Bipolar plate for a fuel cell or flow battery having a hydrophobic surface area and method of manufacturing the same

Abstract

This specification describes a bipolar plate (1) for use in fuel cells or flow batteries. The bipolar plate (1) includes a substrate (3) and a channel (5) extending from a channel inlet (7) on one surface of the substrate (3) into the interior (9) of one of the substrates (3). One surface of the substrate (3) is more hydrophobic in a first region (19) adjacent to the channel inlet (7) inside the channel (5) than in a second region (21). In addition, this prevents moisture from entering the channel (5) and accumulating there.

Description

[Technical Field]

[0001] Field of Invention

[0002] The present invention relates to a bipolar plate for a fuel cell or flow battery and a method for manufacturing such a bipolar plate. [Previous Technology]

[0003] Background of the Invention

[0004] Bipolar plates are intended to perform several different tasks for fuel cells; they are stacked to form the core of a fuel cell system. On one hand, they are intended to interconnect with adjacent fuel cells, that is, to physically and electrically connect the anode of one cell to the cathode of an adjacent cell. On the other hand, they should be able to distribute gas towards the reaction space within the fuel cell, with gas distributed across one surface of the bipolar plate; that is, the bipolar plate should transport the reactant gas into the reaction zone. For this purpose, the bipolar plate typically has flow field profiles (so-called flow fields) on both sides, which can be milled, cast, or molded, with hydrogen flowing through one side and air supplied on the other. The bipolar plate generally also controls the removal of water vapor or the release of heat and electrical energy. Furthermore, the bipolar plate should also provide gas separation between adjacent cells, external sealing, and, if necessary, cooling.

[0005] Bipolar plates typically have channels extending through the interior of one of the substrates of the bipolar plate. These channels are capable of performing certain tasks, for example, during the production of the bipolar plate. For example, an adhesive can be contained within these channels, by means of which the two sub-substrates forming the bipolar plate are bonded together. Alternatively, channels may be provided to perform other functions.

[0006] Problems have been observed when operating fuel cells or flow batteries under certain operating conditions, especially at or after low temperatures. These problems are presumed to be related to the bipolar plates used in fuel cells or flow batteries. [Summary of the Invention]

[0007] Summary of the Invention

[0008] A bipolar plate or a fuel cell or flow battery equipped with a bipolar plate may be required, which can operate reliably, especially under cryogenic or post-cryogenic operating conditions. In particular, a bipolar plate that is simple in design, can be manufactured at low cost, and / or can operate particularly robustly may be required. A method for manufacturing such a bipolar plate may also be required. In particular, a method may be required to manufacture the bipolar plate at low cost, effortlessly, and / or reliably.

[0009] This need can be satisfied by the subject matter of a separate claim. Advantageous embodiments are defined in the separate claim, described in the following detailed description, and illustrated in the figures.

[0010] A first aspect of the present invention relates to a bipolar plate for use in fuel cells or flow batteries, the bipolar plate comprising a substrate and a channel extending from a channel inlet on one surface of the substrate into the interior of the substrate. One surface of the substrate has stronger hydrophobicity in a first region adjacent to the channel inlet inside the channel than in a second region.

[0011] A second aspect of the present invention relates to a method for manufacturing a bipolar plate for a fuel cell or flow battery, the method comprising at least the following steps: providing a substrate having a structure such that a channel extends inside the substrate in the manufactured bipolar plate, the channel extending from a channel inlet at one surface of the substrate into the interior of the substrate; and processing the surface of the substrate in a first region adjacent to the channel inlet, such that the surface of the substrate in the first region is more hydrophobic than the surface of the substrate in a second region.

[0012] Without limiting the scope of the invention in any way, the concepts and possible features related to the embodiments of the invention can be considered, in particular, based on the concepts and findings described below.

[0013] In a brief and broad summary, the basic principles of the concept described herein can be understood as being based on an understanding of problems such as those observed in the operation of fuel cells or flow batteries, particularly at or after cryogenic temperatures, which may be due to water actually penetrating into the channels of the bipolar plate or water vapor condensing and then freezing in these channels, generating forces and / or damage in the bipolar plate due to thermally induced expansion during this process. While the objective previously required sealing measures within or on these channels to prevent water or water vapor penetration, this document proposes, as an alternative, that at least a portion of the substrate surface near the channel inlet, and preferably the exposed area of ​​the surface inside the channel, be more hydrophobic than other portions of the substrate surface. This should prevent water from penetrating into the exposed areas of the channel and / or accumulating there via condensation.

