Method for producing a membrane-electrode assembly for an electrolysis cell via direct membrane deposition and electrolysis cell thus produced
Patent Information
- Application Number
- EP2024722014
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-05-11
- Filing Date
- 2024-04-25
- Publication Date
- 2026-01-14
AI Technical Summary
Current methods for producing membrane electrode assemblies for PEM electrolysis cells are inefficient, requiring complex and costly processes, leading to high production costs and limited scalability due to the use of expensive catalyst materials and fragile, thick membranes, which hinder the achievement of low-cost, high-volume hydrogen production.
A direct membrane deposition method involving a carrier substrate, where pasty catalyst materials and ionomer plastisol are applied and dried to form a thin, mechanically stable membrane electrode assembly with reduced thickness, eliminating the need for expensive pressing processes and enabling roll-to-roll manufacturing.
This method simplifies and cost-effectively produces thin, efficient membrane electrode assemblies, enhancing the electrochemical efficiency and scalability of PEM electrolysis cells, reducing material costs, and maintaining mechanical integrity while avoiding the limitations of conventional coating methods.
Smart Images
Figure EP2024061413_14112024_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] Method for producing a membrane electrode assembly for an electrolysis cell by direct membrane deposition and correspondingly produced electrolysis cell
[0003] The present invention relates to a method for producing or providing a membrane electrode assembly, in particular for a PEM electrolysis cell. Furthermore, a correspondingly produced membrane electrode assembly and a corresponding electrolysis cell or electrolyzer are the subject of the present invention.
[0004] So-called PEM electrolysis (PEM for "polymer electrolyte membrane" or "proton exchange membrane") is gaining increasing potential as an energy carrier, e.g. for industrial applications or as a storage medium, due to its great potential for producing cost-effective green hydrogen. In the wake of climate change, the element hydrogen (H2) and / or the possibility of producing H2 from renewable energy via PEM or water electrolysis has long since emerged as a key factor for the energy industry and related sectors. Even though the majority of hydrogen is still produced today by steam reforming of methane, aggressive investment and funding measures are foreseeable leading to a trend towards renewable hydrogen production.
[0005] A particularly promising process for producing hydrogen (H2) is the electrolysis of water, particularly using renewable electrical energy. Hydrogen can serve, among other things, as an energy store, for example by being used as a fuel to stabilize the electrical energy supply, particularly from renewable sources such as wind power, photovoltaics, or the like. But hydrogen can also be used for other processes that require a fuel or a reducing agent. The hydrogen produced during electrolysis can therefore be used industrially, for example, or electrical energy can be generated electrochemically using fuel cells.
[0006] The separation of water into its chemical components, hydrogen and oxygen (O2), can therefore be carried out using suitable electrolysis cells. A particularly important form is the PEM electrolysis described above, which, due to its less complex peripherals, proves to be very load-dynamic and better suited to coupling fluctuating current levels, particularly compared to alkaline electrolysis approaches. In particular, high current densities and power outputs can be achieved with PEM electrolysis even at higher load gradients, while the high quality and purity of the hydrogen product is advantageously maintained, for example, even under partial or overload operation.
[0007] Hydrogen is already used in countless applications in industry and technology. The potential to produce large quantities of H2 in a climate-neutral manner and / or to store or transport it "carbon-free" using hydrogen carriers such as ammonia will open up completely new ways for the transport, chemical, and steel industries, for example, to supply entire sectors with green energy or to operate them in a climate-friendly manner. Furthermore, hydrogen is already highly interesting as a fuel or additive for conventional fuels, and will also be of interest in the future, due to its potential to produce no or fewer emissions.
[0008] In a PEM electrolysis cell, a membrane is provided which has a respective catalyst layer on opposite surfaces. The catalyst layers are generally bordered by respective gas diffusion layers, which in turn are bordered by respective electrically conductive contact plates, occasionally also called bipolar plates, which serve, among other things, for electrical contact. The gas diffusion layers are preferably also designed in such a way that they can enable the necessary material transport during normal operation of the electrolysis cell. The gas diffusion layer provides the necessary "electrical conductivity" to electrically couple the contact plates and the catalyst layers. This allows the desired electrochemical reaction to be realized in the region of the catalyst layers.
