Solid oxide fuel cell

Abstract

Provided is a solid oxide fuel cell in which a plurality of power generation cells are stacked, the power generation cells each comprising: a solid electrolyte layer; an anode electrode disposed on one surface of the solid electrolyte layer; a cathode electrode disposed on the other surface of the solid electrolyte layer; and a porous metal support layer disposed on at least one among the anode electrode side and the cathode electrode side. Provided between the power generation cells are: a separator provided spaced apart from the porous metal support layers; and interconnectors positioned between the separator and the porous metal support layers. An anode flow path for supplying fuel to the anode electrode is formed between the separator and the anode electrode side of the corresponding power generation cell. A cathode flow path for supplying air to the cathode electrode is formed between the separator and the cathode electrode side of the corresponding power generation cell. Each interconnector has a part which is joined to the separator and a part which is joined to the porous metal support layer. Each interconnector is welded to the porous metal support layer at the part joined to the porous metal support layer.

Description

[Technical Field]

[0001] The present invention relates to a solid oxide fuel cell. [Background technology]

[0002] JP2006-236989A discloses a fuel cell stack in which unit cells are stacked, each having a porous metal support layer on the outside of an anode electrode and a cathode electrode sandwiching a solid electrolyte. This fuel cell stack has metal separators between the unit cells that form fuel gas (anode gas) and air (cathode gas) flow paths, and the separators and the porous metal support layer are metal-bonded. Summary of the Invention

[0003] As a method for joining a metal separator and a porous metal support layer, welding generally has lower electrical resistance between the joined metal separator and porous metal support layer and is more robust against displacement during fuel cell operation, creep of the substrate, etc., compared to joining using contact paste, brazing, etc. In other words, welding has excellent conductivity (power generation efficiency) and robustness.

[0004] However, welding between the metal and the porous layer may cause defects such as blowholes. If cracks or the like occur in the separator due to welding defects when the metal separator and the porous metal support layer are welded, the anode gas and cathode gas will mix, resulting in a decrease in power generation efficiency.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a solid oxide fuel cell that is excellent in power generation efficiency and robustness.

[0006] According to one aspect of the present invention, there is provided a solid oxide fuel cell including a plurality of stacked power-generating cells, each including a solid electrolyte layer, an anode electrode disposed on one side of the solid electrolyte, a cathode electrode disposed on the other side of the solid electrolyte layer, and a porous metal support layer disposed on at least one side of the anode or the cathode. A separator spaced apart from the porous metal support layer and an interconnector located between the separator and the porous metal support layer are provided between each power-generating cell, with an anode flow path for supplying fuel to the anode electrode formed between the anode side of the power-generating cell and the separator, and a cathode flow path for supplying air to the cathode electrode formed between the cathode side of the power-generating cell and the separator. The interconnector has a portion bonded to the separator and a portion bonded to the porous metal support layer, and is welded to the porous metal support layer at the portion bonded to the porous metal support layer. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is an exploded perspective view of a fuel cell stack according to an embodiment of the present invention. [Figure 2] FIG. 2 is an exploded perspective view of a portion where the power generation units of FIG. 1 are stacked. [Figure 3] FIG. 3 is a schematic cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is an enlarged view of the area enclosed by the square A in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] [First embodiment] 1 is an exploded perspective view of a power generation unit 1 constituting a power generation module of a solid oxide fuel cell 100 (hereinafter simply referred to as a "fuel cell") according to this embodiment. The solid oxide fuel cell 100 of this embodiment is mainly mounted on a vehicle or the like, but is not limited to this.

[0010] The power generation unit 1 comprises a power generation cell 2, a metal interconnector 3, and a sealing member 4 for sealing the outer edge of the interconnector 3. The interconnector 3 is bonded to both sides of the active area 2A, which is the region of the power generation cell 2 that contributes to power generation. The sealing member 4 is also bonded to both sides of the outer edge of the power generation cell 2 (see FIG. 2). The method of bonding the power generation cell 2 and the interconnector 3 will be described in detail below.

[0011] Fig. 2 is an exploded perspective view of two stacked power generation units 1. Note that the solid oxide fuel cell 100 is configured by stacking a plurality of power generation units 1, but for convenience, the solid oxide fuel cell 100 in Fig. 2 is configured by stacking two power generation units 1.

[0012] As shown in Fig. 2, a separator 5 is interposed between the two power generation units 1. The two power generation units 1 are stacked by metal-joining the interconnector 3 of one power generation unit 1 to one surface of the separator 5 and the interconnector 3 of the other power generation unit 1 to the other surface of the separator 5. Although two power generation units 1 are stacked in Fig. 2, more power generation units 1 can be stacked in the same manner.

