Solid oxide fuel cell

Abstract

Provided is a solid oxide fuel battery having a plurality of power generation cells stacked one on another, each of said power generation cells being provided with: a solid electrolyte layer; an anode electrode disposed on one surface of the solid electrolyte; and a cathode electrode disposed on the other surface of the solid electrolyte layer. The solid oxide fuel battery has, between every power generation cell: a separator that is separated from the power generation cells; an anode flow path formed between the anode electrode side of the power generation cell and the separator; and a cathode flow path formed between the cathode electrode side of the power generation cell and the separator. In addition, an anode-side support member joined to the separator and the anode electrode side of the power generation cell is provided in the anode flow path, and a cathode-side support member joined to the separator and the cathode electrode side of the power generation cell is provided in the cathode flow path. A second joint section in which the cathode-side support member and the separator are joined has a larger joining area than a first joint section in which the anode-side support member and the separator are joined.

Description

[Technical Field]

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

[0002] JP2019-200878A discloses a fuel cell stack in which multiple power generation cells (single battery cells) are stacked. This fuel cell stack includes separators that form gas flow paths between the power generation cells, and current collecting members that join the separators and the power generation cells within the gas flow paths. Summary of the Invention

[0003] Fuel cells are provided with an anode flow path through which a fuel gas (anode gas) flows and a cathode flow path through which air (cathode gas) flows. However, the gas flow rate in the cathode flow path is generally greater than the gas flow rate in the anode flow path, resulting in a higher internal pressure in the cathode flow path. Therefore, in the fuel cell stack described in JP2019-200878A, the difference in internal pressure between the anode flow path and the cathode flow path causes a relatively large force to act on the joint between the current collecting member and the separator in the cathode flow path, potentially causing the current collecting member to peel off and become damaged.

[0004] On the other hand, if the separator is made thicker to suppress deformation of the separator and thereby strengthen the bonding strength with the current collecting member, the weight of the entire fuel cell stack increases.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a solid oxide fuel cell that is lightweight and prevents damage to the fuel cell.

[0006] According to one aspect of the present invention, there is provided a solid oxide fuel cell in which a plurality of power generation cells are stacked, each of which includes a solid electrolyte layer, an anode electrode disposed on one side of the solid electrolyte, and a cathode electrode disposed on the other side of the solid electrolyte layer. Between each power generation cell, a separator is provided spaced from the power generation cell, an anode flow path is formed between the anode side of the power generation cell and the separator, and a cathode flow path is formed between the cathode side of the power generation cell and the separator. The anode flow path includes an anode-side support member that joins the separator to the anode side of the power generation cell, and the cathode flow path includes a cathode-side support member that joins the separator to the cathode side of the power generation cell. A second joint where the cathode-side support member and the separator are joined has a larger joint area than a first joint where the anode-side support member and the separator are joined. [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 also 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 is disposed between two adjacent power generation 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 generation cell 2) of the power generation 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 generation cell 2) of the power generation 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 is disposed between the active area 2A of the power generating cell 2 and the separator 5, and connects the separator 5 to the porous metal support layers 2B, 2D. The interconnector 3 is a current collecting member having a current collecting function, and also functions as a support member that supports the power generating cell 2 and the separator 5.

[0017] The interconnector 3 includes an anode-side interconnector (anode-side support member) 31 arranged between the anode support layer (porous metal support layer on the anode electrode side) 2D of the power generation cell 2 and the separator 5, and a cathode-side interconnector (cathode-side support member) 32 arranged between the cathode support layer (porous metal support layer on the cathode electrode side) 2B of the power generation cell 2 and the separator 5. The material constituting the interconnector 3 is not particularly limited as long as it is an electrically conductive and thermally conductive material, and for example, ferritic stainless steel containing aluminum is used.

[0018] The anode side interconnector 31 is a member having a first contact portion 311 that contacts the upper surface of the separator 5, a third contact portion 312 that contacts the lower surface of the anode support layer 2D, and a connecting portion 313 that connects the first contact portion 311 and the third contact portion 312. The anode side interconnector 31 and the separator 5 are welded at the first contact portion 311, and the anode side interconnector 31 and the anode support layer 2D are welded at the third contact portion 312. Note that, although laser welding is used as the welding method in this embodiment, the present invention is not limited to this.

