BIPOLAR PLATE

Abstract

A bipolar plate is provided including an outlet port and an inlet port with at least one flow field having a plurality of ducts connecting the inlet port to the outlet port, and with at least one bypass duct at a side of the at least one flow field. A flow resistance in the at least one bypass duct is determined by the design of the at least one bypass duct. A blocking element does not project into a cross section of the at least one bypass duct.

Claims

1. A bipolar plate comprising: an inlet port; an outlet port; at least one flow field having a plurality of ducts connecting the inlet port to the outlet port; and at least one bypass duct at a side of the at least one flow field, wherein a flow resistance in the at least one bypass duct is determined by a design of the at least one bypass duct, and wherein a blocking element does not project into a cross section of the at least one bypass duct.

2. The bipolar plate according to claim 1, wherein the at least one flow field includes a plurality of flow fields, wherein the at least one bypass duct includes a plurality of bypass ducts, and wherein a respective bypass duct is provided on each of opposing sides of each of the flow fields.

3. The bipolar plate according to claim 1, wherein the at least one bypass duct repeatedly changes in direction between the inlet port and the outlet port.

4. The bipolar plate according to claim 3, wherein the changes in direction take place in a regularly distributed manner between the inlet port and the outlet port, and wherein a shape of the at least one bypass duct has a sawtooth profile, a rectangular profile, a double serpentine profile, or a tongue profile.

5. The bipolar plate according to claim 1, wherein a shape of a profile of the cross section of the at least one bypass duct is a V-profile, a rectangular profile, a semicircular profile, a trapezoidal profile, or a hammer head profile.

6. The bipolar plate according to claim 5, wherein sides of the profile of the cross section of the at least one bypass duct are rounded.

7. The bipolar plate according claim 1, wherein a surface in the at least one bypass duct is roughened.

8. The bipolar plate according to claim 1, wherein the at least one bypass duct between the inlet port and the outlet port has at least one branch.

9. The bipolar plate according to claim 1, wherein a beginning of the at least one bypass duct is formed by a branch from a side duct of the at least one flow field.

10. The bipolar plate (10) according to claim 1, wherein a beginning of the at least one bypass duct is formed in a distribution area of the inlet port, upstream of the at least one flow field.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0018] Further advantages, features and details of the disclosure result from the claims, the following description of embodiments and based on the drawings.

[0019] FIG. 1 shows a schematic illustration of a fuel cell device with a fuel cell stack having a plurality of fuel cells, the fuel cells of which have bipolar plates.

[0020] FIG. 2 shows a plan view of a schematic illustration of a bipolar plate known from the prior art.

[0021] FIG. 3 shows a plan view of a schematic illustration of a bipolar plate known from the prior art with the schematically represented drop in concentration of the reactant gas in a flow field and indicated bypass flows.

[0022] FIG. 4 shows a cross section through a bipolar plate known from the prior art in the duct direction of the flow field.

[0023] FIG. 5 shows an illustration of a bipolar plate corresponding to FIG. 4 with a reaction gas bypass and a coolant bypass.

[0024] FIG. 6 shows a schematic diagram for the diversion of the reaction gas bypass from a side duct of the flow field.

[0025] FIG. 7 shows a schematic diagram for the diversion of the reaction gas bypass from a distribution area.

[0026] FIG. 8 shows a schematic diagram for the beginning of the reaction gas bypass adjacent to a medium port for the reaction gas.

[0027] FIG. 9 shows a schematic illustration of a course of the reaction gas bypass next to the flow field.

[0028] FIG. 10 shows a schematic illustration of another course of the reaction gas bypass next to the flow field.

[0029] FIG. 11 shows a schematic illustration of yet another course of the reaction gas bypass next to the flow field.

[0030] FIG. 12 shows a schematic illustration of still another course of the reaction gas bypass next to the flow field.

[0031] FIG. 13 shows a schematic illustration of the course of the reaction gas bypass next to the flow field.

[0032] FIG. 14 shows an illustration corresponding to FIG. 9 including variants with regard to a bifurcation of the reaction gas bypass.

[0033] FIG. 15 shows an illustration of the variants with regard to the cross-sectional profile of the reaction gas bypass.

DETAILED DESCRIPTION

[0034] FIG. 1 shows a schematic illustration of a fuel cell device 1 which has a fuel cell or a plurality of fuel cells combined to form a fuel cell stack 2.

[0035] The fuel cell stack 2 consists of a plurality of fuel cells connected in series. Each of the fuel cells comprises an anode and a cathode, and a proton conductive membrane separating the anode from the cathode. The membrane is formed from an ionomer, such as a sulfonated tetrafluoroethylene polymer (PTFE) or a polymer of perfluorinated sulfonic acid (PFSA). Alternatively, the membrane can be formed as a sulfonated hydrocarbon membrane.

