JPH0722041A - Manufacture of solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To enhance the reliability of electrical connection between cells and to keep a conductive layer from being peeled so as to provide stable power- generating performance over a long period by enhancing the electrical conductivity of the conductive layer itself, and approximating the coefficient of thermal expansion of the conductive layer to that of a solid electrolyte. CONSTITUTION:A solid electrolyte fuel cell, which comprises e.g. an air electrode layer 2, a solid electrolyte layer 3, and a fuel electrode layer 4, all provided on the surface of a cylindrical support tube 1 with a conductive layer 5 formed in electrical connection with either the air electrode layer 2 or the fuel electrode layer 3 by vapor-phase synthesis method to cover the layers, is manufactured. In that case, the conductive layer is made from perovskite composite oxides composed chiefly of metal elements of La, Cr, Mg and Ca with the Ca substituting for the La by 1-30% and the Mg substituting for the Cr by 1-20%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid oxide fuel cell unit, and more particularly to an improvement of a conductive layer for electrically connecting cells.

[0002]

2. Description of the Related Art Solid oxide fuel cells are under development as a power generation system that replaces the conventional hydroelectric power generation and thermal power generation. FIG. 1 is a perspective view showing the structure of a typical cylindrical solid oxide fuel cell unit. Usually, such a cylindrical fuel cell has a cathode electrode 2 made of LaMnO ₃ -based material or the like on the surface of a porous cylindrical support tube 1 and a Y electrode.
_The solid electrolyte layer 3 made of ₂ O ₃ stabilized ZrO ₂ (YSZ) and the fuel electrode layer 4 made of Ni—ZrO ₂ (containing Y ₂ O ₃ ) are formed. During power generation, the cells are electrically connected to each other by the conductive layer 5 arranged so as to arrange the plurality of cells and electrically connect to either one of the air electrode layer 2 and the fuel electrode layer 4. Then, when an oxygen-containing gas such as air is supplied to the air electrode layer 2 side and a fuel gas such as hydrogen gas is supplied to the fuel electrode layer 4 side, power generation is performed at a temperature of 1000 to 1050 ° C.

A LaCrO ₃ type material is generally used as the conductive layer 5 in the above cell. LaCrO
_{Since 3} itself has a conductivity of about 0.5 s / cm, it is necessary to further increase the conductivity. Therefore, conventionally, one in which a part of Cr of LaCrO ₃ is replaced by Mg or Sr, or one in which a part of La of LaCrO ₃ is replaced by Ca is used.

[0004]

In order to increase the electric conductivity of the LaCrO ₃ type material, it is effective to increase the substitution amount of Mg, Sr or Ca, but Mg, Sr or Ca is increased.
When the substitution amount of the solid electrolyte layer is increased, the difference in thermal expansion coefficient between the solid electrolyte layer and the stabilized ZrO ₂ which is in direct contact with the conductive layer becomes large. Then, the conductive layer is peeled off, which causes a problem such as a decrease in power generation capability.

[0005]

The inventors of the present invention have repeatedly studied the structure of the above-mentioned conductive layer, and as a result, L has been used as the conductive layer.
The present invention has been accomplished by finding that it is composed of an aCrO ₃ system composition, and that by adding an appropriate amount of Mg and Ca to the system, the conductivity can be increased and the difference in thermal expansion from the solid electrolyte can be reduced.

That is, according to the method for producing a solid oxide fuel cell of the present invention, the surface of a cylindrical air electrode is sequentially coated with a solid electrolyte layer and a fuel electrode layer, or the surface of a cylindrical support tube is covered with an air electrode layer. A method for producing a solid oxide fuel cell, in which a solid electrolyte layer and a fuel electrode layer are sequentially coated, and then a conductive layer is coated to electrically connect to either one of the air electrode layer and the fuel electrode layer. In, the conductive layer,
It is composed of a perovskite type complex oxide containing La, Cr, Mg and Ca as main components as metal elements, and has a Ca substitution amount for La of 1 to 30% and a substitution amount of Mg for Cr of 1 to 20%. It is what