[0009] Hydrogen is produced electrolytically from water as the reactant. This is an electrochemical process in which water is separated into its chemical components, oxygen and hydrogen. The electrochemical cell reactions can be described and differentiated as follows:
[0010] In polymer electrolyte membrane electrolysis, the two partial reactions are spatially separated by an ion-conductive membrane, which is preferably equipped with electrodes, particularly a cathodic catalyst and an anodic catalyst. In addition to material improvements, improvements in manufacturing processes can also lead to significant cost reductions.
[0011] Since the production of PEM hydrogen electrolyzers (PEMWEs) must increase significantly in terms of throughput and scale (scaling) in order to achieve agreed climate targets, there is a compelling need for technologies that enable the throughput and manufacturing capacity of so-called corresponding catalyst-coated membranes or membrane electrode assemblies to be improved. Very expensive and therefore very rare precious metals are used as catalyst materials in many applications, particularly in PEM water electrolysis. The catalyst material, which is still pasty or paste-like during production, usually consists of the catalyst material itself, an ionomer, possibly a polymeric binder, and a solvent.
[0012] For example, to achieve the US Department of Energy's goal of hydrogen production costs below $2 / kg, technical advances in electrolysis systems are essential. In addition to material improvements, significant cost reductions and efficiency gains can, in principle, be achieved through improvements in manufacturing processes. As the scale-up of polymer electrolyte membrane water electrolyzers (PEMWEs) increases, high-volume roll-to-roll (R2R) manufacturing processes are required to achieve both volume or throughput and cost targets.
[0013] PEM water electrolyzers are primarily measured by their efficiency. In addition to ohmic losses, the operational membrane, as a solid-state electrolyte, represents a significant diffusion barrier. The development trend is therefore toward ever thinner membranes with thicknesses of less than 100 pm. Very thin membranes, for example, less than 50 pm, already represent highly fragile surface structures, which reach their limits with conventional R2R coating methods and known processing steps.
[0014] A large number of technical coating methods based on water-alcohol ionomer dispersions are known from the literature. However, these methods are not very suitable for membrane production and coating because the dispersant water or alcohols lead to significant swelling of the ionomer, which disadvantageously results in a loss of form or dimensional stability. Polymer dispersion-based catalyst inks have a very low viscosity and tend to demix after just a few minutes. The viscosity can often be increased by adding thickeners such as methyl ethyl cellulose. However, such auxiliary substances must be thermally decomposed or burned out at temperatures above 300 °C, which would also decompose the membrane and cause structural damage to the catalysts.To avoid this, the decal or thermal transfer printing process is used in the state of the art, whereby the "decal" usually consists of a thermally stable polyimide film to which the catalyst paste is applied on one side. The OER or HER catalyst is then transferred to the membrane in a further step by thermal pressing of the decal / membrane fabric (lamination process).
[0015] The high number of process steps unfortunately results in long lead times and higher process costs. None of the known processes allows the production of a complete membrane electrode assembly (MEA) for electrolysis cells, including the membrane component.
[0016] Direct coating processes are generally known in the field of fuel cell development (cf. M. Klingele, M. Breitwieser, R. Zengerle, S. Thiele, J. Mater. Chem. A 2015, 3, 11239, Direct deposition of proton exchange membranes enabling high-performance hydrogen fuel cells). However, the known paste technologies are not suitable for R2R production (as described here).
[0017] The invention is therefore based on the object of providing a significantly improved process for the production of membrane electrode assemblies and corresponding PEM electrolysis cells and / or cell stacks. In particular, the present invention is intended to provide means that solve the problems described above and demonstrate simple, novel solutions for producing correspondingly thin membranes in large volumes and throughputs. The advantages of the present invention can thus improve and simplify the entire production process, thus enabling the scaling of electrolyzers to ever higher hydrogen yields.
