Interconnectors for solid oxide electrochemical cell stacks and solid oxide electrochemical cell stacks

Abstract

To provide an interconnector for a solid oxide electrochemical cell stack with a densified protective film that improves adhesion to a metal substrate and enables satisfactory workability for complex shapes.SOLUTION: An interconnector 1 for a solid oxide electrochemical cell stack includes a metal base material 2 made of an iron-based alloy containing chromium and a protective film 3 provided on the surface of the metal base material 2. An intermediate layer 4 capable of relieving stress is interposed between the metal base material 2 and the protective film 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to an interconnector for a solid oxide type electrochemical cell stack and a solid oxide type electrochemical cell stack. [Background technology]

[0002] Hydrogen is cited as one of the new energy sources for a decarbonized society. One area of ​​interest in hydrogen applications is fuel cells, which convert chemical energy into electrical energy by electrochemically reacting hydrogen and oxygen. Fuel cells have high energy efficiency and are being developed for use as large-scale distributed power sources, household power sources, and mobile power sources. Fuel cells are classified according to their operating temperature range and the materials and fuels they use. When classified by the electrolyte material used, they are classified into polymer electrolyte type, phosphoric acid type, molten carbonate type, and solid oxide type.

[0003] Among fuel cells, solid oxide fuel cells (SOFCs), which use solid oxide electrolytes, are attracting attention from the standpoint of efficiency and other factors. On the other hand, since hydrogen does not exist in nature on its own, it is necessary to transport hydrogen to hydrogen systems equipped with fuel cells. Electrolytic cells can carry out the water electrolysis reaction, which is the reverse reaction of a fuel cell, thereby enabling hydrogen production within the hydrogen system. Hydrogen production reactions are classified into alkaline water electrolysis type, solid polymer type, and solid oxide type. For example, solid oxide electrolysis cells (SOECs), which apply the high-temperature steam electrolysis method, in which water is electrolyzed in the state of high-temperature steam, are attracting attention because they have the highest hydrogen production efficiency. The operating principle of SOECs is the reverse reaction of SOFCs, and like SOFCs, they use electrolytes made of solid oxides.

[0004] Solid oxide electrochemical cells (SOFCs) are attracting attention because they can perform both fuel cell and electrolytic cell electrochemical reactions with high efficiency. Solid oxide electrochemical cells used in SOFCs and SOECs have a laminate consisting of an oxygen electrode (air electrode), a solid oxide electrolyte layer, and a hydrogen electrode (fuel electrode). Multiple such laminated electrochemical cells are stacked together via interconnectors to create high-capacity electrochemical cell stacks. Interconnectors for solid oxide electrochemical cell stacks require heat resistance, so high-chromium (Cr) steel with a chromium (Cr) content of 15% by mass or more, which is commonly used as a heat-resistant material, is often used. In high-Cr steel, an oxide film mainly consisting of chromium oxide (Cr2O3) is formed on the surface at high temperatures.

[0005] When high-Cr steel is used in interconnectors for solid oxide electrochemical cell stacks, under the operating environment of the solid oxide electrochemical cell, Cr element evaporates from Cr2O3 and adheres to the electrode portion of the solid oxide electrochemical cell, degrading its performance. To solve these problems, various materials for interconnectors for solid oxide electrochemical cell stacks are being investigated. Regarding Cr scattering, covering the high-Cr steel with a dense protective film is being considered to suppress Cr scattering. Required properties for the protective film include heat resistance, electrical conductivity, and adhesion.

[0006] For example, spinel oxides and perovskite oxides are being considered as protective film materials. Of these, perovskite oxides have excellent electrical conductivity, but the large difference in thermal expansion with the substrate raises concerns about film delamination. On the other hand, even with spinel oxides, which have a small difference in thermal expansion with the substrate, ingenuity is required. For example, adjusting the composition of spinel oxides is being considered to reduce the difference in thermal expansion with the substrate and improve adhesion. However, adjusting the composition of spinel oxides necessitates controlling compositional variations within the interconnector plane and compositional variations between batches, and further restricts the available film deposition methods that can achieve the desired composition. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 5770659 [Patent Document 2] Japanese Patent Publication No. 2019-079628 [Patent Document 3] Japanese Patent Publication No. 2021-096964 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The problem that the present invention aims to solve is to provide an interconnector for a solid oxide type electrochemical cell stack that can suppress peeling of a protective film provided on a high-Cr steel, and a solid oxide type electrochemical cell stack using such an interconnector. [Means for solving the problem]

