JPH07201339A - Separator for solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To provide a thermal expansion characteristic almost equal to that of a solid electrolyte of a fuel cell while having good conductivity excellent in heat resistance and corrosion resistance by providing high density. CONSTITUTION:A device is constituted of a composite comprising heat resistant metal (A) containing at least one kind of heat resistant alloy selected from a cobalt group alloy and iron group alloy and ceramics (B), to provide this heat resistant metal (A) as dispersoid and further the ceramics (B) as matrix, and also ratio of the heat resistant metal to the ceramics, occupying a sectional area, is set to 1:2 to 2:1. Alumina, silica (cristobalite), spinel, etc., are preferable as ceramics. In this way, in addition to reducing a molding cost excellent in moldability capable of performing injection molding, while maintaining conductivity, a thermal expansion characteristic of linear expansion coefficient or the like can be controlled, and each member can be firmly connected in a fuel cell, to improve stability of gas seal and to enable a cell characteristic to improve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel solid oxide fuel cell separator. More specifically, the present invention has high compactness, excellent heat resistance and corrosion resistance, good electrical conductivity, injection moldability, excellent moldability, and low molding cost. While maintaining conductivity, it is possible to control thermal expansion characteristics such as linear expansion coefficient, and since the thermal expansion characteristics can be made substantially equal to that of the solid electrolyte of the fuel cell, it is possible to firmly join each member in the fuel cell, The present invention relates to a solid oxide fuel cell separator capable of improving gas sealing stability and cell characteristics.

[0002]

2. Description of the Related Art A fuel cell uses a combustible chemical substance such as hydrogen, carbon monoxide, or hydrocarbon or a fuel containing the same as an active material and causes an oxidation reaction of the chemical substance or the fuel to be performed electrochemically. A battery that directly converts energy changes in the oxidation process into electric energy, and is expected to have high energy conversion efficiency.

Among them, particularly high efficiency can be expected, and in recent years, the third generation solid oxide fuel cell following the first generation phosphoric acid type and the second generation molten carbonate type, especially the flat plate having a high degree of integration The type is drawing attention. FIG. 1 is a perspective explanatory view of an example of this flat plate type three-stage series cell solid electrolyte fuel cell, in which a cathode 12 and an anode 13 are integrally formed on the upper surface and the lower surface of each solid electrolyte plate 11. The three-layered structure plate is formed by joining and integrating via a separator 14, and external terminals 15 and 16 are provided at both ends, respectively. Similarly, by increasing or decreasing the number of stacked unit cells, a multi-stage series type battery including a large number of cells is formed. The separator 14 electrically connects the electrodes of adjacent cells, and has a groove 14a on the upper surface and a groove 14 on the lower surface.
b is formed to form each gas passage on the anode side and the cathode side of the adjacent cells.

However, in such a flat plate type, the separator usually has a current collecting function, which is also called an interconnector, and is formed of a metal, such as a heat-resistant alloy, which is suitable for the collector. On the other hand, since the solid electrolyte is formed of ceramics mainly composed of zirconia, a thermal expansion coefficient such as a linear expansion coefficient is generated between them due to a change in environmental conditions over a high battery operating temperature of 800 to 1000 ° C. Since there is a considerable difference in expansion characteristics, distortion due to stress occurs between the three-layer structure plate and the separator, and further, the joint strength decreases, cracks occur, and there is a gap in the joint, causing gas leakage. The fuel such as hydrogen and the oxidant gas such as air may cross-leak to impair the function of the active material.

On the other hand, a lanthanum chromite separator is also known, but since it is a composite oxide ceramic, its electrical conductivity is not sufficiently satisfactory, and it has a drawback that it is easily deteriorated in a reducing atmosphere. . Also,
A cylindrical type having a thin film of an aluminum / alumina-based separator has also been proposed, but this has a drawback that it requires an antioxidant coat.