[0019] A plurality of anode-side interconnectors 31 are arranged in the anode flow path 6 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 interconnectors 31, and the anode support layer 2D.

[0020] The cathode side interconnector 32 is a member having a second contact portion 321 that contacts the lower surface of the separator 5, a fourth contact portion 322 that contacts the upper surface of the cathode support layer 2B, and a connecting portion 323 that connects the second contact portion 321 and the fourth contact portion 322. Here, the cathode side interconnector 32 and the separator 5 are joined at the second contact portion 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 contact portion 322.

[0021] A plurality of cathode-side interconnectors 32 are arranged in the cathode flow path 7 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 interconnectors 32, and the cathode support layer 2B.

[0022] As described above, in the solid oxide fuel cell 100, separators 5 are provided between the power generation cells 2, spaced apart from the power generation cells 2, and separating the anode flow path 6 from the cathode flow path 7, and interconnectors (support members) 3 are arranged within the anode flow path 6 and the cathode flow path 7 to connect the separators 5 to the power generation cells 2.

[0023] In a fuel cell, the gas flow rate in the cathode flow channel through which air (cathode gas) flows is generally greater than the gas flow rate in the anode flow channel through which fuel gas (anode gas) flows, resulting in a higher internal pressure in the cathode flow channel. As a result, the difference in internal pressure between the anode flow channel and the cathode flow channel causes a relatively large force to act on the joint between the separator and the interconnector (current collecting member, support member) in the cathode flow channel, potentially causing the interconnector to come off and damaging the fuel cell.

[0024] On the other hand, if the bonding strength between the interconnector and the separator is strengthened by increasing the thickness of the separator and suppressing deformation of the separator, the weight of the entire fuel cell increases.

[0025] Furthermore, when spacers are placed between the interconnector and the separator to absorb the force in the stacking direction of the power generation cells and prevent the separator from deforming, the cross-sectional area of the gas flow paths (anode flow path, cathode flow path) becomes smaller due to the spacers, which increases the internal pressure, requiring additional reinforcing members and making the fuel cell heavier.

[0026] Therefore, in this embodiment, the bonding area of the bonding portion between the cathode side interconnector 32 and the separator 5 is made larger than the bonding area of the bonding portion between the anode side interconnector 31 and the separator 5. This strengthens the bonding strength between the cathode side interconnector 32 and the separator 5, preventing the cathode side interconnector 32 from peeling off from the separator 5 and preventing damage to the fuel cell 100. Furthermore, because the bonding strength between the cathode side interconnector 32 and the separator 5 is improved, the separator 5 can be made thinner, and the weight of the fuel cell 100 can be reduced.

[0027] Hereinafter, the details of joining the interconnector 3 to the separator 5 and the power generating cell 2 will be described with reference to FIGS.

[0028] 3, a plurality of anode-side interconnectors 31 and cathode-side interconnectors 32 are arranged at intervals between the separator 5 and the power-generating cell 2. By arranging the interconnectors 3 at intervals in this manner, the flow path cross-sectional areas of the anode flow path 6 and the cathode flow path 7 are increased. When the flow path cross-sectional area increases, the internal pressure in the flow path decreases, and therefore, by adjusting the size of the intervals between the interconnectors 3, it is possible to suppress an increase in the internal pressure difference between the anode flow path 6 and the cathode flow path 7.

[0029] As described above, the power generating cell 2 includes an anode support layer 2D made of a porous metal body on the anode electrode side, and a cathode support layer 2B made of a porous metal body on the cathode electrode side. The anode-side interconnector 31 is welded to the anode support layer 2D, and the cathode-side interconnector 32 is welded to the cathode support layer 2B. In this manner, the power generating cell 2 includes the porous metal support layers 2B, 2D, and the porous metal support layers 2B, 2D are joined to the metal interconnector 3. If the power generating cell 2 does not include the porous metal support layers 2B, 2D, the joining between the interconnector 3 and the power generating cell 2 would be a joining between metal and ceramic. In contrast, in this embodiment, the joining between the interconnector 3 and the power generating cell 2 is a metal joining, and therefore the joining strength is stronger than that of a joining between ceramic and metal. In addition, welding melts the joint interface when heat is input, destroying the initial surface layer (oxide film) of the interconnector 3 and the porous metal support layers 2B, 2D, reducing the resistance of the joint and improving conductivity, while also being low-cost because no additional materials are required.