[0014] The following explains possible details of embodiments of the bipolar plate and manufacturing method presented herein.

[0015] The substrate forming the bipolar plate is typically flat. Therefore, the substrate has a height and a width that are both significantly greater than the thickness of the substrate, that is, they exceed the thickness of the substrate by, for example, more than ten times. On an outer surface, the substrate may have a structure and / or texture, for example, to guide the reactive fluid along a predetermined path on the substrate surface and / or to expand the substrate surface.

[0016] The substrate is typically composed of a material with excellent conductivity, or at least the material is provided on its surface.

[0017] For example, according to one embodiment, the bipolar plate or its substrate may be formed of or composed of a graphite-containing material.

[0018] As a carbon-containing material, graphite offers advantageous properties for most applications. When used in bipolar plates, for example, graphite provides very high electrical conductivity along with high thermoelasticity and sufficiently high mechanical strength. In bipolar plate applications, graphite particles are embedded in a graphite-containing material within a polymer matrix. These graphite particles impart the desired electrical and / or thermal properties to the material. The polymer matrix serves, among other things, to mechanically hold these graphite particles together. The polymer matrix may contain, for example, epoxy resin. The graphite particles thus act as a filler, and the polymer matrix acts as a type of binder. In addition to graphite particles and polymers, the material mixture may also contain other components, such as carbon black, other binders, or the like. Advantageously, the graphite-containing material may have a graphite content of at least 60%, preferably at least 70%, or even at least 80%. This percentage can be referenced to the volume. Due to this high graphite content, the material can provide, among other things, 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 material described therein can be used in the embodiments of the bipolar plate described herein and can be made locally hydrophobic on its surface. The entire contents of that earlier patent application are incorporated herein by reference in their entirety.

[0019] At least one internal channel, preferably an elongated chamber, is formed in the substrate. The channel extends from a channel inlet on the surface of the substrate into the interior of the substrate. In other words, at the channel inlet, the channel opens to a volume or atmospheric environment surrounding the substrate. The channel extends from the channel inlet into the interior of the substrate and may extend to a channel outlet in another area of ​​the surface of the substrate. The channel may have a small cross-sectional dimension compared to the thickness of the substrate. For example, the cross-sectional dimension may be less than half the thickness of the substrate, preferably less than one-third. The cross-section of the channel may be circular or rectangular or have any other geometry. The channel may be surrounded by the material of the substrate of the bipolar plate along its entire extent. Alternatively, a portion of this extent may be covered by other materials, such as sealants, adhesives, or glues introduced into the channel.

[0020] Conventionally, attempts have been made to seal the channels in the substrate of the bipolar plate in a way that prevents moisture from penetrating. For this purpose, for example, a sealant is introduced into the channel, which fills and seals the channel, at least at the channel entrance, preferably along the entire volume of the channel.

[0021] However, it has been observed that reliably sealing the channel or its inlet may be difficult during the manufacture of the bipolar plate. For example, it may be difficult to apply the sealant in a manner that completely fills the channel or at least adequately seals its inlet. In most cases, only a very small tolerance window is allowed, which may lead to instability in the production process. Furthermore, excessive sealant is often required, for example, so that excessive sealant may leak from the channel inlet, thus failing to adequately seal the channel inlet. However, in this case, the excessive sealant still does not work, and therefore results in excessive sealant consumption. In addition, it may be necessary to redo the sealing of the channel and / or inspect and / or clean the used tools. Furthermore, the material requirements for the sealant may conflict with the technical requirements for the bipolar plate. Moreover, over time, for example, due to thermal stress and associated shape changes, there may be a risk of gradual leakage between the channel and the sealant.

[0022] To at least partially overcome the aforementioned problems or disadvantages, this document describes an alternative to prevent moisture penetration or accumulation inside the channel. Here, a portion of the substrate surface inside the channel is specially treated or configured to achieve greater hydrophobicity than other regions on the substrate surface, particularly the inner side of the channel or other regions of the substrate surface adjacent to the channel. This more hydrophobic portion is referred to herein as the first region. The less hydrophobic region is referred to herein as the second or third region. The second or third region may be directly adjacent to the first region.