[0018] This problem is solved by the subject matter of the independent patent claims. Advantageous embodiments are the subject matter of the dependent patent claims.
[0019] One aspect of the present invention relates to a method for producing a membrane electrode assembly for an electrolytic cell or other electrochemical cell, such as a fuel cell, or the like, by means of direct membrane deposition.
[0020] The method comprises providing a carrier substrate, in particular a gas diffusion layer, for the electrolysis cell. The substrate is preferably the cathodic gas diffusion layer (current collector). This advantageously allows the use of simpler or cheaper materials for these gas- and liquid-permeable layers.
[0021] The method further comprises the subsequent direct application or deposition of a pasty first catalyst material, preferably in the form of a corresponding paste or a plastisol for the HER catalyst (hydrogen evolution reaction) for the hydrogen reaction at the cathode described above. Accordingly, the application is advantageously carried out by means of direct membrane coating.
[0022] The method further comprises subsequently drying or curing the first catalyst material.
[0023] The process further comprises the subsequent direct application of a ionomer plastisol, i.e., the dielectric, for the polymer electrolyte membrane or membrane of the electrolysis cell. This is particularly advantageously carried out at a temperature between, for example, 20 and 60 °C. The application of the ionomer plastisol is preferably carried out in the same way as the deposition of the catalysts by means of direct membrane coating.
[0024] The process further comprises drying or curing the tonomer plastisol.
[0025] The method further comprises subsequently applying directly (also preferably by means of direct membrane coating) a second pasty catalyst material different from the first catalyst material, in particular an OER paste or a corresponding plastisol for the OER catalyst (English: "oxygen evolution reaction"), to the tonomer plastisol.
[0026] Furthermore, the method expediently comprises drying or curing the second catalyst material.
[0027] The process described here advantageously enables the production of the entire electrode structure of the cell, including the membrane, by means of a multilayer or multiple coating on a conductive carrier substrate by direct deposition. The DMD sandwich (Direct Membrane Deposition) produced in this way enables in particular the production of a membrane layer or ionomer layer with a thickness of less than 50 pm, preferably between 5 and 50 pm. The direct connection of both electrodes using ionomer creates a mechanically stable connection. The carrier substrate functions as a current collector. In addition, the method advantageously enables improved ionic and mechanical bonding of the catalyst particles to the membrane dielectric. Further advantages over known solutions are the high material compatibility and very good paste stability with regard to sedimentation behavior.From an economic point of view, cost-intensive pressing processes and post-treatment processes are also eliminated. The present invention therefore advantageously enables direct and easily scalable R2R coating via DMD production of a membrane electrode arrangement that is particularly suitable for PEM water electrolysis. The membrane thickness can advantageously be reduced and the electrochemical efficiency of the electrochemical cell in question can be greatly improved. At the same time, mechanical integrity is sufficiently and robustly guaranteed and, in particular, the above-mentioned disadvantages of known processes are avoided. In addition, the process according to the invention advantageously enables particularly rapid implementation or processing, without specialized process technology, complex pressing processes, or extensive post-processing steps.
[0028] Economically, the separate provision of expensive membranes or membrane materials is eliminated. This allows existing raw materials to be provided highly efficiently, emissions during production reduced, and the availability of rare catalyst materials largely maintained. Furthermore, the process is compatible with the use of fluorine-free ionomers. Finally, the present invention enables cost-effective and particularly large-scale production of MEAs or catalyst-coated membranes for PEM water electrolysis.
[0029] But also the application of the mentioned catalysts or correspondingly catalytically active metals, be it for the hydrogen reaction at the cathode described above, or as OER for an anode-side oxygen reaction, can be advantageously significantly improved by the advantages of the present invention.
[0030] Furthermore, the invention enables mass production of MEAs using roll-to-roll deposition technology, thus advantageously enabling faster throughput times for corresponding electrolyzer components. In one embodiment, the first catalyst material comprises platinum, in particular solid or powdered so-called "platinum black" for the HER catalyst. Alternatively or additionally, Pt / RuCh can be included in said catalyst material.
