Bipolar plate for electrochemical system

Abstract

The invention relates to a bipolar plate for an electrochemical system. The electrochemical system may in particular be a fuel cell system, an electrochemical compressor, an electrolyzer, or a redox flow battery. It may comprise a large number of such separators or bipolar plates.

Description

Technical Field

[0001] The present invention relates to a bipolar plate for an electrochemical system. The electrochemical system may be a fuel cell monomer system, an electrochemical compressor, an electrolyzer, or a redox flow battery. The system may include a large number of such separators or bipolar plates. Background Art

[0002] Known electrochemical systems of the above-mentioned type usually include stacked electrochemical cells separated from each other by bipolar plates. Such bipolar plates can be used, for example, to establish electrical contact with the electrodes of individual electrochemical cells (e.g. fuel cells) and / or to electrically connect adjacent cells (series connection of cells). Usually, the bipolar plate is formed by two adjacent individual plates, which are also referred to as separators within the scope of the present application. The individual plates can be combined together in a material connection, for example by one or more welded joints, in particular by one or more laser welded joints.

[0003] The bipolar plates or individual plates may each have or form a structure of the type explained below, which is provided, for example, for supplying one or more media to the electrochemical cells arranged between adjacent bipolar plates and / or for removing reaction products. The medium may be a fuel (e.g., hydrogen or methanol), a reaction gas (e.g., air or oxygen), or a coolant. In addition, the bipolar plates may be designed to deliver waste heat generated during the conversion of electrical or chemical energy in the electrochemical cells, and to seal different media channels or cooling channels from each other and / or from the outside.

[0004] Furthermore, the bipolar plates generally comprise at least one corresponding through-opening, through which the medium and / or the reaction products can be conducted to or away from the electrochemical cells arranged between adjacent bipolar plates of the stack. The electrochemical cells generally also comprise in each case one or more membrane electrode assemblies (MEAs). The MEAs may have one or more gas diffusion layers (GDLs), which are generally oriented toward the bipolar plates and are designed, for example, as metal felt or carbon felt.

[0005] In particular, channels in the separator and in the bipolar plate separated from each other by webs can provide structures for medium supply and / or medium routing. These channels can be embossed in the form of grooves, for example, can provide flow paths for typical liquid or gaseous media.

[0006] Typically, each separator has an active area with channels for directing the reaction medium and / or reaction products along the outside of the bipolar plate. The active area is opposite the MEA. The active area may also be referred to as a flow field or include a flow field.

[0007] The active area is connected to one of the through openings in a fluid-conducting manner via a so-called distribution area and is fed through this through opening. Via a further distribution area, which can also be referred to as a collection area, the reaction medium and / or the reaction product can be fed from the active area to the further through opening for removal. The distribution area also usually has some separated channels.

[0008] On the inner sides of two separators facing each other and surrounded by the corresponding bipolar plates, the above-mentioned channel-web structures of the flow field and at least one distribution area form complementary web-channel structures. They span the optional flow area for the optional coolant route in the interior of the bipolar plate.

[0009] When forming a ready-to-use stack, a membrane electrode assembly is provided between adjacent bipolar plates, which membrane electrode assembly separates in the flow region the channels for the passage of a reaction medium in a first bipolar plate from the channels for the passage of another reaction medium in a second bipolar plate, the second bipolar plate being separated from the first bipolar plate only by the membrane electrode assembly. The membrane electrode assembly, often abbreviated as MEA, usually extends beyond the active area and into the distribution area(s).

[0010] In their active area, MEAs usually comprise the actual proton-conducting membrane, electrodes applied thereto, and a catalyst layer, on which a conductive layer and a gas-permeable layer, the so-called gas diffusion layer (GDL), are applied. In their edge regions, MEAs usually comprise a polymer-based thin film material which encloses the active area and overlaps in a narrow overlapping region with the material forming the active area or a part thereof. In the stack of electrochemical systems, MEAs define the spacing between the separators. At the same time, the gas diffusion layer (GDL) of the MEAs exhibits relatively large fluctuations in thickness.

[0011] Therefore, the space between the bipolar plates is usually provided in the thickness direction of the stack so that, on the one hand, there is enough space in the active area to accommodate the relevant section of the MEA and, on the other hand, there is just enough space for a defined compression of this section of the MEA. As a result, sometimes there is more space in the distribution area than is absolutely necessary for their function. Thus, an MEA with a thickness greater than average in the active area results in large gaps in the distribution area, while an MEA with a thickness less than average in the active area results in very small gaps or no gaps in the distribution area.

[0012] In conventional plates, bipolar plates are designed so that their separators are placed on top of each other in sections both in the active area and in the distribution area and are welded together in sections at least in these areas. However, pressure fluctuations of the coolant passing between the stacked bipolar plates can lead to movements of the separators relative to each other and expose the connections between the separators of the bipolar plates, in particular the welded connections in the distribution area, to the effects of dynamic pressure fluctuations and loads. These can lead to fractures in the welded joints. This applies in particular if the connections are already exposed to the effects of increased loads due to variations in the thickness of the MEA.

[0013] As a result, unrestricted media flows may occur within the bipolar plate, which leads to pressure losses and thus efficiency losses. In addition, such separators may also have perforations in the area of ​​the welded joints, which endangers the operating capability and, in particular, the operating safety of the bipolar plate and the higher-level electrochemical system. Summary of the invention

[0014] It is therefore an object of the present invention to provide a bipolar plate with which thickness fluctuations of the MEA can be compensated while ensuring increased efficiency and operating reliability.

[0015] This object is achieved by the subject matter of independent claim 1. Advantageous further embodiments are given in the dependent claims, the description and the figures.

[0016] Therefore, a bipolar plate for an electrochemical system is proposed, which comprises several bipolar plates in a stack, in particular several bipolar plates according to the invention, in particular for a fuel cell monolithic system, an electrochemical compressor, an electrolyser or a redox flow battery.

[0017] The bipolar plate comprises a first separator and a second separator, the rear sides of which face each other and the front sides of which face away from each other. The first separator and the second separator are preferably connected to each other, in particular welded, but not in their distribution area.

[0018] The first separator and the second separator each have:

[0019] - at least two through openings, at least two through openings for the reaction medium to pass through the corresponding partition;

[0020] - and on their respective front sides: at least one distribution region and a flow field, the distribution region connecting at least one of the through-openings to the flow field, in particular in a fluid-conducting manner;

[0021] a respective distribution area having channels for guiding one of the reaction media along the respective longitudinal axis of the channel, the channels being separated from one another by webs and each having a width extending parallel to the plate plane of the bipolar plate and perpendicular to the longitudinal axis of the channel,

[0022] Therein, each channel has, in particular in the middle, a channel bottom with a channel base and, on both sides of the respective channel bottom, side wings which connect the channel bottom to the respective web.

