JP3101358B2 - Solid oxide fuel cell separator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel separator for a solid oxide fuel cell. More specifically, in the present invention, the sintered body constituting the separator itself has a high density, is excellent in heat resistance and corrosion resistance, has a good electric conductivity, and is injection moldable and has excellent moldability. In addition to reducing the molding cost, by appropriately changing the ratio between the metal material and the inorganic compound, it is possible to control the thermal expansion characteristics such as the coefficient of linear expansion while maintaining the electrical conductivity. Enables strong joining of battery components,
The present invention relates to a solid oxide fuel cell separator capable of improving the stability of gas sealing.

[0002]

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

[0003] In particular, a particularly high efficiency can be expected in recent years. In recent years, a third-generation solid electrolyte fuel cell has been developed following a first-generation phosphoric acid type and a second-generation molten carbonate type. The type thing is attracting attention. FIG. 4 is a perspective explanatory view of one example of the flat-plate type three-stage series-cell solid oxide fuel cell, in which a cathode 42 and an anode 43 are integrally formed on the upper and lower surfaces of each solid electrolyte plate 41, respectively. The three-layer structure plates are joined and integrated via a separator 44, and external terminals 45 and 46 are provided at both ends, respectively. Similarly, by increasing or decreasing the number of stacked unit cells, a multi-stage series battery including a large number of cells is formed. The separator 44 electrically connects the electrodes of adjacent cells, and has a groove 44a on the upper surface and a groove 44a on the lower surface.
b is formed to form each gas passage on the anode side and cathode side of the adjacent cell.

[0004] However, such a flat type usually has a current collecting function so that the separator is also called an interconnector, and is formed of a metal such as a heat-resistant alloy suitable for the function. On the other hand, since the solid electrolyte is formed of a ceramic mainly composed of zirconia, the solid electrolyte has a thermal expansion coefficient such as a linear expansion coefficient due to a change in environmental conditions ranging from a high battery operating temperature of 800 to 1000 ° C. Since there is a considerable difference in the expansion characteristics, distortion occurs due to stress between the three-layer structure plate and the separator, and further, the joint strength is reduced, cracks are generated, and a gap is generated in the joint, and gas leaks. In addition, a fuel such as hydrogen and an oxidizing gas such as air may cross-leak, thereby impairing the function as an active material.

On the other hand, a lanthanum chromite (magnesium-doped, composite material of LaCrO ₃ and nickel aluminide) separator is also known, but since this is a composite oxide ceramic, its electrical conductivity is low. It is not satisfactory enough and has a disadvantage that it is easily deteriorated in a reducing atmosphere. Further, a cylindrical type in which a nickel-aluminum / alumina-based separator is formed into a thin film has been proposed, but this has a disadvantage that an antioxidant coat is required.

[0006]

SUMMARY OF THE INVENTION The present invention overcomes such disadvantages of the conventional separator, and the sintered body constituting the separator itself has high density, excellent heat resistance and corrosion resistance, and In addition to having excellent electrical conductivity and excellent moldability, it is possible to control thermal expansion characteristics while maintaining electrical conductivity, improve the stability of gas sealing, and do not require an antioxidant film The object of the present invention is to provide a separator for a solid oxide fuel cell.

[0007]

The present inventors have conducted various studies to develop a separator having the above-mentioned preferable properties, and as a result, have found that a nickel-based alloy or a mixture thereof with a specific metal and / or alloy can be used. The present inventors have found that a separator composed of a sintered body obtained by firing a specific inorganic compound under a specific atmosphere is suitable for the purpose, and have completed the present invention based on this finding.

That is, the present invention provides a nickel-based alloy or a mixture thereof with at least one selected from nickel, cobalt, a cobalt-based alloy, iron and an iron-based alloy;
Alumina, silica, titania, indium oxide, stannic oxide, at least one inorganic compound selected from silicon carbide and silicon nitride or a compound capable of forming the same, in a non-oxidizing atmosphere or in a vacuum An object of the present invention is to provide a separator for a solid oxide fuel cell, comprising a sintered body obtained by firing.

The sintered body constituting the separator of the present invention comprises:
A nickel-based alloy or a mixture thereof (hereinafter referred to as a metal material) with at least one selected from nickel, cobalt, a cobalt-based alloy, iron and an iron-based alloy, and the inorganic compound or a compound capable of forming the same Are preferably mixed in powder form, and then calcined in a non-oxidizing atmosphere, for example, in a reducing atmosphere or an inert gas atmosphere, or in a vacuum. When the metal material is the above-mentioned mixture of a nickel alloy and another metal and / or alloy, it is preferable to use a nickel alloy or a nickel metal as a main component because of its excellent heat resistance and corrosion resistance.

