JP6906310B2 - Manufacturing method of solid oxide fuel cell - Google Patents

Description

The present invention relates to a method for manufacturing a cell for a solid oxide fuel cell.

In a cell for a solid oxide fuel cell (hereinafter, appropriately referred to as "SOFC"), an air electrode is bonded to one surface side of the electrolyte layer, and a fuel electrode is bonded to the other surface side of the electrolyte layer. It has a structure in which a single cell is sandwiched between a pair of electron-conducting cell-cell connecting members that transfer electrons to an air electrode or a fuel electrode.
Then, in such a SOFC cell, for example, it operates at an operating temperature of about 700 to 900 ° C., and as the oxide ions move from the air electrode side to the fuel electrode side via the electrolyte membrane, the pair of electrodes An electromotive force is generated in the meantime, and the electromotive force can be taken out and used.

The cell-cell connection member used in such an SOFC cell is made of a material containing Cr, which has excellent electron conductivity and heat resistance. Further, the heat resistance of such an alloy is derived from the dense film of _{chromium (Cr 2} O _{3) formed on the surface of this alloy.} In recent years, the operating temperature of SOFC cells has been lowered, and stainless alloys have come to be used as a material for cell-cell connecting members. A protective film such as a metal oxide is formed on the surface of the base material of the cell-cell connecting member in order to suppress Cr scattering.

Japanese Unexamined Patent Publication No. 60-169546

Hideto Kurokawa et al., "Oxidation behavior of Fe-16Cr alloy interconnect for SOFC under hydrogen potential gradient", Solid State Ionics 168 (2004) 13-21 William Qu et al., "Electrical and microstructural characterization of spinel phases as potential coatings for SOFC metallic interconnects", Journal of Power Sources 153 (2006) 114-124

Here, in addition to the main components Fe and Cr, various elements are added to the stainless alloy in order to impart heat resistance and corrosion resistance. It has been reported that these trace amounts of additive elements form a film-like region of an oxide inside the metal due to the oxygen potential near the metal / protective film interface (Non-Patent Document 1). In this document, it is reported that a composite oxide (spinel compound) of Mn and Cr is formed inside the metal.

It has been reported that the conductivity of a composite oxide of Mn and Cr changes significantly when the composition ratio of Mn and Cr changes (Non-Patent Document 2). For example, Cr-rich MnCr ₂ O ₄ has an electric resistance about 9 times as large as _{that of chromia (Cr 2} O ₃ ) under the operating environment of SOFC (for example, 750 ° C.).

Since the SOFC cell is constructed by alternately stacking single cells and cell-to-cell connecting members, it is required to reduce the electrical resistance of the cell-cell connecting members as much as possible. If an _{oxide having a large electric resistance such as MnCr 2} O ₄ described above is generated inside the base material of the cell-to-cell connection member, there is a concern that the power generation performance of the SOFC cell will be significantly deteriorated. In Patent Document 1, it is reported that _{MnCr 2} O ₄ scale is generated when the Mn content is increased in ferritic stainless steel.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is _{to suppress the formation of MnCr 2} O ₄ having a large electric resistance inside the base material of the cell-to-cell connection member, and to have high power generation performance. The purpose is to provide a cell for SOFC.

The characteristic configuration of the method for manufacturing a cell for a solid oxide fuel cell according to the present invention for achieving the above object is as follows.
A protective film forming step of forming a protective film on the surface of the base material of the cell-cell connecting member,
It has a joining step for joining the cell-to-cell connecting member and an air electrode via a joining layer.
The base material is mainly made of a stainless alloy containing Mn.
The protective film is mainly made of a spinel-type metal oxide containing Mn and Co.
The point is that the baking of the bonding layer in the bonding step is performed at a temperature of 1050 ° C. or higher and 1075 ° C. or lower.

The inventors have found a phenomenon in which the magnitude of the electrical resistance of the cell-cell connecting member and the bonding layer changes depending on the baking temperature of the bonding layer that joins the cell-cell connecting member and the air electrode. When the baking temperature of the bonding layer is 1000 ° C., MnCr ₂ O ₄ is formed inside the base material, and when the baking temperature is 1050 ° C. or higher, the formation of _{MnCr 2} O _{4 is suppressed.} Was confirmed, and the present invention was completed. That is, according to the above-mentioned characteristic configuration, it is possible to provide an SOFC cell having high power generation performance by suppressing the generation _{of MnCr 2} O _{4 having a large electric resistance inside the base material of the cell-to-cell connecting member.}

When the bonding layer is baked at a temperature of 1075 ° C. or lower in the bonding step, MnCr ₂ O ₄ having a large electrical resistance is suppressed from being generated inside the base material of the cell-to-cell connecting member, and the power generation performance is improved. It is suitable because it can provide a high SOFC cell. If the bonding layer is baked at a high temperature exceeding 1075 ° C., resistance such as peeling between the protective film and the base material and increased growth of the oxide film (chromia) may increase. It is not preferable because it becomes expensive.

