JP7357577B2 - Inter-cell connection member, solid oxide fuel cell, SOFC monogeneration system, SOFC cogeneration system, and method for manufacturing inter-cell connection member - Google Patents

Description

The present invention relates to an intercell connection member used in a solid oxide fuel cell, a solid oxide fuel cell, an SOFC monogeneration system, an SOFC cogeneration system, and an intercell connection member used in a solid oxide fuel cell. Regarding the manufacturing method.

A solid oxide fuel cell (hereinafter, appropriately referred to as "SOFC") cell includes a single cell having an air electrode and a fuel electrode, and an intercell connection member. A portion of the inter-cell connection member is joined to the fuel electrode, and another portion of the inter-cell connection member is joined to the air electrode. The intercell connection member used in such SOFC cells is manufactured using a metal base material made of stainless steel that has excellent electronic conductivity and heat resistance.

In the part of the inter-cell connecting member used on the fuel electrode side, phosphorus volatilized from the stainless steel that constitutes the inter-cell connecting member reacts with Ni, which is the main component of the fuel electrode of the SOFC cell, and the fuel electrode This may cause deterioration such as inducing volatilization of Ni from the surface. For example, when Ni used in the fuel electrode of SOFC cells reacts with impurities such as phosphorus volatilized from intercell connecting members under high-temperature operating conditions, the vapor pressure is generally lower than that of metallic Ni. will rise. As a result, Ni volatilizes from the fuel electrode material (mainly cermet of Ni and oxide of electrolyte material), and the Ni metal network in the fuel electrode is disrupted, resulting in a decrease in electronic conductivity and a decrease in cell performance (deterioration). happens. In this case, although the phosphorus contained in the stainless steel metal base material constituting the inter-cell connection member is at a low concentration of, for example, several hundred ppm, it has been reported that it causes deterioration of the fuel electrode.

Patent Document 1 (Japanese Patent No. 3855043) describes a method for manufacturing ultra-low phosphorus stainless steel. By using stainless steel manufactured using this manufacturing method as the metal base material of the inter-cell connecting member, it is possible to suppress the deterioration of the fuel electrode as described above.

Another problem occurs in the portion of the inter-cell connection member used on the air electrode side. Specifically, since the stainless steel that constitutes the inter-cell connection member contains Cr, an oxidation-resistant film of Cr ₂ O ₃ is formed in the part used on the air electrode side under high-temperature operating conditions. . This oxide film is a high-resistance layer that reduces the power generation output of the fuel cell, or reacts with the air electrode of the SOFC cell due to evaporation of Cr from the stainless steel, significantly reducing electrode performance. There is a problem with sexuality.

Patent Document 2 (International Publication No. 2007/083627) describes a firing process in which an inter-cell connecting member manufactured using a metal base material such as a stainless steel alloy containing Cr and an air electrode are fired in a state in which they are bonded together. In doing so, it is described that the alloy or oxide is brought into a Cr(VI) oxide suppressed state that suppresses the formation of Cr(VI) oxide. In order to suppress this Cr(VI) oxide, an n-type semiconductor film made of an oxide whose standard free energy of formation is WO ₃ or less is formed on the surface of the alloy or oxide before the firing process. It is described that a film forming process is performed.
In this way, in order to suppress the formation of high-resistance Cr ₂ O ₃ and to prevent scattering due to evaporation of Cr from stainless steel, a highly electronically conductive material is added to the surface of the metal base material. Forming a ceramic coating as a protective film has been practiced. By applying such a ceramic coating, it has become possible to use inexpensive stainless steel as the material for the metal base material.

Patent No. 3855043 International Publication No. 2007/083627

As described in Patent Document 1, a method for manufacturing stainless steel with a low phosphorus concentration has been proposed, but there is a problem in that the use of such stainless steel increases the cost of the inter-cell connecting member. Furthermore, it is not possible to completely eliminate phosphorus contained in stainless steel.

The method described in Patent Document 2 includes measures for the surface of the metal base material constituting the inter-cell connection member that is to be joined to the air electrode of the single cell constituting the solid oxide fuel cell. This is not a measure for the surface that is joined to the fuel electrode.

In this way, conventional countermeasures include measures for the surface of the metal base material constituting the inter-cell connection member that is bonded to the air electrode, and countermeasures for the surface that is bonded to the fuel electrode. have been discussed separately. In other words, a coating design that takes into account both the side of the surface of the inter-cell connecting member that is bonded to the fuel electrode and the side that is bonded to the air electrode is not performed.

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide an intercell connection member that exhibits good performance on both the fuel electrode side and the air electrode side while the procedure for forming a coating is simple. The present invention provides a solid oxide fuel cell, a SOFC monogeneration system, a SOFC cogeneration system, and a method for manufacturing an intercell connection member.

The characteristic structure of the inter-cell connection member according to the present invention for achieving the above object is an inter-cell connection member used for a solid oxide fuel cell, comprising:
A metal base material made of stainless steel,
Among the surfaces of the metal base material, the surface on the side to be joined to the fuel electrode of the single cell constituting the cell for the solid oxide fuel cell, and the surface on the side to be joined to the air electrode of the single cell. A base coating layer formed using Ni and Co,
The present invention further includes a protective film formed using an oxide containing Mn, which is formed on the surface of the base coating layer that is connected to the air electrode of the unit cell.
Here, the protective film may be formed using any one of Mn oxide, Co--Mn based oxide, Ni--Mn based oxide, and Cu--Mn based oxide.

