Method for producing a catalyst-coated membrane for an electrochemical cell, and electrolyte cell produced accordingly

Abstract

The invention relates to a method for producing a catalyst-coated membrane (25) for an electrochemical cell (25). In the method, a powdery sulphonated fluorine-free polymer (1) is first provided in a step (S1). In a further step (S2) of the method, the sulphonated fluorine-free polymer (1) is dispersed in a water-free solvent (3) to form a plastisol (5). Then, in a step (S3), a catalyst material (7) is mixed with the plastisol (5) to form a catalyst paste (9). In a step (S4), the catalyst paste (9) is then applied to a membrane substrate (11).

Description

[0001] Description

[0002] Process for producing a catalyst-coated

[0003] Membrane for an electrochemical cell and correspondingly manufactured electrolysis cell

[0004] The present invention relates to a method for producing a catalyst-coated membrane for an electrochemical cell, in particular a PEM electrolysis cell. Furthermore, the invention relates to a corresponding electrolysis cell and an electrolysis system comprising the electrolysis cell.

[0005] So-called PEM electrolysis (PEM for "polymer electrolyte membrane" or "proton exchange membrane") is gaining increasing interest due to its great potential for producing cost-effective green hydrogen, for industrial applications, but also as a storage medium or component of such in energy storage. In the wake of climate change, the element hydrogen 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, regulations and funding measures will certainly lead to a foreseeable trend towards renewable hydrogen production.

[0006] A particularly promising process for producing hydrogen (H2) is the electrolysis of water, particularly using renewable electrical energy. Hydrogen can be used here, 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 again electrochemically using fuel cells.

[0007] The separation of water into its chemical components, hydrogen H2 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 power sources, particularly compared to alkaline electrolysis approaches. In particular, PEM electrolysis can achieve high current densities and power levels 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.

[0008] 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," for example using hydrogen carriers such as ammonia, continues to open up completely new ways for various industrial sectors, such as transport, the chemicals, and steel industries, 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 fuel additive, and will also be attractive in the future, due to its potential to produce no or fewer emissions.

[0009] In a PEM electrolysis cell, a membrane is provided which has a respective catalyst layer on opposite surfaces (CCM, Catalyst-Coated Membrane or 3-layer Membrane Electrode Assembly (MEA). The catalyst layers are generally bordered by respective gas diffusion layers, which in turn are bordered by respective electrically conductive contact plates, called bipolar plates, which serve, among other things, for electrical contact. These gas diffusion layers are preferably also designed to 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 area of ​​the catalyst layers.

[0010] 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:

[0011] 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 (CCM). In addition to material improvements, improvements in manufacturing processes can lead to significant cost reductions, among other things.

[0012] Since the production of PEM hydrogen electrolyzers (PEMWE) will increase significantly in terms of throughput and scale (scaling), and indeed must increase significantly to achieve agreed climate targets, there is a compelling need for technologies that enable the throughput and production capacity of so-called CCMs to be improved. A CCM comprises a membrane with a catalyst material on two opposite surfaces. In many applications, particularly in PEM water electrolysis, very expensive and therefore very rare precious metals are used as catalyst material.

[0013] Current processes use a catalyst paste to produce the catalyst layers or electrodes for the anode and cathode. The catalyst paste usually consists of the catalyst powder itself, an ionomer, possibly a polymeric binder and a solvent. After application, the solvent is usually removed thermally. If the catalyst layer is deposited on a thermally stable carrier film, it must be transferred to the membrane in a further process step under the influence of pressure and temperature ("decal process"). This is intended to permanently fix the electrode to the membrane and ensure good ionic contact between the catalyst materials and the membrane. As an alternative to the decal process, the catalyst paste can also be applied directly to the membrane ("direct coating").

