Plate substrate with adhesive channel structure which is widened at node points, and bipolar plate assembled from at least two plate substrates for a fuel cell or a flow battery

Abstract

The invention relates to a plate substrate (3) for a bipolar plate (1) assembled from at least two plate substrates (3) for a fuel cell or a flow battery. The plate substrate has a channel structure (17) with an elongated channel (19) which extends along a surface (5) of the plate substrate and which branches out at node points (21), wherein the channel structure has multiple elongated channel regions (23), and at least one of the channel regions transitions into at least two adjacent channel regions at at least one node point. The channel has, in cross-section along the entire longitudinal extension thereof, a central adhesive region (27) and two overflow regions (29) which adjoin the adhesive region at opposite sides, said channel having a shallower depth in the adhesive region than in the overflow regions. The overflow regions of the channel have a larger cross-section, in particular a larger width, in a node point-near region (33) which is near one of the node points than in a node point-remote region (35) which is remote from said node point (21). Excess adhesive (7) which has been applied near the node point, for example in the form of overlapping sub-regions of an adhesive strand (39), can thus be received in a widened overflow channel portion (37).

Description

[0001] PLATE SUBSTRATE WITH EXTENDED AT NODE POINTS

[0002] ADHESIVE CHANNEL STRUCTURE AND AT LEAST TWO

[0003] BIPOLAR PLATE COMPOSITE SUBSTRATES FOR A

[0004] FUEL CELL OR FLOW BATTERY

[0005] FIELD OF THE INVENTION

[0006] The present invention relates to a plate substrate for a bipolar plate of a fuel cell or a flow battery composed of at least two plate substrates. Furthermore, the invention relates to a bipolar plate formed using such a plate substrate.

[0007] BACKGROUND OF THE INVENTION

[0008] Bipolar plates are designed to fulfil several different functions for fuel cells, which are stacked together to form the core of a fuel cell system. On the one hand, they are designed to connect neighbouring fuel cells to one another, i.e., to physically and electrically connect the anode of one cell to the cathode of a neighbouring cell. On the other hand, gas distribution to reaction spaces within the fuel cells is designed to occur across a surface of the bipolar plate, i.e., the bipolar plate is designed to guide reaction gases into reaction zones. For this purpose, the bipolar plate typically has flow profiles (so-called flow fields) on both sides, which can be milled, formed, or reshaped, and through which hydrogen flows on one side and reaction gas such as air is supplied on the other.The bipolar plate generally also influences the removal of water vapor and the release of thermal and electrical energy. Furthermore, the bipolar plate is intended to provide gas separation between adjacent fuel cells, seal against the outside, and, if necessary, provide cooling.

[0009] Bipolar plates often have channels that extend through the interior of a bipolar plate substrate. Such channels can, for example, fulfill specific functions during the manufacturing of the bipolar plate. For example, an adhesive, sealant, or glue (hereinafter referred to generally as adhesive) can be incorporated within such channel structures, which are used to mechanically bond, seal, or bond the two plate substrates forming the bipolar plate to each other.

[0010] It has been observed that problems can occur during the operation of fuel cells or flow batteries under certain operating conditions, particularly at or after low temperatures. These problems are suspected to be related to the bipolar plate used in the fuel cell or flow battery.

[0011] SUMMARY OF THE INVENTION AND ADVANTAGEOUS EMBODIMENTS

[0012] There may be a need for a bipolar plate or a fuel cell or flow battery equipped therewith that can be operated reliably, particularly under operating conditions at or after low temperatures. In particular, there may be a need for a bipolar plate that is simple in design, can be manufactured cost-effectively, and / or can be operated particularly robustly. Furthermore, there may be a need for a plate substrate that is suitably designed to form such a bipolar plate.

[0013] Such a need can be met by the subject matter of the independent claims. Advantageous embodiments are defined in the dependent claims, described in the following description, and illustrated in the figures.

