Fuel cell

Abstract

[0001] The invention relates to a fuel cell, in particular a PEM fuel cell. The object of the invention is to optimize the specific amount of energy that can be extracted from a fuel cell according to the invention in the form of electrical energy when operating with dry or partially humidified supply gases. [0002] This problem is solved by a fuel cell with a bipolar plate according to the invention, in particular a bipolar plate constructed from half-shell parts for a fuel cell according to the invention, which has the features specified in the main claim. Advantageous embodiments of the invention are the subject of the dependent claims. [0003] The core of the invention is a bipolar plate geometry which, at least in the area of ​​the active cell surface, comprehensively parallelizes the flow direction of the reaction media in the outer reaction flow field channels and the flow direction of the cooling fluid in the inner cooling flow field channels, as well as the hydraulic connection of the inner cooling fluid channels to the cooling fluid ports and the hydraulic connection of the outer reaction flow field channels to the respective reaction fluid ports.

Description

[0001] Fuel cells, particularly polymer electrolyte membrane (PEM) fuel cells, are known from the prior art. These cells comprise a cathode electrode, an electrolyte, and an anode electrode. An oxygen-containing oxidizing agent (e.g., air) is fed into supply channels adjacent to the cathode electrode, and a fuel (e.g., hydrogen) is fed into supply channels adjacent to the anode electrode.

[0002] In this context, "electrode" refers to a flat, often one-piece, arrangement consisting of at least one flat, microporous, catalyst-supporting layer ("CAT") and at least one flat, macroporous "gas diffusion layer" (GDL). The electrochemical electrode reactions take place at the at least one aforementioned catalyst-supporting layer; the at least one macroporous layer serves to electrically contact adjacent components and transport reaction reactants and products to and from the catalyst-supporting layer, thus hydraulically connecting the reaction zone to macroscopic flow field channels.

[0003] An electrode around which fuel flows at least in part is referred to below as an “anode electrode”; an electrode around which oxidizer flows at least in part is referred to below as a “cathode electrode”.

[0004] The core of a PEM fuel cell is a proton-conducting polymer membrane, for example, made of Nafion®, which acts as the electrolyte in the electrochemical cell and is arranged between two electrodes, an anode electrode and a cathode electrode. As already described, these electrodes comprise a layered structure consisting of a macroporous full-surface component (GDL) and a catalyst-coated microporous full-surface component (KAT). The microporous components of the electrodes are arranged directly adjacent to, or in surface contact with, the polymer membrane. The macroporous components are arranged directly adjacent to, or in surface contact with, fluid guidance or fluid distribution structures of an electrically conductive interconnector plate.

[0005] Interconnector plates in the form of monopolar plates or bipolar plates are well known in the art. Such interconnector plates feature superficial macroscopic (visible to the naked eye) fluid guidance, fluid conduction, or fluid distribution structures—hereinafter also referred to as "flow fields"—which can be formed from supply channels or other fluid-conducting structures. These flow fields distribute the respective reaction media, for example, hydrogen or oxygen, across the corresponding electrodes (hydrogen on the anode electrode, oxygen on the cathode electrode).

[0006] In addition, such flow field structures also serve to remove excess reaction gas and liquid water from the fuel cell, which is formed as a reaction product from the hydrogen- and oxygen-containing supply gases (operation often occurs with hydrogen and air). In virtually all prior art cases, the electrodes arranged on both sides of the polymer membrane, or their gas diffusion layers (GDL), are arranged in direct contact with the macroscopic fluid distribution structures or flow fields of adjacent interconnector plates.

[0007] If an interconnector plate is geometrically designed in such a way that it has two external / surface fluid distribution structures ("flow fields"), which can supply two adjacent individual fuel cells with two different reaction media (e.g. hydrogen or atmospheric oxygen), and the interconnector plate also takes over the electron transport between these aforementioned adjacent individual fuel cells, such an interconnector plate is also referred to as a "bipolar plate" (BPP).

[0008] Such interconnector plates often also have at least one internal cooling fluid distribution structure—hereinafter referred to as a "cooling flow field"—which serves to regulate the temperature of the fuel cell or to dissipate reaction heat via a separate cooling fluid. Another function of such interconnector plates is the electron-conducting electrical contacting of the electrodes or (in the case of the two monopolar interconnector plates arranged at the end of a fuel cell stack) of an external electrical conductor circuit.

[0009] Interconnector plates are often made of metal or carbon-based materials. The fluid-tight sealing of the individual functional fluid spaces (anode fluid space with hydrogen-containing fluid, cathode fluid space with oxygen-containing fluid, and possibly cooling fluid space with a cooling fluid, e.g., water) from each other and from the environment, which is required for the function of the fuel cell, is often achieved by elastomer seals molded onto the interconnector plates or arranged directly adjacent to them. In the case of interconnector plates formed from metallic half-shells, this is also achieved, at least in some areas, by material-to-material joining processes such as laser welding, soldering, or adhesive bonding.

[0010] If an interconnector plate interacts with a single neighboring fuel cell and an external conductor circuit only via an external / surface flow field, it is also referred to as a “monopolar plate” (MPP).

[0011] Flow fields that supply a fuel cell with fuel—usually containing hydrogen—are referred to as "anode-side flow fields" and have a negative electrical pole relative to the respective individual fuel cell. Flow fields that supply the PEM fuel cell with an oxidizer—usually containing oxygen—are referred to as "cathode-side flow fields" and have a positive electrical pole relative to the respective individual fuel cell.

[0012] Flow fields that transport a cooling fluid are referred to as "cooling flow fields." They are typically located inside an interconnector or bipolar plate, geometrically positioned between the external anode and cathode-side flow fields.

[0013] State-of-the-art flowfields or flowfield fluid distribution structures generally share several common features: First, the reaction media are guided in macroscopic, two-dimensional channel structures, typically with a rectangular or trapezoidal profile, or similar, with an average channel width of 0.5-2 mm and an average channel depth of 0.2-1 mm. Adjacent flowfield channels or channel segments are separated from each other by suitable webs—channel webs or flowfield webs—with a complementary profile, typically with an average web width of 0.5-2 mm.

[0014] Such channel structures or fluid distribution structures are geometrically adapted to the adjacent, flat electrode area in which the electrochemical conversion of fuel or oxidizer takes place, in the sense of an overall channel-web geometry filling the projection of the electrochemically active cell area onto the interconnector surface (hereinafter also referred to as the "active cell area" of the interconnector plate or fuel cell), so that with a suitable choice of the respective mass flows, a full-surface and sufficient supply of the electrode surfaces with reaction gases or reaction fluids and the removal of the excess reaction products and depleted reaction gases from the same can take place, in the sense of a stationary flow process.

[0015] Such fluid distribution structures or reaction flow fields of the interconnector plates, intended for the application of reaction media, therefore often feature geometric distribution structure patterns in the form of single or multiple parallel channels or channel bundles that meander in a serpentine manner across the often rectangular "active cell surface." Such a distribution structure is referred to below as a serpentine flow field and represents a possible solution to the analogous mathematical problem of an area-filling curve (or a family of area-filling curves).

[0016] The prior art is explained in more detail below with reference to figures. They show first Fig. 1 Top view of an exemplary cathode-side interconnector plate with single serpentine flow field from the z-direction of the coordinate system Fig. 2 Various common flowfield patterns, three-dimensional view. Fig. 3 Typical flow paths of the operating media: fuel fluid, oxidizer fluid, and cooling fluid, illustrated using a bipolar plate according to the state of the art. View from the z-direction of the coordinate system. Fig. 4 Detailed cross-section of the layered structure of a single fuel cell. Section in the xz plane of the coordinate system.

[0017] Unless otherwise indicated in the text, corresponding parts in all figures are designated by the same reference numerals after the heading, and, where appropriate, by the same supplementary suffixes after the reference numerals, separated from the reference numerals by a hyphen. However, the reference numerals are not to be understood as limiting the scope of the subject matter protected by the claims; they serve merely to facilitate the understanding of the claims and the invention.

[0018] An example of such a fluid distribution structure designed for the supply of reaction media according to the state of the art is a so-called single-channel serpentine flow field of a planar interconnector plate, in which a reaction medium is guided through a single channel, or a bundle of parallel channels (shown in gray) separated from each other by channel webs or flow field webs, meandering between diagonally opposite inlet and outlet collector zones ("ports") over a rectangular active cell surface. A single- or multi-channel serpentine flow field can be found on both the anode- and cathode-side interconnector plate. In the fully assembled stack, the membrane electrode assembly (MEA) of the fuel cell rests on the flow field webs in a force-fitting and form-fitting manner and is supplied with reactants via the flow field channels.

[0019] Geometrically, the conditions on the anode and cathode-side interconnector plates are often analogous, except for the often different channel heights of the respective reaction flow fields. The terms "port" and "collector" are used synonymously below.

[0020] In Fig. 1, if necessary with reference to the Fig. 1, is a top view of an interconnector plate (1.02)—exemplarily on the cathode side—from the z-direction of the coordinate system. Shown there as an outline is the electrochemically active area (“active cell area”) (1.28) contacted by the adjacent cathode electrode or projected onto the illustrated interconnector plate, and a single meandering channel (1.06), which, together with the adjacent channel-delimiting webs (1.29), the flow field webs, which are all designed as “finger webs” in this figure, form the cathode flow field of the interconnector plate.

[0021] The oxygen-containing fresh gas flow (1.01) is conveyed from the inlet port (1.30) to the active cell surface (1.28) and from there as the exhaust gas flow (1.03) to the outlet port (1.31) via the respective connection zones (1.32-E before the fresh gas flow enters the active cell surface or 1.32-A after the exhaust gas flow exits the active cell surface). Elastomer seals (not shown) are typically arranged in the area of ​​these connection zones. These seals serve to seal the fuel cell's operating media-carrying chambers from each other and from the outside environment, and merely enable hydraulic connections between the ports (1.30), (1.31) and the respective associated flow fields of the fuel cell. Also shown are the symmetry axis A (1.36) and the symmetry axis B (1.37) of the rectangular active cell surface (1.28).

[0022] With a suitably selected mass flow, the adjacent cathode electrode is supplied with the oxidizer oxygen over its entire area by the cathode flow field in the area of ​​the active cell surface (1.28) and the resulting reaction products, together with the exhaust gas, are removed from the area of ​​the active cell surface in an oxygen-depleted and product water-enriched output gas stream (1.03) and, as already described, fed to the output port (1.31).

[0023] Also shown in the figure are channel segments of the active cell area near the flowfield inflow area of ​​the reaction medium (1.07) and near the flowfield outflow area of ​​the reaction medium (1.08), which are addressed in more detail below.