[0014] An industrially established technology for producing hydrogen is polymer electrolyte membrane water electrolysis (PEMWE), whose name is derived from the electrolyte, the polymer membrane. According to the current state of the art, both the membrane and components of the electrodes are made of polyfluorosulfonic acid (PFSA) ionomers. However, fluoropolymers are suspected of being hazardous to health because they do not degrade in the environment or in the human body due to their outstanding chemical resistance. In response to these findings, the European Chemicals Agency (ECHA) recently published a proposal for a Europe-wide ban on polyfluoroalkyl substances (PEAS), which include PFSA polymers.The impending ban, but also the announcement by major polymer manufacturers, independently of this, that they will soon stop producing all fluorinated substances, highlights the urgency of developing long-term stable, marketable fluorine-free alternatives in order to enable the production of hydrogen by PEMWE electrolysis with an environmentally friendly alternative in the future.

[0015] The invention is therefore based on the object of providing a significantly improved manufacturing approach for the production of catalyst-coated membranes (CCM) and corresponding PEM electrolysis cells and / or cell stacks, which is to be preferred above all from an environmental point of view.

[0016] The object is achieved according to the invention by a process for producing a catalyst-coated membrane for an electrochemical cell, comprising the steps:

[0017] Providing a powdered, sulfonated fluorine-free polymer, dispersing the sulfonated fluorine-free polymer in an anhydrous solvent to form a plastisol, mixing a catalyst material with the plastisol to form a catalyst paste, and applying the catalyst paste to a membrane substrate.

[0018] The invention is based on the recognition that the formulation of the catalyst paste is of crucial importance in the production of a catalyst-coated membrane. It has a significant influence on the formation and long-term stable bonding of the catalyst layer to the membrane substrate. It has been shown that adaptations to known formulations and application processes for catalyst pastes from PFSA technology are only of limited use in the development and bonding of fluorine-free polymers in coating processes.

[0019] Technical coating methods based on water / alcohol ionomer dispersions have also been proposed for fluorine-free polymers. On the one hand, these methods are hardly suitable for direct coating because the dispersant water or alcohols lead to significant swelling of the membrane substrate and the dimensional stability of the membrane or the CCM is thus severely impaired. Catalyst inks based on water / alcohol ionomer dispersions also have a very low viscosity and tend to demix after just a few minutes. The addition of additives such as thickeners, such as methyl ethyl cellulose, often increases the viscosity. However, such additives must be thermally decomposed or burned out at temperatures above 300 °C after the catalyst paste has been applied. This would in turn decompose the membrane or structurally damage the catalyst material.To avoid this, the decal process described above is often used in the prior art. The high number of process steps results in long lead times and higher process costs compared to direct membrane application.

[0020] However, in addition to the advantages and future needs regarding environmental aspects, it has been shown that fluorine-free toners offer further technical advantages over the use of PFSA, e.g. a higher process temperature and lower gas transfer through the membrane.

[0021] One aspect of the present invention relates to a method for producing a catalyst-coated membrane for an electrochemical cell, in particular an electrolysis cell. In contrast to the membrane with a membrane substrate as such, a catalyst-coated membrane (CCM) comprises at least one porous electrode, which is realized by the application and bonding of a catalytically active porous layer. In this case, the choice of solvent in combination with the selection of fluorine-free polymers is of great importance in the paste formulation. Compared to the known coating methods, the invention proposes the use of an anhydrous solvent for the catalyst paste in the production of a CCM.In contrast to previous work on processing fluorine-free ionomers using water / alcohol mixtures based on methanol, ethanol or isopropanol, the electrode compositions described here produce a more stable "interlayer", i.e. an intermediate layer or bonding layer between the membrane substrate and the electrode, which leads to increased electrochemical stability and thus to longer service life when used in water electrolysis. By largely matching the material by choosing a corresponding fluorine-free membrane substrate comprising a sulfonated fluorine-free polymer to the corresponding fluorine-free polymer in the catalyst paste, in combination with the anhydrous solvent, the formation of this adhesion promoter layer as an "interlayer" is achieved.

[0022] The process comprises, in a first step, providing a solid or powdery, i.e. preferably undissolved or in solution, sulfonated fluorine-free polymer.