The characteristic configuration of the method for manufacturing a cell for a solid oxide fuel cell according to the present invention for achieving the above object is as follows.
A protective film forming step of forming a protective film on the surface of the base material of the cell-cell connecting member,
It has a joining step for joining the cell-to-cell connecting member and an air electrode via a joining layer.
The base material is mainly made of a stainless alloy containing Mn.
The protective film is mainly made of a spinel-type metal oxide containing Mn and Co.
The point is that the baking of the bonding layer in the bonding step is performed at a temperature of 1050 ° C. or higher and lower than 1075 ° C.
The inventors have found a phenomenon in which the magnitude of the electrical resistance of the cell-cell connecting member and the bonding layer changes depending on the baking temperature of the bonding layer that joins the cell-cell connecting member and the air electrode. When the baking temperature of the bonding layer is 1000 ° C., MnCr ₂ O ₄ is formed inside the base material, and when the baking temperature is 1050 ° C. or higher, the formation of _{MnCr 2} O _{4 is suppressed.} Was confirmed, and the present invention was completed. That is, according to the above-mentioned characteristic configuration, it is possible to provide an SOFC cell having high power generation performance by suppressing the generation _{of MnCr 2} O _{4 having a large electric resistance inside the base material of the cell-to-cell connecting member.}
Further, when the bonding layer is baked at a temperature of less than 1075 ° C. in the bonding step, the resistance value at 700 ° C. to 800 ° C., which is the actual operating environment of the solid oxide fuel cell, can be suppressed low, which is preferable.

Another characteristic configuration of the method for producing a solid oxide fuel cell according to the present invention is that the stainless alloy as the main material of the base material contains Si.

When the stainless alloy as the main material of the base material contained Si, it was confirmed that a layer _{of SiO 2} was formed in the vicinity of the surface of the base material that had undergone the protective film forming step and the joining step. The layer is thicker at 1050 ° C. or higher than when the bonding layer is baked at 1000 ° C. It is considered that this layer has an effect of inhibiting the diffusion of Mn from the inside of the stainless alloy and suppressing the formation _{of MnCr 2} O _{4 inside the base material.} That is, according to the above-mentioned characteristic configuration, it is possible to more _{effectively suppress the generation of MnCr 2} O ₄ and provide an SOFC cell having high power generation performance.

Another characteristic configuration of the method for producing a solid oxide fuel cell according to the present invention is that the stainless alloy as the main material of the base material contains Ti.

When the stainless alloy, which is the main material of the base material, contains Ti, it was confirmed that a layer _{of TiO 2} was formed in the vicinity of the surface of the base material that had undergone the protective film forming step and the joining step. The layer is thicker at 1050 ° C. or higher than when the bonding layer is baked at 1000 ° C. It is considered that this layer has an effect of inhibiting the diffusion of Mn from the inside of the stainless alloy and suppressing the formation _{of MnCr 2} O _{4 inside the base material.} That is, according to the above-mentioned characteristic configuration, it is possible to more _{effectively suppress the generation of MnCr 2} O ₄ and provide an SOFC cell having high power generation performance.

Another characteristic feature of the manufacturing method of the solid oxide fuel cell according to the present invention, a main material of the protective layer is comprised of cobalt manganese oxide _{Co x Mn y O 4 (0} <x, y <3, x + y = 3) or zinc cobalt manganese oxide Zn _z Co _x Mn _y O ₄ (0 <x, y, z <3, x + y + z = 3).

According to the above-mentioned characteristic configuration, the discrepancy between the coefficient of thermal expansion of the protective film and the coefficient of thermal expansion of the base material and the air electrode can be reduced, and the durability of the SOFC cell can be improved, which is preferable.

Another characteristic feature of the manufacturing method of the solid oxide fuel cell according to the present invention, a main material of the protective film, lies in a Co _1.5 Mn _1.5 O ₄ or Co ₂ MnO _4.

In an experiment using a sample in which the main material of the protective film is Co ₂ MnO ₄ , it has been confirmed that the formation of _{MnCr 2} O _{4 is suppressed.} It is strongly speculated that the same result will be obtained for _{Co 1.5} Mn _1.5 O ₄ , which is a spinel-type metal oxide of the same type. That is, according to the above-mentioned characteristic configuration, it is possible to provide an SOFC cell having high power generation performance by suppressing the generation _{of MnCr 2} O _{4 having a large electric resistance inside the base material of the cell-to-cell connecting member.}

Another characteristic configuration of the method for producing a solid oxide fuel cell according to the present invention is that the protective film is formed by electrodeposition coating in the protective film forming step.