[0030] FIG. 4 is an enlarged view of the area enclosed by the square A in FIG.

[0031] 4, the anode side interconnector 31 is welded to the separator 5 at a first contact portion 311, and a weld portion (first joint portion) 314 is formed in the first contact portion 311. As described above, the anode side interconnector 31 is welded to the anode support layer 2D at a third contact portion 312, and a weld portion (third joint portion) 315 is formed in the third contact portion 312.

[0032] On the other hand, the cathode side interconnector 32 is joined to the separator 5 at the second contact portion 321 by diffusion bonding using a metallic bonding material 8, and a bonding portion (second bonding portion) 324 is formed at the second contact portion 321. As described above, the cathode side interconnector 32 is joined to the cathode support layer 2B at the fourth contact portion 322 by welding, and a welded portion (fourth bonding portion) 325 is formed within the fourth contact portion 322. Here, 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 bonding them by pressing and heating. The bonding area achieved by diffusion bonding is larger than the bonding area achieved by welding. 4, the joint area (second joint area) 324 between the cathode side interconnector 32 and the separator 5 is larger than the joint area (first joint area) 314 between the anode side interconnector 31 and the separator 5. In this embodiment, a bonding material 8 having substantially the same surface area as that of the second contact area 321 is used. Therefore, the contact area (surface area of the second contact area 321) and the joint area (surface area of the second joint area 324) between the cathode side interconnector 32 and the separator 5 are substantially the same. In this embodiment, the joint area (second joint area) 324 between the cathode side interconnector 32 and the separator 5 is formed at a position that covers the joint area (first joint area) 314 between the anode side interconnector 31 and the separator 5 when viewed in the stacking direction of the power generation cell 2.

[0033] In this way, the bonding area of the second bonding portion 324 in the cathode flow path 7 is larger than the bonding area of the first bonding portion 314 in the anode flow path 6, and therefore the bonding strength between the cathode side interconnector 32 and the separator 5 is further strengthened. This prevents the cathode side interconnector 32 from peeling off from the separator 5. Furthermore, because the bonding strength between the cathode side interconnector 32 and the separator 5 is improved, the separator 5 can be made thinner, and the fuel cell 100 can be made lighter. Furthermore, because electrical resistance is proportional to the distance through which current flows, making the separator 5 thinner reduces the electrical resistance between the cathode side interconnector 32 and the separator 5, and the power generation efficiency of the fuel cell 100 also improves. Furthermore, making the separator 5 thinner can reduce the height of the power generation cells 2 in the stacking direction, and the solid oxide fuel cell 100 can be made more compact.

[0034] Furthermore, the joint (first joint) 314 between the anode-side interconnector 31 and the separator 5 is covered by the joint (second joint) 324 between the cathode-side interconnector 32 and the separator 5 when viewed in the stacking direction of the power-generating cells 2, and therefore the first joint 314 and its periphery are reinforced by the second joint 324. Here, if the pressure difference between the anode flow path 6 and the cathode flow path 7 is large, there is a risk that cracks or the like will occur in the separator 5, starting from the first joint 314 and its periphery. In contrast, in this embodiment, the first joint 314 and its periphery, which are likely to be the starting point of cracks or the like, are reinforced by the second joint 324, and therefore deformation of the separator 5 is suppressed, and cracks or the like will be suppressed in the separator 5. Furthermore, the weld bead generated in the separator 5 by welding the anode-side interconnector 31 and the separator 5 is covered by the second joint 324, and therefore oxidation degradation of the bead due to air is prevented.

[0035] In addition, the diffusion bonding reaction progresses due to heat input while the fuel cell 100 is operating, resulting in a stronger bond during operation of the fuel cell 100. The bonding material 8 used in the diffusion bonding can be nickel (Ni), copper (Cu), gold (Au), silver (Ag), platinum (Pt), or an alloy containing any of these. The form of the bonding material 8 is not particularly limited, and can be, for example, a paste, a sheet, a wire, a coating, or the like.

