may be any known form.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1]
And the lutetia (Lu ₂ O ₃₎ powder having a specific surface area of 25 m ² / g 250 g, zirconia having a specific surface area of 10m _² / g (ZrO ²⁾ and 750g of the powder, the specific surface area is 10 m ² / g alumina (Al ₂ 5 g of O ₃ ), 10 g of ammonium polycarboxylate, and 400 ml of ethanol were weighed into a 1000 ml pot. Here, Lu ₂ O _3, compared ZrO _2, it was prepared as a 9.5 mol%. This dispersion was dispersed with a ball mill for 24 hours, and the dispersed slurry was taken out and dried with a dryer for about 100 minutes. Next, the dried powder was heat-treated at 1200 ° C. for 10 hours to obtain a solid solution of alumina-added lutetia stabilized zirconia (LuSZ).

[Example 2]
Solid solution of alumina-added ytterbia stabilized zirconia in the same manner as in Example 1 except that 250 g of ytterbia (Yb ₂ O ₃ ) powder having a specific surface area of 23 g / m ² was used instead of Lu ₂ O ₃ of Example 1. Got.

[Example 3]
Solid solution of alumina-added erbia-stabilized zirconia in the same manner as in Example 1 except that 250 g of erbia (Er ₂ O ₃ ) powder having a specific surface area of 26 g / m ² was used instead of Lu ₂ O ₃ in Example 1. Got.

[Comparative example]
In each of the same compositions of Examples 1 to 3, alumina-added lutetia-stabilized zirconia (Comparative Example 1), alumina-added ytterbia-stabilized zirconia (Comparative Example 2), alumina-added erbia-stabilized zirconia ( A solid solution of Comparative Example 3) was obtained.

[Experimental Example 1]
After preparing the solid solution of alumina-added rare earth oxide stabilized zirconia obtained in Examples 1 to 3, 50 g of powder was press-molded with a 60 mmφ die, and then fired at 1400 ° C. for 4 hours to obtain a sintered body. Obtained. The sintered body was processed to 3 mm × 4 mm × 40 mm, and the stability of the solid solution of alumina-added rare earth oxide stabilized zirconia was tested by measuring the physical properties after 1000 hours in an environment of 1000 ° C. The ionic conductivity at 1000 ° C. was determined by the direct current four-terminal method, and the ZrO ₂ cubic ratio was measured by X-ray crystal diffraction. The strength was measured based on a three-point bending test of JIS R1601. Table 1 shows the measurement results for the electrical conductivity (S / cm) and the ZrO ₂ cubic ratio (%).

  As shown in Table 1, the ionic conductivity at 1000 ° C. was in a range sufficient for use in a solid oxide fuel cell. Even if this result is compared with 0.17 S / cm which is a standard value obtained when a similar test is performed on a solid solution of yttria oxide stabilized zirconia (YSZ) manufactured by the conventional coprecipitation method. Good enough. It was also found that the ratio of cubic crystals did not change even after 1000 hours at 1000 ° C. after the preparation of the alumina-added rare earth oxide-stabilized zirconia solid solution and was stable over time.

  The strength of the solid solutions of Comparative Examples 1 to 3 was measured. As a result, the solid solution of alumina-added rare earth oxide stabilized zirconia of Examples 1 to 3 showed about twice the strength as compared with the solid solutions of Comparative Examples 1 to 3 produced by the coprecipitation method. (See Table 2)

[Experiment 2]
The power generation performance of the solid solution of alumina-added rare earth oxide stabilized zirconia obtained in Examples 1 to 3 was tested. In the test, a solid solution powder sintered body was processed into a disk shape with a diameter of 30 mm and a thickness of 0.3 mm, and LSM / YSZ (mixture of LSM and YSZ of air electrode materials) as an air electrode with a size of 10 mmΦ at the center. Then, NiO / YSZ (mixture of fuel electrode materials NiO and YSZ) was baked as the fuel electrode, air was supplied to the air electrode side, and hydrogen was supplied to the fuel electrode side, and a power generation test was performed by a current interrupt method. As a result, any alumina-added rare earth oxide stabilized zirconia solid solution showed a power density of about 0.6 W / cm ² . The power generation capacity of these alumina-added rare earth oxide stabilized zirconia solid solutions is a standard value obtained when a similar test is performed on a solid solution of yttria oxide stabilized zirconia (YSZ) produced by a conventional coprecipitation method. It is excellent even when compared with 0.5 W / cm ² . (See Table 3)

  Examples of utilization of the present invention include solid oxide membranes used in solid oxide fuel cells and cogeneration systems thereof.

Claims (6)

Rare earth oxide particles having a specific surface area of 20 to 30 m ² / g, zirconia (ZrO ₂ ),
Stabilizing rare earth oxide with alumina (Al ₂ O ₃ ) by mixing 0.1 to 2.0 parts by mass of alumina with respect to 100 parts by mass in total of the rare earth oxide particles and zirconia, followed by heat treatment. A method for producing a solid electrolyte membrane by preparing a solid zirconia solid solution and forming the solid solution into a film. The method according to claim 1, wherein the specific surface area of the alumina is 10 to 15 m ² / g. The method according to claim 1, wherein the specific surface area of the zirconia is 5 to ²⁰ m ² / g. The method according to claim 1, wherein the rare earth oxide is one or more selected from lutetia (Lu ₂ O ₃ ), ytterbia (Yb ₂ O ₃ ), and erbia (Er ₂ O ₃ ). . The solid electrolyte membrane manufactured by the method in any one of Claims 1-4. A solid oxide fuel cell comprising a power generation film in which a fuel electrode, the solid electrolyte membrane according to claim 5 and an air electrode are sequentially stacked, and an interconnector.