Electrochemical device and method for producing a sealing element on a gas diffusion layer of an electrochemical unit

Abstract

To reduce local temperature rise in an edge web region of an electrochemical device comprising: a stack of multiple electrochemical units in succession along a stack direction, said units each comprising an electrochemically active membrane-electrode assembly; a bipolar plate and a sealing arrangement; at least one medium channel; at least one flow field through which a medium can flow from the medium channel to a different medium channel; and at least one communication channel through which the flow field and the medium channel are in fluid communication with one another, the communication channel comprising an edge web through which a flow of medium from the medium channel passes, where a coolant flows through a coolant channel separated from the interior of the edge web by a joining line, the flow field comprising an edge channel which is disposed between the edge web and the coolant channel and through which a flow of the medium from the medium channel passes, and where the sealing arrangement extends around the flow field and includes an inner edge which forms an edge of a cathode-side electrochemically active face or an anode-side electrochemically active face of the membrane-electrode assembly, the proposal is made for the inner edge of the sealing arrangement to lie on the side of the edge web that faces away from the medium channel.

Description

[0001] Electrochemical device and method for producing a sealing element on a gas diffusion layer of an electrochemical unit

[0002] The present invention relates to an electrochemical device comprising a stack of several electrochemical units arranged successively along a stacking direction, each comprising an electrochemically active membrane electrode assembly, a bipolar plate, and a sealing assembly, at least one medium channel extending through several of the electrochemical units along the stacking direction, at least one flow field through which a medium from the medium channel can flow transversely to the stacking direction from the medium channel to another medium channel, and at least one connecting channel through which the flow field and the medium channel are in fluid communication with one another, wherein the connecting channel comprises an edge web through which the medium from the medium channel flows during operation of the electrochemical device,wherein a coolant channel separated from the interior of the edge web by a joining line is flowed through by a coolant during operation of the electrochemical device. The flow field comprises an edge channel arranged between the edge web and the coolant channel and through which the medium flows from the medium channel during operation of the electrochemical device. The sealing arrangement extends along the circumferential direction of the flow field around the flow field and has an inner edge that borders a cathode-side electrochemically active surface or an anode-side electrochemically active surface of the membrane-electrode assembly. Such an electrochemical device can be designed, in particular, as a fuel cell device or as an electrolysis device.

[0003] If the connecting channel, through which a flow field and a medium channel are in fluid communication with one another, is not flowed through by a coolant during operation of the electrochemical device, but rather by another gas, for example, an anode gas or a cathode gas of the electrochemical device, the fluid medium flowing through the edge web contributes nothing to cooling the regions of the membrane-electrode assembly adjacent to the edge web. However, the electrochemical activity in these regions of the membrane-electrode assembly is no lower than in other regions of the membrane-electrode assembly, in particular no lower than in other regions of the membrane-electrode assembly that are arranged adjacent to an edge web that forms part of a coolant connecting channel.

[0004] Due to the greater distance to the first coolant-carrying channel of the coolant flow field (corresponding to the first web within the adjacent gas flow field), a locally higher temperature occurs during operation of the electrochemical device in a region of the membrane electrode assembly adjacent to an edge web that does not carry coolant.

[0005] The present invention is based on the object of creating an electrochemical device of the type mentioned above, in which a local temperature increase due to insufficient cooling in the region of an edge web of a connecting channel through which no coolant flows is avoided or at least reduced. This object is achieved according to the invention in an electrochemical device having the features of the preamble of claim 1 in that the inner edge of the sealing arrangement is located on the side of the edge web facing away from the medium channel.

[0006] This ensures that the sealing arrangement in the area of ​​the connecting channel locally projects beyond the edge web into the area of ​​the edge channel of the flow field.

[0007] As a result, an outer edge of the electrochemically active surface of the membrane electrode assembly is shifted inwards, i.e. towards the center of the flow field, thereby reducing the maximum distance from the outermost channel of the coolant flow field through which the coolant flows.

[0008] According to the invention, the sealing arrangement is preferably widened in the areas in which it crosses the connecting channels through which no coolant flows during operation of the electrochemical device.

[0009] Preferably, the sealing arrangement is widened in regions which extend along the circumferential direction of the sealing arrangement beyond the ends of the edge webs through which coolant does not flow.

[0010] To avoid temperature peaks, the sealing arrangement in the area of ​​the connecting channels, which are not flowed through by a coolant, is extended locally into the area of ​​the respective associated flow field.

[0011] In a preferred embodiment of the invention, the inner edge of the sealing arrangement is located on the side of the coolant channel facing the medium channel. Furthermore, the inner edge of the sealing arrangement can be located in the region of the edge channel.

[0012] In a preferred embodiment of the invention, it is provided that the connecting channel is formed between two bipolar plate layers which are fixed to one another at the joining line.

[0013] The two bipolar plate layers can be firmly bonded to one another, in particular by welding, for example by laser welding.

[0014] In a preferred embodiment of the invention, it is provided that the inner edge of the sealing arrangement lies on the side of the joining line facing away from the medium channel.

[0015] The inner edge of the sealing arrangement can be formed on a sealing element of the sealing arrangement, which is integrally connected to a gas diffusion layer of the respective electrochemical unit.

[0016] The sealing element is preferably made of an elastomer material.

[0017] For example, it can be provided that the elastomer material of the sealing element penetrates a connection area of ​​the gas diffusion layer.

[0018] Furthermore, it can be provided that the sealing element comprises a sealing projection which projects in the region of the connecting channel from a base body of the sealing element in a projection direction facing away from the medium channel.

[0019] Such a sealing projection preferably extends along the circumferential direction of the sealing element's base body only over a portion of the circumference of the sealing element's base body. It is particularly advantageous if the sealing projection extends along the circumferential direction of the sealing element's base body only over less than 50%, particularly preferably over less than 25%, of the circumference of the sealing element's base body.

[0020] In particular, the sealing projection preferably extends only over a part of the circumference of the main body of the sealing element, which crosses a connecting channel through which no coolant flows during operation of the electrochemical device.

[0021] The sealing projection may be locally interrupted.

[0022] The sealing projection may comprise a plurality of sections which are spaced apart from one another along the circumferential direction of the base body.

[0023] The extent (width) of the sealing projection perpendicular to its circumferential direction and perpendicular to the stacking direction is preferably greater than the extent (width) of the edge web of the flow field perpendicular to the circumferential direction and perpendicular to the stacking direction.

[0024] An extension (width) of the sealing arrangement perpendicular to its circumferential direction and perpendicular to the stacking direction is preferably greater in the region of the connecting channel than in at least one region outside the region of the connecting channel. This ensures that the size of the electrochemically active area of ​​the membrane-electrode assembly is reduced only in the region of the connecting channel, in which the edge web is not flowed through by a coolant and therefore does not provide sufficient cooling, while the electrochemically active area of ​​the membrane-electrode assembly is not unnecessarily reduced in the region of a connecting channel through which a coolant flows during operation of the electrochemical device, and in the regions of the membrane-electrode assembly located outside the regions of the connecting channels.In a preferred embodiment of the invention, it is provided that the sealing arrangement is provided in the region of the connecting channel with a plurality of recesses which are spaced apart from one another along the circumferential direction of the sealing arrangement and are formed on a sealing projection which projects in the region of the connecting channel from a base body of the sealing element in a projection direction facing away from the medium channel.

[0025] The sealing projection can form a passivation layer made of an elastomer material, which is preferably injection-molded onto a gas diffusion layer together with at least one sealing lip of the sealing arrangement.

[0026] Overmolding the gas diffusion layer with a passivation layer made of elastomer material in an otherwise thermally highly stressed area of ​​the gas diffusion layer ensures local reaction inactivity and thus a desired reduction in the thermal stress on the gas diffusion layer, which increases the durability of the electrochemical device during operation.

[0027] The elastomer material is molded onto the gas diffusion layer in a cavity of an injection mold. This creates a connection area for the sealing element formed from the elastomer material, in which the porous material of the gas diffusion layer is at least partially penetrated by the elastomer material.

