JP3336171B2 - Solid oxide fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical or flat solid electrolyte fuel cell, and more particularly to a solid electrolyte fuel cell having a fuel electrode using metal fibers.

[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 1000 to 1050 ° C., and is expected as a third generation power generation system.

[0003] In general, a solid oxide fuel cell is known to be a cylindrical type or a flat type. Flat fuel cells are
Although it has the feature that the power density per unit volume of power generation is high, there are problems such as incomplete gas seals and non-uniformity of the temperature distribution in the cell in practical use. 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 oxide fuel cells are being actively researched and developed utilizing their respective features.

As shown in FIG. 4, a single cell of a cylindrical fuel cell has a support tube 1 made of CaO-stabilized ZrO ₂ having an open porosity of about 40%, and a porous air made of a LaMnO ₃ -based material thereon. A pole 2 is formed, and Y ₂ O ₃ stabilized Zr is formed on its surface.
A solid electrolyte 3 made of O ₂ is covered, and a porous Ni-zirconia fuel electrode 4 is provided on this surface. In the fuel cell module, each single cell is La
It is connected via a CrO ₃ -based current collector (inter-connector) 5.

In such fuel cell power generation, each unit cell is maintained at a temperature of 1000 to 1050 ° C., and air (oxygen) 6 is supplied to the inside of the support tube 1 and fuel (hydrogen) 7 is supplied to the outside. It is performed by

In recent years, in order to simplify the process in the cell fabrication process, LaMnO, which is an air electrode material, has been used.
Attempts to use _3-based material as a direct porous support tube have been made. As a support tube material having a function as an air electrode, a LaMnO ₃ solid solution material in which La is substituted with Ca or Sr by 10 to 20 atomic% is used.

As a method of manufacturing the above-described fuel cell, for example, an insulating powder composed of CaO-stabilized ZrO ₂ is formed into a cylindrical shape by an extrusion molding method or the like, and then fired to form a cylindrical support. And a slurry of an air electrode, a solid electrolyte, a fuel electrode, or a current collector is applied to the outer peripheral surface of the support tube, and the resultant is sequentially fired and laminated.

On the other hand, the single cell of the flat fuel cell uses the same material system as that of the cylindrical type, and has a porous air electrode 9 on the upper surface of a solid electrolyte 8 and a porous air electrode on the lower surface as shown in FIG. The fuel electrode 10 is provided. For connection between the single cells, a dense LaCrO ₃ solid solution material called MgO or CaO, called a separator 11, is used.

[0009]

However, in both of the above-described two types of fuel cells, the cylindrical type and the flat type, since the metal (Ni) is used for the fuel electrodes 4 and 10, the metal sinters during power generation. And the volume shrinkage occurs,
In addition, there is a problem that a minute crack is generated, electric conductivity is reduced, and an output density of power generation is reduced with time, and as a result, power generation characteristics are deteriorated.

[0010] It is an object of the present invention to provide a stable and long-life solid oxide fuel cell having an output with very little deterioration in power generation characteristics.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies and as a result, have found that Cr,
Average diameter of 1 to 30 consisting of at least one of Fe
When a metal fiber of 0 μm is present, even if a fine crack occurs due to sintering of metal (Ni), a path for electric conduction can be secured by the metal fiber, and as a result, deterioration of power generation characteristics can be suppressed. And found the present invention.

That is, a solid electrolyte fuel cell according to the present invention is a solid electrolyte fuel cell having a fuel electrode formed on one side of the solid electrolyte and an air electrode formed on the other side. And CeO
₂ , a cermet layer composed of ceramic particles composed of ZrO ₂ or a solid solution thereof, metal particles composed of at least one of Ni, Co, Ti, Cr, and Fe; and a cermet layer formed on an upper surface of the cermet layer. , C
average diameter 1 to at least one of r and Fe
And a metal fiber layer having a thickness of 300 μm.

[0013]

[0014]

[0015]

In the present invention, the fuel electrode includes metal fibers of at least one of Cr and Fe having an average diameter of 1 to 300 μm. For example, the fuel electrode is formed by combining the metal fibers with CeO ₂ and ZrO _2. Alternatively, metal particles such as Ni constituting the fuel electrode are fired during power generation by forming ceramic particles made of these solid solutions and metal particles made of at least one of Ni, Co, Ti, Cr and Fe. Even if it is tied, it is possible to suppress the occurrence of volume shrinkage and disconnection of the electric conduction path, thereby suppressing a reduction in the output density of power generation over time, and as a result, improving the power generation performance. .