[0007]

According to the structure of the present invention, LaCr is used as the conductive layer.
By replacing a part of La with an appropriate amount of Ca and replacing a part of Cr with an appropriate amount of Mg with respect to the O ₃ system, the conductivity can be increased and the coefficient of thermal expansion can be stabilized as a solid electrolyte. It can be approximated to ZrO ₂ (containing 8 to 10 mol% of Y ₂ O ₃ ). Therefore, FIG. 2 shows the relationship between oxygen partial pressure and electrical conductivity of various materials, and FIG. 3 shows the thermal expansion curves of various materials. According to FIG. 2, LaCrMgO ₃
LaCaCrM for materials and LaCaCrO ₃ materials
It can be seen that the gO ₃ material has high electrical conductivity. Furthermore, according to FIG. 3, compared to the LaCrMgO ₃ material,
The thermal expansion curve of LaCaCrMgO ₃ material is stabilized ZrO
_It can be seen that it is close to ₂ .

In the present invention, C in the conductive layer is
The reason why the substitution amount of a or Mg is limited to the above-mentioned range is that high electric conductivity cannot be obtained when the substitution amount of Ca is less than 1 mol%,
This is because if the Mg substitution amount is less than 1%, the difference in thermal expansion with the solid electrolyte becomes large, and the conductive layer is peeled off. The upper limits of the substitution amounts of Mg and Ca are LaC, respectively.
This is because it is a solid solution limit to rO ₃ , and if the substitution amount exceeds the above range, a different phase other than the perovskite type crystal is precipitated and the electric conductivity is significantly reduced.

As described above, according to the fuel cell of the present invention, the conductive layer connecting the cells has high electric conductivity,
Since the coefficient of thermal expansion is similar to that of a solid electrolyte, the power generated by the power generation system can be efficiently extracted, and the separation of the conductive layer due to the difference in thermal expansion does not occur, resulting in stable power generation performance over a long period of time. Can be demonstrated.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 4 is a schematic view of an apparatus for manufacturing the fuel cell of the present invention. According to FIG. 4, the cylindrical substrate 1 serving as a support tube for the fuel cell is installed in the reaction chamber 6.
The cylindrical substrate 1 has a bottomed structure at one end, and is installed in the reaction chamber 6 with the bottomed part facing up. This cylindrical substrate 1 is
It is made of a porous material having a porosity of about 15 to 35%.
La as Ni-ZrO ₂ or as an air electrode
It is composed of MnO ₃ or LaCaMnO ₃ .

Further, the reaction chamber 6 is provided with a gas control device 7 for introducing a halogen-containing gas, a carrier gas and the like into the reaction chamber, and a gas introduction passage 8. A heater 9 is provided around the reaction chamber 6 and is controlled to heat the reaction chamber to a predetermined temperature. Further, in the reaction chamber 6, an evaporation source 10 containing a metal oxide for depositing a film having a desired composition is provided. The inside of the reaction chamber 6 is vertically divided into two parts by an evaporation source 10, and the evaporation source 10 is
A porous evaporation material supporting member 11 is screwed, and the evaporation source material is contained in the upper part thereof.

On the other hand, in the cylindrical substrate 1, the oxygen supply passage 1
The oxygen-containing gas is configured to be supplied from below via 2 Specifically, the oxygen-containing gas is water (H
H ₂ gas and Ar and He gas for diluting oxygen concentration are introduced into ₂ O) to form a mixed gas of H ₂ O water vapor, H ₂ gas and Ar gas.