[0013] Figure 3 is a schematic diagram showing a cross section taken along line III-III in Figure 2. For simplicity, the outer edge of the power generation unit 1 is omitted in Figure 3, and only a portion of the cross section is shown enlarged. Here, the power generation unit 1 is defined as a state in which the interconnector 3 is joined to the power generation cell 2 and the separator 5.

[0014] As shown in Fig. 3, the power-generating cell 2 comprises a membrane electrode assembly 2C having an anode electrode disposed on one surface of a solid electrolyte layer and a cathode electrode disposed on the other surface, a cathode support layer 2B supporting the cathode electrode, and an anode support layer 2D supporting the anode electrode. The cathode support layer 2B and the anode support layer 2D are porous metal bodies configured so as not to impede the supply of anode gas and cathode gas, respectively, and are formed from, for example, ferritic stainless steel. In Fig. 3, the cathode electrode is disposed on the upper surface side of the membrane electrode assembly 2C, and the anode electrode is disposed on the lower surface side.

[0015] The separator 5 has a current collecting function and is disposed between two adjacent power generating cells 2, spaced apart from the cathode support layer (porous metal support layer) 2B and the anode support layer (porous metal support layer) 2D. The separator 5 forms an anode flow path 6 for supplying fuel gas to the anode electrode between the separator 5 and the anode support layer 2D (the anode electrode side of the power generating cell 2) of the power generating cell 2. The separator 5 also forms a cathode flow path 7 for supplying air to the cathode electrode between the separator 5 and the cathode support layer 2B (the cathode electrode side of the power generating cell 2) of the power generating cell 2. The material constituting the separator 5 is not particularly limited as long as it is electrically conductive and thermally conductive, but may be, for example, an alloy or metal containing iron (Fe) or chromium (Cr), or preferably ferritic stainless steel.

[0016] The interconnector 3 has a current collecting function and is disposed between the active area 2A of the power generating cell 2 and the separator 5, connecting the separator 5 to the porous metal support layers 2B and 2D. The interconnector 3 includes an anode-side interconnector 31 disposed between the anode support layer (porous metal support layer on the anode electrode side) 2D of the power generating cell 2 and the separator 5, and a cathode-side interconnector 32 disposed between the cathode support layer (porous metal support layer on the cathode electrode side) 2B of the power generating cell 2 and the separator 5. There are no particular limitations on the material constituting the interconnector 3 as long as it is an electrically conductive and thermally conductive material, and for example, ferritic stainless steel containing aluminum is used.

[0017] The anode side interconnector 31 has a first joint portion 311 joined to the upper surface of the separator 5 and a second joint portion 312 joined to the lower surface of the anode support layer 2D, and the first joint portion 311 and the second joint portion 312 are connected by a connecting portion 313. Here, the anode side interconnector 31 and the separator 5 are welded at the first joint portion 311, and the anode side interconnector 31 and the anode support layer 2D are welded at the second joint portion 312. Note that, although laser welding is used as the welding method in this embodiment, the present invention is not limited to this.

[0018] The anode-side interconnector 31 is formed by arranging a plurality of members, each of which is made up of a first joint portion 311, a second joint portion 312, and a connecting portion 313, in the width direction of the separator 5. As a result, the anode flow path 6 between the separator 5 and the anode support layer 2D is divided into a plurality of flow paths surrounded by the separator 5, the anode-side interconnector 31, and the anode support layer 2D.

[0019] The cathode-side interconnector 32 has a third joint 321 joined to the lower surface of the separator 5 and a fourth joint 322 joined to the upper surface of the cathode support layer 2B, and the third joint 321 and the fourth joint 322 are connected by a connecting portion 323. Here, the cathode-side interconnector 32 and the separator 5 are connected at the third joint 321 by diffusion bonding using a metallic bonding material 8, and the cathode-side interconnector 32 and the cathode support layer 2B are welded at the fourth joint 322.

[0020] The cathode-side interconnector 32 is formed by arranging a plurality of members, each of which is made up of a third joint portion 321, a fourth joint portion 322, and a connecting portion 323, in the width direction of the separator 5. As a result, the cathode flow path 7 between the separator 5 and the cathode support layer 2B is partitioned into a plurality of flow paths surrounded by the separator 5, the cathode-side interconnector 32, and the cathode support layer 2B.

