Bipolar plate

Abstract

The present invention relates to a bipolar plate (10) having: a first inlet port (13) and a flow field (12) with a plurality of channels (11) for connecting the first inlet port (13) to a first outlet port (14) for a first reactant; and a second inlet port (15) and a flow field (12) with a plurality of channels (11) for connecting the second inlet port (15) to a second outlet port (16) for a second reactant, wherein at least one bypass channel (25) is present on an edge side of at least one flow field (12). At least one flow connection (26) is assigned to the bypass channel (25), which branches off from the bypass channel (25) into an adjacent edge channel (27) of the flow field (12).

Description

Field of the Invention

[0001] The present invention relates to a bipolar plate having: a first inlet port and a first flow field having a plurality of channels for connecting the first inlet port to a first outlet port for a first reactant; and a second inlet port and a second flow field having a plurality of channels for connecting the second inlet port to a second outlet port for a second reactant, wherein at least one bypass channel is present at an edge side of at least one of the flow fields, and wherein the bypass channel is assigned at least one flow connection that branches from the bypass channel into an adjacent edge channel of the flow field. Background Art

[0002] A fuel cell includes a membrane electrode assembly formed of a proton-conducting membrane, with an anode constructed on one side thereof and a cathode constructed on the other side thereof. In a fuel cell device, typically a plurality of fuel cells are linearly combined into a fuel cell stack to achieve a sufficiently large power output.

[0003] The electrodes of the fuel cell are supplied with reaction gases by means of bipolar plates, i.e., hydrogen is supplied especially on the anode side and oxygen or an oxygen-containing gas, especially air, is supplied on the cathode side. When supplying the fuel cell with reactants, these reactants are guided through channels into the plate, which, when using the channel or channels, should cause the distribution of the reactants into the active area in order to supply as uniformly as possible the entire surface of the electrode by means of the flow field. Since the chemical reaction takes place over the entire surface of the active area, the fresh reaction gas is always being depleted, such that the partial pressure of the reaction gas from the inlet towards the outlet decreases while the share of the product gas increases.

[0004] In addition to the reaction gas, the cooling medium is also passed through the bipolar plate, so that three different media must be guided technically closely separated in the smallest space. Therefore, two metal molded parts are usually welded to the bipolar plate, wherein an overlapping area must be maintained due to the structural space requirements around the active flow field, in which a cavity is generated due to manufacturing tolerances and assembly tolerances, through which the reaction gas can flow through the flow field, that is, there is an undesirable bypass, the cross section of which is reduced by the blocking element. However, the reaction gas passes through the active area unused to reach the outlet. In DE 10 2017118143A1, a stamped part is constructed as a blocking element in the bypass channel of the first bipolar plate, which interferes with the direction of the reactant flow and causes turbulence and pressure increase, which diverts the reactant from the bypass channel to the gas diffusion layer arranged between the first bipolar plate and the second bipolar plate. US 2012 / 0129071 A1 describes a uniform flow field from an inlet channel for fuel and oxidant, wherein an inlet buffer is arranged downstream of the inlet opening and serves to improve uniform distribution over the entire width of the flow field. DE 10 2016 225 651 A1 describes an end cell heating assembly, in which a bypass flow path is provided in the housing and serves to connect the inlet distributor and the outlet distributor in order to redirect the liquid droplets flowing into the fuel cell stack. Summary of the invention

[0005] The object of the present invention is to provide a bipolar plate in which the utilization of at least one of the reactants is improved.

[0006] This object is achieved by the bipolar plate according to the invention. The invention has a number of advantageous embodiments which are suitable for further development.

[0007] The bipolar plate mentioned at the outset offers the following advantages: less reactant is conducted from the inlet port through the bypass channel directly to the outlet channel and is therefore not available for the reaction. Instead, the losses caused by the bypass flow are reduced and at the same time the concentration reduction in the flow field due to the consumption of reactant is mitigated, since fresh reactant is supplied to the flow field again at the original concentration. The bypass channel itself extends in a region of the plate that is located outside the active region where the electronic reaction takes place.

[0008] The advantages are particularly evident if there are bypass channels on both sides of the first flow field and on both sides of the second flow field, respectively, and if at least one flow connection branches from each of the bypass channels into an adjacent edge channel. This is exploited by the fact that there is usually a reactant current on both sides of each individual flow field, and thus better utilization of each reactant is provided, and fewer reactants are directed directly to the discharge port. As a result, there is also an increase in the reactant concentration at both edges of the respective flow field.

