SEALING ARRANGEMENT FOR PEM-TYPE ELECTROCHEMICAL CELLS

Description

[0001] The invention relates to an electrochemical cell, in particular a stack of electrochemical cells, in particular a sealing arrangement for electrochemical cells of the PEM type, in particular for an electrolyzer.

[0002] Electrochemical cells of the aforementioned type are typically installed in stacks in which a large number of such cells are connected in series and arranged in a stack. Such stacks are state of the art in the field of fuel cells, for example, and are used to generate electricity through the catalytic oxidation of hydrogen. Electrolyzers are also available in such a stack arrangement; these generate hydrogen and oxygen by introducing electrical energy and water, of which one component, usually hydrogen, is typically temporarily stored. In order to make generation and storage as effective as possible, efforts are made to design the stack so that it can be operated at the highest possible operating pressure, for example 100 bar. This often means that recompression of the generated gas can be dispensed with or can be carried out with comparatively little energy expenditure.The higher the pressure in the electrochemical cells, the greater the forces acting on the stack. While the mechanical forces can be absorbed by increasing the strength of the end plates and tie rods, the cell seals become more problematic as pressure increases. As the pressure increases, the seals are subjected to increasing stress, and if one seal fails, the entire stack becomes unusable.

[0003] DE 11 2015 002 427 T5 discloses a metallic bipolar plate for an electrochemical system with a sealing arrangement. A circumferential groove with an M-shaped cross-section is formed in the bipolar plate. The groove was formed by mechanically forming the bipolar plate.

[0004] JP 2007 / 200751 also discloses a bipolar plate with a lateral sealing arrangement. Support structures are provided for this sealing arrangement, which are also formed by mechanically deforming the bipolar plate.

[0005] Accordingly, US 2012 / 107718 A1 discloses a plate with two circumferential seals. Support structures for these seals were formed by mechanically deforming the plate.

[0006] DE 10 2012 221 730 A1 also discloses a bipolar plate for a fuel cell that features a circumferential seal. To position the seal on the bipolar plate, the bipolar plate was formed using a forming process.

[0007] US 2017 / 0279133 A1 also discloses a bipolar plate with a circumferential seal. The bipolar plate has a support structure produced by mechanically forming the bipolar plate.

[0008] Against this background, the invention is based on the object of designing a sealing arrangement for an electrochemical cell of the PEM type, in particular for an electrolyzer, in such a way that the seal can withstand the highest possible pressures.

[0009] This object is achieved according to the invention by a sealing arrangement having the features specified in claim 1. Advantageous embodiments of the invention are specified in the subclaims, the following description, and the drawings.

[0010] The sealing arrangement according to the invention for an electrochemical cell of the PEM type, in particular for an electrolyzer, comprises a metallic plate and a seal arranged thereon, which forms at least one closed sealing ring arranged on the plate. According to the invention, a circumferential inner support structure is formed, which supports the seal inwardly, and an outer support structure, which supports the seal outwardly, are formed, which are formed of sintered metal and are integrally connected to the plate.

[0011] The basic idea of ​​the inventive solution is to provide support structures both inwardly and outwardly on the metallic plate, which typically has media-permeable recesses in the center and is designed there, for example, as a perforated sheet, which, for example, lies on an ion-permeable, gas-tight membrane (PEM membrane) with a carbon fleece interposed as a gas diffusion layer. These support structures support the seal on both sides. According to the invention, these support structures are formed from sintered metal and are integrally bonded to the plate. Preferably, the support structures are formed from the same metal as the plate and are integrally bonded to it, for example by sintering.

[0012] If the seal, in its simplest form, is a circumferential sealing ring arranged on the plate, then this is supported on the inside by a support structure that prevents the sealing material from migrating inward when force is applied, and on the outside by an outer support structure that prevents the material from migrating outward. The seal is thus held between the support structures, preferably in a form-fitting manner, effectively preventing the flow behavior that otherwise occurs at high surface pressures. These support structures not only prevent the seal from flowing, but also form a type of spacer that ensures a minimum distance between the metal plate and the mating surface to be sealed.