[0028] If the gas diffusion layer can move freely in the connection area during the introduction of the elastomer material into the cavity of the injection mold, this can have the disadvantage that the gas diffusion layer floats on the elastomer material and a side of the gas diffusion layer facing the membrane electrode assembly in the assembled electrochemical device is overmolded with elastomer material, although this side of the gas diffusion layer is not intended to be provided with elastomer material.

[0029] Such "floating" of the gas diffusion layer can occur both in the area of ​​the sealing projection and outside the area of ​​the sealing projection. The side of the gas diffusion layer facing the membrane-electrode assembly, which is not intended to be overmolded with elastomer material, can, in particular, be a side of the gas diffusion layer that has a microporous layer (MPL).

[0030] Such a microporous layer makes it difficult or impossible for the elastomer material to penetrate the gas diffusion layer, resulting in a poor, undefined bond between the gas diffusion layer and the elastomer material. Furthermore, such an overmolding process can lead to the formation of elastomer material contamination, which can compromise the subsequent function of the electrochemical cell containing the overmolding gas diffusion layer and thus the subsequent function of the electrochemical device.

[0031] The above-described disadvantages of undesired over-injection of the gas diffusion layer can be avoided if the injection mold comprises one or more deformation limiting elements which limit or prevent deformation of the gas diffusion layer during the introduction of the injection molding material into the cavity.

[0032] Such a deformation-limiting element can be designed, for example, as a hold-down device. The deformation-limiting element, for example in the form of a hold-down device, ensures that during the injection process, the elastomer material introduced into the cavity of the injection mold preferably reaches the side of the gas diffusion layer facing away from the membrane-electrode assembly during operation of the electrochemical device.

[0033] If the gas diffusion layer has a microporous layer (MPL) and a substrate, the elastomer material preferentially reaches the substrate side of the gas diffusion layer.

[0034] This ensures better penetration of the gas diffusion layer with the elastomer material and thus a better and more reliable connection of the sealing element formed from the elastomer material to the gas diffusion layer.

[0035] If the injection molding tool comprises at least one pressing tool part which has a pressing projection for pressing the gas diffusion layer during the injection molding process, the deformation limiting elements which are used in the region of the sealing projection are preferably spaced from the pressing projection of the pressing tool part.

[0036] As a result, the above-mentioned recesses are formed in the region of the sealing projection, which recesses are preferably designed as through-openings extending through the sealing element in the sealing projection of the sealing element.

[0037] These recesses, preferably in the form of through-openings, can in particular have a substantially circular cross-section (taken perpendicular to the stacking direction of the electrochemical device). The sealing arrangement can also be provided with a plurality of recesses in the at least one region outside the connecting channel and thus outside the sealing projection, which are spaced apart from one another along the circumferential direction of the sealing arrangement and are arranged on the inner edge of the sealing arrangement.

[0038] Such recesses are obtained when deformation limiting elements, for example hold-down devices, are used during the injection molding of the sealing element, which are arranged on a pressing projection of a pressing tool part of the injection mold or are formed integrally with a pressing projection of the pressing tool part.

[0039] These deformation limiting elements in the non-passivated area outside the sealing projection weaken the connection between the sealing element formed from the elastomer material on the one hand and the gas diffusion layer on the other.

[0040] However, the geometry and position of the deformation limiting elements, for example in the form of hold-down clamps, are selected in such a way that a required minimum connection force is maintained.

[0041] Instead of a plurality of deformation-limiting elements spaced apart along the circumferential direction of the gas diffusion layer, a deformation-limiting element comprising a wave-shaped outer edge can also be used. This results in the inner edge of the sealing arrangement formed from the elastomer material being wave-shaped in the at least one region outside the connecting channel, in which no connecting projection is formed. It is advantageous if, in the non-passivated regions of the electrochemical device that lie outside the region of the at least one sealing projection, a cathode-side sealing element is connected to the cathode-side gas diffusion layer with the same or a similar connection geometry as an anode-side sealing element is connected to the anode-side gas diffusion layer.

[0042] If recesses are provided on the inner edge of the cathode-side sealing element and on the inner edge of the anode-side sealing element, they preferably lie substantially congruently one above the other in the stacking direction of the electrochemical device in the assembled state of the electrochemical device.

[0043] Alternatively, it can be provided that an inner edge of the cathode-side sealing element, which borders the sealing element towards the center of the cathode-side gas diffusion layer, is moved further inwards, i.e. towards the center of the gas diffusion layer, than the inner edge of the anode-side sealing element.

[0044] For the connection of the sealing element to the gas diffusion layer, it is advantageous if the areas of the gas diffusion layer which are in contact with a deformation limiting element of the injection mold during the introduction of the elastomer material into the cavity of the injection mold are essentially completely penetrated by the elastomer material.

[0045] Alternatively, it can also be provided that these areas of the gas diffusion layer are only partially or not at all penetrated with elastomer material.

[0046] In the region of the at least one sealing projection, by means of which a passivated region of the electrochemical device is created, the deformation-limiting elements, for example the hold-down devices, ensure a defined hold-down of the gas diffusion layer during the introduction of the elastomer material into the cavity of the injection mold. Furthermore, the gas diffusion layer is precisely positioned relative to the sealing element formed from the elastomer material during the injection molding of the elastomer material.

[0047] The deformation limitation, in particular the holding down of the gas diffusion layer, can lead to a reduction in the thickness (extension along the stacking direction) of the gas diffusion layer compared to the unpressed state of the gas diffusion layer in the contact areas where the gas diffusion layer is in contact with the deformation limitation elements, or in the vicinity of these contact areas. This results in the cavity of the injection mold being better filled with elastomer material in the areas between the deformation limitation elements during the injection process. Alternatively, the height of the cavity of the injection mold can also be reduced in this area to reduce the overall height of the gas diffusion layer and the sealing projection.

[0048] Preferably, the deformation-limiting elements are arranged in the cavity of the injection mold on the same side of the gas diffusion layer on which the sealing projection is created. It is particularly advantageous if this side is the substrate side of the gas diffusion layer, i.e., the side of the gas diffusion layer facing away from the microporous layer (MPL) of the gas diffusion layer, since better penetration of the gas diffusion layer with the elastomer material is ensured on the substrate side of the gas diffusion layer. This ensures a good bond between the sealing element produced from the elastomer material and the gas diffusion layer.

[0049] It is advantageous if the gas diffusion layer is essentially completely penetrated by the elastomer material in the areas where it is in contact with the deformation-limiting elements, because this also electrochemically deactivates the areas of the gas diffusion layer in contact with the deformation-limiting elements, such as hold-down devices. Alternatively, the areas of the gas diffusion layer in contact with the deformation-limiting elements can be only partially or not at all penetrated by the elastomer material. This results in the areas of the gas diffusion layer in contact with the deformation-limiting elements being partially or fully electrochemically activated.

[0050] It is advantageous if the height of the edge web, the height of the web of the respective flow field closest to the edge web, or the height of the edge web and the height of the web of the flow field closest to the edge web in the region that lies (along the stacking direction) above or below the at least one sealing projection, is reduced compared to the height of the edge web or the height of the web of the flow field closest to the edge web outside the region of the sealing projection. These local height reductions can be formed in one bipolar plate layer or in two bipolar plate layers.

[0051] These local height reductions serve to create a sufficiently high and easily manufactured sealing protrusion without increasing the overall local height of an electrochemical cell (along the stacking direction). These local height reductions can also be implemented in an area adjacent to the sealing protrusion to accommodate assembly tolerances.

[0052] The size, shape, number, position, and / or spacing of the deformation-limiting elements from one another is preferably selected to achieve a favorable compromise between preventing deformation of the gas diffusion layer on the one hand and ensuring sufficient filling of the injection mold cavity in the region of the sealing projection with the elastomer material on the other. The medium flowing through the connecting channel during operation of the electrochemical device is preferably an anode gas (fuel gas, particularly hydrogen-containing) or a cathode gas (oxidizing agent, particularly oxygen-containing) of the electrochemical device.

[0053] In principle, the inner edge of the sealing arrangement, which is offset inwards, i.e. towards the center of the flow field, can be an inner edge of an anode-side region of the sealing arrangement or an inner edge of a cathode-side region of the sealing arrangement.

[0054] In a preferred embodiment of the invention, it is provided that the inner edge of the sealing arrangement borders a cathode-side electrochemically active surface of the membrane-electrode arrangement.

