WO2024231125A1 - Method for producing a membrane-electrode assembly for an electrolysis cell via direct membrane deposition and electrolysis cell thus produced - Google Patents

Abstract

A method is specified for producing a membrane-electrode assembly (20) for an electrolysis cell (30) via direct membrane deposition. The method comprises (i) providing a carrier substrate (1), more particularly a gas diffusion layer, for the electrolysis cell (30), (ii) directly applying a paste-like first catalyst material (2) to the carrier substrate (1), (iii) drying/curing the first catalyst material (2), (iv) directly applying an ionomer plastisol (3) for the membrane of the electrolysis cell, (v) drying/curing the ionomer plastisol (3), (vi) directly applying a second paste-like catalyst material (4) to the ionomer plastisol (3), and (vii) drying/curing the second catalyst material (4). Additionally specified are a correspondingly produced membrane-electrode assembly (20), an electrolysis cell (30) comprising said assembly, and a corresponding cell stack.

Description

Description

Method for producing a membrane electrode arrangement for an electrolysis cell by means of direct membrane deposition and electrolysis cell produced accordingly

The present invention relates to a method for producing or providing a membrane electrode arrangement, in particular for a PEM electrolysis cell. Furthermore, a correspondingly produced membrane electrode arrangement and a corresponding electrolysis cell or a corresponding electrolyzer are the subject of the present invention.

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 (H ₂ ) and/or the possibility of producing H ₂ 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 most hydrogen is still produced today by steam reforming of methane, aggressive investment and funding measures are foreseeable leading to a trend towards regenerative hydrogen production.

A particularly promising method for producing hydrogen (H ₂ ) is the electrolysis of water, particularly using electrical renewable energy. Hydrogen can serve as an energy storage medium, for example by being used as a fuel to increase the supply of electrical energy, 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 obtained during electrolysis Hydrogen can therefore be used industrially, for example, or electrical energy can be generated electrochemically using fuel cells.

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, which - in particular compared to alkaline electrolysis approaches - has proven to be very load-dynamic and better suited to the coupling of fluctuating current levels due to less complex peripherals. In particular, high current densities and powers can be achieved using PEM electrolysis even at higher load gradients, whereby the high quality or purity of the hydrogen product is advantageously maintained, for example, even in partial or overload operation.

Hydrogen is already used in countless applications in industry and technology. The potential to produce H2 in large quantities in a climate-neutral manner and/or to store or transport it "carbon-free" using hydrogen carriers such as ammonia, for example, will continue to show completely new ways for the transport, chemical or steel industries, for example, to supply entire sectors with green energy or to operate them in a climate-friendly manner. In addition, hydrogen as a fuel or additive for conventional fuels is already highly interesting, but also in the long term, because of its potential to cause no or fewer emissions.

A PEM electrolysis cell is provided with a membrane that has a catalyst layer on opposite surfaces. The catalyst layers are usually bordered by gas diffusion layers, which in turn are bordered by electrically conductive contact plates, sometimes also called bipolar plates, which serve, among other things, for electrical contact. Preferably, the gas diffusion layers are also designed in such a way that they can enable the required material transport during the intended operation of the electrolysis cell. The gas diffusion layer provides the required "electrical conductivity" to electrically couple the contact plates and the catalyst layers to one another. This enables the desired electrochemical reaction to be realized in the area of the catalyst layers.

Hydrogen is produced electrolytically from water as a 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:

In polymer electrolyte membrane electrolysis, the two partial reactions are spatially separated by an ion-conductive membrane, which must be suitably equipped with electrodes, in particular a cathodic catalyst and an anodic catalyst. In addition to material improvements, significant cost reductions can be achieved by improving the manufacturing processes, among other things.

Since the production of PEM hydrogen electrolyzers (PEMWE) must increase significantly in terms of throughput and scale to achieve agreed climate targets, there is a compelling need for techniques that enable improving the throughput and manufacturing capacity of so-called corresponding catalyst-coated membranes or membrane electrode assemblies. 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.

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, improvements in manufacturing processes can in principle lead to significant cost reductions and efficiency gains. As the production of polymer electrolyte membrane water electrolyzers (PEMWEs) increases in scale, high-volume roll-to-roll (R2R) manufacturing processes are therefore required to achieve both volume or throughput and cost targets.

PEM water electrolyzers are primarily measured by their efficiency. In addition to ohmic losses, the operational membrane as a solid-state electrolyte represents a considerable diffusion barrier. The development trend is therefore towards ever thinner membranes with thicknesses of less than 100 pm. Very thin membranes of, for example, less than 50 pm already represent highly fragile surface structures which reach their limits with conventional R2R coating methods and known work steps.