[0006]

DISCLOSURE OF THE INVENTION The present inventors
In order to improve the drawbacks of such a conventional separator,
Consists of a sintered body obtained by firing a refractory metal such as nickel, cobalt, iron, a nickel-based alloy, a cobalt-based alloy, or an iron-based alloy and a heat-resistant inorganic compound in a non-oxidizing atmosphere or in a vacuum. The proposed fuel cell separator has been proposed (Japanese Patent Application No. 3-212978, Japanese Patent Application No. 3-212).
No. 980, Japanese Patent Application No. 3-2122984, Japanese Patent Application No. 3-21
No. 3087), which has excellent heat resistance and corrosion resistance, can improve the stability of gas sealing, and does not require an antioxidant film, but is an important physical property of a fuel cell separator. Not only is the conductivity not fully satisfactory, but there is also the problem that the thermal expansion characteristics differ from those of solid electrolytes such as zirconia, and strain due to stress cannot be avoided. Under such circumstances, the present invention has been made for the purpose of providing a separator for a solid oxide fuel cell which has a sufficient electric conductivity and has a thermal expansion characteristic which is almost the same as that of the solid electrolyte. .

[0007]

The present inventors have conducted various studies to develop a separator having the above-mentioned preferable properties, and as a result, have made a heat-resistant metal such as cermet constituting a separator as previously proposed. -The structure of the ceramic composite has a great influence on the electrical conductivity and thermal expansion characteristics, and further, the ceramic in the composite is used as a matrix, the refractory metal is a dispersoid, and the proportion of the ceramic and the refractory metal in the cross-sectional area is It was found that the object can be achieved by specifying the above, and the present invention has been completed based on this finding.

That is, the present invention provides (A) a heat-resistant metal containing at least one heat-resistant alloy selected from nickel, cobalt, iron, nickel-base alloys, cobalt-base alloys and iron-base alloys, and (B) The heat-resistant metal (A) is present as a dispersoid and the ceramic (B) is present as a matrix, and the ratio of the heat-resistant metal to the ceramic in the cross-sectional area is 1: 2. The solid electrolyte fuel cell separator is characterized by having a ratio of ˜2: 1.

In the present invention, the refractory metal which is one of the constituents of the composite contains at least one refractory alloy selected from nickel-base alloys, cobalt-base alloys and iron-base alloys. However, these heat-resistant alloys may be used alone, but at least one metal selected from nickel, cobalt, and iron may be further included.

Examples of the nickel alloy include Ni-Cr alloys, Ni-Cr-Fe alloys, Ni-Cr-Mo alloys, Ni-Cr-Mo-Co alloys, and other Ni-Cr alloys.
-Mo-Fe based alloys can be mentioned, and among them, Ni-Cr based alloys are particularly preferable. These may be used alone or in combination of two or more.
A typical commercially available product is INCONEL All
oy 600,601,617,625,690, X-
750,751, NIMONIC Alloy 75,8
0A, 90, INCO Alloy HX, UHM and the like.

The cobalt-based alloy is Co-C.
Examples include r-based alloys, Co-Cr-Fe-based alloys, Co-Cr-W-based alloys, Co-Cr-Ni-W-based alloys, and among these, Co-Cr-based alloys are particularly preferable. These may be used alone or in combination of two or more. A typical commercially available product is Haines Alloy N.
o. 25, Haines Alloy No. 188, Mitsubishi Stellite No. 6B, UMCo50, etc.

Fe-Ni-C is an iron-based alloy.
r-based alloy, Fe-Cr-Ni-based alloy, Fe-Cr-Ni
-Co alloys, etc., among which Fe-N
i-Cr alloys are preferred. These may be used alone or in combination of two or more. A typical commercially available product is INCOLOY Alloy80.
0,800H (T), 802, INCO Alloy
330, etc.

The ceramic of the other component constituting the composite is not particularly limited as long as it is heat resistant, and for example, both conductive and non-conductive ceramics can be used. Examples of conductive materials include conductive ceramics of rare earth type, stannic oxide, indium oxide, silicon carbide, zinc oxide and the like.

Non-conductive materials include carbide-based, oxide-based, and nitride-based ceramics such as alumina, silica, titania, and silicon nitride. Further, a composite ceramic such as mullite, spinel, cordierite may be used. These ceramics may be used alone or in combination of two or more, and among them, alumina, silica (cristobalite), spinel and the like are particularly preferable.

As the ceramics, a heat-resistant alloy usually has a coefficient of thermal expansion of 13 to 16 × 10 ⁻⁶ (K ⁻¹ ), so that the coefficient of thermal expansion of the separator is 10 × 10 ⁻⁶ (the coefficient of thermal expansion of the zirconia-based solid electrolyte). to match the K ^-1) is is preferred coefficient of thermal expansion ^{5~9 × 10 -6 (K -1)} . From this point, the ceramic is preferably alumina, silica (cristobalite), spinel, or the like.