[0031] In one embodiment, the second catalyst material comprises iridium (Ir), in particular as a solid or powdered, so-called "iridium black". According to this embodiment, a particularly efficient OER catalyst for the membrane arrangement is provided. Alternatively or additionally, the catalyst material can contain IrOOH, IrCh, Ir / TiCh, IrOOH / TiCh, IrOx / TiCh, Ir / SnCh, IrOx / SnCh or corresponding material systems.
[0032] In one embodiment, ionomer plastisol for the "catalysts" as starting material is of the same type or similar to a corresponding material or plastisol for the membrane substrate. According to this embodiment, the bonding of the catalyst layers to the membrane substrate is simplified.
[0033] In one embodiment, the carrier substrate is open-pored (not necessarily microporous) or is made electrically conductive.
[0034] In one embodiment, the carrier substrate comprises carbon or a carbon nonwoven. Alternatively, a close-meshed metal mesh or corresponding metallic fabric can be used.
[0035] In one embodiment, the drying or curing of the ionomer plastisol is carried out at a temperature of approximately 80 °C, particularly by means of forced-air drying. This promotes effective curing while simultaneously preventing thermal degradation of the structure.
[0036] In one embodiment, a further drying or evaluation step of the ionomer plastisol is carried out at a temperature between 140 and 160 °C, in particular by means of infrared drying. Adapted to the material properties, this embodiment also enables effective drying of the plastisol and prevents excessively high temperatures from being introduced into the layer structure.
[0037] In one embodiment, after the first drying of the ionomer plastisol, a further direct ionomer application is carried out with separate (re-)drying, in particular for 15 to 40 s at at least 140 °C, and / or a treatment with boiling water. In particular, the use of boiling water can have a beneficial effect on the stability of the membrane, the (ionic) binding of the catalyst via the ionomer distribution, and / or through an overall more favorable membrane or electrode morphology, which improves performance.
[0038] In one embodiment, after the curing of the second catalyst material, the layer sequence is thermally treated again at approximately 140 to 160 °C, in particular for 5 to 15 minutes. Preferably, the respective pastes or plastisols are degassed beforehand by a vacuum treatment, for example, at negative pressures between 10 and 100 mbar.
[0039] In one embodiment, the described steps of direct application to the carrier substrate (respectively) are carried out by means of a doctor blade application of a corresponding paste and optionally a vacuum plate, wherein the vacuum plate is designed to hold the carrier substrate.
[0040] In one embodiment, the described steps of direct application to the carrier substrate (respectively) are carried out by means of a roll-to-roll application of a corresponding plastisol paste. In particular, a corresponding oven can be used for heat treatment or drying and / or curing. In one embodiment, the steps of direct application to the carrier substrate are carried out via a slot die.
[0041] In one embodiment, the steps of directly applying a corresponding paste to the carrier substrate are carried out via an application roller.
[0042] The processes mentioned (roll to roll) and the use of a doctor blade application can be particularly advantageous in ensuring a simple, robust and large-area coating.
[0043] For the final production of a finished electrolytic cell, as is also the subject of the present invention, it is expedient to provide a gas diffusion layer on the anode. However, this can also be achieved expediently by pressing a corresponding layer, for example comprising an expanded metal made of titanium or a refractory metal at a certain pressure (e.g. 6 MPa) during the final assembly of the cell with corresponding contact plates.
[0044] A further aspect of the present invention relates to a membrane electrode assembly, in particular a PEM membrane electrode assembly with a gas diffusion layer as a carrier substrate and a catalyst-coated membrane (CCM), wherein the membrane electrode assembly is manufactured or can be manufactured according to the described method, and wherein a membrane thickness is only between 5 and 50 pm. As described above, the method according to the invention advantageously produces such thin membrane layers and thus the corresponding efficiency gains of the cell.
[0045] Yet another aspect of the present invention relates to an electrolysis cell comprising the described (PEM) membrane electrode assembly. Another aspect of the present invention relates to a cell stack and / or an electrolyzer comprising a plurality of electrolysis cells, in particular electrically connected in series, as described above.
