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, which has a densified protective film to improve adhesion to a metal substrate and satisfies workability for a complicated shape.SOLUTION: An interconnector 1 for a solid oxide electrochemical cell stack according to an embodiment includes a metal base 2 containing an iron-based alloy containing chromium, and a protective film 3 provided on the surface of the metal base 2, and the protective film 3 includes a protective film body containing at least one selected from spinel-type oxides and perovskite-type oxides, and a dispersed phase scattered in the protective film body and containing an oxide of at least one element selected from the group consisting of rare earth elements and zirconium.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 Art

[0002] As one of the new energies towards a decarbonized society, hydrogen is mentioned. As a field of hydrogen utilization, fuel cells that convert chemical energy into electrical energy by electrochemically reacting hydrogen and oxygen have attracted attention. Fuel cells have high energy utilization efficiency and are being developed as large-scale distributed power sources, household power sources, and mobile power sources. Among fuel cells, from the viewpoints of efficiency and the like, solid oxide fuel cells (SOFC) that obtain electrical energy by an electrochemical reaction using an electrolyte made of solid oxide have attracted attention. In addition, in hydrogen production, research on solid oxide electrolysis cells (SOEC) to which a high-temperature steam electrolysis method for electrolyzing water in a high-temperature steam state is applied is being advanced. The operating principle of SOEC is the reverse reaction of SOFC, and like SOFC, an electrolyte made of solid oxide is used. In addition, since SOEC can electrolyze carbon dioxide (CO2) to generate carbon monoxide (CO) and synthesize CO and hydrogen (H2) to finally generate fuels such as methane (CH4), it has attracted attention as a technology for realizing a decarbonized society.

[0003] Solid oxide electrochemical cells used in SOFCs and SOECs have a laminate consisting of an air electrode (oxygen electrode), a solid oxide electrolyte layer, and a hydrogen electrode (fuel electrode). Multiple such laminated electrochemical cells are stacked via interconnectors to create high-capacity electrochemical cell stacks. Because interconnectors for solid oxide electrochemical cells require high-temperature resistance, stainless steel alloys with a high chromium content are generally used as the substrate. However, at high temperatures, an oxide film mainly composed of Cr2O3 forms on the surface of stainless steel alloys with a high chromium content. Since Cr2O3 has high electrical resistance, this surface oxide film reduces the electrical conductivity of the interconnector, increasing the resistance of the solid oxide electrochemical cell stack. Furthermore, if the Cr component in the Cr2O3 film gasifies and adheres to the electrodes of the solid oxide electrochemical cell, it degrades the performance of the solid oxide electrochemical cell. To mitigate these problems, various materials for interconnectors used in solid oxide electrochemical cell stacks are being widely investigated.

[0004] Generally, chromium (Cr) dispersion is suppressed by covering interconnectors for solid oxide electrochemical cell stacks with a dense protective film. The functions required of the protective film include suppression of Cr dispersion, electrical conductivity, adhesion, and ease of installation. Suppression of Cr dispersion is a function to suppress the vaporization of Cr contained in interconnectors for solid oxide electrochemical cell stacks, which degrades the performance of the solid oxide electrochemical cell under high-temperature operating conditions. Electrical conductivity is a function to reduce electrical resistance during energization, as electricity is required for the reactions of solid oxide electrochemical cells, thereby minimizing energy loss. Adhesion is a function to prevent the protective film from peeling off due to repeated heating and cooling between high temperatures (600°C or higher) and room temperature. Ease of installation is a function to form a uniform protective film, as interconnectors for solid oxide electrochemical cell stacks often have complex shapes.