[0055] In another embodiment of the invention, it can be provided that the inner edge of the sealing arrangement borders a cathode-side electrochemically active surface of the membrane-electrode arrangement and a further sealing arrangement is provided which borders an anode-side electrochemically active surface of the membrane-electrode arrangement, wherein the inner edge of the cathode-side sealing arrangement lies on the side of the inner edge of the further, anode-side sealing arrangement facing away from the medium channel.

[0056] In this case, an area of ​​the cathode-side electrochemically active surface is always opposite an area of ​​the anode-side electrochemically active surface of the membrane electrode assembly. There is then no area of ​​the membrane electrode assembly that is supplied with oxidant on the cathode side but not also with fuel gas on the anode side. This prevents locally increased aging of the membrane electrode assembly, which can occur if an area of ​​the membrane electrode assembly is supplied only with oxidant but not with fuel gas during operation of the electrochemical device.In a particularly preferred embodiment of the electrochemical device, it is therefore also provided that an outer edge of a cathode-side electrochemically active surface of the membrane-electrode arrangement is offset inwards, i.e. towards the center of the flow field, relative to an outer edge of an anode-side electrochemically active surface of the membrane-electrode arrangement.

[0057] The electrochemical device according to the invention can be designed in particular as a polymer electrolyte membrane (PEM) fuel cell device, in which the membrane electrode units of the electrochemical units of the electrochemical device each contain a polymer electrolyte membrane.

[0058] The present invention further relates to a method for producing a sealing element on a gas diffusion layer of an electrochemical unit, the method comprising:

[0059] Arranging an injection molding tool at the gas diffusion layer;

[0060] Introducing injection molding material into a cavity of the injection mold; wherein the sealing element comprises a sealing projection that projects from a base body of the sealing element in a projection direction pointing into an interior of the sealing element, wherein the sealing projection extends along the circumferential direction of the base body of the sealing element only over a portion of the circumference of the base body of the sealing element. The present invention is further based on the object of creating a method of the aforementioned type in which damage to the gas diffusion layer is avoided and a sealing element with a mechanically stable connection region for connection to the gas diffusion layer is produced.

[0061] This object is achieved according to the invention in a method having the features of the preamble of claim 18 in that the injection molding tool comprises at least one deformation limiting element which limits or prevents deformation of the gas diffusion layer during the introduction of the injection molding material into the cavity, wherein the injection molding tool comprises at least one pressing tool part which has a pressing projection for pressing the gas diffusion layer and wherein the at least one deformation limiting element is spaced from the pressing projection of the pressing tool part during the introduction of the injection molding material into the cavity of the injection molding tool.

[0062] The advantages of such an injection molding process have already been described above.

[0063] In a preferred embodiment of the method, it is provided that the pressing projection of the pressing tool part has at least one rounding and / or at least one bevel.

[0064] This prevents damage to the component pressed between opposing projections of the injection mold, particularly the gas diffusion layer. For the purpose of molding a sealing element made of an elastomer material onto a gas diffusion layer, the gas diffusion layer is inserted between two projections of an injection mold and clamped and pressed together when the injection mold is closed.The porous material of the gas diffusion layer is pressed down to such an extent that the elastomer material introduced into the cavity of the injection mold does not penetrate, or only to a very small extent, the area of ​​the gas diffusion layer located between the pressing projections, so that the central area of ​​the gas diffusion layer surrounded by the pressing projections, i.e. the part of the gas diffusion layer used in the electrochemical device for supplying cathode gas or anode gas to the membrane-electrode arrangement, is only minimally penetrated.

[0065] Known push-off projections of injection molds have rectangular cross-sections that are easy to manufacture and are preferably mirror-symmetrical with respect to a plane oriented perpendicular to the stacking direction.

[0066] The use of such push-off projections may result in damage to the component pressed between the push-off projections, which may directly or indirectly cause damage to the electrochemical cell in which the gas diffusion layer is installed and thus a failure of the entire fuel cell stack.

[0067] It is therefore important to ensure that the gas diffusion layer onto which the sealing element made of an elastomer material is to be molded is free of any pre-damage. Such pre-damage can, for example, be fiber breakage in the gas diffusion layer, structural defects in a microporous layer (MPL) of the gas diffusion layer, or, if the gas diffusion layer being inserted into the injection mold is already provided with an electrode layer and a membrane, pre-damage to the membrane and / or leaks in the electrochemical cell. By designing at least one of the push-off projections with a geometry that deviates from the usual rectangular geometry, the stress on the components pressed between the push-off projections in the contact area with the push-off projections is reduced.

[0068] This can be achieved by at least one of the push-off projections, preferably both push-off projections, having at least one rounded edge, a contact surface with a convexly curved region and / or at least one bevel.

[0069] It is particularly advantageous if the contact surface of the push-off projection has only small changes in direction on the scale of the pore size of the gas diffusion layer.

[0070] The pore size of the gas diffusion layer corresponds, for example, to the distance between the fibers of the gas diffusion layer.

[0071] For example, the change in height of the contact surface of the push-off projection is preferably no more than approximately one pore size over the length of half a pore size. The tangent to the contact surface of the push-off projection is thus preferably inclined at an angle α of less than 60°, particularly preferably less than 45°, relative to a plane perpendicular to the stacking direction (e.g., one of the main planes of the unpressed gas diffusion layer).

[0072] The total width of the push-off projection, i.e., its extension perpendicular to the stacking direction and perpendicular to the circumferential direction of the gas diffusion layer, is preferably a multiple of the pore size of the gas diffusion layer and is particularly preferably more than 0.5 mm, for example, more than 1 mm. However, an excessively large total width of the push-off projection leads to an undesirable reduction in the electrochemically active region of the electrochemical device, since it increases the distance between the sealing structure of the sealing element and the electrochemically active region.

[0073] If the gas diffusion layer is asymmetrically designed, for example, if it has a microporous layer (MPL) on one side, or if it is provided with a catalyst layer, a catalyst layer, and a membrane, or with a complete membrane-electrode assembly on one side, it may be advisable to also design the pressure-relief protrusions between which such an asymmetric gas diffusion layer is pressed asymmetrically. Otherwise, a damaged microporous layer (MPL) of the gas diffusion layer would come into contact with a membrane-electrode assembly during assembly of the electrochemical device, which could cause damage to the membrane-electrode assembly.

[0074] For example, it may be provided that the push-off projection is completely omitted on one side of the gas diffusion layer. This is preferably the side of the gas diffusion layer that is provided with a microporous layer (MPL), a catalyst layer, and / or a membrane, or a complete membrane-electrode assembly.

[0075] If one of the sides of the gas diffusion layer, for example, a side comprising a microporous layer (MPL), a catalyst layer, a membrane, or a complete membrane-electrode assembly, is particularly sensitive to handling, it may be advantageous if this side of the gas diffusion layer is at least partially in contact with a contact element of the injection molding tool, which comprises an elastomer material, during the introduction of the injection molding material into the cavity of the injection mold. Such a contact element can, for example, comprise a coating made of an elastomer material on a region of the injection molding tool and / or a seal—preferably embedded without a groove—made of an elastomer material, for example, a flat seal, arranged in the injection molding tool.

[0076] A coating of an elastomer material can be produced, for example, by means of a pattern printing process, preferably a screen printing process or a pad printing process.

[0077] A seal made of an elastomer material that may be arranged in the injection mold should be structured as little as possible in order to avoid any inhomogeneity of the load when the gas diffusion layer is compressed.

[0078] On the other hand, inserting a sealing cord with a circular cross-section into a groove that leaves gaps at its edges would not be advantageous.

[0079] An advantageous compression of the gas diffusion layer is achieved if the clear dimension between the push-off projections of the closed injection mold is smaller than the height (extension along the stacking direction) of the gas diffusion layer in the compressed fuel cell stack.

[0080] It has proven advantageous if the gas diffusion layer is pressed between the pressure projections of the injection mold to a maximum of 80%, particularly preferably to a maximum of 75%, of the thickness of the gas diffusion layer at a pressure of 0.025 MPa.