[0046] The advantages of the present invention are therefore not only manifested in the small or minimal product unit, such as the membrane or the membrane electrode assembly, but - significantly due to the scale effect - also in the electrolysis cell and a cell stack, electrolyzer or electrolysis system comprising the electrolysis cell, which concerns further aspects of the present invention.
[0047] In particular, the present invention relates to PEM electrolyzers and furthermore to entire electrolysis or "Power-to-X" power plants with the electrolysis system described here.
[0048] Embodiments, features and / or advantages which relate to the process in the present case also relate to the manufactured product itself or the membrane arrangement as well as the electrolysis cell, the cell stack or the electrolysis system, and vice versa.
[0049] As used herein, the term "and / or" or "respectively," 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.
[0050] Further details of the invention are described below with reference to the figures.
[0051] Figure 1 illustrates, using a schematic diagram, the operation of a water electrolysis cell, particularly a PEM electrolysis cell, including a membrane electrode assembly (MEA). Figure 2 illustrates, using a schematic flow diagram, the process steps according to the invention in general.
[0052] Figure 3 shows a simplified schematic view of a multiple layer (membrane electrode arrangement) produced according to the invention.
[0053] Figures 4 and 5 each further indicate particular method steps according to the invention of the method presented.
[0054] Figures 6 and 7 indicate further details of the layer application in the context of the method according to the invention.
[0055] 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.
[0056] Figure 1 shows an electrolysis cell 30, in particular a PEM electrolysis cell for water electrolysis. The core of such a polymer electrolyte membrane electrolysis cell 30 is generally formed by a membrane electrode assembly 20 (MEA), which is indicated in the middle. The MEA 20 has a membrane 3 coated with catalysts. A first catalyst material is identified by the reference numeral 2. In contrast, a second catalyst material, different from the first catalyst material, is shown with the reference numeral 4. For this purpose, the membrane 3 is usually coated with a layer of a respective catalyst material on two surfaces facing away from one another, both on the anode side and on the cathode side. The respective cell reaction of the electrolysis takes place in the region of the layer formed by the respective catalyst material.During normal operation, electrons are diverted to the contact or bipolar plates 32 via the respective catalyst material and a support structure, which may be formed by the gas diffusion layer (see reference numeral 1 below) or may provide it. For this reason, a high electrical conductivity of the catalyst layers is also desired.
[0057] It is also evident that reactant water (H2O) is commonly provided on the anode side, which can be released and recovered by the electrolysis process into oxygen (O2) at the anode and hydrogen (H2) at the cathode.
[0058] The membrane 3 or a starting material which is usually to be coated for coating the membrane 1 with the "catalyst" usually contains a perfluorosulfonic acid material (PFSA), polymer or ionomer 2. This material can also be a solid or powdery, preferably undissolved, sulfonated fluoropolymer or a perfluorinated copolymer with a sulfone group.
[0059] The coating method according to the invention is explained in more detail with reference to Figure 2 and the following figures. Figure 2 merely indicates method steps according to the invention using a schematic flow diagram. The method according to the invention is a process for producing a membrane electrode assembly 20 for an electrolysis cell 30 by means of direct membrane deposition. Without limiting its generality, the method according to the invention is also suitable for producing other electrochemical cells, such as fuel cells.
[0060] The method comprises, in step i), providing a carrier substrate 1, in particular a gas diffusion layer, for the electrolysis cell 30. In the case of a roll-to-roll coating described below (cf. Figures 6 and 7), a continuous, porous carrier substrate can be used, in particular. A microporous HER catalyst layer is then applied to the carrier substrate 1, for example by means of a doctor blade, reverse roll, or slot die application. The substrate 1 can be, for example, a carbon GDL (“Gas Diffusion Layer,” e.g., Freudenberg H23C8), a carbon fleece, or a close-meshed metal fabric or scrim. The carrier substrate 1 must be electrically conductive. Preferably, the GDL should be as open-pored as possible, but microporosity (MPL: microporous layer) is not absolutely necessary, since a HER catalyst layer is applied first, which is microporous.In any case, the GDL must ensure sufficient water and gas transport.
