JP5259480B2 - Interconnector for solid oxide fuel cell and method for forming the same - Google Patents

Description

  The present invention relates to a solid oxide fuel cell interconnector and a method for forming the same, and more particularly, faces the anode side of a solid oxide fuel cell interconnector configured using a heat-resistant alloy material containing Cr. The present invention relates to a solid oxide fuel cell interconnector having a water vapor oxidation inhibiting layer on the surface and a method for forming the water vapor oxidation inhibiting layer.

  A unit cell or cell of a solid oxide fuel cell (hereinafter abbreviated as “SOFC” where appropriate) has an anode and a cathode arranged with an electrolyte composed of a solid oxide, and is a three-layer unit of cathode / electrolyte / anode. Composed. In this specification, the case where air is supplied as an oxidant gas to the cathode side will be described, but the same applies to the case where oxygen-enriched air or oxygen is supplied.

  SOFC has the following features (1) to (5). (1) Since the electrochemical reaction at the electrode proceeds smoothly due to the high operating temperature, there is little energy loss and the power generation efficiency is high. (2) Since the exhaust heat temperature is high, it is possible to further increase the power generation efficiency by using multiple stages. (3) Since the operating temperature is high enough to reform a hydrocarbon fuel such as natural gas, the reforming reaction can be performed inside the battery. For this reason, the fuel processing system (reformer + shift converter) necessary for low-temperature operating fuel cells such as phosphoric acid type and polymer type can be greatly simplified. (4) Since CO can be involved in the power generation reaction, fuel can be diversified. (5) Since all members are made of solid, there is no problem of corrosion or electrolyte evaporation that occurs in phosphoric acid fuel cells or molten carbonate fuel cells.

As the electrolyte material, for example, a sheet-like sintered body such as yttria stabilized zirconia (YSZ) is used, and as the anode, a porous body such as a mixture of nickel and yttria stabilized zirconia (Ni / YSZ cermet) is used. As the cathode, for example, a porous body such as Sr-doped LaMnO ₃ is used, and the cell is usually formed by baking the anode and the cathode on both surfaces of the electrolyte material.

During the operation, oxygen in the air introduced into the cathode becomes oxide ions (O ²⁻ ) at the cathode and reaches the anode through the electrolyte. Here, it reacts with the fuel introduced into the anode and emits electrons to generate electricity and reaction products such as water and carbon dioxide. Spent air at the cathode is discharged as cathode offgas, and spent fuel at the anode is discharged as anode offgas.

  A conventional SOFC has a high operating temperature of about 800 to 1000 ° C., but recently, an SOFC operating at a temperature of about 600 to 800 ° C., which is a lower temperature, for example, about 750 ° C. is being developed. FIG. 1 is a diagram for explaining an example of a flat SOFC cell and shows a cross-sectional view. As shown in FIG. 1, the SOFC cell 1 is configured by disposing an electrolyte membrane 3 on an anode 2 and a cathode 4 on the electrolyte membrane 3.

For example, a zirconia-based or LaGaO ₃ -based electrolyte material is used as the solid oxide electrolyte, which is configured to be supported by a thick anode, and is called a support membrane type. In the support membrane type, the thickness of the electrolyte membrane can be reduced. The thickness of the membrane becomes, for example, about 10 μm, and it can be operated at a low or medium temperature of 600 to 800 ° C. For this reason, it is possible to use a heat-resistant alloy, such as stainless steel, as a constituent material for the interconnector or the like, and it has various advantages such as miniaturization.

  When the SOFC cell is in operation, electric power is obtained by flowing air to the cathode side, flowing fuel to the anode side, and connecting both electrodes to an external load. Since a high voltage cannot be obtained with one cell, cells and cells are stacked by being alternately stacked via an interconnector. That is, in the flat SOFC stack, interconnectors and cells are alternately stacked for the purpose of electrically connecting adjacent cells and distributing, supplying, and discharging air and fuel to and from the cathode and anode, respectively. .

  FIG. 2 is a diagram for explaining a stacking example, that is, a configuration example of stacking support membrane type flat SOFC cells, and showing each member of the support membrane type flat SOFC stack at intervals to show the arrangement relationship. Yes. A stack was constructed with three cells 1 and two interconnectors 5 between them, and interconnectors 6 (this interconnector is also a frame) on the upper surface of the uppermost cell and the lower surface of the lowermost cell. Shows the case.