[0021] It is preferable that the thickness of the separator 5 is equal to or less than the thickness of the interconnector 3. For example, the thickness of the interconnector 3 is set to 0.1 mm to 0.3 mm, and the thickness of the separator 5 is set to 10 μm to 100 μm. Increasing the thickness of the interconnector 3 in this way increases the current-carrying area of ​​the interconnector 3, and decreasing the thickness of the separator 5 shortens the current-carrying distance of the separator 5. This reduces the resistance of the current-carrying path, improving power generation efficiency.

[0022] As described above, in the solid oxide fuel cell 100, the interconnector 3 and the porous metal support layers 2B, 2D are joined by welding. Joining by welding in this manner strengthens the bond between the interconnector 3 and the porous metal support layers 2B, 2D compared to joining using contact paste, brazing, or the like, thereby improving robustness against displacement during operation of the fuel cell 100 and creep of the substrate. Furthermore, in the case of welding, the joining interface between the interconnector 3 and the porous metal support layers 2B, 2D melts, removing the initial surface layers (oxide coatings) of the interconnector 3 and the porous metal support layers 2B, 2D and reducing the resistance of the joint. In other words, welding provides lower resistance and superior conductivity between the interconnector 3 and the porous metal support layers 2B, 2D compared to other joining methods. This improves the power generation efficiency of the power generation unit 1 (fuel cell 100). Furthermore, because welding does not require additional materials, it is less expensive than other joining methods.

[0023] However, when welding between a metal and a porous layer, there is a problem that defects such as blowholes are likely to occur. Therefore, when the interconnector 3 or separator 5, which is a metal member, is welded to the porous metal support layer 2B, 2D, there is a risk of cracks or the like occurring in the interconnector 3 or 5 due to welding defects. In this case, if the anode flow path 6 and the cathode flow path 7 are formed using only the porous metal support layer 2B, 2D and one metal member (the interconnector 3 or the separator 5), there is a risk that the anode gas and the cathode gas will mix due to gas leakage, resulting in a decrease in power generation efficiency.

[0024] In contrast, in this embodiment, the anode flow path 6 and the cathode flow path 7 are separated by a separator 5 provided at a distance from the porous metal support layers 2B and 2D. Specifically, the gas flow paths (anode flow path 6 and cathode flow path 7) are formed using the interconnector 3 and the separator 5, and the interconnector 3 is welded to the porous metal support layers 2B and 2D. Therefore, even if a crack or the like occurs in the interconnector 3 due to a welding defect, the anode flow path 6 and the cathode flow path 7 are separated by the separator 5, so the anode gas and the cathode gas do not mix. This prevents a decrease in power generation efficiency. Furthermore, because the separator 5 is not welded to the porous metal support layers 2B and 2D, the thickness of the separator 5 can be reduced, further improving power generation efficiency. Furthermore, because the thickness of the separator 5 can be reduced, the weight of the fuel cell 100 can be reduced, and the dimension of the power generation cell 2 in the stacking direction can be reduced, resulting in a more compact fuel cell 100. Furthermore, by reducing the thickness of the separator 5, the heat capacity can also be reduced.

[0025] Hereinafter, with reference to FIGS. 3 and 4, details of the bonding between the interconnector 3, the separator 5, and the porous metal support layers 2B and 2D will be described.

[0026] As described above, the anode side interconnector 31 is joined to the separator 5 by welding at the first joint 311, and is joined to the anode support layer 2D by welding at the second joint 312. This makes the joining between the anode side interconnector 31 and the separator 5 and the anode support layer 2D stronger than with other joining methods. Furthermore, welding melts the joining interfaces between the anode side interconnector 31 and the separator 5 and the anode support layer 2D, thereby destroying the initial surface layers (oxide coatings) of the substrates (anode side interconnector 31, separator 5, anode support layer 2D), reducing the resistance of the joints and improving the conductivity.

[0027] 3, the contact surfaces of the anode side interconnector 31 and the separator 5 in the first joint 311 are both formed as flat surfaces, and the contact surfaces of the anode side interconnector 31 and the anode support layer 2D in the second joint 312 are both formed as flat surfaces. That is, the anode side interconnector 31 and the separator 5, and the anode side interconnector 31 and the anode support layer 2D are in flat contact with each other.

[0028] In this way, the anode side interconnector 31 and the separator 5 are in planar contact with each other, so the direction of the force generated by the expansion of the anode flow path 6 when heat is input to the power generation unit 1 (fuel cell 100) is the compression direction (the direction perpendicular to the anode side interconnector 31 toward the separator 5). Therefore, peeling of the anode side interconnector 31 from the separator 5 due to strain caused by the heat input is suppressed.

