JPH07315922A - Solid electrolytic ceramic and supporting member for solid electrolyte - Google Patents

Abstract

PURPOSE:To obtain a solid electrolytic ceramic excellent in electric conductivity by forming from a specific ratio of ZrO2, Y2O3, Al2O3 and inevitable impurities and having a prescribed crystal grain diameter, coefficient of thermal expansion and bending strength. CONSTITUTION:A ZrO2 powder, Y2O3 powder and an Al2O3 powder are blended in the specific ratio and the blended material is wetly mixed by a ball mill or the like and dried, granulated and formed into the prescribed shape. Next, the molded body is fired at 1500-1700 deg.C to obtain the solid electrolytic ceramic formed from 5-10wt.% Y2O3, 0.5-15wt.% Al2O3, 0.5wt.% inevitable impurities such as SiO2 and balance ZrO2 and having 5-15mum average crystal grain diameter, >=9X10<-6>/ deg.C coefficient of thermal expansion at room temp. to 1000 deg.C and >=30kg/cm<3> bending strength. And the supporting body for solid electrolyte is obtained by forming a protective layer composed of a ZrO2 ceramic containing 5-10mol% Y2O3 on the surface of a ZrO2 ceramic containing 10-20mol% CaO and controlled to 20-45% in open porosity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte ceramic and a solid electrolyte support member used for an oxygen separation membrane element, a solid oxide fuel cell, and the like.

[0002]

2. Description of the Related Art In recent years, fuel cell power generation systems have been increasingly expected worldwide as they make a great contribution against the backdrop of energy problems and global environmental problems. The fuel cell power generation system is a system that can directly convert the chemical energy of the fuel into electric energy and is not restricted by the Carnot cycle. Therefore, it has essentially high energy conversion efficiency, can diversify the fuel, and has low pollution. Moreover, the power generation efficiency is not affected by the scale of the facility, and is a very promising technology.

Particularly, unlike the phosphoric acid type fuel cell and the molten carbonate type fuel cell, the solid electrolyte type fuel cell has a simple cell structure because it does not use a liquid or a melt, and includes the use of high temperature exhaust heat. Energy efficiency of 80 to 90% can be expected.

As shown in FIG. 1, the structure of a unit cell of a general solid oxide fuel cell is composed of a porous tubular supporting member 1, an air electrode 2, a solid electrolyte 3 and a fuel electrode 4. The support member 1 is usually made of stabilized ZrO ₂ ceramics containing CaO, and is a porous body having heat resistance and an open porosity of about 20 to 40% so as to allow appropriate gas passage. In addition, La is 10 to 2 on the outer surface of the support member 1.
LaMnO ₃ and LaC substituted with 0 atomic% of Ca and Sr
Air electrode 2 of oO ₃ and dense ZrO containing Y ₂ O ₃
Solid electrolyte 3 composed of ₂ and Ni—ZrO ₂ (Y ₂
A fuel electrode 4 made of cermet (containing O ₃ ) is sequentially provided. Further, an interconnector 5 made of LaCrO ₃ system material for connecting the single cells in series is formed in the cell.

Then, air 6 is placed inside the support member 1.
H ₂ and reformed gas 7 of methane gas are supplied to the outside of the cell, respectively, and the energy when these react through the support member 1, the air electrode 2, the solid electrolyte 3 and the fuel electrode 4 is directly converted into electric power. It is taken out in the form. In addition to the above structure, a reverse structure having the air electrode 2 on the outside and the fuel electrode 4 on the inside has also been proposed. Alternatively, there is also a flat plate type fuel cell using a plate-shaped solid electrolyte.

The method of manufacturing the fuel cell shown in FIG.
The air electrode 2, the solid electrolyte 3 and the fuel electrode 4 are formed on the outer surface of the porous support member 1 made of stabilized zirconia ceramics by using a film forming technique such as CVD, EVD, plasma spraying or low pressure plasma spraying. . Particularly when the thermal spraying method is used, each electrode material or solid electrolyte material melted at high temperature is sprayed onto the surface of the support member 1 as a base material to form each electrode or solid electrolyte film.

