Pfas-free seal concept for alkaline water electrolysis

Abstract

A seal (1) is specified for an apparatus for alkaline electrolysis (30). The seal (1) comprises a polymer matrix and a metallic reinforcement (2) surrounded by the polymer matrix, wherein the seal (1) has a bead (3) comprising a PPSU polymer in an inner region, and a seal lip (4) in an outer region. In addition, the metallic reinforcement (2) extends both into the inner region and into the outer region of the seal (1). Additionally presented is a method of producing the seal specified.

Description

[0001] Description

[0002] PFAS-free sealing concept for alkaline water electrolysis

[0003] The present invention relates to a sealing concept or sealing agent for electrochemical cells. In particular, the present invention relates to a hybrid seal for alkaline water electrolysis, an electrolysis cell comprising this seal, a corresponding cell stack, and a method for producing said seal.

[0004] The sealing concept presented advantageously eliminates the use of so-called PFASs, but still achieves sealing functionality that is at least as good or even improved compared to conventional solutions.

[0005] PFAS are so-called per- and polyfluoroalkyl substances. Due to the persistence of PFAS substances or their degradation products in the environment, these substances (also called "forever chemicals") are discredited and pose serious ecological and health risks. PFAS are particularly suspected of being carcinogenic.

[0006] So-called perfluorosulfonic acids (PFSAs), a subset of PFAS, are currently widely used as cell materials for electrochemical cells or electrolysis cells, as the dissociation of the sulfonic acid upon contact with water results in high mobility of the charge carriers or protons. Polytetrafluoroethylene (PTFE for short), on the other hand, is used as a subset of PFAS, among other things, for seals in electrochemical cells.

[0007] Due to the high risk potential of PFAS and in particular the high follow-up costs associated with containment and minimizing damage caused by spread, for example through contaminated drinking water, far-reaching bans are likely in the near future.

[0008] In light of the energy transition and advancing climate change, very ambitious efforts are underway to significantly increase the installed capacity of water electrolyzers, whether PEM electrolysis or alkaline electrolysis, in the coming years. This also makes a very strong need to develop PEAS-free membranes, separators, or corresponding sealing components and establish them for industrial electrolysis or the production of green hydrogen evident.

[0009] The proposed ban on fluoropolymers in the European Union makes it necessary to replace established fluorinated sealing materials with fluorine-free materials.

[0010] If an electrolysis reaction takes place in the alkaline range, a diaphragm (also called a separator) can be used, or specifically an anion exchange membrane (AEM). If, on the other hand, the electrolysis reaction takes place in the acidic range, a proton exchange membrane (PEM) is used instead.

[0011] The production of green hydrogen from water is now largely achieved electrolytically using the processes mentioned above. This is an electrochemical process in which water is separated into its chemical components, oxygen and hydrogen. The electrochemical cell reactions, or operating mode of alkaline electrolysis, can be summarized as follows: To achieve the political goals, particularly those of the US Department of Energy, of hydrogen production costs below $2 / kg, technical advances in electrolysis systems are required. In addition to material improvements, significant cost reductions and efficiency gains can be achieved through improvements in manufacturing processes.

[0012] Alkaline water electrolysis (AEL) is an industrially established technology that requires low investment costs, resulting from its market maturity. AEL is also characterized by high long-term stability and the fact that virtually no critical raw materials are required.

[0013] Known (pressure) cell concepts are based on Ni-coated steel rings or steel frames, which are sealed to each other and electrically isolated from each other by PTFE flat gaskets. In addition to conventional flat gaskets, O-ring or cord seals are also known, which are inserted into corresponding grooves. However, this sealing variant is limited to plastic cell frames, since electrical insulation between the cells is often not present in alkaline electrolysis stacks.

[0014] Conventional electrolysis cells operate in a pressure range between 30 and 40 bar and at temperatures of 80 to 90°C. The sealing material can be exposed to the following media: H2, O2, NaOH, and / or KOH. This results in special requirements for the sealing material used. Commonly used elastomers such as Viton are also made of fluoropolymers.

[0015] Sealing concepts for electrolyzers are known, for example, from: EP 0 276 351 Bl, EP 2 734 658 Bl, EP 2 993 254 A1, EP 2 993 254 Bl. It is therefore an object of the present invention to solve the problems described above, in particular to provide a PFAS-free alternative of membrane and / or sealing materials for water electrolysis, in particular alkaline electrolysis.

[0016] This problem is solved by the subject matter of the independent patent claims. Advantageous embodiments are the subject matter of the dependent patent claims.

[0017] One aspect of the present invention relates to a, in particular hybrid, seal for a device for alkaline or PEM water electrolysis, in particular for an alkaline electrolyzer. The seal is expediently part of a corresponding electrolysis cell, electrochemical cell, or an arrangement of electrolysis stacks.

