1. Technical Field
The present invention relates to a metal separator for a fuel cell, and particularly relates to the metal separator for the fuel cell capable of improving a sealing performance in peripheral parts of manifold holes.
2. Description of the Related Art
A metal separator which is thinner and stronger than a graphite separator (having thickness of 2 mm or more) is under development, as a separator for a fuel cell. A metal plate having thickness of 0.1 to 0.2 mm is normally used as the metal separator. In a polymer electrolyte fuel cell, a separator and a membrane electrode assembly (MEA), being a power generation layer (power generator, single cell) of the fuel cell are alternatively laminated to form a stack (cell stack).
If compared with the graphite separator, the metal separator has a thin body in a stacking direction of the separator, and such a thin separator has an advantage that it contributes to realizing a compact stack. In addition, if compared with the graphite separator, the metal separator has characteristics such as toughness in spite of its thin body and ductility, having practically sufficient strength, and capable of surely blocking gas because metal does not allow the gas to pass through.
However, when aiming to make the metal separator compact in a stacking direction of the fuel cell, it is difficult to form a gas flow passage to MEA from manifold holes (through holes penetrating the separator, which are the holes for forming a gas communication path common to the stacked fuel cell, for supplying the gas to each cell in the stacking direction), due to the elasticity of the thin metal separator. This invites an unstable gas sealing of this gas flow passage forming part. As a result, there is a possibility that gas leak occurs and power generation characteristics of the fuel cell are unstable.
Namely, a part between the metal separator and the power generation layer of the fuel cell is normally sealed by providing a soft seal member such as rubber. However, dimension accuracy of the soft member such as rubber is low and its strength is also low, and accordingly the strength of a sealing part in the periphery of the manifold holes is insufficient, thus involving a problem of insufficient seal to thereby cause the gas leak to occur by this insufficient seal.
For example, patent documents 1 to 4 are known as conventional techniques regarding the seal of this kind of separator.
Patent document 4 provides an improved technique of the separator of the patent document 3, and basically sealing performance is increased by forming the resin frame 123 of the patent document 3 into a seal frame. Then, the seal frame is formed by screen-printing a seal material composed of an elastic body such as rubber, on the resin frame 123.
When techniques of the patent document 3 and the patent document 4 are used, a compact separator for a fuel cell can be formed, and cell characteristic of the fuel cell is also stable.
(Patent document 2)
(Patent document 3)
(Patent document 4)
The graphite separator of the patent document 1 and the patent document 2 has a structure in which through holes 108, 113 and grooves 107, 114 are provided on the separator, as a gas flow structure to a power generation layer from the manifold holes. These through holes 108, 113, and the grooves 107, 114 are face-sealed by being covered with the separator 106, etc, for inter-layer sealing. This seal is stable owing to face-sealing. However, in order to perform face-sealing, the separator 106, etc, must be separately added, and when the techniques of the patent document 1 and the patent document 2 are applied to the metal separator, thinness and compactness, which are the characteristics of the metal separator, is halved and cost is increased.
Meanwhile, in the separator disclosed in the patent document 3 and the patent document 4, the resin frame 123 or a seal frame is used, thus involving a problem of incurring a high cost as a result. In addition, projection parts for forming inlet grooves 125 on fringe parts of the manifold holes are provided in the resin frame 123 or the seal frame, to form the flow passage. Therefore, stable sealing performance is not ensured.
Thus, when aiming to make the metal separator compact in the stacking direction of the fuel cell, it is difficult to form the gas flow passage to the power generation layer from the manifold holes, thus making the gas seal unstable in this gas flow passage forming part, because the metal separator is thin and has elasticity. This poses a problem of inviting gas leak and unstable power generation characteristics of the fuel cell.
An object of the present invention is to provide a compact metal separator for the fuel cell capable of increasing the sealing performance in the peripheral parts of the manifold holes.