According to the characteristic configuration described above, among the surfaces of the metal base material constituting the inter-cell connection member, the surface on the side to be joined to the fuel electrode of the single cell constituting the cell for solid oxide fuel cell, and the air electrode Since the same base material coating layer is attached to both surfaces to be joined to the metal base material, there is no need to cover the metal base material with a mask or the like when forming the base material coating layer. As a result, the procedure for forming the base material coating layer on the surface of the metal base material becomes simple, and there is an advantage that the manufacturing cost of the inter-cell connecting member is reduced.
Further, among the surfaces of the metal base material constituting the inter-cell connection member, the surface on the side to be joined to the fuel electrode of the single cell constituting the cell for solid oxide fuel cell is made of Ni and Co. A substrate coating layer is formed. Thereby, even if the metal base material contains phosphorus, volatilization of the phosphorus from the metal base material is suppressed. As a result, when the inter-cell connecting member is joined to the fuel electrode of the solid oxide fuel cell, it is possible to suppress the adverse effects of phosphorus on the fuel electrode. In addition, since Ni and Co in the base material coating layer on the fuel electrode side are exposed to a reduced state during power generation operation, they exist in a metallic state and have sufficient electronic conductivity, so an increase in electrical resistance is not considered. You don't have to.
Furthermore, among the surfaces of the metal base material of the inter-cell connection member, the surface on the side to be joined to the air electrode of the single cell constituting the solid oxide fuel cell is made of Ni and Co. A base coating layer is formed, and a protective film made of an oxide containing Mn is further formed on the surface of the base coating layer. In other words, among the surfaces of the metal base material of the inter-cell connection member, the surface on the side to be joined to the air electrode of the single cell constituting the solid oxide fuel cell is coated with a base material coating layer and a protective film. Since a layer consisting of a ternary material containing Ni, Co, and Mn is formed, the formation of high-resistance Cr ₂ O ₃ is suppressed and scattering due to evaporation of Cr from the metal base material is prevented. Ru.

In this way, the base material coating layer formed on both the surface of the metal base material of the inter-cell connection member on the side to be joined to the fuel electrode and the surface on the side to be joined to the air electrode is bonded to the fuel electrode. On the surface to be bonded, it has the effect of suppressing the volatilization of phosphorus from the metal base material, and on the surface to be bonded to the air electrode, high resistance Cr ₂ O ₃ is formed together with a protective film. This has the effect of preventing scattering due to evaporation of Cr from the metal base material. In other words, in this characteristic configuration, the coating design takes into account both the side of the surface of the inter-cell connection member that is bonded to the fuel electrode and the side that is bonded to the air electrode, so that the procedure for forming the coating is simplified. It is possible to provide an inter-cell connection member that is simple but exhibits good performance on both the fuel electrode side and the air electrode side.

A characteristic configuration of the solid oxide fuel cell according to the present invention is that a plurality of the solid oxide fuel cell cells each including the inter-cell connecting member and the single cell are stacked.

According to the characteristic structure described above, it is possible to obtain a solid oxide fuel cell that can suppress phosphorus poisoning of the fuel electrode and suppress Cr poisoning of the air electrode.

A characteristic configuration of the SOFC monogeneration system according to the present invention is that it includes the solid oxide fuel cell described above and supplies the electric power generated by the solid oxide fuel cell to an electric power load.

According to the characteristic configuration described above, it is possible to realize an SOFC monogeneration system that uses a solid oxide fuel cell with high power generation performance and supplies electric power generated by the solid oxide fuel cell to an electric power load.

A characteristic configuration of the SOFC cogeneration system according to the present invention is that it includes the solid oxide fuel cell described above and supplies electric power and heat generated by the solid oxide fuel cell to an electric power load and a heat load.

According to the above characteristic configuration, it is possible to realize an SOFC cogeneration system that uses a solid oxide fuel cell with high power generation performance and supplies electric power and heat generated by the solid oxide fuel cell to an electric power load and a heat load. .

A characteristic configuration of the method for manufacturing an inter-cell connection member according to the present invention is a method for manufacturing an inter-cell connection member used for a solid oxide fuel cell, comprising:
Among the surfaces of the metal base material made of stainless steel, the surface on the side to be joined to the fuel electrode of the single cell constituting the solid oxide fuel cell, and the surface joined to the air electrode of the single cell. A film forming step of forming a base coating layer made of Ni and Co on the surface of the side to be treated;
A protective film forming step of forming a protective film made of an oxide containing Mn on the surface of the base coating layer that is connected to the air electrode of the single cell. It is in.

According to the characteristic structure described above, the film forming process allows both the surface of the metal base material constituting the inter-cell connection member to be bonded to the fuel electrode and the surface to be bonded to the air electrode. Since the same base material coating layer is attached to the base material coating layer, there is no need to cover the metal base material with a mask or the like when forming the base material coating layer. As a result, the procedure for forming the base material coating layer on the surface of the metal base material becomes simple, and there is an advantage that the manufacturing cost of the inter-cell connecting member is reduced.
Furthermore, in the film-forming process, among the surfaces of the metal base material constituting the inter-cell connection member, Ni is applied to the surface of the metal base material constituting the inter-cell connection member on the side to be joined to the fuel electrode of the single cell constituting the solid oxide fuel cell. A base coating layer is formed using Co and Co. Thereby, even if the metal base material contains phosphorus, volatilization of the phosphorus from the metal base material is suppressed. As a result, when the inter-cell connecting member is joined to the fuel electrode of the solid oxide fuel cell, it is possible to suppress the adverse effects of phosphorus on the fuel electrode. In addition, since Ni and Co in the base material coating layer on the fuel electrode side are exposed to a reduced state during power generation operation, they exist in a metallic state and have sufficient electronic conductivity, so an increase in electrical resistance is not considered. You don't have to.
Furthermore, among the surfaces of the metal base material of the inter-cell connection member, the surface on the side to be joined to the air electrode of the single cell constituting the solid oxide fuel cell is made of Ni and Co. A base coating layer is formed, and a protective film made of an oxide containing Mn is further formed on the surface of the base coating layer. In other words, among the surfaces of the metal base material of the inter-cell connection member, the surface on the side to be joined to the air electrode of the single cell constituting the solid oxide fuel cell is coated with a base material coating layer and a protective film. Since a layer consisting of a ternary material containing Ni, Co, and Mn is formed, the formation of high-resistance Cr ₂ O ₃ is suppressed and scattering due to evaporation of Cr from the metal base material is prevented. Ru.

