Fuel cell separator

Abstract

To provide a technology that effectively diffuses gas even in a direction directly below the surface of a gas diffusion layer that faces a separator rib.SOLUTION: A separator 12a includes a plurality of grooves 14a that are recessed from a gas diffusion layer 10a in a fuel cell and form a plurality of gas flow paths 9a, and a plurality of ribs 16a that abut against the gas diffusion layer 10a and separate the plurality of gas flow paths 9a. At least one rib 16a that separates adjacent first flow paths 100 and second flow paths 102 among the plurality of gas flow paths 9a has an abutment surface 20a that abuts against the gas diffusion layer 10a, and is provided with at least one first groove 30 that is recessed from the gas diffusion layer 10a, communicates only with the first flow path 100, and extends toward the second flow path 102.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] The present specification relates to a separator for a fuel cell. [Background technology]

[0002] For example, fuel cells such as polymer electrolyte fuel cells (PEFCs) have a stack structure in which multiple cells are stacked. A cell is composed of a membrane electrode / gas diffusion layer composite (MEGA) in which a membrane electrode consisting of a polymer electrolyte membrane, an anode electrode, and a cathode electrode is further sandwiched between gas diffusion layers, and a pair of separators. The separator has a region with a corrugated cross section consisting of ribs and grooves. The ribs protrude toward the gas diffusion layer and abut against the gas diffusion layer, and the grooves are recessed from the gas diffusion layer, forming flow paths that allow gas to flow through the gas diffusion layer. A cell has multiple such gas flow paths arranged in parallel.

[0003] Here, it is disclosed that fine grooves are formed on the surface of the rib facing the gas diffusion layer so as to connect adjacent flow paths (Patent Document 1).It is described that these fine grooves can capture water that is likely to be produced when gas flows through the rib and can be efficiently drained. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-47443 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, gas diffusion in the gas diffusion layer facing and in contact with the ribs relies solely on simple diffusion. Therefore, gas diffusion in the thickness direction of the gas diffusion layer (hereinafter also referred to as the direction directly below the surface) on the surface of the gas diffusion layer facing the ribs of the separator (hereinafter also referred to as the rib surface) remains insufficient. It is desirable to promote gas diffusion on the rib surface as well, to supply gas more uniformly to the gas diffusion layer, and to improve power generation efficiency.

[0006] The present specification provides a technology for effectively diffusing gas in a direction directly below the surface of a gas diffusion layer that faces a rib of a separator in a fuel cell.

[0007] The technology disclosed in this specification is embodied in a separator for a fuel cell. The separator includes a plurality of grooves recessed from a gas diffusion layer in the fuel cell to form a plurality of gas flow paths, and a plurality of ribs that abut against the gas diffusion layer of the fuel cell to separate the plurality of gas flow paths. At least one rib separating adjacent first and second flow paths among the plurality of gas flow paths has an abutment surface that abuts against the gas diffusion layer, the abutment surface having at least one first groove that is recessed from the gas diffusion layer, communicates only with the first flow path, and extends toward the second flow path.

[0008] With this separator, gas flows into the first groove from the first flow path toward the second flow path. Because the first flow path is connected only to the first flow path, gas flow into the second flow path is blocked. The gas that has flowed in but whose flow is blocked is diffused in a direction directly below the surface of the gas diffusion layer facing the blocking portion. As a result, gas diffusion and / or convection is promoted in a direction directly below the surface and in-plane direction of the gas diffusion layer facing the rib. Gas is supplied more uniformly throughout the gas diffusion layer, improving the power generation efficiency and power generation performance of the fuel cell. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing an outline of a single cell of a fuel cell disclosed in this specification. [Figure 2A] FIG. 2 is an enlarged cross-sectional view of the dotted square frame I in FIG. [Figure 2B] FIG. 2B is a cross-sectional view taken along line 2B-2B in FIG. 2A. [Figure 3A] 1. FIG. 4 is an enlarged cross-sectional view showing another embodiment of the dotted square frame I in FIG. [Figure 3B] FIG. 3B is a cross-sectional view taken along line 3B-3B in FIG. 3A. DETAILED DESCRIPTION OF THE INVENTION