[0023] The flanks have a first radius to the respective web in the first transition region, and each channel has a first width dimension extending between the first transition regions of the flanks and in particular between the ends of these first transition regions facing each other.

[0024] Furthermore, each channel has a second width dimension which indicates the width of a channel base, wherein, at least in the case of a first separator, the channel base contacts a second separator at the rear side in an unassembled state of the bipolar plates in the stack and / or wherein the channel base forms the deepest area of ​​the channel.

[0025] It is provided that the first width dimension of at least the first partition is more than three times, in particular more than five times, more than six times, more than seven times or more than eight times, the second width dimension.

[0026] With the bipolar plates disclosed herein, and in particular the ratio of the first width dimension to the second width dimension, the bipolar plates can have a specifically defined elasticity even when there is contact between the separators, thereby at least partially compensating for variations in the thickness of the MEA. In other words, the geometric features disclosed herein can be used to provide an elastic reserve within the bipolar plate in one thickness direction of the MEA.

[0027] Nevertheless, the contact between the separators provided enables a defined flow of media and reaction products, in particular coolant, which increases efficiency. In particular, by utilizing the increased elasticity of the structure, this contact and thus the defined guidance can be maintained at least in certain areas even with a varying thickness of the MEA. Additionally or alternatively, the increased elasticity makes it possible to reduce or even omit the welds connecting the separators. Therefore, these cannot be torn apart, in particular if the separators are locally perforated. This increases operational safety.

[0028] The separators may be arranged adjacent to each other in a direction perpendicular to the plate plane of the bipolar plate. The plate plane of the bipolar plate may run parallel to the plane of the corresponding separator. This may be a center plane placed between two separators and / or their respective plate planes and / or a plane where the separators touch each other.

[0029] Similarly, the plate plane of the bipolar plate considered here can be a flat surface plane of one of the separators or a plane parallel thereto. In a manner known per se, the flat surface plane can be defined, for example, by the edge of the separator or by flat areas of the separator, which are not deformed by embossing or deep drawing processes to form the web channel structure or flange described here. On the one hand, the flat surface plane can run in the neutral fibers of the corresponding sections of the separator; on the other hand, the surface of the relevant section of the plate can also be considered as a flat surface plane. However, when adopting the latter method, it must be ensured that the material thickness of only one of the two separators considered takes into account distance or similar factors.

[0030] When viewed from above the bipolar plate, the through openings of the separators can be aligned in pairs. For example, two different reaction media can be fed or discharged via the through openings. In particular, however, the separators can each have at least six through openings through which two different reaction media and a cooling fluid can be fed and discharged again.

[0031] Depending on the flow direction, i.e. the flow direction to or from the through opening or flow field, the distribution area can also functionally serve as a collecting area of ​​the above-mentioned type. The flow field and at least one distribution area of ​​each partition can at least partially overlap and / or be arranged opposite to the corresponding flow field and at least one distribution area of ​​the corresponding other partition.

[0032] For example, the flow field can be characterized, for example, by the fact that all the webs and channels it comprises are straight and run parallel to each other and parallel to the main flow direction through the flow field. Alternatively, the webs and channels can also be wavy and run close to each other with the same wave shape and along the main flow direction (or also the main flow axis).

[0033] Additionally or alternatively, the flow field can be characterized by the fact that it is located within the MEA reinforcement edge and, in particular, is surrounded and / or framed by it, at least in sections. However, the MEA reinforcement edge is preferably not relative to the flow field itself, but to the actual active area of ​​the MEA, in particular in the form of its electrolyte membrane. For example, reference is made to DE202020106459 U1 and in particular to the figure marked 3B, which shows an MEA with a reinforcement edge that frames the active area of ​​the MEA. The present application does not include such a figure marked 3B.

[0034] The channels of the corresponding distribution areas can be in the form of grooves, particularly convex grooves, made in the corresponding separators. The channels can be separated from each other by webs protruding from the bipolar plate in the direction of the outside of the bipolar plate and / or relative to the channels and particularly the channel base. The channels in the distribution area can run parallel to each other, be at a certain angle, bend at different radii or be arranged completely randomly at least in some sections. In particular, the channels of the distribution area of ​​the separator under consideration can run parallel to each other over a large area of ​​the distribution area. However, when the structure of the distribution area protrudes into the common plane of the array of channels of the adjacent distribution area of ​​another separator of the bipolar plate, they can intersect, for example, at a positive angle. It is also possible that, at least in one of the two separators, the distribution area is divided into different sub-areas, wherein, for example, the angles of extension of the webs and / or channels are different from each other. The channels and / or webs of the distribution area can also have interruptions and / or depressions.

[0035] In particular, each channel may have a channel bottom with a channel base, whereby the channel base forms the deepest region of the channel. The depth axis and / or depth dimension of the respective channel may run perpendicular to the plate plane of the bipolar plate and / or from the separator including the channel. Alternatively or additionally, the depth axis may be orthogonal to the longitudinal channel axis and / or any width dimension mentioned herein.

[0036] Generally, any width dimension mentioned herein can be aligned according to the aforementioned width or corresponding width axis, i.e., in particular parallel to the plate plane of the bipolar plate and orthogonal to the longitudinal axis of the channel. The longitudinal axis of the channel can be the axis along which the fluid flows through the corresponding channel. It does not have to be a continuous straight axis. For example, the longitudinal axis of any channel described herein can be bent once or multiple times in at least some sections.

[0037] The channel bottom, at least in some sections, can be curved, blunt, trapezoidal or other uneven shapes. The plane considered below, at least in some points, comprising the channel bottom can for example form the central plane of the corresponding curvature, bending or non-planar shape of the channel bottom. In this case, the plane can for example comprise at least two positions or points on the channel bottom, where the plane intersects with the channel bottom. In particular, such a plane can at least comprise the channel base and / or advance tangentially therewith. In the latter case, due to the corresponding at least point-shaped contact with the channel or the channel base, it can also comprise at least one position of the channel bottom in the form of the channel base.

[0038] However, the channel base may also comprise more than one position, for example if it is formed as a kind of depth platform of the channel, as is possible according to embodiments.