In this way, the base material coating layer formed on both the surface of the metal base material of the inter-cell connection member on the side to be joined to the fuel electrode and the surface on the side to be joined to the air electrode is bonded to the fuel electrode. On the surface to be bonded, it has the effect of suppressing the volatilization of phosphorus from the metal base material, and on the surface to be bonded to the air electrode, high resistance Cr ₂ O ₃ is formed together with a protective film. This has the effect of preventing scattering due to evaporation of Cr from the metal base material. In other words, in this characteristic configuration, the coating design takes into account both the side of the surface of the inter-cell connection member that is bonded to the fuel electrode and the side that is bonded to the air electrode, so that the procedure for forming the coating is simplified. It is possible to provide a method for manufacturing an inter-cell connection member that is simple but exhibits good performance on both the fuel electrode side and the air electrode side.

FIG. 1 is a schematic diagram of a solid oxide fuel cell. FIG. 2 is an explanatory diagram of reactions during operation of a solid oxide fuel cell. FIG. 3 is a cross-sectional view showing the structure of an inter-cell connection member. 1 is a diagram showing the configuration of a system including a solid oxide fuel cell.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an inter-cell connection member 1 used in a solid oxide fuel cell (SOFC) cell, a method for manufacturing the same, and a solid oxide fuel cell according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram of a solid oxide fuel cell. FIG. 2 is an explanatory diagram of reactions during operation of a solid oxide fuel cell. As shown in FIGS. 1 and 2, the SOFC cell (solid oxide fuel cell) C includes a single cell 3 and an intercell connection member 1. The single cell 3 includes an air electrode 31 and a fuel electrode 32, and specifically, an electrolyte membrane 30 made of a dense solid oxide that conducts oxygen ions and has an electrode that conducts oxygen ions and electrons on one side of the electrolyte membrane 30. An air electrode 31 made of an electronically conductive porous material is joined to the electrolyte membrane 30, and a fuel electrode 32 made of an electronically conductive porous material is joined to the other side of the electrolyte membrane 30.

The SOFC cell C connects this single cell 3 to a pair of electronically conductive cells in which a groove 2 is formed for transferring electrons to and from an air electrode 31 or a fuel electrode 32 and for supplying air and hydrogen. It has a structure in which a gas seal body is sandwiched between the connecting members 1 and the outer periphery thereof as appropriate. By closely arranging the air electrode 31 and the inter-cell connection member 1, 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 closely arranging the fuel electrode 32 and the inter-cell connection member 1, the groove 2 on the fuel electrode 32 side functions as a fuel flow path 2b for supplying hydrogen to the fuel electrode 32.

Adding an explanation to the general materials used for each element constituting the single cell 3, for example, the material of the air electrode 31 is _LaMO3 (for example, M=Mn, Fe, Co, Ni). A perovskite-type oxide of (La, AE) MO ₃ in which a part of is replaced with an alkaline earth metal AE (AE=Sr, Ca) can be used. As a material for the fuel electrode 32, for example, a cermet of Ni and yttria-stabilized zirconia (YSZ) can be used, and as a material for the electrolyte membrane 30, for example, yttria-stabilized zirconia (YSZ) can be used.

Then, a plurality of SOFC cells C are stacked and held together by a plurality of bolts and nuts while applying a pressing force in the stacking direction to form a cell stack. In this way, a solid oxide fuel cell (cell stack) in which a plurality of SOFC cells C each including an intercell connection member 1 and a single cell 3 are stacked is obtained. In this cell stack, the inter-cell connection members 1 placed at both ends in the stacking direction only need to form one of the fuel flow path 2b or the air flow path 2a; The inter-cell connection member 1 may have a fuel flow path 2b formed on one surface and an air flow path 2a formed on the other surface. In addition, in a cell stack having such a laminated structure, the inter-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 not only for adhesion of the manifold but also for places where sealing is required, such as between the single cell 3 and the intercell connection member 1. A solid oxide fuel cell having such a cell stack structure is generally called a flat solid oxide fuel cell. In this embodiment, a flat solid oxide fuel cell will be described as an example, but the present invention is also applicable to solid oxide fuel cells having other structures.

During operation of a solid oxide fuel cell (cell stack) equipped with such SOFC cells C, as shown in FIG. Air is supplied through the passage 2a, and hydrogen is supplied through the fuel flow passage 2b formed in the inter-cell connection member 1 adjacent to the fuel electrode 32, and it operates at an operating temperature of, for example, about 800°C. . Then, oxygen molecules O ₂ react with electrons e ⁻ at the air electrode 31 to generate oxygen ions O ²⁻ , which move to the fuel electrode 32 through the electrolyte membrane 30 and ^are supplied at the fuel electrode 32. The generated H ₂ reacts with the O ^2- to generate H ₂ O and e ^- , thereby generating an electromotive force E between the pair of inter-cell connecting members 1, and transmitting the electromotive force E to the outside. It can be taken out and used.