[0010] One embodiment of the present specification is a separator for a fuel cell, comprising: a plurality of grooves recessed from a gas diffusion layer in the fuel cell to form a plurality of gas flow paths; and a plurality of ribs that abut against the gas diffusion layer of the fuel cell to separate the plurality of gas flow paths, wherein the abutment surface of at least one rib that separates adjacent first and second flow paths among the plurality of gas flow paths abuts against the gas diffusion layer includes at least one first groove that is recessed from the gas diffusion layer, is connected only to the first flow path, and extends toward the second flow path.

[0011] Another embodiment of the separator further includes at least one second groove that is recessed from the gas diffusion layer, communicates only with the second flow path, and extends toward the first flow path. This allows gas to flow from the second flow path into the second groove, but diffuses in a direction directly below the surface of the gas diffusion layer facing the blocking portion where gas flow into the first flow path is blocked. As a result, gas diffusion and / or convection is promoted in the direction directly below and in-plane of the gas diffusion layer facing the rib.

[0012] In another embodiment of the separator, the at least one first groove and the at least one second groove are provided facing each other in the width direction along the width of the at least one rib. This blocks gas flow in the center portion in the width direction between the facing first groove and second groove. Blocking gas flow in the center portion in the width direction promotes gas diffusion from the surface of the gas diffusion layer facing the center portion of the rib (rib surface) toward a direction directly below the surface of the gas diffusion layer. This promotes gas diffusion and / or convection in the direction directly below and in the in-plane direction of the gas diffusion layer facing the rib.

[0013] In another embodiment, the at least one first groove and the at least one second groove are provided in multiple sets facing each other in the width direction of the rib along the gas flow direction in the first flow path and the second flow path, and a third groove is provided between adjacent sets along the gas flow direction and at the center of the rib width direction, retreating from the gas diffusion layer and isolated from the first flow path, the second flow path, the first groove, and the second groove. This allows gas that diffuses in a direction just below the rib surface via the first groove and the second groove to further diffuse in an in-plane direction and reach the third groove at the center of the rib width direction. The gas that reaches the third groove is again diffused in a direction just below the rib surface. The provision of the first to third grooves promotes gas diffusion and / or convection in the direction just below and in the in-plane direction of the gas diffusion layer facing the rib.

[0014] In the separator of another embodiment, the at least one first groove and the at least one second groove are arranged so as to alternate in the gas flow direction in the first flow path and the second flow path and to overlap with the at least one first groove in the width direction of the at least one rib. In this manner, gas flow in the first groove is blocked at the end of the rib on the second flow path side, and gas flow in the second groove is blocked at the end of the rib on the first flow path side. By blocking gas flow at the end of the rib in the width direction, gas diffusion and / or convection is promoted at the end of the rib from the surface of the gas diffusion layer facing the end (rib surface) toward a direction directly below the surface of the gas diffusion layer.

[0015] One embodiment of the fuel cell disclosed in this specification includes a separator as described above. In such a fuel cell, gas is supplied more uniformly throughout the gas diffusion layer. This improves the power generation efficiency and performance of the fuel cell to which gas is supplied by the gas diffusion layer.

[0016] The fuel cell in this specification is not particularly limited, but may suitably be, for example, a polymer electrolyte fuel cell (PEFC).

[0017] (First embodiment) Hereinafter, embodiments of the separator for a fuel cell disclosed in this specification will be described with reference to the accompanying drawings as appropriate. Figure 1 shows an outline of a cell 2 of a fuel cell.

[0018] FIG. 1 shows a membrane electrode and gas diffusion layer assembly (MEGA) 4 constituting a cell 2 of a PEFC fuel cell, and a pair of separators 12a and 12b that sandwich it.