[0039] Any plane containing the bottom of the channel at least at some points may run substantially parallel to the plane of the web or even the top portion of the web. For example, the top portion of the web may form the highest area of ​​the web when viewed along the depth axis. In particular, a plane containing the bottom of the channel at least at some points and running tangentially to the base of the channel may run parallel to a plane containing the web or at least the top portion of the web, or be at an angle to the plane, for example, less than 40°, less than 30° or less than 20°. Additionally or alternatively, a plane containing the bottom of the channel at least at some points and running tangentially to the base of the channel may run parallel to the plate plane of the bipolar plate.

[0040] However, the flanks connecting the channel bottom to the adjacent web in each case cannot run parallel to the plate plane of the bipolar plate and / or to the plane containing the web or at least the top part of the web. In particular, they can run at a greater angle to at least one or two of these planes than the plane containing the channel bottom at least at certain points and running tangentially to the channel base, for example at least 1.5 times or twice that angle. Additionally or alternatively, the angle between the depth axis mentioned here and the flank can be smaller than the angle between the depth axis and the plane containing the channel bottom at least at certain points and running tangentially to the channel base, for example at least 1.5 times or twice that angle.

[0041] In general, for example, the channel bottom may be rounded and / or curved throughout. In particular, the channel base may form the lowest point of the curvature and / or rounding of the channel bottom. Alternatively or additionally, the rounding or curvature may be mirror-symmetrical around the channel base. The channel bottom may also be trapezoidal, for example, whereby the channel base may define the deepest area of ​​the trapezoidal shape, in particular the floor line. The trapezoidal shape may be characterized by substantially straight sections that converge at an angle to each other and preferably converge at the channel base.

[0042] Any shapes of the channel bottom and / or the channel and / or the web mentioned here can be viewed in cross section, the cross-sectional plane being perpendicular to the longitudinal axis of the channel.

[0043] The flanks may be inclined and / or shaped in opposite directions. In particular, they may be inclined and / or shaped in opposite directions relative to a plane containing the channel base and / or the longitudinal axis of the channel. For example, they may be inclined and / or shaped mirror-symmetrically relative to the plane.

[0044] The webs or at least the web top parts may be flat. In particular, they may be less pronounced and / or less rounded and / or less trapezoidal than the channel bottom. The webs and the channel bottom may be spaced apart from each other by flanks, in particular along the depth axis. In general, the webs may define and / or include a platform-like protrusion.

[0045] In principle, the first transition region may include parts of both the web and the wing merging therewith. The first transition region may be limited by an end of the web facing the adjacent wing. This end may be characterized by a slightly reduced height compared to the other platform-like extensions of the web. In other words, the transition region may start when the height of the web decreases and / or end when the web reaches a constant height level.

[0046] Additionally or alternatively, the first transition region may be limited by the position at which the flank is straight. In other words, the first transition region may end or begin when the flank first runs in a straight line, for example from the perspective of the adjacent web. If the flank is continuously curved, the first transition region may be limited by the inflection point of the flank, in particular by the inflection point closest to the adjacent web.

[0047] In summary, the first transition region can extend in particular between a position of an initial drop in height of the web or an initial stable height and a position of an initial straightness or inflection point of the flank. It goes without saying that webs and flanks that are adjacent to each other and connected by a transition region are considered. The positions mentioned here can correspond to or form a first or second transition point of the type described below.

[0048] The first width dimension can be measured between those positions where the bilateral flanks of the channel merge into the first transition region. As described above, these positions can in particular each include a turning point or a straight flank section starting for the first time, for example from the immediately adjacent web. Additionally or alternatively, these positions can form mutually facing ends of the first transition region on both sides. This arrangement of mutually facing ends can include or be caused by the fact that the flanks run towards each other in the region of the corresponding positions. In particular, compared to the corresponding other ends of the first transition region, at the other ends, the first transition region merges into the web and in particular merges into the web platform, and these mutually facing ends can be closer to each other in the width direction. These ends can be understood as ends that are away from each other.

[0049] Since, according to the invention, the first width dimension is significantly greater than the second width dimension, an elastic reserve is provided despite the intended contact between the partitions. In particular, the channel in the region between the channel base and the mutually facing ends of the transition region, in which region the first width dimension is measured, cannot contact the rear side of the second partition, which is generally not provided in the prior art, or at least not to a considerable extent.

[0050] In particular, sections of the channel bottom and / or sections of the flanks directly adjacent to the channel base can also, at least in some sections, be pressed against the rear side of the second separator as part of the elastic deformation. This can occur during installation and in particular during the pressing of the bipolar plate stack of the electrochemical system. The extent of the possible elastic deformation is determined in principle by the thickness of the adjacent MEA and in particular by compensating for changes in the thickness of the MEA. In addition, there may still be elastic reserves there even after installation and grouting, for example to compensate for pressure differences. Previous welds can be completely eliminated or at least reduced and, due to the elastic reserves, are exposed to less risk of damage.

[0051] A further improvement provides that at least the channel bottom of the first partition is curved and that the rear region of the channel bottom of each channel extends convexly in the direction of the second partition. In other words, the rear region of the channel bottom of each channel can extend convexly therefrom, i.e. from the channel bottom and / or the rear region towards the second partition. The front region of the channel bottom can be curved to complement the rear region, i.e. it can in particular be concave.

[0052] The curvature may have a constant radius or a segmented varying radius. As described above, the curvature may be mirror-symmetrical to the channel base. In particular, the channel base may intersect the symmetry axis running in the depth direction and / or be orthogonal to the plate plane of the bipolar plate.

[0053] The curved shape defines a reliable elastic deformability, for example by the possibility of elastic bending of the channel bottom into a flatter shape and / or elastic bending in the direction of the second web, thereby achieving the desired elasticity according to the invention.

[0054] According to a further embodiment, during the pressing in the bipolar plate stack, at least the channels of the first separator, and more precisely: at least the channels of the distribution area of ​​the first separator, are elastically deformed at least in certain areas. Any elastic deformation of the pipe described herein, in particular a change in the cross-sectional shape of the pipe, may be accompanied by a change in the shape of the pipe compared to the case without deformation. In particular, the orientation of the flanks of the channel and / or the curvature or other shape of the channel bottom may be changed due to the elastic deformation.

[0055] When mounted, at least in certain areas, the baffles are prestressed against each other due to elastic deformation. As a result, they can withstand varying pressures, in particular pressures from any coolant conducted between the baffles, at least partially and possibly without significant shape changes.