[0014] A first aspect of the invention relates to a plate substrate for a bipolar plate composed of at least two plate substrates for a fuel cell or a flow battery. The plate substrate has a channel structure with an elongated channel extending along a surface of the plate substrate and branching at nodes, wherein the channel structure has a plurality of elongated channel regions and at least one of the channel regions merges into at least two adjacent channel regions at at least one node. The channel has, along an entire longitudinal extent of the channel structure in cross section, a centrally arranged adhesive region and two overflow regions adjacent to the adhesive region on opposite sides, wherein the channel has a smaller depth in the adhesive region than in the overflow regions.The overflow areas of the channel have a larger cross-section in a region close to one of the nodes than in a region far from this node.

[0015] A second aspect of the invention relates to a bipolar plate which is composed of at least two plate substrates stacked one above the other, wherein at least one of the plate substrates is formed according to an embodiment of the first aspect of the invention and wherein the plate substrates are glued and sealed to one another by means of a flowable adhesive introduced along the channel structure.

[0016] Without limiting the scope of the invention in any way, ideas and possible features for embodiments of the invention can be considered to be based, among other things, on the thoughts and findings described below.

[0017] Briefly and roughly summarized, a basic idea of ​​the idea described here can be seen in the recognition that problems such as those observed during the operation of fuel cells or flow batteries, particularly at or after low temperatures, could be due to water penetrating into channels of the bipolar plate or adjacent cavities, or water vapor condensing there and then freezing, causing forces or damage in the bipolar plate due to the thermally induced expansion that occurs.As explained in more detail below, it was particularly recognized that due to the way in which adhesive is introduced into a channel in one board substrate in order to then bond this to another board substrate, it can happen that an excessive amount of adhesive is introduced, particularly in certain sections of the channel. This can then be deposited in areas adjacent to the channel between the two board substrates, as a result of which the board substrates no longer lie directly against one another and cavities can form. Under unfavorable conditions, water can collect in such cavities, which can then cause problems when it freezes. Regions close to a node within the channel structure, at which node the channel branches, have been recognized as critical sections of the channel in this regard.When applying adhesive, an above-average amount of adhesive may be applied locally in such a region close to the junction. Since it has been recognized that it can be technically difficult to specifically reduce the amount of adhesive applied in these sub-regions of the sewer, it is hereby proposed to provide locally enlarged overflow areas in such regions close to the junction, so that excess adhesive can be absorbed in the larger overflow areas.

[0018] Possible details of the configurations of the bipolar plate proposed herein and the plate substrate that can be used to form the same are explained below.

[0019] Typically, substrates used to form the bipolar plate are plate-shaped, i.e., designed as plate substrates. Accordingly, the plate substrate has a height and a width that are both significantly greater than the thickness of the substrate, i.e., they exceed the thickness of the substrate by, for example, more than ten times or even more than thirty times. The plate substrate can have structures and / or textures on an external surface, for example, to guide reaction fluids along predetermined paths on the substrate surface and / or to enlarge the substrate surface.

[0020] The plate substrate typically consists of a material with very good electrical conductivity or is at least provided with such a material on its surface.

[0021] For example, according to one embodiment, the bipolar plate or its plate substrate can be formed with a graphite-containing material or consist of such a material.

[0022] As a carbon-containing material, graphite offers advantageous properties for many applications. For use in bipolar plates, for example, graphite offers very high electrical conductivity combined with high thermal resilience and sufficiently high mechanical strength. For bipolar plates, graphite-containing materials are used, among others, in which graphite particles are embedded in a polymer matrix. The graphite particles impart the desired electrical and / or thermal properties to the material. The polymer matrix serves, among other things, to hold the graphite particles together mechanically. The polymer matrix can contain, for example, an epoxy resin. The graphite particles thus act as a filler, and the polymer matrix as a type of binder. In addition to graphite particles and polymers, the material mixture can also contain other components, for example in the form of carbon black, other binders, or similar.Advantageously, the graphite-containing material can have a graphite content of at least 60%, preferably at least 70%, or even at least 80%. The percentages can refer to the volume. Due to the high graphite content, the material can, among other things, offer very good electrical conductivity, which is particularly advantageous when used to form bipolar plates. Examples and possible properties of graphite-containing materials are described, among other things, in the applicant's earlier patent application PCT / EP2020 / 078489. The graphite-containing materials described therein can be used in embodiments of the bipolar plate described herein.