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid oxide fuel cell according to the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the cylindrical fuel cell of the present invention is configured by forming an air electrode 32 on an inner surface of a cylindrical solid electrolyte 31 and a fuel electrode 33 on an outer surface thereof. Is provided with a current collector 35 electrically connected to the air electrode 32.
As shown in FIG. 4, a support tube made of a material having a large electric resistance may be formed, and the air electrode 32, the solid electrolyte 31, and the fuel electrode 33 may be laminated on the outer surface of the support tube.

The air electrode 32 used in the present invention is manufactured by extruding a cylindrical air electrode having a function as a self-supporting tube. The air electrode 32 is formed by converting La having a perovskite type crystal phase as a main phase into Ca, Sr, or the like for 10 to 2 hours.
It is a LaMnO ₃ -based material substituted with 0 atomic%, and its average crystal grain size is desirably 3 to 20 μm, particularly desirably 5 to 15 μm. This is because when the average crystal grain size of the main crystal phase is smaller than 3 μm, the strength is high but the gas permeability is low,
If it exceeds m, the gas permeability increases but the strength becomes insufficient. The open porosity of the air electrode 32 is 20
~ 45%, especially 30-40% is suitable. The average pore diameter in the range of 1.0 to 5.0 μm is excellent in gas permeability.

The solid electrolyte 31 formed on the surface of the air electrode 32 contains 3 to 20 mol% of Y ₂ O ₃ , Yb ₂ O ₃ , Sc.
Partially stabilized or stabilized Zr to which ₂ O ₃ or the like is added
O ₂ , or 5-30 mol% of Gd ₂ O ₃ , Y
It is preferable to use CeO ₂ to which ₂ O ₃ , Nd ₂ O ₃ and CaO are added.

In the present invention, the fuel electrode 33 includes metal fibers of at least one of Cr and Fe having an average diameter of 1 to 300 μm. That is, the fuel electrode 33 is made of a metal fiber made of at least one of Cr and Fe and having an average diameter of 1 to 300 μm, CeO ₂ , Z
It is composed of ceramic particles composed of rO ₂ or a solid solution thereof and metal particles composed of at least one of Ni, Co, Ti, Cr and Fe. CeO
₂ , ZrO _2, or a solid solution of these, as in the case of the solid electrolyte 31 described above, contains 3 to 20 mol% of Y ₂ O ₃ and Yb _2.
ZrO ₂ to which O ₃ , Sc ₂ O _3, etc. are added;
30 mol% of Gd ₂ O ₃ , Y ₂ O ₃ , Nd ₂ O ₃ , Ca
It is preferable to use CeO ₂ to which O is added.

As shown in FIG. 3, the structure of the fuel electrode 33 of the present invention comprises ceramic particles 37 made of ZrO ₂ and N
Cermet layer 39 composed of metal particles 38 of at least one of i, Co, Ti, Cr, Fe
A metal fiber layer 41 made of at least one metal fiber 40 of Cr and Fe is formed on the upper surface of the substrate.
The amount of the metal fibers 40 is 30 to 95 of the entire fuel electrode 33.
% By volume is desirable.

[0021]

The thickness of the cermet layer is 10 to 200.
μm , especially 20 to 1 in view of electric conductivity and gas permeability.
The thickness of the metal fiber layer is preferably 50 to 500 μm.
0 μm, especially 100 to 100 for the same reason as above.
0 μm is desirable.

The metal fibers used are Cr and / or F
e can be used, and a single metal fiber of each of Cr and Fe may be used, or a mixture of these may be used.

Further, the diameter of the metal fiber is 1 to 300 μm. This is because if the diameter of the metal fiber is smaller than 1 μm,
This is because the metal fibers break due to the shrinkage of the fuel electrode, and the electrical conductivity decreases. On the other hand, if the diameter of the metal fiber is larger than 300 μm, the thickness of the fuel electrode increases, the gas permeability in the fuel electrode deteriorates, and the power generation performance decreases. The diameter of the metal fiber is particularly preferably from 10 to 100 μm from the viewpoint of electric conductivity.