[0056] In a further embodiment, the channels of at least the first separator, and more precisely: the channels in at least one distribution area of ​​the first separator under consideration, have an elastic reserve for installation in the stack and for pressing of the stack in the unassembled state. The channels can thus be elastically deformed during installation in the stack and during pressing of the stack, which can be done according to known prior art solutions. However, depending on the dimensional accuracy of the MEA or GDL installed in a particular stack, it is not important or even necessary to completely use up the elastic reserve.

[0057] In a further development, when the bipolar plates are in an unassembled state in the stack, the channel base of each channel of the second separator also contacts the back of the first separator. Preferably, in this case too, the first width dimension of each channel of the second separator is more than three times, in particular more than five times or more than six times, or even more than eight times, the second width dimension. Here, the first width dimension and the second width dimension are defined similarly to what is disclosed here for the channels of the first separator. In this way, the second separator can also be designed to be elastically deformable.

[0058] In this context, it can be provided that the ratio of the first width dimension to the second width dimension in the first separator is different from the corresponding ratio in the second separator. This allows the separator to be particularly adapted to the medium to be conveyed.

[0059] According to a further development, the first transition region has a first transition point or a first position, where the first transition region merges into a wing section that is curved differently from the first radius or has no curvature. Preferably, the first width dimension extends between the first transition points of the bilateral flanks. Thus, these first transition points may include or form the mutually facing ends of the aforementioned bilateral first transition regions.

[0060] Additionally or alternatively, the first transition region has, for example, a second transition point, at which a second section, for example a wing section, curved according to the first radius merges into the web. In particular, the web can be curved differently from the first radius or can also have no curvature and / or define a platform-like height level. The second transition point of the two-sided flank can include or form the ends of the first transition region that face away from each other.

[0061] In one embodiment, it is provided that the second width dimension is less than 1 mm, in particular less than 0.5 mm, in particular less than 0.3 mm, and further in particular less than 0.2 mm. This may mean that the areas adjacent to the base of the channel are relatively large, which areas preferably do not contact the back of the second partition in the undeformed state. In other words, the base of the channel can provide a rear contact area with the second partition, which rear contact area is, for example, smaller in size and / or point-shaped compared to the first width dimension, and the adjacent area of ​​the channel bottom can be elastically bent around and / or relative to this rear contact area. Therefore, the desired elastic deformation capacity according to the present invention is reliably provided by means of a compact structure.

[0062] One embodiment further provides that, at least in the channels of the first partition under consideration, i.e. the channels of the distribution area of ​​the first partition, the channel base has no material connection to the second partition. In particular, this applies to all channels of the distribution area of ​​the first partition and / or the entire distribution area can be free of such connections, in particular free of welds or spot welds. However, outside the distribution area, a material connection to the second partition can in principle be provided. By reducing or even completely eliminating the need for material-to-material connections, the risk of damage to the partition in the event of pressure fluctuations, in particular the risk of local perforation of the partition, is correspondingly reduced.

[0063] According to a further development, the flanks each have a second radius in a second transition region to the channel bottom, and a third width dimension of the channel extends between the second transition regions of the flanks. At least in the case of the first partition, the third width dimension is preferably at least half of the first width dimension, and in particular at least three quarters of the first width dimension.

[0064] This means that the wing accounts for a correspondingly smaller proportion of the total width of the channel, in particular a smaller proportion than the channel bottom. Due to its orientation relative to the plate plane, which preferably has a smaller angle than the wing, the latter is more resilient than the wing to compressive loads orthogonal to the plate plane, such as those resulting from thickness variations of the MEA. By increasing the width of the channel bottom, the elastic flexibility of the channel can be increased compared to the width of the wing.

[0065] In particular, the elastic compliance can be additionally increased in this case by the fact that, in the undeformed state, the rear region of the first partition in the second transition region and preferably the entire channel bottom between the second transition region and the channel bottom are spaced apart from the second partition.

[0066] The present invention also relates to a bipolar plate for an electrochemical system, the electrochemical system comprising a plurality of bipolar plates in a stack, the bipolar plate having a first separator and a second separator, the rear sides of the first separator and the second separator facing each other and the front sides facing away from each other, the first separator and the second separator respectively:

[0067] - at least two through openings, at least two through openings for the reaction medium to pass through the corresponding partition;

[0068] - and on their respective front sides: at least one distribution area and a flow field, the distribution area connecting one of the through-openings to the flow field in a fluid-conducting manner;

[0069] a respective distribution area having channels for guiding one of the reaction media along the respective longitudinal axis of the channel, the channels being separated from one another by webs and each having a width extending parallel to the plate plane of the bipolar plate and perpendicular to the longitudinal axis of the channel,

[0070] Each channel has a channel bottom and side wings on both sides of the respective channel bottom, the side wings connecting the channel bottom to the respective web,

[0071] The channel bottom thus has a second radius on both sides in the second transition region to the respective flank,

[0072] each channel having a third width dimension extending between opposite ends of the second transition region,

[0073] Thus, at least in the case of the first separator, even when the bipolar plates are not assembled in a stack, the channel bottom contacts the second separator on the rear side in some sections.

[0074] characterised in that the channel bottom has a third radius at least in the middle 25% of its width,

[0075] The third radius is greater than the second radius.

[0076] Any explanations and further developments of the same features provided here also apply to the bipolar plate of the further aspect. This applies in particular to all variations with respect to width dimensions and width ratios, as long as they do not conflict with the bipolar plate of the further aspect.

[0077] Preferably, the channel bottom has a third radius at least in the middle 40% of its width, which third radius is greater than the second radius.

[0078] The third radius is at least three times, preferably at least four times, in particular at least five times, the second radius. A larger third radius increases the elasticity of the channel bottom.

[0079] The channel bottom may be uniformly curved according to this third radius. The third radius of the channel bottom may be the radius of curvature of the channel bottom in the direction of the second partition. The third radius may merge directly into the two second radii on both sides, merge into the second radii via a section with a continuously changing radius, or continue in a straight section. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Exemplary embodiments of the present invention will be explained below with reference to the accompanying drawings. In all drawings, comparable features may be indicated using similar reference numerals.

[0081] Figure 1 An electrochemical system according to the invention is shown.

[0082] Figure 2 Shown from Figure 1 Sections of an electrochemical system.

[0083] FIG. 3 shows a partial cross-sectional view of a bipolar plate according to an example of the prior art.

[0084] FIG. 4 shows a perspective view of a region of the bipolar plate shown in FIG. 3 and therefore also relates to an example according to the prior art.

[0085] Figure 5 A partial cross-sectional view of a bipolar plate according to an embodiment of the present invention is shown.