[0019] The MEGA 4 includes a membrane electrode assembly (hereinafter also referred to as MEA) 6 and gas diffusion layers 10a, 10b arranged on both sides thereof. The MEA 6 is composed of an electrolyte membrane 7 and a pair of electrodes 8a, 8b joined to sandwich the electrolyte membrane 7. The electrolyte membrane 7 is, for example, a proton-conductive ion exchange membrane formed of a solid polymer material. The electrodes 8a, 8b are an air electrode (cathode) and a fuel electrode (anode), respectively, and both are made of known materials. The gas diffusion layers 10a, 10b are made of a conductive member such as a gas-permeable porous carbon material. The gas diffusion layer 10a is a diffusion layer for air, which is an example of an oxidant gas, and the gas diffusion layer 10b is a diffusion layer for hydrogen, which is an example of a fuel gas.

[0020] The pair of separators 12 are, for example, plate-like members having a stainless steel substrate. The separators 12a and 12b have a corrugated shape and face the gas diffusion layers 10a and 10b of the MEGA 4, respectively.

[0021] The separator 12a has a plurality of parallel grooves 14a facing the gas diffusion layer 10a and recessed from the gas diffusion layer 10a. Between the grooves 14a of the separator 12a, ribs 16a are provided that protrude toward the gas diffusion layer 10a and abut against the gas diffusion layer 10a. Each of the ribs 16a separates adjacent grooves 14a. The grooves 14a, together with the gas diffusion layer 10a and the ribs 16a, form air flow paths 9a. In the cell 2, the air flows in the air flow paths 9a in the same direction. In FIG. 1, the air flows from the front to the back of the page. The air flow direction can be set as appropriate. For example, the gas diffusion layer 10a may be provided with a spiral or serpentine shape in its planar configuration.

[0022] The surface of the separator 12a that does not face the gas diffusion layer 10a is, although not particularly limited thereto, appropriately coated with a surface treatment film, and is bonded, for example, to the separator 12b of another cell 2 that is stacked adjacently.

[0023] The separator 12b has a plurality of parallel grooves 14b facing the gas diffusion layer 10b and recessed from the gas diffusion layer 10b. Ribs 16b are provided between the grooves 14b, protruding toward the gas diffusion layer 10b and abutting the gas diffusion layer 10b. Each of the ribs 16b separates adjacent grooves 14b. The grooves 14b, together with the gas diffusion layer 10b and the ribs 16b, form hydrogen flow paths 9b. In the cell 2, the hydrogen flows in the same direction in the hydrogen flow paths 9b. In FIG. 1, the direction of hydrogen flow is from the back to the front of the page. Note that the direction of hydrogen flow can be changed as appropriate, similar to that of air. The surface of the separator 12b not facing the gas diffusion layer 10b is bonded to the separator 12a of another adjacent cell 2, similar to the separator 12a.

[0024] 2A and 2B are diagrams illustrating the first groove 30, the second groove 32, and the third groove 38 in the rib 16a. Fig. 2A shows an enlarged view of the rectangular frame I enclosed by the dotted line in Fig. 1, and Fig. 2B shows a cross section taken along line 2B-2B in Fig. 2A.

[0025] 2A, the rib 16a has a contact portion 20 facing the gas diffusion layer 10a and side walls 22a, 22b on both sides of the contact portion 20 that constitute walls of air flow paths 100, 102, which are part of the air flow path 9a. The surface 20a of the contact portion 20 facing the gas diffusion layer 10a has a first groove 30, a second groove 32, and a third groove 38. The air flow paths 100, 102 are examples of the first flow path and the second flow path in this specification.

[0026] As shown in FIGS. 2A and 2B , the first grooves 30 are provided on the surface 20a so as to be recessed from the gas diffusion layer 10a. The first grooves 30 extend along the width direction of the rib 16a from openings 30a, which open toward the flow channels 100 in the side walls 22a of the ribs 16a, toward the flow channels 102. The ends 30b of the first grooves 30 are formed in positions that do not reach the flow channels 102. The first grooves 30 extend to approximately 30% of the width direction length of the ribs 16a. The extension length of the first grooves 30 is not particularly limited, but may be formed over a range of a length less than 50% of the width direction length of the ribs 16a.