[0023] The process comprises, in a further step, dispersing this starting material or sulfonated fluorine-free polymer in an anhydrous solvent, in particular a high-boiling, polar solvent, such as 2-pyrrolidone or γ-butyrolactam, to form a plastisol.

[0024] In a further step, the method comprises the intimate mixing or blending of a, in particular metallic, catalyst starting material, for example in solid form or in powder form, with the plastisol to form a catalyst paste as an application paste, and the subsequent, preferably direct application (direct membrane coating) of the catalyst paste to a corresponding membrane substrate. A previously described catalyst paste can be used very advantageously in a direct membrane coating process. This has a significantly greater potential for use compared to a decal process. The present invention therefore advantageously enables cost-effective and easily scalable production of large-area catalyst-coated membranes for PEM water electrolysis.

[0025] In particular, the application of the catalysts, whether as a so-called HER (hydrogen evolution reaction) for the hydrogen evolution reaction at the cathode described above, or as OER (oxygen evolution reaction) for an anode-side oxygen evolution reaction, can be advantageously significantly improved by the advantages of the present invention, so that the use of fluorine-free catalyst-coated membranes (COM: catalyst-coated membrane) for HER and OER in an electrolysis cell becomes possible.

[0026] Furthermore, the invention opens up the industrial-scale production of fluorine-free membranes (CCMs) coated with catalyst material using a roll-to-roll application technique, thus advantageously enabling faster throughput times for corresponding electrolyzer components. The presented method also advantageously makes it possible to significantly improve both the ionic and mechanical bonding of the catalyst material to the membrane substrate for fluorine-free membrane electrode assemblies (MEAs). Furthermore, the advantageously high material compatibility and very good paste stability of the catalyst paste as well as improved sedimentation behavior of this paste formulation and application are worthy of emphasis. From a technical and economic point of view, complex pressing processes and post-treatment processes are also eliminated.

[0027] In a particularly advantageous embodiment of the process, the anhydrous solvent, in particular a polar, high-boiling solvent, is selected from dimethyl sulfoxide, N,N-dimethylformamide, N,N-diethylformamide, 2-pyrrolidone or γ-butyrolactam, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone. It has been shown that by choosing one of the solvents from the aforementioned group of anhydrous solvents, in particular in combination with the sulfonated fluorine-free polymer, the formation of an intermediate layer ("interlayer") as a functional layer for good and long-term stable adhesion of the catalyst to the membrane substrate is promoted, i.e. a material-tight bond is established. This is achieved by a targeted and increased dissolution of the surface of the membrane substrate compared to water-based solvents.This primarily promotes the electrochemical stability of the catalyst-coated membrane and high long-term stability when used in an electrochemical cell.

[0028] In a further preferred embodiment of the process, the anhydrous solvent is a mixture of N-methyl-2-pyrrolidone and a portion selected from N-ethyl-2-pyrrolidone, γ-butyrolactone, or diethylene glycol monoethyl ether. Using a mixture of solvents provides further flexibility in the production of the catalyst paste, so that, depending on the coating system of the catalyst layer, a sufficiently high degree of dissolution of the catalyst on the surface of the membrane substrate is achieved, and a close bond is achieved in the region of the intermediate layer.

[0029] The catalyst material for the anode-side coating of the membrane substrate preferably comprises iridium Ir, which is provided in particular as a solid or powdered, so-called "iridium black". According to this embodiment, a particularly efficient OER catalyst for a catalyst-coated membrane in a membrane arrangement or CCM is provided. Alternatively or additionally, the anode-side catalyst material can contain IrOOH, IrCh, IrRuCh, or TiCh-, NbCh- or SnCh-supported variants of the aforementioned catalysts or corresponding material systems.

[0030] In a preferred embodiment for the cathode, the catalyst material comprises platinum, in particular in the form of solid or powdered so-called "platinum black" for the HER catalyst. Alternatively or additionally, palladium, ruthenium or carbon-supported variants / mixtures of the aforementioned catalysts may be included.