[0013] In principle, an arrangement of the support structures on both sides of the seal, i.e., on the inside and outside, is advantageous. However, especially when operating the electrochemical cell, especially a cell stack with high internal pressure, as is advantageous in electrolyzers for compressed storage of reaction gases, it may be sufficient to provide only one of the support structures, particularly advantageously an outer support structure, in order to thus form a barrier against outward creep of the seal due to the increased internal pressure.

[0014] According to an advantageous development of the invention, seals are arranged on both sides of the plate, which form at least one closed sealing ring on each side, arranged on the plate, wherein on each side of the plate there is formed a circumferential inner support structure that supports the respective seal inwards and an outer support structure that supports the respective seal outwards, which support structure is made of sintered metal and is integrally connected to the plate. Such an arrangement ensures that the seals on both sides of the plates are stabilized, their flow behavior is prevented under high contact pressure and, moreover, a minimum distance to the counter surface is maintained. In conjunction with the respective counter surface, the support structures form a chamber-like space with the plate and the counter surface, which accommodates the sealing ring arranged therein and prevents compression, i.e.Compressing the sealing ring is limited to the volume of this space.

[0015] According to an advantageous embodiment of the invention, the plate itself is also made of sintered metal and is preferably manufactured using a 3D printing process. Not only the plate itself but also the support structures can be manufactured using this process, preferably in a single step during the printing of the plate.

[0016] The seal forming the sealing ring is advantageously designed such that it preferably completely fills the area between the inner and outer support structure. It is particularly advantageous if the seal rests directly against the metallic plate, at least in the area between the support structures. The tight fit of the seal against the plate ensures, on the one hand, that the seal adheres to the plate and, on the other hand, a good and complete sealing effect. Any required adhesion promoter can be introduced into this area without the risk of this adhesion promoter penetrating areas outside the support structures and thus into the active cell structure. These adhesion promoters damage or destroy the catalyst on the membrane if they come into contact with it, which is why it is important that their area of ​​application is reliably limited locally.

[0017] It is particularly advantageous if the seal preferably completely covers the support structures. While it is generally intended that the seal in the area between the support structures is significantly higher than the support structures themselves to ensure sealing in this area, covering the support structures has the advantage that, at maximum compression of the seal, the sealing material is always located between the top side of the support structure and the counter surface, thus ensuring additional sealing. Furthermore, by covering the support structures with sealing material, the seal can be additionally fixed to the support material, creating an intimate connection between the seal and the plate or the support structures arranged on it.

[0018] It is particularly advantageous if a support structure is formed by a bead. This is advantageously an annular, circumferential bead which supports the seal completely around its circumference. In the area of ​​gas-carrying channels, the bead and / or the seal can be interrupted or have a lower height without thereby restricting the complete support of the seal over the entire circumferential area, since support is unnecessary in the area of ​​such channels. The support structures are advantageously designed and arranged such that they are ramp-shaped on the sides facing one another and taper at a distance from one another. This means that the inner support structure, typically a bead, has a sloped and flat region towards the outer support structure and the outer support structure has a sloped and flat, i.e. ramp-shaped region towards the inner support structure.The ramp-shaped sections taper off at a distance from each other, leaving the area between them free of support structures, allowing the seal to rest directly against the metal plate. On the sides facing away from the seal, the support structures can taper off significantly more steeply, as can the area above the ramp-shaped section, as will be illustrated below using an example.

[0019] This ramp-shaped tapering of the support structures is particularly advantageous in order to achieve the most complete filling possible of the space defined by it with sealing material and to ensure good adhesion of the seal even in the area of ​​the support structures.

[0020] In the simplest form, such a sealing ring arranged between an inner and an outer support structure can be flat on the side facing the mating surface, i.e. on the side facing away from the plate, in which case it rests flat against the mating surface. Such a flat contact is advantageous, for example, for contact with the ion-permeable membrane, since the membrane is then subjected to the same force over the entire surface of the seal. However, particularly on the other side of the plate, it is advantageous if the seal is not designed as a flat surface, but rather has a structure. For example, the seal can advantageously be provided with sealing lips on the side facing away from the plate, which sealing lips preferably run continuously over the entire seal.It is advantageous to form a number of sealing lips, which are arranged like concentric rings on the side of the seal facing the mating surface between the inner and outer support structures. This side of the seal can also have a wave-shaped cross-section, at least on the outward-facing side, which also creates concentric contact surfaces in the area between the support structures.