The nickel alloy includes Ni-Cr alloy, Ni-Cr-Fe alloy, Ni-Cr-Mo alloy, Ni-Cr-Mo-Co alloy, and other Ni-Cr alloys.
-Mo-Fe alloys and the like, among which Ni-Cr 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
OA, 90, INCO Alloy HX, UHM, and the like.

As described above, when a cobalt-based alloy or an iron-based alloy is used together with a nickel-based alloy, the cobalt-based alloy may be a Co—Cr alloy, a Co—Cr—Fe alloy, or a Co—Cr—W alloy. Alloy, a Co-Cr-Ni-W alloy, etc., among which a Co-Cr alloy is particularly preferable. These may be used alone or in combination of two or more. Typical commercial products include Haines Alloy No. 25, Haynes Alloy N
o. 188, Mitsubishi Stellite No. 6B, UMCo50
and so on. Also, as an iron-based alloy, Fe-Ni-Cr
Alloy, Fe-Cr-Ni alloy, Fe-Cr-Ni-
Co-based alloys, among which Fe-Ni
-Cr-based alloys are preferred. These may be used alone or in combination of two or more. A typical commercially available product is INCOLOYAlloy 80
0, 800H (T), 802, INCO Alloy
330 and the like.

The inorganic compound used together with these metal materials is at least one selected from alumina, silica, titania, indium oxide, stannic oxide, silicon carbide and silicon nitride. The inorganic compounds may be used alone or in combination of two or more. Among them, alumina is particularly preferred.

These raw materials usually have a particle size of 0.05 to 500.
The powder is mixed in the form of a μm powder, and is subjected to pressure molding by a cold isostatic press or a hot isostatic press. Then, under a non-oxidizing atmosphere, such as a reducing atmosphere or an inert gas atmosphere,
Alternatively, firing is performed in a vacuum. When firing in a reducing atmosphere, the hydrogen concentration in the atmosphere is not particularly limited, but preferably the hydrogen concentration is about 1 to 10%. The firing temperature is preferably in the range of 1100 to 1400 ° C.

In the separator of the present invention, by appropriately adjusting the ratio of the metal material to the inorganic compound, for example, the volume ratio, it is easy to have a linear expansion coefficient substantially equal to that of a solid electrolyte made of a common zirconia material. Can, 1
In addition to being able to firmly join each member that can sufficiently withstand fluctuations in environmental conditions up to high temperatures up to around 000 ° C., the characteristics of a metal material originally having excellent electrical conductivity are sufficiently practical as a separator. It can be left in the electric conductivity region if the ratio of the inorganic compound is up to a certain level, for example, up to about 75% by volume in the case of alumina. Particularly preferably, the metal material is a nickel-based alloy and the inorganic material is alumina, and the volume ratio of both is nickel-based alloy: alumina in the range of 80:20 to 25:75.

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. In the case of a plate-like body, its thickness is usually 0.05 to 0.5.
3 mm, preferably in the range of 0.08 to 0.25 mm. If the thickness is less than 0.05 mm, the strength is reduced, and if it exceeds 0.3 mm, the current path becomes too long, which is not preferable.

Since the cathode is on the side of an oxidizing gas passage such as oxygen or air, the cathode is formed in a porous shape using a conductive material having corrosion resistance to the oxidizing gas at a high temperature. For example, La
applying a conductive complex oxide powders such as _x Sr _1-x MnO _3. 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. Further, the cathode is formed so as to be porous so as to be gas permeable.

Since the anode is on the side of a fuel gas passage such as hydrogen, a conductive material resistant to fuel gas at high temperatures,
For example, Ni / ZrO ₂ cermet or the like is formed in a porous shape. The anode is also made gas permeable. Further, as long as the cathode and the anode can be made of a porous plate, the porous plate can be attached to and integrated with a solid electrolyte.

The solid electrolyte plate having both electrodes integrally formed on both sides is joined and integrated via a separator, and external terminals are provided at both ends, thereby providing a multi-stage series battery comprising a large number of cells. It is formed. As shown in FIG. 4, the separator 44 electrically connects the electrodes of the adjacent cells, and has grooves 44a and 44b formed on both surfaces to form respective gas passages on the anode side and the cathode side of the adjacent cells. ing. The grooves 44a and 44b are not particularly limited as long as they can supply an oxidizing gas typified by a fuel gas such as hydrogen and an oxygen-containing gas such as air, and the shape and arrangement can be appropriately selected. As shown in FIG. 4, the grooves 44a and 44b are arranged at right angles to each other. With this arrangement, after the cells are integrated, the inlet and outlet of the fuel gas and the inlet and outlet of the oxidizing gas can be respectively arranged on the same surface, and the configuration of the gas supply / discharge system as an integrated cell can be simplified. And easy.