[0009] The interconnector for solid oxide electrochemical cell stacks of this embodiment comprises a metal substrate made of an iron-based alloy containing chromium, and a protective film provided on the surface of the metal substrate, with an intermediate layer interposed between the metal substrate and the protective film that can relieve stress. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing an interconnector for a solid oxide type electrochemical cell stack according to an embodiment. [Figure 2] This is a cross-sectional view showing a solid oxide type electrochemical cell stack of an embodiment. [Figure 3] This is a magnified photograph of the appearance of the interconnector for a solid oxide type electrochemical stack after high-temperature exposure, according to Comparative Example 1. [Figure 4]This is a magnified photograph of the appearance of the interconnector for a solid oxide electrochemical stack according to Example 1 after exposure to high temperature. [Modes for carrying out the invention]

[0011] The following describes the interconnectors and solid oxide electrochemical cell stacks for the embodiments with reference to the drawings. In each embodiment shown below, substantially identical components are denoted by the same reference numerals, and their descriptions may be partially omitted. The drawings are schematic, and the relationship between thickness and planar dimensions, the ratio of the thickness of each part, etc., may differ from those in reality. The symbol "~" used in the following description indicates a range between the upper and lower limits of each numerical value. In this case, each numerical range includes both the upper and lower limits.

[0012] Figure 1 shows a cross-section of an interconnector for a solid oxide electrochemical cell stack according to the first embodiment. The interconnector 1 shown in Figure 1 comprises a metal substrate 2 having a first surface 2a and a second surface 2b. When the interconnector 1 is used in a solid oxide electrochemical cell stack, the first surface 2a of the metal substrate 2 is the surface that is positioned on the oxygen electrode (air electrode) side and is exposed to an atmosphere containing oxygen (air, etc.). The second surface 2b of the metal substrate 2 is the surface that is positioned on the hydrogen electrode (fuel electrode) side and is exposed to an atmosphere containing hydrogen. Note that the second surface 2b side is not limited to flowing hydrogen; for example, in SOFCs, methanol (CH3OH) may flow, so the second surface 2b should be exposed to an atmosphere containing a substance with hydrogen atoms. The first surface 2a side is not limited to flowing air; for example, in SOECs, nothing may flow, or oxygen may flow, so the first surface 2a should be exposed to an atmosphere containing oxygen. A protective film 3 is provided on the first surface 2a of the metal substrate 2. The protective film 3 may be provided on both the first surface 2a and the second surface 2b of the metal substrate 2.

[0013] The interconnector 1 shown in FIG. 1 is used, for example, in the solid oxide type electrochemical cell stack 10 shown in FIG. 2. The solid oxide type electrochemical cell stack 10 shown in FIG. 2 has a structure in which the first electrochemical cell 11 and the second electrochemical cell 12 are stacked via the interconnector 1. Although FIG. 2 shows the structure in which the first electrochemical cell 11 and the second electrochemical cell 12 are stacked, the number of stacked electrochemical cells 12 is not particularly limited, and it may have a structure in which three or more electrochemical cells are stacked. When three or more electrochemical cells are stacked, an interconnector is disposed between each adjacent pair of electrochemical cells, and each pair of electrochemical cells is electrically connected by the interconnector.

[0014] The first electrochemical cell 11 and the second electrochemical cell 12 have the same configuration, and each has a first electrode 13 that functions as a hydrogen electrode (fuel electrode), a second electrode 14 that functions as an oxygen electrode (air electrode), and a solid oxide electrolyte layer 15 disposed between these electrodes 13 and 14. The first and second electrodes 13 and 14 are each formed of a porous electrical conductor. The solid oxide electrolyte layer 15 is made of a dense solid oxide electrolyte and is formed of an ion conductor that allows ions such as oxygen ions (O 2- ) to pass through, but does not allow gas and electricity to pass through. A porous first current collecting member 16 may be disposed between the first electrode 13 and the interconnector 1 as needed. Similarly, a porous second current collecting member 17 may be disposed between the second electrode 14 and the interconnector 1 as needed. The first and second current collecting members 16 and 17 are members that improve the electrical connection between the first and second electrochemical cells 11 and 12 and the interconnector 1 while allowing the reaction gas to pass through.