[0021] The seal arranged between the support structures on the plate, which forms a circumferential sealing ring, is advantageously formed by injection molding the seal after the support structures have been manufactured. Such a seal can be made of FKM (fluororubber), for example, as is state-of-the-art. Injection molding is typically performed using an injection molding process, i.e., in a tool that forms the metallic plate with its support structures and the boundaries.

[0022] The metallic plate is advantageously formed from a foil section, i.e., a metallic sheet section. Cutting the plate from a foil is particularly advantageous; such foils are available inexpensively and can be cut to the desired dimensions of the subsequent sheet section.

[0023] The support structures themselves are advantageously produced using 3D printing. They are either applied directly to the plate or first to a plastic carrier film, with the support structures being bonded to the plate by sintering. When these support structures are applied to the metal plate using 3D printing, the material is either melted during printing, thus forming a bond immediately upon application, or a metal powder is applied with a binder, which is subsequently removed during sintering, bonding the metal powders together and to the underlying metal plate.

[0024] The support structures can advantageously be applied using a screen printing process, which is particularly cost-effective and productive in series production. The support structures are then advantageously bonded to the metal plate by sintering. The support structures can be applied directly to the metal plate by screen printing or onto a plastic film as a carrier.

[0025] If the support structures are applied using a plastic film as a carrier, the plastic film is removed during sintering, which is the process by which the support structures are bonded to the plate. It goes without saying that if support structures are provided on both sides, they are bonded to the plate by sintering simultaneously or in separate steps (first on one side and then on the other).

[0026] Advantageously, the support structure and film are produced in 3D printing in one operation. The film can be made from the binder for the metallic part of the support structure or from another plastic material, which then advantageously not only forms the carrier but covers the entire support structure and is only removed during sintering.

[0027] If the support structures are applied on or in a plastic film as a carrier, they are then placed on the metallic plate and bonded to it by sintering. Typically, the support structures are applied to one side of the plate in a plastic film and then bonded to the plate by sintering.

[0028] If the sealing assembly is intended for a PEM-type electrolyzer, the metallic plate is preferably made of titanium and has a thickness of 0.2 mm to 0.5 mm. If the sealing assembly is intended for a fuel cell, the metallic plate is preferably made of stainless steel and has a thickness between 0.1 mm and 0.2 mm.

[0029] The support structure is advantageously made of the same material as the metallic plate.

[0030] The support structure should be as flat as possible and as high as necessary. Preferably, the support structure extends approximately 0.2 mm to 1.2 mm in a direction perpendicular to the plate.

[0031] The cross-sectional shape of the support structure can vary; typically, two beads are arranged at a distance from each other on one side of the plate, between which the seal is formed. These beads can have a semicircular, trapezoidal, or other cross-section; the bead width is advantageously between 0.2 mm and 2.0 mm.

[0032] As stated above, it is advantageous if the support structure has, in addition to the actual bead, a ramp-shaped, tapered portion, which advantageously has a width of 0.5 mm to 7 mm and is significantly flatter than the actual bead. The ramp-shaped tapered portions are arranged such that they are spaced apart by a certain distance, so that in the area between them, the seal lies directly against the metallic plate. The mean bead spacing, i.e., the distance between the longitudinal center lines of the beads forming the actual support structure, is advantageously between 1.5 mm and 15 mm. The mean spacing in the sense of the invention is understood to mean the distance between the longitudinal centers, as described in Figure 3 shown below.

[0033] The aforementioned dimensions are particularly advantageous for cell arrangements in stacks of, for example, 5 to 250 cells, which are operated as electrolysis cells at a pressure of up to approximately 100 bar.