[0081] Furthermore, it has proven advantageous if the gas diffusion layer is compressed between the pressure projections of the injection mold to at least 40%, particularly preferably at least 50%, of the thickness of the gas diffusion layer at a pressure of 0.025 MPa. If a gas diffusion layer is provided with a catalyst layer, with a catalyst layer and a membrane, or with a complete membrane-electrode assembly, these additional layers can be produced separately from the gas diffusion layer and applied to the gas diffusion layer or laminated to the gas diffusion layer. Alternatively, these additional layers can also be produced in situ on the gas diffusion layer.

[0082] Further features and advantages of the invention are the subject of the following description and the drawings illustrating an exemplary embodiment. The drawings show:

[0083] Fig. 1 is a perspective view of a section of a fuel cell stack of a fuel cell device in the region of a connecting channel which connects a medium channel and a flow field of the fuel cell device to one another, wherein two fuel cell units of the fuel cell stack are shown which are arranged one after the other in a stacking direction of the fuel cell stack, and a bipolar plate of a third fuel cell unit which is arranged above the two fuel cell units;

[0084] Fig. 2 is a top plan view along the stacking direction of the fuel cell stack of the section of the fuel cell stack from Fig. 1;

[0085] Fig. 3 is an enlarged view of area I from Fig. 2;

[0086] Fig. 4 shows a longitudinal section through the fuel cell stack of Figs. 1 to 3, along line 4-4 in Fig. 3; Fig. 5 shows a perspective view of the section of the fuel cell stack corresponding to Fig. 1, wherein only the membrane electrode assembly and the sealing assembly of a single fuel cell unit are shown;

[0087] Fig. 6 is a top plan view along the stacking direction of the membrane electrode assembly and the sealing assembly of Fig. 5;

[0088] Fig. 7 shows a schematic section through an injection molding tool and a gas diffusion layer projecting into a cavity of the injection molding tool, wherein the injection molding tool has a plurality of deformation limiting elements spaced apart from one another in a circumferential direction of the gas diffusion layer, which elements touch the gas diffusion layer before the injection molding material is introduced into the cavity of the injection molding tool and are in contact with a push-off projection of a push-off tool part of the injection molding tool;

[0089] Fig. 8 is a partial top view of an assembly comprising the gas diffusion layer and a sealing element fixed to the gas diffusion layer, which has been produced by means of the injection molding tool of Fig. 7;

[0090] Fig. 9 is a schematic section through an injection molding tool comprising a plurality of deformation-limiting elements spaced apart from one another along the circumferential direction of the gas diffusion layer, spaced apart from a push-off projection of a push-off tool part of the injection molding tool, and contacting the gas diffusion layer before the injection molding material is introduced into the cavity of the injection molding tool; Fig. 10 is a partial plan view of an assembly comprising a gas diffusion layer and a sealing element secured to the gas diffusion layer, which was produced using the injection molding tool shown in Fig. 9;

[0091] Fig. 11 shows a schematic section through an injection molding tool, a gas diffusion layer projecting into a cavity of the injection molding tool, which has a section pressed between two push-off projections of the injection molding tool, and a sealing element made of an elastomer material injection-molded onto the gas diffusion layer, wherein the push-off projections are mirror-symmetrical to one another and have a rectangular cross-section;

[0092] Fig. 12 shows a schematic section through an injection mold, a gas diffusion layer projecting into a cavity of the injection mold, which has a section pressed between two push-off projections of the injection mold, and a sealing element made of an elastomer material injection-molded onto the gas diffusion layer, wherein the push-off projections each have a convexly curved contact surface;

[0093] Fig. 13 shows a schematic section through an injection molding tool, a gas diffusion layer projecting into a cavity of the injection molding tool, which has a section pressed between a push-off projection of a push-off tool part of the injection molding tool and a flat section of another tool part of the injection molding tool, and a sealing element made of an elastomer material injection-molded onto the gas diffusion layer, wherein the push-off projection of the push-off tool part of the injection molding tool has a convexly curved contact surface; Fig.14 a schematic section through an injection mold, a gas diffusion layer protruding into a cavity of the injection mold, which has a section pressed between two push-off projections of the injection mold, and a sealing element made of an elastomer material injection-molded onto the gas diffusion layer, wherein the two push-off projections of the injection mold are designed asymmetrically to one another, both push-off projections have a convex contact surface and the push-off projections protrude to different extents into the material of the gas diffusion layer;.

[0094] Fig. 15 is a schematic section through an injection mold, a gas diffusion layer projecting into a cavity of the injection mold, which has a section pressed between two push-off projections of the injection mold, and a sealing element made of an elastomer material and molded onto the gas diffusion layer, wherein the two push-off projections each have a contact surface which has a section parallel to a main surface of the gas diffusion layer and sections which are each inclined relative to a main surface of the gas diffusion layer, wherein the push-off projections are formed asymmetrically to one another and one of the push-off projections penetrates further into the material of the gas diffusion layer than the other push-off projection;

[0095] Fig. 16 shows a schematic section through an injection mold, a gas diffusion layer projecting into a cavity of the injection mold, which has a section pressed between a push-off projection of a push-off tool part of the injection mold, on the one hand, and an elastic contact element of the injection mold, on the other hand, and a sealing element made of an elastomer material injection-molded onto the gas diffusion layer, wherein the push-off projection of the push-off tool part of the injection mold has a convexly curved contact surface and a section of another tool part of the injection mold opposite the push-off projection of the push-off tool part is provided with a coating of an elastomer material; and

[0096] Fig. 17 shows a schematic section through a tool part of an injection molding tool, which is provided with a contact element for pressing a section of a gas diffusion layer, wherein the contact element is designed as a separate sealing element which has one or more sealing lips and is inserted into a groove formed on the tool part of the injection molding tool.

[0097] Identical or functionally equivalent elements are designated by the same reference numerals in all figures.

[0098] An electrochemical device shown in Figures 1 to 6 and designated as a whole by 100, for example a fuel cell device 102 or an electrolyzer, comprises a stack 104 of electrochemical units 106, for example fuel cell units 108 or electrolyzer units, wherein the stack 104 comprises a plurality of electrochemical units 106 arranged one after the other in a stacking direction 110 and a clamping device (not shown) for applying a clamping force directed along the stacking direction 110 to the electrochemical units 106.

[0099] As best seen from the sectional view in Fig. 4, each electrochemical unit 106 of the electrochemical device 100 comprises a bipolar plate 112 and a membrane electrode assembly (MEA) 114. The membrane electrode assembly 114 comprises, for example, a catalyst-coated membrane ("Catalyst Coated Membrane"; CCM) and two gas diffusion layers 116 and 118, wherein the first gas diffusion layer 116 is arranged, for example, on the anode side and the second gas diffusion layer 118 is arranged, for example, on the cathode side.

[0100] The bipolar plate 112 is formed, for example, from a metallic material.

[0101] The bipolar plate 112 has a plurality of medium passage openings 120, through each of which a fluid medium to be supplied to the electrochemical device 100 (in the case of a fuel cell stack, for example, a fuel gas or anode gas, an oxidizing agent or cathode gas, or a coolant) can pass through the bipolar plate 112. The medium passage openings 120 of the bipolar plates 112 arranged consecutively in the stack 104 and the spaces located between the medium passage openings 120 in the stacking direction 110 together form a medium channel 122.

[0102] Each medium channel 122 through which a fluid medium can be supplied to the electrochemical device 100 is assigned at least one other medium channel 122 through which the respective fluid medium can be discharged from the electrochemical device 100.

[0103] Through an intermediate flow field 124, which is preferably formed on a surface of an adjacent bipolar plate 112 or (for example, in the case of a coolant flow field) in the space between the layers of a multilayer bipolar plate 112, the medium can flow from the first medium channel 122 transversely, preferably substantially perpendicularly, to the stacking direction 110 through the respective flow field 124 to the second medium channel 122. For example, an anode gas medium channel 126 for an anode gas of the electrochemical device 100 is shown in Fig. 4.

[0104] Each medium channel 122 is in fluid communication with the respectively associated flow fields 124 through at least one connecting channel 128.