[0023] In this first region, the substrate surface may be specifically treated such that the contact angle formed by the water droplet and the surface is greater than 40 degrees, preferably greater than 60 degrees, or even greater than 80 degrees. Specifically, the substrate surface in the first region may be superhydrophobic, i.e., the contact angle may be greater than 90 degrees. Specifically, the contact angle in the first region may be greater than the contact angle in the second region, for example, by 5 degrees, preferably 10 degrees, 20 degrees, or even 30 degrees.

[0024] Due to the increased hydrophobicity of the substrate surface in the first region adjacent to the channel inlet, the risk of liquids, especially water, penetrating the channel through the channel inlet can be greatly reduced.

[0025] According to one embodiment, it is advantageous that the first region surrounds the channel inlet in a ring-like manner. In other words, preferably, the entire surface surrounding the channel inlet can be specifically made more hydrophobic. This further minimizes the risk of liquid penetration. The hydrophobic channel inlet can act as a barrier to the supply of liquid and prevent liquid from entering the channel, for example, due to capillary forces.

[0026] Furthermore, according to one embodiment, the first region may include portions of the substrate surface that are in communication with the channel inlet gas inside the channel. In other words, besides a portion of the region adjacent to the channel inlet, the first region may further extend into the interior of the channel and include, in particular, portions of the substrate surface that can be reached by gas from the channel inlet. Gas communication between the channel inlet and the portion of the first region located further inside the channel can be achieved here by gas flow and / or gas diffusion.

[0027] Since the highly hydrophobic first region also includes the portion of the substrate surface inside the channel, among other things, it can reduce the risk of vapor, especially water vapor, entering the interior of the channel through the channel inlet and forming droplets thereby by condensation.

[0028] According to one embodiment, the substrate of the bipolar plate is composed of two flat sub-substrates. The two substrates are bonded together and cover an adhesive surface. An overflow channel extends adjacent to the adhesive surface. Here, the first region extends at least along a portion of the overflow channel. The second region extends along at least such a portion of the adhesive surface. When manufacturing the bipolar plate, the two flat sub-substrates can be provided first as separate components and then bonded together across the adhesive surface.

[0029] In other words, the bipolar plate can be constructed from two or more parts. The flat sub-substrates can first be prefabricated as individual components. Structures in the form of, for example, grooves, trenches or similar features can be formed on one surface, which form channels in the resulting whole substrate after the two sub-substrates have been joined together.

[0030] These structures can be configured to form adhesive surfaces, through which two adjacent sub-substrates stacked together can be bonded to each other. The adhesive surfaces of the stacked sub-substrates can be configured such that they are opposite to each other and very close to each other, and preferably extend parallel to each other. When bonding the two sub-substrates, an adhesive can be applied to one or both of the opposite adhesive surfaces.

[0031] These structures can be further configured such that at least one overflow channel is formed adjacent to the adhesive surfaces. In the region of the overflow channel, a recess in the surface of a sub-substrate can be larger than a recess in the region of the adhesive surfaces. Therefore, one surface of the overflow channel of a sub-substrate can be spaced further from an opposing surface of a second sub-substrate stacked above it than in the case of opposing adhesive surfaces.

[0032] When bonding the two sub-substrates, the adhesive is preferably applied specifically to one or both of the bonding surfaces, rather than into the overflow channel. However, when the two sub-substrates are pressed together, the adhesive may thus flow laterally into the overflow channel and at least partially fill it. The overflow channel can then hold excess adhesive. The two sub-substrates can then be effectively bonded together without excess adhesive preventing the sub-substrates from being pressed tightly together. If necessary, the overflow channel can be located on two opposite sides of the bonding surfaces.

[0033] Since these adhesive surfaces are intended for bonding the two sub-substrates and the adhesive should therefore adhere sufficiently to these adhesive surfaces, these adhesive surfaces can be expediently formed into second regions with relatively low hydrophobicity or even hydrophilicity. This allows the adhesive, which is generally treated in a liquid or flowable state, to adhere over a large area to these adhesive surfaces and form an effective adhesive material bond with them.