<Inter-cell connection member 1>
FIG. 3 is a cross-sectional view showing the structure of the inter-cell connection member 1. As shown in FIG. As shown in the figure, the inter-cell connecting member 1 includes a metal base material 11 made of stainless steel, and a fuel electrode 32 of a single cell 3 constituting a SOFC cell C on the surface of the metal base material 11. A base coating layer 13 made of Ni and Co formed on the surface to be joined and the surface to be joined to the air electrode 31 of the single cell 3; A protective film 12 formed using an oxide containing Mn is formed on the surface of the unit cell 3 on the side that is joined to the air electrode 31.

That is, in the method for manufacturing the inter-cell connection member 1 of this embodiment, the surface of the metal base material 11 made of stainless steel is bonded to the fuel electrode 32 of the single cell 3 constituting the SOFC cell C. A base material made of Ni and Co on the surface of the side to be joined to the air electrode 31 of the single cell 3 (in the case of FIG. 3, the entire surface of the metal base material 11). A film forming process of forming the coating layer 13, and a protection configured using an oxide containing Mn on the surface of the base coating layer 13 on the side that is joined to the air electrode 31 of the single cell 3. and a protective film forming step of forming the film 12.

Ferritic stainless steel is often used as the metal base material 11 of the inter-cell connection member 1, but Fe-Cr-Ni alloy, which is an austenitic stainless steel with better heat resistance, and Ni, which is a nickel-based alloy, are also used. -Cr alloy etc. may also be used. Further, instead of an alloy, a metal oxide such as (La, Ca)CrO ₃ (calcium-doped lanthanum chromite) may be used. As will be described later, the stainless steel that constitutes the metal base material 11 contains a trace amount of phosphorus.

<Base material coating layer 13>
As described above, among the surfaces of the metal base material 11, both the surface on the side to be joined to the fuel electrode 32 of the single cell 3 constituting the SOFC cell C and the surface on the side to be joined to the air electrode 31 A base material coating layer 13 is formed. Note that, as in the example shown in FIG. 3, the base material coating layer 13 may be formed on the entire surface of the metal base material 11. The base material coating layer 13 is formed by coating the metal base material 11 with Ni (nickel) and Co (cobalt). The thickness of the base material coating layer 13 can be set as appropriate, and is, for example, 5 μm. As a method for forming the base material coating layer 13, a plating method, an electrodeposition coating method, a sputtering method, etc. can be used.

<Protective film 12>
As described above, the protective film 12 is formed on the surface of the metal base material 11 on the side to be joined to the air electrode 31 of the single cell 3 constituting the SOFC cell C. The protective film 12 is formed as a thick film by coating the metal base material 11 with a film-forming material containing a conductive ceramic material. The thickness of the thick film is preferably 0.1 μm to 100 μm.

Examples of the method for forming the protective film 12 include the following.
For example, it can be formed by 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, an electroplating method, an electroless plating method, an electrodeposition coating method, and the like. Dry coating methods include, for example, vapor deposition, sputtering, ion plating, chemical vapor deposition (CVD), electrochemical vapor deposition (EVD), ion beam method, laser ablation, and atmospheric pressure plasma. Examples include a film forming method, a reduced pressure plasma film forming method, and a thermal spraying method.

However, as dry coating methods, CVD/EVD methods, thermal spraying methods, etc. have drawbacks such as the process for forming a protective film being complicated and the composition of the protective film 12 being unstable. It has also been considered to form the protective film 12 by a laser ablation method. In addition, if the laser ablation method is adopted, the manufacturing cost will be higher than that of the CVD/EVD method or the thermal spraying method, so in reality, the wet coating method is adopted as a technology that can manufacture the protective film 12 at low cost. There are many cases.

For example, if an electrodeposition coating method is applied, the protective film 12 can be formed by the following method.
Metal oxide fine particles were dispersed in an amount of 100 g per liter of electrodeposition solution, and electrodeposition coating was performed using a mixed solution containing an anion type resin such as polyacrylic acid. Here, (metal oxide fine particles: anionic resin)=(1:1) (mass ratio). Using the mixed liquid, by applying current to the metal base material 11 with positive polarity and the SUS304 plate as a counter electrode with negative polarity, the air in the single cell 3 constituting the SOFC cell C on the surface of the metal base material 11 is removed. An uncured electrodeposition coating film is formed on the surface of the side to be joined to the pole 31. Electrodeposition coating is carried out according to a known method, for example, by completely or partially immersing the metal base material 11 in an energizing tank filled with a liquid mixture to serve as an anode, and then applying electricity. Electrodeposition coating conditions are also not particularly limited, and can vary depending on various conditions such as the type of metal that is the metal base material 11, the type of mixed liquid, the size and shape of the energizing tank, and the use of the resulting intercell connection member 1. It can be selected as appropriate from the range, but usually the bath temperature (mixture temperature) is about 10 to 40°C, the applied voltage is about 10 to 450V, the voltage application time is about 1 to 10 minutes, and the mixed liquid temperature is 10 to 40°C. And it is sufficient. Note that the thickness of the electrodeposited film can be controlled by changing the electrodeposition voltage and electrodeposition time. Moreover, various pre-treatments can also be performed on the metal base material 11. A hardened electrodeposition coating film is formed on the surface of the metal substrate 11 by heat-treating the metal substrate 11 on which the uncured electrodeposition coating film is formed. The heat treatment includes preliminary drying to dry the electrodeposition coating film and curing heating to cure the electrodeposition coating film, and the curing heating is performed after the preliminary drying. Thereafter, it was fired at 1000° C. for 2 hours using an electric furnace, and then slowly cooled to obtain the inter-cell connection member 1.

As the metal oxide fine particles used as the material for forming the protective film, metal oxide fine particles made of an oxide containing Mn are used. Specifically, the metal oxide fine particles used as the material for forming the protective film include Mn (manganese) oxide, Co-Mn type (cobalt manganese type) oxide, and Ni-Mn type (nickel manganese type) oxide. Any one of oxides and Cu--Mn-based (copper-manganese-based) oxides is used.