The ceramics used as the solid electrolyte 3 include ZrO ₂ , CeO ₂ , Th.
Some have O ₂ and Bi ₂ O ₃ as main components. The properties required for solid electrolyte ceramics are high ionic conductivity, almost no electronic conductivity, chemically stable at high temperatures, sufficient mechanical utility at high temperatures, abundant in resources, low in price, etc. is there.

One of those generally used to satisfy these conditions is Y ₂ O ₃ , CaO, MgO, Y.
Zirconia ceramics stabilized with b ₂ O ₃ or the like. In this zirconia ceramic, the crystal structure of ZrO ₂ is fluorite type, and some lattice points are replaced with divalent Ca, trivalent Y or the like instead of tetravalent Zr. The lattice points that oxygen should occupy are vacant by that amount, and the existence of the vacancy points enables the movement of oxygen ions in the crystal, and functions as a solid electrolyte. Also, CaO, Y ₂
By containing O _{3 and the} like, ZrO ₂ becomes a cubic crystal and does not cause crystal transition, and also plays a stabilizing role.

When used in a fuel cell as shown in FIG. 1, since the solid electrolyte 3 is sandwiched between the air electrode 2 and the fuel electrode 4, zirconia ceramics whose thermal expansion coefficient is close to those of these electrode materials are most commonly used. Has been.

[0010]

By the way, as the solid electrolyte 3 used in the fuel cell, a thin electrolyte having a thickness of about 0.1 to 0.5 mm is usually used in order to lower the internal resistance and increase the power generation efficiency. However, since the stabilized zirconia ceramics containing 8 mol% Y ₂ O ₃ which is generally used as the solid electrolyte ₃ has a low bending strength of about 25 kg / mm ² , it is easily damaged when forming the fuel cell, It was difficult to handle. Therefore, there are problems that the manufacturing yield is low and the product reliability is low.

In order to increase the strength, the content of Y ₂ O ₃ is about 2 to 4 mol% to form a partially stabilized zirconia ceramic in which tetragonal zirconia is present, and the crystal grain size is 2 μm or less. Solid electrolyte ceramics have also been proposed (see Japanese Patent Publication No. 3-4505).
However, if the amount of Y ₂ O ₃ is reduced in this way,
There has been a problem that the electric conductivity of the solid electrolyte ceramics is lowered and the characteristics as a solid electrolyte are deteriorated.

On the other hand, in the manufacturing process of the fuel cell using the supporting member 1 made of the above CaO-stabilized ZrO ₂ or in the long-term power generation of the fuel battery cell, the Ca component in the supporting member 1 becomes the air electrode 2. It diffuses and penetrates, and the electric conductivity of the air electrode 2 or the catalytic ability to ionize oxygen decreases,
As a result, there is a problem that the power generation characteristics of the cell are deteriorated.

[0013]

SUMMARY OF THE INVENTION Therefore, a first object of the present invention is to obtain a solid electrolyte ceramic having excellent electrical conductivity and high mechanical strength. The second object of the present invention is C
The purpose is to obtain a solid electrolyte support member that prevents diffusion of the component a.

[0014]

In order to achieve the first object of the present invention, as a stabilizer, 5 to 10 mol% of Y ₂ O is used.
₃ and further 0.5 to 15% by weight of Al ₂ O ₃ ,
The solid electrolyte ceramics were composed of 0.5% by weight or less of unavoidable impurities and the balance ZrO ₂ and the average grain size of the sintered body was 5 to 15 μm.

Here, the content of Y ₂ O ₃ is set to 5 to 10 mol%, because if it is less than 5 mol%, the electric conductivity is lowered and the characteristics as a solid electrolyte are deteriorated.
This is because if it exceeds 0 mol%, the strength will decrease. Within this range, a stabilized zirconia ceramic mainly composed of cubic crystals can be obtained.

Further, although in the present invention can increase the strength by adding Al ₂ O _3, Al ₂ O
_{3 The} amount of addition is 0.5 to 15% by weight, if it is less than 0.5% by weight, the effect of increasing strength is low, while if it exceeds 15% by weight, the coefficient of thermal expansion becomes small and the air electrode and fuel are reduced. This is because there is a difference in thermal expansion from the pole.