[0005] For example, spinel-type oxides exhibiting electrical conductivity are used as protective films for interconnects. For instance, it has been proposed to form a ceramic protective film containing a spinel-structured oxide with Mn, Co, Cu, Y, and O on the surface of a conductive substrate. This ceramic protective film has a spinel structure composed of Mn, Co, and O, doped with Cu and Y. However, because such ceramic protective films have many pores, the contact area between the conductive substrate constituting the interconnect for solid oxide electrochemical cell stacks and the protective film becomes small, resulting in poor adhesion of the protective film and, consequently, increased electrical resistance. It has also been proposed to insert a layer containing rare earth elements between the chromium steel and the protective film. However, since vacuum deposition or the like is used to form the layer containing rare earth elements, it is difficult to deposit a uniform film thickness in complex shapes, resulting in poor workability. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2019 / 078674 [Patent Document 2] Special Publication No. 2009-544850 [Overview of the project] [Problems that the invention aims to solve]

[0007] The problem that the present invention aims to solve is to provide an interconnector for a solid oxide type electrochemical cell stack that densifies the protective film to improve adhesion to a metal substrate, thereby reducing electrical resistance, and also satisfies the requirement for workability on complex shapes, and a solid oxide type electrochemical cell stack using such an interconnector. [Means for solving the problem]

[0008] The embodiment of the interconnector for a solid oxide type electrochemical cell stack comprises a metal substrate containing a chromium-containing iron-based alloy and a protective film provided on the surface of the metal substrate, wherein the protective film comprises a protective film body containing at least one selected from spinel-type oxides and perovskite-type oxides, and a dispersed phase scattered within the protective film body containing an oxide of at least one element selected from the group consisting of rare earth elements and zirconium. [Brief explanation of the drawing]

[0009] [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 schematic cross-sectional view of the protective film of an interconnector for a solid oxide type electrochemical cell stack according to an embodiment. [Figure 4] This is a backscattered electron image of a cross-section of an interconnector for a solid oxide type electrochemical stack according to Comparative Example 1. [Figure 5] This is a backscattered electron image of a cross-section of the interconnector for a solid oxide type electrochemical stack according to Example 1. [Figure 6] This figure shows the electrical resistance of the interconnector for a solid oxide electrochemical stack according to Example 2, compared to the electrical resistance of the interconnector according to Comparative Example 1. [Modes for carrying out the invention]

[0010] The following describes the interconnectors and solid oxide electrochemical cell stacks for the embodiments described below with reference to the drawings. In each of the embodiments 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.

[0011] 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 hydrogen electrode (fuel electrode) side and is exposed to a hydrogen-containing atmosphere. The second surface 2b of the metal substrate 2 is the surface that is positioned on the air electrode (oxygen electrode) side and is exposed to air. Note that the first surface 2a side is not limited to flowing hydrogen; for example, in SOFCs, methanol (CH3OH) may also be flowed, so the first surface 2a only needs to be exposed to an atmosphere containing a substance with hydrogen atoms. The second surface 2b side is not limited to flowing air; for example, in SOECs, nothing may flow through it, or oxygen may flow through it, so the second surface 2b only needs to be exposed to an oxygen-containing atmosphere. Protective films 3 are provided on the first surface 2a and the second surface 2b of the metal substrate 2. Figure 1 shows an interconnector 1 with protective films 3 provided on the first surface 2a and the second surface 2b of a metal substrate 2, but the protective films 3 may be provided on only one of the surfaces, the first surface 2a and the second surface 2b.

[0012] The interconnector 1 shown in Figure 1 is used, for example, in the solid oxide type electrochemical cell stack 10 shown in Figure 2. The solid oxide type electrochemical cell stack 10 shown in Figure 2 has a structure in which a first electrochemical cell 11 and a second electrochemical cell 12 are stacked via the interconnector 1. Although Figure 2 shows a 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 a structure in which three or more electrochemical cells are stacked may be used. When three or more electrochemical cells are stacked, an interconnector is placed between each of two adjacent electrochemical cells, and each electrochemical cell is electrically connected by the interconnector.

[0013] The first electrochemical cell 11 and the second electrochemical cell 12 have the same configuration, each comprising 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 an ion conductor that does not conduct electricity. A porous first current collector 16 may be placed between the first electrode 13 and the interconnector 1 as needed. Similarly, a porous second current collector 17 may be placed between the second electrode 14 and the interconnector 1 as needed. The first and second current collectors 16 and 17 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.

[0014] 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.