[0034] The invention is described below with reference to an embodiment shown in the drawings. Fig. 1 shows a plan view of a sealing arrangement according to the invention, Fig. 2 shows a section through an electrolysis cell of a cell stack in a greatly enlarged schematic representation, and Fig. 3 shows an enlarged schematic sectional view of the metallic plate in the area of ​​the seals and support structures

[0035] The sealing arrangement shown in the figures is part of an electrochemical cell, the structure of which is Figure 2is shown schematically. The embodiment described below relates to a sealing arrangement for an electrolysis cell for generating hydrogen and oxygen from water using electrical energy. It is understood that when using other media or reversing the process (fuel cell), the basic structure of the electrochemical cell remains unchanged; however, various modifications are required, whether regarding the materials used or their arrangement.

[0036] Such electrochemical cells are constructed into cell stacks, so-called stacks, in which a large number of such cells are typically electrically connected in series and arranged one on top of the other. The cell stack is mechanically held in place by tension elements and channels for the supply and removal of media are provided within the cell stack. These channels penetrate the stack vertically in order to connect each individual cell to the corresponding media supply or removal. The basic structure of such cell stacks is state of the art and is therefore not described in detail here. In this context, however, reference is made in particular to DE 102017 108413 A1, where such a structure is described in detail.

[0037] Each cell 1 has, as the sectional view according to Figure 2 As shown, it has a bipolar plate 2, which is equipped with channel-forming elements on both sides. Figure 2Channels 3 are formed on the top side and channels 4 on the bottom side. The top side is the water and oxygen-carrying side during operation, whereas the bottom side forms the hydrogen-carrying side. The bipolar plate 2 is connected to the active area of ​​the cell 1, which is Figure 1 marked with 5, a resilient element 6, which is formed by an expanded metal but can also be designed in another way.

[0038] This spring element 6, which is in Figure 2with its upper side against the bipolar plate 2, rests on the underside against a plate 7, which is part of a sealing arrangement 8. This plate 7 is designed as a perforated plate in the active region 5 of the cell 1, i.e. in the central region 5, the actual sealing arrangement 8 is formed in the edge region. The plate 7 lies in the active region 5 against a media-permeable layer 9, which is referred to as a porous transport layer (PTL). This gas-permeable layer lies in front of a proton-permeable membrane 10, which in the active region 5 of the cell 1 is also provided on the back with such a media-permeable layer 11. The membrane 10 is coated on both sides in a manner known per se with electrodes, which act as a catalyst. This media-permeable layer 11 is then in turn followed by a Figure 2The bipolar plate 2 (not shown) is positioned downwards, forming part of the adjoining electrolysis cell. The cell is constructed such that the media are supplied and discharged through channels 3 and 4 and can reach the membrane 10 in a flat manner, specifically in the active region 5 of the cell 1.

[0039] However, components 6, 7, 9, and 11 would not only have to be media-permeable in order to transport the reactants to or from the membrane 10; they would also have to be electrically conductive in order to supply the current required for the reaction. Contact is made via a bipolar plate 2. In the illustrated embodiment, therefore, bipolar plate 2, resilient element 6, plate 7, and media-permeable layer 11 are made of titanium. Specifically, bipolar plate 2 is made of a stamped sheet, resilient element 6 is made of a sheet designed like expanded metal, plate 7 is made of a titanium foil, and media-permeable layer 11 is made of a knitted fabric made of titanium fibers, similar to felt. Media-permeable layer 9 is made of carbon fleece.

[0040] As from Figure 1As can be seen, the active area 5 of the cell 1 is to be distinguished from the edge 12, which is used to form channels and to secure the cells to one another. Channels 13, 14, 15, and 16 are formed in this edge 12, running vertically through the stack of cells, through which the media is supplied and removed. Furthermore, recesses 17 are provided in the corner areas for the passage of clamping bolts, with which the cell stack is compressed and held together. Further recesses for tension rods can be provided in the edge area.