[0031] In a particularly preferred embodiment of the method, the material of the membrane substrate is composed of a fluorine-free sulfonated polymer, wherein the sulfonated fluorine-free polymer of the catalyst paste is adapted thereto.

[0032] In this embodiment, the sulfonated fluorine-free polymer is specifically matched to be similar or of a material of the membrane substrate. This embodiment significantly improves the bonding of the catalyst layers to the membrane substrate. In other words, the catalyst paste with the anhydrous solvent can simultaneously function as a very effective binder or adhesive for the bonding and inherently promotes the formation of an intermediate layer to promote adhesion. This creates a very stable interlayer in which the material of the membrane substrate is partially dissolved by the application process, thus bringing about and optimizing a permanent and intimate bond in the boundary region to the catalyst layer.

[0033] The term "similar" or "similar" is intended to mean, for example, that both materials mentioned are at least fluorine-free polymers, but not necessarily the same polymer type. It is also possible that both polymers are sulfonated. In this context, one polymer can, for example, be a hydrocarbon-based polymer.

[0034] In one embodiment, the process leads to little, no or almost no adverse sedimentation and / or demixing effects, for example of the sulfonated fluorine-free polymer and / or the catalyst material in the catalyst paste.

[0035] In a preferred embodiment, the sulfonated fluorine-free polymer is provided by a fluorine-free hydrocarbon compound having a cation-conducting group. This can be realized, for example, by an aromatic hydrocarbon compound having a cation-conducting group.

[0036] In this case, a polyaromatic ionomer which has a sulfonated side group as a cation-conducting group is further preferably provided as the sulfonated fluorine-free polymer.

[0037] In a preferred embodiment, the polyaromatic ionomer is selected from the group of sulfonated polyether ketones (sPEEK), sulfonated polyphenylenes (sPPX), and sulfonated polyimides (sPI). These can also be referred to as fluorine-free "hydrocarbons," which are preferably used here as fluorine-free polymer classes for the catalyst paste and for the membrane substrate, in contrast to the perfluorinated ionomers previously commonly used and widely used in PEM electrolysis.

[0038] In principle, a wide variety of fluorine-free polymers can be selected for functionalization to form ionomers for providing a catalyst-coated membrane (CCM) or a membrane electrode assembly (MEA). For PEM water electrolysis, polyaromatic ionomers are of particular interest due to the high demands placed on their chemical, thermal, and mechanical properties. The largest groups of hydrocarbons preferred for PEM electrolysis are poly(arylene ether), polyphenylenes, and polyimides. They all have low gas crossover. The largest group is poly(arylene ether)-based hydrocarbons, which include sulfonated polyetheretherketones (sPEEK). The biggest advantage is its good availability and low cost compared to PFSA. It also has high mechanical strength and high thermal stability.Another group is made up of sulfonated polyphenylenes (sPPX), which have similar properties. Their major advantage is the high stability of the backbone against chemical degradation. There are also sulfonated polyimides (sPI), which also offer high thermal stability, high mechanical strength, and good film formation. The greatest challenge with sPI is the hydrolysis of the imide rings in the hydrogenated state at operating temperatures relevant for PEMWE. The same applies to hydrocarbons with an aliphatic main chain, which have low oxidation resistance.

[0039] Preferably, in the process, the catalyst paste is intimately mixed to form a paste mixture, wherein a high solids content of catalyst material and sulfonated fluorine-free polymer of 35 wt% to 60 wt%, in particular of 45 wt% to 55 wt%, is set in the paste mixture.

[0040] Compared to PFSA-based systems, comparatively higher solids content has proven advantageous for producing a fluorine-free catalyst-coated membrane (CCM) with the required properties for use in a PEM electrolysis cell. This can be adjusted and adapted to the selected application-specific paste formulation, which includes the solvent, the fluorine-free sulfonated fluoropolymer, and the catalyst material system. When mixing the catalyst paste, a solvent ratio (LMA) to solids ratio (EKA) of, for example, 40 / 60, 45 / 55, or 50 / 50 by weight can be preferred, depending on the requirements.