[0015] Although not shown in Figure 2, gas channels are provided around the first and second electrochemical cells 11 and 12. That is, the first and second electrodes 13 and 14 are supplied with supply gases according to the intended use of the electrochemical cell stack 10, respectively, through a portion of the gas channel. The exhaust gas generated and discharged at the first and second electrodes 13 and 14 is discharged from the first and second electrochemical cells 11 and 12 through another portion of the gas channel. The gas supplied to the first and second electrodes 13 and 14 and the atmosphere around the electrodes 13 and 14 are separated by a dense solid oxide electrolyte 15 and an interconnector 1. When the electrochemical cell stack 10 is used as a fuel cell such as an SOFC, the first electrode 13, which serves as the hydrogen electrode (fuel electrode), is supplied with reducing gases such as hydrogen (H2) or methanol (CH3OH) gas, and the second electrode 14, which serves as the oxygen electrode (air electrode), is supplied with oxidizing gases such as air or oxygen (O2). When the electrochemical cell stack 10 is used as an electrolytic cell such as an SOEC using high-temperature steam electrolysis, water vapor (H2O) is supplied to the first electrode 13, which serves as the hydrogen electrode.

[0016] The interconnector 1 shown in Figure 1 is used as an interconnector 1 positioned between the first and second electrochemical cells 11 and 12 in the electrochemical stack 10 shown in Figure 2. In the interconnector 1, the first surface 2a of the metal substrate 2 is positioned on the side of the second electrode 14 as the oxygen electrode, and the second surface 2b of the metal substrate 2 is positioned on the side of the first electrode 13 as the hydrogen electrode. In Figure 2, the first surface 2a of the metal substrate 2 is positioned on the side of the second electrode 14 of the first electrochemical cell 11, and the second surface 2b of the metal substrate 2 is positioned on the side of the first electrode 13 of the second electrochemical cell 12. Therefore, the first surface 2a of the metal substrate 2 is exposed to an oxygen-containing atmosphere such as air supplied to the second electrode 14 as the air electrode. The second surface 2b of the metal substrate 2 is exposed to a hydrogen-containing atmosphere such as hydrogen supplied to the first electrode 13 as the hydrogen electrode, a mixture of hydrogen and water vapor, or a similar hydrogen-containing atmosphere discharged from the first electrode 13.

[0017] In the interconnector 1 used in the electrochemical cell stack 10 shown in FIG. 2, an iron-based alloy containing chromium (Cr), that is, stainless steel (SUS), is used for the metal base material 2. In the electrochemical cell stack 10, a metal base material 2 made of a ferritic stainless steel having a thermal expansion coefficient close to that of the electrochemical cells 11 and 12, such as SUS430 for example, is applied. When stainless steel is used for the metal base material 2, Cr contained in the metal base material 2 may react with oxygen or water vapor and vaporize in a high-temperature range of about 600 to 1000 °C, which is the operating temperature of SOFC or SOEC, and adhere to the second electrode 14 or the like, resulting in a performance degradation. Therefore, in order to suppress the vaporization of chromium and the accompanying diffusion, the interconnector 1 has a protective film 3 that covers at least the first surface 2a of the metal base material 2.

[0018] As the constituent material of the protective film 3, it is preferable to contain at least one selected from spinel-type oxides and perovskite-type oxides that exhibit electrical conductivity in the operating temperature range of SOFC, SOEC, etc. The spinel-type oxide is an oxide represented by AB2O4 (A and B are cationic elements such as the same or different metal elements). The perovskite-type oxide is an oxide represented by ABO3 (A and B are cationic elements such as the same or different metal elements). Since both the spinel-type oxide and the perovskite-type oxide exhibit electrical conductivity in the operating temperature range of SOFC, SOEC, etc., they are suitable for the protective film 3 that requires conductivity.

