BIPOLAR PLATE

Abstract

A bipolar plate has a first inlet port and a flow field comprising a plurality of ducts to connect the first inlet port to a first outlet port for a first reactant, and has a second inlet port and a flow field comprising a plurality of ducts to connect the second inlet port to a second outlet port for a second reactant, wherein at least one bypass duct is present at the margin of at least one of the flow fields. The bypass duct is associated with at least one flow connection branching off from the bypass duct into an adjacent marginal duct of the flow field.

Claims

1. A bipolar plate, comprising: a first inlet port; a first flow field comprising a first plurality of ducts to connect the first inlet port to a first outlet port for a first reactant; a second inlet port; and a second flow field comprising a second plurality of ducts to connect the second inlet port to a second outlet port for a second reactant; wherein at least one bypass duct is present at the margin of at least one of the flow fields; and wherein the bypass duct is associated with at least one flow connection branching off from the bypass duct into an adjacent marginal duct of the at least one of the flow fields.

2. The bipolar plate according to claim 1, wherein both flow fields and one respective bypass duct are present on either side, and at least one flow connection branches off from each of the bypass ducts into the adjacent marginal duct.

3. The bipolar plate according to claim 1, wherein the flow connection is provided in the half of the flow field facing toward the outlet port.

4. The bipolar plate according to claim 1, wherein the bypass duct is associated with multiple flow connections, which are configured at a spacing from each other in the flow direction.

5. The bipolar plate according to claim 1, wherein a bypass blocker is arranged in the bypass duct upstream from the outlet port.

6. The bipolar plate according to claim 1, wherein a marginal duct connection to the adjacent duct of the flow field is provided in the marginal duct downstream from the flow connection.

7. The bipolar plate according to claim 6, wherein respective adjacent ducts have a duct connection downstream from the marginal duct connection in the flow field.

8. The bipolar plate according to claim 1, wherein the ducts of the flow field and the bypass duct are separated from each other by webs, and the flow connection is realized by a reduction of the web height.

9. The bipolar plate according to claim 8, wherein the marginal duct connection and/or the duct connection is realized by a reduction of the web height.

10. The bipolar plate according to claim 8, wherein the web height is entirely reduced.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0014] Further benefits, features and details will emerge from the claims, the following description of embodiments, and the figures.

[0015] FIG. 1 shows a schematic representation of a fuel cell device having a fuel cell stack comprising a plurality of fuel cells, the fuel cells having bipolar plates.

[0016] FIG. 2 shows a top view of a schematic representation of a bipolar plate known from the prior art.

[0017] FIG. 3 shows a top view of a schematic representation of a bipolar plate known from the prior art with the schematically represented concentration drop in the reactant gas in a flow field and the indicated bypass flows.

[0018] FIG. 4 shows a cross section through a bipolar plate known from the prior art in the duct direction of the flow field.

[0019] FIG. 5 shows a representation of an improved bipolar plate.

[0020] FIG. 6 shows a diagram showing the utilization of the bypass flow.

[0021] FIG. 7 shows a simplified schematic representation for the inserting of the bypass flow into the marginal duct of the flow field.

[0022] FIG. 8 shows a representation of an alternative embodiment corresponding to FIG. 6.

[0023] FIG. 9 shows a representation of the embodiment of FIG. 8, corresponding to FIG. 7.

[0024] FIG. 10 shows a diagram showing the utilization of the bypass flow in multiple ducts of the flow field.

[0025] FIG. 11 shows a representation corresponding to FIG. 6 illustrating the embodiment according to FIG. 10.

[0026] FIG. 12 shows a representation of the embodiment of FIG. 10, corresponding to FIG. 7.

[0027] FIG. 13 shows a representation of a further embodiment corresponding to FIG. 11.

[0028] FIG. 14 shows a representation of the embodiment of FIG. 13, corresponding to FIG. 12.

[0029] FIG. 15 shows a representation corresponding to FIG. 10 for the multiple inserting of the bypass flow into the flow field.

DETAILED DESCRIPTION

[0030] FIG. 1 shows schematically a fuel cell device 1, having a fuel cell or a plurality of fuel cells combined into a fuel cell stack 2.

[0031] The fuel cell stack 2 consists of a plurality of fuel cells hooked up in series. Each of the fuel cells encompasses an anode and a cathode as well as a proton-conducting membrane separating the anode from the cathode. The membrane is formed from an ionomer, such as a sulfonated tetrafluorethylene polymer (PTFE) or a polymer of perfluorinated sulfonic acid (PFSA). Alternatively, the membrane can be formed as a sulfonated hydrocarbon membrane.

[0032] In addition, a catalyst may be blended in with the anodes and/or the cathodes, the membranes being coated on their first side and/or on their second side with a catalyst layer of a precious metal or mixtures comprising precious metals such as platinum, palladium, ruthenium or the like, serving as reaction accelerators in the reaction of the respective fuel cell.