  In the embodiment shown in FIG. 2, among the interconnectors 5 and 6, a plurality of groove-like air flow paths for supplying air to the cathode side of the cell are formed on the lower surface of the uppermost interconnector 6. A plurality of groove-like fuel flow paths for supplying fuel to the anode side of the cell are formed on the upper surface of the lower interconnector 6. Further, the interconnector 5 between the uppermost interconnector 6 and the lowermost interconnector 6 has a plurality of groove-like fuel flow paths on its upper surface for supplying fuel to the anode side of the cell. A plurality of groove-like air flow paths for supplying air to the cathode side of the cell are formed on the lower surface.

  And these interconnectors and each cell between them are laminated by applying a load, for example. Such an SOFC stack can be installed upside down or horizontally, so that the fuel flow path on the upper surface of the intermediate interconnector 5, the air flow path on the lower surface of the intermediate interconnector 5, and the uppermost The descriptions of the air flow path on the lower surface of the interconnector 6 and the fuel flow path on the upper surface of the lowermost interconnector 6 are relative. For example, in the case of upside down, the lower surface of the uppermost interconnector 6 serves as a fuel flow path, and the upper surface of the lowermost interconnector 6 serves as an air flow path.

  By the way, many properties of the following (1) to (8) are required for the interconnector. (1) It is dense and does not permeate or leak gas. (2) High electronic conductivity. (3) Ion conductivity is small. (4) The material itself is chemically stable in both high temperature oxidizing and reducing properties. (5) Reaction with other members in contact such as two electrodes and excessive mutual diffusion do not occur. (6) The thermal expansion coefficient is consistent with other battery constituent materials. (7) The dimensional change due to the change in atmosphere is small. (8) It has sufficient strength.

  As such, the interconnector has many strict requirements, limiting its constituent materials. In order to satisfy these requirements as much as possible, a heat-resistant alloy containing Cr is used. Even in the case of SOFC with a low or medium operating temperature (about 600 to 800 ° C.), it is advantageous from the viewpoint of the above properties, performance, and cost to use a heat-resistant alloy containing Cr as a material for manifolds and interconnectors. It is.

  However, when a heat-resistant alloy containing Cr is used as the constituent material of the interconnector, it is common to form a chromium oxide film on the surface in an oxidizing atmosphere during operation of the SOFC. Since the chromium oxide film is not very conductive, the internal resistance of the SOFC cell stack increases when it is used as it is. Conventionally, it is effective to apply a protective film of a conductive material such as conductive ceramics or silver alloy on the surface of the Cr alloy as a means for preventing the generation of vapor species of chromium oxide which is the cause and preventing the internal resistance thereof. It is considered.

  Here, in the SOFC cell, fuel (including hydrogen, carbon monoxide, and water vapor) is flowed to the anode side, and air is flowed to the cathode side. For example, an SOFC stack as shown in FIG. In the connectors 5 and 6, the surface facing the cathode side of the SOFC cell is an oxidizing atmosphere, and the surface facing the anode side is a reducing atmosphere. The fuel may contain methane, which is steam reformed by the catalytic action of Ni in the anode.

  FIG. 3A is a diagram for explaining the outline of the uppermost interconnector 6 in FIG. 2, and shows a perspective view corresponding to FIG. FIG. 3B is a view for explaining a mode in which the conductive coating layer 7 is provided on the interconnector 6, and is a side view on the side where a plurality of grooves for air circulation can be seen. As shown in FIG. 3B, by coating the surface of the heat-resistant alloy interconnector containing Cr with a conductive material, that is, by providing a conductive protective film on the surface, an oxide scale layer on the alloy surface, Exposure to the surface of the chromium oxide layer is avoided, and generation of vapor species of chromium oxide is prevented.

  By the way, in order to densely form conductive ceramics as a conductive material on the surface of a heat-resistant alloy containing Cr, it must be sintered at a high temperature of 1000 ° C. or higher. However, since the Cr-containing alloy is likely to deteriorate at such a high temperature, a device for sintering at a lower temperature is required. Moreover, an inexpensive method such as dipping is desired as a pretreatment for sintering. Therefore, methods such as Non-Patent Documents 1 and 2 have been proposed.

In Non-Patent Document 1, the sintering temperature of Ce _0.9 Gd _0.1 O _1.95 is lowered by adding a sintering aid (Li) to Ce _0.9 Gd _0.1 O _1.95 (hereinafter abbreviated as “CGO” where appropriate). Has been successful. Specifically, when the CGO film is coated on the CGO dense body, 5 mol% of lithium nitrate (LiNO ₃ ) is added to the CGO, whereby the CGO sintering temperature for the CGO dense body is increased from 1200 ° C. The temperature is reduced to 800 ° C.

