PFAS-free sealing design for alkaline water electrolysis

Abstract

A seal (1) for an alkaline electrolysis device (30) is provided. The seal (1) comprises a polymer matrix and a metal reinforcement (2) surrounded by the polymer matrix, wherein the seal (1) has a bulge (3) comprising a PPSU polymer in an inner region and a sealing lip (4) in an outer region. Furthermore, the metal reinforcement (2) extends into the inner region as well as into the outer region of the seal (1). Furthermore, a method for manufacturing the proposed seal is presented.

Description

Technical Field

[0001] This invention relates to sealing designs or sealing mechanisms for electrochemical batteries. In particular, this invention relates to hybrid seals for alkaline water electrolysis, electrolytic cells including said seals, corresponding battery stacks, and methods for manufacturing the aforementioned seals. Background Technology

[0002] The proposed sealing design advantageously eliminates the so-called PFAS, yet still achieves at least the same or even better sealing performance compared to conventional solutions.

[0003] PFAS, or per- and polyfluoroalkyl substances, are notorious for their persistence in the environment (also known as permanent chemicals) and the serious ecological and health risks they pose. In particular, PFAS are suspected of being carcinogenic.

[0004] Perfluorosulfonic acid (PFSA), a subset of PFAS, is currently widely used as a battery material in electrochemical cells or electrolytic cells because the dissociation of sulfonic acid upon contact with water results in high carrier or proton mobility. Polytetrafluoroethylene (PTFE), also a subset of PFAS, is particularly used for sealing components in electrochemical cells.

[0005] Due to the high potential dangers of PFAS, and especially due to the high follow-up costs of containment and damage minimization resulting from their spread (e.g., due to contaminated drinking water), widespread bans are likely to occur in the near future.

[0006] Given the energy transition and escalating climate change, there are very ambitious efforts to significantly increase the installed capacity of water electrolyzers (whether PEM or alkaline) in the coming years. Against this backdrop, the enormous need to develop and establish PFAS-free membranes, separators, or corresponding sealing components for industrial electrolysis or green hydrogen production has also become apparent.

[0007] Therefore, the EU's pursuit of a ban on fluoropolymers has created a necessity to replace established fluorinated sealing materials with fluorine-free ones.

[0008] If the electrolysis reaction is in an alkaline range, a diaphragm (also called a separator) can be used, or in particular, an anion exchange membrane (AEM) can be provided. Conversely, if the electrolysis reaction occurs in an acidic range, a proton exchange membrane (PEM) is provided instead.

[0009] Currently, the production of green hydrogen from water largely occurs via electrolysis, as described above. This involves an electrochemical process in which water is separated into its chemical components, oxygen and hydrogen. The electrochemical cell reaction or operation of alkaline electrolysis can be summarized, for example, as follows:

[0010] To achieve politically set goals, particularly the U.S. Department of Energy's target of reducing hydrogen production costs to below $2 / kg, technological advancements are needed in electrolysis systems. Beyond material improvements, improvements in manufacturing processes can lead to significant cost reductions and efficiency gains.

[0011] Alkaline water electrolysis (AEL) involves an industrially established technology that is capable of operating at relatively low investment costs due to the market maturity of the technology. AEL is also characterized by high long-term stability and the fact that it requires virtually no key raw materials.

[0012] Known (pressure) battery designs are based on nickel-coated steel rings or frames that are mutually sealed and electrically isolated by PTFE flat seals. In addition to the known flat seals, O-ring seals or linear seals are also known, which are introduced into corresponding grooves. However, these seal variations are limited to plastic battery frames because electrical insulation between cells is typically absent in alkaline electrolytic reactors.

[0013] Known electrolytic cells operate within a pressure range of 30 to 40 bar and a temperature range of 80 to 90°C. In this environment, the sealing materials are exposed to media such as H₂, O₂, NaOH, and / or KOH. This places specific requirements on the sealing materials used. Currently known elastomers (such as Viton) are also composed of fluoropolymers.