[0034] Conversely, it is permissible to form a surface of the overflow channel with stronger hydrophobic properties. Admittedly, a portion of this surface may eventually be covered by adhesive, which seeps laterally between the bonded surfaces. However, since the volume of the overflow channel is preferably selected to be incompletely filled with adhesive, at least a portion of the surface of the overflow channel can remain exposed. To prevent moisture from accumulating on this portion of the surface, it can be configured as a first region with increased hydrophobicity.

[0035] Therefore, according to one embodiment, in the completed bipolar plate of one embodiment, the channel can be partially filled with a flowable adhesive. The first region is a portion of the surface of the substrate on the inner side of the channel where the adhesive is not in contact with the substrate. The second region of the substrate forms a portion of the surface of the substrate on the inner side of the channel where the adhesive is in contact with the substrate.

[0036] In other words, the bipolar plate composed of two sub-substrates may, for example, have a channel partially filled with an adhesive. The adhesive may be flowable during processing and subsequent crosslinking or curing. Therefore, the adhesive can adhere to the bonding surfaces on the two sub-substrates and bond the two sub-substrates together. A portion of the surface of the sub-substrates inside the channel where the adhesive contacts the bonding surfaces is preferably configured as a second region with low hydrophobicity. Conversely, a portion of the surface of the sub-substrates not covered by the adhesive after the bonding process may be configured as a first region with strong hydrophobic properties.

[0037] Preferably, the first region inside the channel extends along the entire surface of the substrate where the adhesive is not in contact with the substrate.

[0038] In other words, the first region inside the channel is preferably cut and arranged to the specified dimensions in such a manner that, after the two sub-substrates are bonded together with the adhesive, all surface areas of the substrate inside the channel that are not covered by the adhesive have strong hydrophobicity. Among other things, this ensures that no weakly hydrophobic surface remains inside the channel, for example, where permeated water vapor may condense.

[0039] Generally, various methods are known for treating the surfaces of substrates to impart hydrophobic properties. For example, the surface can be coated with a highly hydrophobic material, for example, due to the absence of polar molecules and their contained groups. Conversely, various suitable methods are known for treating the surfaces of substrates to impart less hydrophobic or hydrophilic properties. For example, the surface can be coated with a material that has at least some hydrophilicity due to the polar molecules and groups contained therein. Alternatively, the surface can be specifically oxidized, for example by treating it with fluorine or sulfur trioxide. Plasma treatment or corona treatment can also produce surface properties with lower hydrophobicity or hydrophilicity.

[0040] According to one embodiment, the first region of the substrate surface described herein can be treated by locally irradiating the substrate surface with a laser to impart stronger hydrophobic properties.

[0041] The laser beam can be specifically directed to the first region on the surface of the substrate. The second region on the surface of the substrate may be left untreated or treated in another way to impart lower hydrophobicity. Using a laser, the first and second regions on the surface of the substrate can be locally configured to have different intensities of hydrophobicity. The laser beam can also be specifically directed to a very small area. In contrast, using other techniques, such as coating a small area with a hydrophobic material, can be a difficult process.

[0042] Therefore, according to one embodiment, the first region of the completed bipolar plate can be locally treated with a laser to produce the desired localized increase in hydrophobicity.

[0043] Due to the use of laser beam irradiation, the first region typically possesses characteristic microscopic properties. For example, a region treated with a laser beam may have been melted for a short period of time and, upon subsequent hardening, achieve a structural and / or compositional characteristic of the laser treatment. Alternately or additionally, material can be locally removed from the surface with the aid of a high-energy laser beam, that is, ablated. Plasma can be generated near the surface, and the material can then be evaporated. Additionally or alternately, the material can undergo chemical changes due to the thermal effects caused by laser irradiation, that is, "crack," and then remain, for example, as a carbon structure or enter the gas phase. Overall, laser treatment can produce a rougher surface texture than an untreated region. Alternately or additionally, the volumetric structure, particularly the crystal structure, of the material treated with laser can be altered in a manner typical of laser treatment.

