Bipolar plates and fuel cell stacks

Abstract

The present invention relates to a bipolar plate (3) formed of two interconnected individual plates (8), each of which has a reactive flow field formed on its surface facing away from each other. The reactive flow field includes a plurality of flow channels (9) for the reactive medium, which are confined by the walls (11) of a bridging portion (10). The flow channel (9) of one of the individual plates (8) and the bridging portion (10) extend relative to the flow channel (9) and the bridging portion (10) of the other individual plate (8) in an active region (13) to form a coolant channel (6) for a coolant flow field extending between the individual plates (8). The reactive flow field and the coolant flow field are respectively flow-technically connected to the medium ports (4, 5) through a distribution area (14) located outside the active region (13), and in the distribution area (14), there is a local cross-guiding of the two reactive media. In order to provide cross-guided coolant in the distribution region (14), at least one of the individual plates (8) has a reduced section (16) in the height of the bridging portion (10) formed on its plate surface facing the other of the individual plates (8) in the cross region (15) for guiding the reaction medium, thereby technically connecting two adjacent flow channels (9) through the reduced section (16). The invention also relates to a fuel cell stack (1) having a plurality of such bipolar plates (3).

Description

Technical Field

[0001] This invention relates to a bipolar plate formed of two interconnected individual plates, each plate having reactant flow fields formed on its surface facing away from each other. Each reactant flow field includes multiple flow channels for the reactant medium, confined by walls of a bridging portion, wherein the flow channels of one of the individual plates and the bridging portion extend relative to the flow channels and the bridging portion of the other individual plate in the active region, thereby forming coolant channels for a coolant flow field extending between the individual plates. The reactant flow fields and the coolant flow fields are technically connected to their respective associated medium ports via distribution regions located outside the active region. In the distribution regions, there is localized cross-guidance of the two reactant media, thereby resulting in homogenization of the distribution of the respective operating media from the respective medium ports into the flow field. The invention also relates to fuel cell stacks having multiple fuel cells, which are equipped with such bipolar plates. Background Technology

[0002] Fuel cell devices are used to chemically convert fuel and oxygen into water to generate electricity. For this purpose, a fuel cell contains a so-called membrane electrode assembly (MEA) as its core component, which is a composite consisting of a proton-conducting membrane and electrodes (anode and cathode) arranged on opposite sides of the membrane. Furthermore, a gas diffusion layer (GDL) can be arranged on either side of the MEA unit, on the side of the electrodes facing away from the membrane. In the operation of a fuel cell device having multiple fuel cells assembled into a fuel cell stack, fuel, especially hydrogen (H2) or a hydrogen-containing gas mixture, is supplied to the anode, where H2 to H2 is converted into water by releasing electrons. + Electrochemical oxidation. Proton H+ is generated via an electrolyte or membrane that airtightly separates the reaction chambers and electrically insulates them. + The transfer from the anode chamber to the cathode chamber. Electrons supplied at the anode are fed to the cathode via electrical lines. Oxygen or an oxygen-containing gas mixture is supplied to the cathode, thus allowing O2 to be transferred to O2 in the presence of electrons. 2- The reduction occurs. Simultaneously, in the cathode chamber, these oxygen anions react with protons transported via the membrane to form water.

[0003] The reactant gases are supplied to the electrodes of the fuel cell via bipolar plates. In addition to the reactant gases, a cooling medium, due to the heat generated during the fuel cell reaction, also passes through the bipolar plates, thus guiding the three different media through the bipolar plates in a minimal space.

[0004] When reactants are supplied to the fuel cell, these reactants are guided through a main channel (port) to the bipolar plates, which should cause the distribution of reactants into the active region so as to supply the entire surface of the electrode as uniformly as possible by means of a flow field. Since multiple bipolar plates with membrane electrode units are stacked in the fuel cell stack, a seal is used to longitudinally seal the main channel through the fuel cell stack. Furthermore, a good seal must be maintained for the cooling medium flowing in the coolant channels.