[0024] Various flowfield patterns commonly used in the state of the art are shown in Fig. 2 using three interconnector plates, if necessary with reference to the Fig. 2 fixed, right-handed Cartesian coordinate system (2.40). Shown there is an interconnector plate with a serpentine flow field and two parallel channels (2.02-A), an interconnector plate with a parallel flow field (2.02-B), and an interconnector plate with an interdigitated flow field (2.02-C). The flow pattern in the respective channels (2.06-A), (2.06-B), (2.06-C) of the various interconnector plates is illustrated as an example for the three designs (2.02-A), (2.02-B), (2.02-C) by flow paths along representative channel center plane(s) (2.20-A), (2.20-B, (2.20-C), each of which runs from an inlet port (2.30) to an outlet port (2.31).

[0025] The input and output ports serve to jointly supply a number of stacked individual fuel cells with the reaction media or - not shown in this figure - the cooling fluid and to jointly transport away reaction products, depleted reaction media and cooling fluid tempered by the fuel cell waste heat (cooling ports not shown) of a number of stacked fuel cells ("fuel cell stack").

[0026] It is known that such, or other, reaction fluid distribution structures effectively distribute the reaction reactants evenly across the adjacent electrode and ensure the uniform removal of reaction products from the active cell area. In virtually all cases, the distribution proceeds from geometrically comparatively small inlet areas (analogous to 1.32-E) across the aforementioned "active cell area" (analogous to 1.28) to equally comparatively small outlet areas (analogous to 1.32-A), which are often arranged diagonally opposite the aforementioned inlet areas and hydraulically connected to the respective inlet and outlet ports via suitable fluid guidance structures.

[0027] Reaction reactants and reaction products are transported within these distribution structures, possibly together with other inert fluid components in a supply fluid, for example, a gaseous supply gas such as oxygen-containing, humid air (on the cathode side) or humidified hydrogen (on the anode side). The transport from the macroscopic distribution structures of an interconnector plate flow field to the catalyst-coated area of ​​the electrode, or back to the flow field, occurs through the gas diffusion layer (GDL) of the electrode via diffusion and, if applicable, convection processes.

[0028] Electrochemically, the following reactions take place at the respective electrodes of a PEM fuel cell, here a H2-supplied PEM fuel cell: At the anode electrode, hydrogen ions (H+) are formed in the presence of a hydrogen-containing fuel gas with the release of electrons (e-) according to the anode-electrode reaction: 2H2 → 4H + + 4e -

[0029] The hydrogen ions (H+) formed in this process migrate through the ion-conducting, membrane-like, polymer electrolyte to the cathode electrode. Meanwhile, the electrons released during the anode reaction migrate, as an electric current, via an external, electron-conducting conductor circuit to the cathode electrode. The technical application of this process is achieved by electrical machines or loads that are connected to this external conductor circuit.

[0030] At the cathode electrode, in the presence of the oxidizer, oxygen, as well as the hydrogen ions and electrons from the anode-electrode reaction, water is formed according to the cathode-electrode reaction: 4H + + O2 + 4 e - → 2H2O

[0031] The following applies to the overall reaction: 2H2 + O2 → 2H2O + electrical energy

[0032] The reaction educts H2 and O2, which are supplied by means of a supply fluid according to the state of the art with a significant stoichiometric excess, based on the reactions taking place at the respective electrodes, starting from an inlet port (analog 1.30) or an inlet area (analog 1.32-E), in the area of ​​the active cell surface (analog 1.28) through the aforementioned distributor structures to the respective electrodes, react there according to the fuel cell type-specific electrode reaction, whereby the local content of fuel (anode electrode) or oxidizer (cathode electrode) in the respective supply fluid decreases.

[0033] The reaction products formed in this process and / or any water precipitating from the vapor phase due to changes in the boundary conditions of the supply fluids (e.g. local temperature) are then led out of the fuel cell together with stoichiometry-related excess fuel or oxidizer and possibly other inert fluids from the respective supply fluid, e.g. atmospheric nitrogen, via the aforementioned distribution structures via an outlet area (analog 1.32-A) and an output port (analog 1.31).

[0034] The resulting waste heat is often conducted through the webs or channel walls of the reaction flow fields via a heat conduction process to a separate cooling flow field, usually located between the outer reaction flow fields, where it is absorbed by a flowing cooling fluid by forced convection and transported out of the fuel cell by the flow of the cooling fluid.

[0035] To achieve high technical efficiency in a fuel cell, in terms of voltage efficiency, power losses must be kept as low as possible. This is achieved, among other things, by distributing the reaction media as evenly as possible across the active cell surface and minimizing transport resistance. For example, if electron and / or ion conduction occurs via poorly conducting components, the voltage efficiency inevitably decreases due to conduction-related power losses.

[0036] It is therefore particularly important that the transport resistance for hydrogen ions through the polymer membrane is particularly low. In conventional polymer membranes, such as Nafion, this is often achieved by swelling the polymer electrolyte membrane to a high water content. To prevent the polymer membrane from drying out due to unsaturated supply gases, the supply gases (e.g., hydrogen and air) are often introduced into the fuel cell at an artificially elevated relative humidity, i.e., pre-humidified with H2O.

[0037] This limits or prevents an undesirably low water content of the polymer electrolyte due to drying out, which leads to an increase in the transport resistance for the hydrogen ions.

[0038] The water balance in a PEM fuel cell is therefore of great importance for its technical functionality and efficiency. Therefore, key processes related to the water balance are explained in more detail below:

[0039] For a polymer membrane electrolyte based on Nafion®, for example, a sufficiently high ionic conductivity only occurs above a certain water content—also referred to as the degree of swelling—of the polymer membrane. In principle, ionic conductivity is favored by high degrees of swelling / water content and reduced by low degrees of swelling / water content.

[0040] In practice, the extent of this degree of swelling / water content results from an equilibrium between the water balance of processes and interactions that take place in the environment of the polymer membrane and at its interfaces with the neighboring electrodes. Of particular importance here are the 1. Water transport from the anode to the cathode side due to electroosmosis 2. the formation of product water on the cathode side as a result of the fuel cell reaction (water synthesis) of hydrogen and oxygen 3. Diffusion-driven water transport resulting from a local H2O concentration gradient between the water content of the membrane and the reaction gas flow passing indirectly past the membrane in the flow field. If a (partial) area of ​​the active cell surface is supplied by a single, longer flow field channel through which supply fluid, i.e., hydrogen-containing fluid on the anode side or oxygen-containing fluid on the cathode side, flows parallel to or along an electrode, the supply fluid becomes increasingly enriched in fuel or oxidizer, starting from the inlet port or channel entry into the active cell surface, along the channel length, and toward the channel exit from the active cell surface or exit port. Particularly on the cathode side, the supply fluid also becomes increasingly enriched with product water and, if applicable, water from electroosmotic transport processes.

[0041] The parameter describing the distance of a channel segment from the channel inlet, following the channel core downstream, is also referred to as “run length” and is assigned the variable name “L”.

[0042] In addition, further side effects can occur along a channel, such as changes in the local total pressure due to hydraulic pressure loss of a flowing medium and / or due to reaction gas depletion, and / or a temperature increase due to the heat of reaction generated. Consequently, the reaction conditions of the reactions taking place at the electrodes differ depending on the location—along the channel length L—due to changing local operating conditions or the local composition / physical properties of the supply fluid.

[0043] Due to geometric limitations in the practical design of interconnector plates (supply of individual fuel cells in the fuel cell stack from common supply or collector channels of the fuel cell stack ("ports") and the constructive expediency of arranging these collectors / ports in the periphery of the interconnector plate), practically all fuel cells according to the state of the art have areas, particularly in the inflow area of ​​the reaction fluid into the flow field (1.07) or onto the "active cell area" formed by the flat electrodes (1.28), which are exposed to a greatly increased local stoichiometry.

[0044] This is due to the fact that such inflow regions (1.07) are, on the one hand, part of the active cell surface and thus contribute to the electrochemical conversion of the reaction media, but, on the other hand, are also required for the flow of reaction media to downstream regions of the active cell surface. For this reason, a significantly higher amount of reaction reactants flows past such regions of the active cell surface than would be required for the local maintenance of the electrochemical reaction, in the sense of a steady-state flow process, at a given local current density.

[0045] If the relative humidity of the reaction media in an area of ​​the active cell surface (1.28), in particular an inflow area (1.07), is lower than 100%, which is the rule for fuel cells according to the state of the art, a concentration gradient with regard to the water content arises during operation between the polymer membrane in this area and the supply gas flow passing indirectly past the electrode or being guided past it, in such a way that water from the polymer membrane passes into the vapor phase due to diffusion and is transported away by the reaction gas flow passing by, which is thereby further saturated with water.

[0046] In areas where such (unsaturated) gas flows along an electrode, there is a risk of local drying out of the polymer electrolyte membrane arranged adjacent to the electrode if the water loss from the membrane due to diffusion cannot be compensated by local water production (water synthesis) or by electroosmosis (on the cathode side).

[0047] If such a balance compensation is not present locally, the transport resistance for hydrogen ions within this polymer electrolyte membrane increases significantly, which initially leads to conduction and power losses and can also lead to lifetime-shortening damage to the polymer electrolyte membrane in these drying areas.

[0048] The size of these drying areas increases with the size of the area of ​​the active cell surface supplied by a single channel - hence the channel length - and with decreasing humidity of the incoming supply gas.

[0049] In order to counteract this problem of undesirable local power loss and undesirable local damage to the polymer membrane due to "drying out", gaseous supply fluids - supply gases - of fuel cells can be pre-humidified, as already briefly described, as is customary according to the state of the art.

[0050] This means that the dew point, or relative humidity, of the supply gases is artificially raised by adding H2O before entering the fuel cell in order to reduce the transfer of water from the polymer membrane into the gas stream passing by the electrode - thus reducing the drying out of the polymer membrane - by reducing the concentration gradient in accordance with Fick's diffusion laws.

[0051] As already described, this drying process of the polymer membrane is locally driven by the concentration gradient between the local water content of the polymer membrane and the water content of the unsaturated supply gas flow passing indirectly past the electrode. In this process, water from the polymer membrane passes into the vapor phase due to diffusion and is carried away by the passing supply gas flow.

[0052] As a result of the previously described successive changes in the local conditions along a reaction flow field channel (hereinafter also referred to as "supply channel") through which a supply gas - hydrogen-containing gas on the anode side or oxygen-containing gas on the cathode side - flows, this concentration gradient also changes successively and until / as the supply gas flow is completely saturated with water and remains locally saturated.

[0053] The proportion of water in a saturated reaction gas stream, or the water vapor partial pressure, depends to a considerable extent on the temperature of the aforementioned reaction gas stream and is known in the literature under the term “water vapor pressure curve”.

[0054] If the dew point of a supply fluid exceeds the local gas temperature of the supply fluid, for example, due to product water entrainment during the fuel cell reaction, liquid water precipitates from the vapor phase of the now fully saturated gas stream. However, the required removal of liquid water from a flow field is significantly more energy-intensive than the removal of vaporous water, which leads to a decrease in overall efficiency and should be avoided or at least limited if possible.