As described above, among the surfaces of the metal base material 11, the surface on the side to be joined to the fuel electrode 32 of the single cell 3 constituting the SOFC cell C and the surface on the side to be joined to the air electrode 31 are covered with a base material. A coating layer 13 is formed, and a protective film 12 is formed on the surface of the base coating layer 13 on the side to be joined to the air electrode 31 of the single cell 3 constituting the SOFC cell C. A connecting member 1 is obtained. In this way, in the inter-cell connection member 1 of this embodiment, both the surface of the metal base material 11 on the side to be joined to the fuel electrode 32 and the surface on the side to be joined to the air electrode 31 are Since the base material coating layer 13 may be attached, that is, there is no need to cover the metal base material 11 with a mask or the like when forming the base material coating layer 13, the base material may be attached to the surface of the metal base material 11 in the film forming process. The procedure for forming the material coating layer 13 is simplified. As a result, there is an advantage that the manufacturing cost of the inter-cell connection member 1 is reduced.

<Adhesion/joining using bonding material>
A cell stack of a fuel cell is formed by sequentially joining in series the inter-cell connecting member 1 and the single cells 3 produced as described above. Specifically, the surface of the air electrode 31 side of the intercell connection member 1 on which the protective film 12 is formed is adhesively bonded to the air electrode 31 of the single cell 3 constituting the SOFC cell C using the bonding material 4. do.

As the bonding material ₄ , Co--Mn-based oxide Co _{x Mn} y is used for the protective film 12 made of Co--Mn-based oxide Co x Mn y O ₄ (0<x, y<3, x+y= ₃ ). A bonding material of O ₄ (0≦x, y≦3, x+y=3), more specifically, when the forming material of the protective film 12 is (Co, Mn)O ₄ , the bonding material 4 is Co _{1 .5} Mn _1.5 O ₄ , Co ₂ MnO ₄ , Co ₃ O ₄ and other oxide materials can be used, and the material for forming the protective film 12 is Co _x Mn _y O ₄ (0<x, y<3 , x ₊ y=3), _the bonding material is _Co In the case of _1.5 Mn _1.5 O ₄ , an oxide material such as Co ₂ MnO ₄ or Co ₃ O ₄ can be used as the bonding material 4. Based on the experimental examples described later, these materials are protective films in which elemental diffusion occurs between the protective film 12 and the air electrode 31 under the energizing conditions of the fuel cell, and diffusion bonding occurs between the protective film 12 and the material forming the protective film 12. It is preferable to select a structure in which adhesive bonding is performed using a bonding material 4 made of an oxide material of the same type as the forming material of No. 12.
That is, if the bonding material 4 is selected, elemental diffusion will occur under the energizing conditions of the fuel cell, and diffusion bonding will occur between it and the material forming the protective film 12.
Furthermore, while baking the protective film 12 requires heating at, for example, 1000° C., adhesion and bonding using the bonding material 4 can be performed at a low temperature, such as from the operating temperature of the fuel cell to 950° C. This is because bonding between the metal base material 11 and the protective film 12 requires a relatively high temperature (slightly higher than the operating temperature of the fuel cell); 4 and the protective film 12 can be bonded together at a relatively low temperature since diffusion bonding can be expected.

<Effects of providing the base material coating layer 13 on the surface of the side to be joined to the fuel electrode 32>
Below, among the surfaces of the metal base material 11 used when manufacturing the inter-cell connection member 1, a base material coating layer 13 is formed on the surface of the side to be joined to the fuel electrode 32 of the single cell 3 constituting the SOFC cell C. Describe the effects of providing this. Here, a sample (Example 1) in which heat treatment was performed after forming the base material coating layer 13 on the surface of the metal base material 11, and a sample in which heat treatment was performed on the metal base material 11 on which the base material coating layer 13 was not formed. A sample without the base coating layer 13 (Comparative Example 1) and a sample in which the metal base material 11 without the base coating layer 13 was heat-treated (Comparative Example 2) were prepared and subjected to ICP analysis.

The samples of Example 1 and Comparative Example 2 were heat-treated to simulate the thermal history that the inter-cell connection member 1 receives during cell stack manufacturing and fuel cell operation. Specifically, the effects of heat received when forming a cell stack using the inter-cell connection member 1 and the single cell 3 (thermal history during manufacturing), and the effect of heat received when generating power using the cell stack. The effects (thermal history during operation) are taken into account. Then, to simulate the thermal history during manufacturing, the samples of Example 1 and Comparative Example 2 were heated at 800°C in the atmosphere to simulate the firing to form the protective film 12 on the inter-cell connection member 1. A treatment was performed in which heating and heating at 700° C. in a reducing atmosphere (hydrogen atmosphere) simulating reduction of the cell stack were performed for 2 hours each. To simulate the thermal history during operation, treatment was performed in a hydrogen/steam atmosphere under the temperature and time conditions described below.

[Sample of Example 1: With base material coating layer 13]
A general-purpose stainless steel material (equivalent to SUS445J1) was used as the metal base material 11, and the base material coating layer 13 was formed by depositing Ni on the surface thereof by a plating method. Thereafter, in order to simulate the thermal history during manufacturing, firing was performed at 800° C. in the air and at 700° C. in a reducing atmosphere (hydrogen atmosphere) for 2 hours each. Furthermore, heat treatment was performed in a hydrogen/steam atmosphere for predetermined times (24 hours, 48 hours, and 300 hours) to simulate the thermal history during operation. The temperature during this heat treatment is 850°C or 900°C.