[0015] 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 first electrode 13 as the hydrogen electrode, and the second surface 2b of the metal substrate 2 is positioned on the side of the second electrode 14 as the air electrode. Therefore, the first surface 2a of the metal substrate 2 is exposed to hydrogen supplied to the first electrode 13 as the hydrogen electrode, a hydrogen-containing atmosphere such as a mixture of hydrogen and water vapor, or a similar hydrogen-containing atmosphere discharged from the first electrode 13. The second surface 2b 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.

[0016] In the interconnector 1 used in the electrochemical cell stack 10 shown in Figure 2, the metal substrate 2 is made of an iron-based alloy containing chromium (Cr), i.e., stainless steel (SUS). In the electrochemical cell stack 10, the metal substrate 2 is made of a ferritic stainless steel, such as SUS430, which has a similar coefficient of thermal expansion to the electrochemical cells 11 and 12. When stainless steel is used for the metal substrate 2, the Cr contained in the metal substrate 2 may react with oxygen and water vapor in the high-temperature range of 600 to 1000°C, which is the operating temperature of SOFCs and SOECs, and vaporize, potentially adhering to the second electrode 14 and degrading performance. Therefore, in order to suppress the vaporization of chromium and the resulting diffusion, the interconnector 1 has a protective film 3 that covers at least the surface 2b of the metal substrate 2.

[0017] As shown in the cross-sectional schematic diagram of FIG. 3, the protective film 3 includes a protective film main body 31 and a dispersed phase 32 dispersed in the protective film main body 31. The protective film main body 31 forms the entire protective film 3, and the constituent material thereof includes 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 main body 31 that requires conductivity.

[0018] Examples of the metal elements contained in the spinel-type oxide and the perovskite-type oxide 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). The spinel-type oxide containing Co is effective as a constituent material of the protective film main body 31. Since Co functions as both the A-site element and the B-site element of the spinel-type oxide, it can form a spinel-type oxide represented by Co3O4. Furthermore, a material obtained by adding at least one selected from Ni, Mn, Cu, Fe, Cr, Zn, Al, and Ti to such a Co-containing spinel-type oxide is also effective, and effects such as improvement of electrical conductivity and relaxation of the mismatch in thermal expansion coefficient can be expected. Furthermore, a spinel-type oxide using Fe, Ni, Mn, etc. instead of Co can be used as a constituent material of the protective film main body 31.

[0019] 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 body 31.

[0020] The aforementioned Co-containing spinel-type oxides exhibit superior adhesion compared to perovskite-type oxides, but their electrical conductivity is inferior. To address this, adding small amounts of rare earth elements or zirconium (Zr) to Co-containing spinel-type oxides can improve electrical conductivity and further enhance adhesion. The same applies when using perovskite-type oxides. Therefore, in the interconnector 1 of this embodiment, a dispersed phase 32 containing oxides of rare earth elements or Zr is scattered within the protective film body 31 that constitutes the protective film 3. Here, scattering the dispersed phase 32 refers to a state in which it exists irregularly in the film thickness direction of the protective film 3 (perpendicular to the surface of the metal substrate 2).

[0021] As the rare earth elements contained in the dispersed phase 32, there are two elements, scandium (Sc) and yttrium (Y), and 15 elements from lanthanum (La) to lutetium (Lu), that is, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), a total of 17 elements. The dispersed phase 32 contains oxides of these rare earth elements and oxides of Zr.

[0022] According to the protective film 3 including the protective film body 31 in which the dispersed phase 32 containing the oxides of the rare earth elements and the oxides of Zr is dispersed, the dispersed phase 32 containing the oxides of the rare earth elements and the oxides of Zr contributes to the improvement of the electrical conductivity and adhesion of the protective film body 31 including spinel-type oxides and perovskite-type oxides. Furthermore, compared with the case where rare earth elements and Zr are added as constituent elements of the protective film body 31, by dispersing the dispersed phase 32 containing the oxides of the rare earth elements and the oxides of Zr in the protective film body 31, the formation of pores at the interface between the metal substrate 2 and the protective film 3 and in the protective film 3 can be suppressed. Thereby, the contact area between the metal substrate 2 and the protective film 3 can be increased, and the adhesion of the protective film 3 can be improved. Furthermore, the electrical resistance of the protective film 3 can be reduced by improving the adhesion of the protective film 3.