[0023] The plate substrate has a channel structure adjacent to one of its surfaces. The channel structure comprises an elongated channel that extends along the surface of the plate substrate and branches off at nodes. The channel is open at the top, i.e., at the surface of the plate substrate. The channel thus represents an elongated depression on the surface of the plate substrate.

[0024] The surface provided with the channel structure is the surface of the plate substrate with which the plate substrate adjoins another plate substrate of a bipolar plate to be formed with it, i.e., said surface forms an inner surface within the bipolar plate. Laterally adjacent to the channel, the surface of the plate substrate can preferably be flat. This surface can also be referred to as an O-plane. Accordingly, in areas adjacent to the channel, the surface of the plate substrate can lie smoothly and gap-free against a likewise flat surface of an adjacent plate substrate.

[0025] The channel may have small cross-sectional dimensions compared to the thickness of the board substrate. For example, the cross-sectional dimensions, in particular a maximum depth of the board substrate, may be less than half, preferably less than one-third, of the thickness of the board substrate.

[0026] The channel structure is designed such that several elongated channel regions merge into one another at nodes. The channel composed of the several channel regions, or at least partial regions thereof, can be continuous and preferably annular. Overall, the channel, or at least partial regions of the channel, can run close to an edge of the board substrate. The channel, or at least partial regions thereof, can enclose internal partial regions of the surface of the board substrate. At a node, a channel region that encloses a first partial region of the surface of the board substrate can merge into a channel region that encloses a second partial region of the surface of the board substrate. A node in the channel structure can thus also be referred to as a branching point.

[0027] The channel can be used, in particular, during production of the bipolar plate to accommodate a flowable adhesive for bonding two adjacent plate substrates together. The adhesive can be a liquid substance during processing, which can subsequently be cured or solidified. The adhesive can be, for example, a resin such as an epoxy resin. Tiny particles can be embedded in the flowable adhesive as solid fillers. Such particles can have particle sizes in the nanometer range up to several tens of micrometers, but preferably be smaller than 50 pm or smaller than 30 pm.

[0028] To bond the board substrates together, the adhesive can be applied as an elongated strand along the channel, for example using a dispenser or a nozzle. Other application methods such as screen printing are also conceivable. The strand can also be referred to as a bead. The cross-sectional geometry of such a strand depends largely on the properties of the dispenser or nozzle. Typically, the thickness of the strand applied using the nozzle or dispenser is initially greater than the depth of the channel, and the width of the strand is narrower than the width of the channel. Accordingly, the strand typically protrudes orthogonally beyond the surface of the board substrate immediately after being introduced into the channel, but does not completely fill the channel in the lateral direction.When the board substrate is pressed together with another board substrate, the protruding part of the adhesive strand is pressed into the channel so that the adhesive is distributed within the channel.

[0029] To achieve the highest possible strength of the final bond between the plate substrates and to ensure reliable bonding, the channel has various sub-areas when viewed in cross-section. In a centrally located bonding area, the channel has a relatively shallow depth. A narrow bonding gap can run along the bonding area between the plate substrate and an adjacent plate substrate of a bipolar plate. Laterally adjacent to opposite sides of the bonding area, the channel has a so-called overflow area of ​​relatively great depth. Such an overflow area can be referred to as a "spill channel."

