JP3323038B2 - 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 solid electrolyte, an air electrode formed on one side of the solid electrolyte, a fuel electrode formed on the other side, and an interconnector or separator for collecting current. The present invention relates to a solid oxide fuel cell having an electric body.

[0002]

2. Description of the Related Art In recent years, research and development have been conducted on two types of solid electrolyte fuel cells, a cylindrical type and a flat type. The flat fuel cell has the feature that the power density per unit volume of power generation is high, but there are problems such as imperfect gas sealing and non-uniform temperature distribution in the cell when put to practical use. On the other hand, the cylindrical fuel cell has the features that although the output density is low, the mechanical strength of the cell is high and the temperature in the cell can be kept uniform. Both types of solid oxide fuel cells are being actively researched and developed utilizing their respective features.

As shown in FIG. 2, 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%, on which a porous air electrode 2 is formed by a slurry dipping method. A LaMnO ₃ -based material is applied, and the surface thereof is coated with a Y ₂ O ₃ -stabilized ZrO ₂ film as the solid electrolyte 3 by a vapor phase synthesis method (EVD) or a thermal spraying method. A fuel electrode 4 made of Ni-zirconia is provided. In the fuel cell module, each single cell is a LaCrO ₃ based interconnector 5.
Connected via The current collection is N
This is performed by contacting an i-felt or a Ni plate. Power generation is performed at a temperature of 1000 to 1050 ° C. by flowing air (oxygen) inside the support tube 6 and fuel (hydrogen) outside 7. In recent years, attempts have been made to use a LaMnO ₃ -based material, which is an air electrode material, directly as a porous support tube in order to simplify the process in this cell fabrication process.

As a supporting tube material having the function of an air electrode, La or Ca of 10 to 20 atomic% is used.
Used is a LaMnO ₃ solid solution material.

[0005] Further, the single cell of the flat plate type fuel cell uses the same material system as that of the cylindrical type, and 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. Power generation is performed at a temperature of 1000 to 1050 ° C. by supplying air (oxygen) to the air electrode side of the cell and fuel (hydrogen) to the fuel electrode side.

[0006]

However, both the conventional cylindrical fuel cell and the flat fuel cell have a large polarization resistance at the interface between the solid electrolyte and the air electrode or the fuel electrode. There has been a problem that the reduction is large and the power generation efficiency is low.

In a cylindrical fuel cell, the contact resistance between the interconnector and the Ni felt (or Ni plate) is increased. In the flat fuel cell, the contact resistance at the interface between the separator and the air electrode or the fuel electrode is increased. Therefore, there is a problem that the voltage drop in the fuel cell is large and the power generation efficiency is low.

Due to such a problem, the conventional solid oxide fuel cell has a problem that the original performance cannot be sufficiently exhibited.

[0009]

Means for Solving the Problems The inventors of the present invention have studied the above problem, and as a result, have found that an interconnector and a Ni ferrule have been developed.
(Ni plate) or separator and air electrode or fuel electrode
The present inventors have found that the polarization resistance and the contact resistance can be reduced by increasing the area of the contact interface with, and the present invention has been achieved.

That is, the solid oxide fuel cell according to the present invention is characterized in that the air electrode or the fuel electrode is formed on the outer surface of the fuel cell body having the solid electrolyte on one surface and the fuel electrode on the other surface. In a solid oxide fuel cell unit provided with a current collector electrically connected, the surface roughness Ra of at least one surface of the current collector satisfies 3 to 200 μm, and at least one of the current collector It is important that the concave portions are periodically formed on one surface .

In the present invention, the surface roughness Ra of at least one surface of the current collector such as an interconnector or a separator is set to 3 to 200 μm.
If a is smaller than 3 μm, the interconnector and N
This is because the effect of reducing the contact resistance at the interface between the i-felt (Ni plate) or the separator and the air electrode or the fuel electrode is small. On the other hand, if Ra exceeds 200 μm, the contact area between the interconnector and the Ni felt (Ni plate) or between the separator and the air electrode and the fuel electrode is reduced, resulting in poor current collection. In particular, the surface roughness Ra of at least one surface of the current collector is 20 from the viewpoint of the contact area.
１００100 μm is desirable.