[0086] Figure 6 Shows Figure 5 A perspective view of a region of a bipolar plate is shown in FIG.

[0087] Figure 7 A partial cross-sectional view of a bipolar plate according to another embodiment of the present invention is shown.

[0088] Figure 8 Shows Figure 7 A perspective view of a region of a bipolar plate is shown in FIG.

[0089] Fig. 9 A partial cross-sectional view of a bipolar plate according to another embodiment of the present invention is shown.

[0090] Fig.10 Shown from Fig. 9 Another partial cross-sectional view of a bipolar plate.

[0091] Fig.11 Shows Fig. 9 and Fig.10 A perspective view of a region of a bipolar plate is shown in FIG.

[0092] Fig.12 Exemplary spring characteristics are shown for the distribution area of ​​a bipolar plate according to the present invention. DETAILED DESCRIPTION

[0093] Figure 1 An electrochemical system 1 is shown, which includes a plurality of bipolar plates 2 of identical structure. The bipolar plates 2 are arranged as an assembly into a stack 6 and are stacked along a z-direction 7. The bipolar plates 2 of the stack 6 are sandwiched between two end plates 3, 4. The z-direction 7 is also referred to as the stacking direction. In the present example, the system 1 is a fuel cell cell stack. Therefore, each two adjacent bipolar plates 2 of the stack 6 enclose an electrochemical cell between them, which is used, for example, to convert chemical energy into electrical energy. In order to form the electrochemical cell of the system 1, a membrane electrode unit (MEA) is arranged between adjacent bipolar plates 2 of the stack 6 (see, for example, Figure 2 ). Each MEA generally includes a membrane, such as an electrolyte membrane. In addition, a gas diffusion layer (GDL) may be arranged on one or both surfaces of the MEA.

[0094] Alternatively, Figure 1 and 2 The system 1 shown in the figure can also be in the form of an electrolyzer, an electrochemical compressor or a redox flow battery. The bipolar plates 2 can also be used in these electrochemical systems. The structure of these bipolar plates 2 can then correspond to the structure of the bipolar plates 2 described in detail herein, although in the electrolyzer, the electrochemical compressor or the redox flow battery, the medium fed to and / or passing through the bipolar plates 2 can in each case differ from the medium used for the fuel cell monomer system.

[0095] The z-axis 7 together with the x-axis 8 and the y-axis 9 define a right-handed Cartesian coordinate system. The bipolar plates 2 each define a plate plane E (see FIG. 3 ) in which the separators 2a, 2b (see FIG. 3 ) forming the metal layers of the bipolar plates 2 are located. Figure 2 ) touch each other. The separators 2a, 2b also form their own plate planes in the areas where they are not formed, whereby the plate planes of the bipolar plate 2 and the separators 2a, 2b are each aligned parallel to the xy plane and are therefore perpendicular to the stacking direction or z-axis 7. The end plate 4 comprises a plurality of medium connections 5, via which a medium can be fed to the system 1 and via which a medium can be discharged from the system 1. The medium that can be supplied to and discharged from the system 1 may include, for example, a fuel such as molecular hydrogen or methanol, a reaction gas such as air or oxygen, a reaction product such as water vapor or a depleted fuel, or a coolant such as water and / or ethylene glycol if desired. In the case of an electrolyzer, water is supplied to the stack and oxygen and hydrogen are discharged from it.

[0096] Figure 2 Shows Figure 11 and a membrane electrode assembly (MEA) 10 which is arranged between the adjacent bipolar plates 2 and is known in principle from the prior art. Figure 2 The MEA 10 in the image is mostly obscured by the bipolar plate 2 facing the viewer. The bipolar plate 2 is formed by two separators 2a and 2b joined together by a material connection. Figure 2 Only the first separator 2a facing the observer is visible over a large area, and the first separator 2a covers the second separator 2b. The separators 2a, 2b can each be made of a metal sheet, for example a stainless steel sheet or a titanium alloy. The sheets can be coated or covered in some sections or on their entire surface, for example, with a coating that prevents corrosion and / or enhances conductivity. The separators 2a, 2b can be connected to each other, for example, by material bonding, such as welding, brazing or gluing, and can be connected in particular by laser welded joints. The MEA 10 has a frame-shaped reinforcement edge along its outer edge, and the MEA is liquid-tightly sandwiched between the two bipolar plates 2 on the reinforcement edge.

[0097] The separators 2a, 2b have through-openings which form through-openings 11a-11c of the bipolar plate 2 and are aligned with each other. When a plurality of bipolar plates of the bipolar plate 2 type are stacked, the through-openings 11a-11c and the aligned through-openings in the reinforced edge of the MEA 10 form lines extending through the stack 6 in the stacking direction 7 (see Figure 1 ). Typically, each of the through-openings formed by the channel openings 11a-11c is fluidically connected to one of the ports 5 in the end plate 4 of the system 1. By means of the pipeline formed by the through-opening 11a, for example, a coolant can be introduced into the stack or discharged from the stack. Conversely, the pipeline formed by the through-openings 11b, 11c can be designed to supply fuel and reaction gases to the electrochemical cells of the fuel cell cell stack 6 of the system 1 and to discharge reaction products from the stack 6. The through-openings 11a-11c for medium conduction are each substantially parallel to the plate plane.

[0098] In order to seal the through-openings 11a-11c relative to the interior of the stack 6 and relative to the surroundings, the first separators 2a can each have a sealing arrangement in the form of a sealing bead 12a-12c which is in each case arranged around the through-openings 11a-11c and in each case completely surrounds the through-openings 11a-11c. Figure 2 On the rear side for an observer, the second partition plate 2b has corresponding sealing beads for sealing the through-openings 11a-11c (not shown).

[0099] In the electrochemically active region 18, the first separator 2a is disposed on its side facing Figure 2On the front side of the observer, there is a flow field 17, which has structures (channels and webs) for guiding the reaction medium along the front side of the partition 2a. Figure 2 In the bipolar plate 2, these structures are provided by a plurality of webs and channels running between and defined by the webs. Figure 2 On the front side of the observer, the first partitions 2a also each have at least one distribution area 20, which distribution area 20 can also be called a collection area in the above-mentioned manner depending on the flow direction. The distribution or collection area 20 includes a structure configured to distribute the medium on the active area 18 and / or collect or gather the medium, the distributed medium is the medium that has been transported from the first of the two through-openings 11b to the distribution or collection area 20, and the collected or gathered medium is the medium that flows from the active area 18 toward the second of the through-openings 11b. Also in Figure 2 The distribution structure of the distribution or collecting area 20 is shown in FIG. 1 by means of webs 21 and channels 22 extending between the webs 21 and delimited by the webs 21. Generally speaking, the elements 17, 18, 20 can therefore be interpreted as embossed structures for guiding the medium.