In Non-Patent Document 2, when forming a film of Mn _1.5 Co _1.5 O ₄ on the surface of a ferritic stainless steel, a dense film can be formed by incorporating a reduction treatment. However, although Mn _1.5 Co _1.5 O ₄ film, which is an oxide film, is relatively dense, there are many pores in the film and it is not completely dense. It cannot be used.

“7th EUROPEAN SOLID OXIDE FUEL CELL FORUM, 3-7 July 2006, Abstract p.49: Low Temperature Constrained Sintering of COG Films for SOFC Applications, 1 outside Jason Nicholas” “Journal of the Electrochemical Society 2005 A1896-A1901: Thermal Growth and Performance of Manganese Cobaltite Spinel Protection on FERRITIC STAINLESS STEEL SOFC INTERCONNECTS, YANG Zhenguo and three others, Available electronically August 8, 2005”

  In order to solve the above problems related to an interconnector using a heat-resistant alloy as a constituent material, the present inventors have conducted conductivity with respect to an interconnector for a solid oxide fuel cell configured using a heat-resistant alloy material containing Cr. A method of densely coating a protective film made of a ceramic material has been developed (Patent Document 1).

Japanese Patent Application No. 2007-328049 (Filing date: December 19, 2007)

  By the way, since the oxidizing atmosphere is mainly formed on the cathode side which is an air atmosphere, the deterioration of the portion facing the cathode side of the interconnector is remarkable. In order to prevent the deterioration, as shown in FIG. In general, a protective film is formed on the interconnector in contact with the cathode side.

  However, also in the portion of the interconnector facing the anode side, the heat-resistant alloy containing Cr, which is a constituent material of the interconnector, is oxidized by the water vapor contained in the fuel gas. As a result, an oxide film grows on the surface of the interconnector facing the anode side, causing an increase in electrical resistance.

  Among the interconnectors, the side facing the anode side is provided with an alumina protective layer on copper or a copper-based alloy as a gas separator member as in Patent Document 2, or in a reducing atmosphere as in Patent Document 3. The separator on the anode side to be exposed was provided with a separator base composed of a cermet made of a refractory metal and an oxide-based conductive ceramic, and the anode gas-corresponding surface of the base so that it was not in direct contact with the anode gas. A method is adopted in which a protective film containing a refractory metal is used.

  However, in Patent Document 2, the separator covered with insulating alumina has a complicated structure to ensure conductivity, and in Patent Document 3, the protective film is limited to the separator composed of cermet, and the cost is reduced. It is not realistic from the viewpoint of practicality.

Japanese translation of PCT publication No. 2003-501796 JP 09-129247 A

  The present invention has been made in order to solve the above problems on the anode side of an interconnector, and is provided on the anode side in an interconnector for a solid oxide fuel cell constructed using a heat-resistant alloy material containing Cr. It is an object of the present invention to provide an interconnector for a solid oxide fuel cell having a water vapor oxidation inhibiting layer on the surface thereof and a method for forming the water vapor oxidation inhibiting layer.

  The present invention (1) is an interconnector for a solid oxide fuel cell configured using a heat-resistant alloy material containing Cr, and the MnCr oxide is sequentially formed on the surface facing the anode side of the interconnector. A solid oxide fuel cell interconnector comprising a layer and a water vapor oxidation inhibiting layer comprising a composite oxide layer containing Mn and Co. The MnCr oxide layer contains impurities such as Fe, but Mn and Cr are the main components as determined by a scanning electron microscope / energy dispersive X-ray analyzer.

The present invention (2) is an interconnector for a solid oxide fuel cell constructed using a heat-resistant alloy material containing Cr, and the MnCr oxide is sequentially formed on the surface facing the anode side of the interconnector. A solid oxide fuel cell interconnector comprising a water vapor oxidation-inhibiting layer comprising a layer and a Mn _x Co ₃ -xO ₄ (0 <x <3) layer. The MnCr oxide layer contains impurities such as Fe, but Mn and Cr are the main components as determined by a scanning electron microscope / energy dispersive X-ray analyzer.

The present invention (3) is a solid oxide fuel cell interconnector configured using a heat-resistant alloy material containing Cr and Mn, and sequentially forms MnCr on the surface facing the anode side of the interconnector. A solid oxide fuel cell interconnector comprising an oxide layer and a water vapor oxidation-inhibiting layer comprising a CoO layer or a Co ₃ O ₄ layer. The MnCr oxide layer contains impurities such as Fe, but Mn and Cr are the main components as determined by a scanning electron microscope / energy dispersive X-ray analyzer. The present invention (3) is a reference invention.