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, since the dispersing agent water or alcohols lead to a strong swelling behavior of the ionomer, which disadvantageously leads to a loss of form or dimensional stability. Polymer dispersion-based catalyst inks have a very low viscosity and tend to separate after just a few minutes. The viscosity can often be increased by adding thickeners such as methylethylcellulose. However, such auxiliary substances must be thermally decomposed or burned out at temperatures above 300 °C, which would also decompose the membrane or structurally damage the catalysts. To avoid this, the state of the art uses the decal or thermal transfer printing process, whereby the "decal" usually consists of a thermally stable polyimide film onto 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 thermally pressing the decal/membrane fabric (lamination process).

The high number of process steps unfortunately results in long processing times and higher process costs. None of the known processes enables the production of a complete membrane electrode assembly for electrolysis cells (MEA) including the membrane component.

Direct coating processes are generally known from 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).

The invention is therefore based on the object of providing a significantly improved method 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 show simple, novel solutions for producing correspondingly thin membranes in large volumes and throughputs. The advantages of the present invention can improve and simplify the entire production process and thus enable the scaling of electrolyzers to ever higher hydrogen yields.

This object is achieved by the subject matter of the independent patent claims. Advantageous embodiments are the subject matter of the dependent patent claims.

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.

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 enables the use of simpler or cheaper materials for these gas and liquid permeable layers.

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 described above at the cathode. Accordingly, the application is advantageously carried out by means of direct membrane coating.

The method further comprises subsequently drying or curing the first catalyst material.

The method further comprises subsequently directly applying a toner 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 ionomer plastisol is preferably applied in the same way as the catalysts are deposited by means of direct membrane coating.

The process further comprises subsequently drying or curing the toner plastisol.

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.

Furthermore, the method expediently comprises drying or curing the second catalyst material.

The process described here advantageously enables the entire electrode structure of the cell, including the membrane, to be produced by direct application of a multilayer or multiple coating onto a conductive carrier substrate. The DMD sandwich (direct membrane deposition) produced in this way enables 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. The method also advantageously enables improved ionic and mechanical bonding of the catalyst particles to the membrane dielectric. Further advantages over known solutions include 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 a 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, the mechanical integrity is sufficiently and robustly guaranteed and, in particular, the above-mentioned disadvantages of known methods are avoided. In addition, the method according to the invention advantageously enables particularly rapid implementation or processing, without specialized process technology, complex pressing processes or extensive post-processing steps.

Economically, the separate provision of expensive membranes or membrane materials is no longer necessary. This means that existing raw materials can be provided highly efficiently, emissions during production can be reduced and the availability of rare catalyst materials can be largely maintained. The process is also 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.

But also the application of the mentioned catalysts or corresponding 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.

Furthermore, the invention enables mass production of MEAs using roll-to-roll application technology and thus advantageously enables 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. As an alternative or in addition, Pt/RuCh can be contained in said catalyst material.

In one embodiment, the second catalyst material comprises iridium (Ir), in particular as a solid or powdered form, so-called "iridium black". According to this embodiment, a particularly efficient OER catalyst is provided for the membrane arrangement. Alternatively or additionally, the catalyst material can contain IrOOH, IrCh, Ir/TiCh, IrOOH/TiCh, IrOx/TiCh, Ir/SnCh, IrOx/SnCh or corresponding material systems.

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 connection of the catalyst layers to the membrane substrate is simplified.

In one embodiment, the carrier substrate is open-pored (not necessarily microporous) or is made electrically conductive.

In one embodiment, the carrier substrate comprises carbon or a carbon fleece. Alternatively, a close-meshed metal fabric or corresponding metallic fabric can be used.

In one embodiment, the drying or curing of the ionomer plastisol is carried out at a temperature of approximately 80 °C, in particular by means of circulating air drying. This supports effective curing and at the same time prevents thermal degradation of the structure.

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 design also enables the plastisol to be dried effectively and prevents excessively high temperatures from entering the layer structure.

In one embodiment, after the first drying of the ionomer plastisol, a further direct application of ionomer with separate (re)drying, in particular for 15 to 40 s at at least 140 °C, and/or a treatment with boiling water is carried out. In particular, the use of boiling water can have an advantageous 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 the performance.

In one embodiment, after the second catalyst material has hardened, the layer sequence is again thermally treated at approximately 140 to 160 °C, in particular for 5 to 15 minutes. Preferably, the respective pastes or plastisols are degassed beforehand by means of a vacuum treatment, for example at negative pressures between 10 and 100 mbar.