[0044] The laser may have the property of allowing the material of the substrate to melt or ablate on the laser-treated surface. The laser may be, for example, a pulsed laser, particularly a short-pulse laser capable of emitting laser pulses with a duration in the nanosecond range or less. For example, the laser may be an infrared laser.

[0045] According to one embodiment, the first region inside the channel can be processed to produce a surface texture that generates a lotus effect.

[0046] The formation of complex microstructures and nanoscale surface structures can cause droplets to form a very small contact area with only one surface, resulting in bead formation on textured surfaces. This effect is also known as the lotus effect and can represent the strong hydrophobicity or even superhydrophobicity of a surface. The surface texture can be formed by many tiny and closely spaced depressions and / or channels.

[0047] For example, the surface texture can be generated by scanning a laser beam along a regular or irregular path on the surface to be textured, briefly melting, stirring and / or ablating the material on the surface.

[0048] According to one embodiment, the same laser used to treat the substrate surface in the first region to make it more hydrophobic can also be used to treat the substrate surface in the second region and / or the third region of the surface.

[0049] It has been established that, with appropriately adapted process control, the hydrophobic properties of a surface can be strengthened or weakened by laser processing. Therefore, it may be particularly advantageous to provide first and second regions with different hydrophobicities on the substrate of the bipolar plate by localized processing using the same laser. If necessary, a third region of the substrate surface can also be processed using the same laser. For example, the substrate surface located in the third region may have a surface layer removed by laser processing. Especially in the case of graphite-containing materials with a polymer matrix, for example, a polymer layer formed on the surface can be opened or removed by laser processing. This simplifies process control and / or reduces the number of required equipment.

[0050] In particular, according to a more specific embodiment, the laser parameters used to operate the laser when processing the second and / or the third region of the substrate surface can be selected to be different from those selected when processing the first region of the substrate surface.

[0051] For example, it has been determined that when laser parameters that result in the formation of a surface texture producing a lotus effect are used, the first region can be advantageously configured to be strongly hydrophobic. On the other hand, when other laser parameters are used, it has been observed that the surface properties become less hydrophobic or even hydrophilic. For example, it has been observed that graphite-containing materials can acquire hydrophilic properties when irradiated with very strong short laser pulses. In this regard, the applicant of this application is filing another patent application entitled "Method for forming a hydrophilic surface on a graphite-containing material and a method for manufacturing a bipolar plate and using the bipolar plate and fuel cell or flow battery". This further patent application describes details of a laser process, which is also used in embodiments of the bipolar plate described herein, as well as in manufacturing operations using the same or similar methods. The entire contents of this further application are incorporated herein by reference.

[0052] The embodiments of the bipolar plate disclosed herein can suppress the penetration of liquids or moisture into the channels of the substrate. For example, this can prevent damage caused by water expansion and freezing. Shorter coating times, such as applying adhesive between the sub-substrates to be bonded, and lower material usage are possible. In summary, more robust processes, wider tolerance ranges, stable process capabilities, lower process costs, and / or less waste can be achieved.

[0053] It should be noted that the possible features and advantages of these embodiments of the present invention are described herein with reference in part to the bipolar plate and in part to the method of manufacturing the bipolar plate. Those skilled in the art will recognize that the features described with respect to individual embodiments can be transferred, adapted and / or interchanged in a similar and suitable manner to other embodiments to achieve further embodiments of the invention and possible complementary effects.

Implementation Method

[0060] Detailed Description of Preferred Embodiments

[0061] Figure 1 shows a highly schematic plan view of a bipolar plate 1 of this type that can be used in fuel cells or flow batteries. Figure 2 shows a schematic cross-sectional view taken through the bipolar plate 1.

[0062] The bipolar plate 1 includes a substrate 3, which may be made of, for example, a graphite-containing material. A channel 5 extends in the substrate 3. The channel 5 extends from a channel inlet 7 into an interior 9 of the substrate 3. In this example, the channel 5 is annular and extends close to the outer periphery of the bipolar plate 3. A plurality of channel inlets 7 are provided. These channel inlets 7 can be used as openings for ventilation of the annular region of the channel 5 and extend toward an outer edge of the substrate 3. In this example, additional openings are provided, which may also be considered as channel inlets 7 or can alternately serve as channel outlets 11 and are directed away from the outer edge toward a center of the substrate 3.