An aspect of the present invention provides a metal separator for a fuel cell, including:
a plurality of flow passage grooves for flowing a fluid for operating the fuel cell;
manifold holes provided on each side of an upper stream and a lower stream of the plurality of flow passage grooves and formed so as to penetrate a separator made of metal for the fuel cell;
communication grooves formed on a separator surface of the separator, for connecting inlets/outlets of the plurality of flow passage grooves and the manifold holes to flow the fluid;
a fluid flowing structure part made of metal, in which a through hole is formed on the separator surface that forms the communication grooves, formed in the vicinity of the manifold hole so as to traverse the communication groove; and
a flat seal surface formed on the fluid flowing structure part, for sealing a surface of a member that shields an opening of the communication grooves in a state of a face contact.
Preferred embodiments of the present invention will be described hereunder, based on the drawings.
As shown in
A plurality of flow passage grooves 6, being fluid supply/discharge passages for supplying/discharging a fluid for operating the fuel cell, are formed in a center part of the rectangular separator 2. The plurality of fluid passages grooves 6 are linearly formed in parallel to each other along a direction of a long line of the rectangular separator 2.
Rectangular manifold holes 7a, 9a, 8b are formed on the separator 2 of one of the inlet/outlet sides of the plurality of flow passage grooves 6, so as to penetrate the separator 2. Also, rectangular manifold holes 8a, 9b, 7b are formed on the separator 2 of the other inlet/outlet side of the plurality of flow passage grooves 6. The manifold holes are the holes for forming the gas communication passage common to the fuel cell, for supplying/discharging the gas to each power generation layer in the stacking direction of the fuel cell in which the separator 2, etc, is stacked (see
The manifold holes 7a and 7b arranged at diagonal positions of four corner parts of the rectangular separator 2 are the holes for supplying/discharging a fuel gas (such as hydrogen gas). A manifold hole 7a is provided for supplying the fuel gas, and a manifold 7b is provided for discharging the fuel gas. Similarly, the manifold holes 8a and 8b arranged at the diagonal positions are the holes for supplying/discharging an oxidant gas (such as air and oxygen gas). The manifold hole 8a is provided for supplying the oxidant gas, and the manifold hole 8b is provided for discharging the fuel gas. A manifold hole 9a positioned between the manifold holes 7a and 8b, and a manifold hole 9b positioned between the manifold holes 8a and 7b are the manifold holes for supplying/discharging a cooling fluid (such as cooling water). The manifold hole 9a is provided for supplying the cooling fluid, and the manifold hole 9b is provided for discharging the cooling fluid. The fluid for operating the fuel cell is the fuel gas, the oxidant gas, and the cooling fluid.
Communication grooves 10 for flowing the fluid for operating the fuel cell are respectively formed between the inlet/outlet of the plurality of flow passage grooves 6 and the manifold holes 7a, 7b, 8a, 8b, 9a, 9b. The communication grooves 10 shown in solid line in
For example, the fuel gas such as the hydrogen gas supplied to the communication grooves 10 from the manifold hole 7a is expandingly flown through the communication grooves 10, then distributed and flown into the plurality of flow passage grooves 6. The fuel gas such as the hydrogen gas flown out from the plurality of the flow passage grooves 6 is merged at the communication groove 10 on the manifold hole 7b side, and flown so as to gradually gather in the communication groove 10, and is discharged from the manifold hole 7b.
A gasket 11, being a seal surface part of the separator 2, is attached to the surface of the separator 2 by adhesive agent, etc. Preferably, the gasket 11 is made by using a material such as resin or rubber, so that no adverse influence is added on the cell characteristics.
The gasket 11 installed on the upper surface of the separator 2 shown in
The upper surface of the separator 2 shown in
Similarly, the fluid flowing structure parts 15, are provided on the communication grooves 10 positioned on the outer peripheral parts of the manifold holes 8a, 8b, so as to traverse the communication grooves 10, 10, on the surface of the separator 2 on which the flow passage for flowing the oxidant gas such as air is formed. Also, similarly the fluid flowing structure parts 15, 15 are provided on the communication grooves 10, 10 positioned on the outer peripheral parts of the manifold holes 9a, 9b, so as to traverse the communication grooves 10, 10, on the surface of the separator 2 on which the flow passage for flowing the cooling fluid such as cooling water is formed.
