BIPOLARPLATTE

Description

[0001] The invention relates to a bipolar plate with 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 with 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 provided at the edge of at least one of the flow fields, and wherein at least one flow connection is assigned to the bypass channel, which branches off from the bypass channel into an adjacent edge channel of the flow field, characterized in that the bypass channel runs in a region of the bipolar plate which lies outside an active region in which the electrochemical reaction takes place, and that the flow connection is formed in the half of the flow field facing the outlet port.in order to introduce the reactant into the area of ​​the flow field where a chemical reduction of a reactant concentration already exists and where a bypass blocker is arranged upstream of the outlet port in the bypass channel.

[0002] A fuel cell comprises a membrane electrode assembly consisting of a proton-conducting membrane, with the anode on one side and the cathode on the other. In a fuel cell device, several fuel cells are typically connected linearly to form a fuel cell stack in order to achieve a sufficiently high power output.

[0003] Reactant gases are supplied to the electrodes of the fuel cell via bipolar plates; specifically, hydrogen on the anode side and oxygen or an oxygen-containing gas, particularly air, on the cathode side. When the fuel cell is supplied with reactants, these are guided into the plate via a channel. The plate, using this channel or multiple channels, is designed to distribute the reactants into an active region, thereby ensuring a uniform supply of the entire electrode surface via a flow field. Due to the chemical reaction occurring across the entire surface of the active region, the fresh reactant gases are continuously consumed, causing the partial pressures of the reactant gases to decrease from inlet to outlet, while the proportion of product gases increases.

[0004] In addition to the reactant gases, a cooling medium also passes through the bipolar plate, meaning that three different media must be kept technically separated within a very small space. Therefore, two metal forming parts are typically welded together to form a bipolar plate. Due to the space requirements around the active flow field, an overlap area must be maintained. However, due to manufacturing and assembly tolerances, cavities can form in this area, allowing reactant gases to bypass the flow field. This creates an undesirable bypass, the cross-section of which is reduced by blocking elements. Nevertheless, reactant gases bypass the active area and reach the outlet unused.In DE 10 2017 118 143 A1, a blocking element is formed in a bypass channel of a first bipolar plate. This element disrupts the direction of the reaction medium flow, causing turbulence and pressure increases that divert the reaction medium from the bypass channel into a gas diffusion layer located between the first and a second bipolar plate. A uniform feeding of the flow fields from the inlet channels for the fuel and the oxidizer is described in US 2012 / 0129071 A1, wherein inlet buffers are formed downstream of the inlets for improved uniform distribution across the entire width of the flow fields. DE 10 2016 225 651 A1 describes an end-cell heating arrangement in which bypass flow paths are provided in a housing to connect the inlet distributors and the outlet distributors in order to divert droplets flowing into the fuel cell stack.US Patent 7,491,463 B2 describes a bipolar plate that has inlet and outlet areas for distributing a medium across the entire width of the flow field via its channels. German Patent DE 101 63 631 A1 describes a bipolar plate that has rows of three ribs each, with the ribs of two adjacent rows being offset in the direction of flow, thus enabling crossflow.

[0005] A bipolar plate with the features of the preamble of claim 1 is known from KR 20120042376 A, in which the channels of the flow field are connected by several bypass channels inclined to the flow direction.

[0006] 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.

[0007] This problem is solved by a bipolar plate with the features of claim 1. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0008] The bipolar plate mentioned earlier offers the advantage that less of the reactant is carried from the inlet port through the bypass channel directly to the outlet channel and thus is not available for the reaction. Instead, the loss through the bypass flow is reduced, and at the same time, the decrease in concentration in the flow field caused by reactant consumption is mitigated, as fresh reactant at its original concentration is supplied to the flow field. The bypass channel itself runs in a region of the plate that lies outside the active area where the electrochemical reaction takes place. The flow connection is located in the half of the flow field facing the outlet port.In this half, there is already a significant reduction in the concentration of the reactants or their partial pressure, so that the introduction of reactants from the bypass channel leads to an increased concentration or partial pressure, thus improving the desired reaction. Undersupply is avoided. Improved utilization of the reactant flow is achieved by placing a bypass blocker upstream of the outlet port in the bypass channel, so that the bypass blocker forces the flow through the flow connection. The bypass blocker can therefore also be formed by a significantly increased flow resistance or by seals or sealing structures, thus forcing the reactant flow onto the path of least resistance through the flow connection.