[0041] How Figure 1As illustrated in the figure, the sealing arrangement 8 is circumferential in the edge 12, i.e., it is designed as a closed ring. This closed ring surrounds the channels 13 to 16 on the outside. Furthermore, this sealing arrangement has self-contained rings, each surrounding the channels 13 to 16 and the active region 5. The height of the latter ring is reduced in sections in order to connect the channels 3 of the respective cell 1 with the channels 14 and 16 running vertically in the stack. The water supply and the removal of the resulting oxygen take place via the channels 14 and 16.

[0042] The hydrogen-side chamber, formed, among other things, by channels 4 and free spaces in the resilient element 6, is connected by the seal 18 being lowered in the areas adjacent to channels 13 and 15 to create a channel connection for the removal of hydrogen. The circumferential seals 18 and 19, which surround channels 13 to 16 on the outside, are designed to fit snugly throughout and seal the respective cell to the outside.

[0043] This sealing arrangement 8 comprises, as the Figures 2 and 3 show an upper seal 18 in the figures, which seals against the bipolar plate 2, and a lower seal 19, which seals against the membrane 10. These seals 18, 19 are made of fluororubber and are injection-molded.

[0044] The seal 18 on the upper side of the plate 7 is surrounded inwards, i.e. towards the channels 13 to 16, by a circumferential inner support structure 20 and outwards by an outer support structure 21. The seal 19 on the underside accordingly has an inner support structure 22 and an outer support structure 23. Each support structure (20-23) consists of a circumferential bead 24 and a ramp-shaped area 25 which adjoins the side into the area below the seal 18 or 19. The ramp-shaped area 25 of each support structure extends from the bead 24, starting at approximately halfway up the plate 7, to the opposite bead 25. A free space is formed between the tapered areas 25, in which the seal 18 or 19 rests directly against the plate 7.

[0045] The plate 7, which in the illustrated embodiment consists of a titanium foil, has a thickness 26 of 0.3 mm. The support structures 20 to 23 extending on both sides of the plates each have a circumferential bead 24, which has an extension 27 perpendicular to the plate 7 of 0.6 mm. The width 28 of a bead 24 in the illustrated embodiment is 1 mm, and the width 31 of the ramp-shaped portion 25 is 1.5 mm. The average distance 29 between the beads 24 of the inner support structure 20 or 22 and the outer support structure 21 or 23 is 8 mm.

[0046] In the illustrated embodiment, plate 7 is formed from a titanium foil, which is perforated in the active region 5 to allow media permeability. The support structures 20 and 21 on the top side and 22 and 23 on the bottom side are 3D printed and also made of titanium. The bond between them and with plate 7 is formed by sintering. The manufacturing process can vary, as stated in the introduction.

[0047] After the plate 7 with the support structures 20 to 23 located thereon has been formed, the upper seal 18 and the lower seal 19 are manufactured by injection molding. The seals lie directly against the plate 7 in the area between the tapered ramp-shaped areas 25. In the present embodiment, the seals completely cover the beads 24. While the lower seal 19 has a flat underside as the sealing side, which is spaced a short distance from the beads 24 of the support structure 22 or 23, the upper seal 18 has a top side that is wavy in cross-section, i.e., the sealing side, wherein the wave troughs lie approximately at the level of the top side of the seal in the area of ​​the beads 24 and the wave peaks form circumferential sealing lips 30, which are significantly raised in comparison. List of reference symbols

[0048] 1Cell 2Bipolar plate 3Channels 4Channels 5Active area of ​​the cell 6Resilient element 7Plate 8Seal arrangement 9Media-permeable layer 10Membrane 11Media-permeable layer 12Edge of the plate 7 13Vertical channels 14Vertical channels 15Vertical channels 16Vertical channels 17Recesses 18Top seal 19Bottom seal 20Inner support structure, top 21Outer support structure, top 22Inner support structure, bottom 23Outer support structure, bottom 24Bead 25Ramp-shaped area 26Thickness of the plate 7 27Height of the bead 24 28Width of the bead 24 29Mean bead spacing 30Sealing lips 31Width of the ramp-shaped area

Claims

1. A sealing arrangement for an electrochemical cell (1) of the PEM type, in particular for an electrolyser, with a metallic plate (7) and a seal (18) arranged thereon, which forms at least one closed sealing ring arranged on the plate (7), characterised in that, a circumferential inner support structure (20) supporting the seal (18) inwards is formed, and / or an outer support structure (21) supporting the seal (18) outwards is formed, which is / are made of sintered metal, and is / are connected to the plate (7) in a materially bonded manner.