When the solid electrolyte plate 41, the separator 44, and the external terminals 45 and 46 are integrated and assembled, the electrodes, ie, the cathodes 4 provided on both surfaces of the solid electrolyte plate 41 are assembled.
2, anode 43 and separator 44 or external terminal 45,
It is necessary to seal so that there is no gas leakage between the gas and the gas. For this purpose, for example, it is sufficient to bond with a zirconia-based inorganic adhesive and seal with a glass paste having a softening point of about 800 ° C. This glass paste moderately softens at the operating temperature of the battery (900 to 1000 ° C.) and seals the gas.

In order to supply the fuel gas and the oxidizing gas to the battery assembled in this manner, each of the grooves 44a, 44 of the battery is required.
Since both ends of b are arranged on the same plane, a manifold may be attached to those planes.
FIG. 5 shows an example of mounting the manifold. The integrated battery body 51 assembled as described above is inserted into the tube of the cylindrical manifold 52, and is arranged such that the outlets of the grooves 44a and 44b face the tube wall. If the connection points (four places) between the battery body 51 and the manifold 52 are gas-sealed, the grooves 44
a and 44b each have a manifold 5
It corresponds to four gas passages 53 to 56 formed by the two cylindrical walls and the battery body 51.

[0021]

According to the separator of the present invention, the sintered body constituting the separator has high density, is excellent in heat resistance and corrosion resistance, has good electric conductivity, and is injection moldable and has good moldability. It is possible to control the thermal expansion characteristics such as the coefficient of linear expansion while maintaining the electrical conductivity by appropriately changing the ratio of the metal material and the inorganic compound, in addition to being able to excellently reduce the molding cost. By optimizing the ratio, it is possible to make the coefficient of linear expansion approximately equal to that of the zirconia-based material used for the solid electrolyte of the fuel cell. The stability of gas sealing can be improved, and the shape and structure can be made into a bulk body. Achieve the effect.

[0022]

Next, the present invention will be described in more detail by way of examples. Production Example 1 After mixing a nickel-based alloy (trade name: Inconel Alloy600, manufactured by INCO) (hereinafter referred to as an alloy) powder having a particle size of 3 to 7 μm and alumina powder having a particle size of 0.2 to 0.5 μm by a ball mill, Molding pressure 2000kg / c
Cold isostatic pressing at m ² . The obtained molded body was fired at 1350 ° C. in a nitrogen atmosphere containing 5% hydrogen to produce a sintered body. This sintered body exhibited a compactness of 90% or more with respect to the theoretical density in the range of the alloy / alumina volume ratio of 2/8 to 9/1.

Next, various physical properties of the sintered body were examined as follows. FIG. 1 is a graph showing the relationship between the alloy content and the electrical conductivity under a reducing atmosphere at 1000 ° C.
This shows that sufficient electrical conductivity can be obtained when the alloy content is about 25% by volume or more, that is, when the alumina content is less than about 75% by volume.

FIG. 2 shows an alloy / alumina volume ratio of 4 /
In the case of No. 6, the relationship between the electric conductivity and the temperature, specifically, the relationship between the electric conductivity and the reciprocal of the absolute temperature, which is 1000 times, is shown in a graph. From this, it can be seen that the electrical conductivity decreases as the temperature rises and shows temperature dependency, and the sintered body has properties as a metal. From this, it is considered that a path of electric conduction is formed by contact between the particles of the alloy. The electric conductivity of the sintered body having a volume ratio of alloy / alumina of 4/6 is 10
880 Scm ⁻¹ at 00 ° C.

FIG. 3 shows the alloy / alumina volume ratio and 1
The relationship with the linear expansion coefficient at 000 ° C. is shown in a graph.
From this, the linear expansion coefficient is 1 at an alloy / alumina volume ratio of 4/6.
It can be seen that the value is 0.5 × 10 ⁻⁶ ° C. ⁻¹ which is close to that of zirconia.

Production Example 2 Except that 30 parts by volume of the nickel-based alloy and 10 parts by volume of the cobalt-based alloy (Haines Alloy No. 25) of Production Example 1 were used as the metal materials, and the amount of alumina used was 60 parts by volume. A sintered body was produced in the same manner as in Production Example 1. Its electrical conductivity and coefficient of linear expansion at 1000 ° C. were 900 Scm ⁻¹ and 10.5 × 10 ⁻⁶ ° C. ⁻¹ , respectively.

Production Example 3 An iron-based alloy (Incoloy 8) was used instead of the cobalt-based alloy.
A sintered body was produced in the same manner as in Production Example 2 except that Example No. 00) was used. Its electrical conductivity and linear expansion coefficient at 1000 ° C. were 890 Scm ⁻¹ and 1 respectively.
0.6 × 10 ⁻⁶ ° C.- ¹ .