As an embodiment of the present invention, a fuel cell in which a solid electrolyte membrane, a fuel electrode membrane, and a conductive film are formed on a porous cylindrical support tube that also serves as an air electrode is manufactured by using the above film forming apparatus. The method will be described. First, LaMnO ₃
A porous cylindrical support tube made of, for example, is prepared. Also,
Masking treatment is performed in advance on the conductive layer formation region of the support tube. On this surface, for example, a solid electrolyte membrane made of stabilized ZrO ₂ in which 8 mol% Y ₂ O ₃ is dissolved is formed. In this case, the evaporation source 10 is provided with a porous body made of ZrO ₂ containing 8 mol% Y ₂ O ₃ . On the other hand, a halogen gas such as HCl gas is supplied from the gas control device 7 through the gas introduction passage 8 at a flow rate of, for example, 0.5 ccm in the early stage of the reaction and 400 ccm in the latter stage of the reaction, and Ar gas as a carrier gas of the HCl gas at a flow rate of 1000 ccm. Is introduced into the reaction chamber 6. The halogenated gas introduced is the evaporation source 1
In contact with 0, a halogenated gas of Zr or Y is generated.
Then, the generated halogenated gas is, for example, H
Ar gas containing oxygen with e gas of 700 ccm is 50
On the surface of the cylindrical substrate 1 introduced at a flow rate of sccm, an oxygen-containing gas is reacted, and the cylindrical substrate 8 mol% Y ₂ O ₃ —Zr
A dense metal oxide solid solution film of O ₂ is obtained. At this time, the oxygen partial pressure near the surface of the cylindrical substrate 1 is set to 10 ⁻⁵ atm.

Next, NiO- is formed on the surface of the solid electrolyte membrane.
A fuel electrode made of stabilized ZrO ₂ (containing 8 mol% Y ₂ O ₃ ) is formed. Specifically, NiO and stabilized ZrO
₂ (containing 8 mol% Y ₂ O ₃ ) in a weight ratio of 8: 2 and a pure water containing a binder were mixed in a ratio of 4: 6.
Mix and stir so that the weight ratio becomes. After dipping and drying the cylindrical substrate 1 having the solid electrolyte membrane formed in this slurry,
Ni by heat treatment in an oxidizing atmosphere at 1400 ° C
A fuel electrode made of O-stabilized ZrO ₂ (containing 8 mol% Y ₂ O ₃ ) can be formed.

The masking portion is removed from the fuel cell obtained as described above, and conversely, the area where the fuel electrode and the like are formed is masked.

After that, a conductive layer is formed in the region which is not masked. According to the present invention, a material in which Ca and Mg are solid-dissolved in LaCrO ₃ is formed as the conductive layer formed here. The pressure inside the reaction chamber 6 is maintained at a predetermined temperature (for example, evaporation source 15
At 1250 ° C., and the vicinity of the cylindrical substrate 11 at 1300 ° C.), while adding HCl gas from the gas introduction path 7 to 0.1 to 1
Ar gas is introduced into the reaction chamber 6 at a flow rate of 00 ccm and at a flow rate of 5000 ccm as a carrier gas.
The HCl gas introduced from the introduction path 7 is (LaCa) Cr.
It reacts with the evaporation source 10 composed of O ₃ and La (MgCr) O ₃ to form LaCl ₃ , MgCl ₂ , CrCl ₂ , CaCl ₂
To produce a metal halide gas. By supplying this generated gas to the surface of the cylindrical substrate 1 and supplying an oxygen-containing gas consisting of H ₂ O, H ₂ and Ar gas for diluting the oxygen concentration from the inside of the cylindrical substrate 1 at a flow rate of 1000 ccm, Oxygen partial pressure near the surface of the substrate 1 is 10 ^-7 atm
And Then, the metal halide gas and the cylindrical substrate 1
By reacting with H ₂ and O ₂ which have permeated through the surface of the cylindrical substrate 1 to form a solid solution of La and Cr with dense Ca and Mg.
A conductive layer of O ₃ is produced.

The flow rate of the halogen-containing gas is 0.1-0.1%.
200 sccm, the temperature of the evaporation source 10 is 1200 to 140
It is desirable that the temperature of the cylindrical substrate 1 is 0 ° C. and 1200 to 1400 ° C., and that the pressure of the reaction chamber 6 is under reduced pressure, preferably 200 torr or less.