[0029] Furthermore, because the anode side interconnector 31 and the anode support layer 2D are in planar contact with each other, a large contact area is ensured between the anode side interconnector 31 and the anode support layer 2D. This reduces stress between the anode side interconnector 31 and the anode support layer 2D during thermal expansion, etc., and prevents damage to the power generation cell 2 due to, for example, depression of the anode support layer 2D.

[0030] On the other hand, as described above, the cathode-side interconnector 32 is joined to the separator 5 at the third joint 321 by diffusion bonding using the metallic bonding material 8, and is joined to the cathode support layer 2B at the fourth joint 322 by welding. Here, when the power generation units 1 are in contact with each other, a welder cannot access the first to fourth joints 311, 312, 321, and 322. Therefore, a joining method other than welding must be used for one of the first to fourth joints 311, 312, 321, and 322. For this reason, in this embodiment, welding is not used for joining the cathode-side interconnector 32 and the separator 5 (the third joint 321). The diffusion bonding between the cathode-side interconnector 32 and the separator 5 is performed by sandwiching the bonding material 8 between the cathode-side interconnector 32 and the separator 5 and applying pressure and heat to join them, but the reaction progresses due to heat input during operation of the fuel cell 100. Therefore, during operation of the fuel cell 100, a lower resistance and higher strength bond is formed.

[0031] Preferably, the separator 5 is formed in a planar shape at least on the active area 2A of the power generating cell 2. This reduces dimensional variations in the stacking direction of the fuel cell 100 and improves contact between the cathode-side interconnector 32 and the separator 5. This improves the quality of diffusion bonding.

[0032] 3, in the third joint 321, the contact surfaces of the cathode side interconnector 32 and the separator 5 are both formed flat, and in the fourth joint 322, the contact surfaces of the cathode side interconnector 32 and the cathode support layer 2B are both formed flat. That is, the cathode side interconnector 32 and the separator 5, and the cathode side interconnector 32 and the cathode support layer 2B are in flat contact.

[0033] In this way, the cathode side interconnector 32 and the separator 5 are in planar contact, and therefore, similar to the anode side, the direction of the force generated by the expansion of the cathode flow path 7 when heat is input to the power generation unit 1 (fuel cell 100) is a compression direction (a direction perpendicular to the cathode side interconnector 32 toward the separator 5). Therefore, peeling of the cathode side interconnector 32 from the separator 5 due to heat input strain is suppressed.

[0034] Furthermore, because the cathode-side interconnector 32 and the cathode support layer 2B are in planar contact with each other, a large contact area is ensured between the cathode-side interconnector 32 and the cathode support layer 2B. This reduces stress between the cathode-side interconnector 32 and the cathode support layer 2B during thermal expansion, etc., and prevents damage to the power generation cell 2 due to, for example, depression of the cathode support layer 2B.

[0035] The bonding material 8 used for diffusion bonding between the cathode side interconnector 32 and the separator 5 is a metal different from those of the cathode side interconnector 32 and the separator 5, and for example, a metal having a linear expansion coefficient in the range of 0 to 50% is used. Specifically, in this embodiment, nickel (Ni) or a nickel alloy is used. The form of the bonding material 8 is not particularly limited, and for example, Ni paste, Ni sheet, Ni wire, Ni coating, etc. can be used. By using a metal having a linear expansion coefficient in the range of 0 to 50%, such as nickel (Ni), as the bonding material 8, an increase in the difference in thermal expansion between the base material (the cathode side interconnector 32 and the separator 5) and the bonding material 8 is suppressed. Furthermore, since the bonding material 8 is thinner than the base material (the cathode side interconnector 32 and the separator 5), it plastically deforms first, and therefore the bonding portion (third bonding portion 321) between the cathode side interconnector 32 and the separator 5 is protected.

[0036] Furthermore, when the anode side interconnector 31 and the separator 5 or the anode support layer 2D are diffusion bonded, the bonding material 8, which is a metal different from the interconnector 3 and the separator 5, may react with the fuel, causing defects in the bond and affecting the anode gas. In particular, nickel (Ni) used in this embodiment is likely to react with the fuel, and there is a risk that the effect on the anode gas may be greater. In contrast, in this embodiment, diffusion bonding using a metal (nickel) is used to bond the cathode side interconnector 32 and the separator 5, so that the bonding material 8 is prevented from reacting with the fuel, preventing defects in the bond and the effect on the anode gas.

