JPH09129245A - Cell for solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain metal in a fuel electrode layer from being sintered by controlling the mean crystal grain size of ZrO2 and CeO2 particles in the fuel electrode layer so as to become larger on the surface thereof than in a part in contact with a solid electrolyte. SOLUTION: A fuel electrode layer 33 is formed out of at least one type of metal selected from Ni, Co, Ti and W, and ZrO2 and/or CeO2 , and the mean crystal grain size of ZrO2 and/or CeO2 on the surface of the fuel electrode layer 33 is made larger than a part in contact with a solid electrolyte. In this case, the mean crystal grain size of ZrO2 and/or CeO2 in the fuel electrode layer 33 is preferably made large gradually from the part in contact with the solid electrolyte toward the surface layer. In addition, 40wt.% to 90wt.% of one type of metal selected from Ni, Co and Ti and W is preferably made present in the fuel electrode layer 33.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell, and more particularly to a solid oxide fuel cell having an improved fuel electrode.

[0002]

2. Description of the Related Art Conventionally, a solid oxide fuel cell has a high power generation efficiency because its operating temperature is as high as about 1000 ° C. and is expected as a third generation fuel cell. Generally, two types of solid oxide fuel cells, known as a cylindrical type and a flat type, are known.

The flat plate type fuel cell has a feature that the power density per unit volume of power generation is high, but in practical use, there are problems such as gas seal imperfections and nonuniform temperature distribution in the cells. . On the other hand, the cylindrical fuel cell has the features that the output density is low, but the mechanical strength of the cell is high and the temperature uniformity in the cell can be maintained. Both types of solid electrolyte fuel cells are currently being actively researched and developed by taking advantage of their respective characteristics.

As shown in FIG. 3, a unit cell of a cylindrical fuel cell is a stabilized ZrO ₂ containing Y ₂ O _{3 on} the surface of a porous cylindrical air electrode layer 1 made of LaMnO ₃ system material.
A solid electrolyte 2 is formed, and a fuel electrode 3 made of porous Ni-zirconia or the like is formed on the surface of the solid electrolyte 2 in a substantially concentric shape. In addition, a current collector 4 (interconnector) made of a LaCrO ₃ system material for connecting cells is connected to the air electrode layer 1, penetrates the solid electrolyte 2, and is in non-contact with the fuel electrode 3. It is exposed on the surface of the cell.

In the plurality of unit cells having the above structure, the current collector 4 of one unit cell contacts the fuel electrode 3 of the other unit cell via the Ni felt, and the plurality of unit cells are connected in series. It was connected.

Power generation of such a solid oxide fuel cell unit is performed at around 1000 ° C. by flowing air (oxygen) 6 inside the air electrode layer 1 and fuel (hydrogen) 7 outside as shown in FIG. Performed at the temperature of.

[0007]

However, since the fuel electrode 3 is exposed to a high temperature of about 1000 ° C. during power generation, sintering of metal such as Ni progresses, and fine cracks are generated in the fuel electrode 3. As a result, there is a problem that the electric conductivity is lowered, and as a result, the power density of power generation is gradually lowered.

[0008]

Means for Solving the Problems The inventors of the present invention have made extensive studies on the above problems, and as a result, have found that ZrO ₂ , Ce in the fuel electrode layer
It was found that the sintering of the metal in the fuel electrode layer can be suppressed by controlling the average crystal grain size of the O ₂ particles so that the surface layer portion of the fuel electrode layer is larger than the portion in contact with the solid electrolyte, The present invention has been completed.

That is, in the solid oxide fuel cell of the present invention, the air electrode layer or the aforesaid air electrode layer is formed on the outer surface of the fuel cell body having the air electrode layer formed on one surface and the fuel electrode layer formed on the other surface of the solid electrolyte. In a solid oxide fuel cell having a current collector electrically connected to the fuel electrode layer, the fuel electrode layer comprises at least one metal selected from Ni, Co, Ti and W, ZrO ₂ and And / or CeO ₂ , and the average crystal grain size of ZrO ₂ and / or CeO _{2 in} the surface layer portion of the fuel electrode layer is made larger than that in the portion in contact with the solid electrolyte. Here, it is desirable that the average crystal grain size of ZrO ₂ and / or CeO ₂ in the fuel electrode layer gradually increases from the portion in contact with the solid electrolyte toward the surface layer portion. Further, it is desirable that at least one metal selected from Ni, Co, Ti, and W be present in the fuel electrode layer in an amount of 40 to 90% by weight.

