JPH0536425A - Alloy separator for solid oxide fuel cell and method for producing the same - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides an alloy separator for a solid oxide fuel cell excellent in electrical conductivity and durability at low cost. [Arrangement] In an alloy separator used for a solid oxide fuel cell comprising a solid electrolyte, a fuel electrode, an air electrode, and a separator, the separator is made of a heat-resistant alloy, and the separator is provided on the fuel electrode side. Is provided with a Ni plating layer, and a LaCrO ₃ layer is provided on the air electrode side by a wet plating method.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a solid oxide fuel cell,
In particular, it relates to an improved alloy separator for a solid oxide fuel cell and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, various fuels have been made to obtain a DC power by reacting a gas such as hydrogen which is easily oxidized with a gas having an oxidizing power such as oxygen through an electrochemical reaction process. A battery has been developed, and one of them is a solid oxide fuel cell using a solid electrolyte showing ionic electrical conduction (Solid Oxide Fuel).
l Cell). The battery has advantages that it does not require an expensive noble metal catalyst such as platinum, has high energy conversion efficiency, and can use low quality fuel such as coal gas.
In addition, since the battery is composed of only solids, it does not have the disadvantage of handling a liquid electrolyte unlike other phosphoric acid electrolyte fuel cells or molten carbonate fuel cells, and is 800-1000.
The high operating temperature of ℃ has the advantage that this waste heat can be utilized.

There are flat type and cylindrical type solid oxide fuel cells. For example, a flat type solid electrolyte fuel cell has a structure in which the unit cell is a solid electrolyte (eg, ZrO 2) as shown in FIG. ₂ ) A plate 3 is provided with a pair of fuel electrode 1 and air electrode 2
, And further, these are sandwiched by a pair of many separators 4 and 4'having a long groove, and these single cells are connected in series to form an assembled battery, which enables practical power supply. Each of these unit batteries has an electrically connecting function for the above-mentioned series connection between the unit batteries and a function of forming a supply passage of a reaction gas (fuel gas and air) to each electrode plate. It is laminated via the separator 4.

[0004] Generally, the electrolyte plate 3 is made of electrolyte stabilizing zirconium.
It is a sintered body such as Konia, and the fuel electrode (anode) 1 is nickel.
Kel porous sintered body, the air electrode (cathode) 2 is
Mainly composed of a perovskite oxide sintered body,
Hydrogen as fuel is introduced between the fuel electrode 1 and the separator 4.
In addition, there is no oxygen or space between the air electrode 2 and the separator 4 '.
Air or the like is introduced, and an electromotive force is generated by the following reaction. Air electrode (reaction at electrolyte interface): O_Two+ 4e → 2O^-2   Fuel electrode (reaction at electrolyte interface): 2H_Two+20^-2→
2H_TwoO + 4e

The separators 4 and 4'are usually made of ceramic or heat-resistant alloy, and are provided orthogonally to each other.
Fuel or air passages composed of a plurality of long grooves are formed in the opposing surfaces of the separators 4 and 4 ', and the fuel or air is diverted and supplied to them. The materials of the separators 4 and 4'include LaCrO ₃ , Mg-added LaCrO ₃ , Sr-added La.
LaCrO ₃ based ceramics such as CrO ₃ or, for example,
Fe-Cr system, Fe-Cr-Ni system, Ni-Cr system, N
Attempts have been made to use heat-resistant alloys such as i-Cr-Mo series, Fe-Al series, and Fe-Cr-Al series.

[0006]

As described above, the separator is required to have a function of electrically connecting between the unit cells and a function of forming a fuel and air supply passage to each electrode plate. Is required, and it is required to prevent mixing of air and fuel gas. However, the heat-resistant alloy separator for use in a high temperature of around 1000 ° C., the oxide film (Cr ₂ in the air electrode side of the alloy elements as a main component together with an oxide mainly mother metal (iron, nickel, etc.) Both O ₃ , Al ₂ O ₃ , SiO ₂ etc. are formed. On the fuel side, a film of an oxide (Cr ₂ O ₃ , Al ₂ O ₃ , SiO ₂ etc.) mainly containing an alloy element is formed. As a result, the electrical conductivity is lowered, and the electrical connection function between the unit cells is impaired. In addition, since a thick film is formed on the air electrode side, the cell (air electrode / electrolyte / fuel electrode) is destroyed.

Therefore, in order to prevent the formation of these films and avoid the deterioration of electric conductivity, a LaCrO ₃ system, a LaMnO ₃ system, a LaMnO ₃ system, a LaMnO ₃ system, a La coating system, etc.
Although it was considered to apply a CoO ₃ based coating,
It was difficult to form a dense film by these methods, and it was not very useful for preventing the oxidation of the separator.

[0008]

As a result of research to prevent the deterioration of the electrical connection function of the separator, the present inventor has found that the separator is wet-plated with a certain metal or metal oxide to form a separator. Helps prevent the oxidation of
They also found that the deterioration of the electrical connection function could be prevented. That is, the present invention is a separator of a solid oxide fuel cell comprising a solid electrolyte, a fuel electrode, an air electrode, and a separator, in which the separators 4 and 4 ′ are made of a heat-resistant alloy, and the fuel electrode 1 surface side of the separator Is a nickel plating layer 4a, and a LaCrO ₃ system plating layer 4b is provided on the side of the air electrode 2 by applying a wet method, and an alloy separator for a solid oxide fuel cell, and a solid electrolyte. A fuel electrode, an air electrode, and a method for manufacturing a solid electrolyte fuel cell separator comprising a separator, wherein the separator is made of a heat-resistant alloy,
Further, a nickel plating layer is provided on the fuel electrode surface side of the separator by a wet plating method, and a LaCr-based plating layer electrodeposited by the wet method is oxidized on the air electrode surface side to provide a LaCrO ₃ -based plating layer. A method for producing an alloy separator for a solid oxide fuel cell, which comprises producing a separator.