[0055] Efficient fuel cells according to the state of the art are therefore operated with reaction media whose inlet humidity is, on the one hand, high enough that undesirable drying of the polymer membrane, especially in the inlet area of ​​an unsaturated supply gas stream into the active cell surface, does not exceed a predetermined acceptable level. On the other hand, the inlet humidity should not be so high that the amount of liquid water subsequently precipitating from the vapor phase becomes so large that the energetic and economic expenditure of liquid water removal and pre-humidification of the reaction gases compensates for or exceeds the energetic advantage of higher membrane humidification. This results in a classic conflict of objectives.

[0056] If one considers the local conditions, one finds that in a fuel cell operated according to the state of the art close to a balanced -integral- efficiency optimum, the local efficiency is often significantly below average in some areas, e.g. in the segments (1.07), (1.08), which are located close to the inlet of the fresh gas into the zone of the active cell area (1.07), or close to the outlet of the active cell area (1.08):

[0057] Firstly, high ion transport resistances occur in segment (1.07) due to a below-average humidified ion conductor. This is because this region (1.07) is flowed through by a significantly overstoichiometric amount of relatively dry (rH<100%) reaction medium, and water is extracted and transported away from the drying polymer membrane.

[0058] The same applies, on the other hand, with regard to a below-average local efficiency, but with different causes, for segment (1.08), if liquid water is present here and the removal of liquid product water requires additional energetic expenditure (in the form of an additional pressure loss / friction losses for the fluid flowing through a channel).

[0059] The necessity inherent in the state of the art to first humidify reaction media and then to transport a significant portion of the humidification water - often all of it - out of the fuel cell as liquid water leads to additional technical effort, additional investment and operating costs, increased system complexity and reduced system efficiency.

[0060] It would therefore be desirable to have a fuel cell that operates with reduced or even no humidification of the reaction gases, or at least of the cathode-side reaction gas (the cathode gas), without locally unfavorable efficiencies due to local drying out of the polymer electrolyte or unnecessary precipitation of liquid water. This is because, as already indicated, this simultaneously increases the efficiency of the fuel cell and eliminates the energy expenditure for humidifying the fresh gases and condensing water from the fuel cell exhaust gas (to supply the fresh gas humidifier with water). In addition, system costs can be reduced through downscaling or even the elimination of individual system components associated with fresh gas humidification.

[0061] Furthermore, it would be desirable to have a fuel cell that utilizes its cooling water as efficiently as possible to reduce the energy consumption of the cooling water pump. This can be achieved, for example, by reducing parasitic cooling water flows that flow through the bipolar plate or fuel cell with a comparatively small temperature increase compared to the average temperature increase of the cooling water flow between the cooling water inlet port and the cooling water outlet port. These flows thus make a significant contribution to the power consumption of the cooling fluid pump but hardly contribute to the removal of reaction waste heat from the fuel cell. This problem is particularly relevant for bipolar plates with an internal cooling flow field, which are assembled from formed half-shells:

[0062] The media flow in a bipolar plate (3.33) with a typical 4-channel serpentine flow field on the anode and cathode side according to the state of the art is shown schematically in three views from the z-direction of the coordinate system (3.40), simultaneously from one side of the bipolar plate, here the cathode flow field side. Fig. 3, with reference to the Fig. 3, right-handed Cartesian coordinate system (3.40). In the three top views, the areas of the respective operating media (hydrogen-containing anode gas fluid, oxygen-containing cathode gas fluid, cooling fluid) through which the respective fluid flows during operation are colored in grey. Also in Fig. Figure 3 shows the position of the symmetry axes A (3.36) and B (3.37) relative to the position of the corresponding active cell area (3.28).

[0063] In the Fig. 3 -Top view left-, shown in grey is the space on the cathode side of the bipolar plate through which the cathode gas flows, thus the cathode flow field channels (3.06-KA) with the cathode-side inlet port (3.30-KA), the cathode-side outlet port (3.31-KA), as well as the edge zone surrounding the flow field or the edge webs (3.34).

[0064] In the Fig. 3 - Center view - The space on the anode side of the bipolar plate through which the anode gas flows is shown in gray, including the anode flow field channels (3.06-AN), the anode-side inlet port (3.30-AN), and the anode-side outlet port (3.31-AN). Also shown in outline, representative of all three views, is the area of ​​the active cell surface (3.28) and the area covered by the gas diffusion layer (3.09) (GDL) of the fuel cell membrane electrode assembly (MEA).

[0065] The gas diffusion layers (3.09) of the MEA (only shown in Fig. 3-middle) are slightly larger than the electrochemically active cell area (3.28), since they usually represent the adhesive surface of the polymer membrane with the plastic frame surrounding the polymer membrane, hereinafter referred to as the subgasket (see Fig. 4), overlaps. This means that the GDL is characterized by a peripheral edge that is inert to the fuel cell reaction and can typically be 1-3 mm wide.

[0066] These geometric features at the periphery of the active cell surface are of particular importance for understanding the conditions. They are Fig. 4 as a section in the xz-plane of the coordinate system (4.40) and are therefore shown here in more detail using Fig. 4 explains:

[0067] There ( Fig. 4) shows a section of the structure of a state-of-the-art PEM fuel cell. It depicts the proton-conducting polymer membrane (4.05), which is coated on both sides with a catalyst material (not shown) (the electrodes) in the area of ​​the active cell surface and covered with gas diffusion layers (GDLs), which are often made of carbon fiber felt. The polymer membrane (4.05) is held at its edge by a so-called subgasket frame (4.35). The zone (4.12), in which the subgasket frame (4.35) is overlapped by the GDLs (4.09-AN) and (4.09-KA), is electrochemically inactive and partially rests on the edge zone (4.34), which is often designed as a boundary web of the flow field. The anode-side GDL is designated (4.09-AN) in the figure, and the cathode-side GDL is designated (4.09-KA).

[0068] The described structure consisting of polymer membrane, catalyst, GDLs, and subgasket frame is collectively referred to as a “membrane electrode assembly” (MEA).

[0069] This MEA is flanked on both sides - top and bottom, here on the cathode and anode sides of the MEA shown - by two bipolar plates: the bipolar plate (4.33-KA), which is arranged adjacent to the cathode-side GDL (4.09-KA), and the bipolar plate (4.33-AN), which is arranged adjacent to the anode-side GDL (4.09-AN).

[0070] Also in Fig. 4 shows in section cathode- and anode-side flow field channels (4.06-AN, 4.06-KA), as well as cooling flow field channels (4.06-COOL) and, by way of example, flow field webs (4.29) of the reaction flow fields, wherein the aforementioned flow field webs (4.29) and edge zone webs (4.34) are parts of the cathode-side (4.02) and anode-side (4.17) interconnector plates or bipolar plate half-shells, which are each joined in a common joining plane (4.16) in a suitable manner with respect to the environment and with respect to adjacent operating media fluid spaces and together form a bipolar plate (4.33-AN) or (4.33-KA). The sealing of the functional fluid spaces of the fuel cell, which are supplied with the operating media, against each other or to the outside is usually achieved by suitably arranged elastomer seals (4.11).

[0071] In the following, after this insertion, the explanation of Fig. 3, also using references to Fig. 4, continued: In the Fig. 3 -Top view right- the space of the bipolar plate through which the cooling fluid flows, i.e. the cooling flow field, is shown in grey between the inlet (3.30-COOL) and outlet port (3.31-COOL) of the cooling flow field.

[0072] This space, or rather its shape and its channels (3.06-COOL), results in a bipolar plate formed from half-shell elements, e.g. sheet metal forming parts, e.g. from a hydroforming process, by combining the cavities that arise inside the (analogous to 4.33) joined half-shells by forming the external reaction gas flow fields (or interconnector plates, analogous to (4.02) or (4.17)) as a "negative" of the same.

[0073] In the illustrated Fig. 3 - Top view right - when exposed to a cooling fluid flow, this essentially results in a parallel flow of the cooling fluid across the active cell surface from the inlet port (3.30-COOL) to the outlet port (3.31-COOL). Due to the requirement to design the edge zone (3.34), (4,34) as an edge web in the outer flow field wider than the other webs of the reaction flow fields (4.02) in order not to impair the uniformity of the electrochemical reaction along parallel reaction flow field channels (4.06-AN, 4.06-KA), which would be adversely affected by electrochemically inactive zones in the catchment area of ​​such reaction flow field channels, cooling channels (4.04) with a significantly larger hydraulic diameter than the other "standard" cooling channels (4.06-COOL) in the active cell surface area are created in the inner cooling flow field below these edge webs.

[0074] Therefore, a comparatively higher flow of cooling fluid occurs through the cooling channels (4.04) located below the edge region webs (4.34) or formed by the edge region webs than in the narrower cooling channels (4.06-COOL) formed by the flow field webs (4.29) in the active cell area. However, since in the electrochemically inactive zone (4.12) a lower area-specific waste heat from the fuel cell reaction is lost via the edge region webs (4.34) because only part of this zone is electrochemically active, the overall result here (4.04) is a bipolar plate area-specifically increased cooling fluid mass flow with a simultaneously reduced absolute heat transport capacity.

[0075] This reduces the efficiency of the fuel cell system, since a disproportionate amount of drive energy must be expended for the cooling water pump to achieve this suboptimal cooling fluid mass flow rate under the edge webs, because at the same time the cooling channels (4.06-COOL) formed by the flowfield webs (4.29) must be sufficiently supplied with cooling fluid for local heat dissipation if the risk of hotspot formation is to be limited.

[0076] In order to achieve a uniform electrochemical reaction in the area of ​​the active cell surface with high local efficiency, it would therefore be desirable to present a bipolar plate that is suitable for absorbing reaction gases with lower or no humidification compared to the state of the art, in particular low or no humidification of the cathode gas, and yet to supply the fuel cell MEA locally with reaction gases of suitable local humidification.

[0077] Furthermore, it would be desirable if this bipolar plate were also suitable for conducting the cooling water to dissipate the resulting waste heat evenly past the active cell surface, minimizing or even eliminating parasitic cooling fluid flows at the edge of the active cell surface - by means of cooling channel type (4.04) -, with a comparatively lower overall cooling contribution.

[0078] The object of the invention is to address these two points and to describe bipolar plates according to the invention for fuel cells, wherein a fuel cell equipped with bipolar plates according to the invention, which is supplied with at least one dry or only partially humidified reactant-containing supply gas, achieves a higher integral voltage efficiency and / or lower integral losses due to cooling fluid pump drive power under comparable operating conditions than fuel cells equipped with bipolar plates according to the prior art.

[0079] This object is achieved by a bipolar plate according to the invention, which has the features specified in claim 1. Advantageous developments of the invention are the subject of the dependent subclaims.

[0080] The present invention initially takes up the idea that water is produced as a reaction product from hydrogen and oxygen during the electrochemical fuel cell reaction—water synthesis. With a suitable local temperature and humidity level of the cathode gas stream flowing past the MEA, the product water formed on the cathode side is quite capable of maintaining the polymer membrane at a suitable moisture level through back diffusion into the membrane body, thus preventing local drying out.