The present invention (4) is an interconnector for a solid oxide fuel cell constructed using a heat-resistant alloy material containing Cr, and the FeCr oxide is sequentially formed on the surface facing the anode side of the interconnector. it is interconnector for a solid oxide fuel cell characterized by having a layer and _{Fe X Co 3-X O 4} (0 <x <3) consisting of layers steam oxidation suppression layer. The FeCr oxide layer also contains impurities such as Mn, but Fe and Cr are the main components as determined by a scanning electron microscope / energy dispersive X-ray analyzer. The present invention (4) is a reference invention.

The present invention (5) is a method of forming a water vapor oxidation inhibiting layer on the surface facing the anode side of a solid oxide fuel cell interconnector composed of a heat-resistant alloy material containing Cr, wherein After applying a slurry of Mn _X Co _3-X O ₄ (0 <x <3) to which the low-temperature sintering aid is added on the surface facing the anode side of the connector, reduction treatment is performed at 700 to 900 ° C., Oxidation treatment at 750 to 850 ° C. suppresses steam oxidation consisting of an MnCr oxide layer and an Mn _X Co _{3 -X} O ₄ (0 <x <3) layer on the surface of the interconnector on the anode side. A method for forming a water vapor oxidation inhibiting layer in an interconnector for a solid oxide fuel cell, characterized in that a layer is formed.

According to the present invention, the following effects (1) to (3) can be obtained.
(1) Suppressing steam oxidation on the anode side of the interconnector by means of a steam oxidation inhibiting layer formed on the surface of the anode side of the interconnector made of a heat-resistant alloy containing Cr in the solid oxide fuel cell Can do.
(2) Of the water vapor oxidation inhibiting layers formed on the surface of the interconnector on the anode side, the outermost layer contains metal Co, so that the contact resistance is low and the conductivity is not impaired.
(3) Since the formation of the steam oxidation inhibiting layer can be performed by a wet method, the film formation is easy and the manufacturing cost can be reduced.

FIG. 1 is a diagram for explaining an example of a support membrane type flat SOFC cell. FIG. 2 is a diagram showing a configuration example in which support membrane type flat SOFC cells are stacked. FIG. 3 is a view (prior art) for explaining an embodiment in which a protective film of a conductive material such as conductive ceramics is applied to the Cr alloy surface. FIG. 4 is a diagram for explaining the outline of the steam oxidation suppression layer, taking the intermediate connector 5 in FIG. 2 as an example. FIG. 5 is a diagram showing an outline of the process of forming the steam oxidation inhibiting layer in the present invention. FIG. 6 is an example with a steam oxidation inhibiting layer (protective film), and is a diagram showing a cross-sectional SEM photograph. FIG. 7 is an example without a water vapor oxidation inhibiting layer (protective film), and is a diagram showing a cross-sectional SEM photograph. FIG. 8 is an example with a steam oxidation inhibiting layer (protective film), and is a diagram showing a Cr map pink SEM photograph of the cross section. FIG. 9 is an example without a steam oxidation inhibiting layer (protective film), and is a diagram showing a Cr map pink SEM photograph of the cross section.

  The present invention (1) is an interconnector for a solid oxide fuel cell constructed using a heat-resistant alloy material containing Cr. The interconnector further includes a water vapor oxidation suppression layer comprising a MnCr oxide layer and a composite oxide layer containing Mn and Co on the surface facing the anode side. Here, the MnCr oxide layer means a composite oxide layer containing Mn and Cr, and is the same in this specification.

The present invention (2) is a solid oxide fuel cell interconnector configured using a heat-resistant alloy material containing Cr, and MnCr oxidation is sequentially performed on the surface facing the anode side of the interconnector. It is characterized by having a water vapor oxidation inhibiting layer comprising a physical layer and a Mn _x Co ₃ -xO ₄ (0 <x <3) layer.

The present invention (3) is a solid oxide fuel cell interconnector configured using a heat-resistant alloy material containing Cr and Mn. The interconnector further includes a water vapor oxidation suppression layer composed of an MnCr oxide layer and a CoO layer or a Co ₃ O ₄ layer on the surface facing the anode side.

The present invention (4) is a solid oxide fuel cell interconnector constructed using a heat-resistant alloy material containing Cr. Then, the surface facing the anode side of the interconnector, sequentially, and characterized by having a FeCr oxide layer and _{Fe X Co 3-X O 4} (0 <x <3) consisting of layers steam oxidation suppression layer To do.