[0061] The method comprises in step ii) the direct application of the in particular pasty first catalyst material 2 onto the carrier substrate 1.
[0062] The process comprises in step iii) drying or curing the first catalyst material 2.
[0063] The process comprises in step iv) the direct application or deposition of an ionomer plastisol 3 for the membrane of the electrolysis cell 30.
[0064] The process further comprises in step v) drying or curing the ionomer plastisol 3.
[0065] The method comprises, in step vi), the direct application of a second pasty catalyst material 4 onto the ionomer plastisol 3, and, in step vii), the drying or curing of the second catalyst material 4.
[0066] Figure 3 shows a schematic view of a layer sequence as part of the membrane electrode assembly 20 according to the invention. The illustration below shows the aforementioned carrier substrate, preferably the cathodic gas diffusion layer 1. Instead of the cathode of the cell, the coating of the following layers can in principle also be carried out on the anode, i.e. an anodic gas diffusion layer is used as the carrier substrate 1. However, this design is somewhat less favorable in practice because, due to the chemical requirements, refractory metal, preferably titanium, niobium or tantalum, must then be applied as a fiber fleece or similar, which is technically more difficult than if a corresponding carbon material forms the basis at the cathode.
[0067] The first catalyst material 2 is then deposited in the form of a paste (cf. reference numeral 6 below) directly onto the GDL carrier substrate 1, as described. The ionomer membrane 3, also in the form of a paste 6, is then applied directly thereon using the method mentioned. The same applies to the second (pasty) catalyst material 4, which follows the layer for the ionomer membrane 3. The finished membrane 3 can advantageously be produced using the method according to the invention described here with layer thicknesses between 5 and 50 pm, preferably well below 50 pm, such as 40 pm, 30 pm, 20 pm or even 10 pm. This results, as described above, advantageously low contact resistances at the membrane, which significantly improve the electrochemical efficiency of the cell 30 in contrast to known solutions.
[0068] The catalyst layer thicknesses in the finished state of the cell 30 can, for example, each be between 5 and 20 pm. The first catalyst material 2 preferably comprises platinum, in particular solid or powdered so-called "platinum black" for the HER catalyst. As an alternative or in addition, Pt / RuCb can be contained in said catalyst material. The second catalyst material 4 preferably comprises iridium (Ir), in particular as solid or powdered so-called "iridium black". Alternatively or in addition, the catalyst material can contain IrOOH, IrCl, Ir / TiCp, IrOOH / TiCp, IrOx / TiCp, Ir / SnCp, IrOx / SnCp or corresponding material systems. Catalyst pastes 2 and 4 should preferably have a solids content of 15 to 50 wt.%. The ionomer content of catalyst pastes should ideally be between 5 and 15 wt.%. The viscosity of the paste should also be between 500 and 2500 mPas.
[0069] Advantageously, a catalyst paste should be provided that enables efficient coating of the catalyst particles with ionomer or PFSA and provides a stable paste for industrial-scale applications, but in particular exhibits little or no demixing or sedimentation. This has proven successful with the conditions described here.
[0070] As will be explained in more detail below, a paste or a corresponding plastisol generally designated (independent of layer or application) with the reference symbol 6 should ideally be applied in a temperature range between 20 and 60 ° C.
[0071] With reference to Figures 4 and 5, additional details of the method according to the invention will now be explained in two different embodiments.
[0072] Figure 4 shows a first embodiment, according to which the roll-to-roll process for high layer throughputs is already indicated by the rollers 16 (see also Figures 6 and 7 below). According to the invention, the carrier substrate 1 mentioned is then also provided in step i) by means of this process technology.