[0014] Sealing designs for electrolytic cells are known for example in: EP 0 276 351 B1, EP 2 734 658 B1, EP 2993 254 A1, EP 2 993 254 B1. Summary of the Invention

[0015] Therefore, the object of the present invention is to solve the above-mentioned problems, and in particular to provide PFAS-free alternatives for membranes and / or sealing materials used in water electrolysis, especially alkaline electrolysis.

[0016] The stated objective is achieved through the subject matter of the independent claim. Advantageous designs are the subject matter of the dependent claims.

[0017] One aspect of the invention relates to a seal for alkaline or PEM water electrolysis equipment, particularly for alkaline electrolyzers, especially for mixed applications. This seal is suitably part of the respective electrolytic cell, electrochemical cell, or electrolytic stack device.

[0018] The seal according to the invention comprises a polymer matrix and a metal reinforcement. The reinforcement can be an armor or a stapler that ensures sufficient stability or mechanical cohesion of the seal.

[0019] The mechanical reinforcement is surrounded by a polymer matrix.

[0020] The seal and / or polymer matrix have raised portions in the internal region, the raised portions comprising PPSU polymer (polyphenylene sulfone) or corresponding chemically sufficiently inert thermoplastic polysulfone.

[0021] The seal and / or polymer matrix have a preferably extended or stretched sealing lip or flat seal in an (outer) region that is located further out than the aforementioned inner region.

[0022] In one design, the sealing lip is made of EPDM polymer (ethylene propylene diene monomer rubber) or a similar synthetic rubber with a saturated main chain.

[0023] For mechanical anchoring of the two polymers, metal reinforcements also extend into both the internal and external regions.

[0024] Through the hybrid, reinforced, or similar composite material sealing design and geometry described herein, and particularly the selection of polymer materials, high-performance alternatives to conventional PFAS-based sealing materials can be provided. Specifically, by directly joining the two materials with the aid of a reinforcing member, a mechanically very robust composite is formed. In other words, this method achieves mechanical anchoring of the flat seal via a PPSU ring located inside the battery.

[0025] From an economic perspective, it advantageously eliminates the costly additional steps involved in processing the battery frame.

[0026] For example, compared to PTFE-based flat seals, the design described herein also offers the following advantages: no significant creep behavior occurs, and the corresponding battery does not need to be mechanically and costly re-tensioned during operation.

[0027] Furthermore, in terms of circular economy, resource conservation, and ecological sustainability, the seals according to the invention can be advantageously reused and do not necessarily have to be completely discarded. Because thermoplastics are typically composed of uncrosslinked chain molecules, they are deformable under heat and remeltable at higher temperatures. Therefore, waste thermoplastics, as valuable materials, can be recycled energy-efficiently, at least through simple mechanical crushing.

[0028] Furthermore, it is advantageous to eliminate the need for additional manufacturing of sealing blades or sealing folds in the battery frame of the electrolytic cell. In this context, the additional cutting steps for manufacturing the sealing grooves in the battery frame are also eliminated.

[0029] The proposed sealing design is generally compatible with the steel frame structure of electrolyzers used for operation at pressures, for example, 30 to 40 bar.

[0030] In one design, the seal is configured to retain a diaphragm or membrane in a pressure-operated water electrolyzer (e.g., a PEM system or a system for alkaline water electrolysis). Advantageously, this complies with the requirements of modern industrial electrolysis processes.

[0031] In one design, the seal is designed to seal an alkaline electrolyzer at a pressure of 30 to 40 bar and a temperature of 80 to 100°C, and / or is designed to resist media such as H2, O2, NaOH (preferably at a high concentration of, for example, 30% by weight) and / or KOH. In this way, the seal can be advantageously used in a wide range of applications, particularly in the large-scale industrial production of green hydrogen from renewable energy sources.