[0033] Through anode spaces inside the fuel cell stack 2, the anodes are supplied with fuel (such as hydrogen). In a polymer electrolyte membrane fuel cell (PEM fuel cell), fuel or fuel molecules are split at the anode into protons and electrons. The membrane allows the protons (for example, H.sup.+) to pass, but is impervious to the electrons (e). The following reaction will occur at the anode: 2H.sub.2.fwdarw.4H.sup.++4e.sup.− (oxidation/electron donation). While the protons pass through the membrane to the cathode, the electrons are taken by an external circuit to the cathode or to an energy accumulator. Through cathode spaces inside the fuel cell stack 2, cathode gas (such as oxygen or air containing oxygen) can be supplied to the cathodes, so that the following reaction occurs at the cathode side: O.sub.2+4H.sup.++4e.sup.−.fwdarw.2H.sub.2O (reduction/electron uptake).

[0034] Air compressed by a compressor 4 is supplied to the fuel cell stack 2 via a fresh cathode gas line 3. In addition, the fuel cell is connected to a cathode exhaust line 6. At the anode side, hydrogen kept on hand in a hydrogen tank 5 is supplied to the fuel cell stack 2 via a fresh anode gas line 8 in order to provide the reactants needed for the electrochemical reaction in a fuel cell. These gases are transferred to bipolar plates 10, in which ducts 11 are formed, and which are assembled to form a flow field 12 for the distribution of the gases to the membrane. In addition, the bipolar plates 10 are provided to carry a coolant, so that three different media are carried in the smallest space. Bipolar plates 10 known from the prior art are shown in FIGS. 2 to 4, where FIG. 2 shows the inserting through a first inlet port 13 for a membrane, with handover to the flow field 12, and drainage through a first outlet port 14. For the second reactant, the back side of the bipolar plate 10 is available in comparable manner with a second inlet port 15 and a second outlet port 16. The first inlet port 13 and the second inlet port 15 may be combined with a medium port 17 for a coolant to form an inlet header 18. Analogously, an outlet header 19 is available.

[0035] A bypass flow streams past the flow field 12, which may not be fully prevented by bypass-blocking structures 20. FIG. 3 shows the fundamental fact that, due to the consumption of the reactant, its partial pressure decreases from the inlet header 18 to the outlet header 19. FIG. 4 shows the known layout of bipolar plates 10, for which two molded metal pieces 21 are provided with sealing grooves 22 and welded together. Above and below the bipolar plates 10 are arranged the membrane electrode assemblies MEA 23. Also shown are the ducts 11 for the fuel and the oxidation agent and the ducts 24 for the coolant.

[0036] In a bipolar plate 10 shown as an example in FIG. 5 and having a first inlet port 13 and a first flow field 12 comprising a plurality of ducts 11 for connecting the first inlet port 13 to a first outlet port 14 for a first reactant, and having a second inlet port 15 and a second flow field comprising a plurality of ducts 11 for connecting the second inlet port 15 to a second outlet port 16 for a second reactant, wherein at least one bypass duct 25 is present at the margin of at least one of the flow fields 12, the design is such that the bypass duct 25 is associated with at least one flow connection 26, which branches off from the bypass duct 25 into an adjacent marginal duct 27 of the flow field 12. In the embodiments shown, a respective bypass duct 25 is present on both sides of the first flow field 12 and on both sides of the second flow field 12, and at least one flow connection 26 branches off from each of the bypass ducts 25 into the adjacent marginal duct 27. This is shown in FIG. 5 for one of the flow fields 12 for one of the reactants, the relations being designed accordingly for the second flow field.

[0037] FIG. 5 also reveals that the flow connection 26 is formed in the half of the flow field 12 facing toward the outlet port 14, in order to introduce the reactants into the region of the flow field 12 where a significant reduction of the reactant concentration already exists.

[0038] FIG. 15 shows that multiple flow connections 26 can also be associated with the bypass duct 25, being spaced apart from each other in the flow direction, i.e., fresh gas can be resupplied to the flow field 12 at different points.

[0039] FIGS. 10 and 11 show that a marginal duct connection 28 to the adjacent duct 11 of the flow field 12 is formed in the marginal duct 27 downstream from the flow connection 26. Also, respective adjacent ducts 11 have a duct connection 29 downstream from the marginal duct connection 28 in the flow field 12. Thus, the possibility exists of resupplying fresh gas transversely to the flow direction in the flow field 12, so that not just the marginal duct 27 of the flow field 12 can make use of the bypass flow.

[0040] FIG. 4 shows that the ducts 11 of the flow field 12 and the bypass duct 25 are separated from each other by webs 30. In the embodiments shown, the flow connection 26 is realized by a reduction of the web height, also in relation to the marginal duct connection 28 and the duct connection 29, and the reduction of the web height may be complete, that is, the web 30 disappears in these regions, as is shown in FIGS. 7 and 12.

[0041] Upstream from the outlet port 14 there is arranged in the bypass duct 25 a bypass blocker, namely, the bypass-blocking structure 20 (FIG. 6), which serves for the bypass flow taking the path of least resistance and streaming through the flow connection 26.

[0042] Aspects of the various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.