[0027] The second grooves 32 are provided so as to face the first grooves 30 in the width direction of the rib 16a. The second grooves 32 are provided on the surface 20a so as to be recessed from the gas diffusion layer 10a. The second grooves 32 extend along the width direction of the rib 16a from openings 32a, which open toward the flow channels 102 in the side walls 22b of the rib 16a, toward the flow channels 100. The ends 32b of the second grooves 32 are formed in positions that do not reach the flow channels 100. The second grooves 32 extend to approximately 30% of the width direction length of the rib 16a. The extension length of the second grooves 32 is not particularly limited, but, like the first grooves 30, may be formed over a range of a length less than 50% of the width direction length of the rib 16a.

[0028] The ends 30b of the first grooves 30 and the ends 32b of the second grooves 32 face each other, leaving a central portion in the width direction of the rib 16a, to form pairs 34. The central portion of the rib 16a separating the first grooves 30 and second grooves 32 that form pairs 34 serves as a blocking portion 36 that blocks the flow of gas flowing in from the first grooves 30 and the second grooves 32. Pairs 34 of first grooves 30 and second grooves 32 that face each other in the width direction of the rib 16a are arranged at predetermined intervals along the gas flow direction, which is also the extension direction of the rib 16a. The blocking portions 36 are also formed at predetermined intervals in the central portion in the extension direction of the rib 16a.

[0029] The rib 16a further has a third groove 38. The third groove 38 is formed between pairs 34 adjacent to each other in the extension direction of the rib 16a and in a range including the center of the rib 16a in the width direction. The third groove 38 is formed on the surface 20a of the rib 16a so as to be retracted from the gas diffusion layer 10a. The third groove 38 does not communicate with the air flow paths 100, 102, the first groove 30, or the second groove 32, and is open only toward the gas diffusion layer 10a. A plurality of third grooves 38 are formed between the plurality of pairs 34.

[0030] The shapes of the first grooves 30, second grooves 32, and third grooves 38 are not particularly limited, but are formed as grooves that do not penetrate the separator 12a outside the cells 2. The patterns, cross-sectional shapes, and depths of these grooves 30, 32, and 38 may be the same or different and are not particularly limited. These grooves can be obtained by cutting, bending, or molding the separator 12a into the intended shape.

[0031] Next, the effects that the first grooves 30, the second grooves 32, and the third grooves 38 have on the diffusion of air, which is an example of an oxidant gas, into the gas diffusion layer 10a will be described.

[0032] 2A and 2B, when air flows through the flow paths 100 and 102 serving as the air flow path 9a in the gas flow direction, the air enters the rib 16a through the first groove 30 opening in the side wall 22a. The air also enters the rib 16a through the second groove 32 opening in the side wall 22b.

[0033] 2A and 2B, the air that hits the blocking portion 36 at the ends 30b, 32b of the first groove 30 and the second groove 32 is diffused from the rib surface in a direction immediately below the surface in the vicinity of the blocking portion 36. As a result, the diffusion and / or convection of air in a direction immediately below the surface of the blocking portion 36 is promoted. The air that has diffused in a direction immediately below the surface of the blocking portion 36 is further diffused in the gas diffusion layer 10a toward the second groove 32, the first groove 30, and the third groove 38.

[0034] This allows air to diffuse and / or convect in the direction just below the surface and in the in-plane direction even on the rib surface 11a of the gas diffusion layer 10a facing the rib 16a. In this embodiment, the first groove 30 and the second groove 32 are provided opposite each other in the width direction of the rib 16a, and the blocking portion 36 is provided in the center of the rib 16a, so that air can penetrate in the direction just below the surface around the center of the rib 16a.

[0035] Furthermore, in this embodiment, the third groove 38 is provided in the center in the width direction of the rib 16a between the pair 34, so that air diffuses through the gas diffusion layer 10a from the ends of the first groove 30 and the second groove 32 toward the third groove 38. This further promotes diffusion and / or convection of air in the in-plane direction and directly below the plane of the gas diffusion layer 10a facing the center of the rib 16a.