[0037] FIG. 4 is an enlarged view of the area enclosed by the square A in FIG.

[0038] As shown in FIG. 4 , the anode side interconnector 31 and the cathode side interconnector 32 are joined to the separator 5 so that the first joint 311 and the third joint 321 overlap when viewed in the stacking direction of the power generation cells 2. This minimizes the current-carrying distance between the anode side interconnector 31 and the cathode side interconnector 32. Since electrical resistance is proportional to the current-carrying distance, by configuring the first joint 311 and the third joint 321 to overlap when viewed in the stacking direction of the power generation cells 2, it is possible to minimize the resistance between the anode side interconnector 31 and the cathode side interconnector 32. This improves the power generation efficiency of the fuel cell 100. Furthermore, by configuring the first joint 311 and the third joint 321 to overlap when viewed in the stacking direction of the power generation cells 2, the rigidity of the joints 311, 321 is enhanced.

[0039] 4, a first joint 311 where the anode side interconnector 31 and the separator 5 are joined (contacted) includes a welded portion 314 where the anode side interconnector 31 and the separator 5 are welded. Then, as shown in FIG. 4, a third joint 321 where the cathode side interconnector 32 and the separator 5 are diffusion-bonded is formed so as to cover the welded portion 314 in the first joint 311 when viewed in the stacking direction of the power generation cell 2. As a result, the heat input due to welding the anode side interconnector 31 and the separator 5 removes the initial surface layer (oxide coating) of the separator 5, the metal bonding material 8, and the cathode side interconnector 32 in the third joint 321, and the electrical resistance between the cathode side interconnector 32 and the separator 5 is reduced.

[0040] 4, the second joint 312 joining the anode side interconnector 31 and the anode support layer 2D, and the fourth joint 322 joining the cathode side interconnector 32 and the cathode support layer 2B are formed at corresponding (opposing) positions (overlapping positions in the stacking direction) when viewed in the cross section of the power generating cell 2. The loads generated when fastening the layers of the power generating cell 2 or when they thermally expand are borne by the anode side interconnector 31 and the cathode side interconnector 32, but because the second joint 312 and the fourth joint 322 are formed at corresponding positions when viewed in the cross section of the power generating cell 2, bending input to the power generating cell 2 is suppressed. Therefore, damage to the power generating cell 2 is prevented.

[0041] Note that, as in this embodiment, the rigidity of the joints 311, 321 is further strengthened by configuring the first joint 311 and the third joint 321 to completely overlap when viewed in the stacking direction of the power generating cells 2, but this is not necessarily limited to this. If the first joint 311 and the third joint 321 at least partially overlap when viewed in the stacking direction of the power generating cells 2, the current flow distance is shorter than when they are separated, and power generation efficiency is improved.

[0042] According to the solid oxide fuel cell 100 of the above embodiment, the following effects can be obtained.

[0043] The solid oxide fuel cell 100 includes a separator 5 spaced apart from the porous metal support layers 2B, 2D between the power generation cells 2, and an interconnector 3 located between the separator 5 and the porous metal support layers 2B, 2D. An anode flow path 6 is formed between the anode electrode side of the power generation cell 2 and the separator 5, and a cathode flow path 7 is formed between the cathode electrode side of the power generation cell 2 and the separator 5. The interconnector 3 is welded to the porous metal support layers 2B, 2D. Because the anode flow path 6 and the cathode flow path 7 are separated by the separator 5 spaced apart from the porous metal support layers 2B, 2D, even if a crack occurs in the interconnector 3 due to a welding defect between the interconnector 3 and the porous metal support layers 2B, 2D, the anode gas and the cathode gas do not mix. This means that a decrease in power generation efficiency is suppressed, making it possible to provide a solid oxide fuel cell 100 with good power generation efficiency.

[0044] Furthermore, because the interconnector 3 and the porous metal support layers 2B, 2D are joined by welding, the joint is stronger and more robust than with other joining methods. Furthermore, the heat input from the welding melts the joint interface between the interconnector 3 and the porous metal support layers 2B, 2D, removing the initial surface layer (oxide film) of the interconnector 3 and the porous metal support layers 2B, 2D, thereby reducing the resistance of the joint and improving power generation efficiency. Furthermore, because welding does not require additional materials, costs can be reduced.