[0005] US 2007 / 0 269 697 A1 describes a fuel cell configuration with bipolar plates, in which selected membrane electrode assemblies are arranged to create two distinct gas channels on either side of an axis. DE 20 2016 107 302 U1 discloses a separator for a fuel cell system, wherein uniformity of the reaction medium flow should be induced within the distribution area. DE 102015 104 300 U1 discloses a bipolar plate in which the bridging portion of the reaction medium forms an interruption within the distribution area.

[0006] The guiding of the cooling medium on or within the bipolar plate has so far been less important than the guiding of the reactant stream during the development phase. As a result, conventional bipolar plates have not yet provided optimal uniform distribution of the cooling medium in the distribution area, which may lead to localized overheating (so-called "hot spots") in the active region due to the presence of only small volumetric flow in certain areas.

[0007] EP 2 348 567 A1, DE 10 2014 206 333 A1, US 2010 / 0028 42 A1, and US2019 / 0288302 A1 disclose bipolar plates with intersecting coolant channels. US 2003 / 215695 shows a bipolar plate with coolant channels that extend without intersecting, wherein the bridging height of the reactant channels is not reduced in the intersecting region. Summary of the Invention

[0008] Therefore, the objective of this invention is to provide a bipolar plate and a fuel cell stack that not only promotes the uniform distribution of the reaction medium, but also promotes the uniform distribution of the coolant.

[0009] This task is accomplished using the bipolar plate according to the invention and the fuel cell stack according to the invention. The invention has several advantageous design solutions with suitable improvements.

[0010] The bipolar plate according to the invention is particularly characterized in that, in order to guide the coolant without crossing in the distribution area, at least one of the individual plates has a reduced height of the bridging portion formed on its plate surface facing the other individual plate in the cross region of the reaction medium guidance, such that two flow channels extending adjacent to each other are technically connected by the reduced height through the reduced portion.

[0011] For coolant distribution, correspondingly, only in one of the two half-plates is there no structure already used for gas distribution left free; in principle, all such surfaces in which the distribution structures do not overlap. The following may therefore occur: when the distribution structures overlap, coolant-guided intersections also occur, resulting in eddies, and thus turbulence, which leads to uneven coolant distribution. This uneven distribution is overcome by reducing the height of the bridging section according to the invention in the intersection region guided by the reaction medium. The interruption of the bridging section guiding the flow between the two gas channels has almost no impact on the flow and uniformity at the inlet side of the distribution region. Therefore, however, crossflow in the coolant can be avoided, which would otherwise suffer excessive additional pressure loss due to the mixing of the two intersecting coolant medium flows. Furthermore, it is also possible to proactively influence the coolant distribution to achieve optimal uniformity.

[0012] Advantageously, the coolant is guided from the negative electrode of one of the individual plates to the cross-region of the reaction media, and from the cross-region of the reaction media to the negative electrode of the other individual plate. Therefore, the distribution and introduction of the coolant can occur, for example, through the flow field of the distribution region by means of the first reaction medium (e.g., fuel / anode plate), wherein the transfer of coolant to the other reaction medium (e.g., air / cathode plate) in the cross-region occurs without cross-regional flow guidance.

[0013] Therefore, in this process, it is suitable and advantageous for the coolant to be guided from the negative electrode of one of the reactant fields of the individual plates to the cross region, and from the cross region to the negative electrode of the other reactant field of the individual plates.

[0014] For the desired uniform distribution of coolant in the distribution area and thus in the active area, it is meaningful to have multiple reductions in the height of the bridging portion of one of the individual plates along the bridging portion of the other individual plate, where there is no reduction. Of course, it is also important to avoid creating crossflow of coolant.

[0015] To ensure this, it is advantageous that the number of bridging sections decreases with increasing flow distance at the associated medium ports. Therefore, when fuel or cathode gas flows continuously, the number of interruptions in the bridging section is reduced, thus suppressing cross-flow of coolant on the inner side of the plate.

[0016] Another advantage is that the bridging section without a reduction section in a single plate gradually decreases in length as the flow distance to its associated medium port increases. This also avoids cross-flow of coolant.