[0073] After the application of the HER catalyst 2 in steps ii) and iii), the application of the membrane layer 3 (not shown in detail in Figure 4) takes place in step iv). For the membrane 3, a plastisol with a polymer content of 10 to 30 wt. % is best used. The layer is then dried at 80 °C, ideally in a circulating air dryer. The pure ionomer layer (dielectric) is then deposited by ionomer plastisol application, for example using the application technique mentioned above. A further drying step is carried out at 140 to 160 °C, preferably in an infrared drying device, e.g., for a duration of 15 to 40 s. In this step v), a further ionomer application can be carried out simultaneously or subsequently, with renewed drying for 15 to 40 s at 140 °C and a treatment with boiling water (cf. H2O at 100 °C).
[0074] Finally, according to the invention, the coating is carried out using OER catalyst 4 and a further drying at about 80°C (cf. steps vi) and vii) ).
[0075] It is not excluded that the multilayer structure produced in this way (cf. "sandwich" structure, as shown in Figure 3) is subsequently subjected to further mechanical and / or thermal treatments. The sandwich 20 could preferably be post-treated in a "curing" step at 140 to 160°C for 5 to 15 minutes. Preferably, the respective pastes or plastisols 6 are further degassed beforehand, for example by a vacuum treatment at a negative pressure of 10 to 100 mbar. For particularly large paste batches or applications, a vacuum disperser (e.g. CDS 3000) can also be advantageous.
[0076] In contrast to Figure 4, Figure 5 does not depict the use of boiling water for membrane separation. Instead, a second ionomer deposition, indicated by the arrow, is explicitly marked.
[0077] For the deposition of the respective plastisol layers 6, the following approaches or parameters can be used:
[0078] The paste for the first catalyst (HER) 2 may, for example, comprise 10 g of a PFSA plastisol in at least 14 wt% proportions in a solvent such as 2-pyrrolidone, and in particular 10 g of Pt black catalyst, and 35 g of additional 2-pyrrolidone.
[0079] The paste for the second catalyst (OER) 4 may, for example, comprise 13 g of a PFSA plastisol (Pemion) in at least 14 wt . % proportions in a solvent, such as 2-pyrrolidone, and in particular 13 g of Ir-black particles, and 35 g of additional 2-pyrrolidone.
[0080] For membrane three, for example, a PFSA or perfluorinated copolymer such as Nafion from Chemours, in particular 20 wt% in water or spray-dried powder dissolved in 30 g of 2-pyrrolidone, can be used.
[0081] In principle, N-methyl-2-pyrrolidone, dimethyl sulfoxide, gammabutyrolactone, dimethyl formamide, or diethyl formamide can be used as solvents.
[0082] Alternative ionomers such as 3M EW 825, Aquivion EW 870, Aquivion EW 980 and Aquivion EW 720 can be used.
[0083] Alternatively, the membrane layer 3 can be applied by extrusion in melt flow.
[0084] The technical implementation of the innovative multilayer application can be achieved using standardized application technology, e.g., using slot die, doctor blade, or roller applicators, as schematically illustrated in Figures 6 and 7. The dimension (coating width) is, in principle, not subject to any limitations, so the scalability of the electrolysis cells is not restricted by the process.
[0085] Figure 6 shows part of a schematic side or sectional view of an application device 10, which uses the general roll-to-roll principle. Specifically, the paste 6 is preferably applied via so-called slot dies 13, which are shown as an example on the right. A first layer application, as described in more detail above with reference to Figures 3 and 4, can be carried out via the die 13 shown on the right, for example for the first catalyst material 2.
[0086] The layer application (also not explicitly shown in Figure 6) can then be dried or pre-dried or even cured in an oven 15 (see above).
[0087] A media dosage during the wide slot die application of the paste 6 can be carried out, for example, via so-called eccentric screw pumps and under the condition that the system 10 has a decoiler with brake, a strip tension (e.g. 50 Nm), a double-sided slot die coater with a passage width of approx. 10 cm, a substrate thickness of approx. 90 pm, a strip speed between 0.8 and 1.2 m / min, an application thickness (wet film) of less than 50 pm, in a viscosity range of 500 to 1000 mPas, a "wet load" of 30 mg / cm 2and drying in a circulating air dryer (drying temperature, for example, 80 to 100 °C) with a solids content of the processable paste of 20 to 50 wt . %. Coating via slot dies advantageously offers the possibility of controlling the desired wet film thickness by means of the measured mass flow and a predetermined substrate speed.