[0009] The advantages become particularly clear when a bypass channel is present on both sides of the first flow field and on both sides of the second flow field, and when at least one flow connection branches off from each of the bypass channels into the adjacent boundary channel. This takes advantage of the fact that reactant flows are generally present on both sides of each individual flow field, thus allowing for better utilization of each reactant and reducing the amount of reactant flowing directly to the outlet port. Furthermore, this results in an increased reactant concentration at both edges of the respective flow field.

[0010] It is also advantageous if the bypass channel has several flow connections that are spaced apart from each other in the direction of flow, as this allows for better utilization of the reactant flow in the bypass channel and can correct incomplete drainage through the first flow connection through the subsequent flow connections.

[0011] If a boundary channel connection to the adjacent channel of the flow field is formed in the marginal channel downstream of the flow connection, and if adjacent channels downstream of the boundary channel connection in the flow field each have a channel connection, then the fresh gas of the reactant can be provided transversely to the flow direction in the flow field for several channels, so that not only the outermost channel of the flow field, i.e. the boundary channel, benefits from the bypass flow.

[0012] The production of the bipolar plate typically involves forming metallic plates so that the flow field channels and the bypass channel are separated by webs. The flow connection can then be easily achieved by reducing the web height. This advantage also applies if the edge channel connection and / or the channel connection is achieved by reducing the web height. In this case, the web height can even be completely reduced, i.e., to zero, as this simplifies the forming process.

[0013] The features and combinations of features mentioned above in the description, as well as those subsequently mentioned in the figure description and / or shown in the figures alone, can be used not only in the combinations specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or explained in the figures, but which can be derived and generated from the explained embodiments by separate combinations of features, are also to be considered as encompassed and disclosed by the invention.

[0014] Further advantages, features, and details of the invention will become apparent from the claims, the following description of preferred embodiments, and the drawings. These show: Fig. 1 a schematic representation of a fuel cell device with a fuel cell stack comprising a plurality of fuel cells, the fuel cells of which have bipolar plates, Fig. 2 a top view of a schematic representation of a bipolar plate known from the prior art, Fig. 3 a top view of a schematic representation of a bipolar plate known from the prior art with the schematically represented concentration drop of the reactant gas in a flow field and indicated bypass flows, Fig. 4 a cross-section through a bipolar plate known from the prior art in the channel direction of the flow field, Fig. 5 one of the Figure 3 Fig. 6 shows a corresponding representation of a bipolar plate not according to the invention, Fig. 6 shows a schematic diagram for using the bypass current, Fig. 7 shows a simplified schematic representation accordingly. Figure 4 to introduce the bypass flow into the edge channel of the flow field, Fig. 8 one of the Figure 6corresponding representation of an alternative embodiment, Fig. 9 one of the Figure 7 corresponding representation of the embodiment Figure 8 , Fig. 10 a schematic diagram for the use of the bypass flow in several channels of the flow field, Fig. 11 one of the Figure 6 corresponding representation to explain the embodiment according to Figure 10 , Fig. 12 one of the Figure 7 corresponding representation of the embodiment Figure 10 , Fig. 13 one of the Figure 11 A corresponding illustration of another embodiment, Fig. 14, one of the Figure 12 corresponding representation of the embodiment Figure 13 , and Fig. 15 one of the Figure 10 A corresponding representation of the multiple introduction of the bypass current into the flow field.

