JP2000260440A - Solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent break of a cell due to thermal expansion in the air or in hydrogen gas during operation by specifying a difference between a thermal expansion coefficient of a collector layer in the air and that of a solid electrolyte layer in the air to a specific value or less. SOLUTION: This solid electrolyte fuel cell has an air electrode layer 21, a solid electrolyte layer 22, a fuel electrode layer 23, and a collector layer 24, and these layers are laminated together into a multilayer cylinder shape. When a difference α2-α1 between a thermal expansion coefficient α1 of the collector layer 24 in the air and that α2 of the solid electrolyte layer 22 in the air is represented by Δα21, α1<α2 and Δα21>=0.5×10-6/ deg.C. The air electrode layer 21 is formed of a LaMnO3 group material or LaCoO3 group material prepared by replacing La with 10-30 at% of Ca, Sr, while the solid electrolyte layer 22 is formed of stabilized ZrO2 containing 3-15 at% of Y2O3, Yb2O3 and the like or CeO2 containing Y2O3, Yb2O3, Sc2O3, Nd2O3, Sm2O3, CaO and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical solid oxide fuel cell.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional typical solid oxide fuel cell (Solid Oxide Fuel Cell, hereinafter referred to as SO fuel cell) F (see Japanese Patent Application Laid-Open No. 8-162140). FIG. 1 is a sectional view of an SO fuel cell F,
Is a case containing the whole, 2 is a cylindrical SO fuel cell F cell (hereinafter abbreviated as a cell) made of ceramic or the like,
One end is open and the other end is closed. Also,
The cross section of the cell 2 has a multilayer cylindrical shape, and has a configuration in which an air electrode, a solid electrolyte, a fuel electrode, and the like are stacked.

A partition member 3 made of a heat insulating material and holding and fixing the upper end side of the cell 2 is a combustion chamber, and a fuel gas (H ₂ , CO ₂ ) supplied from a supply port 13 at a lower end of the case 1 is provided. , CH _4, etc.) from the partition member 3
The oxygen and the hydrogen gas which are mixed with the exhaust of the air in the combustion chamber 5 through the ventilation holes (not shown) formed in the combustion chamber 5 and not reacted in the cell 2 are burned in the combustion chamber 5. Reference numeral 6 denotes an air pipe for passing air into the cell 2. The air once sent from the air supply port 12 to the air distributor 14 reaches the bottom of the cell 2 through the air pipe 6 and contributes to the power generation reaction. Then, the inside of the cell 2 is directed upward and reaches the combustion chamber 5 from the opening on the upper end side.

[0004] Reference numeral 7 denotes an exhaust port through which exhaust gas from the combustion chamber 5 is discharged, 8 denotes a current collector provided on the outermost surface of the cell 2 assembly, 9 denotes a current collecting rod for extracting electric power to the outside, and 10 denotes Ni. The felt 11 is an interconnector for electrically connecting the cells 2. In the case of the drawing, a plurality of cells 2 are connected in series to obtain a desired power, and are so-called stacked.

[0005] Here, the power generation reaction occurs as follows. Each layer of the cell 2 has a thickness of about several μm to 2.5 mm, and has functions such as conductivity, air permeability, solid electrolyte, and electrochemical catalysis. When air or the like as an oxidant is flowed inside the cell 2 maintained at a temperature of about 1000 ° C., and hydrogen gas is flown outside, the O ²⁻ ions move inside the cell 2 to cause an electrochemical reaction, A potential difference is generated between the air electrode and the fuel electrode, and power generation becomes possible.

In recent years, such an SO fuel cell F has a small operating temperature in the cell 2 in addition to a small size.
Since the temperature is as high as 050 ° C., the power generation efficiency is high and is expected as a third generation power generation system.

In general, two types of cells for an SO fuel cell F are known, a cylindrical cell 2 and a flat cell. The flat plate cell has a feature that the output density per unit volume is high. However, in practical use, there are problems of imperfect gas sealing and non-uniformity of temperature distribution in the flat plate cell. On the other hand, although the cylindrical cell 2 has a low output density, its shape has high mechanical strength and its internal temperature distribution can be maintained uniformly.