[0036] Furthermore, in this embodiment, the cathode side interconnector 32 and the separator 5 are joined by diffusion bonding, but this is not necessarily limited to this, and any joining method other than welding may be used. For example, the cathode side interconnector 32 and the separator 5 may be brazed. Even with such a joining method, the joining area is larger than with welding, and the joining strength between the cathode side interconnector 32 and the separator 5 is further strengthened.

[0037] According to the solid oxide fuel cell 100 of the above embodiment, the following effects can be obtained.

[0038] The solid oxide fuel cell 100 includes separators 5 disposed between the power generation cells 2 and spaced apart from the power generation cells 2, an anode flow path 6 formed between the anode electrode side of the power generation cells 2 and the separators 5, and a cathode flow path 7 formed between the cathode electrode side of the power generation cells 2 and the separators 5. The anode flow path 6 includes an anode-side interconnector (anode-side support member) 31 that joins the separator 5 to the anode electrode side of the power generation cells 2, and the cathode flow path 7 includes a cathode-side interconnector (cathode-side support member) 32 that joins the separator 5 to the cathode electrode side of the power generation cells 2. A second joint 324 that joins the cathode-side interconnector (cathode-side support member) 32 to the separator 5 has a larger joint area than a first joint 314 that joins the anode-side interconnector (anode-side support member) 31 to the separator 5. This strengthens the bonding strength between the cathode side interconnector 32 and the separator 5, preventing the cathode side interconnector 32 from peeling off from the separator 5 and preventing damage to the fuel cell 100. Furthermore, because the bonding strength between the cathode side interconnector 32 and the separator 5 is improved, the separator 5 can be made thinner, thereby reducing the weight of the fuel cell 100. In other words, it is possible to provide a solid oxide fuel cell 100 that is lightweight and prevents damage.

[0039] Furthermore, because electrical resistance is proportional to the distance through which current flows, thinning the separator 5 reduces the electrical resistance between the cathode-side interconnector 32 and the separator 5, improving the power generation efficiency of the solid oxide fuel cell 100. Furthermore, thinning the separator 5 can reduce the height of the power generation cells 2 in the stacking direction, allowing the solid oxide fuel cell 100 to be made more compact.

[0040] In the solid oxide fuel cell 100, the anode side interconnector (anode side support member) 31 and the separator 5 are welded, and the cathode side interconnector (cathode side support member) 32 and the separator 5 are joined by a joining method other than welding (such as diffusion bonding using a metal). As a result, the joint (second joint) 324 between the cathode side interconnector 32 and the separator 5 is formed with a larger joint area than the joint (first joint) 314 between the anode side interconnector 31 and the separator 5. Therefore, the joining strength between the cathode side interconnector 32 and the separator 5 is strengthened, preventing the cathode side interconnector 32 from peeling off from the separator 5, and also allowing the separator 5 to be made thinner, thereby reducing the weight of the fuel cell 100.

[0041] In the solid oxide fuel cell 100, the joint (first joint) 314 between the anode-side interconnector 31 and the separator 5 is covered by the joint (second joint) 324 between the cathode-side interconnector 32 and the separator 5 when viewed in the stacking direction of the power generation cell 2. As a result, the first joint 314 and its surroundings are reinforced by the second joint 324. In other words, since the first joint 314 and its surroundings, which are likely to become the starting point of cracks, are reinforced by the second joint 324, deformation of the separator 5 is suppressed, and the occurrence of cracks, etc. in the separator 5 is suppressed.

[0042] Furthermore, the weld bead that is generated on the separator 5 by welding the anode-side interconnector 31 and the separator 5 is covered by the second joint portion 324, and therefore the bead portion is prevented from being oxidized and deteriorated by air.