The fluid flowing structure parts 15, 15 will be further specifically described. A fluid flowing structure part 15 provided facing the fringe part of the manifold hole 7a will be described hereunder, by using the drawings. However, the fluid flowing structure part 15 installed on the other communication groove 10 has also the same structure.
As shown in
Reinforcing members 13 for reinforcing the seal member 12 are provided in the through holes 14 between the attachment parts 12b, 12b. The reinforcing members 13 receive a surface pressure such as 10 kg/cm2 added to the seal member 12 in the stacking direction (plate thickness direction of the separator 2) at the time of stacking the separator 2, and the seal member 12 is supported thereby in parallel to the separator surface 2a, so as to withstand this seal surface pressure. As shown in
Since the reinforcing members 13 are provided in the through holes 14, as shown in
Since a plurality of reinforcing members 13 are provided along the communication groove 10 at predetermined intervals in a groove width direction of the communication groove 10, the gas can be uniformly flown into the communication groove 10 in the groove width direction of the communication groove 10. Further, since the communication groove 10 is a flow passage, with its groove width gradually increasing toward the inlet/outlet side of the flow passage grooves 6, uniformity of a gas pressure in the communication groove 10 is achieved, and the gas, with uniform flow rate, is flown into each flow passage groove 6.
The fluid flowing structure part 15 is a structure having a predetermined rigidity, by providing the attachment part 12b and the reinforcing member 13, on the plate-shaped seal member 12. As a result, deformation of the seal member 12 is restrained, and the sealing performance in the peripheral part of the manifold holes, into which the fluid is supplied/discharged, is considerably improved.
For example, as shown in
Accordingly, sealing failure of the peripheral part of the manifold hole and gas leak can be prevented, and consequently the fuel cell characteristics can be stabilized, by the separator 2 made of metal according to this embodiment.
Note that although the reinforcing member may not be a member with arch-like cross-section, preferably the reinforcing member and the attachment part have a slightly deformable elastic structure, while uniformly supporting the pressure in the surface added to the seal member 12.
The fluid flowing structure part 15 is formed of a metal plate of the same kind or similar kind as that of the separator 2 made of metal, from a viewpoint of strength and chemical stability. Although not surface conductivity is necessary like the separator 2 made of metal, for example Ti (titanium) clad material or Ti plate material is preferably used, and a plate material having a thickness of 0.2 mm or less and 50 μm or more is preferably used. Although smaller thickness is favorable for the plate material for use, provided that the flow passage can be ensured, in a case of an excessively small thickness, the strength is decreased. Therefore the thickness is preferably set at 0.2 mm or less and 50 μm or more.
The fluid flowing structure part 15 of this embodiment is formed separately from the separator 2 and installed on the separator 2. Therefore, a thinner plate material than that of the separator 2 can be used. This makes it possible to optimize a flow passage sectional area of the through hole 14, and also optimize the sealing performance/sealing surface pressure, by appropriately selecting dimension/number of the seal member 12 and the reinforcing member 13. In addition, an attachment position of the fluid flowing structure part 15 on the communication groove 10 can be freely adjusted.
Next, an example of a polymer electrolyte fuel cell using the aforementioned separator 2 will be described.