Further, the above Y ₂ O ₃ , Al ₂ O ₃ and Zr
As components other than O ₂ , SiO ₂ , Fe ₂ O ₃ , Mg
Although impurities such as O, CaO and TiO ₂ may be included, the total amount of these impurities is set to 0.5% by weight or less because the electrical conductivity decreases when the amount of impurities exceeds 0.5% by weight. The reason is that In order to set the amount of impurities within this range, it is sufficient to use raw material powder with high purity and prevent impurities from being mixed in during the manufacturing process, for example, by using zirconia balls during grinding.

Further, the reason why the average crystal grain size of the solid electrolyte ceramics is set to 5 to 15 μm is that it is mainly cubic crystals, so that it is difficult to make the crystal grain size smaller than 5 μm. This is because the strength decreases when the diameter is larger than 15 μm.

Such a solid electrolyte body of the present invention can be obtained by molding a raw material powder prepared so as to be within the above composition range into a predetermined shape and firing it at a temperature of 1500 to 1700 ° C. And the obtained solid electrolyte ceramics has a bending strength of 30 kg / mm ² or more,
The coefficient of thermal expansion between room temperature and 1000 ° C. can be 9 × 10 ⁻⁶ / ° C. or less.

To achieve the second object of the present invention, a zirconia ceramic containing 5 to 10 mol% of Y ₂ O ₃ and having an average crystal grain size of 5 to 50 μm and an open porosity of 20 to 45% is used. A solid electrolyte support member was formed.

In order to achieve the second object of the present invention, it contains 10 to 20 mol% of CaO and has an open porosity of 20.
5 to 10% on the surface of ~ 45% zirconia ceramics
A support member for a solid electrolyte was constituted by including a protective layer made of zirconia ceramic containing mol% of Y ₂ O ₃ .

That is, at least the surface of the solid electrolyte support member is formed of zirconia ceramics containing Y ₂ O ₃ so as to prevent the diffusion of the Ca component into the air electrode, the solid electrolyte body and the like.

Further, in the fuel cell, in addition to the structure shown in FIG. 1, the same material is used and Ni-Zr is formed on the surface of the supporting member.
A structure in which a fuel electrode of O ₂ (containing Y ₂ O ₃ ) is formed, and then a solid electrolyte and an air electrode are provided thereon is also proposed. Also in this structure, the supporting member of the present invention can be used.

[0024]

EXAMPLES Example 1 First, examples of the present invention relating to solid electrolyte ceramics will be described.

Average particle size of 1 to ₂ μm containing 8 mol% of Y ₂ O ₃
m ZrO ₂ raw material powder was prepared by a coprecipitation method, and Al ₂ O ₃ powder having an average particle diameter of 0.2 to 1 μm was added to the raw material powder at various ratios shown in Table 1 and wet-mixed in a ball mill for 20 hours. After drying, granulating, and molding, firing was performed at 1500 ° C. for 2 hours to obtain a ceramic sintered body in the shape of a bending test piece based on JIS R1601. Table 1 shows the measurement results of the bending strength and the coefficient of thermal expansion of this sintered body.

Generally, the bending strength of a solid electrolyte is 30 kg /
If it is mm ² or more, there is almost no damage due to handling at the time of forming an electrode, so that whether the bending strength is 30 kg / mm ² or more was used as a criterion for judgment. Therefore, it can be seen from Table 1 that this criterion is satisfied when the addition amount of Al ₂ O ₃ is 0.5% by weight or more.

One of the reasons why zirconia is used as a solid electrolyte for fuel cells is that it has a coefficient of thermal expansion close to that of the electrode material, but the coefficient of thermal expansion of the electrode material (from room temperature to 1
(000 ° C.) is about 11 × 10 ⁻⁶ / ° C., the thermal expansion coefficient (normal temperature to 1000 ° C.) of the solid electrolyte is 9.0 × 1.
It is necessary to be 0 ^-6 / ° C or higher, and therefore, from Table 1, it is appropriate that the amount of Al ₂ O ₃ added be 15% by weight or less.

From the above, the added amount of Al ₂ O ₃ is 0.5 to 1
A suitable material is obtained with 5% by weight.

[0029]

[Table 1]

The solid electrolyte ceramics of the present invention as described above can be suitably used in a solid electrolyte fuel cell, an oxygen separation membrane element or the like in the form of a column or a plate.

Example 2 Next, an example of the present invention relating to a solid electrolyte support member will be described.