[0032] In one design, the metal reinforcement is formed by a wire braid, which is rolled into a raised section on one side. The wire braid can, in principle, be made of stainless steel wire or wire made of nickel or a nickel-based alloy. This method allows for suitable mechanical reinforcement.

[0033] In one design, the surface of the polymer matrix is ​​free of metal; instead, the reinforcement is entirely surrounded by polymer. This design ensures a good seal—within a reliable mechanical reinforcement.

[0034] In one design, the metal reinforcement has nickel on its surface, or is particularly composed of nickel or nickel-plated metal. Through this embodiment, the metal reinforcement—despite having a polymer coating—can be advantageously implemented to provide exceptional chemical resistance to corrosive media (see above).

[0035] In one design, the raised portion is configured to prevent the seal from sliding outwards during specified operation.

[0036] In an alternative design, the (flat) sealing lip also comprises PPSU or, for example, PPSU foam. With this embodiment, the lifespan and oxidation resistance of the seal, particularly when used at the anodic half-cell, can be further improved, for example, compared to shapes made of EPDM.

[0037] Another aspect of the invention relates to an electrolytic cell, particularly an electrolytic cell for alkaline water electrolysis, which includes the described seals on the anode side and / or cathode side.

[0038] Another aspect of the invention relates to a stack or battery stack or stack device having a plurality of such electrolytic cells.

[0039] Another aspect of the invention relates to an electrolytic cell having a plurality of stacks as described above.

[0040] Another aspect of the invention relates to a method for manufacturing the described seal, comprising providing a metal reinforcement as a wire braid, the wire braid being rolled into a raised portion on one side.

[0041] In addition, the method involves pouring PPSU starting material into the region of the raised portion to obtain a raised portion thickness of approximately 3 mm to 5 mm.

[0042] The method also includes casting the sealing lip with EPDM peroxide starting material or PPSU starting material.

[0043] In one design, the sealing lip comprises a PPSU foam layer, which is heat-pressed, for example, with the separator or diaphragm of the corresponding electrolytic cell. This allows the advantages of the design embodiments described above to be utilized. Furthermore, the method advantageously achieves mechanical fixation and cushioning of the diaphragm. Moreover, the resulting "laminate," for example, is fully media-compatible (for alkaline electrolysis applications), unlike fluorine-free elastomer seals (such as EPDM).

[0044] In other words, the sealing design described herein, in a preferred embodiment, depicts a hybrid seal composed of a chemically inert PPSU polymer (thermoplastic) and an external sealing lip (e.g., composed of peroxide-crosslinked EPDM (elastomer)). To enhance compressive strength, the two polymers are mechanically reinforced and bonded by means of an embedded nickel wire knit fabric.

[0045] The present invention relates to the design, features and / or advantages of seals or electrolytic cells, and further to the methods for manufacturing seals or the overall electrolytic cell, and vice versa.

[0046] The expressions “and / or” or “or” used in this article, when used in a series of two or more elements, mean that each of the listed elements can be used alone, or any combination of two or more of the listed elements can be used. Attached Figure Description

[0047] Other details of the invention are described below with reference to the accompanying drawings.

[0048] Figure 1 An electrolytic cell with a sealing design according to the invention, comprising multiple electrolytic cells, is schematically shown.

[0049] Figure 2 A mechanical reinforcement is shown as part of the sealing design according to the invention.

[0050] Figure 3 A simplified view shows a seal according to the invention for use in an electrolytic cell.

[0051] Figure 4 Show Figure 4 Detailed view of the seal.

[0052] Figure 5 A schematic flowchart illustrating the method steps according to the invention for manufacturing the corresponding seal is shown. Detailed Implementation

[0053] In the embodiments and figures, elements that are the same or have the same function may be provided with the same reference numerals. The elements shown and their relative dimensions should not be considered to scale in principle, but rather, for better visibility and / or for better understanding, the individual elements may be shown with exaggerated thickness or dimensions.