The cell 2 is made of ceramics as described above, and has a CaO-stabilized Zr having an open porosity of about 30%.
A multi-porous air electrode layer made of a LaMnO ₃ -based material or the like in which O ₂ or the like is used as a support tube and Ca and Sr are dissolved as a solid solution, a solid electrolyte layer made of Y ₂ O ₃ stabilized ZrO ₂ or the like,
A fuel electrode layer made of a cermet such as Ni—ZrO ₂ having high air permeability is sequentially provided. LaC in which Ca, Sr, and Mg are dissolved in a part of the air electrode layer and the solid electrolyte layer
A current collector layer (interconnector layer) made of an rO ₃ -based material or the like is provided.

In recent years, in such a cell 2, in order to simplify the manufacturing process, an air electrode layer, a solid electrolyte layer,
A so-called co-sintering method has been proposed in which at least two of the constituent members such as the fuel electrode layer and the current collector layer are simultaneously fired. In the co-sintering method, for example, a solid electrolyte layer molded body and a current collector layer molded body are wound in a roll shape around a cylindrical air electrode layer molded body and simultaneously fired, and then a fuel electrode layer is formed on the surface of the solid electrolyte layer. How to This co-sintering method reduces the number of manufacturing steps, so that the manufacturing yield is improved and the cost is reduced.

[0010]

However, after the air electrode layer, the solid electrolyte layer, and the current collector layer are co-sintered by the above-described co-sintering method, or further, the fuel electrode layer is sintered on the surface of the solid electrolyte layer. After that, even if there is no abnormality in the cell 2 and the condition is good, if the fuel electrode layer is subjected to reduction treatment or hydrogen gas is introduced as a fuel gas for power generation, a difference due to a difference in coefficient of thermal expansion causes a collection. There has been a problem that the conductor layer is destroyed.

Accordingly, the present invention has been completed in view of the above circumstances, and an object of the present invention is to destroy a cell due to thermal expansion in air and hydrogen gas which is an atmosphere gas during operation. That is to solve the problem.

[0012]

The solid oxide fuel cell of the present invention has an air electrode layer, a solid electrolyte layer, a fuel electrode layer and a current collector layer laminated in a multilayer cylindrical shape. When the coefficient of thermal expansion of the layer in air is α1, and the coefficient of thermal expansion of the solid electrolyte layer in air is α2, the difference between α2 and α1 is α2−α.
If 1 is Δα21, α1 <α2 and Δα21
≦ 0.5 × 10 ⁻⁶ / ° C.

According to the present invention, a co-sintering step of the air electrode layer, the solid electrolyte layer and the current collector layer in the air, a sintering step of the fuel electrode layer on the surface of the solid electrolyte layer, The thermal stress generated in the current collector layer during the fuel electrode layer reduction step and the power generation is minimized, and the current collector layer can be prevented from being broken due to thermal expansion.

In the present invention, preferably, the thermal expansion coefficient of the current collector layer in hydrogen gas is α3, the thermal expansion coefficient of the solid electrolyte layer in hydrogen gas is α4, and the difference α3 between α3 and α4 is α3.
When −α4 is Δα34, α3> α4 and Δ
α34 ≦ 0.3 × 10 ⁻⁶ / ° C.

That is, although the current collector layer is sintered in the air,
At the time of power generation, a part of the current collector layer is exposed to a reducing atmosphere.
Therefore, as the current collector layer material, a material whose thermal expansion coefficient hardly changes both in the air and in a reducing atmosphere is preferable. However, LaCrO ₃ -based materials currently used are more preferably used in a reducing atmosphere (hydrogen gas) than in air. There is a feature that the coefficient of thermal expansion in ()) is large. Therefore, to minimize the stress acting on the cell in each step, the thermal expansion coefficient of the current collector layer in air should be smaller than the thermal expansion coefficient of the solid electrolyte layer, and the current It has been found that it is better to make the thermal expansion coefficient of the solid electrolyte layer larger than that of the solid electrolyte layer.