In the separator of the present invention, the refractory metal (A) in the composite is present as a dispersoid, the ceramics (B) is present as a matrix, and the refractory metal (A) and the ceramics in the cross-sectional area are present. It is important that the ratio with (B) is in the range of 1: 2 to 2: 1. By taking such an existence form and a ratio in the cross-sectional area, it is possible to easily give a linear expansion coefficient almost equal to that of a solid electrolyte made of a commonly used zirconia-based material.
It becomes possible to have a high electric conductivity of 0 Ω ⁻¹ cm ⁻¹ or more. Particularly preferably, a nickel-base alloy-alumina composite having a ratio of nickel-base alloy to alumina in the cross-sectional area in the range of 2: 3 to 6: 5 is used.

To prepare the composite material constituting the separator of the present invention, first, the refractory metal and the ceramic or the compound capable of forming the ceramic are preferably in powder form,
For example, it is important to completely mix and disperse the powder in the form of powder having a particle size of 0.05 to 500 μm, and it is preferable that the resulting mixture is prepared so as not to spontaneously separate even when left standing for several hours. In the case of powder for cold forming such as CIP, dry granulation is preferable, and in the case of dispersion liquid for slurry forming such as casting, polycarboxylic acid is added to improve dispersibility. It is preferable to add a dispersant such as an acid salt type, an amine type nitrogen-containing alcohol type alcohol, an alcohol type or a mannuronanate type to make a uniform slurry.

The mixture thus obtained is subjected to pressure molding,
For example, after cold isostatic pressing, hot isostatic pressing, slurry, etc., in a temperature range in which ceramics sinter and the heat resistant alloy does not melt, in a non-oxidizing atmosphere, for example, in a reducing atmosphere or under a non-oxidizing atmosphere. Firing is performed in an active gas atmosphere or in vacuum. When firing in a reducing atmosphere, the hydrogen concentration in the atmosphere is not particularly limited, but preferably about 1-10%.
The firing temperature is preferably in the range of 1100 to 1500 ° C. Since the sinterability of ceramics also depends on the particle size of the powder, it is possible to improve the sinterability by using a relatively fine primary particle size of 0.05 to 5 μm. As the heat-resistant alloy, one having a relatively large particle diameter of 1 to 500 μm is usually used. In this way, it is possible to prepare a composite body in which the ceramic is used as the matrix and the refractory metal is used as the dispersoid.

Next, a solid oxide fuel cell using the separator of the present invention will be described. First, each member will be described. The solid electrolyte is not particularly limited as long as it has oxygen conductivity, and examples thereof include known solid electrolytes such as yttria-stabilized zirconia (YSZ) and calcia-stabilized zirconia (CSZ). Is formed in a plate shape.

Since the cathode is on the side of an oxidant gas passage such as oxygen or air, it is formed of a porous material so as to be gas permeable by using a conductive material having a corrosion resistance against the oxidant gas at a high temperature. For example, a conductive complex oxide powder such as La _x Sr _1-x MnO ₃ is applied. As the coating method, a brush coating method, a screen printing method or the like is used.
In addition, as a method for forming the porous film, a CVD method, a plasma CVD method, a sputtering method, a thermal spraying method, or the like is used.

Since the anode is on the side of the fuel gas passage such as hydrogen, a conductive material resistant to the fuel gas at high temperature,
For example, Ni / ZrO ₂ cermet or the like is formed into a porous shape so as to have gas permeability. Further, if the cathode and the anode can be formed as a porous plate, the porous plate can be used by adhering and integrating with the solid electrolyte.

As described above, the solid electrolyte plate on which both electrodes are integrally formed is joined and integrated through the separators, and external terminals are provided at both ends to form a multi-stage series type battery composed of a large number of cells. It is formed. As shown in FIG. 1, the separator 14 electrically connects the electrodes of adjacent cells, and has grooves 14a and 14b formed on both surfaces to form gas passages on the anode side and the cathode side of the adjacent cells. ing. The grooves 14a and 14b are not particularly limited as long as they can supply an oxidant gas typified by a fuel gas such as hydrogen and an oxygen-containing gas such as air, and the shape, arrangement, etc. can be appropriately selected. As shown in FIG. 1, the grooves 14a and 14b are arranged at right angles to each other. With this arrangement, after the cells are integrated, the fuel gas inlet and outlet and the oxidant gas inlet and outlet can be placed on the same plane, which simplifies the configuration of the gas supply / exhaust system as an integrated cell. And can be easy.