In order to make the surface roughness Ra of the surface of the interconnector or the separator 3 to 200 μm, for example, a method in which a metal mesh is pressed against the surface of a green sheet for the interconnector or the separator produced by a doctor blade method, The sheet can be formed by pressing a sheet against a surface of metal or the like having irregularities on the surface, and firing the sheet at a predetermined temperature. When a method of pressing a metal mesh against the surface of a green sheet, or a method of pressing a green sheet against a surface of a metal or the like having irregularities on the surface, a concave portion is periodically formed on the surface of the current collector, Uniform power generation can be obtained over the entire surface of the current collector.

The green sheet may be sintered by a predetermined method and then blasted by a sand blasting machine to perform a surface treatment. In this case, using a mold in which holes are formed periodically, and sandblasting from above the mold,
The concave portions can be formed periodically.

[0014]

The power generation is carried out at a temperature of 1000 to 1050 ° C. by supplying air (oxygen) to the air electrode side and fuel (hydrogen) to the fuel electrode side. In this power generation, the cause of the cell voltage drop is as follows.
There are cell resistance, polarization resistance at the interface between the fuel electrode and the air electrode and the solid electrolyte, and contact resistance at the interface between the fuel electrode and the air electrode and the separator. Although there are some differences depending on the shape, each of the above-mentioned contributions to the voltage drop of the resistor is 1
It is about / 3 each. The same applies to the case of a cylindrical fuel cell.

In the present invention, the surface roughness Ra of at least one surface of the current collector such as the interconnector or the separator is set to 3 to 200 μm, and the contact area between the interconnector and the Ni felt (Ni plate) or the separator and the fuel As a result of increasing the contact area with the electrode or the air electrode, the contact resistance at the interface can be reduced, the voltage drop of the cell can be suppressed, and the power generation efficiency can be improved.

That is, in the present invention, by forming irregularities on at least one surface of the current collector, the area of each interface can be increased, and the power generation output can be improved.

That is, in the present invention, the concave portion is periodically formed on at least one surface of the current collector to reduce the surface roughness Ra to 3
By setting the thickness to 200 μm, uniform power generation can be obtained over the entire fuel cell unit.

In the present invention, the current collector has a surface roughness Ra of 3 to 3.
By setting the thickness to 200 μm, in the case of a flat fuel cell, the contact resistance at the interface between the fuel electrode and the air electrode and the separator can be reduced, and the voltage drop of the cell can be suppressed to further improve the power generation efficiency. .

[0019]

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. Typical called by the structure of the fuel cell and the plate-type fuel cell, partially stabilized ZrO addition of Y ₂ O ₃ and Yb ₂ O ₃ as shown in FIG. 3 3-15 mole% of the present invention ₂ and stabilized ZrO ₂ ,
Alternatively, (La, Sr) MnO ₃ or (La, Sr) MnO ₃ is formed on the upper surface of a plate-like solid electrolyte 8 made of a CeO ₂ solid solution to which Y ₂ O ₃ , Yb ₂ O ₃ , Sm ₂ O ₃ , and Gd ₂ O ₃ are added. Ca) MnO ₃
A porous air electrode 9 made of Ni or Z
A porous fuel electrode 10 made of rO ₂ (Y ₂ O ₃ stabilized) cermet or the like is formed, and a fuel cell body 12 is formed. Then, as a member connecting the cells as a single cell, the separator 11 is disposed at a position connecting the air electrode of one cell and the fuel electrode of the adjacent cell, that is, the separator 11 is disposed on the fuel cell body 12. I have. This separator 11 is made of dense LaC doped with Mg or Ca.
It is composed of an rO ₃ solid solution.

In the present invention, as shown in FIG. 1, periodic concave portions 13, for example, large undulations or small holes are provided on the surface of the separator 11 on the fuel electrode side to increase the surface area. Surface roughness Ra of 3 to 200 μm
m. A porous air electrode or fuel electrode is in contact with this surface. This air electrode or fuel electrode needs to have an open porosity of about 10 to 70% in order to improve gas permeability. The fuel electrode is
It is more effective to form a skeleton made of a solid electrolyte material (for example, ZrO ₂ ) on the surface of the solid electrolyte and fill the skeleton with Ni.