[0018] The seal according to the invention comprises a polymer matrix and a metallic reinforcement. The reinforcement can be a reinforcement or a bar, which ensures sufficient stability or mechanical cohesion of the seal.

[0019] The mechanical reinforcement is enclosed by the polymer matrix.

[0020] The seal and / or the polymer matrix has a bead in the inner region which comprises a PPSU polymer (polyphenylsulfone) or a corresponding chemically sufficiently inert, thermoplastic polysulfone.

[0021] The seal and / or the polymer matrix has a preferably elongated or expanded sealing lip or flat gasket in an (outer) region located further outward than the aforementioned inner region. In one embodiment, the sealing lip comprises an EPDM polymer (ethylene propylene diene rubber) or a comparable synthetic rubber with a saturated main chain.

[0022] The metallic reinforcement extends further into both the inner and outer regions for the purpose of mechanical anchoring of both polymers.

[0023] The hybrid, reinforced, or composite-like sealing concept described above, along with the geometry described above and, in particular, the choice of polymer materials, provides a high-performance alternative to conventional PFAS-based sealing materials. In particular, the direct bonding of both materials via the reinforcement creates a mechanically very robust composite. In other words, the method enables mechanical anchoring of the flat gasket through the PPSU ring located inside the cell.

[0024] From an economic point of view, cost-intensive additional work steps in the processing of the cell frame are advantageously eliminated.

[0025] Compared to PTFE-based flat seals, for example, the concept described here offers the further advantage that no significant creep behavior occurs and the corresponding cell does not have to be mechanically re-tensioned during operation.

[0026] Furthermore, the seal according to the invention can advantageously be reused in the spirit of a circular economy, resource conservation, and ecological sustainability, and does not need to be completely disposed of. This is because thermoplastics generally consist of uncrosslinked chain molecules and are therefore malleable when heated and meltable again at higher temperatures. Thus, old thermoplastics can be recycled as valuable materials in an energy-saving manner, at least through simple mechanical shredding.

[0027] Furthermore, the additional production of sealing edges or sealing folds in the cell frame of the electrolysis cells can be advantageously dispensed with. In this context, additional machining steps for producing sealing grooves in the cell frame are also eliminated.

[0028] The sealing concept presented is generally compatible with steel frame constructions for pressure-operated electrolyzers at, for example, 30 bar to 40 bar.

[0029] In one embodiment, the seal is designed to hold a diaphragm or membrane in a pressure-operated water electrolyzer, such as a PEM system or an alkaline water electrolysis system. This advantageously meets the requirements of modern industrial electrolysis processes.

[0030] In one embodiment, the seal is designed to seal an alkaline electrolysis cell at pressures of 30 to 40 bar, at temperatures of 80°C to 100°C, and / or is resistant to the media H2, O2, NaOH (preferably in high concentrations of, for example, 30% by weight), and / or KOH. In this way, the seal can be used advantageously in a wide range of applications, particularly in the large-scale industrial production of green hydrogen from renewable energy.

[0031] In one embodiment, the metallic reinforcement is formed by a wire mesh that is rolled into the bead on one side. The wire mesh can generally be made of stainless steel wire or a wire made of a nickel or nickel-based alloy. In this way, a suitable mechanical reinforcement can be achieved.

[0032] In one embodiment, a surface of the polymer matrix is ​​free of metal, but the reinforcement is completely enclosed with polymer. This design ensures a good sealing effect while providing reliable mechanical reinforcement.

[0033] In one embodiment, the metallic reinforcement has nickel on one surface, or in particular consists of nickel or nickel-plated metal. This embodiment allows the metallic reinforcement—despite being coated with a polymer—to be advantageously chemically particularly resistant to corrosive media (see above).

[0034] In one embodiment, the bead is or will be designed in such a way that it prevents the seal from slipping (outwards) during normal operation.

[0035] In an alternative embodiment, the (flat) sealing lip also comprises PPSU or, for example, consists of a PPSU foam. This design can further increase the service life and oxidation resistance of the seal, particularly when used on the anodic half-cell, compared to a seal made of EPDM, for example.

[0036] A further aspect of the present invention relates to an electrolysis cell, in particular for alkaline water electrolysis, comprising the described seal on the anode and / or cathode side.

[0037] A further aspect of the present invention relates to a stack or cell stack or a stack arrangement comprising a plurality of such electrolysis cells.

[0038] A further aspect of the present invention relates to an electrolyzer having a plurality of stacks as described.

[0039] Yet another aspect of the present invention relates to a method of manufacturing the described seal, comprising providing the metallic reinforcement as a wire mesh which is rolled on one side to the bead.

[0040] Furthermore, the method comprises pouring a PPSU starting material in the region of the bead so that a bead thickness of approximately 3 mm to 5 mm is obtained.