[0081] This requires, with reference to the run length parameter L, a steady, successive increase of the local gas temperature along a reaction flow field channel, especially in the cathode-side reaction flow field channels in the region of the active cell area, according to the water absorption capacity of the successively saturating cathode gas flow and according to the product water available through the reaction.

[0082] Since the local gas temperature is essentially determined by the local temperature of the flow field channel walls due to the low absolute heat capacity of a gas, it is desirable to route the cooling fluid that tempers the flow field channel walls (and thus controls the flow field channel wall temperature), or the cooling flow field channels, in the region of the active cell area as largely parallel as possible to the reaction flow field channels. In this context, "largely parallel" means a parallel channel layout of cooling and reaction flow field channels in the region of the active cell area over at least 60% of the respective channel length in the region of the active cell area, preferably more than 90%, more preferably more than 98%, and most preferably 100%. The reaction flow field channels and the cooling flow field channels therefore run directly adjacent and synchronously in the region of the active cell area.This is achieved by the geometric design of a bipolar plate according to the invention in accordance with the main claim and, where applicable, the dependent subclaims. Illustrative examples of synchronously meandering reaction and cooling flow field channels in the region of the active cell surface are shown, for example, in . Fig. 5 and Fig. 7 shown.

[0083] Deviating from the prior art, in which the supply ports of the bipolar plate are generally arranged next to one another, and in which the run length parameters L of adjacent anode- and cathode-side flow field channels, measured from the entry of the respective channel into the active cell area, differ, in some cases considerably, at almost all points on the active cell area, a bipolar plate according to the invention has a port arrangement and a hydraulic connection of the ports to the associated flow fields, in which the reaction fluid distribution structure geometry and the cooling fluid distribution structure geometry, or the associated fluid flows, are preferably, at least in regions, successively coupled into or out of a common rod, a main rod (5.15), for the purpose of parallelizing the flow directions of the functional operating media (anode gas, cathode gas, cooling fluid) and, if necessary, also for setting the individually desired run length parameters L.

[0084] The invention is explained below, analogously to the prior art above, also with reference to further figures. Fig. 5 Representation analogous to Fig. 3 using the example of a bipolar plate according to the invention Fig. 6 Schematic representation of the ports for the operating media and the inventive interaction of these ports with the associated main line when coupling or decoupling the operating media into this respective main line Fig. 7 Section of a bipolar plate according to the invention and 3D view of the anode side (bottom right) and cathode side (top left) using the example of a cathode input port arranged at the front of the main strand Fig. 8 Detail of a bipolar plate according to the invention for exemplary illustration of the elements “flux breaker” and “spillover stage set”. Fig. 9 Schematic representation of a bipolar plate according to the invention and 3D view of the anode and cathode sides using the example of a cooling fluid outlet port arranged at the front of the main strand.

[0085] Unless otherwise indicated in the text, corresponding parts in all figures are provided with the same reference numerals after the heading, and where appropriate, with additional suffixes after the reference numerals, separated from the reference numerals by a hyphen. However, the reference numerals are not to be understood as limiting the scope of the subject matter protected by the claims; they serve merely to facilitate the understanding of the claims and the invention.

[0086] In the following, the invention and advantageous developments thereof, but without limitation thereto, are explained using some basic principles and basic features and some examples:

[0087] In the following figures, the symmetry axes A (section 5.36 and analogues) of the active cell surface are always arranged transversely to a main strand direction (section 5.19 and analogues), and the symmetry axes B (section 5.37 and analogues) are always arranged parallel to a main strand direction. This is without limiting an arrangement according to the invention to such an arrangement: It goes without saying that other arrangements of the aforementioned symmetry axes to main strand directions can also be represented and are also in accordance with the invention. The general main flow direction of the operating media in the area of ​​the main strands runs essentially parallel to the main strand direction before an operating medium is coupled out of a main strand or after an operating medium is coupled into a main strand.

[0088] The schematic arrangement of fluid conduction structures or operating fluid flows on or in a bipolar plate according to the invention, here in particular the fluid conduction geometries, whose features during operation provide for the sequential coupling of the operating media into a main strand and the largely parallel guidance of the operating media in the area of ​​the active cell surface - here represented by a meandering of the continuation of the main strand geometry in the area of ​​the active cell surface - is shown by way of example in Fig. 5 shown.

[0089] The flow of the media on or in an exemplary bipolar plate according to the invention (5.33), here a bipolar plate for a PEM fuel cell operated with hydrogen and air with water as the liquid cooling medium with a four-channel serpentine flow field on the anode and cathode side and resulting in a parallel 3-channel serpentine flow field for the cooling medium flowing inside the bipolar plate, is shown schematically in three views from the z-direction of the coordinate system (5.40), simultaneously views from one bipolar plate side, here from the cathode flow field side. Fig. 5. This is shown with reference to the Fig. 5 defined right-handed Cartesian coordinate system (5.40).

[0090] There ( Fig. 5), each colored in gray in front of the outline of the bipolar plate, the areas exposed to or flowed through by the respective operating medium during operation are shown next to each other: cathode gas or cathode flow field left view, cooling fluid or cooling flow field central view and anode gas or anode flow field right view.

[0091] At the cooling flow field -in Fig. 5 in the middle plan view - the area acted upon by the cooling fluid is not necessarily identical with the significantly flowed through areas of the cooling flow field, since some acted upon areas have a "dead zone character" without any significant flow during operation without further modifications according to the invention (e.g. finger web zones, (5.18), see below).

[0092] In Fig. 5 -left view- the space on the cathode side through which the reaction fluid flows is shown in grey, i.e. the cathode flow field channels (5.06-KA) and the cathode inlet (5.30-KA) and outlet ports (5.31-KA) as well as the edge zone surrounding the cathode flow field or the edge webs (5.34).

[0093] Also shown here are the two main branches, the inlet main branch (5.15-E) and the outlet main branch (5.15-A), located at the top and bottom of the respective bipolar plate (bipolar plate view), where the operating media are coupled in and out from their respective ports into a parallel flow pattern. These main branches (5.15-E and 5.15-A) are abstractly comparable to the conventional connection zones from port to flow field. Fig. 1, there (1.32-E or 1.32-A for inlet and outlet areas).

[0094] In the Fig. 5 - middle view - colored gray, as already outlined, is the inner space formed by the outer half-shells of the bipolar plate, which is wetted by the cooling fluid during operation. Analogous to the cathode gas fluid, the cooling fluid is coupled into and out of the main strands (5.15-E and 5.15-A, respectively) from a cooling fluid inlet port (5.30-COOL), here by rotating it 90° relative to the main strand direction (5.19). The meandering cooling channels of the cooling flow field (5.06-COOL) run downstream of the coupling point and upstream of the coupling point, and in the area of ​​the active cell surface (5.28), parallel to the anode and cathode flow field channels (5.06-AN), (5.06-KA). The cooling fluid is finally extracted from the cooling fluid outlet port (5.31-COOL).

[0095] In the Fig. 5 - Right view - The area of ​​the anode side of the bipolar plate through which anode fluid flows during operation is shown in gray, including the anode flow field channels (5.06-AN), the anode-side inlet port (5.30-AN), and the anode-side outlet port (5.31-AN). Also shown, representative of all three views, are the area of ​​the active cell surface (5.28) and the area covered by the gas diffusion layer (5.09) (GDL) of the fuel cell membrane electrode assembly (MEA). The connection of the anode ports (5.30-AN, 5.31-AN) to the respective adjacent main string (5.15-E for the input main string or 5.15-A for the output main string) is made laterally towards the main string direction with a 90° deflection, with which the four anode channels coming from the respective port pivot towards the main direction of the respective directly adjacent main string (5.15-E or 5.15-A), the main string direction (5.19), or parallel to it.

[0096] In the Fig. 5 - right view - the flow area on the anode side of the bipolar plate is shown in gray, including the anode flow field channels or the anode flow field (5.06-AN), the anode-side inlet port (5.30-AN), and the anode-side outlet port (5.31-AN). Also shown are the active cell area (5.28) and the area covered by the gas diffusion layer (5.09) (GDL) of the fuel cell membrane electrode assembly (MEA). The connection of the anode ports (5.30-AN, 5.31-AN) to the directly adjacent main string (5.15-E or 5.15-A) is made laterally towards the main string direction with a 90° deflection, with which the four anode channels coming from the port pivot towards the main direction of the directly adjacent main string, the main string direction (5.19).

[0097] In the present Fig. 5, the two main strands (5.15-E and 5.15-A), or the main strand direction (5.19) are arranged parallel to the symmetry axis B (5.37) and orthogonal to the symmetry axis A (5.36) of the active cell surface (5.28). The naming in Fig. 5 assumes, for example, that all three operating media - fuel fluid, oxidizer fluid and cooling fluid - are conducted in co-flow.

[0098] Of course, it is obvious to the skilled person that during operation all relative fluid flow types - co- and counter-flow (or co- and counter-flow) of the three operating media in all conceivable permutations - with the Fig. 5 present, or similar, geometry are possible and any combinations of input and output ports arranged according to this scheme represent technical developments of the invention.

[0099] In the reference to such further developments, main lines which are directly hydraulically connected to the directly adjacent inlet ports of at least two media are referred to as input main lines, and main lines which are directly hydraulically connected to the directly adjacent outlet ports of at least two media are referred to as output main lines.

[0100] “Directly hydraulically connected” means that the hydraulic connection between a port and a main strand does not essentially occur via the fluid conduction structure of the flow field in the area of ​​the active cell surface.

[0101] In Fig. 5, a bipolar plate (5.33) according to the invention is shown from the cathode side view, in the sense of three side-by-side views from the z-direction of the coordinate system (5.40) analogous to the representation in Fig. 3. This for the flow fields of the three operating media ( Fig. 5 left: oxidizer fluid, Fig. 5 Middle: Cooling fluid, Fig. 5 right: fuel fluid). The role of the main strands is described in more detail below.

[0102] Shown in Fig. 5, or with reference to the three supervisions presented there (hereinafter referred to as “ Fig. 5") is - per plan view - an inlet main line (5.15-E), which is directly hydraulically connected to a directly adjacent first cathode inlet port (5.30-KA) by first fluid distribution structures of this main line. Further, Fig. 5 a first cooling fluid inlet port (5.30-COOL), which is also arranged directly adjacent to the inlet main line and is directly hydraulically connected to the main line (5.15-E) by second fluid distribution structures of this main line.

[0103] In the further course of the main strand (5.15-E), the channels of the aforementioned first and second fluid distribution structures of the main strand are arranged parallel to each other at least in some areas.

[0104] Finally, a first fuel gas inlet port (5.30-AN) is shown, which is also arranged directly adjacent to the main line (5.15-E) and is hydraulically connected to this main line (5.15-E) by third fluid distribution structures of this main line.

[0105] In the further course of the main strand (5.15-E), the channels of the aforementioned first, second and third fluid distribution structures of the main strand are arranged parallel to each other at least in some areas.