[0030] During the production of a bipolar plate, the adhesive bead is preferably applied to the bonding area. The adhesive is typically overdosed, meaning more adhesive is applied than is needed to fill the bonding gap, ensuring that the bonding gap is completely filled after bonding the plate substrates and that no air is trapped there.

[0031] The depth of the channel in the adhesive region can be selected such that the adhesive layer formed thereon is sufficiently thin to ensure a mechanically stable and strong bond between the board substrate and an adjacent board substrate along the adhesive region. For example, according to one embodiment, the adhesive region can have a depth of at least 10 pm, preferably at least 20 pm, at least 30 pm or at least 40 pm, but less than 300 pm, preferably less than 200 pm, less than 100 pm, less than 70 pm or less than 60 pm. The smaller the depth of the adhesive region, the thinner the adhesive layer ultimately formed along the adhesive region between the board substrates to be bonded and the higher the mechanical strength of such an adhesive layer.However, the depth of the bonding area should not be chosen to be too small, since otherwise there may be a risk, for example due to manufacturing tolerances, that when the board substrates are bonded, no adhesive layer will be formed at all in some parts of the bonding area and that continuous bonding of the board substrates along the entire channel structure could therefore be locally interrupted. This can also have a negative impact on the required gas tightness of the bipolar plate. In order to ensure, on the one hand, that sufficient adhesive can be applied and distributed along the bonding area to ensure a sufficiently strong bond there, and, on the other hand, to prevent excess adhesive from getting between the adjacent surfaces of the board substrates to be bonded.When the board substrates are pressed together, overflow areas are provided in the channel structure laterally adjacent to the adhesive area. These overflow areas are intended to absorb excess adhesive that has been displaced laterally from the central adhesive area when the board substrates were pressed together. An overflow area is arranged on each of the laterally opposite sides of the corresponding adhesive area and extends along the entire adhesive area. This overflow area also serves to expel the air displaced by the adhesive.

[0032] In order to make the volume of these overflow regions sufficiently large to absorb any excess adhesive, and in order not to excessively increase the width of the entire channel, the overflow regions are designed with a greater depth than the adhesive region. For example, according to one embodiment, the overflow region can have a depth of at least 60 pm, preferably at least 70 pm, at least 80 pm, at least 90 pm, at least 100 pm, or even at least 200 pm, but typically less than 500 pm, less than 300 pm, or less than 250 pm. The depth of the channel in the overflow region can, for example, be relatively greater than the depth of the channel in the adhesive region by more than 10%, more than 20%, more than 30%, or even more than 60%.Furthermore, the depth of the channel in the overflow region can preferably be less than 60%, preferably less than 40%, less than 30%, less than 20% or even less than 10% of the thickness of the board substrate. On the one hand, the depth of the channel in the overflow region should be sufficiently large to provide the overflow region with sufficient volume to absorb excess adhesive, despite its preferably small width. On the other hand, the depth of the channel in the overflow region should not be so large that, for example, the mechanical strength of the board substrate would be reduced. As already indicated in detail, it has now been recognized that in the conventional bonding of board substrates, the adhesive is usually introduced into the channel as a strand with a cross-sectional geometry that depends on the properties of a nozzle or dispenser used.In general, this cross-sectional geometry cannot be easily changed, ie the adhesive strand usually has the same width and height along its entire length along the channel structure.

[0033] However, it has now been recognized that problems can arise with the conventional method of bonding board substrates. These can arise from the fact that, in order to achieve a continuous bond, the adhesive bead to be applied is sometimes applied multiple times at the nodes along the channel structure. In other words, continuous bonding can often only be achieved if the adhesive bead is introduced continuously into the channel using the nozzle or dispenser and applied continuously along its elongated bonding area. However, this can result in a double application of adhesive at the nodes. Accordingly, an above-average accumulation of adhesive can occur in the regions near the nodes.