The separator 1 having such a surface structure
1 is a method in which a metal mesh is pressed against the surface of a green sheet produced by a doctor blade method, or a method in which a green sheet is pressed against a surface of a metal or the like having irregularities on the surface, which is fired at a predetermined temperature to produce a green sheet. can do. Alternatively, after sintering the green sheet by a predetermined method, the surface structure may be formed by blasting using a sand blasting machine. Also, the solid electrolyte and the interconnector of the cylindrical fuel cell shown in FIG. 2 have a surface roughness of 3 to 200 μm by the same method.
It can be.

[0022]

EXAMPLES Reference Example 1 ZrO _{2 having a} particle diameter of 0.6 μm by a doctor blade method
A green sheet having a thickness of 400 μm containing (8 mol% Y ₂ O ₃ ) was prepared, and the sheet was cut out so that the size of the sintered body was 5 cm × 5 cm, and calcined at 1500 ° C. for 4 hours to obtain a theoretical density ratio. A 98% flat solid electrolyte was prepared. The surface roughness (center line average roughness) Ra of the obtained flat solid electrolyte surface was measured with a surface roughness meter. On one surface of the solid electrolyte, a commercially available La _0.9 Sr having a particle diameter of 1 μm was applied.
A slurry for an air electrode containing _0.1 MnO ₃ was applied to a thickness of 50 μm by screen printing, and ZrO ₂ containing 70 wt% NiO (8 mol% Y ₂
A slurry for the fuel electrode containing O _{3 (} containing O ₃ ) was applied by screen printing to a thickness of 50 μm,
Annealing was performed at 00 ° C. for 1 hour to form an air electrode on one surface of the solid electrolyte and a fuel electrode on the other surface, thereby producing a cell body.
This cell body is made of La _0.8 Ca _0.22 C having a thickness of 350 μm.
A flat-plate type fuel cell was manufactured by sandwiching it with a separator made of a rO ₃ sintered body. It was set to 1.

Further, using a green sheet similar to the above-mentioned green sheet for a solid electrolyte, a stainless mesh of 40 to 330 mesh is pressed against one or both surfaces of the sheet to periodically form irregularities on the green sheet. Calcined at 1500 ° C for 4 hours and the theoretical density ratio is 99.6
% Of the solid electrolyte was prepared. The surface roughness Ra of the obtained flat solid electrolyte surface was measured with a surface roughness meter.
The fuel electrode and the air electrode were formed on the flat solid electrolyte by the same method as described above, and the cell body was manufactured. This cell body is made of La _0.8 Ca _0.22 Cr having a thickness of 350 μm.
A flat-plate type fuel cell was produced by sandwiching it with a separator made of an O ₃ sintered body.

Then, oxygen was supplied to the air electrode side and hydrogen was supplied to the fuel electrode side to generate power continuously at 1000 ° C. for 1000 hours, and the output density at the time of power generation was measured. Table 1 shows the results.

[0025]

[Table 1]

As shown in Table 1, the surface roughness Ra of the solid electrolyte was the same as that of Sample No. No effect is obtained when the particle size is smaller than 3 μm as in Sample No. 1; As can be seen from FIGS. 7 and 10, when the thickness exceeds 200 μm, the output density decreases. Regarding the improvement of the surface structure, it can be seen that when the surface treatment is performed on the air electrode side, the performance is improved as in the case where the surface treatment is performed on the fuel electrode side. In addition, the sample No. 11 and 12 show that the surface treatment of both surfaces in contact with the air electrode and the fuel electrode further improves the power generation performance.

Further, as an example in which irregularities are not periodically formed, the surface of the sintered body of the solid electrolyte was directly subjected to surface treatment by sandblasting, and the surface roughness Ra was measured. Then, a fuel electrode and an air electrode were prepared on the solid electrolyte by the same method as described above, and a cell body was prepared. This cell body was sandwiched by the same separator as above to produce a fuel cell, and power was generated in the same manner as above, and the output density during power generation was measured. As a result, the surface roughness Ra of the solid electrolyte was 25 μm and 6 μm.
3 μm, and the initial output power density was 0.1 μm.
A 29W / cm ² and 0.30 W / cm ^2, it showed excellent performance. However, the cells were destroyed 30 hours and 22 hours after the start of power generation. This is presumably because a temperature distribution was formed in the cell due to variations in the power density in the cell, and as a result, the cell was broken by thermal stress. On the other hand, when the above-mentioned periodic irregularities were formed on the surface of the solid electrolyte, no destruction was observed even in the invention for 1000 hours.