[0105] In the embodiment shown in the drawing, each bipolar plate 112 comprises a first bipolar plate layer 130 and a second bipolar plate layer 132, which are secured to one another in a fluid-tight manner along connecting lines 134 which run perpendicular to the plane of the drawing in Fig. 4, preferably in a material-to-material manner, in particular by welding, for example by laser welding.

[0106] As can be seen from Fig. 4, the anode gas medium channel 126 is in fluid communication with a flow field 138 for the anode gas, of which only an edge channel 140 is shown, via an anode gas connection channel 136, which is formed by a gap between the first bipolar plate layer 130 and the second bipolar plate layer 132. This edge channel 140 forms the outermost channel of the flow field 138, is open toward the membrane-electrode assembly 114, and is delimited on its outer side, facing the medium channel 122, by an edge web 142, which bears sealingly against the membrane-electrode assembly 114.

[0107] During operation of the electrochemical device 100, the medium flows from the medium channel 122 through the connecting channel 128 into the interior space 144 of the edge web 142, from where it passes through passage openings 145 through the flank 146 of the edge web 142, which separates the interior space 144 of the edge web 142 from the edge channel 140, into the edge channel 140. A coolant channel 148, through which a coolant flows during operation of the electrochemical device 100 and which is formed between the first bipolar plate layer 130 and the second bipolar plate layer 132 of each bipolar plate 112, is separated from the interior space 144 of the edge web 142 by a joining line 134, which connects the first bipolar plate layer 130 and the second bipolar plate layer 132 to one another.

[0108] An undesired escape of the fluid media from the flow fields 124 of the electrochemical device 100 is prevented by a sealing arrangement 150 which extends along the circumferential direction 152 of the flow fields 124 around the flow fields 124 and has two inner edges 155, namely an anode-side inner edge 154 and a cathode-side inner edge 156.

[0109] The anode-side inner edge 154 of the sealing arrangement 150 defines an anode-side electrochemically active area 158 of the membrane-electrode assembly 114, and the cathode-side inner edge 156 of the sealing arrangement 150 defines a cathode-side electrochemically active area 160 of the membrane-electrode assembly 114.

[0110] As best seen in Fig. 4, the sealing arrangement 150 preferably comprises two sealing elements 161, wherein a first sealing element 162 is preferably fixed to the anode-side gas diffusion layer 116 and a second sealing element 164 is preferably fixed to the cathode-side second gas diffusion layer 118 of the membrane-electrode arrangement 114.

[0111] For example, it can be provided that the sealing elements 162 and 164 are injection-molded or cast onto the respectively associated gas diffusion layer 116 and 118, respectively. The first sealing element 162 preferably has one or more sealing lips 166, with which the first sealing element 164 bears fluid-tight against the first bipolar plate layer 130 of an adjacent bipolar plate 112.

[0112] The first sealing element 162 can further comprise further sealing lips 168, with which the first sealing element 162 abuts fluid-tight against the first bipolar plate layer 130 of a first adjacent bipolar plate layer 112 and against the second bipolar plate layer 132 of a second adjacent bipolar plate 112 in order to form a medium channel section 170 of the sealing arrangement 150, which extends around a medium channel 122 of the electrochemical device 100, so that escape of medium from the medium channel 122 into the environment of the electrochemical device 100 and / or in flow fields 124 of the electrochemical device 100 associated with other media is prevented.

[0113] The second sealing element 164 preferably has one or more sealing lips 166, with which the second sealing element 164 rests fluid-tight against the second bipolar plate layer 132 of an adjacent bipolar plate 112.

[0114] The sealing elements 162 and 164 of the sealing arrangement 150 are preferably formed from an elastomer material.

[0115] This elastomer material preferably also penetrates the regions of the first gas diffusion layer 116 and the second gas diffusion layer 118 adjacent to the sealing elements 162 and 164, respectively, so that the gas diffusion layers 116 and 118 are not porous in these penetration regions, but cannot be penetrated by either the anode gas or the cathode gas.

[0116] The anode-side inner edge 154 of the sealing arrangement 150 is arranged on the side of an edge web 142 of a bipolar plate 112 facing the medium channel 122. If the cathode-side inner edge 156 of the sealing arrangement 150 were also arranged on the side of an edge web 142 of a bipolar plate 112 facing the medium channel 122, as is the case with known electrochemical devices 100, both the cathode-side electrochemically active surface 160 and the anode-side electrochemically active surface 158 of the membrane-electrode arrangement 114 would extend into the region of the membrane-electrode arrangement 114 that lies between the edge webs 142 and the medium channel 122.

[0117] However, the outer edge region of these electrochemically active surfaces 158, 160 would be so far removed from the outermost coolant channel 148 that sufficient cooling of this outer edge region by the coolant flowing through the coolant channel 148 would not be ensured, so that the temperature of the electrochemical device 100 would locally increase in this outer edge region of the membrane-electrode assembly 114.

[0118] In order to eliminate this problem of a local temperature increase during operation of the electrochemical device 100, the sealing arrangement 150 in the embodiment of an electrochemical device 100 shown in the drawing is designed such that the cathode-side inner edge 156 of the sealing arrangement 150 lies on the side of the edge web 142 facing away from the medium channel 122.

[0119] This ensures that, during operation of the electrochemical device 100, electrochemical activity does not already occur in the outer edge region of the membrane-electrode assembly 114, which lies between the edge webs 142 and the medium channel 122, but only in the further inner region of the membrane-electrode assembly 114, which borders the edge channels 140 and is thus closer to the coolant channels 148. The outermost edge of the membrane-electrode assembly 114, which exhibits electrochemical activity during operation of the electrochemical device 100, is thus shifted inward in the illustrated embodiment of an electrochemical device 100, i.e., toward the center of the flow fields 124, thereby reducing the maximum distance of an electrochemically active region of the membrane-electrode assembly 114 from the channels of the coolant flow field.

[0120] The extent to which the cathode-side inner edge 156 of the sealing arrangement 150 is moved inward, toward the center of the flow fields 124, depends on the geometric structure of the sealing arrangement 150 and the bipolar plate 112 in this area, as well as on the extent of the connection area of ​​the sealing arrangement 150, in which the elastomer material of the sealing arrangement 150 penetrates the adjacent gas diffusion layers 116 and 118, respectively, and on the desired temperature distribution, which in turn depends on the width of the edge channels 140 and the coolant channels 148, as well as on the thermal conductivity of the materials of the membrane-electrode assembly 114 and the bipolar plates 112. The occurrence of pressure peaks due to the extension of the sealing arrangement 150 toward the center of the flow fields 124 should be avoided.

[0121] By extending the sealing arrangement 150 in the region of a connecting channel 128 beyond the positions of the edge webs 142 of the bipolar plates 112 inwards, towards the center of the flow fields 124, local temperature peaks during operation of the electrochemical device 100 can be effectively avoided.

[0122] Preferably, the cathode-side inner edge 156 of the sealing arrangement 150 is located on the side of the coolant channel 148 facing the medium channel 122. Furthermore, it is favorable if the cathode-side inner edge 156 of the sealing arrangement 150 is located in the region of the edge channel 140.

[0123] It is furthermore advantageous if the cathode-side inner edge 156 of the sealing arrangement 150 is located on the side of the joining line 134 facing away from the medium channel 122, at which the first bipolar plate layer 130 and the second bipolar plate layer 132 of a bipolar plate 112 are fixed to one another.

[0124] Outside the area of ​​the connecting channels 128 for the anode gas or for the cathode gas, through which the anode gas or the cathode gas flow from their respective medium channels 122 into the respectively associated flow fields 124 or flow from the respective flow fields 124 into the respectively associated medium channels 122, the interior spaces 144 of the edge webs 142 of the bipolar plates 112 are not components of such connecting channels 128, but rather are traversed by coolant. Therefore, the above-explained problem of locally insufficient cooling in the vicinity of the edge webs 142 only exists where the connecting channels 128 for the anode gas or for the cathode gas are located.

[0125] The cathode-side inner edge 156 of the sealing arrangement 150 therefore only needs to be moved to the side of the edge webs 142 facing away from a medium channel 122 where these connecting channels 128 for anode gas or cathode gas are located.