The present invention (5) is a method of forming a water vapor oxidation inhibiting layer on the surface facing the anode side of a solid oxide fuel cell interconnector constructed using a heat-resistant alloy material containing Cr. Then, after applying a slurry of the Mn _X Co _3-X O ₄ with the addition of low temperature sintering aids to the anode side facing the surface of the interconnector (0 <x <3), reduction treatment at 700 to 900 ° C. And then performing oxidation treatment at 750 to 850 ° C. to sequentially form a water vapor oxidation suppression layer comprising a MnCr oxide layer and a MnCo ₂ O ₄ layer on the surface of the interconnector on the anode side. And

  Here, in this specification, the steam oxidation suppression layer refers to an interconnector made of a heat-resistant alloy containing Cr in the SOFC cell or SOFC stack, by the steam contained in the fuel gas supplied to the anode side during its operation. This means a layer that serves to suppress oxidation of the surface facing the anode side of the interconnector. Although it can be said that the water vapor oxidation suppression layer is a kind of protective layer, it is referred to as a water vapor oxidation suppression layer from the viewpoint of its function and operation.

  FIG. 4 is a diagram for explaining the outline of the steam oxidation inhibiting layer, taking the intermediate connector 5 in FIG. 2 as an example. FIG. 4A shows the interconnector 5 taken out, and FIG. 4B is a side view of the interconnector 5 provided with a water vapor oxidation inhibiting layer. As shown in FIG. 4B, a steam oxidation suppression layer (protective layer) 8 is formed on the surface of the interconnector 5 on the side facing the anode side of the SOFC cell.

As the heat-resistant alloy material containing Cr in the present invention, any heat-resistant alloy material containing Cr used as a solid oxide fuel cell interconnector can be used. For example, the following materials (1) to (3) may be mentioned, but the material is not limited thereto. These are known as ferritic heat resistant alloys.
(1) C: 0.02% (mass%, the same applies hereinafter), Mn: 0.50%, Ni: 0.26%, Cr: 21.97%, Zr: 0.22%, La: 0.04 %, Si: 0.40%, Al: 0.21%, Fe: Balance.
(2) C: 0.03%, Mn: 0.47%, Ni: 0.26%, Cr: 22.14%, Zr: 0.20%, La: 0.04%, Si: 0.40 %, Al: 0.21%, Fe: balance.
(3) C: 0.02%, Mn: 0.48%, Ni: 0.33%, Cr: 22.04%, Zr: 0.20%, La: 0.08%, Low Si, Low Al , Fe: balance.

As a material for forming the water vapor oxidation suppression layer in the present invention, an oxide containing Co or a composite oxide containing Co is used. Among them, as the composite oxide containing Co, a composite oxide containing Mn and Co, a composite oxide containing Fe and Co, and the like can be used. Preferably, a composite oxide containing Mn and Co is used. Further, as the composite oxide containing Mn and Co, preferably Mn _x Co ₃ -x O ₄ (0 <x <3) can be used. Examples thereof include MnCo ₂ O ₄ , Mn _1.5 Co _1.5 O ₄ and Mn ₂ CoO ₄ . Further, as the composite oxide containing Fe and Co, Fe _x Co ₃ -x O ₄ (0 <x <3) can be preferably used.

  Li compound is used as the low temperature sintering aid in the present invention. Examples of the Li compound include, but are not limited to, lithium oxide, lithium hydroxide, lithium nitrate, lithium carbonate, lithium acetate, and lithium halide. These Li compounds are reduced by the reduction treatment described later to become Li, and at the time of subsequent firing and oxidation in the air atmosphere described later, a role of densely sintering the material for forming the water vapor oxidation suppression layer at a lower temperature than before. To do. The “low temperature” in the low temperature sintering aid means the low temperature in “at a lower temperature than in the past”.

  In the present invention, a slurry obtained by adding a low-temperature sintering aid to the material for forming the steam oxidation suppression layer is applied to the surface of the heat-resistant alloy material containing Cr, and then subjected to a reduction treatment in a temperature range of 700 to 900 ° C. Next, it is fired and oxidized in a temperature range of 750 to 850 ° C. in an air atmosphere. The amount of the low-temperature sintering aid added to the material for forming the steam oxidation-suppressing layer is preferably 3 mol% or more with respect to 100 mol% of the material for forming the steam-oxidation suppressing layer, and the range is preferably 3 to 8 mol. % Range.