In the above embodiment, the conductive layer 5 was formed after the solid electrolyte layer 3 and the fuel electrode layer 4 were formed. However, as another example, the surface of the cylindrical substrate 1 other than the conductive layer 5 forming region is formed. Alternatively, the conductive layer 5 may be formed by the method described above after masking, and then the solid electrolyte layer 3 and the fuel electrode layer 4 may be sequentially formed by the method by masking the surface of the formed conductive layer.

According to the present invention, when the conductive layer 5 is formed, by changing the composition of the evaporation source, LaCrO ₃
On the other hand, several kinds of complex oxides having different substitution amounts of Mg and Ca as shown in Table 1 were prepared. With respect to each of the obtained composite oxides, the electrical conductivity under an oxygen partial pressure of 10 ⁻⁵ atm and the coefficient of thermal expansion at 1000 ° C. were measured. Of this,
FIG. 2 shows the relationship between the oxygen partial pressure and the electrical conductivity of Samples No. 1, 1, 3 and 4, and Samples No. 1, 4, and 8 mol% Y
The relationship between the temperature and the coefficient of thermal expansion of ₂ O ₃ -containing ZrO ₂ is shown in FIG.

[0021]

[Table 1]

As shown in Table 1, FIG. 2 and FIG. 3, the conductive layer having the composition of the present invention in which Ca and Mg were substituted for LaCrO ₃ within the scope of the present invention as the conductive layer was compared with the conventional product. As a result, it shows a high electric conductivity, and its thermal expansion coefficient is close to that of stabilized ZrO ₂ which is a solid electrolyte. In addition, when the Ca substitution amount exceeds 30% and the Mg substitution amount exceeds 20%, a different phase is generated and the electric conductivity is significantly lowered.

[0023]

As described above in detail, according to the present invention, when a conductive layer for connecting cells of a cylindrical solid oxide fuel cell is formed by vapor deposition, LaC is formed.
By forming a composite oxide in which Mg and Ca are substituted for rO ₃ as a conductive layer, the electrical conductivity of the conductive layer itself can be increased and the coefficient of thermal expansion with the solid electrolyte can be approximated. It is possible to improve the reliability of the electrical connection between the cells, suppress the occurrence of peeling of the conductive layer, and provide stable power generation performance for a long period of time.

[Brief description of drawings]

FIG. 1 is a diagram showing the structure of a fuel cell of the present invention.

FIG. 2 is a diagram showing a relationship between oxygen partial pressure and electric conductivity of various composite oxides.

FIG. 3 is a diagram showing the relationship between the temperature and the coefficient of thermal expansion of various composite oxides.

FIG. 4 is a schematic diagram of a film forming apparatus used in an example of the present invention.

[Explanation of symbols]

 1 Cylindrical Support Tube (Substrate) 2 Air Electrode Layer 3 Solid Electrolyte Layer 4 Fuel Electrode Layer 5 Conductive Layer 6 Reaction Chamber 7 Gas Control Device 8 Gas Introducing Path 9 Heating Heater 10 Evaporation Source 11 Evaporative Substance Supporting Member 12 Oxygen Supply Path

Claims (1)

[Claims] 1. A fuel cell comprising a solid electrolyte layer and a fuel electrode layer on the surface of a cylindrical air electrode, or an air electrode layer, a solid electrolyte layer and a fuel electrode layer on the surface of a cylindrical support tube. In the method for producing a solid oxide fuel cell in which a conductive layer is coated by a vapor phase synthesis method so as to be electrically connected to either one of the air electrode layer and the fuel electrode layer of the cell, the conductive layer is a metal. It is composed of a perovskite-type composite oxide containing La, Cr, Mg and Ca as main components as elements, and the amount of Ca substitution with respect to La is 1 to 30%, C
The method for producing a solid oxide fuel cell, wherein the substitution amount of Mg with respect to r is 1 to 20%.