When the solid electrolyte plate 11, the separator 14, and the external terminals 15 and 16 are integrated and assembled, the electrodes, that is, the cathodes 1 arranged on both surfaces of the solid electrolyte plate 11.
2, the anode 13 and the separator 14 or the external terminal 15,
It is necessary to seal so that there is no gas leak between 16 and 16. For this purpose, for example, they may be bonded with a zirconia-based inorganic adhesive and sealed with a suitable glass paste having a softening point of about 800 ° C., for example. This glass paste is used at a battery operating temperature (e.g.
It softens moderately at 00 ° C) and seals the gas.

In order to supply the fuel gas and the oxidant gas to the cell thus assembled, each groove 14a, 14 of the cell is provided.
Since both ends of b are arranged on the same plane, the manifold may be attached to those planes.
FIG. 2 shows an example of mounting the manifold. The integrated battery main body 21 assembled as described above is inserted into the pipe of the cylindrical manifold 22 and arranged so that the outlets of the grooves 14a and 14b face the pipe wall. If the connection points (four points) between the battery body 21 and the manifold 22 are gas-sealed, the groove 14
Both ends of a and 14b are manifold 2 respectively.
It corresponds to the four gas passages 23 to 26 formed by the two cylindrical walls and the battery body 21.

[0025]

EFFECT OF THE INVENTION The separator of the present invention has a high density, excellent heat resistance and corrosion resistance, good electrical conductivity of 10 Ω ⁻¹ cm ⁻¹ or more, and is injection moldable and excellent in moldability. In addition to reducing the molding cost, the refractory metal has a structure in which the dispersoid is the ceramic and the ceramic is the matrix, so that it is possible to control the thermal expansion characteristics such as the linear expansion coefficient while maintaining the electrical conductivity. By setting the cross-sectional area ratio of the refractory metal and the ceramics in the structure within a predetermined range, the thermal expansion characteristics of the solid electrolyte of the fuel cell, for example, the thermal expansion coefficient of about 8.5 to 12 × 10 ⁻⁶ (K ⁻¹ ) and the zirconia system are obtained. Since it can be made almost equal to that of the solid electrolyte,
In a fuel cell incorporating the separator, each member can be firmly joined, the stability of gas sealing can be improved, and the cell characteristics can be improved, and the shape and structure of the fuel cell can be a bulk body. As described above, the remarkable effect that the oxidation does not spread over the whole is exhibited.

[0026]

The present invention will be described in more detail with reference to Examples.

Production Examples 1 to 4 Alumina powder of each particle size shown in Table 1 and powder of nickel-based alloy INCONEL Alloy 600 (hereinafter referred to as alloy), 1% by weight of the total amount of these powders, and an appropriate amount of the dispersant. Water was thoroughly stirred to prepare a slurry in which these powders were thoroughly mixed and dispersed. This slurry is so stable that the alumina and the alloy do not separate for several hours after standing still.
This slurry was cast into a porous mold at a pressure of ² to 3 kg / cm ² to produce a green molded body. After drying this green compact, it was fired at 1370 to 1390 ° C. in a nitrogen atmosphere to prepare four types of composites. In these four types of composites, the alloy is present as a dispersoid and the alumina is present as a matrix. Scanning electron microscope (SEM) photographs of the cross sections of the crystal structures of these four types of composites are shown in FIGS. 3 to 6. Table 1 shows the cross-sectional area ratio of the alloy to the ceramics of these composites, the electric conductivity at room temperature, the coefficient of thermal expansion, and the relative density (measured density relative to the theoretical density).

[0028]

[Table 1]

Comparative Production Example 1 Nickel-based alloy (INCONEL A) having a particle size of 3 to 7 μm
4 parts by volume of powder and a particle size of 0.2 to 0.5
After mixing 1 part by volume of alumina powder having a diameter of μm with a ball mill, cold isostatic pressing was performed at a molding pressure of 2000 kg / cm ² . The obtained molded body was placed in a nitrogen atmosphere containing 5% hydrogen 13
It was fired at 70 ° C. to prepare a composite consisting of an alloy and alumina, the alloy being a matrix. This product had a large coefficient of thermal expansion of 14 × 10 ⁻⁶ (K ⁻¹ ) and could not be used for a fuel cell separator.