[0045] Furthermore, because the separator 5 is not welded to the porous metal support layers 2B, 2D, the thickness of the separator 5 can be reduced, further improving power generation efficiency. Furthermore, because the thickness of the separator 5 can be reduced, the weight of the fuel cell 100 can be reduced, and the dimension of the power generation cells 2 in the stacking direction can be reduced, allowing the fuel cell 100 to be made more compact.

[0046] In the solid oxide fuel cell 100, the interconnector 3 includes an anode-side interconnector 31 having a first joint 311 joined to the separator 5 and a second joint 312 joined to the anode support layer (porous metal support layer on the anode electrode side) 2D, and a cathode-side interconnector 32 having a third joint 321 joined to the separator 5 and a fourth joint 322 joined to the cathode support layer (porous metal support layer on the cathode electrode side) 2B. The anode-side interconnector 31 is welded to the anode support layer (porous metal support layer on the anode electrode side) 2D at the second joint 312, and the cathode-side interconnector 32 is welded to the cathode support layer (porous metal support layer on the cathode electrode side) 2B at the fourth joint 322. In this way, the interconnector 3 is welded to the porous metal support layers 2B, 2D on both the anode electrode side and the cathode electrode side, thereby further improving the power generation efficiency of the fuel cell 100.

[0047] The solid oxide fuel cell 100 is configured so that a first joint 311 at which the anode side interconnector 31 is joined to the separator 5 and a third joint 321 at which the cathode side interconnector 32 is joined to the separator 5 at least partially overlap when viewed in the stacking direction of the power generation cells 2. This shortens the current-carrying distance between the anode side interconnector 31 and the cathode side interconnector 32, making it possible to reduce electrical resistance. In other words, the power generation efficiency of the fuel cell 100 is further improved. In addition, because the first joint 311 and the third joint 321 overlap when viewed in the stacking direction of the power generation cells 2, the rigidity of the joints 311, 321 is strengthened.

[0048] In the solid oxide fuel cell 100, the anode side interconnector 31 is welded to the separator 5. This strengthens the bond between the anode side interconnector 31 and the separator 5, improving robustness. Furthermore, the heat input during welding melts the bonded interface between the anode side interconnector 31 and the separator 5, removing the initial surface layers (oxide coatings) of the anode side interconnector 31 and the separator 5, thereby reducing the resistance of the bonded portion and improving power generation efficiency. Furthermore, since welding does not require additional materials, costs can be reduced.

[0049] In the solid oxide fuel cell 100, the cathode side interconnector 32 and the separator 5 are diffusion bonded using a bonding material 8 made of a metal different from the cathode side interconnector 32 and the separator 5. In the diffusion bonding using a metal, the reaction proceeds due to the heat input while the fuel cell 100 is in operation, so that the bond has lower resistance and higher strength while the fuel cell 100 is in operation.

[0050] Furthermore, the cathode side interconnector 32 and the separator 5 are diffusion bonded with a metal (bonding material 8), and the anode side interconnector 31 and the separator 5 are bonded without using diffusion bonding with the bonding material 8. This prevents the bonding material 8 from reacting with the fuel, causing defects in the bond, or affecting the anode gas. Therefore, a decrease in the power generation efficiency of the fuel cell 100 is prevented.

[0051] In the solid oxide fuel cell 100, the bonding material 8 that diffusion-bonds the cathode-side interconnector 32 and the separator 5 is nickel (Ni) or a nickel alloy. By using nickel or a nickel alloy for the bonding material 8, an increase in the difference in thermal expansion and contraction between the substrate (cathode-side interconnector 32 and separator 5) and the bonding material 8 is suppressed. In addition, since the bonding material 8 is thinner than the substrate (cathode-side interconnector 32 and separator 5), it plastically deforms first, and therefore the bonding portion (third bonding portion 321) between the cathode-side interconnector 32 and the separator 5 is protected.

[0052] In the solid oxide fuel cell 100, the interconnector 3 and the separator 5 are in planar contact with each other. This causes the direction of the force generated by the expansion of the anode and cathode flow paths 6, 7 when heat is input to the power generation unit 1 (fuel cell 100) to be a compression direction (a direction perpendicular to the separator 5 from the interconnector 3). This prevents the interconnector 3 from peeling off from the separator 5 due to strain caused by the heat input.

[0053] In the solid oxide fuel cell 100, a third joint 321 where the cathode side interconnector 32 and the separator 5 are joined is formed so as to cover a welded portion 314 where the anode side interconnector 31 and the separator 5 are welded. As a result, the heat input caused by welding the anode side interconnector 31 and the separator 5 removes the initial surface layer (oxide coating) of the separator 5, the metal bonding material 8, and the cathode side interconnector 32 at the third joint 321, thereby reducing the electrical resistance between the cathode side interconnector 32 and the separator 5. Therefore, the power generation efficiency of the fuel cell 100 is improved.