According to the above-mentioned feature configuration, a dense and strong protective film can be realized, which is suitable.

Schematic diagram of solid oxide fuel cell cell Explanatory drawing of reaction at the time of operation of solid oxide fuel cell Cross-sectional view of the cell-to-cell connecting member joining structure Schematic diagram of energization test jig Graph showing changes in electrical resistance over time SEM image and EPMA diagram of the cross section of the solid oxide fuel cell SEM image and EPMA diagram of the cross section of the solid oxide fuel cell Graph showing changes in electrical resistance over time Graph showing initial temperature characteristics (electrical resistance)

Hereinafter, a cell for a solid oxide fuel cell (SOFC) will be described, and a manufacturing method and an experimental example thereof will be shown. Preferable examples of the present invention will be described below, and each of these examples has been described in order to more specifically illustrate the present invention, and various changes may be made without departing from the spirit of the present invention. It is possible, and the present invention is not limited to the following description.

[Solid oxide fuel cell (SOFC)]
In the SOFC cell C shown in FIGS. 1 and 2, an air electrode 31 made of an oxygen ion-conducting porous body is provided on one side of an electrolyte membrane 30 made of an oxygen ion-conductive solid oxide dense body. In addition to joining, a single cell 3 formed by joining a fuel electrode 32 made of an electron-conducting porous body is provided on the other surface side of the electrolyte membrane 30.
Further, the SOFC cell C is a pair of electron conductive cells in which the single cell 3 is formed with a groove 2 for transmitting and receiving electrons to the air electrode 31 or the fuel electrode 32 and supplying air and hydrogen. It has a structure in which a gas-sealed body is appropriately sandwiched between cell-cell connecting members 1 made of an alloy or an oxide at an outer peripheral edge portion. By arranging the air electrode 31 and the cell-cell connecting member 1 in close contact with each other, the groove 2 on the air electrode 31 side functions as an air flow path 2a for supplying air to the air electrode 31. By arranging the fuel electrode 32 and the cell-cell connecting member 1 in close contact with each other, the groove 2 on the fuel electrode 32 side functions as a fuel flow path 2b for supplying hydrogen to the fuel electrode 32. The cell-to-cell connecting member 1 may have a configuration in which a member that electrically connects the interconnector and the cell C is connected.

To add a description of the general materials used in each element constituting the single cell 3, for example, the material of the air electrode 31 is LaMO ₃ (for example, M = Mn, Fe, Co, Ni). A perovskite-type oxide of _{(La, AE) MO 3} in which a part of La in the metal is replaced with an alkaline earth metal AE (AE = Sr, Ca) can be used. Cermet of Ni and yttria-stabilized zirconia (YSZ) can be used as the material of the fuel electrode 32, and yttria-stabilized zirconia (YSZ) can be used as the material of the electrolyte membrane 30. can.

Then, in a state where the plurality of SOFC cells C are stacked and arranged, the cells are sandwiched by applying a pressing force in the stacking direction by a plurality of bolts and nuts to form a cell stack.
In this cell stack, the cell-to-cell connecting members 1 arranged at both ends in the stacking direction need only be one in which only one of the fuel flow path 2b and the air flow path 2a is formed, and are arranged in the middle of the other. As the cell-cell connecting member 1, a member in which a fuel flow path 2b is formed on one surface and an air flow path 2a is formed on the other surface can be used. In a cell stack having such a laminated structure, the cell-cell connecting member 1 may be called a separator.
The cell stack is attached to a manifold that supplies fuel gas (hydrogen) with an adhesive such as a glass sealant. As the glass sealing material, for example, crystallized glass is used. The glass sealing material is used in places where sealing is required, such as between the single cell 3 and the cell-to-cell connecting member 1, in addition to adhering the manifold.
An SOFC having such a cell stack structure is generally called a flat plate type SOFC. In the present embodiment, the flat plate type SOFC will be described as an example, but the present invention can also be applied to SOFCs having other structures.

Then, when the SOFC provided with the SOFC cell C is operated, as shown in FIG. 2, air is introduced through the air flow path 2a formed in the cell-to-cell connecting member 1 adjacent to the air electrode 31. At the same time, hydrogen is supplied via the fuel flow path 2b formed in the inter-cell connecting member 1 adjacent to the fuel electrode 32, and operates at an operating temperature of, for example, about 800 ° C. Then, oxygen molecules O ₂ in the air electrode 31 is an electron e ^- is reacted with oxygen ions O ^2- is generated, the O ^2- passes through the electrolyte membrane 30 to move to the fuel electrode 32, provided at the fuel electrode 32 been H ₂ reacts with the O ^2-H ₂ O and e ^- and that is generated, the electromotive force E is generated between the pair of cell connecting member 1, outside the electromotive force E Can be taken out and used.