Stabilized ZrO ₂ raw material powders having a Y ₂ O ₃ addition amount of 5, 8, 10 mol% and a CaO addition amount of 10, 15, 17 mol% synthesized by the coprecipitation method were each prepared at 1200 ° C.
After calcination for 0 hour, a zirconia ball was used to grind to a predetermined particle size by a vibration mill to prepare a raw material for evaluation. Next, as a molding binder, a 100% PVA aqueous solution was added while stirring and mixing so that the solid content was 5% with respect to the obtained raw material powder. After drying at 120 ° C. for 10 hours, a raw material for press molding was produced through a No. 80 nylon mesh. This raw material was molded at a molding pressure of 1 t / cm ² using a mold having a diameter of 30 mm, and then, in the atmosphere,
A porous zirconia ceramic was obtained by firing at 250 to 1700 ° C., which was used as a sample of a supporting member for evaluation.

Next, as an air electrode material, a purity of 99.7%,
Commercially available La _0.9 Sr _0.1 MnO ₃ having an average particle size of 3 μm
The powder is used as a slurry on the surface of the supporting member for evaluation described above.
It was applied so as to have a thickness of 0 μm, and heat-treated in the air at 1200 ° C. for 500 hours. After that, the diffusion penetration depth of Ca and Y into the air electrode of the cut surface was measured by an EPMA apparatus.

As the results are shown in Table 2, C which is a comparative example.
Diffusion of the Ca component into the air electrode material was observed in all of the supporting members made of zirconia ceramics containing aO, regardless of the amount of CaO added, the particle size of the sintered body, and the open porosity.

On the other hand, Y ₂ O _{3 according} to the present invention is used.
Regarding the supporting member made of zirconia ceramics containing, no diffused state of the Y component was observed in all the samples. However, even for zirconia ceramics containing Y ₂ O ₃ , if the particle size is less than 5 μm, the open porosity at a firing temperature of 1300 ° C., which is similar to the heat treatment temperature, must satisfy the standard value of 20 to 45%. In addition, if the particle size is 50 μm or more, the sinterability is poor and the above open porosity standard cannot be satisfied even at a high temperature of 1800 ° C. Therefore,
It was unsuitable as a support member for electrolyte.

Further, in this embodiment, the entire supporting member is Y
_{Since it is made of 2} O ₃ -stabilized zirconia ceramics, the mechanical strength can be increased.

[0037]

[Table 2]

Embodiment 3 Next, another embodiment of the present invention relating to a solid electrolyte support member will be described.

Addition amount of CaO synthesized by coprecipitation method 1
Each of 0, 15, and 20 mol% of the stabilized ZrO ₂ raw material powder was calcined at 1300 ° C. for 3 hours, and then pulverized to a mean particle size of 10 μm with a vibration mill using zirconia balls to prepare a raw material for evaluation. As a molding binder, PVA10 is added so that the solid content is 5% with respect to the above raw material powder.
A 0% aqueous solution was added with stirring and mixing. At 120 ℃,
After drying for 10 hours, a No. 80 nylon mesh was passed through to prepare a raw material for press molding.

The obtained raw material was molded at a molding pressure of 1 t / cm ² using a mold having a diameter of 30 mm, and was then molded in the atmosphere at 14
By firing at 50 to 1700 ° C., a sample of a supporting member made of porous zirconia ceramics having different open porosities was prepared.

Further, as a material for the protective film, a stabilized ZrO ₂ raw material having a Y ₂ O ₃ addition amount of 5, 8, and 10 mol% synthesized by the same coprecipitation method as described above was calcined at 1250 ° C. for 3 hours. After that, a zirconia ball was used to pulverize the particles into an average particle size of 2, 5, 8, 10, and 15 μm by a vibration mill to prepare a raw material powder. 2% in solid content based on the obtained raw material powder
An 80% PVA aqueous solution was added with stirring and mixing so that the addition amount was obtained, to obtain a zirconia paste.

This zirconia paste was printed on the surface of the supporting member so that the thickness was about 50 μm, and the temperature was 120 ° C.
Then, after drying for 2 hours, it was baked in air at 1400 ° C. for 2 hours to form a protective layer made of Y ₂ O ₃ -stabilized zirconia.