[0015] In the Figure 1 A fuel cell device 1 is shown schematically, comprising a fuel cell or a plurality of fuel cells grouped together to form a fuel cell stack 2.

[0016] Fuel cell stack 2 consists of a plurality of fuel cells connected in series. Each fuel cell comprises 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, preferably a sulfonated tetrafluoroethylene polymer (PTFE) or a perfluorinated sulfonic acid (PFSA) polymer. Alternatively, the membrane can be formed as a sulfonated hydrocarbon membrane.

[0017] A catalyst may be added to the anodes and / or the cathodes, wherein the membranes are preferably coated on their first side and / or on their second side with a catalyst layer made of a precious metal or of mixtures comprising precious metals such as platinum, palladium, ruthenium or the like, which serve as reaction accelerators in the reaction of the respective fuel cell.

[0018] Fuel (for example, hydrogen) is supplied to the anodes via anode compartments 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 allows the protons (for example, H⁺) to pass through but is impermeable to the electrons (e⁻). The following reaction takes place at the anode: 2H₂ → 4H⁺ + 4e⁻ (oxidation / electron release). While the protons pass through the membrane to the cathode, the electrons are conducted to the cathode or to an energy storage device via an external circuit.

[0019] Cathode gas (for example, oxygen or oxygen-containing air) can be supplied to the cathodes via cathode spaces within the fuel cell stack 2, so that the following reaction takes place on the cathode side: O 2 + 4H +< + 4e -< → 2H 2 O (reduction / electron uptake).

[0020] Compressed air is supplied to the fuel cell stack 2 via a cathode fresh gas line 3 through a compressor 4. The fuel cell is also connected to a cathode exhaust line 6. On the anode side, hydrogen stored in a hydrogen tank 5 is supplied to the fuel cell stack 2 via an anode fresh gas line 8 to provide the reactants required for the electrochemical reaction in a fuel cell. These gases are transferred to bipolar plates 10, in which channels 11 are formed and combined to form a flow field 12 for distributing the gases to the membrane. The bipolar plates 10 are also designed to allow the passage of a cooling medium, so that three different media are carried in a very small space. Bipolar plates 10 known from the prior art are used in the Figures 2 to 4 shown, whereby Figure 2For a medium, the introduction is shown through a first inlet port 13, with transfer to the flow field 12 and discharge through a first outlet port 14. Similarly, the back side of the bipolar plate 10 is available for the second reactant, with a second inlet port 15 and a second outlet port 16. The first inlet port 13 and the second inlet port 15, together with a medium port 17 for a coolant, can be combined in an inlet header 18. An outlet header 19 is available analogously.

[0021] A bypass current flows past river field 12, which cannot be completely blocked even by bypass-blocking structures 20. Figure 3 refers to the fundamental fact that, due to the consumption of the reactants, their partial pressure decreases from the inlet header 18 to the outlet header 19. Figure 4The figure refers to the known structure of bipolar plates 10, for which two metallic formed parts 21 are provided with sealing grooves 22 and welded together. The membrane electrode assemblies MEA 23 are arranged above and below the bipolar plates 10. The channels 11 for the fuel and the oxidizer and the channels 24 for the cooling medium are also visible.

[0022] For example, in Figure 5The bipolar plate 10 shown 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 a first reactant, and has 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 a second reactant, wherein at least one bypass channel 25 is located at the edge of at least one of the flow fields 12, the design is such 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.In the illustrated embodiments, a bypass channel 25 is provided on both sides of the first flow field 12 and on both sides of the second flow field 12, with at least one flow connection 26 branching off from each of the bypass channels 25 into the adjacent edge channel 27. Shown in the . Figure 5 This is for one of the flow fields 12 for one of the reactants, whereby the conditions for the second flow field are designed in the same way.