[0041] The paste formulation or paste production is divided into the following steps:

[0042] Production of the ionomer dispersion and the subsequent mixing process with catalyst material in particle form. Special consideration must be given to the interactions between the components, as these essentially determine the material properties of the catalyst paste. The rheological properties play a decisive role in the coating step following paste formulation, influencing, for example, the electrode structure, thickness, and weight. The aim is preferably to achieve a balance between the disadvantages of low-viscosity pastes (thickness variation, demixing) and high-viscosity pastes (blockage of the coating tool, problems with the mixing process).In general, higher viscosity catalyst pastes are preferable for applying the catalyst paste to the membrane substrate in fluorine-free CCMs in order to give preference to a good electrode structure of the CCS and a particularly intimate, uniform and at the same time long-term stable bonding of catalyst material to the membrane substrate and the formation of a stable intermediate layer, the interlayer.

[0043] In a preferred embodiment, the catalyst paste is applied directly to the membrane substrate by means of a doctor blade application and optionally with the aid of a vacuum plate designed to hold the membrane substrate. According to an embodiment with a vacuum plate, the process according to the invention is then carried out in a laboratory or on a small-scale industrial scale, e.g., for a test or for small industrial series of catalyst-coated membranes.

[0044] In a particularly preferred embodiment of the method, the direct application of the catalyst paste to the membrane substrate is carried out by means of a roll-to-roll application method, in particular using an oven for a heat treatment during the paste application to drive off the solvent.

[0045] According to this design, the manufacturing process itself is subject to virtually no limitations, for example, with regard to coating width, and can thus be scaled to ever-increasing throughputs or production batches, significantly increasing overall manufacturing capacities for electrolysis cells. In particular, these advantages mean that one is no longer bound to the procedural limitations of the state of the art.

[0046] In one embodiment, during the direct order the

[0047] Catalyst paste on the membrane substrate expediently undergoes a heat treatment via an oven, for example a multi-chamber oven in the case of double-sided coating of the membrane substrate, to drive off the solvent and / or a binder optionally introduced into the catalyst paste after the application of the catalyst paste.

[0048] In a preferred embodiment, the catalyst paste is further applied to the membrane substrate, i.e., for example, by roll-to-roll coating, via a slot die or slot die coating, in particular via so-called wide slot dies. This embodiment advantageously offers the possibility of controlling the desired wet film thickness of the coating by means of the measured mass flow and a predetermined substrate speed.

[0049] In one embodiment, however, the catalyst paste is applied to the membrane substrate via an applicator, metering, or anilox roller. This embodiment advantageously allows the coating to be carried out simply and self-metered, as well as intermittently, i.e., interrupted as needed.

[0050] The catalyst paste is preferably applied to the membrane substrate on both sides, in particular with different catalyst materials on the opposite sides or surfaces of the membrane substrate. Due to the described requirements of the electrolysis reaction at the cathode and anode, there is usually a need to apply different catalyst coatings to the cathode and anode.

[0051] In one possible embodiment, the catalyst paste is applied to only one side of the membrane substrate or membrane, and on the side facing away from this first side—the functional membrane surface—a so-called decal process is used for the coating. According to this embodiment, the invention can also be advantageously used for "single-sided" coating systems if required. However, the greater advantages for industrial application arise from direct coating for the production of fluorine-free coated membranes with a corresponding catalyst layer on the anode side and on the cathode side, as described above.

[0052] In a particularly preferred embodiment of the method, after the catalyst paste has been applied to the membrane substrate, a drying step is carried out in which drying, curing and, if necessary, thermal post-treatment of the catalyst material on the coated membrane substrate is brought about.

[0053] Typically, drying is carried out in a circulating air dryer at a drying temperature of, for example, 60 ° to 80 ° C, alternatively up to 100 ° C.