In the present invention, Fe is used as the heat-resistant alloy.
-Cr system, Fe-Cr-Ni system, Ni-Cr system, Ni-
Cr-Mo type, Fe-Al type, Fe-Cr-Al type, etc. are mentioned. The reason why the Ni plating layer 4a is applied as the plating layer on the surface of the fuel electrode 1 is that the heat-resistant alloy element is oxidized.
This is to prevent a high resistance film such as Cr ₂ O ₃ or Al ₂ O _{3 from} being formed, and also LaCrO ₃ on the air electrode 2 surface side.
Reason to form a layer 4b is, LaCr ₂ O ₃ has excellent electrical conductivity, and excellent oxidation resistance, _Cr 2 O ₃ and Al
_{This is because} the formation of a high resistance film such as ₂ O ₃ is prevented.

In the above invention, the thickness of the plating layer is 3
-30 μm is preferable, and the plating method is wet electroplating to form nickel plating on the fuel electrode side. The LaCrO ₃ layer on the air electrode side can be formed by applying LaCr plating and then performing actual operation oxidation treatment. When the thickness of the plating layer is less than 3 μm, the effect of preventing oxidation is small, and when it exceeds 30 μm, the electric resistance increases. Therefore, the thickness is 3 to 30 μm, and the deterioration of the electrical connection function can be sufficiently prevented.

Good results can be obtained by applying cobalt plating instead of nickel plating. LaCrO ₃
As a system, in addition to LaCrO ₃ , La ₀ . ₉ Mg ₀ .
₁ CrO ₃ , La ₀ . ₉ Sr ₀ . ₁ CrO ₃ or the like is preferable, and similarly, it can be formed by a wet plating method.

The cross-sectional structure of the separator is, for example, as shown in FIG. 2 (A), an integrated type in which long grooves on the fuel electrode side and air groove side are provided on the front and back sides, and FIG. 2 (B). As shown in the figure, the fuel electrode side member and the air electrode side member are sandwiched between heat-resistant alloys in a three-division type, and further, the fuel electrode side thin plate and the air electrode side thin plate shown in FIG. A two-division type or the like can be used. In the figure, 4a is N
i plating layer and 4b represent LaCrO ₃ plating layer.

[0013]

EXAMPLES The present invention will be described in detail below with reference to examples. A Ni-Cr-Mo alloy is used as an alloy separator, a Ni layer is formed on the fuel electrode side surface, and a LaC is formed on the air electrode side surface.
The rO ₃ layer was coated. The Ni layer is nickel sulfate (NiS
Using O ₄ · _6H 2 O) bath at a current density of 2~10A / dm ^2, was electrodeposited to a thickness of 20 to 30 [mu] m. LaCrO
₃ layers using _{[(NH 4) 2 Cr 2} O 7 + La (NO 3) 3] bath, at a constant potential (-2.0V~-1.5VvsSCE) electrodeposition, the number of La / Cr molar ratio 1 [mu] m After forming a film with the thickness of, the La in the air oxidation treatment at 700 ℃ ~ 1000 ℃
It was a CrO ₃ layer.

FIG. 3 shows changes with time in output characteristics when the alloy separator thus obtained is used in a solid oxide fuel cell. The figure also shows the change over time in output characteristics when an alloy separator having no plated layer is used. From the figure, it can be seen that the performance of the plated alloy separator of the present embodiment is less degraded by the long-term operation, as compared with the case of using the unplated alloy separator. When the alloy separator after the operation was observed, the plated separator of the example did not change much, but the untreated one had a thick oxide film formed. The reason why the performance deterioration of the plated material of the example is small is that the formation of the oxide film is suppressed and the increase of the electric resistance is small.

[0015]

As described above, the alloy separator of the present invention is low in cost and has no deterioration in electrical connection function, and the solid oxide fuel cell having the separator is excellent in performance without being deteriorated by continuous use. Becomes

[Brief description of drawings]

FIG. 1 is an exploded perspective view illustrating a unit cell of a solid oxide fuel cell.

FIG. 2 is a cross-sectional structural view of various separators of a flat plate solid oxide fuel cell according to an embodiment of the present invention.

FIG. 3 is a graph showing changes over time in output characteristics when the alloy separator of the example and the alloy separator not subjected to plating treatment are used in a solid oxide fuel cell.

[Explanation of symbols]

1: anode, 2: air electrode, 3: a solid electrolyte plate, 4,4 ': Separator, 4a: Ni plating layer, 4b: LaCrO ₃ coating layer

Claims (3)

[Claims] 1. A separator of a solid oxide fuel cell comprising a solid electrolyte, a fuel electrode, an air electrode, and a separator, wherein the separator is made of a heat-resistant alloy, and nickel is provided on the fuel electrode side of the separator. An alloy separator for a solid oxide fuel cell, comprising a plating layer and a LaCrO ₃ system plating layer provided on the air electrode surface side by wet plating. 2. The alloy separator for a solid oxide fuel cell according to claim 1, wherein the plating layer has a thickness of 3 to 30 μm. 3. A method for manufacturing a separator of a solid oxide fuel cell comprising a solid electrolyte, a fuel electrode, an air electrode, and a separator, wherein the separator is made of a heat-resistant alloy and the separator has a fuel electrode surface side. A nickel plating layer is formed on the air electrode surface side by a wet plating method, and the LaCr-based plating layer electrodeposited by a wet method is oxidized on the air electrode surface side to form LaCr.
A method for producing an alloy separator for a solid oxide fuel cell, which comprises providing an O ₃ -based plating layer to produce a separator.