[0100] In conventional bipolar plates, the separators lie directly on top of each other and bear against each other in the region of the bottom of the channels in the distribution region. The two separators are usually connected to each other at the contact point in the distribution region, in particular welded.

[0101] Figure 2 The sealing ridges 12a-12c of the example in the embodiment have feedthroughs 13a-13c for passing a medium through the sealing ridges. For example, the feedthrough 13a allows coolant to pass between the through-opening 12a and the distribution area 20, so that the coolant enters or is guided out of the distribution area between the partitions 2a, 2b. In addition, the feedthrough 13b allows hydrogen to pass between the through-opening 12b and the distribution area 20 on the upper side of the partition 2a. The passage 13c enables air to pass, for example, between the through-opening 12c and the distribution area 20, so that the air enters the distribution area 20 on the lower side of the lower partition 2b and is guided out of the distribution area 20. The through-opening 11a or the pipelines formed by the through-opening 11a through the plate stack of the system 1 are each fluidly connected to each other via the cavity 19 enclosed by the partitions 2a, 2b. If necessary, this cavity 19 can be used to conduct a coolant through the bipolar plate 2 , in particular in order to cool the electrochemically active area 18 of the bipolar plate 2 .

[0102] The first separators 2a of the bipolar plates 2 of the stack 6 also each have an additional sealing arrangement in the form of a peripheral flange 12d, which surrounds the flow field 17 of the active area 18, the distribution and collection area 20 and the through openings 11b, 11c, and seals them with the through opening 11a, that is, with the coolant circuit, that is, with the coolant circuit, and with the environment of the system 1. The second separators 2b each include a corresponding peripheral flange 12d. In an alternative plate design, the peripheral flange can also enclose the coolant opening and thus the entire coolant circuit. The structure of the active area 18, the web 21 and the channel 22 of the distribution or collection area 20, and the sealing flanges 12a-12d are each formed as one piece with the separator 2a and molded into the separator 2a, for example, by embossing, deep drawing or hydraulic forming. The same applies to the corresponding distribution structure and sealing flange of the second separator 2b.

[0103] In particular in the case of fuel cell monomers, the separators 2a, 2b of the bipolar plate 2 can each be formed, for example, from a stainless steel sheet having a thickness of less than 100 μm. In the case of an electrolyzer, sheets made of a titanium alloy or sheets made of fully coated stainless steel can be used. The thickness of the sheets in an electrolyzer is generally greater; for example, they can be 100-800 μm, 150-500 μm, in particular 200-300 μm. The bipolar plate 2 generally has a substantially rectangular shape, but it can also be rounded or oval, in particular in the case of an electrolyzer.

[0104] Figure 2 An exemplary layer of the section plane AA is shown. The section plane AA is substantially orthogonal to the plate plane E of the bipolar plate 2 shown in FIG. 3 and runs in one of the distribution areas 20 of the first separator 2a. Furthermore, it runs in the area in which the distribution area 20 of the second separator 2b extends, the second separator 2b being Figure 2 This means that Figure 2 The left distribution areas 20 of the partitions 2a and 2b overlap in the section plane AA. In addition, the rear sides or inner sides of the partitions 2a and 2b are also opposite to each other at this location, and the shapes of the partitions 2a and 2b are set to be complementary to the corresponding distribution areas 20.

[0105] FIG. 3 shows a partial cross-sectional view of a bipolar plate 2, which is in principle Figure 2 The bipolar plate 2 shown in FIG. 1 is designed in the same manner, but has a distribution area 20 formed according to the prior art. The cross-sectional plane is similar to Figure 2 FIG. 4 shows a perspective view of the cross-sectional area shown in FIG. 3 .

[0106] As can be seen in particular from Figure 4, the section plane AA runs along the rear side of the channel 22 of the second separator 2b, so that the latter is shown essentially as a straight line in Figure 3. However, for the first separator 2b, at least some sections of the second channel 22 and the web 21 located between the second channel 22 and the web 21 can be seen in Figure 3. The longitudinal channel axis L (see Figure 4) is perpendicular to the sheet plane of Figure 3. The separators 2a, 2b touch each other along the plate plane E of the bipolar plate 2 shown in Figure 3.

[0107] The web 21 is designed as a horizontal high platform. The channel 22 has a flat channel bottom 24, which forms a low platform extending parallel to the high platform of the web 21. The depth and height dimensions each refer to a depth axis T orthogonal to the plate plane E. The distance H between the web 21 and the channel bottom 24 along the depth axis T is shown.

[0108] The channel bottoms 24 are each connected to the adjacent web 21 via double-sided flanks 26. The channel bottoms 24 are flat and also have a corresponding flat rear side, the channel bottoms 24 each resting on the rear side of the opposite inner side of the second partition 2b. In this contact area, a weld (not shown) can be provided for connecting the partitions 2a, 2b.

[0109] Due to the large contact surface around the rear of the channel bottom 24 and the weld provided there, the partitions 2a, 2b are connected to each other relatively rigidly. Therefore, the elastic deformation capacity, in particular along the depth axis T, is correspondingly low.

[0110] In the first transition region 28, the flanks 26 merge with a first radius R1 into the directly adjacent web 21. In the second transition region 30, the flanks 26 merge with an opposite curvature radius R2 into the directly adjacent channel bottom 24.

[0111] FIG. 3 also shows various width dimensions for one of the channels 22 , which also apply to the other channels 22 of the distribution area 20 of the first partition 2 a and are similarly provided in the embodiments of the invention hereinafter.

[0112] The first width dimension B1 is related to the width dimension of the channel 22 in the first transition region 28. More precisely, it is considered that at those ends of the bilateral transition region 28 of the channel 22, the radius R1 changes into a straight flank section, or in other words, a straight flank section appears for the first time. If there is no such straight edge section, the edge 26 has an inflection point (not shown) as expected, at which, for example, the curvature changes between the radii R1, R2. In this case, the first width dimension B1 can be measured between the turning points of the bilateral flanks 26 of the corresponding channel 22.