[0036] As described above, the separator 12a of this embodiment promotes air diffusion and / or convection in the sub-surface and in-plane directions of the gas diffusion layer 10a facing the ribs 16a. As a result, air is supplied uniformly throughout the gas diffusion layer 10a, improving power generation efficiency and performance. Because it is sometimes more difficult to supply air uniformly to the gas diffusion layer 10a than hydrogen, the first grooves 30, second grooves 32, and third grooves 38 are useful.

[0037] In the first embodiment, the first groove 30 and the second groove 32 are provided, but only one of them may be provided. Even when only one groove is provided, air diffusion and / or convection is promoted in the direction directly below the surface of the gas diffusion layer 10a facing the center portion of the rib 16a in the width direction. In addition, although the third groove 38 is provided, it is not necessarily required to provide the third groove.

[0038] Although the present embodiment has been described only with respect to the separator 12a, the ribs 16b of the separator 12b may also be formed with the same first grooves 30, second grooves 32, and third grooves 38. This promotes more uniform gas diffusion and / or convection in the gas diffusion layer 10b for hydrogen, which is an example of a fuel gas, thereby improving power generation efficiency and performance.

[0039] (Second embodiment) In this embodiment, a separator 112a having the same configuration as in the first embodiment will be described, except that it has a first groove 130 and a second groove 132 but does not have a third groove. In the following description, the characteristic configuration of this embodiment will be mainly described, and the same reference numerals will be used as necessary for components common to the first embodiment, or their description will be omitted.

[0040] 3A and 3B are diagrams illustrating the first groove 130 and the second groove 132 in the rib 116a of the separator 112a. Fig. 3A shows an enlarged view of the portion surrounded by the dotted line in Fig. 1 as this embodiment, and Fig. 3B shows a cross section taken along line 3B-3B in Fig. 3A.

[0041] 3A, the rib 116a has a contact portion 120 facing the gas diffusion layer 10a and side walls 122a, 122b on both sides thereof that constitute the walls of the air flow paths 100, 102. The surface 120a of the contact portion 120 facing the gas diffusion layer 10a has a first groove 130 and a second groove 132.

[0042] The first grooves 130 are provided on the surface 120a so as to be recessed from the gas diffusion layer 10a. The first grooves 130 communicate with the flow channels 100 from openings 130a that open in the side walls of the ribs 116a, and extend along the width direction of the ribs 116a toward the flow channels 102. The ends 130b of the first grooves 130 are formed in positions that do not reach the flow channels 102. The first grooves 130 extend beyond half the length of the ribs 116a in the width direction. The extension length of the first grooves 130 is not particularly limited, but may be formed over a range of 80% or less of the width direction length of the ribs 116a.

[0043] The second grooves 132 are arranged so as not to face the first grooves 130 in the width direction of the rib 116a, so as to alternate with the first grooves 130 in the gas flow direction, and so as to overlap in the width direction. The second grooves 132 are also arranged on the surface 120a so as to be recessed from the gas diffusion layer 10a. The second grooves 132 extend from openings 132a in the sidewall 22b to the flow channels 102 and toward the flow channels 100. The ends 132b of the second grooves 132 are formed in positions that do not reach the flow channels 100. The second grooves 132 overlap with the first grooves 130 in the width direction of the rib 116a for more than half the length of the width direction of the rib 116a. The extension length of the second grooves 132 is not particularly limited, but may be formed over a range of 80% or less of the width direction length of the rib 116a.

[0044] The first grooves 130 and second grooves 132 are arranged alternately at predetermined intervals along the gas flow direction in the flow paths 100 and 102, respectively. As a result, blocking portions 136a that block the flow of air that has flowed into the first grooves 130 are formed at predetermined intervals on the end of the rib 116a on the flow path 102 side. In addition, blocking portions 136b that block the flow of air that has flowed into the second grooves 132 are formed at predetermined intervals on the end of the rib 116a on the flow path 100 side.

[0045] Next, the effects that the first grooves 130 and the second grooves 132 have on the diffusion of air, which is an example of an oxidizing gas, into the gas diffusion layer 10a will be described.