[0126] Where no such connecting channels 128 extend, the cathode-side inner edge 156 of the sealing arrangement 150 can, however, lie on the side of the edge webs 142 facing the respective medium channel 122, thereby increasing the available electrochemically active area of ​​the membrane electrode assemblies 114 in the regions outside the connecting channels 128 for anode gas and for cathode gas. In the embodiment of an electrochemical device 100 illustrated in the drawing, it is therefore provided that the cathode-side inner edge 156 of the sealing arrangement 150 is provided on a sealing projection 172 of the second sealing element 164, wherein the sealing projection 172 protrudes in the region of a connecting channel 128 from a base body 174 of the second sealing element 164 in a projection direction 176 facing away from the medium channel (see Figs. 5 and 6).

[0127] If the circumferential direction of the flow fields 124 varies in the region of the connecting channel 128, as is the case in particular at corner regions of the flow fields 124, the projection direction 176 can have locally different orientations (see Figs. 5 and 6).

[0128] The sealing projection 172 extends along the circumferential direction of the base body 174 of the first sealing element 162 only over a part of the circumference of the base body 174 of the first sealing element 162, preferably over less than 50% of the circumference of the base body 174 of the first sealing element 162, particularly preferably over less than 25% of the circumference of the base body 174 of the first sealing element 162.

[0129] The extension (width B) of the sealing projection 172 perpendicular to its circumferential direction and perpendicular to the stacking direction 110 is preferably greater than the extension (width b) of an edge web 142 perpendicular to its circumferential direction and perpendicular to the stacking direction 110.

[0130] The width B of the sealing projection 172 taken perpendicular to the circumferential direction of the sealing projection 172 is thus greater than the width b of the edge web 142 taken perpendicular to the circumferential direction of an edge web 142. Due to the presence of the sealing projection 172, the extension of the sealing arrangement 150 perpendicular to its circumferential direction is greater in the region of at least one connecting channel 128 than in at least one region outside the region of the connecting channel.

[0131] In a variant of the embodiment of an electrochemical device 100 shown in Figs. 1 to 6, it is provided that the sealing arrangement 150 is provided in the at least one region outside the connecting channel 128 and thus outside the sealing projection 172 with a plurality of recesses 182 which are spaced apart from one another along the circumferential direction 134 of the sealing arrangement 150 and are arranged on the inner edge 155 of the sealing arrangement 150, as shown in Fig. 8.

[0132] Such recesses 182 are obtained when deformation limiting elements, for example hold-down devices 186, are used during the injection molding of the sealing element 161, which are arranged on a push-off projection 188 of a push-off tool part 190 of an injection molding tool 192 in which the process of injection molding the sealing element 161 made of the elastomer material onto the gas diffusion layer 116 or 118 is carried out.

[0133] Alternatively, it can be provided that at least one of the deformation limiting elements 184 is formed integrally with the pressing projection 188 of the pressing tool part 190.

[0134] Such an injection molding tool 192 is shown schematically in Fig. 7.

[0135] The injection molding tool 192 is designed in several parts and comprises a pressing tool part 190 and a supporting tool part 194. The pressing tool part 190 and the supporting tool part 194 together enclose a cavity 196 into which an injection molding material, preferably a starting material for an elastomer material, is introduced in a flowable state during the injection molding process.

[0136] The gas diffusion layer 116, 118 projects into this cavity 196.

[0137] The pressing tool part 190 has the pressing projection 188, which is provided with a pressing edge 198.

[0138] The gas diffusion layer 116, 118 inserted into the injection mold 192, which is mechanically compressible in its thickness direction 200 (in the assembled state of the electrochemical device 100, parallel to the stacking direction 110 of the electrochemical device 100), is locally compressed by means of the push-off projection 188 and the opposing support tool part 194. As a result, the capillary pressure in the pores of the porous gas diffusion layer 116, 118 increases locally, and the penetration of the gas diffusion layer 116, 118 by the injection molding material is limited in the x- and y-directions perpendicular to the thickness direction (z-direction).

[0139] When producing the sealing element 161 by means of an injection molding process in the injection molding tool 192, very high injection pressures occur in the cavity 196 of the injection molding tool 192.

[0140] If the injection point or points through which the injection molding material is introduced into the cavity 196 are located outside the connection areas between the sealing element 161 and the gas diffusion layer 116, 118, folding, i.e., deformation, of the gas diffusion layer 116, 118 may occur in these connection areas during the filling of the cavity 196 of the injection molding tool 192 with the injection molding material. This deformation process locally deforms the gas diffusion layer 116, 118 from its original flat shape and subject it to bending stress.

[0141] Due to the bending of the gas diffusion layer 116, 118 in the deformed connection area, the gas diffusion layer 116, 118 may be damaged, for example by breakage.

[0142] In addition, in the event of a strong bending of the gas diffusion layer 116, 118, the connection region can be mechanically weakened by the gas diffusion layer 116, 118 protruding into the connection region 202, which lies above the gas diffusion layer 116, 118 in the thickness direction 200 and is also referred to as the connection lip 204, and thus preventing the flow of (in particular elastomeric) injection molding material in this region.

[0143] It is then not guaranteed that the cavity 196 of the injection mold 192 is completely filled in the area of ​​the connection lip 204, which increases the risk of mechanical damage to the connection area 202 of the sealing element 161, in particular due to cracking.

[0144] After the injection molding material has been introduced into the cavity 196 of the injection mold 192 and the injection molding material has hardened to form the sealing material of the sealing element 161, the production of the sealing element 161 on the gas diffusion layer 116, 118 and thus the formation of an assembly 206, which comprises the gas diffusion layer 116, 118 and the sealing element 161 fixed to the gas diffusion layer 116, 118 and is also referred to as a seal-on-GDL unit 208, is completed.

[0145] After opening the injection mold 192 by removing the push-off tool part 190 from the support tool part 194, the assembly 206 can be used in assembling the membrane electrode assembly 114 and assembling the electrochemical device 100. The sealing element 161 of the finished assembly 206 comprises a sealing region 210 with a sealing lip 212, a penetration region 214, in which the injection molding material has penetrated into the porous material of the gas diffusion layer 116, 118 and which extends from an outer edge 216 of the gas diffusion layer 116, 118 inward into the region of the push-off edge 198, and a connection region 202 in the form of a connection lip 204, located outside the gas diffusion layer 116, 118, in the thickness direction 200 above and / or below the gas diffusion layer 116, 118.

[0146] In order to prevent the above-described deformation process on the gas diffusion layer 116, 118 when the injection molding material is introduced into the cavity 196 of the injection molding tool 192, a plurality of deformation limiting elements 184 are provided in the cavity 196 of the injection molding tool 192, which are spaced apart from one another in a circumferential direction 152 of the gas diffusion layer 116, 118 aligned parallel to the outer edge 216 of the gas diffusion layer 116, 118 and parallel to the pressing edge 198 of the pressing tool part 190.

[0147] In the illustrated embodiment, the deformation limiting elements 184 are formed separately from the pressing tool part 190 and separately from the supporting tool part 190 of the injection molding tool 192.

[0148] In principle, the deformation limiting elements 184 can also be formed integrally with another component of the injection molding tool 192, for example with the pressing tool part 190 or with the supporting tool part 194.

[0149] In the embodiment according to Fig. 7, the deformation limiting elements 184 are in contact with the push-off projection 188 of the push-off tool part 190. Furthermore, the deformation limiting elements 184 already touch the gas diffusion layer 116, 118 at its main surface 218 facing the push-off edge 198 before the injection molding material is introduced into the cavity 196 of the injection molding tool 192.

[0150] An outer edge 220 of each deformation limiting element 184 facing away from the pressing edge 198 is arranged between the outer edge 216 of the gas diffusion layer 116, 118 on the one hand and the pressing edge 198 of the injection molding tool 192 on the other hand, so that the deformation limiting elements 184 do not completely cover the region of the gas diffusion layer 116, 118 projecting into the cavity 196 of the injection molding tool 192.

[0151] The deformation limiting elements 184 arranged in the connection area between the gas diffusion layer 116, 118 and the sealing element 161 in the injection mold 192 prevent the gas diffusion layer 116, 118 from deforming under the internal mold pressure or injection pressure occurring during the introduction of the injection molding material into the cavity 196 of the injection mold 192.