[0113] The further width dimension corresponds to the second width dimension B2 described below, which represents the width of the channel base 32. The channel base 32 is the area of ​​the channel bottom 24 that touches the other partition 2b at the rear and / or that forms the deepest area of ​​the channel 22 along the depth axis T. In the prior art example shown, these width dimensions B2 correspond to the width of the channel bottom 24 minus the width area in which the radius R2 extends, which is due to the flat shape of the channel base 32.

[0114] In the previously known examples of FIGS. 3 and 4 , the first width dimension B1 is no more than twice the second width dimension B2 .

[0115] Figure 5 A similar cross-sectional view to FIG. 3 is shown, but in accordance with an example of the present invention. Figure 6 yes Figure 5 Stereoscopic diagram of the example in .

[0116] In this example according to the invention, the channel bottom 24 of the first partition 2a is curved. More precisely, its rear side extends convexly outwards in the direction of the second partition 2b. The channel base 32 forms the deepest area within the channel bottom 24 and touches the rear side of the second partition 2b. The channel base 32 intersects the symmetry axis S, with respect to which the curvature of the channel bottom 24 is mirror-symmetrical.

[0117] Entering the plate plane E, the plate plane E coincides with a plane tangential to the rear part of the channel base 32. The latter plane runs parallel to the platform-like outer side of the web 21.

[0118] In this case, the second width dimension B2 does not extend along the entire section between the mutually facing ends of the radius R2, as explained with respect to Figure 3, but includes only the channel base 32, which has a width smaller than the channel bottom 24 and smaller than this section. The section of the channel bottom 24 adjacent to the channel base 32 is spaced apart from the second partition 2b at the rear.

[0119] The first width dimension B1 again extends between the first transition region 28, between the flanks 26 and the web 21. Again, considering Figure 5 The first transition point 36 marked as an example in FIG. 1 , at which the straight section of the wing 26 begins from the perspective of the adjacent web 21 , see also Figure 6 .

[0120] Figure 5 A third width dimension B3 is also shown, which corresponds substantially to the width dimension of the channel bottom 24. More precisely, the width dimension B3 in the example shown extends between the exemplarily marked second transition point 38, where the channel region curved according to the radius R2 merges into the flank 26.

[0121] Figure 5 It is shown that the first width dimension B1 is greater than the second width dimension B2 and also greater than the third width dimension B3. More precisely, it is approximately ten times the second width dimension B2 and at least 1.33 times the third width dimension B3. For example, the first width dimension B1 is about 1.025 mm and the second width dimension B2 is about 0.1 mm.

[0122] For the sake of completeness, Figure 5 Further width dimensions B4 and B5 are shown in . The width dimension B4 relates to a web width of, for example, 1.04 mm, and the width dimension B5 relates to a composite web channel width of, for example, 2.54 mm.

[0123] Figure 4 and Figure 5 The bipolar plates 2 in the unassembled state, but here the separators 2a, 2b already touch. However, these are not welded together in their distribution area 20. Instead, they are placed against each other while retaining a reserve for elastic deformation. In particular, the channel bottom 24 provides such a reserve for elastic deformation, for example, when pressing the stack 6 of bipolar plates 2 (see Figure 1 ), depending on the thickness tolerance of the MEA, it is pressed closer in the direction of the second separator 2b and may be pressed to contact the rear side of the second separator 2b.

[0124] For another embodiment of the present invention, Figure 7 is similar to Figure 3 and Figure 5 In addition, Figure 8 is similar to Figure 4 and Figure 6 Stereoscopic diagram.

[0125] In this further embodiment example, the channel bottom 24 is provided with a radius R3, which embodiment example does not have a clear channel base 32. Instead, the partition 2a contacts the partition 2b in a point-shaped cross-section in the uncompressed state and in a straight line shape in the direction of the channel 22. The three radii R2, R3 and R2 converge along the direction of the channel bottom 24. The radius R3 extends approximately over the middle 2 / 3 of the width B3, as shown by the dotted line. In this embodiment, the radius R3 is approximately 3.5 times the radius R2. The large radius extends over most of the width of the channel bottom 24, which gives it additional elasticity. Therefore, although Figure 5 and Figure 6 The example has a trapezoidal channel bottom 24, but Figure 7 and Figure 8 The channel bottom 24 of the example is rounded. Its advantages are similar to those of, for example Figure 5 and Figure 6 Describe the advantages.

[0126] Figure 9-11 Further embodiments of the invention are shown. The first and second baffles 2a, 2b differ significantly from one another in terms of their channel web structure in the respective distribution area 20 , in particular with regard to the first width dimension B1 of the respective channel 22 .

[0127] Fig. 9 Shown from Fig.11 A sectional view of a stereoscopic view containing the sectional axis CC. Fig.10 Shown from Fig.11 A sectional view of a stereoscopic view containing the sectional axis BB. Fig. 9 The cross-sectional view in the figure basically corresponds to Figure 5 , so please refer to the description there.

[0128] Fig.10 The cross-sectional view of FIG. 2 shows the width ratio of the web channel structure of the second baffle 2b. The width dimensions B1, B2, B5 shown are defined for the first baffle 2a, similar to Fig. 9 and Figure 5 As can be seen from the example in Fig. 9 Compared with the case of FIG. 1 , the first width dimension B1 more significantly exceeds the second width dimension B2. More precisely, the first width dimension B1 is 1.95 mm, and the second width dimension B2 is 0.1 mm, so the first width dimension B1 is substantially twenty times the second width dimension B2.

[0129] Fig.12 Shown with Figure 7 The rounded channel bottom 24 shown in FIG. 2 (short dashed characteristic curve) and the Figure 5An example of the spring characteristics of a bipolar plate 2 with a trapezoidal channel bottom 24 (long dashed characteristic curve) shown. The distribution areas 20 of the two exemplary bipolar plates 2 are initially compressed by 0.03 mm each and subsequently released, rebounding by about 0.01 mm in each case. Therefore, they have plastic and elastic compression components. If they are pressed again to the previously achieved maximum value of 0.03 mm, i.e. 0.01 mm each time, no additional plastic deformation occurs within this pressing range. In addition to elastic deformation, plastic deformation only occurs again when the total compression exceeds 0.03 mm. For the two rebounds with maximum compressions of 0.06 and 0.09 mm, it can be seen that the plastic deformation ratio is about 2 / 3, while the elastic deformation ratio is only about 1 / 3. At first glance, this seems to be a very highly plastic component, but it is important here that there is a significant elastic deformation component, which can be sufficiently elastically recovered even after plastic deformation to compensate for the tolerances of very thin MEAs or GDLs, and thus respond to pulsations of the medium, especially the coolant. A comparison of the two spring characteristic curves also shows that, given the same deformation over a large area, the bipolar plate 2 with rounded channel bottoms 24 can absorb slightly more force than the bipolar plate 2 with trapezoidal channel bottoms 24 .