Comparative Production Example 2 A nickel-base alloy having a particle size of 500 μm was used, and a composite having a refractory metal particle size of 1 mm or more and 50% was produced in the same manner as in Production Example 1. Since this product has a low electric conductivity of 10 Ω ⁻¹ cm ⁻¹ or less, it cannot be used as a fuel cell separator.

Example 1 A solid oxide fuel cell of a three-stage series cell was prepared as follows according to the integration mode shown in FIG. First, the separator 1
4, the external terminals 15 and 16 were produced using the composite body obtained in Production Example 1. These separator 14 and external terminal 1
In all, 5 and 16 are grooves 14a, 14b, 15 having a groove width of 2 mm and a groove depth of 2 mm on a square plate of 50 × 50 × 5 mm.
b, 16a are formed. In the separator 14, the directions of the grooves 14a and 14b formed on both surfaces are orthogonal to each other.

Further, as the solid electrolyte plate 11, a 50 × 50 × 0.2 mm plate made of partially stabilized zirconia which is zirconia added with 3 mol% of yttria was used. Then, La ₀ . ₉ Sr ₀ . ₁ MnO
0.3m thick by brush coating ₃ powders (average particle size 5μm)
m on the hydrogen passage side to form Ni / Z
A cermet mixed powder of rO ₂ (10/1 weight ratio) was applied to a thickness of 0.3 mm by a brush coating method to form an anode 13. The solid electrolyte plate 11 provided with this electrode, the separator 14, and the external terminals 15 and 16 are integrated as shown in FIG. 1, and the solid electrolyte plate with the electrode and the separator 14 are bonded with a zirconia-based inorganic adhesive to soften them. A glass paste having a point of about 800 ° C. was applied and gas-sealed. This glass paste softens at the operating temperature of the battery and seals the gas.

The battery main bodies 21 thus integrated were housed in the cylindrical alumina manifold 22 shown in FIG. The contact portion between the manifold 22 and the battery body 21 was coated with glass paste and gas-sealed. Platinum lead wires 27 and 28 were inserted into the external terminals 15 and 16 for electrical connection.

Each fuel cell produced in this way was heated. That is, the solvent of the glass paste was evaporated by heating from room temperature to 150 ° C at 1 ° C / min. 150-3
The temperature was raised up to 50 ° C at 5 ° C / min. At 350 ° C. or higher, nitrogen gas was flown on the hydrogen passage side to prevent oxidation of the anode, and the temperature was raised to 1000 ° C. at 5 ° C./min. Then, the temperature was maintained at 1000 ° C., hydrogen was flown to the anode side and oxygen was flown to the cathode side to start power generation. Open voltage is 3.3V
Met. The discharge characteristics are shown in Table 2. The gas cross leak was 2% or less for hydrogen.

Examples 2 to 4 Example 1 was the same as Example 1 except that the separators and the external terminals were replaced by the separators and the external terminals produced by using the composites obtained in Production Examples 2 to 4, respectively. Similarly, each fuel cell was produced and generated. Table 2 shows each discharge characteristic. The gas cross leak was 2% or less for hydrogen in all cases.

[0036]

[Table 2]

[Brief description of drawings]

FIG. 1 is a perspective explanatory view of an example of a solid oxide fuel cell body of a flat plate type three-stage series cell using a separator of the present invention.

FIG. 2 is an explanatory view of a fuel cell which is a completed product by accommodating the cell body of FIG. 1 in a manifold.

FIG. 3 is a scanning electron micrograph of a cross section of the crystal structure of the composite obtained in Production Example 1.

FIG. 4 is a scanning electron micrograph of a cross section of a crystal structure of the composite obtained in Production Example 2.

5 is a scanning electron micrograph of a cross section of the crystal structure of the composite obtained in Production Example 3. FIG.

FIG. 6 is a scanning electron micrograph of a cross section of the crystal structure of the composite obtained in Production Example 4.

[Explanation of symbols]

 11 Solid Electrolyte Plate 12 Cathode 13 Anode 14 Separator 14a, 14b Grooves 15, 16 External Terminal 21 Battery Main Body 22 Manifold

Claims (1)

[Claims] 1. A composite comprising (A) a heat-resistant metal containing at least one heat-resistant alloy selected from nickel-based alloys, cobalt-based alloys and iron-based alloys, and (B) ceramics, The refractory metal (A) is present as a dispersoid, the ceramics (B) is present as a matrix, and the ratio of the refractory metal to the ceramics in the cross-sectional area is 1: 2 to 2: 1. Solid electrolyte fuel cell separator.