[0041] The method further comprises casting the sealing lip with an EPDM peroxide starting material or a PPSU starting material.

[0042] In one process embodiment, the sealing lip comprises PPSU foam layers that are hot-pressed, for example, onto a separator or diaphragm of the corresponding electrolysis cell. This allows the advantages of the design embodiment described above to be utilized. Furthermore, this process advantageously achieves mechanical fixation and padding of the diaphragm. Furthermore, the resulting "laminate" is completely media-compatible (for alkaline electrolysis applications), unlike fluorine-free elastomer seals such as EPDM.

[0043] In other words, the sealing concept described here describes, in a preferred embodiment, a hybrid seal made of a chemically inert PPSU polymer (thermoplastic) and an outer sealing lip, e.g., made of a peroxide-cured EPDM (elastomer). Both polymers are mechanically reinforced and bonded with an internal nickel wire mesh to increase compressive strength.

[0044] Configurations, features, and / or advantages that relate to the seal or the electrolysis cell herein also relate to the method for manufacturing the seal or the electrolyzer as a whole, and vice versa. The term "and / or" or "or," as used herein, when used in a series of two or more elements, means that any one of the listed elements may be used alone, or any combination of two or more of the listed elements may be used.

[0045] Further details of the invention are described below with reference to the figures.

[0046] Figure 1 schematically shows an electrolyzer comprising several electrolysis cells with the sealing concept according to the invention.

[0047] Figure 2 shows a mechanical reinforcement as part of the sealing concept according to the invention.

[0048] Figure 3 shows a seal according to the invention for an electrolysis cell using a simplified view.

[0049] Figure 4 shows a detailed view of the seal from Figure 4 .

[0050] Figure 5 shows a schematic flow diagram with process steps according to the invention for producing the corresponding seal.

[0051] In the exemplary embodiments and figures, identical or equivalent elements may be provided with the same reference numerals. The illustrated elements and their relative sizes are generally not to scale; rather, individual elements may be exaggeratedly thick or oversized for clarity and / or clarity.

[0052] Figure 1 schematically shows an electrochemical device 30, such as a fuel cell or an electrolyzer. The electrolyzer 30 is preferably a device for alkaline water electrolysis. The electrolyzer 30 preferably comprises a stack arrangement 20, which in turn comprises a plurality of electrochemical cells 10 (indicated only schematically in Figure 1 by dashed lines).

[0053] The core of the present invention is a sealing concept comprising a seal 1 which is preferably used for each of the described electrolysis cells of alkaline electrolysis.

[0054] Each cell 10 therefore preferably comprises at least two seals 1 and a diaphragm 5 or a corresponding separator arranged therebetween.

[0055] The diaphragm 5 can be arranged between the two (similar) seals 1 shown and connected and / or pressed in a form-fitting or material-fitting manner, particularly for the production of the electrochemical cell.

[0056] Outside the structure thus described, there are expediently two electrodes 7, each of which is schematically indicated by the ring-like or elliptical structures at the top and bottom; without limiting the generality, each can concern the anode or the cathode side. To further seal the "cell" against neighboring cells (cf. dashed boxes at the top and bottom in the illustration of Figure 1) against the relevant media, additional similar seals 1 can be provided.

[0057] The seal 1 according to the invention is preferably adapted and manufactured for a device for alkaline electrolysis. The seal 1 comprises a polymer matrix and a metallic reinforcement (cf. reference numeral 2 in Figure 2) which is enclosed by the polymer matrix. Accordingly, the seal can be a novel material composite. Figure 2 shows metal or wire mesh or a meshwork or corresponding woven or knitted fabric. The wire mesh 2 can consist, for example, of stainless steel wire or a wire made of a nickel or nickel-based alloy.

[0058] As can be seen from the figure, the metallic braid on the left side is partially rolled up to form the bead 3. The diameter of the bead 3 can, for example, be 1 mm to 2 mm.

[0059] The metallic reinforcement 2 preferably has a nickel surface or is completely coated with nickel, for example, by means of a galvanic coating process. A nickel-plated surface provides the seal with particularly reliable resistance to corrosive or oxidative media and thus a long service life.

[0060] Figure 3 shows the seal 1, which is preferably annular. The round design generally serves to improve force distribution when pressure is applied in (alkaline) electrolysis cells 10.

[0061] In the illustration, recesses 6 (crescent-shaped) are also provided on diametrically opposite sides of the annular seal 1, which can be designed for the anodic or cathodic fluid supply or discharge.

[0062] The detailed view in Figure 4 shows the described internally arranged bead 3 in somewhat greater detail. This bead 3 is located in an inner region of the seal 1. The inner region (not explicitly marked) comprises a PPSU polymer.

[0063] The seal 1 further comprises an outer region, which is clearly formed by a flatter sealing lip 4. The sealing lip 4, however, may comprise an EPDM polymer. It may also be provided that this "elastomer region" has a surface structure, for example, to achieve an even better sealing effect.