[0152] This ensures that the areas of the cavity 196 located outside the deformation-limiting elements 184 are completely filled with the injection-molding material. This reduces the risk of mechanical damage to the connection area 202 of the sealing element 161, in particular crack formation.

[0153] Furthermore, damage to the gas diffusion layer 116, 118 caused by bending stress due to deformation of the gas diffusion layer 116, 118 is avoided. As can be seen from Fig. 8, which shows a partial plan view of the finished assembly 206 comprising the gas diffusion layer 116, 118 and the sealing element 161, removed from the injection mold 192, the connection region 202 of the sealing element 161 is provided with recesses 182 on an inner edge 222 of the injection mold 192 due to the presence of the deformation-limiting elements 184 in the cavity 196 of the injection mold 192. These recesses are arranged at the locations at which the deformation-limiting elements 184 were arranged while the gas diffusion layer 116, 118 was inserted into the injection mold 192.

[0154] As can be seen from Fig. 8, it can be provided, for example, that the deformation limiting elements 184 have a cross-section in the shape of a segment of a circle, in particular a semicircle, taken perpendicular to the thickness direction 200 of the gas diffusion layer 116, 118.

[0155] Between the recesses 182, stabilization regions 222 are arranged in the connection region 202 of the sealing element 161, in which stabilization regions the sealing element 161 has a greater material thickness than in the region of the recesses 182, so that the stabilization regions 222 ensure a stable mechanical connection of the sealing element 161 to the gas diffusion layer 116, 118.

[0156] The position of the outer edge 216 of the gas diffusion layer 116, 118 is indicated in Fig. 8 by the double-dotted line 216.

[0157] The position of the tip of the sealing lip 212 of the sealing element 161 is indicated in Fig. 8 by the broken line 224.

[0158] In a particular variant of the electrochemical device 100 described above, it is further provided that the sealing arrangement 150 is provided in the region of the connecting channel 128 with a plurality of recesses 182 which are spaced apart from one another along the circumferential direction 152 of the sealing arrangement 150 and are formed on the sealing projection 172 which, in the region of the connecting channel 128, projects from the base body 174 of the sealing element 161 in a projection direction 176 facing away from the medium channel 122.

[0159] The sealing projection forms a passivation layer made of an elastomer material, which is preferably injection-molded onto a gas diffusion layer 116, 118 together with at least one sealing lip 212 of the sealing arrangement 150.

[0160] The injection of the elastomer material onto the gas diffusion layer 116, 118 takes place in a cavity 196 of an injection mold 192, as shown schematically in Fig. 9.

[0161] The injection molding tool 192 comprises a plurality of deformation limiting elements 184, which are spaced apart from one another along the circumferential direction 152 of the gas diffusion layer 116, 118, are spaced apart from the pressure edge 198 of the injection molding tool 192 and already touch the gas diffusion layer 116, 118 before the injection molding material is introduced into the cavity 196 of the injection molding tool 192.

[0162] Fig. 10 shows a partial plan view of an assembly 206 produced by means of the injection molding tool 192 from Fig. 9.

[0163] The connection region 202 of the sealing element 161 of this assembly 206 is provided with recesses 182, which are arranged outwardly from the inner edge 155 of the connection region 202 and spaced apart from one another in the circumferential direction 152 of the gas diffusion layer 116, 118. As can be seen from Fig. 10, the deformation-limiting elements 184 in this embodiment have, for example, a circular cross-section—taken perpendicular to the thickness direction 200 of the gas diffusion layer 116, 118—so that the recesses 182 in the connection region 202 also have a circular cross-section.

[0164] In this embodiment, the deformation limiting elements 184 are arranged between the outer edge 216 of the gas diffusion layer 116, 118 and the pressing edge 198 of the injection molding tool 192, so that in the finished assembly 206 in the region of the sealing projection 172, the outer edge 216 of the gas diffusion layer 116, 118 - viewed along the thickness direction 200 of the gas diffusion layer 116, 118 - does not intersect the recesses 182 in the connection region 202 of the sealing element 161.

[0165] Regardless of whether the sealing element 161 is provided with one or more recesses 182 in the region of the at least one sealing projection 172 or in at least one region outside a sealing projection 172, the sealing element 161 can also be injection-molded onto the gas diffusion layer 116, 118 in an injection mold 192 of the type shown in Fig. 11.

[0166] The pressing tool part 190 and the supporting tool part 194 each have a pressing projection 188, wherein a section 226 of the gas diffusion layer 116, 118 is clamped and pressed between the two pressing projections 188.

[0167] The porous material of the gas diffusion layer 116, 118 is pressed down to such an extent that the elastomer material introduced into the cavity 196 of the injection mold 192 does not penetrate, or only to a very small extent, the region of the gas diffusion layer lying between the push-off projections 188, so that the central region 228 of the gas diffusion layer 116, 118 surrounded by the push-off projections 188, i.e. the part of the gas diffusion layer 116, 118 used in the electrochemical device 100 for supplying cathode gas or anode gas to the membrane-electrode arrangement 114, is only minimally penetrated.

[0168] The push-off projections 188 of the injection molding tool 192 from Fig. 11 have rectangular cross-sections that are easy to manufacture and are preferably mirror-symmetrical to one another with respect to a transverse center plane 230 of the gas diffusion layer 116, 118 that is oriented perpendicular to the stacking direction 110 and parallel to the main surfaces 218 of the gas diffusion layer 116, 118.

[0169] The use of such push-off projections 188 may result in damage to the component pressed between the push-off projections 188, which may directly or indirectly cause damage to the electrochemical cell in which the gas diffusion layer 116, 118 is installed, and thus a failure of the entire fuel cell stack.

[0170] By designing at least one of the push-off projections 188 with a geometry that deviates from the usual rectangular geometry, as shown in Fig. 12, the load on the components pressed between the push-off projections 188 in the contact area with the push-off projections 188 is reduced.

[0171] This can be achieved by at least one of the push-off projections 188, preferably both push-off projections 188, each having at least one rounded edge, a convexly curved contact surface 232, and / or at least one bevel. The total width W of each push-off projection 188, i.e., its extension perpendicular to the stacking direction 110 and perpendicular to the circumferential direction 152 of the gas diffusion layer 116, 118, is preferably a multiple of the pore size of the gas diffusion layer 116, 118 and is particularly preferably more than 0.5 mm, for example, more than 1 mm.

[0172] The height h of the push-off projection 188 of the push-off tool part 190 and the height h' of the push-off projection 188 of the support tool part 194 of the injection molding tool 192, that is to say their extent along the thickness direction 200 of the gas diffusion layer 116, 118 and / or the distance by which the respective push-off projection 188 penetrates into the porous material of the gas diffusion layer 116, 118 during compression of the gas diffusion layer 116, 118, can be substantially equal to one another or can differ from one another.

[0173] If the gas diffusion layer 116, 118 is designed asymmetrically, for example because it has a microporous layer (MPL) on one side or is provided on one side with a catalyst layer, a catalyst layer and a membrane, or with a complete membrane-electrode assembly 114, it is expedient to also design the pressure projections 188, between which such an asymmetric gas diffusion layer 116, 118 is pressed, asymmetrically, as shown in Fig. 14 (in the embodiments according to Figs. 14 and 15, the sealing element 161 comprises a second sealing lip 212', which can be opposite the first sealing lip 212).

[0174] The injection molding tool 192 is advantageously designed such that the tool part of the injection molding tool 192 which is arranged on the side of the gas diffusion layer 116, 118 having a microporous layer or on the side of the gas diffusion layer 116, 118 provided on one side with a catalyst layer, with a catalyst layer and a membrane, or with a complete membrane-electrode arrangement 114, extends less far into the material of the gas diffusion layer 116, 118 than the other tool part of the injection molding tool 192. For example, it can be provided that on one side of the gas diffusion layer 116, 118 the push-off projection 188 of the relevant tool part of the injection molding tool 192 is completely omitted, as shown in Fig. 13.

[0175] This is preferably the side of the gas diffusion layer 116, 118 which is provided with a microporous layer (MPL), with a catalyst layer, with a catalyst layer and a membrane or with a complete membrane electrode assembly 114.