[0010]

[Action] In the solid electrolyte type fuel cell, the fuel electrode layer is composed of a ceramic metal and ZrO ₂ such as Ni, ceramics such as ZrO ₂ is, preventing sintering of the metal in the generator at a high temperature Has been added to
It is hard to say that it is fully effective. In fact, Ni
Since metals such as the above are exposed to high temperature during power generation, sintering progresses, fine cracks are generated in the fuel electrode layer, and electric conductivity is lowered, and as a result, power density is gradually lowered.

In the present invention, Z in the fuel electrode layer
By controlling the average crystal grain size of ceramics such as rO ₂ so that the surface layer portion is larger than the portion in contact with the solid electrolyte, for example, gradually increasing from the portion in contact with the solid electrolyte to the surface layer portion on the opposite side. By increasing the size, sintering of metal such as Ni in the fuel electrode layer can be suppressed.

That is, since ceramic particles having a small particle size are present in the portion of the fuel electrode layer that is in contact with the solid electrolyte, the contact area between the solid electrolyte and the metal of the fuel electrode layer is large, and power generation performance is improved. Along with being able to, in addition, in the surface layer portion of the fuel electrode layer on the side opposite to the solid electrolyte, since ceramic particles having a large particle size are present, it is possible to suppress the metal sintering and suppress the particle growth, The generation of cracks is prevented and the electric conductivity is improved. As a result, the power generation performance can be further improved by the above two effects.

Further, Ni, Co, Ti, W is formed on the fuel electrode layer.
40-90% by weight of at least one metal selected from
By making it exist, the sintering of the metal can be further suppressed.

The fuel electrode layer in the present invention does not require a particularly high technique and can be formed easily and inexpensively by the slurry dip method, the doctor blade method or the like which has been conventionally used for forming the fuel electrode layer. Therefore, it is extremely preferable from the economical point of view.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, a cylindrical solid electrolyte fuel cell of the present invention has a cylindrical solid electrolyte 31 having an air electrode layer 32 formed on the inner surface and a fuel electrode layer 33 formed on the outer surface. Thus, the fuel cell main body 34 is configured, and the current collector 35 electrically connected to the air electrode layer 32 is provided on the outer surface of the fuel cell main body 34. That is, the notch 36 is formed in a part of the solid electrolyte 31, and a part of the air electrode layer 32 formed on the inner surface of the solid electrolyte 31 is exposed. The exposed surface 37 and the solid in the vicinity of the notch 36 are exposed. The surface of the electrolyte 31 is covered with a current collector 35.
In the cylindrical fuel cell of the present invention, a porous support tube made of a material having a large electric resistance is formed, and the air electrode layer 32, the solid electrolyte 31, and the fuel electrode layer 33 are formed on the outer surface of the porous support tube.
May be sequentially laminated.

A current collector 3 electrically connected to the air electrode layer 32.
No. 5 is formed on the outer surface of the fuel cell main body 34 so as to cover the substantially same continuous surface 39 having no step, and is not electrically connected to the fuel electrode layer 33. The current collector 35 is electrically connected to the fuel electrode layer of another cell via the Ni felt when the cells are connected to each other, thereby forming a fuel cell module.

The continuous flush surface 39 exposes a part of the air electrode layer 32 formed on the inner surface of the solid electrolyte 31, and the end face of the solid electrolyte 31 and the exposed surface 3 of the air electrode layer 32.
7 and the same continuous surface (the end surface of the solid electrolyte 31 and the exposed surface 37 of the air electrode layer 32 are substantially flat with no step)
And is configured. This continuous same surface 39 is formed by polishing the outer peripheral surface of the cell body until a part of the solid electrolyte molded body and a part of the air electrode layer molded body are continuous and substantially flush with each other.

In the solid oxide fuel cell of the present invention, the fuel electrode layer 33 is composed of at least one metal selected from Ni, Co, Ti and W and ZrO ₂ and / or CeO _2. Z in the fuel electrode layer 33
The average crystal grain size of rO ₂ and / or CeO ₂ is formed so that the surface layer portion is larger than the portion in contact with the solid electrolyte 31. That is, as shown in FIG. 2, the surface layer portion B is larger than the portion A in contact with the solid electrolyte 31.