[0054] Figure 1 An electrochemical device 30, such as a fuel cell or electrolyzer, is schematically shown. The electrolyzer 30 is preferably a device for alkaline water electrolysis. Preferably, the electrolyzer 30 includes a stack 20, which in turn includes a plurality of electrochemical cells 10 (in... Figure 1 (The text is only schematically indicated by the dotted lines).

[0055] The core of this invention is a sealing design, which includes a seal 1, preferably applicable to each electrolytic cell used for alkaline electrolysis.

[0056] Therefore, each battery 10 preferably includes at least two seals 1 and a diaphragm 5 or a corresponding separator disposed therebetween.

[0057] The diaphragm 5 is specifically designed for the manufacture of electrochemical cells and can be arranged between the two (same type) seals 1 shown, and is connected and / or compressed in a form-fitting or material-fitting manner.

[0058] Two electrodes 7 are suitably present outside the structure described herein, schematically indicated by annular or elliptical structures at the top and bottom, respectively; without limitation, each side can relate to either the anode side or the cathode side. To further define the "cell" relative to an adjacent cell (see...), Figure 1 (The top and bottom dashed boxes in the illustration) are used to seal the relevant media, and additional seals of the same type 1 can be provided.

[0059] The seal 1 according to the invention is preferably adapted and assembled for use in alkaline electrolysis equipment. The seal 1 comprises a polymer matrix and a metal reinforcement surrounded by the polymer matrix (see...). Figure 2 (See reference numeral 2 in the attached figure). Accordingly, the seal can be a novel material composite.

[0060] Figure 2 This illustrates a metal or wire braided or meshed fabric or a corresponding woven or knitted fabric. The wire braid 2 can be made, for example, of stainless steel wire or wire made of nickel or a nickel-based alloy.

[0061] As can be seen from the accompanying drawings, the metal braid is partially rolled into a raised portion 3 on the upper left side. The diameter of the raised portion 3 can be, for example, 1 mm to 2 mm.

[0062] The metal reinforcement 2 preferably has nickel on its surface, or the entire surface is coated with nickel, for example by means of an electroplating coating method. The nickel-plated surface particularly gives the seal reliable resistance to corrosive or oxidizing media, thereby giving it a long service life.

[0063] exist Figure 3 The image shows seal 1, which is preferably annular in shape. The circular design is typically used for better force distribution when pressure is applied in the (alkaline) electrolytic cell 10.

[0064] In the illustration, a (crescent-shaped) recess 6 is also provided on the opposite side of the diameter of the annular seal 1, which can be designed for fluid input or output of the anode or cathode.

[0065] exist Figure 4 In the detailed view, the raised portion 3 of the described internal arrangement is shown more precisely. The raised portion 3 is located in the internal region of the seal 1. The internal region (not explicitly marked) comprises PPSU polymer.

[0066] The seal 1 also has an outer region, which is identifiablely formed by a relatively flat sealing lip 4. The sealing lip 4 can comprise an EPDM polymer. It is also possible that the "elastomer region" has a surface structured design, for example, to achieve a better sealing effect.

[0067] The metal reinforcement 2 described herein extends into both the inner and outer regions of the seal 1 for mechanical anchoring. Here, the metal protrusion 3 of the reinforcement 2 forms or defines the entire sealing protrusion 3, which, together with the polymer matrix, can then have a size or diameter of, for example, 3 mm to 5 mm.

[0068] The raised portion 3 is also configured to reliably prevent the seal from sliding outwards during specified operation.

[0069] Specifically, the seal 1 is configured to retain the separator 5 in a pressure-operated (alkaline) water electrolyzer. Accordingly, the separator is designed to seal the alkaline electrolyzer, particularly at pressures of 30 to 40 bar and temperatures of 80 to 100°C, and / or to resist media such as H2, O2, NaOH, and / or KOH (at high concentrations).