[0009] Particularly preferably, the flow connection is configured in the half of the flow field facing the discharge port. In this half, a significant reduction in the concentration of the reactants or their partial pressures already exists, such that supplying the reactants from the bypass channel again results in an increase in concentration or partial pressure, and thus the desired reaction proceeds better. An insufficient supply is avoided.

[0010] It is also advantageous if the bypass channel is assigned a plurality of flow connections which are configured spaced apart from one another in the flow direction, since the reaction flow in the bypass channel is thus better utilized and an incomplete diversion through the first flow connection can be corrected by subsequent flow connections.

[0011] The improved utilization of the reaction flow is also used by arranging a bypass blocker upstream of the discharge port in the bypass channel, such that due to the bypass blocker, the diversion takes place through the flow connection. Thus, the bypass blocker can also be formed by a significantly increased flow resistance or by a seal or a sealing structure in order to thereby force the reactants to flow through the flow connection along the path of least resistance.

[0012] If an edge channel connection to an adjacent channel of the flow field is configured in the edge channel downstream of the flow connection and if the channels adjacent to one another in the flow field each have a channel connection downstream of the edge channel connection, then fresh gas of the reactants can be provided for a plurality of channels transversely to the flow direction in the flow field, such that not only the outermost channels of the flow field (i.e., the edge channels) benefit from the bypass flow.

[0013] The manufacture of the bipolar plate generally involves forming a metal plate such that the channels of the flow field and the bypass channel are separated from one another by a bridging portion. The flow connection can then be simply achieved by reducing the height of the bridging portion. This advantage also applies analogously if the edge channel connection and / or the channel connection are achieved by reducing the height of the bridging portion. Here, the height of the bridging portion can also be completely reduced, i.e., until the height of the bridging portion is zero, since the forming is thus simplified.

[0014] Without departing from the scope of the invention, the features and combinations of features mentioned in the above description and the features and combinations of features mentioned in the following description of the drawings and / or shown individually in the drawings can be used not only in the respective combinations described, but also in other combinations or individually. Thus, the following embodiments should also be regarded as included and disclosed by the invention, which are not explicitly shown or explained in the drawings, but are known from the embodiments explained by means of individual combinations of features and can be generated therefrom. Description of the Drawings

[0015] Other advantages, features and details of the invention can be derived from the following description of the preferred embodiments and the drawings. Among them:

[0016] Figure 1 Schematic view showing a fuel cell device with a fuel cell stack having a plurality of fuel cells, the fuel cells having bipolar plates,

[0017] Figure 2 Top view showing a schematic view of a bipolar plate known in the prior art,

[0018] Figure 3 Top view showing a schematic view of a bipolar plate known in the prior art, in which the concentration drop of the reaction gas in the flow field is schematically shown and the bypass flow is represented,

[0019] Figure 4 Cross-section through a bipolar plate known in the prior art in the channel direction of the flow field,

[0020] Figure 5 Showing corresponding to Figure 3 Illustration of an improved bipolar plate,

[0021] Figure 6 Schematic view for using the bypass flow,

[0022] Figure 7 Showing corresponding to Figure 4 Simplified schematic view for introducing the bypass flow into the edge channels of the flow field,

[0023] Figure 8 Showing the illustration corresponding to Figure 6 of an alternative embodiment,

[0024] Figure 9 Showing Figure 8 the illustration corresponding to the embodiment in Figure 7 of,

[0025] Figure 10 Schematic view for using the bypass flow in a plurality of channels of the flow field,

[0026] Figure 11 Showing corresponding to Figure 6 the illustration for explaining the embodiment according to Figure 10 of,

[0027] Figure 12 Showing Figure 10 the illustration corresponding to the embodiment in Figure 7 of,

[0028] Figure 13 Showing the illustration corresponding to Figure 11 of another embodiment,

[0029] Figure 14 Showing Figure 13 the illustration corresponding to the embodiment inFigure 12 illustrations of, and

[0030] Figure 15 show corresponding to Figure 10 illustrations for introducing a bypass flow into the flow field multiple times. Detailed Description

[0031] Figure 1 The fuel cell device 1 is schematically shown in [the specific implementation], which has a fuel cell or a plurality of fuel cells combined into a fuel cell stack 2.

[0032] The fuel cell stack 2 is composed of a plurality of fuel cells connected in series. Each fuel cell in the fuel cell includes an anode and a cathode, and a proton-conducting membrane that separates the anode and the cathode. The membrane is formed of an ionomer, preferably a sulfonated tetrafluoroethylene polymer (PTFE) or a perfluorosulfonic acid polymer (PFSA). Alternatively, the membrane can be formed as a sulfonated hydrocarbon membrane.