[0106] In the geometric progression of the main strand (5.15-E), the channels (5.06-KA), (5.06-COOL), (5.06-AN) of the aforementioned first, second, and third fluid distribution structures of the main strand (5.15-E) are thus successively formed, at least in some regions, parallel to one another. The main strand (5.15-E) geometrically ends at an imaginary position / line (5.23-E) at which the channels (5.06-KA), (5.06-COOL), (5.06-AN) of the aforementioned first, second, and third fluid distribution structures of the main strand (5.15-E) are essentially parallel, preferably exclusively parallel, to one another, or the normal vectors of the respective channel cross-sections are essentially parallel to one another. Typically, the direction of these normal vectors then corresponds to the corresponding main strand direction (5.19) or runs parallel to it.

[0107] An angular deviation of these normal vectors from one another of max. 20°, preferably max. 10°, particularly preferably < 3°, fulfills the inventive requirement of “essentially existing parallelism” both in the area of ​​an input main strand and in the area of ​​an output main strand.

[0108] Further presented in the Fig. 5 is the active cell area of ​​the bipolar plate (5.28), which is formed by the respective flow fields of the three operating media. At the position of the input main strand (5.15-E) point-symmetrically opposite the intersection point of the symmetry lines (5.36), (5.37), an output main strand (5.15-A) is arranged, which in turn geometrically begins at an imaginary position / line (5.23-A).

[0109] In the geometric course of the output main branch (5.15-A), starting from the position (5.23-A) towards the adjacent ports, the first, second and third fluid distribution structures of the output main branch (5.15-A) initially run, which are formed analogously to the first, second and third fluid distribution structures of the input main branch (5.15-E), such that the channels (5.06-KA, 5.06-COOL, 5.06-AN) of the associated first, second and third fluid distribution structures of the output main branch are aligned substantially parallel, preferably exclusively parallel, to one another, or the normal vectors of the respective channel cross-sections are substantially parallel to one another.

[0110] As a rule, the direction of these normal vectors corresponds to the corresponding main strand direction (5.19) or runs parallel to it, analogous to the geometric situation of the input main strand (5.15-E).

[0111] Further presented in Fig. 5 is a first fuel gas outlet port (5.31-AN) which is arranged directly adjacent to the outlet main line (5.15-A) and is hydraulically connected to this main line (5.15-A) by third fluid distribution structures of this outlet main line.

[0112] In the further course of the output main branch (5.15-A) towards the oxidizer outlet port (5.31-KA), after the decoupling of the third fluid distribution structures, which carry hydrogen-containing fluid during operation, from the output main branch (5.15-A) towards the fuel gas outlet port (5.31-AN), the channels of the first and second fluid distribution structures of the output main branch (5.15-A) are arranged parallel to one another at least in some regions, wherein the output main branch (5.15-A) is essentially still formed by the first and second fluid distribution structures of the output main branch after the geometric decoupling of the third fluid distribution structures, which carry fuel gas during operation, towards the fuel gas outlet port.

[0113] Further presented in Fig. 5 is a first cooling fluid outlet port (5.31-COOL) which is arranged directly adjacent to the outlet main line (5.15-A) and is hydraulically connected to this main line (5.15-A) by second fluid distribution structures of this outlet main line which carry cooling fluid during operation.

[0114] In the further course of the output main line (5.15-A) towards the oxidizer output port (5.31-KA), after the decoupling of the second fluid distribution structures, which carry cooling fluid during operation, from the output main line (5.15-A) towards the cooling fluid output port (5.31-COOL), the output main line is essentially still formed by first fluid distribution structures of the output main line (5.15-A), which carry oxygen-containing fluid during operation, via which the output main line (5.15-A) is directly hydraulically connected to a directly adjacent oxidizer output port (5.31-KA).

[0115] “Directly adjacent” in the sense of the invention is understood to mean a minimum distance between the edge of a port closest to the main line and the fluid guide structures of the associated main line hydraulically connected to the aforementioned port of at most 100 mm, preferably less than 50 mm, particularly preferably less than 10 mm, even more preferably less than 3 mm.

[0116] A further essential characteristic of the first, second, and third fluid distribution structures of a main line, which are individually connected to three adjacent ports (of the three operating media), is that these fluid distribution structures are essentially fluid-tightly separated or sealed from one another. A leakage rate of <100 standard ml / minute between two fluid-tightly separated fluid distribution structures at nominal operating pressure, preferably <20 standard ml / minute, particularly preferably <5 standard ml / minute, and even better <1 standard ml / minute, fulfills the inventive requirement of "essentially existing fluid tightness."

[0117] Depending on the geometric design of a bipolar plate according to the invention or an associated membrane electrode assembly (MEA), parts of a main strand can also belong to the projection area of ​​the active cell surface (5.28) onto the bipolar plate and thus participate in energy generation. This applies in particular to fluid distribution structures with which a main strand is directly hydraulically connected to a reaction fluid port in the immediate vicinity of the active cell surface (5.23-E or 5.23-A). Such geometric designs are also according to the invention.

[0118] Structurally, the geometrically parallel coupling or decoupling of two or three operating media from adjacent ports into at least one main branch (not shown in the figure) - in the sense of at least partially "simultaneous" coupling from both sides, e.g., right and left, of a main branch - is also feasible and just as inventive as the parallel or successive coupling or decoupling of two operating media into two sub-branchs and the combining of sub-branchs into a main branch (also not shown in the figure). However, such arrangements are less advantageous than geometric solutions that allow a successive coupling or decoupling of the three operating media into a single main branch. The terms "coupling or decoupling" and "input or output" are used synonymously in this description.

[0119] With a bipolar plate geometry according to the invention, it is possible, for example, to conduct all three functional operating media (anode gas, cathode gas, cooling fluid) in co-flow with essentially locally comparable run-length parameters L, and also with locally complementary run-length parameters (relative to the total run-length L, in countercurrent flow). Of course, all conceivable co- and counter-flow combinations of the operating media in this geometry are also in accordance with the invention and, depending on the application, particularly suitable.

[0120] The inventive arrangement of the input and output ports (5.30, 5.31) of the three operating media (anode fluid, cathode fluid, cooling fluid) around a directly adjacent main branch (5.15-E or -A) is basically possible in several arrangements / permutations but is particularly useful in some arrangements (see description of Fig. 6). Particular advantages of a bipolar plate geometry according to the invention arise in particular from the setting of a significant temperature gradient between the cooling fluid inlet and outlet ports of preferably 5-80°C, preferably 10-50°C, particularly preferably 20-40°C, and suitably adapted stoichiometry and inlet humidification for the reaction media.

[0121] Further relevant for a bipolar plate according to the invention or shown in Fig. 5 are edge zones (5.34) which are arranged in the edge area of ​​the active cell surface (5.28) and are at least partially electrochemically inactive, since here, as already mentioned Fig. 4, the gas diffusion layer or GDL (5.09) extends over the subgasket, whereby cooling flow field edge channels with a comparatively enlarged hydraulic diameter are formed in the area of ​​the cooling flow field.

[0122] To reduce or suppress parasitic cooling fluid flows, further geometric elements, referred to below as "flux breakers" (5.13), are shown, which geometrically interrupt these cooling flow field edge channels. These are, for example, indentations in the area of ​​the edge web, which interrupt the edge web or reduce its cross-section. In the present figure, two flux breakers (5.13) are arranged in the edge area and on the axis of symmetry (5.36). The arrangement on the axis of symmetry is particularly preferred; however, depending on the application, a point-symmetrical arrangement of flux breakers with respect to the intersection point of the axes of symmetry A and B (5.36) and (5.37), or an arrangement offset parallel to the axis of symmetry (5.36) are also expedient and in accordance with the invention.

[0123] In this example, these are constructed in such a way that the two half-shells forming the bipolar plate have at least some sections of at least positive direct contact between the half-shells, whereby the hydraulic diameter of the edge channels formed in the cooling flow field is largely reduced at this contact point, preferably reduced to almost zero. Another possibility, not shown here, for reducing or interrupting the cooling fluid flows in this edge region is, for example, the arrangement of a "plug" as a "flow breaker" in a comparable position inside the bipolar plate component, e.g., by gluing a plastic plug into the space between the half-shells.

[0124] For the purposes of this invention, “largely reduced” means a reduction of the hydraulic diameter of the cooling channel type (4.04) in the edge region at the “flow breaker position” by at least 50%, preferably at least 70%, particularly preferably at least 90%, most particularly preferably >99%.

[0125] If flow breakers (5.13) are used that completely interrupt the cooling fluid flow under an edge web - in cooling channels of type (4.04) -, significant flow in the cooling flow field from the corresponding inlet to the outlet port only takes place along the meandering cooling flow field serpentines - in cooling channels of type (5.06-COOL) and, with additional use of spillover stage sets (5.14), to a lesser extent under the finger webs (5.18) and in the spillover stage set area (5.14), see below.

[0126] Further relevant or presented in Fig. 5 are so-called "finger bridges" (5.18) of an external (reaction) flow field. A finger bridge acts as a delimiting channel wall of an external reaction flow field at positions where the outermost channel of a meandering channel bundle undergoes a 180° deflection, provided that the deflected channel subsequently continues away from itself by only a single bridge. If only a single-channel serpentine flow field is present, only finger bridges occur at deflections, for example.

[0127] Finger webs (5.18) in a bipolar plate according to the invention, which is formed from two half-shells, occur synchronously in both (reaction) flow fields arranged on the outer sides of the bipolar plate—that is, in the anode-side and the cathode-side flow fields—due to the principle of the bipolar plate. This results in a "dead end" or a cooling channel that ends "blindly" for the inner cooling flow field, which, due to the half-shell design, is determined by the complementary geometry of the outer reaction flow fields.

[0128] In practice, there are two problems with such "cooling channel dead ends": Firstly, during operation, the waste heat dissipation in such areas essentially no longer takes place through forced convection with the cooling fluid, but mainly through heat conduction of the cooling fluid "standing" in the "dead end" - which can lead to an undesirable temperature profile in the area of ​​the finger webs (5.18).

[0129] Furthermore, in case of improper handling or the occurrence of gas bubbles in the cooling water (e.g. due to leaks), there is a risk that large gas bubbles could form stationary below the finger webs, i.e. in the aforementioned "cooling channel dead ends", which would lead to a significant further reduction in the waste heat transport of the fuel cell reaction heat from the area of ​​the finger webs.

[0130] Further presented in Fig. 5 is therefore a "spillover step set" (5.14) according to the invention, which is designed here as a straight extension or continuation of a finger bridge (5.18) of an outer flow field in the form of lowered steps, with a step height typically corresponding to 10-70% of the local channel / finger bridge height, preferably 10-40% of the local finger bridge height, preferably on the side of the cathode flow field.