[0054] In the solid oxide fuel cell 100, the second joint 312 where the anode-side interconnector 31 and the anode support layer 2D are joined, and the fourth joint 322 where the cathode-side interconnector 32 and the cathode support layer 2B are joined are formed at corresponding (opposing) positions (positions overlapping in the stacking direction) when viewed in the cross-sectional direction of the power generating cell 2. This suppresses bending input to the power generating cell 2, preventing damage to the power generating cell 2.

[0055] In the solid oxide fuel cell 100, the interconnector 3 and the porous metal support layers 2B, 2D are in planar contact at the second joint 312 and the fourth joint 322. This ensures a large contact area between the interconnector 3 and the porous metal support layers 2B, 2D. Therefore, stress between the interconnector 3 and the porous metal support layers 2B, 2D during thermal expansion, etc. is reduced, preventing damage to the power generation cell 2 due to, for example, the collapse of the porous metal support layers 2B, 2D.

[0056] In the solid oxide fuel cell 100, the separator 5 is formed in a planar shape at least on the active area 2A of the power generation cell 2. This reduces dimensional variations in the stacking direction of the fuel cell 100 and improves contact between the cathode-side interconnector 32 and the separator 5. This improves the quality of diffusion bonding.

[0057] In the solid oxide fuel cell 100, the thickness of the separator 5 is equal to or less than the thickness of the interconnector 3. Increasing the thickness of the interconnector 3 increases the current-carrying area of ​​the interconnector 3, and decreasing the thickness of the separator 5 shortens the current-carrying distance of the separator 5. Therefore, the resistance of the current-carrying path decreases, improving power generation efficiency.

[0058] The positional relationship between the anode side interconnector 31, the cathode side interconnector 32, and the separator 5, the size of the joints, and the like shown in this embodiment are preferred forms and are not necessarily limited to these. As long as the separator 5 at least separates the anode flow path 6 and the cathode flow path 7 and the interconnector 3 and the porous metal support layers 2B, 2D are welded, effects such as improved robustness and power generation efficiency can be obtained.

[0059] In this embodiment, the power generating cell 2 is configured to have porous metal support layers 2B, 2D on both the anode electrode side and the cathode electrode side, but this is not necessarily limited to this, and the power generating cell 2 may be configured to have a porous metal support only on either the anode electrode side or the cathode electrode side. In this case, too, the interconnector 3 and the porous metal support layer are welded together, and the anode flow path 6 and the cathode flow path 7 are separated by the separator 5, which improves power generation efficiency and prevents mixing of the anode gas and the cathode gas.

[0060] Furthermore, as in this embodiment, it is preferable to diffusion bond the cathode side interconnector 32 and the separator 5 at the third joint 321, but the joint using diffusion bonding is not necessarily limited to the third joint 321. For example, the anode side interconnector 31 and the separator 5 may be diffusion bonded at the first joint 311. Even in this case, the interconnector 3 and the porous metal support layer are welded together, and the anode flow path 6 and the cathode flow path 7 are separated by the separator 5, which improves power generation efficiency and prevents mixing of the anode gas and the cathode gas.

[0061] Furthermore, in this embodiment, a joining method other than welding and diffusion joining are used, but this is not necessarily limited to this, and for example, the cathode-side interconnector 32 and the separator 5 may be joined using brazing or contact paste.

[0062] In addition, in this embodiment, the bonding material 8 used for diffusion bonding between the cathode-side interconnector 32 and the separator 5 is nickel (Ni), but this is not necessarily limited to this. For example, gold (Au) or a gold alloy, which has a linear expansion coefficient in the range of 0 to 50% like nickel (Ni), may be used as the bonding material 8.

[0063] Furthermore, for example, copper (Cu) or a copper alloy containing 80% or more of copper (Cu) may be used as the bonding material 8. By using a highly ductile material such as copper (Cu) or a copper alloy, the difference in thermal expansion and contraction between the bonding material 8 and the substrate (cathode-side interconnector 32, separator 5) can be absorbed, and stress in the third bonding portion 321 is suppressed. In other words, the bonding portion between the cathode-side interconnector 32 and the separator 5 is protected. Furthermore, silver (Ag) or platinum (Pt), which has a high ductility like copper, may be used as the bonding material 8. Note that a copper alloy containing 80% or more of copper (Cu) is classified as copper (Cu) in JIS (Japanese Industrial Standards).