[0176] In the injection molding tool 192 shown in Fig. 15, the push-off projections 188 are designed such that their contact surfaces 232 are not continuously convexly curved, but have a central section 234 which is aligned substantially parallel to the main surfaces 218 of the gas diffusion layer 116, 118, and two inclined sections 236 which are inclined at an angle a or a' relative to the main surfaces 218 of the gas diffusion layer 116, 118.

[0177] It is preferably provided that the angle of inclination a or a' is less than 60°, particularly preferably less than 45°.

[0178] If one of the sides of the gas diffusion layer 116, 118, for example a side which has a microporous layer (MPL), a catalyst layer, a membrane or a complete membrane electrode assembly 114, is particularly sensitive to handling, it may be advantageous if this side of the gas diffusion layer 116, 118 is at least partially in contact with a contact element 238 of the injection molding tool 192 during the introduction of the injection molding material into the cavity 196 of the injection mold 192, which contact element is elastically deformable, as shown in Fig. 16.

[0179] Such a contact element 238 can, for example, comprise a coating 240 made of an elastomer material. Such a coating 240 made of an elastomer material can, for example, be produced on one of the tool parts of the injection mold 192 by means of a pattern printing process, preferably a screen printing process or a pad printing process.

[0180] Alternatively or additionally, it can be provided that the injection molding tool 192 comprises a contact element 238 which is manufactured separately from the pressing tool part 190 and separately from the supporting tool part 194 of the injection molding tool 192 and, after its manufacture, is arranged on the pressing tool part 190 or on the supporting tool part 194, as shown in Fig. 17.

[0181] The contact element 238 can in particular be arranged in a groove 242 on the relevant tool part 190 or 194.

[0182] Furthermore, the contact element 238 may have one or more support lips 244.

Claims

Claims: Electrochemical device comprising a stack (104) of several electrochemical units (106) arranged successively along a stacking direction (110), each unit comprising an electrochemically active membrane electrode arrangement (114), a bipolar plate (112), and a sealing arrangement (150); at least one medium channel (122) extending along the stacking direction (110) through several of the electrochemical units (106); at least one flow field (124) through which a medium can flow from the medium channel (122) to another medium channel transversely to the stacking direction (110); and at least one connecting channel (128) through which the flow field (124) and the medium channel (122) are in fluid communication with each other, wherein the connecting channel (128) comprises a rib (142) which, during operation of the electrochemical device (100), is protected from the medium flowing from the medium channel (124). (122) is flowing through,wherein a coolant channel (148) separated from the interior (144) of the edge web (142) by a joining line (134) is through which a coolant flows during operation of the electrochemical device (100), wherein the flow field (124) comprises an edge channel (140) which is arranged between the edge web (142) and the coolant channel (148) and through which the medium from the medium channel (122) flows during operation of the electrochemical device, and wherein the sealing arrangement (150) extends around the flow field (124) along the circumferential direction (152) of the flow field (124) and has an inner edge (155) which borders a cathode-side electrochemically active surface (160) or an anode-side electrochemically active surface (158) of the membrane electrode arrangement (114), characterized in that the inner edge (155) of the sealing arrangement (150) lies on the side of the edge rib (142) facing away from the medium channel (122). Electrochemical device according to claim 1, characterized in that the inner edge (155) of the sealing arrangement (150) lies on the side of the coolant channel (148) facing the medium channel (122). Electrochemical device according to one of claims 1 or 2, characterized in that the inner edge (155) of the sealing arrangement (150) lies in the region of the edge channel (140). Electrochemical device according to one of claims 1 to 3, characterized in that the connecting channel (128) is formed between two bipolar plate layers (130, 132) which are fixed to one another at the joining line (134).An electrochemical device according to any one of claims 1 to 4, characterized in that the inner edge (155) of the sealing arrangement (150) is located on the side of the joining line (134) facing away from the medium channel (122). An electrochemical device according to any one of claims 1 to 5, characterized in that the inner edge (155) of the sealing arrangement (150) is formed on a sealing element (161) of the sealing arrangement (150), which is metallurgically bonded to a gas diffusion layer (118) of the respective electrochemical unit (106). An electrochemical device according to claim 6, characterized in that the sealing element (161) is formed from an elastomeric material. An electrochemical device according to claim 7, characterized in that the elastomeric material of the sealing element (161) penetrates a connection area of ​​the gas diffusion layer (118). An electrochemical device according to any one of claims 6 to 8, characterized in that the sealing element (161) comprises a sealing projection (172) which projects from a base body (174) of the sealing element (161) in the region of the connecting channel (128) in a projection direction (176) facing away from the medium channel (122). An electrochemical device according to claim 9, characterized in that the sealing projection (172) extends along the circumferential direction (152) of the base body (174) of the sealing element (161) only over a portion of the circumference of the base body (174) of the sealing element (161).An electrochemical device according to claim 9 or 10, characterized in that the extent (B) of the sealing projection (172) perpendicular to its circumferential direction (152) is greater than the extent (b) of the edge web (142) perpendicular to the circumferential direction (152). An electrochemical device according to any one of claims 1 to 11, characterized in that an extent of the sealing arrangement (150) perpendicular to its circumferential direction (152) in the region of the connecting channel (128) is greater than in at least one region outside the region of the connecting channel (128). An electrochemical device according to claim 12, characterized in that the sealing arrangement (150) in the region of the connecting channel (128) is provided with several recesses (182) which. The sealing arrangement (150) is spaced apart from one another along its circumferential direction (152) and is formed on a sealing projection (172) which extends from a base body (174) of the sealing element (161) in the region of the connecting channel (128) in a projection direction (176) facing away from the medium channel (122). An electrochemical device according to one of claims 12 or 13, characterized in that the sealing arrangement (150) is provided in the at least one region outside the connecting channel (128) with several recesses (182) which are spaced apart from one another along the circumferential direction (152) of the sealing arrangement (150) and are arranged on the inner edge (155) of the sealing arrangement (150), and / or that the inner edge (155) of the sealing arrangement (150) is corrugated in the at least one region outside the connecting channel (128).An electrochemical device according to any one of claims 1 to 14, characterized in that the medium flowing through the connecting channel (128) during operation of the electrochemical device (100) is an anode gas or a cathode gas of the electrochemical device (100). An electrochemical device according to any one of claims 1 to 15, characterized in that the inner edge (155) of the sealing arrangement (150) borders a cathode-side electrochemically active surface (160) of the membrane electrode arrangement (114). An electrochemical device according to any one of claims 1 to 16, characterized in that an outer edge (178) of a cathode-side electrochemically active surface (160) of the membrane electrode arrangement (114) is offset inwards relative to an outer edge (180) of an anode-side electrochemically active surface (158) of the membrane electrode arrangement (114). Method for producing a sealing element (161) on a gas diffusion layer (116, 118) of an electrochemical unit (106), the method comprising the following: Arranging an injection mold (192) at the gas diffusion layer (116, 118); Introducing injection molding material into a cavity (196) of the injection molding tool (192); wherein the sealing element (161) comprises a sealing projection (172) which projects from a base body (174) of the sealing element (161) in a projection direction (176) pointing into an interior of the sealing element (161), wherein the sealing projection (172) extends along the circumferential direction (152) of the base body (174) of the sealing element (161) only over a portion of the circumference of the base body (174) of the sealing element (161), characterized in that the injection mold (192) comprises at least one deformation limiting element (184) which limits or prevents deformation of the gas diffusion layer (116, 118) during the introduction of the injection molding material into the cavity (196), wherein the injection mold (192) comprises at least one ejection tool part (190) which has an ejection projection (188) for grouting the gas diffusion layer (116,118) and wherein the at least one deformation limiting element (184) is spaced apart from the ejection projection (188) of the ejection tool part (190) during the introduction of the injection molding material into the cavity (196) of the injection molding tool (192). A method according to claim 18, characterized in that the ejection projection (188) of the ejection tool part (190) has at least one rounded section and / or at least one chamfer. A method according to claim 18 or 19, characterized in that one side of the gas diffusion layer (116, 118) is provided with at least one catalyst layer and this side of the gas diffusion layer (116, 118) is in contact, at least partially, with a contact element (238) of the injection mold (192), which comprises an elastomeric material, during the introduction of the injection molding material into the cavity (196) of the injection mold (192).

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