As shown in
The support frame 1b is a seal part in a face contact with the gaskets 11a, 11b of the separator 2, and is also a member for forming a power generation flow passage part including a plurality of flow passage grooves 6, and an expanded flow passage including the communication groove 10. Three manifold holes 1c communicating with the manifold holes 7a, 7b, 8a, 8b, 9a, 9b of the separator 2 at the time of laminating the stack, are formed on both sides of the support frame 1b. A diffusion layer 3 of a reaction gas (common designation of the fuel gas and oxidant gas) is provided between the power generation flow passage part of the separator 2 on which a plurality of flow passage grooves 6 are formed, and the MEA 1a. Also, a diffusion layer 4 of a cooling fluid is provided on the opposite side to the diffusion layer 3 side of the separator 2. The diffusion layer 3 and the diffusion layer 4 are manufactured by using a carbon cross and carbon paper, etc. Note that the material of the diffusion layer 4 is not limited to the carbon cross and the carbon paper, and may be a material having conductivity, cushioning property, and not contaminating water.
In
As shown in (a), (b), (c) of
Next, the flow of the fluid in one unit U shown in
Two kinds of reaction gas are used as the fluid for power generation. Here, the H2 gas is used as the fuel gas, and air is used as the oxidant gas. Also, water is used as the cooling fluid.
The H2 gas of the fuel gas is flown through the upper surface of the separator 2 positioned on the lower side of the unit U. Namely, the H2 gas flowing through the manifold hole 7a passes through the fluid flowing structure part 15, then passes through the communication groove 10 on the upper stream side, a plurality of flow passage grooves 6, and the communication groove 10 on the lower stream side, and flows into the manifold hole 7b, and is discharged to outside through the manifold hole 7b. The H2 gas is supplied to the electrode on the lower side of the MEA1a via the diffusion layer 3, while flowing through a plurality of flow passage grooves 6.
The air of the oxidant gas flows through a lower surface of the separator 2 which is positioned on the upper side of the unit U (air flows through a plurality of flow passage grooves 6 reversely to the H2 gas). Namely, the air flowing through the manifold hole 8a passes through the fluid flowing structure part 15, then passes through the upper stream side communication groove 10, a plurality of flow passage grooves 6, the lower stream side communication groove 10, and flows into the manifold hole 8b, and is discharged to the outside through the manifold hole 8b. The air is supplied to the electrode on the upper side of the MEA1a via the diffusion layer 3, while flowing through the plurality of flow passage grooves 6.
Water for cooling the fluid flows through an upper surface of the separator 2 positioned on the upper side of the unit U. Namely, the water flowing through the manifold hole 9a flows through the fluid flowing structure part 15, then passes through the communication groove 10 on the upper stream side, the plurality of flow passage grooves 6, and the communication groove 10 on the lower stream side, and flows into the manifold hole 9b on the lower stream side, and is discharged to the outside through the manifold hole 9b. The water is supplied to the diffusion layer 4 while flowing through the plurality of flow passage grooves 6. Also, similarly the water of the cooling fluid flows through the lower surface of the separator 2 positioned on the lower side of the unit U.
A function of the separator is to press the polymer electrolyte membrane of MEA at a constant pressure, then make electric conductivity, and separate the fuel gas flown to the cathode side from the oxidant gas flown to the anode side of the MEA, so as not to be directly mixed with each other. Sealing between the outer peripheral part of the MEA and the separator is relatively easy. However, it is difficult to seal the gas inlet/outlet of the manifold hole, because the layer for the gas to go in and out and a layer for sealing the gas are alternately present in the laminating direction. Therefore, power generation characteristics are greatly influenced, if inlet/outlet of the gas and sealing are not surely performed.
As a specific example of this embodiment, a Ti layer is cladded on the surface of a thin-plate shaped stainless steel (SUS), and further an Au (gold) layer is formed on the Ti layer by nano-level coating using a sputtering method, to thereby form a metal material (clad material M-TST by HITACHI CABLE, having thickness of 0.2 mm). Then, by using this metal material, the separator 2 is formed and the fluid flowing structure part 15, which is formed by using the Ti plate material having thickness of 80 μm, is spot-welded to the separator 2. The stack in which 30 units are laminated, is manufactured by using this separator, and it is found that even under a constant surface pressure (about 10 kg/cm2) during power generation, excellent power generation characteristics without seal leakage can be exhibited.