[0019] Metallic elements included in spinel-type oxides and perovskite-type oxides include at least one selected from the group consisting of cobalt (Co), nickel (Ni), manganese (Mn), copper (Cu), iron (Fe), chromium (Cr), zinc (Zn), aluminum (Al), titanium (Ti), lanthanum (La), and strontium (Sr). Co-containing spinel-type oxides are effective as constituent materials for protective film 3. Since Co functions as both the A-site element and the B-site element of spinel-type oxides, it can form spinel-type oxides represented as Co3O4. Furthermore, materials to which at least one selected from Ni, Mn, Cu, Fe, Cr, Zn, Al, and Ti is added to such Co-containing spinel-type oxides are also effective, and effects such as improved electrical conductivity and mitigation of thermal expansion mismatch can be expected. In addition, spinel-type oxides using Fe, Ni, Mn, etc. instead of Co can be used as constituent materials for protective film 3.

[0020] Examples of perovskite-type oxides include oxides containing Co and at least one selected from La and Sr, such as LaCoO3, SrCoO3, and (La,Sr)CoO3. Materials obtained by adding at least one selected from Ni, Mn, Cu, Fe, Cr, Zn, Al, and Ti to such perovskite oxides may also be used, such as La(Co,Fe)O3, Sr(Co,Fe)O3, and (La,Sr)(Co,Fe)O3. Perovskite-type oxides in which Mn or Ni are added instead of Fe may also be used. Furthermore, perovskite-type oxides containing Mn, Fe, or Ni instead of Co, such as SrMnO3, SrFeO3, and SrNiO3, or perovskite-type oxides in which the above-mentioned metal elements are added, can be used as constituent materials for the protective film 3.

[0021] As described above, Cr element generally reacts with oxygen and water vapor in the operating temperature range of solid oxide electrochemical cells 11 and 12 to vaporize, and this Cr vapor is a factor that degrades the performance of solid oxide electrochemical cells 11 and 12. To suppress this, it is important to coat the metal substrate 2 containing Cr with a protective film 3 and to suppress cracking and peeling of the protective film 3. The cause of cracking and peeling of the protective film 3 is that stress is generated in the protective film 3 due to the difference in thermal expansion between the metal substrate 2 and the protective film 3 when the temperature rises to the operating temperature and when it cools down from the operating temperature, or when there is a chemical reaction such as oxidation after the protective film 3 is formed, due to volume contraction / expansion caused by the chemical reaction. To alleviate the stress generated by this difference in thermal expansion between the metal substrate 2 and the protective film 3, an intermediate layer 4 is interposed between the metal substrate 2 and the protective film 3. The intermediate layer 4 has the function of alleviating the above-mentioned stress and suppressing cracking and peeling of the protective film 3.

[0022] We will examine the stress relaxation provided by the intermediate layer 4 described above, and the suppression of cracks and delamination of the protective film 3 due to stress relaxation. Here, we will focus on the self-diffusion coefficient and Young's modulus. The self-diffusion coefficient refers to the diffusion coefficient of the elements constituting the base material as they diffuse within the base material. For example, in the Fe-Cr high-Cr steel used in the interconnector 1 of the embodiment, Fe and Cr elements diffuse within the high-Cr steel. The self-diffusion coefficients of Fe and Cr elements in high-Cr steel are, for example, 2 to 3 × 10⁻¹⁶ in a temperature range of about 700°C. -17 m 2 It exhibits a self-diffusion coefficient of approximately / s. It is thought that the larger the self-diffusion coefficient, the more the elements diffuse into the base material to relieve stress when stress occurs, causing deformation and thus relieving the stress. For this reason, if the self-diffusion coefficient of the constituent elements of the intermediate layer 4 is greater than that of the constituent elements (Fe and Cr) of the metal substrate 2, the intermediate layer 4 will exert a stress-relieving effect.