[0017] There is a possibility that the coolant flow is conducted through multiple intersection regions with reduced heights at the bridging points, and that the coolant flow is deflected at exactly one intersection region. Thus, the coolant flow is only deflected and not further separated.

[0018] However, in order to cause further separation of the coolant flow, it is advantageous that the coolant flow is guided through multiple intersection regions with reduced bridging heights, and the coolant flow is separated at at least two intersection regions.

[0019] Turbulence caused by the cross-flow of coolant can be effectively avoided by reducing the bridging section height to zero; the bridging section is thus completely interrupted without causing mixing of the operating medium.

[0020] The advantages, favorable design, and effects of the bipolar plate interpretation according to the invention also apply to the fuel cell stack according to the invention, which is equipped with multiple fuel cells having bipolar plates according to the invention. The fuel cell stack also excels in improved thermal management by avoiding localized overheating in the distribution area, which can be achieved by suppressing cross-flow of coolant.

[0021] The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the drawings and / or shown separately in the drawings, can be used not only in the combinations described separately, but also in other combinations or individually, without departing from the scope of the invention. Therefore, the following embodiments, which are not explicitly shown or explained in the drawings, but are derived from and can be produced by individual combinations of features from the explained embodiments, should also be considered as included and disclosed by the invention. Attached Figure Description

[0022] Other advantages, features, and details of the invention can be appreciated from the following description of preferred embodiments and with reference to the accompanying drawings. Wherein:

[0023] Figure 1 A schematic diagram of a fuel cell stack with multiple fuel cells is shown, featuring bipolar plates that illustrate the main channel.

[0024] Figure 2 It shows Figure 1 A schematic and detailed illustration of the cross-section II-II of the bipolar plate.

[0025] Figure 3A schematic detailed top view of the bipolar plate distribution area is shown, wherein the guidance of the first reaction medium is indicated by dotted dashed lines, and the guidance of the second reaction medium is indicated by dashed lines.

[0026] Figure 4 The corresponding Figure 3 A schematic diagram of the bipolar plate distribution area, wherein the guidance of the first reaction medium is shown by dotted dashed lines, the guidance of the second reaction medium is shown by dashed lines, and the guidance of the coolant is shown by solid lines.

[0027] Figure 5 A detailed view of the distribution area is shown, revealing a reduction in bridging height at the cross-regions where the reaction medium guides the flow, thus preventing the coolant from crossing itself.

[0028] Figure 6 The corresponding non-cross-guided coolant is shown. Figure 5 An alternative design in which the cooling medium branches / leads out at multiple intersections of the reaction medium. Detailed Implementation

[0029] Figure 1 The fuel cell stack 1 shown consists of multiple fuel cells 2 connected in series. Each of the fuel cells 2 includes an anode and a cathode, and a proton-conducting membrane separating the anode and cathode. The two electrodes together with the membrane form a membrane electrode assembly 7 (MEA). This 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.

[0030] Fuel (e.g., hydrogen) is supplied to the anode via the anode chamber within fuel cell stack 1. In a polymer electrolyte membrane fuel cell (PEM fuel cell), fuel or fuel molecules split into protons and electrons at the anode. The membrane allows protons (e.g., H+) to be released. + ) passes, but for electrons (e - It is impermeable. At the anode, the following reaction occurs: 2H₂ → 4H₂ + +4e - (Oxidation / Electron Release). During the passage of protons through the membrane to the cathode, electrons are conducted to the cathode or energy storage via an external circuit. Cathode gas (e.g., oxygen or oxygen-containing air) can be supplied to the cathode via the cathode chamber within fuel cell stack 1, thereby allowing the following reaction to occur on the cathode side: O₂ + 4H₂O + +4e - →2H2O (reduction / electron absorption).

[0031] Compressed air is supplied to fuel cell stack 1 via a cathode fresh gas line. Fuel cell stack 1 is also connected to a cathode exhaust gas line. On the anode side, hydrogen prepared in a hydrogen tank is supplied to fuel cell stack 1 via an anode fresh gas line to provide reactants required for the electrochemical reactions in fuel cell 2. These gases are transferred to bipolar plates 3, which have main channels 4 (ports) for distributing the gases to the membrane and outlet. Furthermore, the bipolar plates have main coolant channels 5 (ports) for guiding the passage of coolant in coolant channels 6, allowing the three different media to be guided within a very small space.