[Cell-to-cell connection member]
As shown in FIGS. 1 and 3, the cell-cell connecting member 1 is formed in a groove plate shape that enables connection while forming an air flow path 2a and a fuel flow path 2b with the single cell 3. By providing the protective film 12 described later on the surface of the base material 11, Cr poisoning can be suppressed, which is suitable as a cell for a solid oxide fuel cell.

The material of the cell-cell connecting member 1 is Cr, which is a material having excellent electron conductivity and heat resistance, such as Fe-Cr alloy which is a ferrite-based stainless steel and Fe-Cr-Ni alloy which is an austenitic stainless steel. An alloy containing is used. In this embodiment, in particular, the main material of the base material 11 of the cell-to-cell connecting member 1 is a stainless alloy containing Mn, preferably a ferrite type, preferably containing Si, and Ti. It is preferable to contain it.

[Oxide film]
An oxide film 13 is formed on the surface of the base material 11. The oxide film 13 is formed by oxidizing the surface of the alloy of the substrate 11 with oxygen in the ambient atmosphere. In the case of a stainless alloy containing Cr as in the present embodiment, the oxide film 13 is mainly chromium (Cr ₂ O ₃ ) and is formed as a dense film. The oxide film 13 is formed by heat treatment in the manufacturing process of the SOFC cell, such as sintering the protective film 12 and baking the bonding layer.

〔Protective film〕
A protective film 12 is formed on the surface of the base material 11 in order to suppress Cr poisoning. The protective film 12 is mainly made of a spinel-type metal oxide containing Mn and Co. The main material of the protective film 12 is cobalt manganese oxide Co _x Mn _y O ₄ (0 <x, y <3, x + y = 3) or zinc cobalt manganese oxide Zn _z Co _x Mn _y O ₄ (0). <X, y, z <3, x + y + z = 3) may be used. Co _1.5 Mn _1.5 O ₄ or Co ₂ may be MnO _4. The "main material" means that it is the main material, and it is also possible to use a mixture of a plurality of types of metal oxides or a mixture of other components.

The protective film 12 can be formed on the base material 11 by, for example, a wet coating method or a dry coating method. Examples of the wet coating method include a screen printing method, a doctor blade method, a spray coating method, an inkjet method, a spin coating method, a dip coating method, an electroplating method, an electroless plating method, and an electrodeposition coating method.
Examples of the dry coating method include a vapor deposition method, a sputtering method, an ion plating method, a chemical vapor deposition (CVD) method, an electrochemical vapor deposition (EVD) method, an ion beam method, a laser ablation method, and an atmospheric pressure plasma. Examples thereof include a film forming method, a reduced pressure plasma film forming method, and a thermal spraying method.

For example, if the electrodeposition coating method is applied, the protective film can be formed by the following method.
Metal oxide fine particles are dispersed so as to be 100 g per liter of electrodeposition liquid, and electrodeposition coating is performed using a mixed solution containing an anionic resin such as polyacrylic acid. Here, (metal oxide fine particles: anionic resin) = (1: 1) (mass ratio).
An uncured electrodeposition coating film is formed on the surface of the base material 11 by using the mixed solution and energizing the electrode plate of SUS304 with the base material 11 as a positive and a counter electrode as a negative polarity.
Electrodeposition coating is carried out, for example, by completely or partially immersing the base material 11 in an energizing tank filled with the mixed solution to form an anode and energizing.
The electrodeposition coating conditions are also not particularly limited, and are wide depending on various conditions such as the type of the metal as the base material 11, the type of the mixture, the size and shape of the energizing tank, and the application of the obtained inter-cell connecting member 1. It can be appropriately selected from the range, but usually, the bath temperature (the mixed solution temperature) is about 10 to 40 ° C., the applied voltage is about 10 to 450 V, the voltage application time is about 1 to 10 minutes, and the liquid temperature of the mixed solution is 10 to 40 ° C. And it is sufficient.
The film thickness of the electrodeposited coating film can be controlled by changing the electrodeposition voltage and the electrodeposition time. In addition, various pretreatments can be performed on the base material.
By heat-treating the base material 11 on which the uncured electrodeposition coating film is formed, a cured electrodeposition coating film is formed on the surface of the base material 11.
The heat treatment includes pre-drying for drying the electrodeposition coating film and curing heating for curing the electrodeposition coating film, and curing heating is performed after the pre-drying. Then, it is fired in an electric furnace at, for example, 1000 ° C. for 2 hours, and then slowly cooled.