Further, the aspect ratio (length / diameter) of the metal fiber is preferably in the range of 3 to 10,000. This is because if the aspect ratio is smaller than 3, the electric conductivity is likely to decrease. If the ratio is greater than 10,000, it is difficult to uniformly disperse the fibers, and the output during power generation tends to vary. The aspect ratio of the metal fiber is desirably 10 to 1000 from the viewpoints of electric conductivity and fiber dispersibility.

Further, the purity of the metal fibers is Cr,
The content of at least one of Fe is preferably 70% or more, particularly preferably 95% or more. The metal fiber may be a single crystal in addition to a polycrystal.

In the above example, a cylindrical solid oxide fuel cell has been described. However, the same material as described above can be used for a flat plate.

Next, the production method of the present invention will be described. The method for producing a cylindrical fuel cell of the present invention is, for example, a method in which a solid electrolyte molded body is laminated on the outer peripheral surface of a cylindrical air electrode molded body, and the solid electrolyte molded body is formed at a temperature of 1000 to 1300 ° C. Calcination is performed for about 3 hours, and a current collector molded body is further laminated on the surface of the solid electrolyte calcined body. The air electrode / solid electrolyte / current collector laminate thus produced is oxidized in the air or the like. Sintering is performed by simultaneous firing at a temperature of 1300 to 1600 ° C. for about 3 to 15 hours in an atmosphere. Alternatively, the laminate may be formed by forming a cylindrical solid electrolyte molded body, and then laminating a molded body of an air electrode molded body and a current collector on the inner and outer surfaces thereof.

[0029]

In the solid oxide fuel cell unit shown in FIG. 3 of the present invention , for example, after forming a cermet layer using ZrO ₂ (containing Y ₂ O ₃ ) powder and Ni powder, predetermined Cr, F
e. A dispersion of the fibers in an organic solvent is applied to the upper surface of the cermet layer by a slurry dipping method in the case of a cylindrical cell, or by a screen printing in the case of a flat cell, as described above, and the solid electrolyte is formed. The fuel electrode compact is laminated on the surface.

Thereafter, the fuel electrode molded body may be subjected to a heat treatment at a low temperature at which the metal fibers are not oxidized, or may be in an applied state. After the formation of the air electrode / solid electrolyte / current collector laminated body, the fuel electrode body can be further laminated and fired simultaneously.

The metal fiber layer 41 of the solid oxide fuel cell shown in FIG. 3 may be formed by winding a single fiber or a metal felt woven with long fibers as the metal fiber. Note that a fuel electrode may be formed on the inner surface of the solid electrolyte and an air electrode may be formed on the outer surface.

[0033]

Reference Example 1 A green sheet was prepared by a doctor blade method using a commercially available ZrO ₂ powder containing 10 mol% of Y ₂ O ₃ having an average particle diameter of 0.7 μm and then fired at 1500 ° C. for 3 hours. And theoretical density ratio 98.2%, diameter 30mm, thickness 200μ
m of a disk-shaped solid electrolyte was prepared. On one side of this solid electrolyte, a commercially available La _0.9 Sr _0.1 MnO _{3 having} a particle diameter of 1 μm was applied.
A slurry containing the powder and the solvent was applied to a thickness of 50 μm and baked at 1200 ° C. for 2 hours to form an air electrode.
Further, Z containing 10 mol% of Y ₂ O ₃ having an average particle diameter of 2 μm is used.
rO ₂ powder or 5 mol% Y ₂ O ₃ having an average particle diameter of 3 μm
Containing CeO ₂ powder, Ni, C having an average particle size of 2 μm
A fuel electrode slurry was prepared by mixing o, Ti, Cr, Fe powder and a solvent.

On the other hand, a fuel electrode slurry was prepared by adding Cr and Fe fibers having an aspect ratio of 10 and metal fibers having an average diameter of 0.5 μm to 510 μm as shown in Table 1 and a solvent to the ZrO ₂ / metal powder, and a solvent. .

The two types of fuel electrode slurries were applied to the other surface of the solid electrolyte so as to have a thickness of 100 to 3000 μm as shown in Table 1 to form a fuel electrode. A fuel electrode in which metal fibers were dispersed was prepared (Sample Nos. 2 to 16). Then, power was generated at 1000 ° C. for 500 hours while flowing oxygen on the air electrode side and hydrogen on the fuel electrode side, and the reduction rate of the output density was determined after 5 hours and 500 hours. Table 1 shows the results.