[0023] Because oxides of rare earth elements and Zr oxides have low electrical conductivity, if there is too much dispersed phase 32 scattered on the protective film body 31, it may reduce the electrical conductivity of the protective film 3. For this reason, it is preferable that the protective film 3 contains oxides of rare earth elements and Zr oxides constituting the dispersed phase 32 in a range of 3% to 30% by mass in terms of the amount of metallic elements. If the content of oxides of rare earth elements and Zr oxides in the protective film 3 is less than 3% by mass in terms of the amount of metallic elements, the amount of dispersed phase 32 scattered on the protective film body 31 is too small, and the effect of improving the electrical conductivity and adhesion of the protective film body 31 cannot be sufficiently obtained. If the content of oxides of rare earth elements and Zr oxides in the protective film 3 exceeds 30% by mass in terms of the amount of metallic elements, the amount of dispersed phase 32 is too large, and the low electrical conductivity of the dispersed phase 32 affects the entire protective film 3, which may conversely reduce the electrical conductivity of the protective film 3.

[0024] The protective film 3 preferably has a film thickness of 1 μm or more and 100 μm or less. More preferably, the film thickness of the protective film 3 is 2 μm or more and 20 μm or less. If the film thickness of the protective film 3 is less than 1 μm, the protective effect of the protective film 3 on the metal substrate 2 may not be sufficiently obtained. If the film thickness of the protective film 3 exceeds 100 μm, the adhesion of the protective film 3 may decrease, making it easier for the protective film 3 to peel off from the metal substrate 2. In particular, by setting the film thickness of the protective film 3 to 20 μm or less, the protective effect of the protective film 3 on the metal substrate 2 can be obtained, and the adhesion of the protective film 3 to the metal substrate 2 can be increased to improve the peeling suppression effect. Furthermore, the porosity of the protective film 3 is preferably 30% or less. If the porosity of the protective film 3 exceeds 30%, the adhesion of the protective film 3 to the metal substrate 2 decreases. However, since the voids in the protective film 3 have the effect of mitigating thermal expansion, the protective film 3 may have some voids, for example, about 5% or more.

[0025] The method for forming the protective film 3 is not particularly limited, and for example, electroplating, electroless plating, electrodeposition, spin coating, dip coating, sol-gel method, etc., can be applied. These methods for forming the protective film 3 offer superior workability compared to methods such as vacuum deposition. By using a metal substrate with a protective film to which such a formation method can be applied, it becomes possible to provide an interconnect with excellent adhesion and workability.

[0026] For example, when applying electroplating to form the protective film 3, the metal substrate 2 is immersed in a plating bath containing a metal element (e.g., Co) as a constituent element of the protective film body 31 and rare earth oxides or Zr oxides as constituent materials of the dispersed phase 32, and electroplating is performed. Next, heat treatment is performed at a temperature of 600°C or higher in an oxidizing atmosphere, such as air or an oxygen atmosphere. Since the metal element as a constituent element of the protective film body 31 is easily oxidized, oxides such as spinel-type oxides and perovskite-type oxides are generated by oxidation treatment at high temperatures. The generated oxides can be controlled by the ratio of metal elements in the plating bath and the acidic atmosphere. Furthermore, since rare earth oxide particles and Zr oxide particles are contained in the plating bath, these oxide particles can be dispersed in the metal plating film. Then, by oxidizing the plating film, it becomes possible to form a protective film 3 on the surface of the metal substrate 2, which has a protective film body 31 in which dispersed phases 32 containing rare earth element oxides and Zr oxides are scattered. Even when using other film formation methods, applying similar conditions will yield an interconnector 1 having the metal substrate 2 described above and a protective film 3 provided on its surface.

[0027] 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]

[0028] Next, we will describe specific examples of interconnectors according to the embodiment and their evaluation results.