[0034] It has been observed, or at least suspected, that the increased volume of adhesive applied in the area of ​​the nodes when the plate substrates to be bonded are pressed together cannot be fully absorbed in the adjacent overflow areas, and that this can lead to adhesive being pressed between the surfaces of the two plate substrates in areas adjacent to the channel. This can be referred to as "pulling in" or "wicking" of adhesive between the plate substrates serving as half-shells of the bipolar plates. This can result in so much adhesive being pressed between the plate substrates that the adjacent surfaces of the plate substrates are pressed away from each other by more than a tolerable amount, thus no longer guaranteeing a so-called zero gap between the plate substrates.The tolerable dimension can be, for example, less than 20 pm, preferably less than 10 pm and in particular less than a particle size of particles absorbed in the adhesive.

[0035] Furthermore, there may be a risk that excess adhesive may enter functional geometries that are arranged laterally adjacent to the channel structure, thus impairing the function of the bipolar plate.

[0036] There may also be a risk of increased scrap due to components that do not conform to the drawings.

[0037] In order to be able to locally absorb an increased volume of adhesive in a region close to one of the nodes, which is also referred to hereinafter as the region near the node, it is therefore proposed to design the channel structure in the region near the node with locally enlarged overflow areas. The cross-section of the overflow areas of the channel should be larger in the region close to the node than in a region far from the node. In other words, the cross-section of the overflow areas should be larger where an overflow area extends close to a node than away from this node. In other words, the cross-section of the overflow areas should vary according to the situation along the course of the channel structure and should be larger at or near the nodes than in areas between two nodes.

[0038] The volume or cross-section of the overflow areas should preferably be varied and adapted in such a way that, on the one hand, all excess adhesive can be completely absorbed in the overflow areas, both in the regions close to the node and in the regions remote from the node. On the other hand, however, the overflow areas are not designed to be too voluminous, in order to avoid them not being completely filled with adhesive after bonding the board substrates, and to prevent cavities from remaining in which, in the worst case, moisture could accumulate. According to one embodiment, the overflow areas of the channel can have a greater width in the region close to the node than in the region remote from the node.In other words, the overflow areas can extend parallel to the bonding area they surround and have a width away from a node as has already been used in conventional board substrates, but have a locally increased width near and at a node.

[0039] Due to the larger width of the overflow areas in the region near the junction, more adhesive can be absorbed locally, which is pushed laterally from the adhesive area in the region near the junction towards the overflow areas.

[0040] For example, the width of the overflow areas in the region close to the node may be at least 5%, preferably at least 10%, at least 20%, at least 30%, at least 50% or possibly at least 100%, but preferably less than 500%, less than 300%, less than 200% or possibly less than 120% greater than in an adjacent region remote from the node.

[0041] According to one embodiment, the overflow areas of the channel can have the same depth in the region near the node and in the region far from the node. In other words, the overflow areas can have a substantially constant depth or a flat bottom along their entire length, including the regions far from the node and the regions near the node. In other words, the enlarged cross-section of the overflow areas to be achieved in the regions near the node can be realized only as a result of a locally increased width, but not a locally increased depth, of the overflow areas.

[0042] In this context, "same depth" can be understood as meaning that the depth of the overflow region is constant within a tolerance range of, for example, less than 30% relative, preferably less than 20%, less than 10%, or less than 5% relative. Alternatively, it can be understood that the depth of the overflow region varies between the regions near the node and the regions far from the node, preferably by less than 30 pm, preferably less than 20 pm, less than 10 pm, or less than 5 pm.

[0043] A consistent depth of the channel, and especially of its overflow areas, can ensure sufficiently high stability of the substrate in all its areas and regions. Alternatively, a greater depth of the overflow areas in the regions near the nodes could otherwise lead to local mechanical weakening of the substrate.

[0044] According to one embodiment, the overflow areas of the channel in an overflow channel section in the region close to the node can have a volume which is at least 5%, preferably at least 10%, at least 20%, at least 30% or even at least 40%, but preferably at most 100%, at most 80% or even at most 60% larger than in a channel section of the same length in a region remote from the node.