Claims

1. A bipolar plate (2) for an electrochemical system (1), the electrochemical system (1) comprising a plurality of bipolar plates (2) in a stack (6), the bipolar plate (2) comprising a first separator (2a) and a second separator (2b), the back sides of the first separator (2a) and the second separator (2b) facing each other and the front sides facing away from each other, the first separator and the second separator (2a, 2b) respectively comprising: at least two through openings (11a-11c) for allowing the reaction medium to pass through the respective partitions (2a, 2b); - and on their respective front sides: at least one distribution area (20) and a flow field (18), said distribution area (20) connecting one of said through-openings (11a-11c) to said flow field (18) in a fluid-conducting manner; wherein the respective distribution area (20) has a channel (22) for guiding one of the reaction media along the respective longitudinal channel axis (L), wherein The channels (22) are separated from each other by webs (21) and each have a width extending parallel to the plate plane (E) of the bipolar plate (2) and orthogonal to the longitudinal channel axis (L), Each of the channels (22) has a channel bottom (24) with a channel base (32), and has side wings (26) on both sides of the corresponding channel bottom (24), the side wings connecting the channel bottom (24) to the corresponding web (21) wherein the flank (26) has a first radius (R1) in a first transition region (28) to the corresponding web (21), Each of the channels (22) has a first width dimension (B1) and a second width dimension (B2), the first width dimension (B1) extending between the ends of the first transition region (B1) of the two side wings (26) facing each other, and the second width dimension representing the width of the channel base (32), wherein at least in the first separator (2a), in an unassembled state of the bipolar plates (2) forming the stack (6), the channel base (32) contacts the back of the second separator (2b), It is characterized in that, at least in the first partition (2a), the first width dimension (B1) is greater than three times, in particular greater than five times or greater than six times, the second width dimension (B2).

2. The bipolar plate (2) according to claim 1, It is characterized in that At least the channel bottom (24) of the first partition (2a) is curved, and the rear region of the channel bottom (24) of each of the channels (22) thereby extends convexly in the direction of the second partition (2b).

3. The bipolar plate (2) according to any one of the preceding claims, It is characterized in that At least the channel (22) of the first partition (2a) in the unassembled state in the stack (6) has an elastic reserve for installation in the stack (6) and for pressing the stack (6).

4. The bipolar plate (2) according to any one of the preceding claims, It is characterized in that When the bipolar plates (2) forming the stack (6) are in an unassembled state, the channel bottom (24) of each channel (22) of the second separator (2b) also contacts the back of the first separator (2a), and the first width dimension (B2) of each channel (22) of the second separator (2b) is greater than three times, in particular greater than five times or greater than six times, the second width dimension (B2).

5. The bipolar plate (2) according to claim 4, It is characterized in that The ratio of the first width dimension to the second width dimension (B1, B2) in the first separator (2a) is different from the corresponding ratio in the second separator (2b).

6. The bipolar plate (2) according to any one of the preceding claims, It is characterized in that The first transition region (28) has a first transition point (36), at which the first transition region (28) merges into a wing section that is curved in a manner different from the first radius (R1) or has no curvature, and the first width dimension (B1) extends between the first transition points (36) of the wing (26) on both sides.

7. The bipolar plate (2) according to any one of the preceding claims, It is characterized in that The second width dimension (B2) is smaller than 1 mm, in particular smaller than 0.5 mm, in particular smaller than 0.3 mm, and further in particular smaller than 0.2 mm.

8. The bipolar plate (2) according to any one of the preceding claims, It is characterized in that At least in the channels (22) of the first separator (2a), the channel bottom (24) is not bonded to the material of the second separator (2b) in any case.

9. The bipolar plate (2) according to any one of the preceding claims, It is characterized in that The side wings (26) each have a second radius (R2), the second radius (R2) is in a second transition area (32) to the bottom (24) of the channel, and a third width dimension (B3) of the channel, the third width dimension (B3) extending between the second transition areas (32) of the side wings (26) on both sides, the third width dimension (B3) of at least the first partition (2a) being at least half of the first width dimension (B3), and in particular at least three quarters of the first width dimension (B1).

10. The bipolar plate (2) according to claim 9, It is characterized in that The rear region of the first partition (2a) is spaced apart from the second partition (2b) in the second transition region.

11. A bipolar plate (2) for an electrochemical system (1), the electrochemical system (1) comprising a plurality of bipolar plates (2) in a stack (6), the bipolar plate (2) comprising a first separator (2a) and a second separator (2b), the back sides of the first separator (2a) and the second separator (2b) facing each other and the front sides facing away from each other, the first separator and the second separator (2a, 2b) respectively comprising: at least two through openings (11a-11c) for allowing the reaction medium to pass through the respective partitions (2a, 2b); - and on their respective front sides: at least one distribution area (20) and a flow field (18), said distribution area (20) connecting one of said through-openings (11a-11c) to said flow field (18) in a fluid-conducting manner; wherein the respective distribution area (20) has a channel (22) for guiding one of the reaction media along the respective longitudinal channel axis (L), wherein The channels (22) are separated from each other by webs (21) and each have a width extending parallel to the plate plane (E) of the bipolar plate (2) and orthogonal to the longitudinal channel axis (L), Each of the channels (22) has a channel bottom (24) and side wings (26) on both sides of the corresponding channel bottom (24), the side wings connecting the channel bottom (24) to the corresponding web (21), wherein the channel bottom has a second radius (R2) in a second transition region (30) on both sides to the respective flank (26), wherein each of said channels (22) has a third width dimension (B3) extending between opposite ends of said second transition region (30), wherein, at least in the case of the first separator (2a), in the unassembled state of the bipolar plates (2) forming the stack (6), the channel bottom (24) contacts the second separator (2b) in some sections on the rear side, characterised in that the channel bottom (24) has a third radius (R3) at least in the middle 25% of its width (B3), Wherein the third radius (R3) is greater than the second radius (R2).

12. The bipolar plate according to the preceding claim, It is characterized in that The channel bottom (24) has a third radius (R3) at least in the middle 40% of its width (B3), the third radius (R3) being greater than the second radius (R2).

13. The bipolar plate according to any one of the two preceding claims, It is characterized in that The third radius (R3) is at least three times, preferably at least four times, in particular at least five times, the second radius (R2).

Images