The base material coating layer 13 used in this Example 1 does not contain Co and is not composed of Ni and Co, but in principle, if Ni is present, there will be no problem. It is considered that there is no (Co has no adverse effect). In other words, the effect obtained when the base material coating layer 13 is composed of Ni is considered to be the same as the effect obtained when the base material coating layer 13 is composed of Ni and Co. In this Example 1, the results using the base coating layer 13 made of Ni are shown.

[Sample of Comparative Example 1: No base coating layer 13]
A general-purpose stainless steel material (equivalent to SUS445J1) was used as the metal base material 11. No Ni film was formed on the surface (no base material coating layer 13 was formed). The sample of Comparative Example 1 was not subjected to either heat treatment to simulate the heat history during manufacturing or heat treatment to simulate the heat history during operation.

[Sample of Comparative Example 2: No base coating layer 13]
A general-purpose stainless steel material (equivalent to SUS445J1) was used as the metal base material 11. Ni is not formed on the surface (base material coating layer 13 is not formed). Thereafter, in order to simulate the thermal history during manufacturing, firing was performed at 800° C. in the air and at 700° C. in a reducing atmosphere (hydrogen atmosphere) for 2 hours each. Furthermore, heat treatment was performed in a hydrogen/steam atmosphere for a predetermined period of time (24 hours, 300 hours) to simulate the thermal history during operation. The temperature during this heat treatment is 850°C or 900°C.

In the ICP analysis, a test piece of 5 mm square and 0.4 mm thick was prepared for each sample, the entire amount was dissolved, and the concentration of phosphorus (P) contained in each test piece was detected. Tables 1 and 2 below show ICP analysis results.

First, the difference between the sample of Comparative Example 1 and the samples of Example 1 and Comparative Example 2 when the heat treatment time in a hydrogen/steam atmosphere was 0 hours is that for Example 1 and Comparative Example 2, the manufacturing The sample of Comparative Example 1 was not subjected to the heat treatment, whereas the sample of Comparative Example 1 was subjected to heat treatment to simulate the thermal history. As can be seen from Tables 1 and 2, compared to the phosphorus concentration (280 ppm) of the sample of Comparative Example 1, the phosphorus concentration of the sample of Comparative Example 2 when the heat treatment time in the hydrogen/steam atmosphere was 0 hours. The concentration is as low as 220 ppm. In other words, it was found that the heat treatment that simulates the thermal history during manufacturing significantly volatilizes phosphorus from the surface of the metal base material 11.

Also, focusing on the sample of Example 1, as can be seen from Tables 1 and 2, the heat treatment time in a hydrogen/steam atmosphere was 0 hours compared to the phosphorus concentration (280 ppm) of the sample of Comparative Example 1. In this case, the phosphorus concentration of the sample of Example 1 was as low as 190 ppm. This is considered to be because a small amount of phosphorus chemically bonded to Ni disappeared from the surface of the metal base material 11 during the heat treatment in the atmosphere, which simulates the thermal history during manufacturing. However, among the heat treatments that simulate the thermal history during manufacturing, the heat treatment in the atmosphere is a process that simulates baking for forming the protective film 12 on the inter-cell connection member 1. Since this process is performed in a state where the fuel electrode 1 and the single cell 3 are not bonded, phosphorus does not have an adverse effect on the fuel electrode 32.

In the sample on which the base material coating layer 13 of Example 1 was formed, the difference in phosphorus concentration before and after heat treatment in a hydrogen/steam atmosphere was almost the same, regardless of the heat treatment temperature in a hydrogen/steam atmosphere that simulated the thermal history during operation. There wasn't. In other words, in the sample in which the base material coating layer 13 of Example 1 was formed, it was found that almost no volatilization of phosphorus from the metal base material 11 occurred by heat treatment that simulated the thermal history during operation.

On the other hand, in the sample of Comparative Example 2, when the heat treatment temperature in a hydrogen/steam atmosphere was 850°C, the phosphorus concentration decreased from 220 ppm to 120 ppm after 300 hours of heat treatment; In the case of 900° C., the phosphorus concentration decreased from 220 ppm to 100 ppm by heat treatment for 24 hours. In other words, it was found that in the sample of Comparative Example 2 in which the base material coating layer 13 was not formed, phosphorus volatilization from the metal base material 11 occurred to a greater extent than in the heat treatment simulating the thermal history during operation.

As mentioned above, in the sample of Example 1, as shown in Tables 1 and 2, it seems that phosphorus has been volatilized from the metal base material 11 due to the heat treatment that simulates the thermal history during manufacturing, but during operation The volatilization of phosphorus from the metal base material 11 is effectively prevented by the heat treatment that simulates the heat treatment. Therefore, by using the inter-cell connecting member 1 in which the base material coating layer 13 is formed on at least the surface of the metal base material 11 on the side to be joined to the fuel electrode 32 of the single cell 3, actual solid oxidation can be achieved. It is considered that phosphorus poisoning of the fuel electrode 32 can be suppressed even in a physical fuel cell.

<Effects of providing the base material coating layer 13 and the protective film 12 on the surface of the side to be joined to the air electrode 31>
Below, among the surfaces of the metal base material 11 used when manufacturing the inter-cell connection member 1, a base material coating layer 13 is formed on the surface of the side to be joined to the air electrode 31 of the single cell 3 constituting the SOFC cell C. The effect of providing the protective film 12 on the surface of the base material coating layer 13 will be described. Here, as shown in Table 3 below, samples (Examples 3 and 4) in which a base material coating layer 13 and a protective film 12 were formed on the surface of a metal base material 11, a base material coating layer 13 was formed, and a protective film 12 was formed on the surface of a metal base material 11. A sample in which the film 12 was not formed (Comparative Example 3) and a sample in which the base coating layer 13 was not formed and a film corresponding to the protective film 12 was formed (Comparative Example 4) were prepared, and the electrical resistance was measured. .