Preferably, Δα21> Δα34.
That is, in the cylindrical cell, the potential gradient in the current collector layer is greatly reduced on the air electrode layer side as indicated by the electric conductivity of the current collector layer. That is, during the power generation, the electric conductivity decreases rapidly on the air electrode layer side of the current collector layer. This means that most of the current collector layer was exposed to the environment of hydrogen gas during power generation, and the coefficient of thermal expansion of the solid electrolyte layer was almost constant regardless of the atmospheric gas. It is better to reduce the difference in thermal expansion coefficient between the current collector layer and the current collector layer. Therefore, by setting Δα21> Δα34, it is possible to minimize the thermal stress acting on the cell in all steps from the manufacturing process to the execution of power generation.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cell of the present invention will be described below.
FIG. 1 shows the basic structure of a cylindrical cell 2 of the present invention,
Is an air electrode layer; 22 is a solid electrolyte layer coated and sintered on the outer surface of the air electrode layer; 23 is a fuel electrode layer coated and sintered on the outer surface of the solid electrolyte layer 22; The current collector layer (interconnector) 24 partially contacts the outer surface of the air electrode layer 21 through the notch. That is, the inside (the center side of the cell 2) end face of the current collector layer 24 is connected to the air electrode layer 21, and the outside (the outside surface side of the cell 2) end face of the current collector layer 24 is N
It is connected to the fuel electrode layer 23 of another cell 2 via a connecting member such as i-felt 10 and is stacked (see FIG. 2).

In the present invention, the layer structure of the cell 2 is such that the air electrode layer 2 is provided inside the cylindrical solid electrolyte layer 22 as described above.
1, a structure in which the fuel electrode layer 23 is formed on the outside, or the fuel electrode layer 23 on the inside of the solid electrolyte layer 22 and the air electrode layer 21 on the outside
May be formed. In a configuration in which the fuel electrode layer 23 is formed inside the solid electrolyte layer 22 and the air electrode layer 21 is formed outside, the current collector layer 24 is formed of the solid electrolyte layer 22.
Is connected to a part of the outer surface of the fuel electrode layer 23 through the notch.

In the cell 2 of the present invention, the thermal expansion coefficient of the current collector layer 24 in air is α1, the thermal expansion coefficient of the solid electrolyte layer 22 in air is α2, and the difference between α2 and α1 is α2- α1 = Δ
When α21, α1 <α2 and Δα21 ≦
0.5 × 10 ⁻⁶ / ° C. By defining α1, α2 and Δα21 as described above, it is possible to obtain a cell 2 that is not broken by thermal expansion in all steps from the production process by co-sintering to the time of power generation. In particular, Δα21 is 0.5 × 10 ⁻⁶
If the temperature exceeds / ° C, the cell 2 is broken after co-sintering.

Preferably, the thermal expansion coefficient of the current collector layer 24 in hydrogen gas is α3, the thermal expansion coefficient of the solid electrolyte layer 22 in hydrogen gas is α4, and the difference between α3 and α4 is α3-α.
When 4 = Δα34, α3> α4, and Δα34
≦ 0.3 × 10 ⁻⁶ / ° C. By defining α3, α4, and Δα34 as described above, it is possible to obtain a cell 2 that is not damaged by thermal expansion during power generation, not to mention in the production process by co-sintering.

The thermal expansion coefficients α1 to α4 are 3 mm × 3
A test piece having a size of 10 mm × 10 mm was prepared and determined from the elongation of the test piece from room temperature to 1000 ° C. using a thermal expansion coefficient measuring apparatus. Α1 and α2 are in air, α3 and α4 are forming gas (hydrogen gas 12.5% by volume, nitrogen gas 8
7.5% by volume). Since the forming gas has a high possibility of explosion when pure hydrogen gas is used, substantially the same result as that obtained in hydrogen gas can be obtained when measuring the coefficient of thermal expansion.

Each layer of the cell 2 of the present invention will be described below. The air electrode layer 21 is composed of La and Ca, Sr of 10 to 30 a.
La (MnO ₃ ) material substituted by t (atomic)% or La
The solid electrolyte layer 22 is made of a CoO ₃ -based material,
Stabilized Z containing 5 at% of Y ₂ O ₃ , Yb ₂ O _3, etc.
rO ₂ or partially stabilized ZrO ₂ , or Y ₂ O ₃ , Yb
₂ O ₃ , Sc ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ , CaO
It consists CeO ₂ containing such.