It is desirable that the average crystal grain size of ZrO ₂ and / or CeO _{2 in} the fuel electrode layer 33 gradually increases from the portion A in contact with the solid electrolyte 31 toward the surface layer portion B on the opposite side. That is, regarding ZrO ₂ and CeO ₂ particles, the average crystal grain size of the portion A contacting the solid electrolyte 31 is 0.5 to 3 μm, and the surface layer portion B of the fuel electrode layer 33 on the side opposite to the solid electrolyte 31 is 5 It is preferable that the average crystal grain size is increased continuously from the vicinity of the solid electrolyte 31 toward the surface layer between the particles having a particle size of up to 30 μm.

Such a fuel electrode layer is prepared by preparing a plurality of types of slurries in which mixed powders of ceramic particles and metal particles having different average crystal grain sizes are dispersed in an aqueous solution, and thereafter a solid electrolyte is formed. The formed cylindrical sintered body is formed by successively dipping it from a fine slurry of ceramic particles, whereby the average crystal grain size of the ceramic can be continuously increased from the vicinity of the solid electrolyte toward the surface layer. For example, when preparing a fuel electrode layer having a thickness of about 100 μm, 3 to 5 kinds of slurries having different average crystal grain sizes of ceramics are suitable. Further, in the case of producing a fuel electrode layer having a thickness of more than 100 μm, a mixed powder of ceramic particles and metal particles having different average crystal grain sizes is used, and a plurality of types of green shavings of 30 to 50 μm are prepared by a doctor blade method. It is possible to prepare by preparing a sheet-like layer and then sequentially laminating it on the surface of the solid electrolyte so that the average crystal grain size of the ceramic particles is continuously increased.

As ZrO ₂ or CeO ₂ particles in the fuel electrode layer, 1 to 30 mol% of Y ₂ O is used because of crystal stability.
₃ and Yb ₂ O ₃ , Sc ₂ O ₃ , Dy ₂ O ₃ , Nd ₂
ZrO ₂ containing oxides of rare earth elements such as O ₃
Alternatively, CeO ₂ particles are preferable.

The average crystal grain size of metals such as Ni and Co is 1 to 20 from the viewpoint of metal sinterability and polarization performance.
μm, particularly 5 to 10 μm is preferable. As the metal component forming the fuel electrode layer, W and Ti are included in the present invention in addition to Ni and Co, and Ni is particularly preferable.

Further, Ni, Co, Ti,
It is desirable that at least one metal selected from W is present in an amount of 40 to 90% by weight. This has a metal content of 40
When the amount is less than 10% by weight, the electric conductivity of the fuel electrode layer becomes small, and when the amount is more than 90% by weight, the effect of suppressing the sintering of the metal such as Ni and Co by the ZrO ₂ or CeO ₂ particles becomes small. . The metal content is preferably 60 to 80% by weight from the viewpoint of conductivity and sinterability.

In the cylindrical solid oxide fuel cell unit of the present invention, for example, first, a cylindrical molded body is produced using the powder forming the air electrode layer. This cylindrical molded body is formed, for example, by subjecting the air electrode layer forming powder to extrusion molding or hydrostatic molding (rubber pressing). As still another method, after forming the air electrode layer forming powder into a sheet by a doctor blade method or the like, by winding the sheet-shaped formed body around the surface of a predetermined columnar support and joining the ends by joining. It is also possible to produce a cylindrical molded body. The wall thickness of the cylindrical molded body is suitably 1 to 3 mm.

The powder forming the air electrode layer is LaM.
It is composed of an nO ₃ -based composition, and specifically, has a La content of 15 to 2
LaMnO ₃ -based compositions in which 0 atomic% is replaced with alkaline earth elements such as Ca, Sr, and Ba are mentioned. These are LaMnO ₃ -based compounds obtained by calcining a mixture of metal oxides at a predetermined ratio. A powder is desirable.

A suitable thickness of the sheet-like molded product made of the air electrode layer forming powder is 100 to 3000 μm.

Next, a sheet-shaped molded body of the solid electrolyte and the current collector is prepared from the powder for forming the solid electrolyte and the current collector. This sheet-shaped molded body is manufactured by a known method by a doctor blade method or an extrusion molding method.