Example 1 A three-stage series cell solid oxide fuel cell was manufactured as follows in accordance with the integration mode shown in FIG. First, the separator 4
4. The external terminals 45 and 46 were manufactured using the sintered body having the alloy / alumina volume ratio of 4/6 obtained in Production Example 1. Each of these separators 44 and external terminals 45 and 46 is 50 ×
50mm x 5mm square plate with groove width 2mm and groove depth 2mm
Of the grooves 44a, 44b, 45b, 46a. In the separator 44, grooves 44a, 4
The direction of 4b was made orthogonal.

As the solid electrolyte plate 41, 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
₃ powder (average particle size 5 μm) 0.3m thick by brushing method
m / m to form a cathode 42, and Ni / Z
An anode 43 was formed by applying a cermet mixed powder of rO ₂ (10/1 weight ratio) to a thickness of 0.3 mm by brushing.

The solid electrolyte plate 41 provided with the electrodes, the separator 44, and the external terminals 45 and 46 are integrated as shown in FIG. 4, and the solid electrolyte plate with the electrodes and the separator 44 are bonded with a zirconia-based inorganic adhesive. And the softening point is about 800
A glass paste at ℃ was applied and gas sealing was performed. This glass paste softens at the operating temperature of the battery and seals the gas.

Each of the battery bodies 51 thus assembled was placed in a cylindrical alumina manifold 52 shown in FIG. The contact portion between the manifold 52 and the battery body 51 was gas-sealed by applying a glass paste. Platinum lead wires 57 and 58 were inserted into the external terminals 45 and 46 to make electrical connection.

Each of the fuel cells thus produced was heated. That is, heating was performed at a rate of 1 ° C./minute from room temperature to 150 ° C. to evaporate the solvent of the glass paste. 150-3
The temperature was raised at a rate of 5 ° C./min up to 50 ° C. At 350 ° C. or higher, a nitrogen gas was flowed through the hydrogen passage side to prevent oxidation of the anode, and the temperature was raised to 1000 ° C. at 5 ° C./min. Thereafter, while maintaining the temperature at 1000 ° C., hydrogen was supplied to the anode side and oxygen was supplied to the cathode side to start power generation. Open voltage is 3.8V
Met. Table 1 shows the discharge characteristics. The gas cross leak was 0.1% or less with hydrogen.

Embodiments 2 and 3 In place of the separator and external terminals of Embodiment 1, Production Example 2
Each fuel cell was produced and power was generated in the same manner as in Example 1 except that the separator and the external terminal were respectively produced using the sintered body obtained in and the sintered body obtained in Production Example 3. Table 1 shows the discharge characteristics. The gas cross leak was 0.1% or less with hydrogen.

[Table 1]

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an alloy content and electric conductivity in one example of a sintered body.

FIG. 2 is a graph showing the relationship between electric conductivity and temperature in one example of a sintered body having an alloy / alumina volume ratio of 4/6.

FIG. 3 is a graph showing a relationship between an alloy / alumina volume ratio and a coefficient of linear expansion at 1000 ° C. in one example of a sintered body.

FIG. 4 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 the separator of the present invention.

FIG. 5 is an explanatory view of a completed fuel cell in which the cell body of FIG. 4 is housed in a manifold.

[Explanation of symbols]

 41 Solid electrolyte plate 42 Cathode 43 Anode 44 Separator 44a, 44b Groove 45, 46 External terminal 51 Battery body 52 Manifold

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshihiko Yoshida 1-3-1, Nishitsurugaoka, Oi-machi, Iruma-gun, Saitama Prefecture Tonen Co., Ltd. Chome 3-1 Tonen Co., Ltd. (56) References JP-A-1-100866 (JP, A) JP-A-3-71561 (JP, A) JP-A-64-41172 (JP, A) JP-A 64-7475 (JP, A) JP-A-59-201371 (JP, A) JP-A-2-288162 (JP, A) JP-A 4-188564 (JP, A) (58) Int.Cl. ⁷ , DB name) H01M 8/00-8/24 C22C 19/03

Claims (3)

(57) [Claims] A nickel-based alloy or a mixture thereof with at least one selected from nickel, cobalt, a cobalt-based alloy, iron and an iron-based alloy, and alumina, silica,
At least one inorganic compound selected from titania, indium oxide, stannic oxide, silicon carbide and silicon nitride or a compound capable of forming the same is fired in a non-oxidizing atmosphere or in vacuum. A separator for a solid oxide fuel cell, comprising a sintered body. 2. The method according to claim 1, wherein the inorganic compound is alumina.
The separator as described. 3. The separator according to claim 1, wherein the volume ratio between the nickel-based alloy and alumina is 80:20 to 25:75.