[0036]

[Table 1]

According to Table 1, the average diameter of the metal fibers is 1 to
Sample No. containing no metal fiber was sample No. 300 containing no metal fiber. No. 1, the rate of decrease in the output density was smaller, and the average diameter of the metal fibers was smaller than 1 μm. In Sample No. 2, there was no effect of containing metal fibers, and in Sample No. 2, the average diameter of which was larger than 300 μm.
8, 11, and 14, the output density of the power generation is small.

Example 1 ZrO ₂ containing 10 mol% of Y ₂ O ₃ having an average particle diameter of 2 μm
Powder, Ni, Co, Ti, Cr having an average particle diameter of 2 μm,
Table 2 shows the slurry prepared by mixing the Fe powder and the solvent.
To form a cermet layer by applying to the surface of the solid electrolyte prepared in Reference Example 1 so as to have a thickness as shown in
On the surface of this cermet layer, Cr having an aspect ratio of 5 and an average diameter of 0.5 μm to 510 μm as shown in Table 2 was used.
A slurry in which Fe fibers are dispersed in a solvent is applied so as to have a thickness as shown in Table 2, and as shown in FIG. 3, a solid electrolyte type having a fuel electrode having a metal fiber layer formed on the surface of a cermet layer as shown in FIG. A fuel cell was made. Thereafter, power generation was performed in the same manner as in Reference Example 1, and the rate of decrease in output density was measured. Table 2 shows the results.

[0039]

[Table 2]

According to Table 2, the sample coated with the metal fiber having an average diameter of the metal fiber of the metal fiber layer of 1 to 300 μm is as follows:
In each of the sample Nos. It can be seen that the reduction rate of the output density is smaller than that of No. 1. The average diameter of the metal fibers was smaller than 1 μm. In No. 17, the effect of containing fiber was not recognized. The average diameter of the metal fibers is 300
No. larger than μm. In the case of No. 24, it can be seen that the decrease in the output density is large.

REFERENCE EXAMPLE 2 Cr and Fe fibers having an average diameter of 5 μm and different aspect ratios as shown in Table 3 were added to a fuel electrode material comprising ZrO ₂ powder and Ni powder as in Example 1 and mixed. Materials were made. This was applied to a solid electrolyte so as to have a thickness as shown in Table 3 according to Reference Example 1, and a solid oxide fuel cell as shown in FIG. 2 was prepared.

Thereafter, power generation was performed in the same manner as in Reference Example 1, and the rate of decrease in output density was measured. Table 3 shows the results.

[0043]

[Table 3]

It can be seen from Table 3 that when the aspect ratio of the metal fiber is in the range of 3 to 10,000, the decrease in the output density is small.

[0045]

According to the solid oxide fuel cell unit of the present invention, the fuel electrode contains metal fibers of at least one of Cr and Fe having a diameter of 1 to 300 μm. Even if the metal particles such as Ni constituting the sintered body are sintered, it is possible to prevent the volumetric shrinkage from breaking the electric conduction path, and to prevent the output density of power generation from decreasing over time. As a result, the power generation performance can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a cylindrical solid oxide fuel cell according to the present invention.

FIG. 2 is a conceptual diagram showing a state in which a fuel electrode in which metal fibers are dispersed in a cermet layer is formed on the upper surface of a solid electrolyte.

FIG. 3 is a conceptual diagram showing a state in which a cermet layer is formed on an upper surface of a solid electrolyte and a metal fiber layer is formed on an upper surface of the cermet layer.

FIG. 4 is a perspective view showing a conventional cylindrical solid oxide fuel cell.

FIG. 5 is a perspective view showing a conventional plate-type solid oxide fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 31 ... Solid electrolyte 32 ... Air electrode 33 ... Fuel electrode 35 ... Current collector 37 ... Ceramic particle 38 ... Metal particle 39 ... Cermet layer 40 ... Metal fiber 41 ... Metal fiber layers

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/86 H01M 8/12

Claims (1)

(57) [Claims] 1. A solid electrolyte fuel cell having a fuel electrode on one surface and an air electrode on the other surface, wherein the fuel electrode is formed on the surface of the solid electrolyte.
A cermet layer composed of ceramic particles composed of CeO ₂ , ZrO ₂ or a solid solution thereof, metal particles composed of at least one of Ni, Co, Ti, Cr and Fe, and formed on the upper surface of the cermet layer And a metal fiber layer made of at least one of Cr and Fe and having an average diameter of 1 to 300 [mu] m.