In one embodiment, the described steps of direct application to the carrier substrate (in each case) are carried out by means of a doctor blade application of a corresponding paste and, if necessary, a vacuum plate, wherein the vacuum plate is designed to hold the carrier substrate.

In one embodiment, the described steps of direct application to the carrier substrate (in each case) 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 nozzle.

In one embodiment, the steps of directly applying a corresponding paste to the carrier substrate are carried out via an application roller.

The above-mentioned processes (roll to roll) and the use of a doctor blade application are particularly advantageous for ensuring a simple, robust and large-area coating.

For the final production of a finished electrolysis 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 still 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.

A further aspect of the present invention relates to a membrane electrode arrangement, in particular a PEM membrane electrode arrangement with a gas diffusion layer as a carrier substrate and a catalyst-coated membrane (CCM), wherein the membrane electrode arrangement 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 brings about the production of such thin membrane layers and thus the corresponding efficiency gains of the cell.

Yet another aspect of the present invention relates to an electrolysis cell comprising the described (PEM) membrane electrode assembly. A further 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.

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 arrangement, 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.

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.

Embodiments, features and/or advantages which relate to the method 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.

As used herein, the term "and/or" or "respectively," when used in a series of two or more elements, means that any of the elements listed may be used alone, or any combination of two or more of the elements listed may be used.

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

Figure 1 shows a schematic diagram of the functioning of a water electrolysis cell, particularly a PEM electrolysis cell, including a membrane electrode assembly (MEA). Figure 2 generally indicates method steps according to the invention using a schematic flow diagram.

Figure 3 shows a simplified schematic view of a multiple layer (membrane electrode arrangement) produced according to the invention.

Figures 4 and 5 each indicate further particular method steps according to the invention of the method presented.

Figures 6 and 7 indicate further details of the layer application in the context of the method according to the invention.

In the embodiments and figures, identical or equivalent elements can be provided with the same reference symbols. The elements shown and their relative sizes to one another are generally not to be regarded as being to scale; rather, individual elements can be shown to be exaggeratedly thick or large for better representation and/or understanding.

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 usually formed by a membrane electrode arrangement 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 symbol 2. In contrast, a second catalyst material, different from the first catalyst material, is shown with the reference symbol 4. For this purpose, the membrane 3 is usually coated with a layer of a respective catalyst material on both the anode side and the cathode side on two surfaces facing away from one another. The respective cell reaction of the electrolysis takes place in the area of the layer formed by the respective catalyst material. During normal operation, electro- The electrical energy is transferred to the contact or bipolar plates 32 via the respective catalyst material and a carrier structure, which can be formed by the gas diffusion layer (see reference numeral 1 below) or can provide this. For this reason, a high electrical conductivity of the catalyst layers is also desired.

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.

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.

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 arrangement 20 for an electrolysis cell 30 by means of direct membrane deposition. Without limiting the generality, the method according to the invention is also suitable for producing another electrochemical cell, such as fuel cells.

The method comprises in step i) the provision of 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), in particular a continuous, porous carrier substrate strat can be used. A microporous HER catalyst layer is then applied to the carrier substrate 1 using a doctor blade, "reverse roll" or "slot die" application. A carbon GDL ("Gas Diffusion Layer" e.g. Freudenberg H23C8) or a carbon fleece or a close-meshed metal fabric or scrim can be used as the substrate 1. The carrier substrate 1 must be electrically conductive. The GDL should preferably 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 enable sufficient water and gas transport.

The method comprises in step ii) the direct application of the in particular pasty first catalyst material 2 to the carrier substrate 1.

The method comprises in step iii) drying or curing the first catalyst material 2.

The method comprises in step iv) the direct application or deposition of an ionomer plastisol 3 for the membrane of the electrolysis cell 30.

The process further comprises in step v) the drying or curing of the ionomer plastisol 3.

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.

Figure 3 shows a schematic view of a layer sequence as part of the membrane electrode arrangement 20 according to the invention. At the bottom, the illustration shows the carrier substrate mentioned, preferably the cathodic gas diffusion layer 1. Instead of at the cathode of the cell, the coating can be The application of the following layers can in principle also take place on the anode, i.e. an anodic gas diffusion layer is used as the carrier substrate 1. However, this design is somewhat less favourable in practice, since due to the chemical requirements, refractory metal, preferably titanium, niobium or tantalum, must then be applied as a fibre fleece or similar, which is technically more difficult than if a corresponding carbon material forms the basis on the cathode.