The current collector layer 24 is composed mainly of a perovskite-type composite oxide containing at least La and Cr as metal elements, and contains 0.5 to 3.0 wt.% (By weight) of La ₂ O _3.
% Of MgO and 5 to 30 wt% of MgO. Preferably, the Cr of the LaCrO ₃ -based material is 5-3.
Those substituted with 0 at% Mg are preferable. La ₂ O ₃ is 0.
If it is less than 5 wt% or more than 3.0 wt%, the sinterability is reduced. In order to improve sinterability, preferably
It is preferable to contain 1.0 to 3.0 wt%. In addition, Mg
By adjusting the O content, the thermal expansion coefficient of the current collector layer 24 can be controlled.

The fuel electrode layer 23 is made of Ni, Co, Fe, Ru.
And a porous cermet of ZrO ₂ or CeO ₂ containing the same.

The thickness of the current collector layer 24 is 30 to 300 μm.
m is preferably less than 30 μm, the diffusion of oxygen ions to the fuel electrode layer 23 side is large, and the power generation performance is reduced.
If the thickness exceeds 0 μm, the electric resistance of the current collector layer 24 increases and the power generation performance decreases. More preferably 50 to 150 μm
It is.

The thicknesses of the air electrode layer 21, the solid electrolyte layer 22 and the fuel electrode layer 23 are determined so that the sheet resistance of the air electrode layer 21 and the fuel electrode layer 23 is as small as possible in order to generate power over the entire solid electrolyte layer 22 of the cell. The thickness is preferably 1.5 mm to 2.5 mm, the thickness of the solid electrolyte layer 22 is 40 to 100 μm, and the thickness of the fuel electrode layer 23 is 50 to 400 μm. .

Further, as another basic structure, CaO-stabilized ZrO ₂ having an open air porosity of about 30% is used as a support tube, and the air electrode layer 21 and the solid electrolyte layer 2 are formed on the outer surface thereof.
2. In some cases, a fuel electrode layer 23 and a current collector layer 24 are formed.

The method for producing the cell 2 of the present invention comprises the following steps [A
1] to [A5].

[A1] A molded body for the air electrode layer 21 is produced by an extrusion molding method or a rubber molding method to obtain a cylindrical support tube.

[A2] A sheet of the solid electrolyte layer 22 produced by the doctor blade method is attached to the outer surface of the air electrode layer 21 except for a cutout for the current collector layer 24.

[A3] A current collector layer 2 formed by a doctor blade method is provided in the cutout portion of the solid electrolyte layer 22.
Paste the sheet of No. 4. In [A2] and [A3], the cutout for the current collector layer 24 is formed by the solid electrolyte layer 22.
May be formed by a polishing method or the like after sticking to the outer surface of the air electrode layer 21.

[A4] Further, a sheet of the fuel electrode layer 23 produced by the doctor blade method is attached to the outer surface of the solid electrolyte layer 22 except for the current collector layer 24. At this time, the fuel electrode layer 23 may be formed by a slurry dipping method.

[A5] 2 at a temperature of 1500 to 1600 ° C.
Co-sinter for 10 hours in air.

The method of manufacturing the sheet of the current collector layer 24 will be described with reference to the following steps [B1] to [B3].

[B1] A predetermined amount of La ₂ (CO ₃ ) ₃ , C
A mixed powder of r ₂ O ₃ and MgO is calcined at 1000 to 1500 ° C. to synthesize a perovskite-type composite oxide, and then 0.1 to 5.0 μm by a known method such as a rotary mill using zirconia balls. Crush to size.

[B2] La ₂ (CO ₃ ) ₃ is converted to La ₂ O ₃
0.5 to 3.0 wt% in conversion, 5 to 30 wt% MgO
Add and mix using zirconia balls.

[B3] Water and a binder resin are added to the obtained powder, and after mixing, 30 to 1 by a doctor blade method.
Sheets are formed to a thickness of 00 μm.

The cell 2 of the present invention has a structure in which one end is open and one end is closed as shown in FIG. 2, a structure in which both ends are open, or a structure in which both ends are closed.
Various configurations such as those supplied from the middle can be adopted.