[0131] A spillover stage set is thus characterized by at least one geometric extension or at least one geometric branch from a finger bridge in the form of one or more lowered stages, which are arranged in at least one reaction flow field channel crossed by the aforementioned spillover stage set. In a typical embodiment, a spillover stage set represents a sequence of lowered stages in all reaction flow field channels crossed by the aforementioned spillover stage set, starting from the end of a finger bridge (5.18) up to an edge bridge (5.34).

[0132] As a result, by forming a spillover stage set into at least one bipolar plate half-shell inside the bipolar plate, i.e., in the cooling flow field, a defined hydraulic connection is formed between the cooling flow field zone within the aforementioned finger web and the cooling flow field zone within the aforementioned edge web. This defined hydraulic connection functions as a defined hydraulic "short circuit" with a comparatively significantly reduced hydraulic diameter between the cooling flow field zone within a finger web and the cooling flow field zone within an edge web.

[0133] In this context, “significant reduction of the hydraulic diameter” is understood to mean a reduction of at least 10%, preferably more than 30%, particularly preferably more than 50%, even more preferably more than 80%, compared to the hydraulic diameter of a cooling channel meandering with the reaction flow field channels - cooling channel type (5.06-COOL).

[0134] The formation of spillover step sets on the anode-side interconnector plate or half-shell of the bipolar plate is particularly expedient. Further variants according to the invention include the formation of spillover step sets on both the anode-side and the cathode-side interconnector plate or half-shell of the bipolar plate, as well as solely on the cathode-side interconnector plate or half-shell of the bipolar plate.

[0135] In a particularly preferred embodiment, spillover step sets are designed in the sense of a lowered direct extension of a finger bar, as shown, for example, in Fig. 5 or Fig. 7. In another preferred embodiment (see Fig. 10), one or more spillover step sets extend at an angle (10.38) according to the invention from the end (10.39) of a finger web (10.18) in the direction of adjacent cooling channels, preferably up to the circumferential edge zone (10.34).

[0136] Such an embodiment according to the invention is described in Fig. 10 and described in more detail below. The purpose of such spillover stage sets (5.14) is twofold in addressing the above-mentioned problem: Firstly, during operation, the zone below a finger web (5.18) of the outer flow fields can be flowed through with cooling fluid in a defined and limited manner, which then also allows waste heat transport of the reaction heat through forced convection with the cooling fluid.

[0137] On the other hand, with suitable operation, spillover stage sets (5.14) ensure that no stationary gas bubbles, e.g. air bubbles, can collect in the aforementioned "dead ends", regardless of whether the "dead end property" is eliminated when using spillover stage sets: In particular, if the cooling circuit is occasionally subjected to pressure surges and the bipolar plate or the bipolar plate stack is arranged relative to the gravity vector in such a way that the direction of the spillover stage sets promotes, or at least does not hinder, an "ascent" of gas bubbles against the gravity vector.

[0138] Avoiding the formation of stationary gas bubbles in the cooling flow field in the area of ​​the active cell surface is important because the formation of standing gas accumulations, especially below finger bridges (5.18), could further impair the waste heat removal from the electrochemical reaction in this area, even leading to the formation of so-called material-damaging hotspots.

[0139] The inventive reduction of the hydraulic diameter for the cooling fluid in the area of ​​spillover stage sets, when guided from the finger web end (10.39) to the edge area (10.34), has the function of limiting a direct outflow of cooling fluid towards the edge area or to the cooling fluid outlet port, in the sense of a defined cooling fluid short circuit, to a level that is harmless for the system efficiency.

[0140] In conjunction with flow breakers that completely or partially block the cooling fluid, it is also suitable for matching the specific reaction heat dissipation via the peripheral areas to the heat dissipation via the cooling fluid channels following the meandering main line. This contributes to reducing the cooling fluid pump power and thus increasing system efficiency while maintaining the same cooling result.

[0141] As already outlined above, an inventive arrangement of the input and output ports of the three operating media (anode fluid, cathode fluid, cooling fluid) around a directly adjacent main strand is basically possible in several arrangements / permutations but is particularly useful in some arrangements:

[0142] This will be explained below using Fig. 6 is explained by way of example, if necessary with reference to the Fig. 6. This example assumes that all three operating media move in cocurrent / coflow, i.e., parallel and in the same flow direction, past the active cell surface of the BPP, and that all ports shown in the figure are input ports. The coupling of the operating media from the three directly adjacent input ports (6.30) to the three geometric port positions (6.21-A), (6.21-B), and (6.21-C) relative to the main strand (6.15) occurs according to the dashed arrows from the respective port positions.

[0143] This means that the coupling into the main strand (6.15) from position 6.21-A is carried out from the Fig. 6 port located below the main strand without deflection, and the coupling from positions (6.21-B) and (6.21-C) occurs by rotating 90° to the left onto the main strand (6.15) or in the direction of the main strand (6.19). Beyond, or in the figure above, the imaginary position (6.23), the main strand then transitions into the active cell area (not shown).

[0144] An arrangement not shown in the figure, in which position (6.21-A) is also arranged next to the main line like the other two positions, which also requires a 90° deflection of the inflowing fluids for coupling into the main line, represents another arrangement according to the invention of the directly adjacent ports relative to the associated main line.

[0145] Although all permutations are conceivable for the allocation of anode, cathode and cooling fluid to the respective port positions, some permutations involve increased design and manufacturing complexity and are therefore less preferable, although in accordance with the invention.

[0146] However, the following arrangements are particularly preferred (see Fig. 6): Position C: Anode gas port; Position B: Cooling fluid port; Position A: Cathode gas port Position C: Anode gas port; Position B: Cathode gas port; Position A: Cooling fluid port Position C: Cathode gas port; Position B: Anode gas port; Position A: Cooling fluid port

[0147] These arrangements are particularly preferred because they allow for a particularly simple geometric / structural coupling of the cooling fluid into the main line.

[0148] Regarding the inventive decoupling of operating media from the output main line to the output ports (not shown in the figure), all permutations are conceivable, but symmetrical arrangements (analogous to the input main line) are particularly preferred. Therefore, the following arrangements are also particularly preferred: Position C: Anode gas outlet port; Position B: Cooling fluid outlet port; Position A: Cathode gas outlet port Position C: Anode gas outlet port; Position B: Cathode gas outlet port; Position A: Cooling fluid outlet port Position C: Cathode gas outlet port; Position B: Anode gas outlet port; Position A: Cooling fluid outlet port

[0149] Also not depicted is the inventive "mixing" of input and output ports relative to a directly adjacent main line. Analogous to the above, the following arrangements are particularly preferred: Position C: anode gas outlet port, Position B: cooling fluid inlet port; Position A: cathode gas inlet port Position C: Anode gas inlet port, Position B: Cooling fluid outlet port, Position A: Cathode gas outlet port Position C: Anode gas outlet port, Position B: Cooling fluid outlet port, Position A: Cathode gas inlet port Position C: Anode gas inlet port, Position B: Cooling fluid inlet port, Position A: Cathode gas outlet port

[0150] The following preferred variants mentioned above: Position C: Anode gas (inlet or outlet) port; Position B: Cooling fluid (inlet or outlet) port; Position A: Cathode gas (inlet or outlet) port in all conceivable permutations of inlet and outlet at positions (A, B, C) are particularly advantageous because the coupling of the cooling fluid, e.g. by forming a wide pocket, which in the area of ​​a sealing zone, e.g. via transverse steps of reduced height (7.27) analogous to the aforementioned spillover stage sets (see Fig. 7) on the anode-side interconnector plate, or the half-shell forming the anode-side interconnector plate, without adversely affecting the cathode-side channel structure of the main strand.

[0151] The other preferred variants Position C: Anode gas (inlet or outlet) port; Position B: Cathode gas (inlet or outlet) port; Position A: Cooling fluid (inlet or outlet) port in all conceivable permutations of inlet and outlet at positions (A, B, C) are particularly advantageous because they provide for the coupling of the cooling fluid at the front side of the main strand, which is also easy to implement in terms of design and manufacturing technology, but also requires some effort in sealing the cathode or anode gas chamber against the cooling fluid ports, for example by creating a section through transverse steps (9.25) ( Fig. 9) partially raised and / or “floating” sealing groove, comparable to (7.27).

[0152] The decoupling of the operating media from a main line is expediently, but not necessarily, carried out in the reverse order to the coupling into a main line, so that a point-symmetrical pattern or port layout is preferably produced on the bipolar plate according to the invention.

[0153] In the following, Fig. 7, if necessary with reference to the Fig. An exemplary geometric solution for coupling the operating media into the main line is described in the right-handed Cartesian coordinate system (7.40) specified in Figure 7, without limiting the scope of the invention to this specific representation. The uncoupling of the operating media or their fluid conducting structures from the main line at the outlet ports, which is not shown graphically, can be carried out geometrically and structurally in principle analogous to the coupling, but in the reverse order.

[0154] In Fig. Figure 7 shows views of the anode and cathode sides of a section of a bipolar plate according to the invention, which is assembled from 0.1 mm thick hydroformed stainless steel half-shells (anode- and cathode-side interconnector plates) using a laser welding process. The top left shows the cathode-side view; the bottom right shows the anode-side view of the same bipolar plate section.

[0155] In detail, Fig. 7 shows the inlet ports for the anode fluid (7.30-AN), the cathode fluid (7.30-KA), and the cooling fluid (7.30-Cool). Therefore, in this example, without limiting the scope of the invention to this embodiment, it is assumed that all three operating media are flowing in cocurrent or coflow. The present geometry is, of course, also suitable for other relative flow directions, for example, countercurrent or counterflow of one medium to the other two operating media.

[0156] Further presented in Fig. 7 is an inlet main branch (7.15-E) and a main branch direction (7.19), with the respective operating media being geometrically coupled to the main branch from their respective ports (7.30-AN, 7.30-KA, 7.30-COOL) as shown in the figure by the corresponding fluid guidance structures. Due to the half-shell design, the cooling flow field is formed inside the externally visible webs.

[0157] The cooling fluid is coupled into the interior of the anode-side interconnector plate / half-shell of the bipolar plate below transverse steps (7.27) molded into the anode-side half-shell. This is analogous to the cooling fluid routing under "spillover step sets" of a spillover step set height corresponding to half the height of the anode flow field channel. These half-height transverse steps are themselves geometrically arranged below an elastomer seal (not shown), in the form of a sealing groove or sealing base. The various operating media spaces of the bipolar plate and the associated ports are also sealed from each other and the environment by suitable elastomer seals made of FKM (not shown).

[0158] Also shown in the Fig. 7 are "spillover" step sets (7.14), which run from the finger webs to the edge zone or edge web (7.34) and are each formed at half the flow field channel height, as well as "flow breakers" (7.13), which are arranged on both half-shells of the bipolar plate in the same position and symmetrically to the joining plane and hermetically interrupt the cooling fluid flow, or the hydraulic connection, along the respective edge area (7.34).

[0159] Finally also shown in Fig. 7 is the position of the symmetry axis B (7.37) of the active cell area (7.28) shown with its outer edge in dashed lines and the imaginary boundary (7.23) at which the main strand merges into the active cell area.