The first catalyst material 2 is then deposited directly on the GDL carrier substrate 1 in the form of a paste (see reference numeral 6 below), as described. The ionomer membrane 3 - also in the form of a paste 6 - is then applied directly on top of this 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 significantly below 50 pm, such as 40 pm, 30 pm, 20 pm or even 10 pm. This results in advantageously low contact resistances on the membrane, as described above, which significantly improve the electrochemical efficiency of the cell 30 in contrast to known solutions.

The catalyst layer thicknesses in the finished state of the cell 30 can, for example, be between 5 and 20 pm each. The first catalyst material 2 preferably comprises platinum, in particular solid or powdered so-called "platinum black" for the HER catalyst. As an alternative to this 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, IrC>2, 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.

Advantageously, a catalyst paste should be provided which enables efficient coating of the catalyst particles with ionomer or PFSA and a stable paste for applications on an industrial scale, but in particular shows little or no demixing or sedimentation. This has proven to be successful with the conditions described here.

As will be explained in more detail below, a paste generally designated with the reference symbol 6 (regardless of the layer or application) or a corresponding plastisol should ideally be applied in a temperature range between 20 and 60 °C.

With reference to Figures 4 and 5, additional details of the method according to the invention in two different embodiments are now explained.

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). By means of this process technology, the carrier substrate 1 mentioned is then also provided in step i) according to the invention.

After the application of the HER catalyst 2 in steps ii) and iii), the membrane layer 3 (not shown in detail in Figure 4) is applied 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 iono- mer layer (dielectric) by applying ionomer plastisol, for example using the application technique mentioned above. A further drying step takes place at 140 to 160 °C, preferably in an infrared drying device, e.g. for a period 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 treatment with boiling water (cf. H2O at 100°C).

Finally, according to the invention, the coating is carried out using OER catalyst 4 and a renewed drying at about 80°C (cf. steps vi) and vii) ).

It is not ruled out 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.

In contrast to Figure 4, Figure 5 does not show the use of boiling water by way of membrane separation according to the invention. Instead, a second ionomer application indicated by the arrow is explicitly marked.

For the deposition of the respective plastisol layers 6, the following approaches or parameters can be used:

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 sondere 10 g Pt-black catalyst, and 35g additional 2-pyrrolidone.

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.

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.

In principle, N-methyl-2-pyrrolidone, dimethyl sulfoxide, gamma-butyrolactone, dimethyl formamide, or diethyl formamide can be used as solvents.

Alternative ionomers such as 3M EW 825, Aquivion EW 870, Aquivion EW 980 and Aquivion EW 720 can be used.

Alternatively, the membrane layer 3 can be applied by extrusion in melt flow.

The technical implementation of the innovative multi-layer application can be achieved using standardized application technology, e.g. using slot nozzle, doctor blade or roller applicators, as is schematically explained in Figures 6 and 7. The dimension (coating width) is in principle not subject to any limitation, so that the scalability of the electrolysis cells is not restricted by the process.

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 application of the paste 6 is preferably carried out via so-called slot nozzles 13, which are shown as an example on the right in the illustration. A first layer application, as more precisely described above with reference to Figures 3 and 4, can be carried out via the nozzle 13 shown on the right, for example for the first catalyst material 2.

Thereafter, the layer application (also not explicitly shown in Figure 6) can be dried or pre-dried or even cured in an oven 15 (see above).

Media dosing during the wide slot nozzle application of the paste 6 can, for example, be carried out via so-called eccentric screw pumps and under the proviso that the system 10 has an unwinder with brake, a strip tension (e.g. 50 Nm), a double-sided slot nozzle coater with a passage width of approx. 10 cm, a substrate thickness of approx. 90 pm, a belt 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 ² and with 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 nozzles advantageously offers the possibility of controlling the desired wet film layer thickness of the application by means of the measured mass flow and a predetermined substrate speed.

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. The process can otherwise be carried out essentially analogously to the description of Figures 3 to 6.

This type of coating (also called reverse roll coating) is particularly useful for producing uniformly coated membrane electrode arrangements 20. Here, a double-chamber furnace 15 with spatial dimensions of significantly more than 1 m can also be used, as well as corresponding Suitable circulating air or floating dryers are used to apply the coating as evenly and as widely as possible on the membrane 1 .

For this purpose, for example, a simple doctor blade application (not explicitly marked in the figures) can be carried out, whereby 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 design 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 electrolysis cell (30) by means of 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 toner plastisol (3) , - (vi) directly applying a second pasty catalyst material (4) to the toner 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 toner 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 toner plastisol (3) is carried out at a temperature between 140 and 160°C, in particular by means of infrared drying. 5. Process according to one of claims 3 or 4, wherein after the first drying of the toner 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 direct application 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 manufactured or can be manufactured 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. Cell stack comprising a plurality of electrolysis cells (30) according to claim 12.