[0028] Examples of the solid electrolyte _{powder, Y 2 O 3, Yb 2} O 3 stabilized material was dissolved in a proportion of 3 to 15 mol% partially stabilized ZrO ₂ or stabilized ZrO such relative ZrO ₂ CeO ₂ powder containing 10 to 30 mol% of ₂ powder, Y ₂ O ₃ , Yb ₂ O ₃ , Gd ₂ O _{3 and the} like is used. Further, as the powder forming the current collector, Ca, M
LaCrO _{3 in} which g and Sr are dissolved is used.

Next, after winding a solid electrolyte sheet-shaped molded body around the surface of the air-electrode layer cylindrical molded body obtained as described above, the end portion of the solid electrolyte sheet-shaped molded body is polished. Then, the sheet-shaped molded body of the current collector is laminated and pressure-bonded. In some cases, the sheet-shaped molded body of the fuel electrode layer may be wound around the surface of the solid-electrolyte sheet-shaped molded body. Adhesion is improved by interposing an adhesive such as an acrylic resin or an organic solvent between each sheet-shaped molded body.

The laminated molded body obtained as described above is fired in an oxidizing atmosphere at the same time as the sheet-shaped molded body laminated with the cylindrical molded body. Specifically, 1300 to 1 in the atmosphere
By firing at 700 ° C. for about 3 to 15 hours, firing is performed so that at least the solid electrolyte becomes dense with a relative density of 96% or more. The air electrode layer has a relative density of 60 to 7
About 5% is sufficient.

First, the fuel electrode layer is formed of Ni, Co, Ti and W.
A slurry containing at least one metal selected from the above and ceramic particles of ZrO ₂ or CeO ₂ is prepared, and a plurality of types of slurries having different average crystal grain sizes of ceramic particles are prepared. These slurries were obtained by sequentially immersing the obtained air electrode layer, the solid electrolyte, and the surface of the solid electrolyte of a cylindrical integral sintered body composed of a current collector in order from a slurry having a small average crystal grain size of ceramic particles. The fuel electrode layer in which the average crystal grain size of the ceramic particles increases is formed almost continuously from the solid electrolyte side toward the surface layer portion. Further, by using a mixed powder composed of ceramic particles having different average crystal grain sizes and a metal, a doctor blade method is used to obtain a thickness of 30 to 50 μm.
After preparing a plurality of types of green sheets, the green sheets may be sequentially laminated on the surface of the fixed electrolyte so that the average crystal grain size of the ceramic particles continuously increases.

In the fuel electrode layer, an oxide of at least one metal selected from Ni, Co, Ti and W may be used. These oxides are reduced during power generation and N
This is because it becomes a metal of i, Co, Ti, and W.

In the present invention, as shown in FIG.
By forming the continuous coplanar surface 39 on the surface of the fuel cell main body 34 and forming the current collector 35 on the continuous coplanar surface 39, the current collector 35 is laminated without distortion, and unreasonable stress is applied to the current collector. State, no continuous cracks on the top of the current collector 35 or peeling off at a part of the end of the current collector 35, no defects occur on the current collector 35, but the surface of the solid electrolyte 31 is not polished Alternatively, the current collector 35 may be laminated to form a fuel electrode layer on the surface of the solid electrolyte 31. Further, the present invention may be applied to the conventional solid oxide fuel cell unit shown in FIG.

Further, although the example in which the present invention is applied to the cylindrical fuel cell is explained, it may be applied to the fuel electrode layer of the flat plate fuel cell.

[0035]

【Example】

Example 1 La _0.85 Ca _0.15 MnO ₃ powder having an average crystal grain size of 6 μm was used as a powder for forming an air electrode layer, and Y ₂ O ₃ having an average crystal grain size of 0.5 μm was used as a powder for forming a solid electrolyte in an amount of 10 mol%. Coprecipitation method ZrO ₂ powder contained at a ratio, and La _0.8 C having an average crystal grain size of 1 μm as powder for forming a current collector.
a _0.21 CrO ₃ powder was prepared.

Further, as powders for forming the fuel electrode layer, Ni, Co, W, and Ti powders having an average crystal grain size of 2 μm and Z having an average crystal grain size of 0.5 to 20 μm and having different average crystal grain sizes.
rO ₂ (containing 10 mol% Y ₂ O ₃ ) powder and CeO ₂
The powder (containing 5 mol% Y ₂ O ₃ ) was used as a solvent, and Zr
Several types of slurries having different average crystal grain sizes of O ₂ and CeO ₂ ceramic particles were prepared.