2. The sealing arrangement in accordance with Claim 1, characterised in that, seals (18, 19) are arranged on both sides of the plate (7), which seals form at least one closed sealing ring arranged on the plate (7) on each side, wherein a circumferential inner support structure (20, 22) supporting the respective seal (18, 19) inwards is formed on each side of the plate (7), and / or an outer support structure (21, 23) supporting the respective seal outwards is formed, which is / are formed from sintered metal, and is / are connected to the plate (7) in a materially bonded manner.

3. The sealing arrangement in accordance with Claim 1 or 2, characterised in that, the plate (7) consists of sintered metal, and is produced using 3D-printing.

4. The sealing arrangement in accordance with one of the preceding claims, characterised in that, the seal (18, 19) fills the area between the inner and outer support structure (21, 22; 22, 23), and preferably lies directly against the plate (7), at least in the area between the support structures.

5. The sealing arrangement in accordance with one of the preceding claims, characterised in that, the seal (18, 19) preferably covers the support structure (20-23) completely.

6. The sealing arrangement in accordance with one of the preceding claims, characterised in that, one, preferably each, support structure (20-23) has an annular circumferential bead (24).

7. The sealing arrangement in accordance with Claim 6, characterised in that, the support structure (20-23) and / or the seal (18) is flatter in the areas in which channels (3) are formed than in the other areas, or is interrupted.

8. The sealing arrangement in accordance with one of the preceding claims, characterised in that, the support structures (20-23) are designed to be ramped on the sides facing each other, and are spaced apart from each other.

9. The sealing arrangement in accordance with one of the preceding claims, characterised in that, one seal (19) is designed to be flat on its side facing away from the plate (7), and / or the other seal (18) is designed to have sealing lips (30), preferably wavy, on its side facing away from the plate (7).

10. The sealing arrangement in accordance with one of the preceding claims, characterised in that, the seal (18, 19) is formed after the production of the associated support structures (20-23) using injection moulding.

11. The sealing arrangement in accordance with one of the preceding claims, characterised in that, the plate (7) is formed by a section of film.

12. The sealing arrangement in accordance with one of the preceding claims, characterised in that, the support structures (20-23) are produced using 3D-printing.

13. The sealing arrangement in accordance with one of the preceding claims, characterised in that, the support structures (20-23) are applied to the panel (7) using the screen printing method.

14. The sealing arrangement in accordance with one of the preceding claims, characterised in that, the support structures (20-23) are formed by means of sintering.

15. The sealing arrangement in accordance with one of the preceding claims, characterised in that, the support structures (20-23) are connected to the plate (7) by means of sintering.

16. The sealing arrangement in accordance with one of the preceding claims, characterised in that, a support structure (20-23) is applied or introduced on or in a plastic film as a carrier, wherein the plastic film is arranged on the plate (7), and removed during the sintering.

17. The sealing arrangement in accordance with one of the preceding claims, characterised in that, the plate (7) consists of titanium, and has a thickness (26) of 0.2 to 0.5 mm.

18. The sealing arrangement according to one of the preceding claims, characterised in that, the plate (7) is made of stainless steel and has a thickness of 0.1 to 0.2 mm.

19. The sealing arrangement according to one of the preceding claims characterised in that, the support structure (20-23) has an extent (27) perpendicular to the plate of 0.2 to 1.2 mm.

20. The sealing arrangement according to one of the preceding claims, characterised in that, the support structure (20-23) is formed as a bead (24) with a bead width (28) of 0.2 to 2.0 mm.

21. The sealing arrangement according to one of the preceding claims, characterised in that, the ramped part (25) of the support structure (20-23) has a width (31) of 0.5 to 7 mm.

22. The sealing arrangement according to one of the preceding claims, characterised in that, the support structure (20-23) has an average bead spacing (29) of 1.5 to 15 mm.