[0032] Figure 1 The diagram also shows main channels 4, 5, which are paired combinations of multiple fuel cells 2 forming a fuel cell stack 1 and have bipolar plates 3.

[0033] fuel cell stack 1 along Figure 1 The detailed section of section II-II in Figure 2 As shown in the diagram, this cross-section extends through the active region 13 of the fuel cell stack 1. The active region 13 of the bipolar plate 3 is not electrochemically active in itself, but it is arranged adjacent to those parts of the fuel cell 2 where the electrochemical fuel cell reaction takes place. It can be seen that the bipolar plate 3 has reactant flow fields on its opposing surfaces in the active region 13, which are arranged opposite each other and thus configured in an opposing configuration. Each reactant flow field has a plurality of flow channels 9 for the corresponding reaction medium, defined by the walls 11 of the bridging portions 10. The bridging portion 10 and flow channel 9 of one of the individual plates 8 are therefore designed in the active region 13 to extend opposite to the bridging portion 10 and flow channel 9 of the other individual plate 8. In this way, coolant channels 6 form coolant flow fields extending between the individual plates 8.

[0034] If the coolant in the coolant channel 6 is not present at the same pressure or with the same volumetric flow, localized overheating areas (so-called "hot spots") may occur. Therefore, a more uniform distribution of coolant flow is required to avoid such localized overheating areas. The bipolar plate 3 according to the invention begins here.

[0035] from Figure 3 As can be seen, the bipolar plate 3 according to the present invention has a distribution region 14 between its main channel and active region 13, in which two reaction media are locally intersected. The region in which the guidance of the two reaction media intersects is hereinafter referred to as the intersection region 15.

[0036] To ensure that the coolant is guided without crossing in the distribution area 14, at least one of the individual plates (8) has a reduced section 16 in the cross region 15 where the reaction medium is guided, on its plate surface facing the other individual plate 8. The height of the bridging section 10 is reduced to 0, thereby completely interrupting the associated bridging section 10. Through this reduced section 16 or interruption, two adjacent and extending flow channels 9 are technically interconnected through the reduced section 16.

[0037] Figure 4 The text describes how, in bipolar plate 3, the coolant up to the cross region 15 is guided by the negative electrode of one of the individual plates 8, while from the cross region 15 onwards, the coolant is guided by the negative electrode of the other individual plate 8. Specifically, it can be configured such that, in the distribution region 14 of bipolar plate 3 up to the cross region 15, the coolant is guided by the negative electrode of one of the reactant flow fields of the individual plate 8, and from the cross region 15 onwards, the coolant is guided by the negative electrode of the other reactant flow field of the individual plate 8.

[0038] Figure 5 and 6 It is pointed out that there is a possibility that, along the bridging portion 10 of one of the individual plates 8 without a reduction portion, there are multiple reduction portions 16 of the height of the bridging portion 10 of the other individual plate 8, and the number of reduction portions 16 decreases as the flow distance of the associated medium port 4 increases. According to... Figure 5 In the example, the quantity is reduced from three reduction sections 16 to two reduction sections 16, and then to a single reduction section 16 (from left to right). In addition, it can be seen that the other bridging section 10 without reduction section in the individual plate 8 has a gradually decreasing length as the flow distance of its associated medium port 4 increases.

[0039] also, Figure 5 This illustrates the possibility that the coolant flow, indicated by solid lines, is guided through intersecting regions 15 of multiple reduction sections 16 with bridging heights, and that the coolant flow is deflected at exactly one intersecting region 15, at one end of a bridging section 11 of another reaction medium without reduction. The coolant flow is thus guided non-intersectingly from the main coolant channel 5 through the distribution region 14 to the active region 13.

[0040] In contrast, Figure 6 This indicates the possibility that the coolant flow, shown by solid lines, is guided through multiple intersection regions 15 of reduced sections 16 with bridging heights, and that the coolant flow is split at at least two intersection regions 15. The coolant flow is thus guided non-intersectingly from the main coolant channel 5 through the distribution region 14 to the active region 13.