[0023] The stress relaxation effect based on the self-diffusion coefficient described above can be obtained because the self-diffusion coefficient of the constituent elements of the intermediate layer 4 is larger than the self-diffusion coefficient of the constituent elements (Fe or Cr) of the metal substrate 2. Although it varies depending on the constituent material of the metal substrate 2, the constituent material of the protective film 3, the film thickness, etc., the self-diffusion coefficient of the constituent elements of the intermediate layer 4 is preferably at least one digit larger than the self-diffusion coefficient of the constituent elements of the metal substrate 2. By applying the intermediate layer 4 having such a self-diffusion coefficient, the stress relaxation effect by the intermediate layer 4 can be expected with better reproducibility. As a result, it becomes possible to suppress cracks and peeling of the protective film 3.

[0024] Examples of the constituent material of the intermediate layer 4 having a self-diffusion coefficient larger than the self-diffusion coefficient of the constituent elements (Fe or Cr) of the metal substrate 2 include Cu, Au, Ag, etc. As described above, the self-diffusion coefficients of Fe element and Cr element are, for example, 2 - 3×10 -17 m 2 / s in the temperature range of about 700 °C. In contrast, in the temperature range of about 700 °C, the self-diffusion coefficient of Cu is 10 -16 ~10 -15 m 2 / s, the self-diffusion coefficient of Ag is 10 -15 ~10 -14 m 2 / s, and the self-diffusion coefficient of Au is 10 -15 ~10 -14 m 2 / s. Cu, Au, and Ag may be applied as a single metal material to the constituent material of the intermediate layer 4, or may be applied as an alloy containing at least one of them to the constituent material of the intermediate layer 4. Further, when a metal material having a fcc structure is used as the metal substrate 2, since the fcc structure is a close-packed structure, the self-diffusion coefficient tends to be small in the bcc structure which is not a close-packed structure, and it can be a candidate material for the intermediate layer 4.

[0025] On the other hand, Young's modulus indicates the degree of ease of deformation when stress is applied, and materials with a small Young's modulus deform greatly with small stress. In other words, materials with a small Young's modulus can be deformed greatly with small stress when stress occurs, and this is thought to relieve stress. For this reason, by applying an intermediate layer 4 made of a material having a Young's modulus smaller than that of the metal substrate 2, the intermediate layer 4 can be deformed and the stress can be reduced. Consequently, the stress generated between the metal substrate 2 and the protective film 3 can be reduced by the intermediate layer 4, making it possible to suppress cracks and delamination of the protective film 3.

[0026] The Young's modulus of high-Cr steel such as SUS430 is 201 GPa. A material with a Young's modulus lower than that of the metal substrate 2 made of such high-Cr steel is a metallic material containing at least one metallic element selected from the group consisting of Mg, Al, Cu, Pd, Au, Ag, Zn, and Ti. The above-mentioned metallic elements may be applied to the intermediate layer 4 as single metallic materials, or as alloys containing at least one of them. For example, the Young's modulus of Al is 70.3 GPa, the Young's modulus of Cu is 129.8 GPa, the Young's modulus of Pd is 16.1 GPa, the Young's modulus of Au is 78 GPa, the Young's modulus of Ag is 82.7 GPa, the Young's modulus of Zn is 48 GPa, and the Young's modulus of Ti is 107 GPa. Furthermore, alloys containing at least one of the above-mentioned metallic elements include Mg alloys with a Young's modulus of 45 GPa, Al alloys with a Young's modulus of 69-76 GPa, and brass (Cu-Zn alloy) with a Young's modulus of 103 GPa.

[0027] In the interconnector 1 in which a protective film 3 is formed on a metal substrate 2 via an intermediate layer 4 as described above, wrinkles may occur on the surface of the interconnector 1 as a result of deformation of the intermediate layer 4. It is presumed that the wrinkles occur when stress is applied, and the presence of wrinkles is due to the stress relaxation function of the intermediate layer 4 being fully utilized. The wrinkles on the surface of the interconnector 1 referred to here refer to fine deformation of the surface in the form of irregularities, and specifically refer to the state shown in the enlarged photograph of Figure 4, which is the result of Example 1 described later.