[0064] The described metallic reinforcement 2 extends—for the purpose of mechanical anchoring—both into the inner and outer regions of the seal 1. The metallic bead 3 of the reinforcement 2 forms or defines the entire sealing bead 3, which, together with the polymer matrix, can then have a dimension or diameter of, for example, 3 mm to 5 mm.

[0065] The bead 3 is further designed in such a way that the slipping of the seal during normal operation (outwards) is advantageously reliably prevented.

[0066] In particular, the seal 1 is designed to hold the separator 5 in a pressure-operated (alkaline) water electrolyzer. Accordingly, it is configured to seal an alkaline electrolysis cell, in particular at pressures of 30 to 40 bar, at temperatures of 80°C to 100°C, and / or against the media H2, O2, NaOH, and / or KOH (in high concentrations).

[0067] In an alternative embodiment, the described sealing lip 4, like the inner polymer bead 3, can comprise a PPSU plastic or consist entirely of it. This embodiment with a PPSU sealing lip enables favorable mechanical fixation and padding of the diaphragm 5 in the cell 10.

[0068] Figure 5 also schematically indicates process steps according to the invention for producing the seal using a simplified flow diagram. The process for producing the seal comprises in S 1 the provision of the metallic reinforcement as a wire mesh, which is rolled on one side to form the bead,

[0069] The method further comprises, in S2, the pouring of a PPSU starting material in the region of the bead or for its formation, so that a bead thickness of, for example, 3 mm to 5 mm is obtained; and, in S3, the pouring of the sealing lip with an EPDM peroxide or also a polysulfone.

[0070] After casting, there is preferably no metal left on the surface of the polymer matrix, but the reinforcement 2 is completely enclosed with polymer.

[0071] According to the above-described design of the sealing lip 4 made of PPSU, the sealing lip can be (hot-) pressed with the diaphragm 5 in a subsequent process step, for example as a (multi-layer) PPSU foam. This can be done in particular using heated dies between 180 °C and 230 °C. The "laminate" produced in this way is, in contrast to fluorine-free elastomer seals such as those made of EPDM, completely compatible with all media. Compared to PTFE flat seals, the concept described here advantageously exhibits no or significantly less creep behavior under pressure applications.

Claims

Patent claims 1. Seal (1) for a device for alkaline electrolysis (30), comprising a polymer matrix and a metallic reinforcement (2) which is enclosed by the polymer matrix, wherein the seal (1) has a bead (3) comprising a PPSU polymer in an inner region and a sealing lip (4) in an outer region, wherein the metallic reinforcement (2) further extends both into the inner region and into the outer region of the seal (1).

2. Seal (1) according to claim 1, which is designed to hold a diaphragm (5) in a pressure-operated water electrolyzer (30).

3. Seal (1) according to claim 1 or 2, which is designed to seal an alkaline electrolysis cell (10) at pressures of 30 to 40 bar, at temperatures of 80 °C to 100 °C, and / or resistant to the media H2, O2, NaOH and / or KOH.

4. Seal (1) according to one of the preceding claims, wherein the metallic reinforcement (2) is formed by a wire mesh which is rolled on one side to the bead (3).

5. Seal (1) according to one of the preceding claims, wherein the metallic reinforcement (2) has nickel on one surface, in particular consists of nickel or nickel-plated metal.

6. Seal (1) according to one of the preceding claims, wherein no metal is present on the surface of the polymer matrix, but the reinforcement (2) is completely enclosed with polymer.

7. Seal (1) according to one of the preceding claims, wherein the bead (3) is designed to prevent the seal (1) from slipping during normal operation.

8. Seal (1) according to one of the preceding claims, wherein the sealing lip (4) comprises an EPDM polymer.

9. Seal (1) according to one of claims 1 to 7, wherein the sealing lip (4) also comprises a PPSU.

10. Electrolysis cell (10), in particular for alkaline water electrolysis, comprising on the anode and / or cathode side a seal (1) according to one of the preceding claims.

11. Stack arrangement (20) with a plurality of electrolysis cells (10) according to claim 10.

12. Electrolyzer (30) with a plurality of stacks (20) according to claim 11.

13. A method for producing a seal (1) according to any one of claims 1 to 9, comprising: - (Sl) providing the metallic reinforcement (2) as a wire mesh, which is rolled on one side to the bead (3), - (S2) pouring a PPSU starting material in the area of the bead (3) so that a bead thickness of 3 mm to 5 mm is obtained, and - (S3) the casting of the sealing lip (4) with an EPDM peroxide or PPSU starting material.

14. The method according to claim 13, wherein the sealing lip (4) comprises PPSU foam layers which are hot-pressed with a separator (5) of an electrolysis cell (10).

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