Next, the metal separator for the fuel cell according to a second embodiment of the present invention will be described.
In the aforementioned first embodiment, the fluid flowing structure part 15 formed separately from the separator 2 is attached to the separator 2. However, in this second embodiment, a fluid flowing structure part 20 is formed by folding, etc, a part of the separator 2. The other structure of the separator 2 is the same as that of the separator 2 according to the first embodiment.
Each step will be specifically described by using
In the punching step, an opening part 21i is punched, so that reinforcing parts 21m, being reinforcing members, are arranged in a comb-teeth shape at equal intervals along the groove width direction of the communication groove 10. Simultaneously, slits 21j connected to an opening part 21i are formed on both sides of the communication groove 10 in the groove width direction. The slits 21j are cut into approximately the same dimension as that of the manifold hole 7b formed after a folding step as will be described later. Also, simultaneously with forming the slits 21j, a plurality of holes 21k are formed between end portions of the slits 21j, 21j, along the groove width direction of the communication groove 10. The holes 21k are formed so as to be positioned between the adjacent reinforcing parts 21m at the same intervals as those of the reinforcing parts 21m.
In the next pressing step, the reinforcing parts 21m are press-molded, and center line parts of the thin and long reinforcing parts 21m are molded into an arch-shape in a state of being sagged downwards of a paper surface of
Folding operation is performed twice in the next folding step.
In the first folding step, the reinforcing parts 21m are folded to the communication groove 10 side at about 180° via the upper part of the paper surface of
In the second folding step, the part of the separator 2 between the slits 21j, 21j where the folded reinforcing parts 21m are present, is folded at about 180° to the communication groove 10 side, with the center line of a plurality of holes 21k set as a folding line q. Thus, a seal part 21n, being the seal member parallel to the separator surface 2a, is formed. The reinforcing parts 21m having arch-like sectional faces, being reinforcing members, are provided between the seal part 21n and the separator surface 2a, and the seal part 21n is supported by the reinforcing parts 21m. In addition, the opening part 21i is expanded by second folding, and the manifold hole 7a is thereby formed.
This step is performed as needed, in a viewpoint of strength. In the fixing step, a contact point, etc, between each reinforcing part 21m formed by press-molding and the seal part 21n is fixed by spot welding, etc. Note that this fixing step may be performed after the first folding step.
By the above-described step, as shown in
As a specific example of this embodiment, the Ti layer is cladded on the surface of a thin-plate shaped stainless steel (SUS), and further an Au (gold) layer is formed on the Ti layer by nano-level coating using a sputtering method, to thereby form a metal material (clad material M-TST by HITACHI CABLE, having thickness of 0.1 mm). Then, by using this metal material, the separator 2 is formed and the fluid flowing structure part 20 is formed on the Ti layer by punching, pressing, folding, and fixing. The stack, in which 10 units are laminated, is manufactured by using this separator 2, and when a power generation test is performed, excellent power generation characteristics can be obtained.
Note that when the fluid flowing structure parts 15, 20 are installed or formed, after press-molding a plurality of flow passage grooves 6 on the separator 2, or after fitting the gaskets 11a, 11b to the separator 2, the sealing performance is ensured, mass productivity can be realized, and decrease of cost can be expected.
In addition, irrespective of the above-described embodiments, the inventors of the present invention study on a structure that a plurality of projection parts for forming the inlet/outlet grooves or openings are formed on the separator surface of the peripheral parts of the manifold holes, and the upper surface, etc, of these projection parts are sealed. However, the sealing performance in this case is not ensured, and a lot of trouble is taken to perform sealing. Meanwhile, in the structure of the above-described embodiment, assembly of the stack can be efficiently performed, and the sealing performance is ensured.
Number | Date | Country | Kind |
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2008-072203 | Mar 2008 | JP | national |
2009-17749 | Jan 2009 | JP | national |