Thus, the present invention has the effect of eliminating the problem that cells are destroyed due to thermal expansion in air and in hydrogen gas, which is an atmospheric gas during operation.

It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention.

[0041]

Embodiments of the present invention will be described below.

(Embodiment) The cell 2 of FIG.
1] to [a10].

[A1] The purity of the material of the air electrode layer 21 is 9
9.9% or more of La ₂ O ₃ , MnO ₂ , and CaCO ₃ powders are prepared, weighed and mixed so as to have a stoichiometric composition of La _0.8 Ca _0.2 MnO ₃ , and then mixed at 1500 ° C. for 3 hours. The powder was calcined and pulverized to obtain a solid solution powder having an average particle diameter of 6 μm.

[A2] A binder resin is added to the solid solution powder, and the cylindrical air electrode layer 21 is formed by extrusion molding.
Was formed.

[A3] After drying the formed body of the air electrode layer 21,
The material was calcined at 1250 ° C. for 10 hours to remove the binder, thereby producing a calcined body.

[A4] Y ₂ O ₃ obtained by the coprecipitation method
Having an average particle size of 1.0 μm containing
Toluene and a binder resin were added to the rO ₂ powder to prepare a slurry, and the slurry was prepared to a thickness of 10 by a doctor blade method.
A sheet for the solid electrolyte layer 22 of 0 μm was obtained.

[A5] La having a purity of 99.9% or more
Each powder of ₂ O ₃ , Cr ₂ O ₃ , and MgO was prepared, weighed and mixed so as to have a stoichiometric composition of LaMg _0.1 Cr _0.9 O ₃ , calcined at 1500 ° C. for 3 hours, and pulverized. Thus, a solid solution powder having an average particle size of 2 μm was obtained. Furthermore, La ₂
1.0 wt% of O ₃ and a predetermined amount of MgO were added and mixed.

[A6] Toluene and a binder resin were added to the solid solution powder to prepare a slurry, and a sheet for the current collector layer 24 having a thickness of 75 μm was prepared by a doctor blade method. At this time, solid solution powders having different addition amounts of MgO and sheets having various changes in the solid solution amount of Mg in LaMg _0.1 Cr _0.9 O ₃ were also produced.

[A7] A sheet for the solid electrolyte layer 22 is wound into a roll around the cylindrical air electrode layer 21 sintered body,
After calcining at 00 ° C. for 3 hours, the surface of the calcined body of the solid electrolyte layer 22 corresponding to the lamination position of the sheet for the current collector layer 24 is polished with a plane, and the air electrode layer 21 is partially exposed to collect. The sheet of the electric body layer 24 was stuck on the exposed portion.

[A8] Sheets of the cylindrical air electrode layer 21 sintered body, solid electrolyte layer 22 calcined body, and current collector layer 24 were co-sintered at 1530 ° C. for 6 hours in the atmosphere.

The stability of this co-sintered body to water was evaluated by a pressure cooker method. Specifically, the co-sintered body was placed in a humidifying and pressurizing device, and the temperature was 150 ° C. and the relative humidity was about 1
It was left at 00% for 3 days, and the chemical stability of the current collector layer 24 was evaluated. That is, if unreacted lanthanum oxide remains in the current collector layer 24, it deliquesces with water and breaks the current collector layer 24.

Further, air is pressurized and injected into the inside of the cell 2 so that the internal pressure becomes 1 kgf / cm ² higher than the external pressure. The cell 2 in this state is submerged, and the current collector layer is determined based on the presence or absence of bubbles. 24 were evaluated for failure.

[A9] NiO powder having an average particle size of 1.0 μm and ZrO ₂ having an average particle size of 1.5 μm containing 8 mol% of Y ₂ O ₃ were used as raw material powders for the fuel electrode layer 23. The mixture was mixed at a ratio of 8: 2 to prepare a slurry.

[A10] A slurry for the fuel electrode layer 23 was applied to the above-mentioned co-sintered body, and sintered at 1400 ° C. for 2 hours in the air to prepare a cell 2.