[0028] If the thickness of the intermediate layer 4 is too small, it becomes difficult to form the intermediate layer 4 uniformly, and it may not be able to function sufficiently as a stress relaxation layer. Therefore, it is preferable that the thickness of the intermediate layer 4 be 0.3 μm or more. On the other hand, depending on the constituent material of the intermediate layer 4, if the thickness of the intermediate layer 4 is large and the intermediate layer 4 deforms too much, it may adversely affect the integrity of the protective film 3. Therefore, it is preferable that the thickness of the intermediate layer 4 be 10 μm or less. Considering that it is preferable for the protective film 3 to be formed uniformly in order to suppress Cr scattering, the thickness is preferably 0.3 μm or more. Also, depending on the stress relaxation ability of the intermediate layer 4, if the thickness of the protective film 3 is too large, it may lead to peeling or cracking of the protective film 3. Therefore, it is preferable that the thickness of the protective film 3 be 20 μm or less.

[0029] The method for forming the protective film 3 and the intermediate layer 4 is not particularly limited, and methods such as electroplating, electroless plating, electrodeposition, spin coating, dip coating, and sol-gel can be applied. When applying an oxide as described above to the protective film 3, the protective film 3 may be formed by oxidation after the formation of the metal film. As for the intermediate layer 4, a metal film may be formed, or an oxide film or the like may be formed and then reduced. When oxidation is performed after the formation of the metal film or reduction after the formation of the oxide film, the interconnect with the protective film may be oxidized or reduced individually, or it may be oxidized or reduced after being incorporated into a cell stack or module.

[0030] In the embodiments described above, the application of the solid oxide electrochemical cell and the cell stack 10 in which it is stacked has been mainly explained in relation to SOFCs and SOECs. However, the solid oxide electrochemical cell and the cell stack 10 in the embodiments can also be applied to CO2 electrolytic reaction apparatuses and the like. [Examples]

[0031] Next, we will describe specific examples of interconnectors according to the embodiment and their evaluation results.

[0032] (Comparative Example 1) A ferritic stainless steel substrate made of SUS430 was prepared as the metal substrate. This SUS substrate was immersed in a Co plating bath and electroplated to form a 4 μm thick Co film. Next, the SUS substrate with the Co plated film was exposed to air at 700°C to oxidize the Co plated film. The oxidized Co film was confirmed to be a Co oxide film mainly composed of Co spinel-type oxide represented by Co3O4. The SUS substrate with the Co oxide protective film obtained in this way was evaluated by visual inspection. A magnified photograph showing the appearance of the SUS substrate with the Co oxide protective film is shown in Figure 3. As shown in Figure 3, it can be seen that peeling and other defects have occurred on the surface of the SUS substrate with the Co oxide protective film that does not have an intermediate layer.

[0033] (Example 1) A ferritic stainless steel substrate made of SUS430 was prepared as the metal substrate. This SUS substrate was immersed in an Ag plating bath and electroplated, and then immersed in a Co plating bath and electroplated again. In this way, a 1 μm thick Ag film and a 4 μm thick Co film were sequentially formed on the SUS substrate. Next, the SUS substrate with the Ag and Co films was exposed to air at 700°C to oxidize the Co plating film on the outermost surface. The oxidized Co film was confirmed to be a Co oxide film mainly composed of Co spinel-type oxide represented by Co3O4. It was also confirmed that the Ag film was not oxidized. The SUS substrate with the Ag intermediate layer and Co oxide protective film obtained in this way was evaluated by visual inspection. Figure 4 shows magnified photographs of the appearance of the SUS substrate with the Ag intermediate layer and Co oxide protective film. As shown in Figure 4, no delamination was observed on the surface of the SUS substrate with the Ag intermediate layer and Co oxide protective film. Also, in Figure 4, it was confirmed that wrinkles had formed in the protective film. This is thought to be a wrinkle caused by stress between the SUS substrate and the protective film, and it is believed that the formation of this wrinkle is preventing the protective film from peeling off.

[0034] As shown in Comparative Example 1 and Example 1 above, in the SUS substrate with a protective film without an intermediate layer, delamination and other damage occurred in the protective film, whereas in the SUS substrate with an intermediate layer and protective film, wrinkles appeared in the protective film, indicating that the stress between the SUS substrate and the protective film was relieved. As a result, delamination of the protective film is suppressed in the SUS substrate with an intermediate layer and protective film, and the integrity of the protective film can be improved. By applying an interconnect consisting of such an intermediate layer and protective film-equipped SUS substrate, it is possible to increase the durability of the solid oxide type electrochemical cell stack.