[0160] In Fig. 8, if necessary with reference to the Fig. 8, a constructive solution according to the invention for the representation of "spillover stages" and "flow breakers" is described in detail by way of example, without limiting the claimed scope of the invention to this specific representation. Fig. 8 shows a section of the bipolar plate according to the invention from Fig. 7, here with a view of the cathode side of the bipolar plate, which, as usual, is formed from a cathode-side interconnector plate (8.02) and an anode-side interconnector plate (8.17) - both half-shells -, whereby the bipolar plate, or the cutout, is joined in the area of ​​the half-shell joining plane (8.16) shown in dashed lines.

[0161] There -in Fig. 8- Also shown is a cathode-side finger bridge (8.18), to which a "spillover" step set (8.14), here executed in approximately 30% of the channel height of the cathode flow field, is executed in the sense of a geometric extension, continuously to the next adjacent edge bridge or edge region (8.34).

[0162] From the cutout in the area of ​​the spillover stage set (8.14) and the flux breakers (8.13) it can be seen that a spillover stage set (8.14) is arranged only on the cathode-side half-shell (8.02) and that in the Fig. 8 both the cathode-side half-shell and the anode-side half-shell are formed with flux breakers (8.13) which, in the area of ​​the joining plane (8.17), hermetically seal the cooling channel (8.04) formed inside the edge area or the half-shell edge webs (8.34) in the area of ​​the flux breakers (8.13) by positive locking.

[0163] This also functionally prevents the flow of cooling fluid in this internal cooling channel (8.04) during operation. For illustrative purposes in Fig. 8 also named is a “standard” cooling channel of type (8.06-COOL)

[0164] In Fig. 9, if necessary with reference to the Fig. 9, a constructive solution for an inventive connection of a cooling port is shown as an example. Fig. Figure 9 therefore shows views of the anode and cathode sides of a schematic section of a bipolar plate according to the invention in the region of a main strand (9.15). In this schematic representation, the two anode- and cathode-side half-shells (9.17) and (9.02), respectively, which together form the bipolar plate, are shown with vertical channel walls, such as can be achieved, for example, by manufacturing the parts using metal 3D printing.

[0165] Top left in the Fig. Figure 9 shows the cathode-side view; the bottom right shows the anode-side view of the same bipolar plate section.

[0166] In detail, Fig. 9 shows the inlet ports for the anode fluid (9.30-AN), the cathode fluid (9.30-KA), and the outlet port for the cooling fluid (9.31-COOL). In this example, without limiting the scope of the invention to this embodiment, it is assumed or illustrated that the two reaction media (in this example: H2 / air) are conducted in co-flow (direct current) to each other, and the cooling fluid, in this example water, is conducted in counterflow (countercurrent) to the two reaction media. Therefore, the cooling fluid outlet port, together with the two reaction media inlet ports, is arranged directly adjacent to the main branch (9.15), more precisely, a main inlet branch according to the above-mentioned convention.

[0167] Particularly preferred according to the invention, but not shown here in the figure, is the parallel guidance of cooling fluid and cathode gas fluid on / in the bipolar plate in countercurrent to the anode gas fluid.

[0168] It goes without saying that all other permutations of cocurrent and countercurrent flow of the three operating media in a bipolar plate according to the invention can also be expedient and are in accordance with the invention, depending on the application.

[0169] Further presented in Fig. 9 is therefore a main branch (9.15) and a main branch direction (9.19), whereby the respective operating media are hydraulically coupled into and out of the main branch from their respective ports (9.30-AN), (9.30-KA), (9.31-COOL) following their individual fluid conduction structures (as shown in the figure). The main branch extends between the imaginary position (9.23), i.e., the edge of the active cell area (not shown), and the cooling fluid outlet port (9.31-COOL) located on the front side of the main branch. The cooling fluid is coupled out of the main branch through front-side openings (9.26) on the bipolar plate into the cooling fluid outlet port (9.31-COOL) located on the front side.

[0170] In order to connect the front-side openings (9.26) with the internal cooling flow field of the bipolar plate, it is expedient here to provide the circumferential sealing grooves (9.24), which seal the fluid spaces of the fuel cell from one another and from the MEA and the environment by means of an inserted elastomer seal made of silicone (not shown), with transverse steps (9.25) in the sealing zone in the area of ​​the front-side openings (9.26), which in the present case are designed on both half-shells at half the anode flow field channel height and form a transport path for the cooling fluid, or a cooling channel, between the port and the internal cooling flow field, under the seal (or the seal base).

[0171] The hydraulic connection of the anode inlet port (9.30-AN) and the cathode inlet port (9.30-KA), which are arranged adjacent to the main line, with the respective fluid conducting structures on the main line, or the coupling of the respective connection to the main line, is carried out structurally following the respective fluid conducting structures, from the side of the main line by means of a 90° deflection from the respective coupling port.

[0172] With appropriate geometric design of a bipolar plate according to the invention and suitable adaptation of the load conditions and operating conditions for the adjacent reaction media, such a bipolar plate is capable of receiving slightly or unhumidified operating media and of preparing them locally for the adjacent membrane electrode assembly (MEA) along the respective flow field channels and a suitable temperature gradient in such a way that local drying out of the polymer membrane is limited or avoided.

[0173] This is achieved while simultaneously limiting the energy required to remove liquid water from the reaction gas flow fields. This is made possible by a temperature along the reaction gas channels that steadily increases along the run length parameter L of a reaction channel (or, in the case of countercurrent / counterflow of the cooling fluid to a reaction medium, steadily decreases along the run length parameter L of a reaction channel). This can be combined with the welcome side effect that the volume flow to be pumped by the cooling fluid pump can be reduced without any significant loss of efficiency.

[0174] In Fig. 10, if necessary with reference to the Fig. 10, right-handed Cartesian coordinate system (10.40), shown is a section of a bipolar plate, which is formed from an anode-side half-shell (10.17) and a cathode-side half-shell (10.02), here joined at the common contact surface (10.16) by a high-temperature soldering process.

[0175] Also shown is an embodiment according to the invention of two spillover step sets (10.14), which are arranged at an angle (10.38), hereinafter referred to as "departure angle", of approximately 30° to the direction of travel (10.41) of a finger web (10.18), specifically starting from the end (10.39) of a finger web (10.18) towards an edge zone (10.34), specifically in such a way that the angle (10.38) is or will be formed by the main direction (10.41) of a finger web and the main direction (10.42) of a spillover step set (10.14).

[0176] For illustrative purposes, see the Fig. 10 are a cooling channel type (10.04), which is formed from the edge webs, and a "standard" cooling channel type (10.06-COOL) of the cooling flow field in the area of ​​the active cell surface. The cooling channel profile or cross-section inside the finger webs, outside of the spillover stage sets, essentially corresponds to the cooling channel profile or cross-section of a "standard" cooling channel type (10.06-COOL). Also shown for illustrative purposes in the Fig. 10 shown

[0177] In a particularly preferred embodiment, the angle (10.38) is less than 45°, particularly preferably less than 30°, and even more preferably less than 10°. An angle of 0° corresponds to a direct continuation of the finger bar (10.18) toward the edge zone (10.34).

[0178] In a further preferred embodiment not shown in the figure, a bipolar plate according to the invention has at least one spillover step set, even more preferably two or more spillover step sets, at at least one finger bridge of a reaction flow field at a departure angle > 5° to the direction of the associated finger bridge, wherein at least one direction of at least one spillover step set, in the sense of a direction vector, contains at least one vector component which runs parallel to the gravity vector and is opposite to the direction of the gravity vector.

[0179] In an advantageous embodiment of the invention, this vector component has a share of at least 10%, better more than 30%, even better more than 50%, particularly preferably more than 90%, of the amount of the associated spillover step set direction vector.

[0180] A directional component of a spillover stage set that is opposite to the gravity vector contributes to the design of ensuring that gravity, or the buoyancy of gas bubbles in a liquid, supports the removal of such gas bubbles from a finger-web zone. The combination of such a geometric arrangement with an operating mode that, at suitable intervals—at least once per day, preferably at least once per hour, even better at least once per minute—indicates at least one pressure surge with an amplitude of at least 5% of the nominal absolute pressure value on the cooling circuit, contributes to a particularly reliable prevention of unwanted gas bubble formation in the cooling flow field.

[0181] A further embodiment of a bipolar plate, not shown in the figure, with a plurality of spillover step sets arranged at at least one end of at least one finger web has a plurality of spillover step sets extending at equidistant or different angle dimensions from the end of at least one finger web, or close to the end of the aforementioned finger web.

[0182] In a further preferred embodiment not shown in the figure, a bipolar plate according to the invention has at least two spillover step sets on at least one finger web, wherein the departure angles of the direction of travel of at least two individual spillover step sets have different angle amounts, preferably angle amounts which differ only by their sign.

[0183] As previously outlined, “spillover stage set” basically means a depressed stage or a sequence of depressed stages arranged one after the other in reaction flow field channels between the end of a corresponding finger web and the edge zone, whereby the edge zone does not necessarily have to be reached hydraulically.

[0184] Due to the bipolar plate's half-shell design, steps and ridges of the outer reaction flow fields form the fluid conduction structures, or channels, in the inner cooling flow field. A lowered step in an outer reaction flow field thus corresponds to a channel of reduced height in the cooling flow field.

[0185] In the context of this description of the invention, the abstract, and the patent claims, the terms "spillover stage set" and "spillover stage" may be used synonymously. In particular, the term "spillover stage set" also encompasses a single lowered stage of a reaction flow field, a "spillover stage." List of reference symbols

[0186] Fig. 1 1.01 cathode-side fresh gas flow 1.02 cathode-side interconnector plate 1.03 cathode-side exhaust gas flow 1.06 Flowfield channel 1.07 Channel segment near the inflow area of ​​the reaction medium into the area of ​​the active cell surface 1.08 Channel segment near the outflow area of ​​the reaction medium from the area of ​​the active cell surface 1.28 Area of ​​the active cell surface 1.29 Flowfield bridges 1.30 Input port 1.31 Output port 1.32-A Exit connection zone or exit area 1.32-E Entry connection zone or entry area 1.36 Symmetry axis “A” of the rectangular active cell area 1.37 Symmetry axis “B” of the rectangular active cell area 1.40 Reference coordinate system for the figure

[0187] Fig. 2 2.02-A cathode-side interconnector plate type A (serpentine flow field) 2.02-B cathode-side interconnector plate type B (parallel flow field) 2.02-C cathode-side interconnector plate type C (interdigitated flow field) 2.06-A Flowfield channel in flowfield “A” 2.06-B Flowfield channel in flowfield “B” 2.06-C Flowfield channel in flowfield “C” 2.20-A Channel mid-plane in flow field “A” 2.20-B Channel mid-plane in flow field “B” 2.20-C Channel mid-plane in flow field “C” 2.30 Input port 2.31 Output port 2.40 Reference coordinate system for the figure