[0023] Figure 5 This also shows that the flow connection 26 is formed in the half of the flow field 12 facing the outlet port 14, in order to introduce the reactant into the region of the flow field 12 where a significant reduction in reactant concentration already exists. Upstream of the outlet port 14, a bypass blocker, namely the bypass-blocking structure 20, is arranged in the bypass channel 25 ( Figure 6), which ensures that the bypass current follows the path of least resistance and flows through the flow connection 26.

[0024] Figure 15 points out that the bypass channel 25 can also be assigned several flow connections 26, which are spaced apart from each other in the direction of flow, so that fresh gas can be fed back into the flow field 12 at different points.

[0025] The Figures 10 and 11 The diagram shows that in the marginal channel 27 downstream of the flow connection 26, a marginal channel connection 28 is formed to the adjacent channel 11 of the flow field 12. Downstream of the marginal channel connection 28, adjacent channels 11 in the flow field 12 also have a channel connection 29. This makes it possible to supply fresh gas to the flow field 12 perpendicular to the flow direction, so that not only the marginal channel 27 of the flow field 12 can utilize the bypass flow.

[0026] The Figure 4 Figure 1 shows that the channels 11 of the flow field 12 and the bypass channel 25 are separated from each other by webs 30. In the illustrated embodiments belonging to the invention, the flow connection 26 is realized by a reduction of the web height, also with regard to the edge channel connection 28 and the channel connection 29, whereby the reduction of the web height can be complete, i.e., the web 30 is omitted in these areas, as shown in the Figure 7 and 12 shown. REFERENCE MARK LIST:

[0027] 1 Fuel cell assembly 2 Fuel cell stack 3 Cathode fresh gas line 4 Compressor 5 Hydrogen tank 6 Cathode exhaust line 7 Anode recirculation line 8 Anode fresh gas line 9 Anode exhaust line 10 Bipolar plate 11 Channels 12 Flow field 13 First inlet port 14 First outlet port 15 Second inlet port 16 Second outlet port 17 Medium port 18 Inlet header 19 Outlet header 20 Bypass blocking structure 21 Forming part 22 Sealing track 23 Membrane electrode assembly 24 Cooling medium channel 25 Bypass channel 26 Flow connection 27 Edge channel 28 Edge channel connection 29 Channel connection 30 Web

Claims

1. A bipolar plate (10) with a first inlet port (13) and a flow field (12) having a plurality of channels (11) for connecting the first inlet port (13) to a first outlet port (14) for a first reactant, and with a second inlet port (15) and a flow field (12) comprising 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 provided at the edge of at least one of the flow fields (12), at least one bypass channel (25) is provided, wherein 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), characterized in that the bypass channel (25) runs in an area of the bipolar plate (10) that lies outside an active area in which the electrochemical reaction takes place, in that the flow connection (26) is formed in the half of the flow field (12) facing the outlet port (14) in order to introduce the reactant into the area of the flow field (12) in which chemical reduction of a reactant concentration is already present, and that a bypass blocker (20) is arranged upstream of the outlet port (14) in the bypass channel (25).

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

3. The bipolar plate (10) according to claim 1 or 2, characterized in that the bypass channel (25) has several flow connections (26) assigned to it, which are spaced apart from each other in the direction of flow.

4. The bipolar plate (10) according to any one of claims 1 to 3, characterized in that an edge channel connection (28) to the adjacent channel (11) of the flow field (12) is formed in the edge channel (27) downstream of the flow connection (26).

5. The bipolar plate (10) according to claim 4, characterized in that downstream of the edge channel connection (28) in the flow field (12), adjacent channels (11) each have a channel connection (29).

6. The bipolar plate (10) according to any one of claims 1 to 5, characterized in that the channels (11) of the flow field (12) and the bypass channel (25) are separated from each other by webs (30), and in that the flow connection (26) is realized by reducing the web height.

7. The bipolar plate (10) according to claim 6, characterized in that the edge channel connection (28) and / or the channel connection (29) is realized by reducing the web height.

8. The bipolar plate (10) according to claim 6 or 7, characterized in that the web height is completely reduced.