<Formation process of steam oxidation suppression layer>
The formation process of the steam oxidation suppression layer in the present invention is as follows (1) to (4). FIG. 5A shows an outline of the process. Here, Mn _X Co _{3 -X} O ₄ (0 <x <3) is taken as an example of a composite oxide containing Mn and Co, but other composite oxides containing Mn and Co or Fe and Co are used. The same applies to the composite oxide containing the same.

(1) First, preparation of a slurry containing Mn _x Co ₃ -xO ₄ (0 <x <3), which is a material for forming a steam oxidation inhibiting layer, and a low-temperature sintering aid is performed using water or water and alcohol as a solvent. A mixed solvent is used, and a material for forming the steam oxidation inhibiting layer, a low-temperature sintering aid, an organic binder, and a dispersing agent are mixed therein, and the mixture is sufficiently stirred with a ball mill or the like to form a slurry.

  (2) Next, the slurry is applied to the surface of the heat-resistant alloy material containing Cr. This coating can be performed by a screen printing method, a dipping method, or the like.

  (3) Next, reduction treatment is performed at 700 to 900 ° C. The temperature of the reduction treatment is more preferably 750 to 850 ° C. The reducing atmosphere during the reduction treatment is a gas atmosphere containing hydrogen. A preferable example thereof is a nitrogen atmosphere containing hydrogen. Moreover, the time of a reduction process should just be the time which can fully reduce | restore the component in the surface of the heat-resistant alloy material containing Cr, and the slurry apply | coated on the surface, Preferably it is 12 to 24 hours. The Li compound that is a low-temperature sintering aid is reduced to Li by a reduction treatment.

  (4) Next, firing and oxidation are performed at 750 to 850 ° C. in an air atmosphere. The firing and oxidation time in an air atmosphere is preferably 12 to 24 hours.

In the present invention, by the steps (1) to (4) above, the MnCr oxide layer is formed on the surface of the heat-resistant alloy material containing Cr, which is the constituent material of the SOFC interconnector, and the Mn on the upper surface of the MnCr oxide layer. _A water vapor oxidation suppression layer composed of an _X Co _{3 -X} O ₄ (0 <x <3) layer is formed.

The interconnector thus configured will be described with reference to FIGS. 4 and 5A. In FIG. 4, 5 is an interconnector composed of a heat-resistant alloy material containing Cr or a heat-resistant alloy material containing Cr, and 8 is an anode thereof. It is a water vapor oxidation suppression layer coated on the surface on the side. As shown in the frame following the “oxidation” step in FIG. 5A, the steam oxidation suppression layer 8 is a MnCr oxide layer, that is, a composite oxide layer of Mn and Cr, on the upper surface of the heat-resistant alloy material containing Cr. forming a mainly constructed by forming a layer of _{Mn X Co 3-X O 4} (0 <x <3) on top of the MnCr oxide layer.

Among these, the MnCr oxide layer is Mn contained in Mn _X Co _{3 -X} O ₄ (0 <x <3), which is a material for forming the water vapor oxidation suppression layer, and Cr in the heat-resistant alloy containing Cr. And produced by the reaction. The MnCr oxide layer in the present invention (1) to (3) also contains impurities such as Fe derived from a heat-resistant alloy containing Cr, but the amount of impurities is very small.

_{Further, Mn X Co 3-X O} 4 formed on the MnCr oxide layer (0 <x <3) _{layer, Mn X Co 3-X O} 4 (0 <x <3) is the (3 ) Reduction step and (4) oxidation step. More specifically, the Mn _X Co _3-X O ₄ (0 <x <3) layer is once converted into MnO and Co by the reduction process, and then Mn _X Co _3-X O ₄ (0 <X <3), and the film is densely formed on the MnCr oxide layer in the process of changing in this way.

When an interconnector having a water vapor oxidation suppression layer is incorporated in a SOFC cell or SOFC stack and used, the water vapor oxidation suppression layer side becomes an anode atmosphere, and therefore a reducing atmosphere is formed. Therefore, as shown at the right end in FIG. 5A, the components of the Mn _x Co ₃ -xO ₄ (0 <x <3) layer formed on the MnCr oxide layer change to MnO and Co. To do. Among these, Co, which is a metal, is conductive, so that the contact resistance is low, and the generated power can be taken out favorably.

  In addition, although the application example with respect to the interconnector for flat plate type SOFC is shown in FIG. 4, the steam oxidation suppression layer of this invention is applied also to the interconnector for SOFC of another type.