[Joining layer]
The joining layer joins the cell-to-cell connecting member 1 and the air electrode 31 of the single cell 3. Specifically, the protective film 11 formed on the surface of the base material 11 of the cell-to-cell connecting member 1 and the air electrode 31 of the single cell 3 are adhered and bonded by a bonding layer. As the main material of the bonding layer, a perovskite-type oxide similar to the air electrode 31 or a spinel-type oxide is used. For example, LSCF6428 (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _3-δ ) is used.

[Manufacturing method of solid oxide fuel cell]
Next, a method for manufacturing a cell for a solid oxide fuel cell will be described. A method for manufacturing a cell for a solid oxide fuel cell includes a protective film forming step and a joining step.

[Protective film formation step]
In the protective film forming step, the protective film 12 is formed on the surface of the base material 11 of the cell-to-cell connecting member 1. The protective film 12 is formed by various methods illustrated. For example, according to the wet coating method, it is performed by a film forming step and a sintering step.

In the film forming step, a coating film is wet-deposited on the base material 11 of the cell-to-cell connection member 1 using a slurry containing a fine powder of a metal oxide. The wet film formation may be carried out by immersing the base material 11 in the slurry (dip) and pulling it up, by an electrodeposition coating method, or by using any of the methods exemplified above. The wet film formation may be performed on the entire base material 11, or may be performed on only one surface of the flat plate-shaped base material 11. In the latter case, the surface on which the protective film 12 is formed by the wet film formation is joined to the air electrode 31 of the single cell 3. The surface where the material of the base material 11 is exposed without the wet film formation is joined to the fuel electrode 32 of the single cell 3.

In the sintering step, the base material 11 on which the coating film is wet-deposited is heat-treated, and the fine powder of the metal oxide is sintered to form the protective film 12 on the surface of the base material 11. The heat treatment is performed at, for example, 1000 ° C. for 2 hours. Various choices can be made as the atmosphere during the heat treatment. When the slurry containing the fine powder is applied to one surface of the base material 11 and the material of the base material 11 is exposed on the other surface, the heat treatment is performed in an atmosphere of an inert gas or a reducing gas. If it is carried out below, oxidation of the exposed surface of the material of the base material 11 can be suppressed, which is preferable.

[Joining step]
In the joining step, the cell-to-cell connecting member 1 and the air electrode 31 are joined via a joining layer. Specifically, the paste containing the material of the above-mentioned bonding layer is applied to the cell-cell connecting member 1 to bond with the single cell 3, and heat treatment is performed to form the bonding layer by baking. Normally, the heat treatment is performed at a low temperature of the operating temperature of the fuel cell to 950 ° C., but in the present embodiment, the heat treatment is performed at a high temperature of 1050 ° C. or higher. It is more preferable to carry out at a temperature of 1075 ° C. or lower, more preferably at a temperature of less than 1075 ° C., and even more preferably at 1050 ° C.

[Changes in electrical resistance and element distribution of cell-cell connection members due to baking temperature of the bonding layer]
Experimental samples were prepared according to the method for producing SOFC cells described above, and changes in electrical resistance over time, SEM observation of cross sections, and EPMA elemental analysis were performed.

[Creation of experimental sample]
[Experimental Example 1 (1000 ° C.): Comparative Example]
A coating film was formed on the surface of a 1 mm thick 22 wt% Cr high-purity ferritic stainless steel plate by an anion electrodeposition coating method using a slurry containing a fine powder of _{Co 2} MnO _4. The plate was heated in an air atmosphere of 1000 ° C. for 2 hours to form a protective film containing _{Co 2} MnO _{4 as a main material.} LSCF6428 was applied to both sides of the plate, dried, and baked at 1000 ° C. for 2 hours to form a bonding layer (a layer simulating). As described above, a sample of Experimental Example 1 imitating the cell-to-cell connection member 1 of the solid oxide fuel cell cell was prepared.

[Experimental Example 2 (1025 ° C.): Comparative Example]
The baking temperature of the bonding layer was changed to 1025 ° C., and the other conditions were the same as in Experimental Example 1 to prepare a sample of Experimental Example 2.

[Experimental Example 3 (1050 ° C.): Example]
The baking temperature of the bonding layer was changed to 1050 ° C., and the other conditions were the same as in Experimental Example 1, and a sample of Experimental Example 3 was prepared.

[Experimental Example 4 (1075 ° C.): Example]
The baking temperature of the bonding layer was changed to 1075 ° C., and the other conditions were the same as in Experimental Example 1 to prepare a sample of Experimental Example 4.

[Changes in electrical resistance over time]
The time course of electrical resistance was measured for the samples of Experimental Examples 1 to 4. The results up to 800 hours are shown in the graph of FIG. The measurement was carried out by setting each sample on the energization test jig 5 shown in FIG. 4 and measuring the electric resistance with time in a constant current state in an environment of 900 ° C. The energization test jig 5 has a structure in which a sample is sandwiched between a pair of metal plates 51 and fixed with screws 52. The Pt mesh 53 was in contact with the bonding layer, and the resistance value of the sample was measured by measuring the resistance value between the pair of Pt mesh 53.