[0054] Drying in the drying step is an important process step in MEA manufacturing according to the method described here, as it influences the evaporation rate of the solvent and the volume reduction, thus contributing significantly to the formation of the electrode structure. It is dominated by evaporation in catalyst pastes with a high solids content.

[0055] The drying process can be divided into three phases: liquid, gel, and solid. First, the paste film shrinks to the final electrode thickness before the pores empty due to evaporating solvent. A high drying temperature generally results in high porosity and the ionomer migrates to the upper free surface. However, this leads to lower adhesion of the electrode to the membrane, which can cause delamination. Therefore, moderate drying temperatures are preferable, particularly for the fluorine-free CCM according to the invention; 70°C to 80°C are preferred. The drying step can also include an adapted thermal post-treatment of the laminated structure, the so-called "curing."This curing by carefully dosed heat input is preferably monitored and, if necessary, applied iteratively until the specified structural properties of the electrode applied to the membrane and the CCM are achieved.

[0056] In a particularly preferred embodiment of the process, an ionomer content of 6 wt% to 15 wt%, in particular of 9 wt% to 12.5 wt%, is set on the anode side and / or cathode side in the layer applied to the membrane substrate and comprising the catalyst material.

[0057] The ionomer content can be adjusted in the paste formulation via the weight fraction of the solids content of added powdered sulfonated fluoropolymer in the catalyst paste, i.e. in the dispersion or pasty mixture of the anhydrous solvent, the catalyst material and the fluorine-free polymer, so that after the drying step a correspondingly preferred ionomer content results. It has been shown that ionomer contents with the above-mentioned preferred weight fraction are particularly useful for the function of the fluorine-free CCM and for providing the required transport properties. Sufficient porosity is necessary for the removal of water and gas. It is typically around 60%. Poor gas transport results in increased gas pressure, which can lead to gas crossover through the membrane. The gas crossover is therefore related to the ionomer content.A favorable operating point for the ionomer content for the formulation of the catalyst paste and the dried CCM is therefore a compromise between small pore volume and mass transport losses, with a comparatively high ionomer content and poor proton conduction and ionic ohmic voltage losses at a rather low ionomer content.

[0058] The ionomer content depends on the components and the respective use in the anode or cathode and can also assume higher values ​​of up to 30 wt% compared to the generally preferred, somewhat lower ionomer content. Last but not least, the final microstructure is influenced by the type of coating and drying process. A further aspect of the present invention relates to a catalyst-coated PEM membrane or membrane assembly, which is or can be produced by the described method.

[0059] Yet another aspect of the present invention relates to an electrolytic cell which uses a variant of the previously described CCMs, for example with double- or single-sided electrodes.

[0060] A further advantageous aspect of the invention is a plurality of such electrolysis cells stacked and electrically connected in series. These form a cell stack or electrolysis stack that is scalable for large electrolysis capacities.

[0061] Therefore, in a particularly preferred embodiment of the invention, an electrolysis plant is proposed which has such a cell stack.

[0062] The merits of the present invention are therefore not only manifested in the small or minimal product unit, such as the membrane or the CCM, but also significantly, due to the economy of scale, in the electrolysis cell and a cell stack, electrolyzer, or electrolysis system comprising the electrolysis cell, which concerns further aspects of the present invention. From an environmental perspective, this makes a manufacturing approach for future fluorine-free CCMs for water electrolysis and their applications on an industrial scale possible.

[0063] In particular, the present invention relates to PEM electrolyzers and furthermore to entire electrolysis or power-to-X power plants which have an electrolysis system as described herein.

[0064] 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, the electrolysis plant and / or an entire Power-to-X power plant, and vice versa.

[0065] 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.