REFERENCE EXAMPLE 2 The thickness was about 250 μm and 20
A green sheet for a solid electrolyte of about 200 μm was prepared. Using a multi-punching system (MPS), the green sheet having a diameter of 30 to 50 μm can be used.
m holes are formed at intervals of 30 to 100 μm,
After forming irregularities on the green sheet surface by laminating the green sheet surface on the sheet surface, the resultant was fired in the air at 1500 ° C. for 4 hours to produce a flat solid electrolyte having a theoretical density ratio of 98%.
The surface roughness Ra of the solid electrolyte is measured in the same manner as in Reference Example 1 above, and then the air electrode and the fuel electrode are formed in the same manner as in Reference Example 1 to generate power, and the output density during power generation is measured. did.

The results are shown in Table 2.

[0030]

[Table 2]

From Table 2, it can be seen that, for all samples, Sample No. A power density greater than one was shown.

Example 1 La _0.8 Ca having a particle diameter of 1 μm was obtained by a doctor blade method.
A green sheet having a thickness of 400 μm containing _0.22 CrO ₃ was prepared, and the sheet was cut out so that the size of the sintered body was 5 cm × 5 cm. The sheet was fired in the air at 1500 ° C. for 8 hours, and the theoretical density ratio was 98% or more. A flat separator was produced.

Further, using a green sheet similar to the above-mentioned separator green sheet, a stainless mesh of 40 to 330 mesh is pressed against one or both surfaces of the sheet to form irregularities on the green sheet.
The plate was fired in the air at 00 ° C. for 4 hours to produce a plate-like separator having a theoretical density ratio of 98% or more. The surface roughness Ra of the obtained plate-shaped separator was measured by a surface roughness meter, and the results are shown in Table 3.

Then, in this separator, Reference Example 1
No. 1 in Table 1 1 and No. 3 by sandwiching the cell body and supplying oxygen to the air electrode side and hydrogen to the fuel electrode side
Power was continuously generated at 00 ° C. for 1000 hours, current was collected through the separator, and the output density during power generation was measured. Table 3 shows the results.

[0035]

[Table 3]

It can be seen from Table 3 that Sample No. having a small surface roughness of the separator whose surface was in contact with the fuel electrode had a small surface roughness.
Sample No. 19 was surface-treated. The output density was as low as 18. Further, in Sample No. in which the surface roughness of the separator surface was larger than 200 μm. Also in No. 24, the power generation performance decreased. Similarly, the performance of the separator whose surface is in contact with the air electrode is improved. For samples No. 25 to No. 28, both the solid electrolyte and the separator were surface-treated.

[0037]

According to the solid oxide fuel cell of the present invention, the surface roughness Ra of at least one surface of a current collector such as an interconnector or a separator is 3 to 200 μm.
By increasing the contact area between the interconnector and the Ni felt (Ni plate) or between the separator and the fuel electrode or the air electrode, the contact resistance at each interface can be reduced, and the voltage drop of the cell can be reduced. The power generation efficiency can be improved by suppressing the power generation.

Therefore, the fuel cell of the present invention has a significantly improved power generation performance as compared with the conventional cell in both the cylindrical type and the flat type, and can provide a long-term stable cell.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view showing a surface state of a solid electrolyte of a flat solid electrolyte fuel cell unit according to the present invention.

FIG. 2 is a perspective view showing a conventional cylindrical fuel cell.

FIG. 3 is a perspective view showing a plate-type solid oxide fuel cell.

[Explanation of symbols]

 8 solid electrolyte 9 air electrode 10 fuel electrode 11 separator 12 fuel cell body 13 recess

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-89736 (JP, A) JP-A-7-73890 (JP, A) JP-A-7-14585 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01M 8/02 H01M 8/12

Claims (1)

(57) [Claims] 1. A current collector electrically connected to the air electrode or the fuel electrode is provided on an outer surface of a fuel cell body having an air electrode formed on one surface of the solid electrolyte and a fuel electrode formed on the other surface. In the solid oxide fuel cell unit, a concave portion is periodically formed on at least one surface of the current collector ,
The surface roughness Ra of the surface of the current collector on which the concave portions are formed is 3 to
A solid oxide fuel cell having a thickness of 200 μm.