[0041] As a result, by utilizing the present invention, heat is thus uniformly distributed in the distribution region 14, because the coolant can be uniformly distributed on the bipolar plates 3 and thereby uniformly distributed throughout the fuel cell stack 1.

[0042] Reference Symbol List

[0043] 1. Fuel Cell Stack

[0044] 2. Fuel Cell

[0045] 3 Bipolar plates

[0046] 4. Main channel for reactants

[0047] 5. Main coolant passage for cooling medium

[0048] 6 Coolant passages

[0049] 7. Membrane Electrode Assembly (MEA)

[0050] 8. Individual boards

[0051] 9. Flow channel

[0052] 10 Bridging section

[0053] 11 walls

[0054] 12 Through openings

[0055] 13 Active regions

[0056] 14 Distribution Area

[0057] 15. Intersecting Areas (Distribution Areas)

[0058] 16. Reduction of departments

[0059] 17 Collection Area.

Claims

1. A bipolar plate (3), which is formed by two interconnected individual plates (8), Each of the individual plates (8) has a reactive material field formed on its surface that is far apart from each other. The reactant flow field includes a plurality of flow channels (9) for the reactant medium, confined by walls (11) of bridging portions (10), wherein the flow channel (9) of one of the individual plates (8) and the bridging portion (10) extend relative to the flow channel (9) and the bridging portion (10) of the other individual plate (8) in the active region (13) to form a coolant channel (6) for a coolant flow field extending between the individual plates (8). in, The reactant flow field and the coolant flow field are respectively connected to the medium ports (4,5) via a distribution area (14) located outside the active region (13). Furthermore, within the distribution area (14), there is a localized cross-guiding of the two reaction media. Its features are, In order to guide the coolant without cross-contamination in the distribution area (14), at least one of the individual plates (8) has a reduced section (16) in the height of the bridging section (10) formed on its plate surface facing the other of the individual plates (8) in the cross-contamination area (15) of the reaction medium guidance, so that two flow channels (9) extending adjacent to each other are technically connected through the reduced section (16).

2. The bipolar plate (3) according to claim 1, characterized in that, The coolant is guided by the negative electrode of one of the individual plates (8) up to the cross region (15), and the coolant is guided by the negative electrode of the other of the individual plates (8) from the cross region (15).

3. The bipolar plate (3) according to claim 1 or 2, characterized in that, The coolant is guided by the negative electrode of one of the reactive stream fields of the individual plates (8) up to the cross region (15), and the coolant is guided from the cross region (15) by the negative electrode of the other reactive stream field of the individual plates (8).

4. The bipolar plate (3) according to any one of claims 1 to 3, characterized in that, Along the bridging portion (10) of one of the individual plates (8) without reduction, there are multiple reduction portions (16) in the height of the bridging portion (10) of the other individual plate (8).

5. The bipolar plate (3) according to claim 4, characterized in that, The number of reduction sections (16) decreases with the increase in flow distance of the associated medium port (4).

6. The bipolar plate (3) according to claim 4 or 5, characterized in that, The bridging section (10) of one of the individual plates (8) without a reduction section has a gradually decreasing length as the flow distance of its associated medium port (4) increases.

7. The bipolar plate (3) according to any one of claims 1 to 6, characterized in that, The coolant flow is guided through the intersection regions (15) of the reduction sections (16) having a bridging height, and the coolant flow is deflected at exactly one of the intersection regions (15).

8. The bipolar plate (3) according to any one of claims 1 to 6, characterized in that, The coolant flow is guided through the intersection regions (15) of the reduction sections (16) having a bridging height, and the coolant flow is separated at at least two of the intersection regions (15).

9. The bipolar plate (3) according to any one of claims 1 to 8, characterized in that, The height of the bridging portion formed by the reduction portion (16) is 0.

10. A fuel cell stack (1) comprising a plurality of fuel cells (2) having bipolar plates (3) according to any one of claims 1 to 9.

Images