From the results shown in FIG. 5, the sample of Experimental Example 3 (1050 ° C.) had the lowest electrical resistance, followed by Experimental Example 4 (1075 ° C.), which had the lowest electrical resistance, and Experimental Example 1 (1000 ° C.) and Experimental Example 2 ( 1025 ° C.) is recognized as having a relatively large electrical resistance.

In Experimental Example 3 (1050 ° C.), the initial resistance at the start of the experiment was also the smallest, and then the resistance value gradually decreased until around 300 hours. It tends to increase slightly after 300 hours, but even after 800 hours, the electrical resistance is the smallest among the experimental samples.

In Experimental Example 4 (1075 ° C.), the initial resistance at the start of the experiment was about the same as that of Experimental Example 1 (1000 ° C.) and Experimental Example 2 (1025 ° C.), but the resistance value gradually increased until around 500 hours thereafter. It has decreased. After that, it tends to increase slightly, but the rate of increase is small, and even at 800 hours, the electrical resistance is the second smallest after Experimental Example 3 (1050 ° C.).

Experimental Example 1 (1000 ° C.) had the largest initial resistance at the start of the experiment, and consistently experienced Experimental Example 3 (1050 ° C.) and Experimental Example 4 (1075 ° C.) during a rapid increase, a gradual decrease, and a gradual increase. The electrical resistance is greater than (° C).

In Experimental Example 2 (1025 ° C.), the initial resistance at the start of the experiment was about the same as that in Experimental Example 3 (1050 ° C.), but after that, it continued to increase rapidly and gradually, and the electrical resistance was the highest after 200 hours. big.

The graph of FIG. 8 shows the results of the change in electrical resistance over time up to 4500 hours. From the results shown in FIG. 8, it was found that the experimental sample of Experimental Example 3 (1050 ° C.) had the smallest increase in long-term electrical resistance and the highest durability.

In Experimental Example 1 (1000 ° C.) and Experimental Example 2 (1025 ° C.), the electrical resistance increased after 3000 hours. This increase in resistance is due to the fact that _{the layers of TiO 2} and SiO ₂ (described later) formed at the metal / oxide film interface are thinner than those of Experimental Example 3 (1050 ° C) and Experimental Example 4 (1075 ° C), resulting in a high temperature environment. It is considered that this is due to the _{increase in the thickness of the Cr 2} O ₃ coating under (900 ° C.) or the abnormal oxidation of the stainless steel base material ( _{formation of Fe 2} O _{3 and high temperature corrosion of the metal).}

[Initial temperature characteristics (electrical resistance)]
For the samples of Experimental Examples 1 to 4, the initial temperature characteristics of the electric resistance were measured before measuring the time-dependent change of the electric resistance described above. The results are shown in the graph of FIG. The measurement was carried out by setting the sample in the same state as the above-mentioned time-dependent change measurement and measuring the electric resistance at a temperature of 600 ° C. to 900 ° C. in increments of 50 ° C.

From the results shown in FIG. 5, it is recognized that Experimental Example 4 (1075 ° C.) has the highest electrical resistance in the actual operating environment of the solid oxide fuel cell, 700 ° C. to 800 ° C. _{It is considered that this is because the layers of TiO 2} , SiO ₂ , and Cr ₂ O ₃ (described later) formed at the metal / oxide film interface are the thickest in the experimental examples.

From the above initial temperature characteristics and the measurement results of the change with time, Experimental Example 4 (1075 ° C.) showed the smallest electrical resistance with time change at 900 ° C., but in the actual operating environment of the solid oxide fuel cell. It was found that the electrical resistance increased at a certain 700 ° C. to 800 ° C. Therefore, if the bonding layer is baked at a temperature of less than 1075 ° C. in the bonding step, the resistance value at 700 ° C. to 800 ° C., which is the actual operating environment of the solid oxide fuel cell, can be suppressed low, which is preferable. .. It is even more preferable that the bonding layer is baked at 1050 ° C. in the bonding step.

[Changes in element distribution]
The prepared samples of Experimental Examples 1, 3 and 4 were subjected to SEM observation of cross sections and EPMA elemental analysis. The observation and analysis were carried out in a state after the sample was prepared (after the bonding layer was baked) (FIG. 6) and in a state where the heat treatment was performed at 900 ° C. for 400 hours (FIG. 7). Observation and analysis are performed on Experimental Example 1 (1000 ° C., upper part of each figure), Experimental Example 3 (1050 ° C., middle part of each figure) and Experimental Example 4 (1075 ° C., lower part of each figure).