[Sample of Example 2]
A general-purpose stainless steel material (equivalent to SUS445J1) is used as the metal base material 11, a film containing NiCO ₂ O ₄ is formed on the surface by dip coating, and heat treatment is performed in a reducing atmosphere (1000°C) to form Ni and metal in a metallic state. A base coating layer 13 made of Co was formed. Furthermore, a material containing Ni ₂ MnO ₄ is formed on the surface of the base coating layer 13 by dip coating, and heat-treated in the air (1000° C.) to form a Ni-Mn-based oxide (Ni ₂ MnO ₄ ). A protective film 12 was formed using the following.

[Sample of Example 3]
A general-purpose stainless steel material (equivalent to SUS445J1) is used as the metal base material 11, a film containing NiCO ₂ O ₄ is formed on the surface by dip coating, and heat treatment is performed in a reducing atmosphere (1000°C) to form Ni and metal in a metallic state. A base coating layer 13 made of Co was formed. Furthermore, a material containing Cu ₂ MnO ₄ is formed on the surface of the base coating layer 13 by dip coating, and heat-treated in the air (1000° C.) to form a Cu-Mn-based oxide (Cu ₂ MnO ₄ ). A protective film 12 was formed using the following.

[Sample of Comparative Example 3]
A general-purpose stainless steel material (equivalent to SUS445J1) is used as the metal base material 11, a film containing NiCO ₂ O ₄ is formed on the surface by dip coating, and heat treatment is performed in a reducing atmosphere (1000°C) to form Ni and metal in a metallic state. A base coating layer 13 made of Co was formed. Note that in the sample of Comparative Example 3, the protective film 12 was not formed on the surface of the base coating layer 13.

[Sample of Comparative Example 4]
A general-purpose stainless steel material (equivalent to SUS445J1) is used as the metal base material 11, and a film containing Co ₂ MnO ₄ is formed on the surface by dip coating, and by heat treatment in the air atmosphere (1000 ° C.), Cu-Mn-based oxidation is applied. A protective film 12 made of a material (Cu ₂ MnO ₄ ) was formed. Note that in the sample of Comparative Example 4, the base material coating layer 13 was not formed.

Table 4 shows the results of the temperature dependence of the resistance values of Examples and Comparative Examples at 600 to 900°C.
The sample of Example 2 showed lower resistance than the samples of Comparative Example 3 and Comparative Example 4. The sample of Example 2 had a low resistance value even though two thick layers (base material coating layer 13 and protective film 12) were formed on the surface of the metal base material 11 through two heat treatments. It shows. In other words, a layer made of a ternary material containing Ni, Co, and Mn is formed on the surface of the metal base material 11 of the inter-cell connection member 1 by forming the base material coating layer 13 and the protective film 12. In addition to the advantages of being able to suppress the formation of high-resistance Cr ₂ O ₃ and the ability to prevent scattering due to evaporation of Cr from the metal base material 11, the advantage of low resistance can be obtained. Considering this, it can be said that the sample of Example 2 has much higher performance than the samples of Comparative Examples 3 and 4.
The resistance value of the sample of Example 3 was slightly increased compared to the samples of Comparative Examples 3 and 4. However, considering that the sample of Example 3 also has the advantage of being able to suppress the formation of high-resistance Cr ₂ O ₃ and the advantage of being able to prevent scattering due to evaporation of Cr from the metal base material 11, It cannot be said that the performance is lower than the samples of Comparative Examples 3 and 4.

As described above, in this embodiment, among the surfaces of the metal base material 11 constituting the inter-cell connection member 1, the surface on the side to be joined to the fuel electrode 32, and the surface on the side to be joined to the air electrode 31. Since the same base material coating layer 13 is attached to both, there is no need to cover the metal base material 11 with a mask or the like when forming the base material coating layer 13. As a result, there is an advantage that the procedure for forming the base material coating layer 13 on the surface of the metal base material 11 is simplified, and the manufacturing cost of the inter-cell connection member 1 is reduced. In addition, the base material coating layer 13 formed on both the surface of the metal base material 11 of the inter-cell connection member 1 on the side to be joined to the fuel electrode 32 and the surface on the side to be joined to the air electrode 31, The surface to be joined to the fuel electrode 32 has the effect of suppressing phosphorus from volatilizing from the metal base material 11, and the surface to be joined to the air electrode 31 has a high resistance film together with the protective film 12. The formation of Cr ₂ O ₃ is suppressed, and scattering due to evaporation of Cr from the metal base material 11 is prevented.

If only the performance of the surface of the inter-cell connecting member 1 that is bonded to the air electrode 31 is considered, Ni-Co-Mn should be applied to the surface of the surface that is bonded to the air electrode 31. There is also a method of forming a film of a ternary material containing a single layer (in one layer). However, if this method is adopted, a material containing Ni-Co-Mn will also be deposited on the surface of the inter-cell connecting member 1 that is to be joined to the fuel electrode 32, so the cell Mn precipitates on the surface of the interconnecting member 1 on the fuel electrode side, and since Mn exists as an oxide in the reducing atmosphere on the fuel electrode side in the SOFC operating temperature range, there is a problem in that it exhibits high resistance.
Therefore, in this embodiment, Ni-Co (base material coating layer 13), which is good in terms of performance and durability, is formed as a first layer coating on the fuel electrode side on the surface of the metal base material 11, and on the air electrode side An oxide containing Mn (protective film 12) was formed as a second layer on the surface of the first base material coating layer 13. In other words, by designing a coating that takes into account both the side of the surface of the inter-cell connection member 1 that is bonded to the fuel electrode 32 and the side that is bonded to the air electrode 31, the procedure for forming the coating is simplified. However, it is possible to provide an inter-cell connection member 1 that exhibits good performance on both the fuel electrode side and the air electrode side.