[0045] It was recognized that a local volume increase of the overflow areas in the regions close to the nodes in the mentioned volume ranges is typically sufficient to be able to absorb at least to a large extent all excess adhesive in the overflow areas next to the bonding area when bonding the board substrates and still avoid the formation of cavities not filled with adhesive.

[0046] The local cross-sectional enlargement of the overflow areas at regions close to the nodes in a channel structure of a plate substrate for a bipolar plate, as proposed herein, can achieve at least some of the following advantages: the risk of adhesive wicking between the plate substrates serving as half-shells of the bipolar plate can be reduced. This can, among other things, prevent the plate substrates from not fitting sufficiently tightly against one another and / or the formation of cavities between the plate substrates in which moisture could accumulate and, upon freezing, lead to mechanical damage to the bipolar plate. In particular, when applying the adhesive to the bonding area of ​​the channel structure, a more stable process window can be achieved, allowing the adhesive to be applied at higher application speeds.As a result, cycle time can be reduced.

[0047] - The risk of adjacent functional geometries of the bipolar plate becoming “blocked” with adhesive can be reduced.

[0048] - Adhesive joints at or near the junction points can be reinforced.

[0049] - Scrap during the production of bipolar plates can be reduced.

[0050] - A process window in the production of bipolar plates can be more stable than in conventional production.

[0051] - The organizational availability of a plant used to manufacture bipolar plates can be increased.

[0052] It should be noted that possible features and advantages of embodiments of the invention are described herein partly with reference to a bipolar plate and partly with reference to a plate substrate usable for forming a bipolar plate. A person skilled in the art will recognize that the features described for individual embodiments can be transferred, adapted, and / or exchanged in an analogous and suitable manner to other embodiments in order to achieve further embodiments of the invention and possibly synergistic effects.

[0053] BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Advantageous embodiments of the invention are further explained below with reference to the accompanying drawings, whereby neither the drawings nor the explanations are to be interpreted as limiting the invention in any way. Figure 1 shows a plan view of a bipolar plate according to one embodiment of the present invention.

[0055] Figure 2 shows a sectional view through a bipolar plate according to an embodiment of the present invention.

[0056] Figure 3 shows an enlargement of section A marked in Figure 1.

[0057] Figure 4 shows an enlargement of section B marked in Figure 2.

[0058] The figures are merely schematic and not to scale. The same reference numerals designate the same or equivalent features in the various drawings.

[0059] DESCRIPTION OF ADVANTAGEOUS EMBODIMENTS

[0060] Figure 1 shows a highly schematic top view of a bipolar plate 1, such as can be used in a fuel cell or a flow battery. Figure 2 shows a highly schematic sectional view through the bipolar plate 1. Figure 3 illustrates, enlarged, section A marked in Figure 1. Figure 4 illustrates, enlarged, section B marked in Figure 2.

[0061] The bipolar plate 1 comprises two plate substrates 3, which are stacked such that they touch along an O-plane with their opposing surfaces 5 and which are bonded together using a flowable adhesive 7. The plate substrates 3 are made of a graphite-containing material. On the opposing surfaces 5, which run inside the bipolar plate 1, and / or on outwardly facing surfaces 9, the plate substrates 3 each have functional geometries 11, for example in the form of process gas-conducting surface structures 13 or cooling channels 15 (highly schematic in the figures and shown only on partial surfaces of the bipolar plate). As illustrated in particular in Figures 1 and 3, a channel structure 17 is formed on at least one of the plate substrates 3.The channel structure 17 comprises an elongated channel 19 that extends along the inward-facing surface 5 of the plate substrate 3. The channel 19 branches off at nodes 21. The channel structure 17 thus has a plurality of elongated channel regions 23, some of these channel regions 23 merging into at least two adjacent channel regions 23 at one of the nodes 21. In other words, at least three different channel regions 23 merge into one another at a node 21. Accordingly, flowable material can flow between the different channel regions 23 across the node 21. The channel regions 23 surround, for example, one or more of the functional geometries 11. At least some of the channel regions 23 run on or near a circumferential edge of the bipolar plate 1 and thus surround an inner region of the bipolar plate 1 in an annular manner.The channel structure 17 also has channel accesses 25, which can serve, for example, as ventilation openings.