The leftmost row of each figure shows the image of SEM observation, and the other four rows show the EPMA element mapping diagram (Cr, Mn, Si and Ti). In the SEM image, the base material 11, the oxide film 13, the protective film 12, and the bonding layer are shown from the upper side of the image. In the EPMA element mapping diagram (hereinafter referred to as “EPMA diagram”), the positions where the element concentration is high are shown in dark colors. The concentration scales of the four elements are different, and even if the same dark color appears between different elements, it does not mean that they have the same concentration.

The field of view of the SEM image and the field of view of the EPMA diagram are in agreement. For example, in the EPMA diagram of Cr of the 1000 ° C. sample (Experimental Example 1) of FIG. 6, a dark Cr distribution region exists at the lower part of the diagram, but this region coincides with the region of the oxide film 13 of the SEM image. ing. _{This is because Cr contained in chromia (Cr 2} O ₃ ), which is the main component of the oxide film 13, appears in the EPMA diagram. It is recognized that Cr is lightly distributed in the region of the base material 11 and does not exist in the region of the protective film 12 and the bonding layer. This is consistent with the composition of the base material 11, the protective film 12, and the bonding layer.

First, focusing on the distribution of Cr, in the state after sample preparation shown in FIG. 6, the Cr distribution region 6 is formed in the region of the oxide film 13 in all of Experimental Examples 1, 3 and 4. The state is maintained even after being heat-treated at 900 ° C. for 400 hours as shown in FIG. 7, and no significant change is observed. That is, it is considered that the distribution state of Cr has not changed significantly by the heat treatment at 900 ° C. for 400 hours.

[Distribution of Mn]
Next, focusing on the distribution of Mn, in the state after sample preparation shown in FIG. 6, the Mn distribution region 7 is formed in the region of the protective film 12 in all of Experimental Examples 1, 3 and 4. The Mn distribution region 7 does not exist in the region of the base material 11. Comparing this with the state of heat treatment at 900 ° C. for 400 hours shown in FIG. 7, in Experimental Example 1 (1000 ° C.), in addition to the Mn distribution region 7, an island-shaped region 7a was formed on the upper side thereof. It is recognized that it is. The position of the island-shaped Mn distribution region 7a is recognized to be inside the base material 11 from the comparison with the EPMA diagram of Cr and the SEM image. That is, in Experimental Example 1 (1000 ° C.), it is recognized that Mn moved from the protective film 12 and the Mn distribution region 7a was formed inside the base material 11 by the heat treatment at 900 ° C. for 400 hours.

From thermodynamic considerations, the Mn of this island-shaped Mn distribution region 7a is bound to Cr contained in the base material 11 by the oxygen potential near the metal / protective film interface, and exists as _{MnCr 2} O _4. It is thought that it is. Since MnCr ₂ O ₄ has a very large electrical resistance in the temperature range under the operating environment of SOFC as _{compared with chromia (Cr 2} O _{3 ), the Mn Cr 2} O _{4 in the} Mn distribution region 7a is used in Experimental Example 1. It is probable that the electrical resistance of the sample in was increased.

Then, in Experimental Example 3 (1050 ° C.), even in the state of being heat-treated at 900 ° C. for 400 hours shown in FIG. 7, only the band-shaped Mn distribution region 7 formed in the region of the protective film 12 is present. It is recognized that the island-shaped region as in Experimental Example 1 does not exist inside the base material 11. Therefore, in Experimental Example 3 (1050 ° C.), _{it is considered that the high resistance MnCr 2} O ₄ as in Experimental Example 1 was not generated, and therefore the electrical resistance was reduced.

In Experimental Example 4 (1075 ° C.), it is recognized that a small island-shaped Mn distribution region 7b is formed above the band-shaped Mn distribution region 7. From the comparison with the SEM diagram and the EPMA diagram of Cr, it is recognized that these island-shaped regions exist inside the oxide film 13. In Experimental Example 1, the island-shaped Mn distribution region 7a was located inside the substrate 11. That is, the location of the island-shaped Mn distribution region 7b in Experimental Example 4 is different from that in Experimental Example 1.

From the thermodynamic point of view, the Mn distribution region 7b located inside the oxide film 13 (that is, inside the chromia (Cr ₂ O _{3 )) of Experimental Example 4 is not Mn Cr 2} O 4 of Experimental Example 1 but more. It is considered that it exists as _{Mn 2} CrO _{4 having} a small electric resistance. As a result, it is considered that the electrical resistance of Experimental Example 4 is significantly smaller than that of Experimental Example 1.