Further, the purity of the air electrode material is 99.7.
%, Commercially available La _0.9 Sr _0.1 Mn having an average particle size of 3 μm
O ₃ powder was applied as a slurry to the surface of the supporting member for evaluation so as to have a thickness of 100 μm, and was applied in air at 1200
It heat-processed at 500 degreeC for 500 hours. After that, regarding the cut surface, C
The diffusion penetration depths of a and Y into the air electrode were measured by an EPMA device.

As shown in the results in Tables 3 and 4, the supporting member made of only CaO-stabilized zirconia ceramics without forming a protective layer, which is a comparative example, was added with CaO.
Diffusion of the Ca component was observed in the air electrode material in all of them regardless of the amount and the porosity of the sintered body.

On the other hand, in the case of the support member of the present invention provided with the protective layer of Y ₂ O ₃ stabilized zirconia, the diffusion of the Ca component was blocked in all the samples regardless of the amount of Y ₂ O ₃ , and No diffusion into the polar material was observed.
Further, no diffusion of Y to the air electrode was observed.

As a result of various experiments, it was found that the thickness of the protective layer was 5 μm or more, preferably 10 μm or more, so that the diffusion of the Ca component could be prevented.

In this embodiment, most of the supporting members are C
Since it is made of aO-stabilized zirconia ceramics, it can be manufactured at low cost.

[0048]

[Table 3]

[0049]

[Table 4]

The solid electrolyte support member of the present invention as described above can be suitably used in a solid electrolyte fuel cell, an oxygen separation membrane element or the like in a cylindrical shape or a flat plate shape.

[0051]

As described above, according to the present invention, 5 to 10 mol% of Y ₂ O ₃ is contained as a stabilizer, and further 0.5
By constructing the solid electrolyte ceramics, Al ₂ O ₃ of ˜15 wt%, unavoidable impurities of 0.5 wt% or less, and the balance ZrO ₂ are used, and the average crystal grain size of the sintered body is 5 to 15 μm. The bending strength can be increased to 30 kg / mm ² or more while maintaining sufficient electric conductivity and thermal expansion coefficient. Therefore, when the solid electrolyte ceramics of the present invention is used in a fuel cell, since it has sufficient strength for handling and is not likely to be damaged, the manufacturing yield is high and the reliability can be improved.

According to the present invention, the solid electrolyte support member is formed of zirconia ceramics containing 5 to 10 mol% of Y ₂ O ₃ and having an average crystal grain size of 5 to 50 μm and an open porosity of 20 to 45%. Alternatively, a protective layer made of zirconia ceramic containing 5 to 10 mol% of Y ₂ O ₃ is provided on the surface of zirconia ceramic containing 10 to 20 mol% of CaO and having an open porosity of 20 to 45%. By configuring the support member for the electrolyte, it is possible to prevent the diffusion of the Ca component into the air electrode during the heat treatment during the manufacturing process as the fuel cell, and to manufacture the fuel cell power generation cell that can operate for a long time. Become.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing a structure of a general solid oxide fuel cell.

[Explanation of sign]

 1: Support member 2: Air electrode 3: Solid electrolyte 4: Fuel electrode 5: Interconnector 6: Air 7: Fuel

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01M 8/12 9444-4K // B01D 71/02 500 9153-4D

Claims (4)

[Claims] 1. A Y ₂ O ₃ content of 5 to 10 mol%, and 0.5 to 1
5% by weight of Al ₂ O ₃ , 0.5% by weight or less of unavoidable impurities, and the balance of ZrO ₂ and having an average crystal grain size of 5 to 5.
A solid electrolyte ceramic having a thickness of 15 μm. 2. The coefficient of thermal expansion between room temperature and 1000 ° C. is 9 ×
More than 10 ^-6 / ° C and bending strength of 30 kg / mm
The solid electrolyte ceramics according to claim 1, wherein the solid electrolyte ceramics is ² or more. 3. A solid electrolyte support member comprising zirconia ceramics containing 5 to 10 mol% of Y ₂ O ₃ and having an average crystal grain diameter of 5 to 50 μm and an open porosity of 20 to 45%. 4. A surface of zirconia ceramics containing 10 to 20 mol% of CaO and having an open porosity of 20 to 45%,
A support member for a solid electrolyte, comprising a protective layer of zirconia ceramics containing 5 to 10 mol% of Y ₂ O ₃ .