[0029] (Comparative Example 1) A SUS430 substrate was prepared as the metal substrate. This SUS substrate was immersed in a Co plating bath and electroplated. The Co plating bath did not contain rare earth oxides or Zr oxides. Next, the SUS substrate with the Co plating film was exposed to air at 700°C to oxidize the Co plating film. The oxidized Co film was confirmed to be a Co oxide film mainly composed of Co spinel-type oxide represented by Co3O4. The backscattered electron image of the cross-section of the SUS substrate with the Co oxide film obtained in this way was observed. The electron reflection image of Comparative Example 1 is shown in Figure 4.

[0030] (Example 1) A SUS430 substrate was prepared as the metal substrate. This SUS substrate was immersed in a Co plating bath and electroplated. As the plating bath, a Co plating bath in which Y2O3 particles were dispersed was used. The Y2O3 particles were added to the Co plating bath so that the amount of Y element in the plating film was 8 to 16 mass%. Next, the SUS substrate with the Co plating film containing Y2O3 particles was exposed to air at 700°C to oxidize the Co plating film. The oxidized Co film was confirmed to be a Co oxide film mainly composed of Co spinel-type oxide represented by Co3O4, with scattered Y2O3 dispersed phases. The backscattered electron image of the cross-section of the SUS substrate with the Co oxide film containing the Y2O3 dispersed phase obtained in this way was observed. The electron reflection image according to Example 1 is shown in Figure 5.

[0031] As shown in Figure 4, continuous voids horizontal to the surface of the SUS substrate are observed in the protective film of Comparative Example 1, as indicated by the arrows. Furthermore, voids are observed at the interface between the SUS substrate and the protective film, as enclosed by the dotted rectangle in Figure 4. Many voids are observed in the protective film of Comparative Example 1, both internally and at the interface with the SUS substrate. It was confirmed that approximately 20% of the protective film of Comparative Example 1 is void. Areas with many such voids reduce the adhesion between the protective film and the SUS substrate, raising concerns about the protective film peeling off. When such a metal substrate with a protective film is used as an interconnect for a solid oxide type electrochemical cell stack, peeling of the protective film will reduce electrical conductivity and become a factor in structural failure of the electrochemical cell stack.

[0032] In contrast to the protective film of Comparative Example 1, the protective film of Example 1, as shown in Figure 5, was observed to have dispersed phases mainly composed of Y2O3 within a film mainly composed of Co spinel-type oxide, as indicated by the arrows in the figure. A reduction in voids within the protective film and at the interface between the SUS substrate and the protective film was observed. The void ratio in the protective film of Example was approximately 6%. In this way, by dispersing a dispersed phase mainly composed of Y2O3 within the protective film, voids within the protective film and at the interface between the protective film and the SUS substrate can be reduced, thereby improving the adhesion between the protective film and the SUS substrate. Since a plating method is applied to form the protective film, workability can be improved. Therefore, according to Example 1, it is possible to provide a metal substrate with a protective film that has excellent adhesion and workability, and an interconnect for a solid oxide type electrochemical cell stack using the same.

[0033] (Example 2) A SUS430 substrate was prepared as the metal substrate. This SUS substrate was immersed in a Co plating bath and electroplated. The plating bath used was a Co plating bath in which Y2O3 particles were dispersed. The Y2O3 particles were added to the Co plating bath so that the amount of Y element in the Co plating film was 1-2 mass%. The amount of Y element in a Co plating film with a thickness of 5 μm was measured by X-ray fluorescence analysis (XRF) and was found to be 1.83 mass%. Next, the SUS substrate with the Co plating film containing Y2O3 particles was exposed to air at 700°C for 10 hours to oxidize the Co plating film. The oxidized Co film was confirmed to be a Co oxide film mainly composed of Co spinel-type oxide represented by Co3O4, with scattered Y2O3 dispersed phases.

[0034] The electrical resistance of the SUS substrate with a Co oxide film containing the Y2O3 dispersed phase obtained in this manner was measured. The electrical resistance was measured by forming a Pt electrode on the Co oxide film by Pt deposition and measuring it at 700°C using the four-terminal method. Similarly, the electrical resistance of the SUS substrate with a Co oxide film that did not contain the Y2O3 dispersed phase, formed according to Comparative Example 1, was measured in the same manner. These measurement results are shown in Figure 6. As is clear from Figure 6, it was confirmed that forming a Co oxide film containing the Y2O3 dispersed phase on the SUS substrate reduces the electrical resistance compared to forming a simple Co oxide film (without the Y2O3 dispersed phase) on the SUS substrate. Therefore, it becomes possible to provide an interconnector for solid oxide type electrochemical cell stacks with excellent properties.