[0062] Figure 2, and enlarged in Figure 4, show a cross-sectional view of a channel region 23 of channel 19. Along its entire longitudinal extent, viewed in cross-section, channel 19 has a centrally arranged, flat adhesive region 27 as well as two overflow regions 29, which laterally adjoin the adhesive region 27 on opposite sides.

[0063] In the bonding area 27, the channel 19 has a smaller depth of, for example, 50 μm than in the overflow areas 29, whose depth can be, for example, 100 μm. In the bonding area 27, a narrow bonding gap 31 is thus formed between the two board substrates 3 to be bonded, at which adhesive 7, between a partial area of ​​the inwardly directed surface 5 in the bonding area 27 of a first of the board substrates 3 and an opposite inwardly directed surface 5 of a second of the board substrates 3, stably bonds the two board substrates 3 to one another as a layer only approximately 50 μm thick.Laterally adjacent to the adhesive area 27, there is then one of the overflow areas 29 on each of the two sides of the adhesive area 27, in which, due to its greater depth and thus its relatively large volume, excess adhesive 7, which is laterally displaced from the adhesive area 27 during bonding of the two plate substrates 3, can be absorbed.

[0064] Figure 3 shows that the overflow areas 29 of the channel 19 in a region 33 close to the node point, near one of the node points 21, have a greater width and thus a larger cross-section than in a region 35 remote from the node point, far from this node point 21. In other words, the overflow area 29 in the region 33 close to the node point has a locally widened overflow channel section 37.

[0065] In this region 33 near the node, the overflow area 29 thus has a width that is, for example, at least 10% or even at least 50% greater than in an adjacent region 35 far from the node. The depth of the overflow area 29 can be substantially the same in the region 33 near the node and in the region 35 far from the node. In other words, a floor of the overflow area 29 can extend in the same plane in the region 33 near the node and in the region 35 far from the node. Due to its locally increased width, the overflow area 29 in the widened overflow channel section 37 in the region 33 near the node has a volume that is, for example, 40% ± 10% greater, in some cases even up to 80% greater, than in a channel section of the same length in the region 35 far from the node.

[0066] In order to bond the two plate substrates 3 of the bipolar plate 1 together, a strip of adhesive 39 is applied centrally along the bonding area 27 of the channel structure 17 using a nozzle or dispenser. The strip of adhesive 39 has a smaller width than the bonding area 27, but is initially applied with a layer thickness that is significantly greater than the thickness of the bonding gap 31 to be formed between the plate substrates 3 in the area of ​​the channel structure 17. For example, the strip of adhesive 39 can be applied as a bead, surface (web), or bead with a thickness of approximately 0.4 mm. Due to the properties of the nozzle or dispenser, the strip of adhesive 39 is applied everywhere with the same cross-sectional geometry. In the area of ​​nodes 21, sections of the strip of adhesive 39 can intersect, so that more adhesive 7 is deposited there.

[0067] During the subsequent pressing together of the two plate substrates 3, the adhesive 7 is then pressed orthogonally between the two plate substrates 3 and thus flows laterally first towards an edge of the adhesive region 27 and then into the overflow regions 29 adjacent there. A geometry of the overflow regions 29 is at least approximately dimensioned such that the entire volume of excess adhesive 7, which is displaced from the adhesive region 27, can be absorbed in the adjacent overflow regions 29 and preferably fills them completely and without any remaining cavities.