[0088] Figure 7 shows an alternative embodiment, namely that of a coating device 10 with application or metering rollers 14, by means of which the coating can advantageously be carried out in a simple and self-metering manner. Otherwise, the process can be carried out essentially analogously to the description of Figures 3 to 6.
[0089] This type of coating (also called reverse-roll coating) is particularly useful for producing uniformly coated membrane electrode assemblies 20. A double-chamber furnace 15 with spatial dimensions of significantly more than 1 m can also be used here, as well as corresponding circulating air or floating dryers, in order to apply the coating as evenly and as extensively as possible on the membrane 1.
[0090] For this purpose, for example, a simple doctor blade application (not explicitly marked in the figures) can be carried out, wherein the paste 6 is distributed and / or applied with a doctor blade onto the carrier substrate 1, which is held and / or moved, for example, by a vacuum plate (not explicitly marked in the figures). This embodiment is particularly useful for test batches or laboratory samples on a smaller scale. With or without a short drying time, the GDL carrier 1 coated with the paste 6 can be dried, for example, in an oven as described above.
Claims
Patent claims 1. A method for producing a membrane electrode assembly (20) for an electrolytic cell (30) by direct membrane deposition, comprising the steps: - (i) providing a carrier substrate (1), in particular a gas diffusion layer, for the electrolysis cell (30), - (ii) directly applying a pasty first catalyst material (2) to the carrier substrate (1) - (iii) drying or curing the first catalyst material (2) - (iv) direct application of a tonomer plastisol (3) for the membrane of the electrolysis cell, - (v) drying or curing the tonomer plastisol (3) , - (vi) directly applying a second pasty catalyst material (4) to the tonomer plastisol (3), and - (vii) drying or curing the second catalyst material ( 4 ).
2. The method according to claim 1, wherein the carrier substrate (1) is produced to be open-pored and electrically conductive and comprises carbon or a carbon fleece.
3. The method according to claim 1 or 2, wherein the drying or curing of the tonomer plastisol (3) is carried out at a temperature of approximately 80°C, in particular by means of circulating air drying.
4. Method according to one of the preceding claims, wherein a further drying step of the tonomer plastisol (3) is carried out at a temperature between 140 and 160°C, in particular by means of infrared drying.
5. The method according to claim 3 or 4, wherein after the first drying of the tonomer plastisol (3) a further direct ionomer application with separate drying and a treatment with boiling water is carried out.
6. Method according to one of the preceding claims, wherein the layer sequence is again thermally post-treated at 140 to 160°C, in particular for 5 to 15 minutes, after the curing of the second catalyst material (4).
7. Method according to one of the preceding claims, wherein the steps of direct application to the carrier substrate (1) are carried out by means of a doctor blade application of a corresponding paste (6) and optionally a vacuum plate which is designed to hold the carrier substrate (1).
8. Method according to one of the preceding claims, wherein the steps of direct application to the carrier substrate (1) are carried out by means of a roll-to-roll application of a corresponding paste (6), in particular using an oven (15) for a heat treatment.
9. The method according to claim 8, wherein the steps of applying directly to the carrier substrate (1) are carried out via a slot nozzle (13).
10. The method according to claim 8, wherein the steps of directly applying a corresponding paste (6) to the carrier substrate (1) are carried out via an application roller (14).
11. Membrane electrode assembly (20) with a gas diffusion layer as a carrier substrate and a catalyst-coated membrane (CCM), wherein the membrane electrode assembly (20) is produced or can be produced according to the method according to one of the preceding claims, and wherein a membrane thickness is only between 5 and 50 pm.
12. Electrolysis cell (30) comprising a membrane electrode assembly (20) according to claim 11.
13. A cell stack comprising a plurality of electrolysis cells (30) according to claim 12.