FIG. 4 is a diagram showing the configuration of a system including a solid oxide fuel cell (cell stack) equipped with SOFC cells C manufactured by the method described above. In particular, FIG. 4 shows a SOFC cogeneration system that includes a solid oxide fuel cell (SOFC) 20 and supplies electric power and heat generated by the solid oxide fuel cell 20 to an electric power load and a heat load. FIG. 3 is a diagram showing the configuration. This solid oxide fuel cell 20 has a cell stack in which a plurality of SOFC cells C manufactured as described above are stacked. Although not shown, the solid oxide fuel cell 20 includes a reformer for producing fuel gas such as hydrogen supplied to the fuel electrode 32 by reforming hydrocarbons such as city gas. may also be added.

Electric power output from the solid oxide fuel cell 20 is supplied to a power line 22 connected to a commercial power system 21 via a power converter 24 such as an inverter. The power line 22 is connected to various power load devices 23 such as lighting equipment and air conditioning equipment used in the facility where the solid oxide fuel cell 20 is installed. That is, power is supplied from at least one of the commercial power system 21 and the solid oxide fuel cell 20 to the power load on the power load device 23 .

The heat discharged from the solid oxide fuel cell 20 is used to respond to the heat load of various heat load devices 26 such as water heaters and heating devices installed in the facility where the solid oxide fuel cell 20 is installed. will be supplied. Further, as shown in the figure, if a heat storage device 25 for storing a heat storage medium is provided, the heat discharged from the solid oxide fuel cell 20 can be recovered by the heat storage medium and stored in the heat storage device 25. Then, when heat demand occurs in the heat load device 26, heat can be supplied from the heat storage device 25 to the heat load device 26.

<Another embodiment>
<1>
In the above embodiment, the inter-cell connection member 1, the solid oxide fuel cell, the SOFC cogeneration system, and the method for manufacturing the inter-cell connection member 1 of the present invention have been explained using specific examples. Its configuration can be changed as appropriate.
For example, the composition of each material can be changed as appropriate.
Furthermore, the method for forming the base material coating layer 13 and the protective film 12 can be selected as appropriate. For example, a Ni--Co film as the base material coating layer 13 is formed by plating on the surface of the metal base material 11 made of stainless steel, and then a Co--Mn based oxide is formed as the protective film 12, for example. The film may be formed by electrodeposition coating or the like. In this case, even if the metal base material 11 is plated with Ni-Co, the electronic conductivity of the metal base material 11 is not lost. It becomes possible to form a film using a conventional method.

<2>
In the embodiment described above, an example was explained in which a cogeneration system including a solid oxide fuel cell (cell stack) is constructed, but a monogeneration system including a solid oxide fuel cell may also be constructed. That is, it is also possible to construct an SOFC monogeneration system that includes a solid oxide fuel cell and supplies electric power generated by the solid oxide fuel cell to a power load.

<3>
The configuration disclosed in the above embodiment (including another embodiment, the same applies hereinafter) can be applied in combination with the configuration disclosed in other embodiments, unless a contradiction occurs, and the configuration disclosed in this specification can be applied in combination with the configuration disclosed in other embodiments. The embodiments are illustrative, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the purpose of the present invention.

The present invention provides an intercell connection member, a solid oxide fuel cell, and an SOFC monogeneration system that exhibits good performance on both the fuel electrode side and the air electrode side while the procedure for forming a coating is simple. , SOFC cogeneration system, and method for manufacturing an inter-cell connection member.

1 Cell-to-cell connection member 3 Single cell 11 Metal base material 12 Protective film 13 Base material coating layer 20 Solid oxide fuel cell (cell stack)
31 Air electrode 32 Fuel electrode C Solid oxide fuel cell cell (SOFC cell)

Claims (6)

An intercell connection member used in a solid oxide fuel cell,
A metal base material made of stainless steel,
Among the surfaces of the metal base material, the surface on the side to be joined to the fuel electrode of the single cell constituting the cell for the solid oxide fuel cell, and the surface on the side to be joined to the air electrode of the single cell. A base coating layer formed using Ni and Co,
An inter-cell connection member comprising: a protective film formed using an oxide containing Mn and formed on a surface of the base coating layer that is connected to the air electrode of the single cell. The protective film between cells according to claim 1, wherein the protective film is formed using any one of Mn oxide, Co--Mn oxide, Ni--Mn-based oxide, and Cu--Mn oxide. Connection member. A solid oxide fuel cell in which a plurality of cells for the solid oxide fuel cell are stacked, each of which includes the intercell connection member according to claim 1 or 2 and the single cell. An SOFC monogeneration system comprising the solid oxide fuel cell according to claim 3 and supplying electric power generated by the solid oxide fuel cell to a power load. An SOFC cogeneration system comprising the solid oxide fuel cell according to claim 3 and supplying electric power and heat generated by the solid oxide fuel cell to an electric power load and a heat load. A method for manufacturing an inter-cell connection member used in a solid oxide fuel cell, comprising:
Among the surfaces of the metal base material made of stainless steel, the surface on the side to be joined to the fuel electrode of the single cell constituting the solid oxide fuel cell, and the surface joined to the air electrode of the single cell. A film forming step of forming a base coating layer made of Ni and Co on the surface of the side to be treated;
A cell comprising a protective film forming step of forming a protective film made of an oxide containing Mn on the surface of the base coating layer that is connected to the air electrode of the single cell. A method for manufacturing an interconnecting member.

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