Hereinafter, the present invention will be described in more detail based on experimental examples, but the present invention is not limited to the experimental examples. Here, as a representative example, an experimental example using MnCo ₂ O ₄ as a material for forming the water vapor oxidation suppression layer is described, and the formation process of the water vapor oxidation suppression layer is shown in FIG.

<(1) Preparation of slurry for forming water vapor oxidation inhibiting layer>
Material for forming the steam oxidation inhibiting layer: An oily slurry of MnCo ₂ O ₄ was prepared. MnCo of ₂ O ₄ powder (d50 = 1 [mu] m, a specific surface area ^{= 2.3m 2 / g), LiNO} 3, an organic binder, dispersing agent, ethanol were mixed, stirred for 10 days at a bench ball mill, oily MnCo ₂ O ₄ A slurry was prepared.

As the MnCo ₂ O ₄ oily slurry, various oily slurries were prepared in which the addition ratio of LiNO ₃ to MnCo ₂ O ₄ was changed. MnCo ₂ O ₄ is a material for forming a steam oxidation inhibiting layer, and LiNO ₃ is a low temperature sintering aid. Among these, the specific surface area of the MnCo ₂ O ₄ powder is 2.3 m ² / g.

<(2) Application of slurry for forming water vapor oxidation inhibiting layer to interconnector material>
Heat-resistant alloy material containing Cr [manufactured by Hitachi Metals, Ltd., ZMG (registered trademark) 232L. Composition: C = 0.02% (mass%, the same applies hereinafter), Mn = 0.48%, Ni = 0.3%, Cr = 22.04%, Zr = 0.20%, La = 0.08% , Si = trace, Al = trace, Fe = balance]. The surface dimension of each plate is 1 cm × 1 cm (= 1 cm ² ).

For each of these plates, an oily slurry prepared in the above-mentioned <(1) Preparation of slurry for forming water vapor oxidation inhibiting layer> with different addition ratios of LiNO ₃ to MnCo ₂ O ₄ was screen-printed on the surface. Was applied. After the application, it was dried in a thermostatic bath where the solvent, ethanol, was kept at around 100 ° C. In this way, each sample was prepared by coating and drying slurry with different addition ratios of LiNO ₃ to MnCo ₂ O ₄ for each plate.

<(3) Reduction treatment>
<(2) Application of Slurry for Forming Steam Oxidation Prevention Layer to Interconnector Material> In each electric furnace, each sample obtained in a nitrogen atmosphere containing hydrogen [N ₂ 96% to H ₂ 4% (volume% ) In an atmosphere containing) at 20O <0> C for 20 hours. In this process, LiNO ₃ is reduced to Li. Since Li ^{+ in} LiNO ₃ is monovalent, the mol% as LiNO ₃ is the same in Li.

<(4) Oxidation treatment = Baking treatment>
<(3) Reduction treatment> Each sample after was oxidized in an electric furnace in an air atmosphere at 800 ° C. for 12 to 24 hours.

<Observation of each prepared sample by SEM>
About the sample produced at the process of (1)-(4) above, the surface and the cross section were observed with SEM (scanning electron microscope). As a result, it was observed that a dense MnCr oxide layer was formed on the surface of each plate, and a dense MnCo ₂ O ₄ layer was formed on the MnCr oxide layer. In these two layers, MnCo ₂ O ₄ is formed through the reduction and oxidation steps (3) to (4). Among them, the MnCo ₂ O ₄ layer is changed to MnO and Co once by the reduction treatment, and changed to MnCo ₂ O ₄ by the subsequent oxidation step. A film is formed.

<Observation after each sample was processed in an anodic reducing atmosphere>
The sample prepared in the above steps (1) to (4) and a heat-resistant alloy material containing Cr that does not perform the steps (1) to (4) as an example without the water vapor oxidation suppression layer (protective film) [step (2 In the anode reducing atmosphere [oxygen partial pressure 2 × 10 ⁻¹⁹ atm, about 20% humidification (water vapor capacity%)], after annealing at a temperature of 800 ° C. for 500 hours, The cross section of the sample was observed by SEM (scanning electron microscope).

  FIG. 6 is an example with a steam oxidation inhibiting layer (protective film), and shows a cross-sectional SEM photograph, and FIG. 8 shows a Cr element distribution along the cross-section. FIG. 7 is an example without a steam oxidation inhibiting layer (protective film), and shows a cross-sectional SEM photograph, and FIG. 9 shows a Cr element distribution on the cross-section.