[0033] The anode and / or the cathode can additionally be mixed with a catalyst, wherein the membrane is preferably coated on its first side and / or its second side with a catalyst layer composed of a noble metal or a mixture including noble metals (such as platinum, palladium, ruthenium, etc.), which acts as a reaction accelerator in the reaction of the corresponding fuel cell.

[0034] Fuel (such as hydrogen) is supplied to the anode via the anode chamber within the fuel cell stack 2. In a polymer electrolyte membrane fuel cell (PEM fuel cell), the fuel or fuel molecules split into protons and electrons at the anode. The membrane allows protons (such as H + ) to pass through, but is impermeable to electrons (e - ). Here, the following reaction occurs at the anode: 2H2 → 4H + + 4e - (oxidation / electron release). During the protons passing through the membrane to reach the cathode, the electrons are conducted to the cathode or an energy storage via an external circuit. The cathode gas (such as oxygen or oxygen-containing air) can be supplied to the cathode via the cathode chamber within the fuel cell stack 2, so that the following reaction occurs on the cathode side: O2 + 4H + + 4e - → 2H2O (reduction / electron reception).

[0035] Compressed air is supplied to the fuel cell stack 2 via the cathode fresh gas line 3 by means of a compressor 4. In addition, the fuel cell is connected to the cathode exhaust gas line 6. On the anode side, hydrogen prepared in the hydrogen tank 5 is supplied to the fuel cell stack 2 via the anode fresh gas line 8 to provide the reactants required for the electrochemical reaction in the fuel cell. These gases are transferred to the bipolar plate 10, in which channels 11 are constructed and combined into a flow field 12 for distributing the gases to the membrane. In addition, the bipolar plate 10 is provided for guiding the passage of the cooling medium, so that three different media can be guided in the smallest space. The bipolar plate 10 known from the prior art is shown in Figures 2 to 4 wherein, Figure 2 the introduction of the medium through the first inlet port 13, the transfer to the flow field 12, and the extraction through the first outlet port 14 are shown for the medium. For the second reactant, the back side of the bipolar plate 10 is similarly available for use, which has a second inlet port 15 and a second outlet port 16. The first inlet port 13 and the second inlet port 15 can be combined with the medium port 17 for the coolant in the inlet manifold 18. Similarly, there is an outlet manifold 19 available for use.

[0036] A bypass flow flows through the flow field 12, and even the bypass-blocking structure 20 cannot completely suppress this bypass flow. Figure 3 It is pointed out the following basic fact: due to the consumption of the reactants, their partial pressures decrease from the inlet manifold 18 towards the outlet manifold 19. Figure 4 It is pointed out the known structure of the bipolar plate 10, in which sealing tracks 22 are provided for two metal forming parts 21 and they are welded. The membrane electrode assembly MEA 23 is arranged above and below the bipolar plate 10. Also visible are the channels 11 for the fuel and the oxidant and the channel 24 for the cooling medium.

[0037] In the bipolar plate 10 shown, for example, in Figure 5 the bipolar plate 10 has: a first inlet port 13 and a first flow field 12 having a plurality of channels 11 for connecting the first inlet port 13 to a first outlet port 14 for the first reactant; and a second inlet port 15 and a second flow field having a plurality of channels 11 for connecting the second inlet port 15 to a second outlet port 16 for the second reactant, wherein at least one bypass channel 25 is present on the edge side of at least one of the flow fields 12, designed such that the bypass channel 25 is assigned at least one flow connection 26 that branches from the bypass channel 25 into an adjacent edge channel 27 of the flow field 12. In the shown embodiment, bypass channels 25 are present on both sides of the first flow field 12 and on both sides of the second flow field 12, wherein at least one flow connection 26 branches from each of the bypass channels 25 into the adjacent edge channel 27. This is in Figure 5is shown for one of the flow fields 12 for one of the reactants, wherein the situation for the second flow field is suitably designed identically.

[0038] Figure 5 It can also be seen that the flow connection 26 is constructed in the half of the flow field 12 facing the discharge port 14, so as to thereby introduce the reactant into the region of the flow field 12 where there is already a significant reduction in the reactant concentration.

[0039] Figure 15 It is pointed out that the bypass channel 25 can also be assigned a plurality of flow connections 26, which are constructed spaced apart from one another in the flow direction, so that fresh gas can be supplied again to the flow field 12 at different locations.