[0063] A first region 19 on the surface of the substrate 3 inside the channel 5 is treated or configured to be more hydrophobic than a second region 21. On one hand, the first region 19 extends to the channel inlet 7 and preferably surrounds the channel inlet 7 in a circumferential manner. On the other hand, the first region 19 inside the channel 5 also partially extends into the interior 9 of the substrate 3, particularly at the location where an inner surface of the substrate inside the channel 5 is exposed, so that gas or vapor from the channel inlet 7 can reach this portion of the first region 19. Furthermore, the first region 19 may also extend to the channel outlet 11 and preferably surround it in a circumferential manner.

[0064] Two sub-substrates 13 may be provided to manufacture the bipolar plate 1. In the sub-substrates 13, near the outer periphery of the sub-substrates 13, by means of localized recesses, a structure may be configured such that, on the one hand, an adhesive surface 15 is formed, and on the other hand, an overflow channel 17 is formed on any side adjacent to the adhesive surface 15. The adhesive surface 15 and the overflow channel surround a central region of the bipolar plate 1 in a circumferential manner. The adhesive surface 15 is configured as a second region 21 with lower hydrophobicity or even hydrophilicity, while the surface adjoining the overflow channel 17 is configured as a first region 19 with greater hydrophobicity. On the outward-facing surface, the sub-substrates 13 of the bipolar plate 1 have a surface structure 31 in their central region, for example, for targeted conduction of reactant gases (shown only in FIG. 2, not illustrated in FIG. 1 for clarity). On the inward-facing surface, the sub-substrate 13 has other surface structures, such as forming cooling channels 33 inside the bipolar plate 1.

[0065] For example, the surface of the substrate 3 in the first region 19 can be irradiated with a laser 27. The laser parameters of the laser 27 can be set in such a way that a microstructure and / or nanostructure of a surface texture 25 is formed on the surface of the first region 19, resulting in a lotus effect and / or a chemical and / or physical effect and thus strong hydrophobicity. In FIG3, the surface texture 25 is schematically symbolically represented in a partially enlarged section.

[0066] The second region 21 may not be irradiated by the laser 27, or other laser parameters may be set, which result in the second region 21 having less hydrophobic or hydrophilic properties. Similarly, the third region 29 may be treated with the laser 27 by setting appropriate laser parameters to, for example, produce strong hydrophilic properties there.

[0067] To bond the two sub-substrates 13 together, for example, an adhesive 23 in the form of a flowable adhesive is applied between the bonding surfaces 15. Due to the low hydrophobicity or hydrophilicity of the second region 21 disposed therein, this adhesive 23 can adhere strongly to the bonding surfaces 15. When the two sub-substrates 13 are pressed together, excess adhesive 23 can flow laterally into the overflow channel 17. However, it is not necessary to apply an excessive amount of adhesive 23, as is sometimes used in conventional methods, such that the overflow channel 17 leading to the channel inlet 7 is completely filled with adhesive 23 to seal the entire channel 5. Alternatively, portions of the overflow channels 17 can remain exposed and therefore their inner surfaces can remain uncovered. The strong hydrophobicity of the first region 19 formed therein means that moisture cannot deposit on the exposed surfaces inside the channel 5, even though they are in gas communication with the channel inlet 7. The frost damage caused by the freezing moisture inside channel 5 can thus be avoided.

[0068] Finally, it should be noted that terms such as "having" and "comprising" do not exclude other elements or steps, and terms such as "one" or "a" do not exclude a plurality. It should be further noted that features or steps described with reference to one of the above embodiments can also be used in combination with other features or steps of the other embodiments described above. Symbols in these claims should not be construed as limiting. [Simplified Explanation of the Diagram]

[0054] The following description, with reference to the accompanying drawings, further explains advantageous embodiments of the invention, which should not be construed as limiting the invention in any way.

[0055] FIG1 shows a plan view of a bipolar plate according to one embodiment of the present invention.

[0056] Figure 2 shows a cross-sectional view taken through a bipolar plate according to one embodiment of the present invention.

[0057] Figure 3 shows an enlarged view of one of the segments marked A in Figure 1.

[0058] Figure 4 shows an enlarged view of one of the segments marked B in Figure 2.