A slurry was prepared by using the above La _0.85 Ca _0.15 MnO ₃ powder with water as a solvent, and using this slurry, a cylindrical molded body having an inner diameter of 13 mm and an outer diameter of 16 mm was obtained by an extrusion molding apparatus. On the other hand, the above Y ₂ O ₃ stabilized ZrO ₂
A slurry was prepared using the powder and La _0.8 Ca _0.21 CrO ₃ powder with water as a solvent, and a sheet-like compact having a thickness of 150 μm was prepared by the doctor blade method. Then, through the adhesive made of acrylic resin on the surface of the cylindrical molded body, the solid electrolyte sheet is wound, the end faces are polished to form a continuous same surface, and the adhesive is provided on this surface. Then, sheet-like molded bodies of current collectors were laminated, pressure-bonded, and baked in the air at 1500 ° C. for 5 hours.

As the fuel electrode layer, the cylindrical sintered body was sequentially dipped into each of the above-mentioned plural kinds of slurries so as to have the thickness shown in Table 1, and dried to form the fuel electrode layer.
A solid oxide fuel cell as shown in FIG. 1 was produced.

Power generation was carried out at 1000 ° C. by flowing oxygen inside the cylindrical cell and flowing hydrogen outside, and the power density after 1000 hours was measured. The metal content of the fuel electrode layer is ICP.
The thickness of each dip layer was measured by an emission spectroscopic analysis with a scanning electron microscope. Table 1 shows the results.

[0040]

[Table 1]

From Table 1, the sample No. prepared by the conventional method is shown. Compared with No. 1, all the samples of the present invention in which the average crystal grain size of the ceramic particles gradually increased from the portion in contact with the solid electrolyte toward the surface layer portion showed a large power density. In addition, Sample No. having a metal content of less than 40% by weight. 2 and sample Nos. 8
Then, although the output density was larger than that of the sample No. 1, no significant improvement in the output density was observed.

Example 2 Using the powder for forming the fuel electrode layer of Example 1, a slurry was prepared using water as a solvent, and using this, a plurality of types of sheets having a thickness of 50 μm and ceramic particles having different average crystal grain sizes were prepared. A molded body was produced by the doctor blade method. After stacking these sheet-shaped compacts on the surface of the cylindrical sintered body produced in Example 1, power generation was performed by the same method as in Example 1. Table 2 shows the results.

[0043]

[Table 2]

From Table 2, it can be seen that the samples No. 16 and 23 in which the average crystal grain size of the ceramic particles are the same over the entire region have small output densities, but the samples of the present invention show excellent output densities. .

[0045]

In the present invention, by controlling the average crystal grain size of ceramic particles such as ZrO ₂ in the fuel electrode layer so that the surface layer portion is larger than the portion in contact with the solid electrolyte, for example, By gradually increasing the size from the portion in contact with the solid electrolyte toward the surface layer portion on the opposite side, it is possible to suppress the sintering of metals such as Ni in the fuel electrode layer and suppress the occurrence of cracks in the fuel electrode layer. It is possible to provide a cell with high output and long-term stability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a cylindrical fuel cell of the present invention.

FIG. 2 is an enlarged cross-sectional view showing the fuel electrode of FIG. 1 and its vicinity.

FIG. 3 is a perspective view showing a conventional cylindrical fuel cell unit.

[Explanation of symbols]

 31 ... Solid electrolyte 32 ... Air electrode layer 33 ... Fuel electrode layer 35 ... Current collector

Claims (3)

[Claims] 1. A current collector electrically connected to the air electrode layer or the fuel electrode layer on the outer surface of the fuel cell main body in which the air electrode layer is formed on one surface of the solid electrolyte and the fuel electrode layer is formed on the other surface. In a solid oxide fuel cell having a body, the fuel electrode layer comprises at least one metal selected from Ni, Co, Ti and W, and ZrO ₂ and / or CeO ₂ , and the fuel A solid oxide fuel cell, wherein the average crystal grain size of ZrO ₂ and / or CeO _{2 in} the surface layer portion of the electrode layer is made larger than that in the portion in contact with the solid electrolyte. 2. ZrO ₂ and / or Ce in the fuel electrode layer
_2. The solid oxide fuel cell unit according to claim 1, wherein the average crystal grain size of O ₂ gradually increases from the portion in contact with the solid electrolyte toward the surface layer portion. 3. The solid oxide fuel cell according to claim 1, wherein 40 to 90% by weight of at least one metal selected from Ni, Co, Ti, and W is present in the fuel electrode layer. .