[0070] In an alternative design, the described sealing lip 4, like the internal polymer protrusion 3, can comprise PPSU plastic, or be entirely composed of it. This design, with a sealing lip made of PPSU, provides advantageous mechanical fixation and cushioning of the separator 5 within the battery 10.

[0071] also, Figure 5 The simplified flowchart schematically illustrates the method steps according to the invention for manufacturing a seal. In S1, the method for manufacturing a seal includes providing a metal reinforcement as a wire braid, the wire braid being rolled into a raised portion on one side.

[0072] The method further includes in S2 casting a PPSU starting material in the region of the raised portion or for its construction, such that a raised portion thickness of, for example, 3 mm to 5 mm is obtained; and in S3, a sealing lip is cast with EPDM peroxide or similarly with polysulfone.

[0073] After casting, it is preferable that no metal is present on the surface of the polymer matrix, and that the reinforcement 2 is completely surrounded by polymer.

[0074] Based on the design of the sealing lip 4 made of PPSU described above, the sealing lip can be (hot-)pressed with a diaphragm 5 as a (multilayer) PPSU foam in subsequent process steps, for example. This can be done specifically via a heated mold between 180°C and 230°C. The resulting "laminate" is completely media-compatible, unlike fluorine-free elastomer seals (e.g., made of EPDM). Compared to PTFE flat seals, the design described herein advantageously exhibits little or no creep behavior at pressure applications.

Claims

1. A seal (1) for an alkaline electrolysis device (30), the seal comprising a polymer matrix and a metal reinforcement (2) surrounded by the polymer matrix, wherein, The seal (1) has a raised portion (3) comprising PPSU polymer in the inner region and a sealing lip (4) in the outer region, wherein the metal reinforcement (2) also extends into the inner region and the outer region of the seal (1).

2. The seal (1) according to claim 1, wherein the seal is configured to retain the diaphragm (5) in a water electrolyzer (30) operating under pressure.

3. The seal (1) according to claim 1 or 2, wherein the seal is designed to seal an alkaline electrolytic cell (10) at a pressure of 30 to 40 bar and a temperature of 80°C to 100°C, and / or is designed to resist media H2, O2, NaOH and / or KOH.

4. The seal (1) according to any one of the preceding claims, wherein, The metal reinforcement (2) is formed by a metal wire braid, which is rolled into the raised portion (3) on one side.

5. The seal (1) according to any one of the preceding claims, wherein, The metal reinforcement (2) has nickel on its surface, particularly made of nickel or nickel-plated metal.

6. The seal (1) according to any one of the preceding claims, wherein, There is no metal on the surface of the polymer matrix, but the reinforcement (2) is completely surrounded by polymer.

7. The seal (1) according to any one of the preceding claims, wherein, The raised portion (3) is configured such that the raised portion prevents the seal (1) from sliding during specified operation.

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

9. The seal (1) according to any one of claims 1 to 7, wherein, The sealing lip (4) also includes PPSU.

10. An electrolytic cell (10), particularly an electrolytic cell for alkaline water electrolysis, said electrolytic cell comprising a seal (1) according to any one of the preceding claims on the anode side and / or cathode side.

11. An electric stack device (20) having a plurality of electrolytic cells (10) according to claim 10.

12. An electrolytic cell (30) having a plurality of fuel cells (20) according to claim 11.

13. A method for manufacturing a seal (1) according to any one of claims 1 to 9, the method comprising: - (S1) Provide the metal reinforcement (2) as a wire braid, and roll the wire braid into the raised portion (3) on one side. - (S2) Pour PPSU starting material into the region of the raised portion (3) to obtain a raised portion thickness of 3 mm to 5 mm, and - (S3) Cast the sealing lip (4) using EPDM peroxide or PPSU starting material.

14. The method according to claim 13, wherein, The sealing lip (4) includes a PPSU foam layer, which is hot-pressed with the separator (5) of the electrolytic cell (10).

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