[0046] As shown in Figures 3A and 3B, when air flows through the flow paths 100, 102, etc. of the air flow path 9a formed in the cell 2 along the gas flow direction, the air enters the inside of the rib 116a through the first groove 130 and the second groove 132 opening in the side walls 122a, 122b.

[0047] 3A and 3B, the air impinges on the blocking portions 136a and 136b at the ends 130b and 132b of the first groove 130 and the second groove 132. As a result, the air is diffused in a direction directly below the surface of the gas diffusion layer 10a facing the blocking portions 136a and 136b. As a result, the diffusion and / or convection of the air in a direction directly below the surface of the blocking portions 136a and 136b is promoted.

[0048] Conventionally, air tends to be difficult to diffuse at the ends of the rib 116a that are close to the flow paths 100 and 102. However, in this embodiment, by providing the first groove 130 and the second groove 132 and forming the blocking portions 136a and 136b at the ends, air diffusion and / or convection in the direction directly below the surface of the ends is promoted. As a result, air can be supplied more uniformly in the gas diffusion layer 10a, improving the power generation efficiency and power generation performance of the cell 2.

[0049] Although the present embodiment has been described with respect to the separator 112a, the other separator that makes a pair may also have the first grooves 130 and the second grooves 132 formed in a similar configuration. This allows hydrogen, which is an example of a fuel gas, to be supplied more uniformly in the gas diffusion layer 10b, improving the power generation performance of the cell 2.

[0050] In addition, although the present embodiment is provided with the first groove 130 and the second groove 132, it is also possible to provide only one of them. Air diffusion and / or convection is promoted in the direction directly below the surface of the gas diffusion layer 10a facing one end of the rib 116a.

[0051] In the first and second embodiments, different groove patterns are described for the ribs 16a, 116a of the separators 12a, 112a. However, these groove patterns may be combined as appropriate. For example, in the second embodiment, a third groove 38 may be provided in the center of the rib 116a in the width direction. Furthermore, in the multiple ribs 16a, 116a provided on the separators 12a, 112a, the groove patterns of the first and second embodiments may be combined for each rib or within a single rib as appropriate. [Explanation of symbols]

[0052] 2 fuel cell cell, 4 MEA, 6 MEGA, 7 electrolyte membrane, 8a cathode, 8b anode, 12a, 12b, 112a separator, 14a, 14b separator groove, 16a, 16b, 116a separator rib, 20, 120 contact portion where separator contacts gas diffusion layer, 20a, 120a contact portion surface, 30, 130 first groove, 32, 132 second groove, 38 third groove, 36, 136a, 136b interrupter portion

Claims

1. A separator for a fuel cell, a plurality of grooves recessed from the gas diffusion layer in the fuel cell to form a plurality of gas flow paths; a plurality of ribs that abut against the gas diffusion layer and separate the plurality of gas flow paths; Equipped with a separator, wherein at least one rib separating adjacent first and second flow paths among the plurality of gas flow paths has an abutment surface that abuts against the gas diffusion layer, the abutment surface including at least one first groove that is retracted from the gas diffusion layer, communicates only with the first flow path, and extends toward the second flow path.

2. The separator according to claim 1 , further comprising at least one second groove that is recessed from the gas diffusion layer, communicates only with the second flow path, and extends toward the first flow path.

3. The separator according to claim 2 , wherein the at least one first groove and the at least one second groove are provided opposite each other in a width direction of the rib.

4. a plurality of sets of the at least one first groove and the at least one second groove are provided facing each other in a width direction of the rib and along a gas flow direction in the first flow path and the second flow path; 4. The separator according to claim 3, further comprising a third groove, which is recessed from the gas diffusion layer and isolated from the first flow path, the second flow path, the first groove, and the second groove, at a center portion of the width direction of the rib between the plurality of sets adjacent to each other in the gas flow direction.

5. 3. The separator according to claim 2, wherein the at least one first groove and the at least one second groove are arranged so as to alternate in a gas flow direction in the first flow path and the second flow path and to overlap with the at least one first groove in a width direction of the at least one rib.

6. A fuel cell comprising the separator according to any one of claims 1 to 5.

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