[0066] Examples of the invention are explained in more detail with reference to the accompanying drawings. These show schematically and in a highly simplified manner the

[0067] FIG 1 shows the operation of an electrolysis cell for water electrolysis, in particular a PEM electrolysis cell, with a catalyst-coated membrane used therein;

[0068] FIG 2 shows a schematic flow diagram of method steps according to the invention in general;

[0069] FIG 3 shows an application method for coating a membrane substrate to produce a catalyst-coated membrane;

[0070] FIG 4 shows a variant of the application method shown in FIG 3 for coating a membrane substrate;

[0071] FIG 5 shows an alternative application method for coating a membrane substrate;

[0072] FIG. 6 shows, by way of example and using a polarization curve, an electrochemical characterization of a fluorine-free catalyst-coated membrane (CCM), which is produced by direct membrane application of the catalyst material to a membrane substrate; FIG. 7 shows, by way of example, the long-term stability of two different fluorine-free CCMs at a given current density.

[0073] FIG 8 shows a simplified representation of the interlayer for a CCM, which is formed by the application process between the membrane substrate and the catalyst layer.

[0074] In the exemplary embodiments and FIGS, 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.

[0075] In FIG. 1, an electrolysis cell 25, in particular a PEM electrolysis cell for water electrolysis, is shown in the left-hand section. An important functional element of such a polymer electrolyte membrane electrolysis cell 25 is generally formed by a catalyst-coated membrane 23, also referred to as a catalyst-coated membrane or CCM for short. Such a membrane 23 or CCM is shown in more detail in an illustration to the right of the electrolysis cell 25 in FIG. 1.

[0076] The catalyst-coated membrane 25 has a membrane substrate 11 coated on both sides with a catalyst material 7. For this purpose, the membrane substrate 11 is usually coated on both the anode side and the cathode side on two opposite, mutually remote surfaces with a layer of a respective catalyst material 7. The respective cell reaction of the electrolysis takes place in the region of the layer formed by the respective catalyst material 7. During normal operation, electrons are diverted to the contact or bipolar plates 29 via the respective catalyst material 7 and a support or channel structure, which can be formed by the gas diffusion layer 27 or can provide it, compare the electrolysis cell 25 in the illustration on the left.

[0077] It can also be seen that demineralized reactant water (H2O) is typically provided on the anode side and fed to the PEM electrolysis cell 25. The reactant water (H2O) is decomposed into oxygen (O2) and hydrogen (H2) during the electrolysis process. Oxygen (O2) and hydrogen (H2) are formed as electrolysis products at the anode and at the cathode as product gases, which are then recovered separately and discharged from the PEM electrolysis cell 25.

[0078] The catalyst-coated membrane 23 comprises a membrane substrate 11 made of a membrane material which, during the production of a coated membrane 23, is coated with a pasty, viscous catalyst paste 9 as a coating material. The catalyst paste contains the catalyst material 7. The membrane substrate 11 is fluorine-free and contains, or is formed from, a sulfonated hydrocarbon polymer, a so-called hydrocarbon, as the ionomer for proton conduction. Materials from the sulfonated polyaromatics are selected as the fluorine-free polymer for the membrane substrate. For example, as illustrated in FIG. 2, so-called sPEEK or sPPX can be used for the membrane substrate 11 or the membrane substrate 11 can be formed from them. The largest group are the poly (arylene ether) based hydrocarbons, which include sulfonated polyetheretherketones, sPEEK.Another group are sulfonated polyphenylenes (sPPX), which have similar properties. Their major advantage is their high stability against chemical degradation. Ionomers are polymers with ionic groups, which give them the characteristic property of proton conductivity. In the case of PEM water electrolysis, the ionic groups are sulfonic acid groups (-SO3H). These can be randomly distributed or fixedly arranged. In PEM water electrolysis, ionomers are used primarily because of their proton conductivity and simultaneous electrical insulation capacity as membrane material in the membrane substrate 11 and in the electrode applied to the membrane substrate 11, i.e. in the layer comprising the catalyst material 7, so that here a material adaptation has been made in particular for the fluorine-free catalyst-coated membrane 23.

[0079] The provision of the coating material is explained in more detail with reference to FIG. 2. FIG. 2 merely indicates method steps according to the invention using a schematic flow diagram, in particular to illustrate the paste formulation for the catalyst paste 9. The method according to the invention is a process for producing a catalyst-coated membrane 23 for an electrochemical cell, in this case an electrolysis cell 25 for water electrolysis.