As shown in FIG. 2, air was generated at 1000 ° C. by flowing air into the cell 2 and hydrogen gas outside. Table 1 shows the results of investigation on α1, α3, Δα21, Δα34, whether the cell 2 was broken during co-sintering, and whether the cell 2 was broken during power generation.

[0056]

[Table 1]

In Table 1, α1 to α4 were measured by pressing the raw material powder for the current collector layer 24 into a disk shape and sintering it at 1500 ° C. for 6 hours in the atmosphere. A sample was cut out, and the coefficient of thermal expansion from room temperature to 1000 ° C. was measured in air and hydrogen gas. In addition, a sample of the solid electrolyte layer 22 was prepared in the same manner, and the coefficient of thermal expansion was measured.

As shown in Table 1, the thermal expansion coefficient of the current collector layer 24 in air and hydrogen gas can be adjusted by adding MgO. NO. To which MgO was not added. 1
NO. In No. 2, since the coefficient of thermal expansion α1 in the air was small, the difference Δα21 from the coefficient of thermal expansion α2 of the solid electrolyte layer 22 was large, and the cell 2 was destroyed during co-sintering. NO. 3,4
Then, both α1 and α3 increase, but Δα21 and Δα34
Was small, and no destruction of the cell 2 occurred during co-sintering and during power generation.

N having no Mg solid solution component in LaCrO ₃
O. NO. 6 and NO. Even if it is 7, M
By increasing the amount of gO added, α1 and α3 are controlled and Δ
α21 and Δα34 can be reduced, and the destruction of the cell 2 during co-sintering and power generation can be prevented. In addition, N, which has a high Mg solid solution component,
O. In No. 9, even if the added amount of MgO was reduced, α1 was decreased and Δα21 was increased, and the cell 2 was broken during co-sintering. N with a high content of both Mg solid solution component and MgO
O. In No. 12, Δα34 increased, and the cell 2 was destroyed during power generation.

In both the Mg solid solution component and the added amount of MgO, NO. 8, and Mg solid solution components are large, but M
In the case of NO. In 10 and 11,
No destruction of the cell 2 occurred during co-sintering and during power generation.

As described above, the Mg solid solution amount is set to 5 to 30 at.
%, MgO added amount within the range of 6 to 18 wt%, α1, α3, Δα21, Δα34 could be controlled.

[0062]

According to the present invention, the thermal expansion coefficient of the current collector layer in air is α1, and the thermal expansion coefficient of the solid electrolyte layer in air is α1.
2. When the difference between α2 and α1 is α2-α1 = Δα21,
When α1 <α2 and Δα21 ≦ 0.5 × 10 ⁻⁶ / ° C., the cell is destroyed in air and in hydrogen gas, which is an atmosphere gas during operation, due to a difference in thermal expansion coefficient. This has the effect of eliminating the problem of

[Brief description of the drawings]

FIG. 1 is a perspective view of a partial cross section of an SO fuel cell unit of the present invention.

FIG. 2 is a sectional view of the basic configuration of the entire SO fuel cell F;

[Explanation of symbols]

 1: Case 2: Cell 5: Combustion chamber 6: Air tube 10: Ni felt 11: Interconnector (current collector layer) 21: Air electrode layer 22: Solid electrolyte layer 23: Fuel electrode layer 24: Current collector layer

Claims (3)

[Claims] An air electrode layer, a solid electrolyte layer, a fuel electrode layer, and a current collector layer laminated in a multilayer cylindrical shape, wherein the current collector layer has a coefficient of thermal expansion in air of α1, and a solid electrolyte layer. When the thermal expansion coefficient in the air is α2, and the difference α2−α1 between α2 and α1 is Δα21, α1 <α2 and Δα21 ≦ 0.5 × 1
A solid oxide fuel cell having a temperature of 0 ^-6 / ° C. 2. The thermal expansion coefficient of the current collector layer in hydrogen gas is α3, and the thermal expansion coefficient of the solid electrolyte layer in hydrogen gas is α3.
4, when the difference α3-α4 between α3 and α4 is Δα34, α
3. The solid oxide fuel cell according to claim 1, wherein 3> α4 and Δα34 ≦ 0.3 × 10 ⁻⁶ / ° C. 3. The solid oxide fuel cell according to claim 2, wherein Δα21> Δα34.