[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, 31...Protective film body, 32...Dispersed phase, 10...Electrochemical cell stack, 11,12...Electrochemical cell, 13...First electrode, 14...Second electrode, 15...Solid oxide electrolyte layer.

Claims

1. A metal substrate containing 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, The protective film comprises a protective film body containing at least one selected from spinel-type oxides and perovskite-type oxides, and a dispersed phase scattered within the protective film body containing an oxide of at least one metal element selected from the group consisting of rare earth elements and zirconium. The protective film contains an oxide of the metal element in an amount equivalent to 3% by mass or more and 30% by mass or less of the metal element. An interconnect for a solid oxide type electrochemical cell stack, wherein the porosity of the protective film is 30% or less.

2. The protective film contains an oxide of the metal element in an amount equivalent to 8% by mass or more and 16% by mass or less, according to claim 1, as an interconnect for a solid oxide type electrochemical cell stack.

3. The protective film has a thickness of 100 μm or less, as described in claim 1 or claim 2, for an interconnector for a solid oxide type electrochemical cell stack.

4. The interconnect for a solid oxide type electrochemical cell stack according to claim 1 or claim 2, wherein the porosity of the protective film is 6% or less.

5. The protective film body comprises at least one metal element selected from the group consisting of Co, Ni, Mn, Cu, Fe, Cr, Zn, Al, Ti, La, and Sr, as an interconnect for a solid oxide type electrochemical cell stack according to claim 1 or claim 2.

6. The protective film body comprises Co and at least one metallic element selected from the group consisting of Ni, Mn, Cu, Fe, Cr, Zn, Al, and Ti, as an interconnect for a solid oxide type electrochemical cell stack according to claim 1 or claim 2.

7. The protective film body comprises at least one selected from the spinel-type oxide containing Co and the 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 2.

8. 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 disposed between the first electrode and the second electrode so as to be electrically connected to the first electrode of the first electrochemical cell and the second electrode of the second electrochemical cell, The interconnect comprises a metal substrate containing a chromium-containing iron-based alloy and a protective film provided on the surface of the metal substrate. The protective film comprises a protective film body containing at least one selected from spinel-type oxides and perovskite-type oxides, and a dispersed phase scattered within the protective film body containing an oxide of at least one metal element selected from the group consisting of rare earth elements and zirconium. The protective film contains an oxide of the metal element in an amount equivalent to 3% by mass or more and 30% by mass or less of the metal element. A solid oxide type electrochemical cell stack in which the porosity of the protective film is 30% or less.

9. The solid oxide type electrochemical cell stack according to claim 8, wherein the protective film contains an oxide of the metal element in an amount equivalent to 8% by mass or more and 16% by mass or less of the metal element.

10. The solid oxide type electrochemical cell stack according to claim 8 or claim 9, wherein the protective film has a thickness of 100 μm or less.

11. The solid oxide type electrochemical cell stack according to claim 8 or claim 9, wherein the porosity of the protective film is 6% or less.

12. The solid oxide type electrochemical cell stack according to claim 8 or claim 9, wherein the protective film body contains at least one metal element selected from the group consisting of Co, Ni, Mn, Cu, Fe, Cr, Zn, Al, Ti, La, and Sr.

13. The solid oxide type electrochemical cell stack according to claim 8 or 9, wherein the protective film body comprises Co and at least one metallic element selected from the group consisting of Ni, Mn, Cu, Fe, Cr, Zn, Al, and Ti.

14. The solid oxide type electrochemical cell stack according to claim 8 or 9, wherein the protective film body comprises at least one selected from the spinel-type oxide containing Co and the perovskite-type oxide containing at least one selected from the group consisting of Co, La, and Sr.

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