[0036] Additionally, a catalyst can be blended with the anodes and/or the cathodes, and the membranes may be coated with a catalyst layer made of a noble metal or mixtures comprising noble metals such as platinum, palladium, ruthenium or the like on their first side and/or on their second side, which serve as a reaction accelerator in the reaction of the respective fuel cell.

[0037] Fuel (for example hydrogen) is supplied to the anodes via anode chambers within the fuel cell stack 2. In a polymer electrolyte membrane fuel cell (PEM fuel cell) fuel or fuel molecules are split into protons and electrons at the anode. The membrane lets the protons (for example, H.sup.+) through, but is impermeable to the electrons (e.sup.-). The following reaction takes place at the anode: 2H.sub.2 ➜ 4H.sup.+ + 4e.sup.- (oxidation/donation of electrons). While the protons pass through the membrane to the cathode, the electrons are conducted via an external circuit to the cathode or to an energy store. Via cathode chambers within the fuel cell stack 2, cathode gas (for example oxygen or oxygen-containing air) can be supplied to the cathodes, so that the following reaction takes place on the cathode side: O.sub.2 + 4H.sup.+ + 4e.sup.- ➜ 2H.sub.2O (reduction/electron acceptance).

[0038] Via a cathode fresh gas line 3, compressed air is supplied to the fuel cell stack 2 by a compressor 4. In addition, the fuel cell is connected to a cathode exhaust gas line 6. On the anode side, hydrogen stored in a hydrogen tank 5 is supplied to the fuel cell stack 2 in order to provide the reactants required for the electrochemical reaction in a fuel cell. These gases are transferred to bipolar plates 10 in which ducts 11 are formed and combined to form a flow field 12 for distribution of the gases to the membrane. In addition, the bipolar plates 10 are provided for the passage of a coolant duct 19, so that three different media can be routed in a very small space. Bipolar plates 10 known from the prior art are shown in FIGS. 2 to 4, with FIG. 2 showing the inflow of a medium though an inlet port 13 with the transfer to the flow field 12, and the outflow through a first outlet port 14. The rear side of the bipolar plate 10 is available to the second reactants in a comparable manner. The inlet ports 13 can be combined in an inlet header 16 together with a medium port 15 for the coolant. Similarly, an outlet header 17 is available.

[0039] A bypass flow flows past the flow field 12, which bypass flow cannot be completely prevented even by bypass-blocking structures, the production of which represents additional effort. To avoid such bypass blocking structures 5, the bipolar plate 10 shown in FIG. 5 is configured in such a way that at least one bypass duct 18 is present at the side of at least one of the flow fields 12, with the flow resistance in the bypass duct 18 being determined by the design of the bypass duct 18 while dispensing with a blocking element projecting into the cross section of the bypass duct 18. In some embodiments, there is a correspondingly designed bypass duct 18 on both sides of both flow fields 12.

[0040] In this case, the length of the bypass duct 18 is increased by repeated changes in direction 20 between the inlet port 13 and the outlet port 14, the changes in direction 20 taking place in a regularly distributed manner between the inlet port 13 and the outlet port 14. Different changes in direction 20 of the bypass duct 18 are shown in FIGS. 9 to 13, and are shaped according to a shape that is selected from a group comprising a sawtooth profile 21, a rectangular profile 22, a double serpentine profile 23, a tongue profile 24. The angle of the change in direction 20 can also vary, so that the sawtooth profile 21 can be present, for example, symmetrically as a zigzag line. The tongue profile from FIG. 9 also improves the frost start properties of a fuel cell stack 2, since the volume for a coolant flow between a side duct 25 of the flow field 12 and the bypass duct 18 is reduced and so the thermal mass of the coolant in the fuel cell stack 2 is low.

[0041] In the alternatives of FIG. 15 (from top to bottom), the cross-section of the bypass duct 18 is shaped according to a cross-sectional shape with a V-profile, a rectangular profile, a semicircular profile, a trapezoidal profile, a hammerhead profile, with the sides of the profiles being rounded with radii for a simplified manufacturing by forming processes.

[0042] There is a possibility that the surface in the bypass duct 18 is roughened.

[0043] FIG. 14 shows alternatives in which the bypass duct 18 has branches 26 between the inlet port 13 and the outlet port 14, namely bifurcation 26 into two branches (left), into three branches (middle) or a repeated bifurcation 26 into two branches (right).

[0044] FIG. 6 shows a variant in which the beginning of the bypass duct is formed by a branch 27 from a side duct 25 of the flow field 12, while FIGS. 7 and 8 indicate that the beginning of the bypass duct 18 is formed in a distribution area 28 of the inlet port 13 upstream of the flow field 12 with different approaches to the inlet port 13.

[0045] 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.