[0068] Due to the locally increased volume of the overflow areas 29 in the locally widened overflow channel sections 37 in the regions 33 near the junction point, the adhesive 7 deposited there in excess can also be sufficiently absorbed in the adjacent overflow area 29. In other words, an excess of adhesive 7, which was applied near the junction point 21, for example, as overlapping partial areas of the adhesive strand 39, can be absorbed in the widened overflow channel section 37. The risk of excess adhesive 7 being pressed or drawn between the plate substrates 3 can thus be minimized.

[0069] Finally, it should be noted that terms such as "having," "comprising," etc., do not exclude other elements or steps, and terms such as "a" or "an" do not exclude a plurality. Furthermore, it should be noted that features or steps described with reference to one of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Reference symbols in the claims are not to be considered as limiting. List of Reference Symbols

[0070] I Bipolar plate

[0071] 3 Plate substrate

[0072] 5 inward-facing surface of the plate substrate

[0073] 7 Adhesives

[0074] 9 outward-facing surface of the disk substrate

[0075] II Functional Geometry

[0076] 13 Surface structure

[0077] 15 Cooling channel

[0078] 17 channel structure

[0079] 19 Channel

[0080] 21 Junction

[0081] 23 Channel area

[0082] 25 Channel access

[0083] 27 Adhesive area

[0084] 29 Overflow area

[0085] 31 Adhesive gap

[0086] 33 region close to the node

[0087] 35 remote region

[0088] 37 widened overflow channel section

[0089] 39 Adhesive strand

Claims

Claims 1. A plate substrate (3) for a bipolar plate (1) for a fuel cell or a flow battery, said plate substrate (3) being composed of at least two plate substrates (3), wherein the plate substrate (3) has a channel structure (17) with an elongated channel (19) extending along a surface (5) of the plate substrate (3) and branching at nodes (21), wherein the channel structure (17) has a plurality of elongated channel regions (23) and at least one of the channel regions (23) merges into at least two adjacent channel regions (23) at at least one node (21), wherein the channel (19) has, along an entire longitudinal extent of the channel structure (17), a centrally arranged adhesive region (27) in cross section and two overflow regions (29) adjacent to the adhesive region (27) on opposite sides, wherein the channel (19) has a smaller depth in the adhesive region (27) than in the overflow regions (29),wherein the overflow areas (29) of the channel (19) in a region (33) close to the node near one of the nodes (21) have a larger cross-section than in a region (35) remote from the node (21).

2. A disk substrate according to claim 1, wherein the overflow areas (29) of the channel (19) have a greater width in the region (33) near the node than in the region (35) far from the node.

3. A disk substrate according to any one of the preceding claims, wherein the overflow areas (29) of the channel (19) have the same depth in the region (33) near the node and in the region (35) remote from the node.

4. A disk substrate according to any one of the preceding claims, wherein the overflow regions (29) of the channel (19) in a widened overflow channel section (37) in the region (33) close to the node have a volume that is at least 5% larger than in a channel section of the same length in the region (35) remote from the node.

5. A disk substrate according to any one of the preceding claims, wherein the overflow regions (29) of the channel (19) in an overflow channel section (37) in the region (33) close to the node point have a volume that is at most 100% greater than in a channel section of the same length in the region (35) remote from the node point.

6. A disk substrate according to any one of the preceding claims, wherein the adhesive region (27) has a depth of between 10 pm and 300 pm.

7. A disk substrate according to any one of the preceding claims, wherein the overflow region (29) has a depth of between 60 pm and 500 pm.

8. Plate substrate according to one of the preceding claims, wherein the plate substrate (3) is formed with a graphite-containing material.

9. Bipolar plate (1) which is composed of at least two plate substrates (3) stacked one above the other, wherein at least one of the plate substrates (3) is designed according to one of the preceding claims and wherein the plate substrates (3) are glued to one another by means of a flowable adhesive (7) introduced along the channel structure (17).

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