  As shown in FIG. 6, with the protective film, the film thickness of the oxide layer containing Cr is about 1 μm in the cross section, whereas as shown in FIG. In the cross section, the film thickness of the oxide layer containing Cr is as thick as about 2 μm.

Further, as shown in FIG. 8, in the case where the protective film is applied, the film thickness of the oxide film containing Cr in which Cr is distributed in the cross section is about 1 μm corresponding to FIG. As shown in FIG. 9, in the case without the protective film, the film thickness of the oxide film containing Cr in which Cr is distributed in the cross section is as thick as about 2 μm, corresponding to FIG. In FIG. 8, there is a layer shown as the layer of MnCo ₂ O _{4 in} FIG. 6 on the upper surface of the layer (MnCr oxide layer) shown as the distribution of Cr in the oxide film containing Cr. Shows the distribution of only the component Cr, and therefore, the layer of MnCo ₂ O ₄ that does not contain Cr does not appear.

  Thus, it can be seen that the steam oxidation suppression layer of the interconnector made of the heat-resistant alloy material containing Cr suppresses the growth of the oxide film containing Cr in the anode atmosphere.

DESCRIPTION OF SYMBOLS 1 Cell 2 Anode 3 Electrolyte membrane 4 Cathode 5 Interconnector arranged between SOFC cells 6 Interconnector arranged on top or bottom 7 Conductive material coating layer 8 Steam oxidation suppression layer

Claims (10)

  An interconnector for a solid oxide fuel cell configured using a heat-resistant alloy material containing Cr, and a MnCr oxide layer and Mn and Co are sequentially included on a surface facing the anode side of the interconnector. An interconnector for a solid oxide fuel cell, comprising a water vapor oxidation inhibiting layer comprising a composite oxide layer. An interconnector for a solid oxide fuel cell configured using a heat-resistant alloy material containing Cr, wherein an MnCr oxide layer and an Mn _x Co ₃₋ are sequentially formed on a surface facing the anode side of the interconnector. A solid oxide fuel cell interconnector comprising a water vapor oxidation-inhibiting layer comprising _X O ₄ (0 <x <3) layers. A method of forming a water vapor oxidation inhibiting layer on a surface facing an anode side of a solid oxide fuel cell interconnector configured using a heat-resistant alloy material containing Cr, the surface facing the anode side of the interconnector after the slurry of the low-temperature sintering additive Mn _X Co _3-X O ₄ was added (0 <x <3) were applied to the surface, subjected to reduction treatment at 700 to 900 ° C., and then oxidized at 750 to 850 ° C. characterized by, said interconnector anode of the side surface of the sequentially forming a MnCr oxide layer and _{Mn X Co 3-X O 4} (0 <x <3) consisting of layers steam oxidation suppression layer A method for forming a water vapor oxidation inhibiting layer in an interconnector for a solid oxide fuel cell. 4. The method for forming a water vapor oxidation suppression layer in an interconnector for a solid oxide fuel cell according to claim 3 , wherein the low-temperature sintering aid is a Li compound. 5. The water vapor oxidation inhibiting layer in an interconnector for a solid oxide fuel cell according to claim 4 , wherein the Li compound is lithium oxide, lithium hydroxide, lithium nitrate, lithium carbonate, lithium acetate or lithium halide. Forming method. In any one of claims 3 to 5, 3 to 8 mol% with respect to the low temperature co-addition amount of sintering aid _{Mn X Co 3-X O 4} (0 <x <3) 100 mol% A method for forming a water vapor oxidation inhibiting layer in an interconnector for a solid oxide fuel cell. The method for forming a water vapor oxidation inhibiting layer in an interconnector for a solid oxide fuel cell according to any one of claims 3 to 6 , wherein the reducing atmosphere of the reduction treatment is a hydrogen-containing nitrogen atmosphere. The method for forming a water vapor oxidation suppression layer in an interconnector for a solid oxide fuel cell according to any one of claims 3 to 7 , wherein a reducing atmosphere temperature of the reduction treatment is set to 750 to 850 ° C. The method for forming a water vapor oxidation suppression layer in an interconnector for a solid oxide fuel cell according to any one of claims 3 to 8 , wherein the reduction treatment time is 12 to 24 hours. The interconnector for a solid oxide fuel cell according to any one of claims 3 to 9 , wherein the oxidation atmosphere of the oxidation treatment is an air atmosphere, and the oxidation treatment time is 12 to 24 hours. A method for forming a steam oxidation inhibiting layer.

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