[0059] These diagrams are for illustrative purposes only and are not drawn to scale. The same representative symbols in these different diagrams represent features that have the same or the same function.

Claims

1. A bipolar plate (1) for a fuel cell or flow battery, wherein the bipolar plate (1) comprises: a substrate (3), and a channel (5) extending from a channel inlet (7) at one surface of the substrate (3) into one interior (9) of the substrate (3), wherein one surface of the substrate (3) is more hydrophobic in a first region (19) adjacent to the channel inlet (7) inside the channel (5) than in a second region (21), wherein the channel (5) is partially filled with a flowable adhesive (23), the first region (19) forming a portion of the surface inside the channel (5) of the substrate (3), wherein the adhesive (23) is not in contact with the substrate (3), and the second region (21) of the substrate (3) forming a portion of the surface inside the channel (5) of the substrate (3), wherein the adhesive (23) is in contact with the substrate (3).

2. The bipolar plate of claim 1, wherein the first region (19) surrounds the channel entrance (7) in a ring shape.

3. The bipolar plate of claim 1 or 2, wherein the first region (19) comprises a plurality of portions of the surface of the substrate (3) inside the channel (5), the portions being in gas communication with the channel inlet (7).

4. A bipolar plate as claimed in either claim 1 or 2, wherein the substrate (3) of the bipolar plate (1) is composed of two flat sub-substrates (13) bonded together across an adhesive surface (15), and an overflow channel (17) extends adjacent to the adhesive surface (15), the first region (19) extends at least along a plurality of portions of the overflow channel (17), and the second region (21) extends at least along a plurality of portions of the adhesive surface (15).

5. The bipolar plate of claim 1, wherein the first region (19) extends along the entire surface of the substrate (3) inside the channel (3), wherein the adhesive (23) is not in contact with the substrate.

6. A bipolar plate as requested in either 1 or 2, wherein the first region (19) is locally treated by laser (27) to provide locally increased hydrophobicity.

7. A bipolar plate as requested in either 1 or 2, wherein the first region (19) has a surface texture (25) that produces a lotus effect.

8. The bipolar plate of either claim 1 or 2, wherein the bipolar plate (1) is made of a graphite-containing material.

9. A method of manufacturing a bipolar plate (1) for a fuel cell or flow battery, the method comprising: providing a substrate (3) having a structure such that a channel (5) extends inside the substrate (1) in the manufactured bipolar plate (1), the channel (5) extending from a channel inlet (7) located on one surface of the substrate (3) into one interior (9) of the substrate (3); and processing the surface of the substrate (3) in a first region (19) near the channel inlet (7) of the channel (5) such that the surface of the substrate (3) in the first region (19) has stronger hydrophobicity compared to the surface of the substrate (3) in a second region (21), wherein the channel (5) is partially filled with a flowable adhesive (23). The first region (19) forms part of the surface inside the channel (5) of the substrate (3), wherein the adhesive (23) is not in contact with the substrate (3), and the second region (21) of the substrate (3) forms part of the surface inside the channel (5) of the substrate (3), wherein the adhesive (23) is in contact with the substrate (3).

10. The method of claim 9, wherein the substrate (3) is provided having two flat sub-substrates (13), an adhesive surface (15) is configured to be located on the two flat sub-substrates (13) and an overflow channel (17) is configured to be adjacent to the adhesive surface (15), the first region (19) extends at least along a plurality of portions of the overflow channel (17), and the second region (21) extends at least along a plurality of portions of the adhesive surface (15), the method further comprising bonding the two flat sub-substrates (13) together across the adhesive surface (15).

11. The method of claim 9 or 10, wherein the first region (19) is processed by locally irradiating the surface of the substrate (3) with a laser.

12. The method of claim 11, wherein the method further comprises processing the substrate with a laser (27) in the second region (21) of the surface of the substrate (3) and / or a third region (29) of the surface of the substrate (3).

13. The method of claim 12, wherein the laser (27) operates with different laser parameters when processing the second and / or third regions (21, 29) of the surface of the substrate (3) and when processing the first region (19) of the surface of the substrate (3).

14. The method of any one of claims 9 or 10, wherein the first region (19) of the surface of the substrate (3) is formed by processing with a surface texture (25) that produces a lotus effect.

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