[0064] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

Claims

1. A solid oxide fuel cell in which a plurality of power generation cells are stacked, each cell comprising a solid electrolyte layer, an anode electrode disposed on one surface of the solid electrolyte layer, a cathode electrode disposed on the other surface of the solid electrolyte layer, and porous metal support layers disposed on both sides of the anode electrode and the cathode electrode to support the electrodes, a separator provided between each power generation cell and spaced apart from the porous metal support layer, and an interconnector located between the separator and the porous metal support layer; an anode flow path for supplying fuel to the anode electrode is formed between the anode electrode side of the power generation cell and the separator, and a cathode flow path for supplying air to the cathode electrode is formed between the cathode electrode side of the power generation cell and the separator; the interconnector includes an anode-side interconnector having a first joint portion joined to the separator and a second joint portion joined to the porous metal support layer on the anode electrode side, and a cathode-side interconnector having a third joint portion joined to the separator and a fourth joint portion joined to the porous metal support layer on the cathode electrode side, the anode-side interconnector is welded to the separator at the first joint and to the anode-side porous metal support layer at the second joint; the cathode-side interconnector is joined to the separator at the third joint portion by a joining method other than welding, and is welded to the cathode electrode-side porous metal support layer at the fourth joint portion. Solid oxide fuel cell.

2. 2. The solid oxide fuel cell according to claim 1, the first joint portion and the third joint portion at least partially overlap each other when viewed in the stacking direction of the power generating cells; Solid oxide fuel cell.

3. 3. The solid oxide fuel cell according to claim 1 or 2, the cathode-side interconnector and the separator are diffusion-bonded at the third joint portion using a bonding material made of a metal different from that of the cathode-side interconnector and the separator; Solid oxide fuel cell.

4. The solid oxide fuel cell according to claim 3, The joining material is nickel or a nickel alloy, or gold or a gold alloy. Solid oxide fuel cell.

5. The solid oxide fuel cell according to claim 3, The joining material is copper or a copper alloy. Solid oxide fuel cell.

6. 6. A solid oxide fuel cell according to claim 1, the interconnector and the separator are in planar contact at the first joint portion and the third joint portion; Solid oxide fuel cell.

7. 7. The solid oxide fuel cell according to claim 1, the anode-side interconnector is welded to the separator at the first joint portion, the third joint portion is formed so as to cover the welded portion of the first joint portion when viewed in the stacking direction of the power generation cells. Solid oxide fuel cell.

8. 8. The solid oxide fuel cell according to claim 1, the second joint portion and the fourth joint portion are formed at positions facing each other when viewed in a cross-sectional direction of the power generation cell. Solid oxide fuel cell.

9. 9. The solid oxide fuel cell according to claim 1, the interconnector and the porous metal support layer are in planar contact with each other at the second joint portion and the fourth joint portion; Solid oxide fuel cell.

10. 10. The solid oxide fuel cell according to claim 1, the separator is formed in a planar shape at least on an active area which is a region that contributes to power generation of the power generating cell; Solid oxide fuel cell.

11. 11. A solid oxide fuel cell according to claim 1, The thickness of the separator is equal to or less than the thickness of the interconnector. Solid oxide fuel cell.

12. A solid oxide fuel cell in which a plurality of power generation cells are stacked, each cell comprising a solid electrolyte layer, an anode electrode disposed on one surface of the solid electrolyte layer, a cathode electrode disposed on the other surface of the solid electrolyte layer, and a porous metal support layer disposed on at least one side of the anode electrode or the cathode electrode and supporting the electrode, a separator provided between each power generation cell and spaced apart from the porous metal support layer, and an interconnector located between the separator and the porous metal support layer; an anode flow path for supplying fuel to the anode electrode is formed between the anode electrode side of the power generation cell and the separator, and a cathode flow path for supplying air to the cathode electrode is formed between the cathode electrode side of the power generation cell and the separator; the interconnector has a portion bonded to the separator and a portion bonded to the porous metal support layer, and is welded to the porous metal support layer at the portion bonded to the porous metal support layer; When the solid oxide fuel cell includes the porous metal support layer on both sides of the anode electrode and the cathode electrode, at least one of the interconnector on the anode electrode side and the interconnector on the cathode electrode side is joined to the separator by a method other than welding, The thickness of the separator is equal to or less than the thickness of the interconnector. Solid oxide fuel cell.

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