[Distribution of Si]
Next, focusing on the distribution of Si, in the state after sample preparation shown in FIG. 6, in each of Experimental Examples 1, 3 and 4, the Si distribution region 8 is inside the base material 11, and the base material 11 and the oxide film are formed. It is formed in a band shape along the interface with 13. That is, it is considered that Si contained in the stainless alloy of the base material 11 _{forms a layer of SiO 2 in the vicinity of the surface of the base material 11.} Comparing Experimental Examples 1, 3 and 4, it is recognized that the thickness of the Si distribution region 8 of Experimental Examples 3 and 4 is larger than the thickness of the Si distribution region 8 of Experimental Example 1. Therefore, it is recognized that the higher the baking temperature of the bonding layer, the larger the thickness of the Si distribution region 8, that is, the thickness of the SiO _{2 layer.} The SiO ₂ layer has the effect of inhibiting the diffusion of Mn from the protective film 12 into the base material 11 and suppressing the formation _{of Mn Cr 2} O _{4 inside the base material 11 as in Experimental Example 1.} Conceivable. From the comparison between FIGS. 6 and 7, it is recognized that the thickness of _{the SiO 2} layer is increased even by the heat treatment at 900 ° C. for 400 hours.

[Distribution of Ti]
Finally, focusing on the distribution of Ti, in the state after sample preparation shown in FIG. 6, in all of Experimental Examples 1, 3 and 4, the Ti distribution region 9 is inside the base material 11, and the base material 11 and the oxide film are formed. It is formed in a band shape along the interface with 13. That is, it is considered that Ti contained in the stainless alloy of the base material 11 _{forms a layer of TiO 2 in the vicinity of the surface of the base material 11.} Comparing Experimental Examples 1, 3 and 4, it is recognized that the thickness of the Ti distribution region 9 of Experimental Examples 3 and 4 is larger than the thickness of the Ti distribution region 9 of Experimental Example 1. Therefore, it is recognized that the higher the baking temperature of the bonding layer, the larger the thickness of the Ti distribution region 9, that is, the thickness of the TiO _{2 layer.} The TiO ₂ layer has the effect of inhibiting the diffusion of Mn from the protective film 12 into the base material 11 and suppressing the formation _{of Mn Cr 2} O _{4 inside the base material 11 as in Experimental Example 1.} Conceivable. From the comparison between FIGS. 6 and 7, it is recognized that the thickness of _{the TiO 2} layer is increased even by the heat treatment at 900 ° C. for 400 hours.

1: Cell-to-cell connecting member 11: Base material 12: Protective film 13: Oxide film 2: Groove 2a: Air flow path 2b: Fuel flow path 3: Single cell 30: Electrolyte film 31: Air pole 32: Fuel pole 4: Joining Material C: Solid oxide fuel cell

Claims (7)

A method for manufacturing a cell for a solid oxide fuel cell, which is formed by joining a cell-to-cell connecting member and an air electrode.
A protective film forming step of forming a protective film on the surface of the base material of the cell-cell connecting member,
It has a joining step for joining the cell-to-cell connecting member and an air electrode via a joining layer.
The base material is mainly made of a stainless alloy containing Mn.
The protective film is mainly made of a spinel-type metal oxide containing Mn and Co.
The bonding layer is baked in the bonding step at a temperature of 1050 ° C. or higher and 1075 ° C. or lower.
A method for manufacturing a cell for a solid oxide fuel cell. A method for manufacturing a cell for a solid oxide fuel cell, which is formed by joining a cell-to-cell connecting member and an air electrode.
A protective film forming step of forming a protective film on the surface of the base material of the cell-cell connecting member,
It has a joining step for joining the cell-to-cell connecting member and an air electrode via a joining layer.
The base material is mainly made of a stainless alloy containing Mn.
The protective film is mainly made of a spinel-type metal oxide containing Mn and Co.
The bonding layer is baked in the bonding step at a temperature of 1050 ° C or higher and lower than 1075 ° C.
A method for manufacturing a cell for a solid oxide fuel cell. The method for producing a solid oxide fuel cell according to claim 1 or 2 , wherein the stainless alloy as the main material of the base material contains Si. The method for producing a cell for a solid oxide fuel cell according to any one of claims 1 to 3 , wherein the stainless alloy as the main material of the base material contains Ti. The main material of the protective film is cobalt manganese oxide Co _x Mn _y O ₄ (0 <x, y <3, x + y = 3) or zinc cobalt manganese oxide Zn _z Co _x Mn _y O ₄ (0). The method for producing a cell for a solid oxide fuel cell according to any one of claims 1 to 4 , wherein <x, y, z <3, x + y + z = 3). The main material of the protective film, Co _1.5 Mn _1.5 O ₄ or Co ₂ MnO ₄ The method of manufacturing a solid oxide fuel cell according to any one of claims 1 to 5,. The method for producing a solid oxide fuel cell according to any one of claims 1 to 6 , wherein the protective film is formed by electrodeposition coating in the protective film forming step.

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