[0043] In the solid oxide fuel cell 100, a plurality of anode-side interconnectors (anode-side support members) 31 and cathode-side interconnectors (cathode-side support members) 32 are arranged at intervals between the separators 5 and the power generation cells 2. Since the interconnectors 3 are arranged at intervals in this manner, the flow path cross-sectional areas of the anode flow path 6 and the cathode flow path 7 are increased, and the internal pressure within the flow paths is reduced. Therefore, by adjusting the size of the intervals between the interconnectors 3, the pressure difference between the anode flow path 6 and the cathode flow path 7 can be reduced, and peeling is suppressed between the power generation cells 2 and the interconnectors (support members) 3, and between the interconnectors (support members) 3 and the separators 5.

[0044] In the solid oxide fuel cell 100, the power generating cell 2 has a cathode support layer (porous metal support layer) 2B on the cathode electrode side, and the cathode side interconnector (cathode side support member) 32 and the cathode support layer (porous metal support layer) 2B are metal-bonded together. This strengthens the bond between the power generating cell 2 and the cathode side interconnector (cathode side support member) 32 compared to when the power generating cell 2 does not have the cathode support layer (porous metal support layer) 2B (i.e., when metal and ceramic are bonded together).

[0045] In the solid oxide fuel cell 100, the power generating cell 2 has an anode support layer (porous metal support layer) 2D on the anode electrode side, and the anode side interconnector (anode side support member) 31 and the anode support layer (porous metal support layer) 2D are metal-bonded together. This strengthens the bond between the power generating cell 2 and the anode side interconnector (anode side support layer) 32 compared to when the power generating cell 2 does not have the anode support layer (porous metal support layer) 2D (i.e., when metal and ceramic are bonded together).

[0046] Note that the positional relationships of the anode-side interconnector (anode-side support member) 31, the cathode-side interconnector (cathode-side support member) 32, and the separator 5, as well as the positional relationships of the joints, shown in this embodiment, are shown as preferred forms and are not necessarily limited to these. If at least the second joint portion in the cathode flow path 7 has a larger joint area than the first joint portion in the anode flow path 6, the joint strength between the cathode-side interconnector 32 and the separator 5 is further strengthened, and the separator 5 can be made thinner. In other words, the effects of strengthening the joint strength between the members and reducing the weight can be obtained.

[0047] Furthermore, as in this embodiment, it is preferable that the power generation cell 2 is provided with porous metal support layers 2B, 2D on the anode electrode side and the cathode electrode side, but this is not necessarily limited to this, and the power generation cell 2 may be configured to have a porous metal support layer only on either the anode electrode side or the cathode electrode side, or may not be configured to have a porous metal support layer.

[0048] 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 including a solid electrolyte layer, an anode electrode disposed on one surface of the solid electrolyte layer, and a cathode electrode disposed on the other surface of the solid electrolyte layer, a separator provided between each power-generating cell and spaced from the power-generating cell; an anode flow path formed between the anode electrode side of the power-generating cell and the separator; and a cathode flow path formed between the cathode electrode side of the power-generating cell and the separator, an anode-side support member that joins the separator and the anode electrode side of the power-generating cell is provided within the anode flow path; a cathode-side support member that joins the separator and the cathode electrode side of the power-generating cell is provided within the cathode flow path, a second joint portion at which the cathode-side support member and the separator are joined has a larger joint area than a first joint portion at which the anode-side support member and the separator are joined; the first joint portion is covered by the second joint portion when viewed in the stacking direction of the power generating cells; Solid oxide fuel cell.

2. 2. The solid oxide fuel cell according to claim 1, the anode-side support member and the separator are welded at the first joint, the cathode-side support member and the separator are joined at the second joint portion by a joining method other than welding; Solid oxide fuel cell.

3. 3. The solid oxide fuel cell according to claim 1 or 2, a plurality of the anode-side support members and a plurality of the cathode-side support members are disposed at intervals between the separator and the power-generating cell; Solid oxide fuel cell.

4. 4. The solid oxide fuel cell according to claim 1, the power-generating cell further includes a porous metal support layer on the cathode electrode side; The cathode-side support member and the porous metal support layer are metal-bonded. Solid oxide fuel cell.

5. 5. The solid oxide fuel cell according to claim 1, the power-generating cell further includes a porous metal support layer on the anode electrode side; the anode-side support member and the anode-side porous metal support layer are metal-bonded together; Solid oxide fuel cell.

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