[0188] Fig. 3 3.06-AN flowfield channels, anode-side reaction flowfield (anode flowfield) 3.06-COOL flowfield channels, cooling flowfield 3.06-KA flow field channels, cathode-side reaction flow field (cathode flow field) 3.09 Projected outline of the gas diffusion layer (GDL) of the MEA 3.28 Area of ​​the active cell surface 3.30-AN inlet port anode fluid or fuel fluid 3.30-KA input port cathode fluid or oxidizer fluid 3.30-COOL input port cooling fluid 3.31-AN Output port anode fluid or fuel fluid 3.31-COOL Cooling fluid outlet port 3.31-KA Output port cathode fluid or oxidizer fluid 3.33 Bipolar plate 3.34 Edge zone or edge webs 3.36 Symmetry axis “A” of the rectangular active cell area 3.37 Symmetry axis “B” of the rectangular active cell area 3.40 Reference coordinate system for the figure Fig. 4 4.02 Cathode-side interconnector plate or cathode-side half-shell of the bipolar plate 4.04 Cooling channel, formed by edge webs or below the edge zones 4.05 Polymer electrolyte membrane 4.06-AN flowfield channel, anode-side reaction flowfield (anode flowfield) 4.06-COOL flowfield channel, cooling flowfield 4.06-KA flowfield channel, cathode-side reaction flowfield (cathode flowfield) 4.09-AN anode-side gas diffusion layer (GDL) of the MEA 4.09-KA cathode-side gas diffusion layer (GDL) of the MEA 4.11 Elastomer seal 4.12 electrochemically inactive zone 4.16 Joining surface of the interconnector plates / bipolar plate half-shells 4.17 anode-side interconnector plate or anode-side half-shell of the bipolar plate 4.29 Flowfield bridges 4.33-AN Bipolar plate- here: Anode-side bipolar plate related to the single cell shown 4.33-KA Bipolar plate - here: Cathode-side bipolar plate related to the single cell shown 4.34 Edge zone or edge web 4.35 Subgasket frame 4.40 Reference coordinate system for the figure

[0189] Fig. 5 5.06-AN Flowfield channel, anode-side reaction flowfield (anode flowfield) 5.06-COOL flowfield channel, cooling flowfield 5.06-KA flowfield channel, cathode-side reaction flowfield (cathode flowfield) 5.09 Projected outline of the gas diffusion layer (GDL) of the MEA 5.13 River breakers 5.14 Spillover stage set 5.15-A Output Main Line 5.15-E Input main line 5.18 Finger bridge 5.19 Main strand direction 5.23-A Geometric boundary of the initial main rank to the active cell area 5.23-E Geometric boundary of the input main row to the active cell area 5.28 Area of ​​the active cell surface 5.30-AN inlet port anode fluid or fuel fluid 5.30-COOL input port cooling fluid 5.30-KA input port cathode fluid or oxidizer fluid 5.31-AN Output port anode fluid or fuel fluid 5.31 -COOL Cooling fluid outlet port 5.31-KA Output port cathode fluid or oxidizer fluid 5.33 Bipolar plate 5.34 Flowfield edge area or flowfield edge webs 5.36 Symmetry axis “A” of the rectangular active cell area 5.37 Symmetry axis “B” of the rectangular active cell area 5.40 Reference coordinate system for the figure

[0190] Fig. 6 6.15 Main strand. Here: Input main strand 6.19 Main strand direction 6.21-A Location of port “A” to the main line 6.21-B Location of port “B” to the main line 6.21-C Location of port “C” to the main line 6.23 Geometric boundary of the main strand to the active cell surface 6.30 Input ports 6.40 Reference coordinate system for the figure

[0191] Fig. 7 7.13 River breaker 7.14 Spillover level set 7.15-E Input main line 7.19 Main strand direction 7.23 Geometric boundary of the main strand to the active cell surface 7.27 Cooling fluid coupling position in the area of ​​the sealing groove 7.28 Area of ​​the active cell surface 7.30-AN inlet port anode fluid or fuel fluid 7.30-COOL inlet port cooling fluid 7.30-KA input port cathode fluid or oxidizer fluid 7.34 Edge area or edge web 7.37 Symmetry axis “B” of the active cell surface 7.40 Reference coordinate system for the figure

[0192] Fig. 8 8.02 Section of a cathode-side interconnector plate or cathode-side half-shell 8.04 Cooling channel formed from the edge webs or under the edge zone 8.06-COOL "Standard" cooling channel of the cooling channel flow field in the area of ​​the active cell surface or its cross-sectional profile for illustrative purposes 8.13 River breakers 8.14 Spillover stage set 8.16 Joining plane of the half shells / formed parts 8.17 Section of an anode-side interconnector plate or anode-side half-shell 8.18 Finger bridge 8.34 Edge area or edge web 8.40 Reference coordinate system for the figure

[0193] Fig. 9 9.02 cathode-side interconnector plate or cathode-side half-shell 9.15 Main strand. Here: Entrance main strand 9.17 anode-side interconnector plate or anode-side half-shell 9.19 Main strand direction 9.23 Geometric boundary of the main strand to the active cell surface 9.24 Sealing groove 9.25 cross steps 9.26 Front-side cooling fluid inlets and outlets 9.30-AN inlet port anode fluid or fuel fluid 9.30-KA input port cathode fluid or oxidizer fluid 9.31-COOL Cooling fluid outlet port 9.40 Reference coordinate system for the figure

[0194] Fig. 10 10.02 cathode-side interconnector plate or cathode-side half-shell 10.04 Cooling channel formed from the edge webs or under the edge zone 10.06-COOL "Standard" cooling channel of the cooling channel flow field in the area of ​​the active cell surface or its cross-sectional profile for illustrative purposes 10.14 Spillover level set 10.16 Joining surface of the half shells / formed parts 10.17 Anode-side interconnector plate or anode-side half-shell 10.18 Finger bridge 10.34 Edge area or edge web 10.38 Departure angle of the spillover stage set 10.39 End of the finger bridge 10.40 Reference coordinate system for the figure 10.41 Main direction of the finger bridge 10.42 Main direction of the spillover stage

Claims

[1] Fuel cell with at least two bipolar plates (4.33-AN), (4.33-KA), wherein a bipolar plate comprises at least one first anode-side interconnector plate (4.17) formed from a first half-shell with at least one superficial, first fluid conducting structure arranged adjacent to an anode-side gas diffusion layer (4.09-AN), and at least one first cathode-side interconnector plate (4.02) formed from a second half-shell with at least one superficial, second fluid conducting structure arranged adjacent to a cathode-side gas diffusion layer (4.09-KA), and an internal, third fluid conducting structure arranged at least in regions between the aforementioned first and second half-shells, with the following features: -A first fluid guide structure is formed from at least two flow field channels (4.06-AN) or has at least two such flow field channels. -A second fluid guide structure is formed from at least two flow field channels (4.06-KA) or has at least two such flow field channels. -A third fluid conduction structure has at least one flow field channel (4.06-COOL). -Flowfield channels of the first, second and third fluid conducting structure (4.06-AN), (4.06-KA), (4.06-COOL) are arranged parallel to each other, at least in the region of the active cell area (5.28), (7.28), at least in some areas. [2] Bipolar plate according to claim 1, having the following features: -the bipolar plate has at least a first main strand (6.15) -the bipolar plate has at least one first port, at least one second port and at least one third port, which are arranged adjacent to the at least one first main strand -at least a first port is, at least indirectly, hydraulically connected to superficial flow field channels (4.06-AN) of a first anode-side interconnector plate (4.17) -at least a second port is, at least indirectly, hydraulically connected to superficial flow field channels (4.06-KA) of a first cathode-side interconnector plate (4.02) -at least a third port is, at least indirectly, hydraulically connected to flow field channels (4.06-COOL) formed by the half-shells of the interconnector plates (4.02), (4.17) inside the bipolar plate -at least one first main strand has at least one first, one second and one third fluid guide structure, wherein these three fluid guide structures are separated from one another in a fluid-tight manner, and wherein at least one first fluid guide structure of a main strand is hydraulically directly connected to a first port, and wherein at least one second fluid guide structure of a main strand is hydraulically directly connected to a second port, and wherein at least one fluid guide structure of a main strand is hydraulically directly connected to a third port -the first, second and third fluid conducting structures of a main strand run parallel to one another at least in some regions, preferably in the transition region between the main strand and the active cell surface (6.23), (7.23), or are arranged parallel to one another at least in some regions. [3] Bipolar plate according to at least one of claims 1-2 with the following features: -the first, superficial, fluid conducting structure of the anode-side interconnector plate (4.17) and the second, superficial, fluid conducting structure of the cathode-side interconnector plate (4.02) have the same number of parallel channels in the region of the active cell surface (5.28), (7.28), [4] Bipolar plate according to at least one of claims 1-3 with the following features: -the surface fluid conducting structures of the at least one first anode-side interconnector plate (4.17) and the at least one first cathode-side interconnector plate (4.02) each comprise at least one first edge region or a first edge web (4.34), (7.34), (8.34) -the edge regions or edge webs of the first anode-side interconnector plate (4.17) and the first cathode-side interconnector plate (4.02) each have at least one flux breaker (7.13), (8.13), wherein at least one flux breaker of the first anode-side interconnector plate (4.17) and at least one flux breaker of the first cathode-side interconnector plate (4.20) are arranged directly adjacent. -The hydraulic diameter of at least one cooling channel (8.04) formed by the edge webs (7.34), (8.34) is reduced in the region of at least one flow breaker (7.13) (8.13), at least in some regions, by at least 30%, preferably by more than 80%, particularly preferably by more than 95%, preferably by 100%. [5] Bipolar plate according to at least one of claims 1-4 with the following features: -The at least two half-shells from which the bipolar plate is formed enclose at least one first space which is formed at least in regions by at least one first finger web (8.18), (10.18) and is hydraulically connected to at least one port. -This at least one first space is hydraulically connected via at least one first channel, which is formed at least in regions by at least one spillover stage set (7.14), (8.14), (10.14), to at least one adjacently arranged cooling channel (4.06-COOL) but preferably via a number of adjacently arranged cooling channels, to an adjacently arranged first edge region (4.34), (5.34), (8.34). -The main direction (10.42) of at least one spillover step set (10.14) and the main direction (10.41) of an associated finger bar (10.18) enclose an angle (10.38) in the xy plane of the coordinate system (10.40) of at most 90°, preferably at most 60°, more preferably at most 45°, even more preferably less than 30°, or most preferably 0°. [6] Fuel cell stack with bipolar plates according to claims 1-5, having the following features: -At least one bipolar plate comprises at least one spillover stage set (10.14) -At least one first vector arranged parallel to a main direction (10.42) of at least one spillover stage set (10.14) has a vector component that runs parallel to the gravity vector, wherein the aforementioned vector component of this first vector contributes a proportion of at least 10%, preferably more than 30%, particularly preferably more than 40%, very particularly preferably more than 60%, to the mathematical amount of this first vector.

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