[0035] The configurations of each embodiment described above can be applied in combination, and can also be partially replaced. Although several embodiments of the present invention have been described here, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as described in the claims. [Explanation of symbols]

[0036] 1...Interconnector, 2...Metal substrate, 3...Protective film, 4...Intermediate layer, 10...Electrochemical cell stack, 11,12...Electrochemical cell, 13...First electrode, 14...Second electrode, 15...Solid oxide electrolyte layer.

Claims

1. A metal substrate made of an iron-based alloy containing chromium, An interconnect for a solid oxide type electrochemical cell stack, comprising a protective film provided on the surface of the metal substrate, An intermediate layer capable of relieving stress is interposed between the metal substrate and the protective film. The intermediate layer comprises a material in which the self-diffusion coefficient of the elements constituting it is greater than that of the iron and chromium in the metal substrate, in an interconnector for a solid oxide type electrochemical cell stack.

2. The interconnect for a solid oxide type electrochemical cell stack according to claim 1, wherein the self-diffusion coefficient of the elements constituting the intermediate layer is one order of magnitude larger than the self-diffusion coefficient of iron and chromium in the metal substrate.

3. The interconnector for a solid oxide type electrochemical cell stack according to claim 1, wherein the intermediate layer includes a material whose Young's modulus is smaller than that of the metal substrate.

4. The intermediate layer is made of a metallic material containing at least one metallic element selected from the group consisting of Cu, Au, and Ag, as described in claim 1, for an interconnector for a solid oxide type electrochemical cell stack.

5. A metal substrate made of an iron-based alloy containing chromium, An interconnect for a solid oxide type electrochemical cell stack, comprising a protective film provided on the surface of the metal substrate, An intermediate layer capable of relieving stress is interposed between the metal substrate and the protective film. The intermediate layer comprises a material whose Young's modulus is smaller than that of the metal substrate, and is an interconnector for a solid oxide type electrochemical cell stack.

6. The interconnector for a solid oxide type electrochemical cell stack according to claim 5, wherein the intermediate layer is made of a metallic material containing at least one metallic element selected from the group consisting of Mg, Al, Cu, Pd, Au, Ag, Zn, and Ti.

7. The interconnector for a solid oxide type electrochemical cell stack according to claim 1 or 5, wherein wrinkles are present on the surface of the interconnector.

8. The protective film is made of an oxide containing at least one selected from the group consisting of Co, Ni, Mn, Cu, Fe, Cr, and Zn, as an interconnect for a solid oxide type electrochemical cell stack according to claim 1 or claim 5.

9. The protective film comprises at least one selected from a spinel-type oxide containing Co and a perovskite-type oxide containing at least one selected from the group consisting of Co, La, and Sr, as an interconnect for a solid oxide type electrochemical cell stack according to claim 1 or claim 5.

10. The intermediate layer has a thickness of 0.3 μm or more and 10 μm or less, as described in claim 1 or claim 5, for an interconnector for a solid oxide type electrochemical cell stack.

11. The protective film has a thickness of 0.3 μm or more and 20 μm or less, as an interconnect for a solid oxide type electrochemical cell stack according to claim 1 or claim 5.

12. A first electrochemical cell comprising a first electrode in contact with an atmosphere containing a substance having hydrogen atoms, a second electrode in contact with an atmosphere containing oxygen, and a solid oxide electrolyte layer interposed between the first electrode and the second electrode, A second electrochemical cell comprising a first electrode in contact with an atmosphere containing a substance having hydrogen atoms, a second electrode in contact with an atmosphere containing oxygen, and a solid oxide electrolyte layer interposed between the first electrode and the second electrode, A solid oxide electrochemical cell stack comprising an interconnector according to claim 1 or claim 5, disposed between the first electrode and the second electrode so as to electrically connect the second electrode of the first electrochemical cell and the first electrode of the second electrochemical cell, The interconnector is arranged such that at least the protective film is located on the second electrode side of the first electrochemical cell, in a solid oxide type electrochemical cell stack.

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