[0040] Figure 10 and Figure 11 It is shown that in the edge channel 27 downstream of the flow connection 26, an edge channel connection 28 to the adjacent channel 11 of the flow field 12 is constructed. The channels 11 adjacent to each other in the flow field 12 also have channel connections 29 downstream of the edge channel connection 28. Thereby, there is the feasibility of supplying fresh gas again transversely to the flow direction in the flow field 12, such that not only the edge channel 27 of the flow field 12 can make full use of the bypass flow.

[0041] Figure 4 It is shown that the channels 11 of the flow field 12 and the bypass channel 25 are separated from each other by a bridging part 30. In the shown embodiment belonging to the present invention, the flow connection 26 is achieved by reducing the height of the bridging part, more precisely also with respect to the edge channel connection 28 and the channel connection 29, wherein the reduction of the height of the bridging part can be accomplished such that the bridging part 30 in these regions is omitted, as Figure 7 and Figure 12 shown in.

[0042] Upstream of the discharge port 14, a bypass blocker, namely a bypass-blocking structure 20 ( Figure 6 ), is arranged in the bypass channel 25, which ensures that the bypass flow follows the path of least resistance and flows through the flow connection 26.

[0043] List of reference numerals

[0044] 1 Fuel cell device

[0045] 2 Fuel cell stack

[0046] 3 Cathode fresh gas line

[0047] 4 Compressor

[0048] 5 Hydrogen tank

[0049] 6 Cathode Exhaust Gas Line

[0050] 7 Anode Circulation Line

[0051] 8 Anode Fresh Gas Line

[0052] 9 Anode Exhaust Gas Line

[0053] 10 Bipolar Plate

[0054] 11 Channel

[0055] 12 Flow Field

[0056] 13 First Inlet Port

[0057] 14 First Discharge Port

[0058] 15 Second Inlet Port

[0059] 16 Second Discharge Port

[0060] 17 Medium Port

[0061] 18 Inlet Header

[0062] 19 Discharge Header

[0063] 20 Bypass Blocking Structure

[0064] 21 Molding Part

[0065] 22 Sealing Track

[0066] 23 Membrane Electrode Assembly

[0067] 24 Channel for Cooling Medium

[0068] 25 Bypass Channel

[0069] 26 Flow Connection Part

[0070] 27 Edge Channel

[0071] 28 Edge Channel Connection Part

[0072] 29 Channel Connection Part

[0073] 30 Bridging Part.

Claims

1. A bipolar plate (10) having: a first inlet port (13) and a flow field (12) with a plurality of channels (11) for connecting the first inlet port (13) to a first outlet port (14) for a first reactant; and a second inlet port (15) and a flow field (12) with a plurality of channels (11) for connecting the second inlet port (15) to a second outlet port (16) for a second reactant, wherein, At least one bypass channel (25) is present on the edge side of at least one of the flow fields (12), characterized in that at least one flow connection (26) is assigned to the bypass channel (25), which branches off from the bypass channel (25) into an adjacent edge channel (27) of the flow field (12), wherein a bypass blocker (20) is arranged in the bypass channel (25) upstream of the first discharge port (14) and / or the second discharge port (16).

2. The bipolar plate (10) according to claim 1, characterized in that, Bypass channels (25) are present on both sides of the two flow fields (12) respectively, and at least one flow connection (26) branches off from each of the bypass channels (25) into an adjacent edge channel (27).

3. The bipolar plate (10) according to claim 1 or 2, characterized in that, The flow connection (26) is constructed in the half of the flow field (12) facing the discharge port (14).

4. The bipolar plate (10) according to any one of claims 1 to 2, characterized in that, The bypass channel (25) is assigned a plurality of flow connections (26), which are constructed at intervals from one another in the flow direction.

5. The bipolar plate (10) according to any one of claims 1 to 2, characterized in that, Downstream of the flow connection (26), an edge channel connection (28) to an adjacent channel (11) of the flow field (12) is constructed in the edge channel (27).

6. The bipolar plate (10) according to claim 5, characterized in that, Downstream of the edge channel connection (28), the channels (11) adjacent to one another in the flow field (12) respectively have channel connections (29).

7. The bipolar plate (10) according to any one of claims 1 to 2, characterized in that, The channels (11) of the flow field (12) and the bypass channel (25) are separated from one another by a bridging portion (30), and the flow connection (26) is achieved by reducing the height of the bridging portion.

8. The bipolar plate (10) according to claim 7, characterized in that, The edge channel connection (28) and / or the channel connection (29) are achieved by reducing the height of the bridging portion.

9. The bipolar plate (10) according to claim 7, characterized in that, The height of the bridging portion is completely reduced.

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