[0080] In step S1, the process first comprises providing a fluorine-free ionomer as starting material in solid form, i.e., this starting material is preferably not in solution, but in the form of a finely granular powder. A powdered sulfonated polymer 1 from the group of hydrocarbons is selected as the ionomer, in this case, for example, a sulfonated polyetheretherketone comprising sPEEK.

[0081] For the preparation of the powdered fluorine-free polymer 1 in step S 1, for example, commercially available ready-made dispersions which already contain the fluorine-free polymer to be used in each case can be used. These can be converted beforehand, for example, by a spray-drying step into the desired powder for obtaining or separating the powdered fluorine-free polymer from the dispersion. Such spray or atomization drying is a method from process engineering for drying solutions or, for example, suspensions. The material to be dried is introduced into a hot gas stream or atomized therein, which dries it to a fine powder in a short time.

[0082] The drying process can be carried out, for example, under the following parameters or conditions: injection temperature of 120°C, injection pressure of 10 bar, nozzle dimension of 0.5 mm, jacket or wall temperature of 250°C, a gas temperature of 380°C, and / or at a gas flow of approximately 50 rpm. Alternatively, vacuum spray drying can be carried out with a single- or two-component nozzle under the following parameters: a pressure of, for example, 100 mbar, a nozzle bore of approximately 0.3 mm, an injection temperature of 130°C, a jacket temperature of 200°C, and a nozzle pressure of, for example, 10 bar.

[0083] The method further comprises, in step S2, dispersing, introducing, or processing the fluorine-free polymer 1 in an anhydrous solvent 3 to form a plastisol 5. The term "plastisol" is intended to generally refer to a dispersion or a heterogeneous mixture. For example, the anhydrous solvents 3 or solvent combinations listed in the table above with the further specified specifications, in particular for the possible ionomer content, can be used. These specified value ranges for the ionomer contents and paste viscosities are generally preferred windows for the formulation and can be adapted to the respective requirements. Mixed solutions of two of the solvents 3 mentioned, for example binary mixtures of N-methyl-2-pyrrolidone and a proportion selected from N-ethyl-2-pyrrolidone, γ-butyrolactone or diethylene glycol monoethyl ether, have proven successful. Depending on the application and material composition of the catalyst paste 9 for a particular membrane substrate 11, viscosities greater than 500 mPas are also possible, for example up to 1000 mPas.

[0084] The process according to the invention further comprises, in a process step S3, the intimate and homogeneous mixing of a catalyst material 7 with the plastisol 5. From this process step S3, a pasty, generally viscous or highly viscous coating material is obtained, which forms the catalyst paste 9. The paste mixture catalyst paste 9 is adjusted such that it has an overall high solids content of catalyst material 7 and sulfonated fluorine-free polymer 1 of 35 wt% to 60 wt%, in particular of 45 wt% to 55 wt%.

[0085] Furthermore, the method further comprises, in step S4, the direct application of the catalyst paste 9 to a membrane substrate 11 made of a similar material, e.g., a corresponding fluorine-free polymer 1 such as sPEEK. A direct coating process is used to apply the catalyst paste 9 obtained in method step S3 to the membrane substrate 11. The present invention thus particularly advantageously enables cost-effective and scalable production of a large-format, fluorine-free catalyst-coated membrane 23. Such a catalyst-coated membrane (CCM) is particularly environmentally friendly and can be used for PEM water electrolysis.Due to the paste formulation used and the resulting and adaptable viscosity properties (rheology), the fluorine-free catalyst pastes 9 described here enable and promote the use of industrially standardized R2R (roll-to-roll) application methods for direct membrane coating and, if necessary, also other application methods, as explained further below in FIGS. 3 and 4. After the catalyst paste 9 has been applied to the membrane substrate 11, a drying step S4 follows. This involves drying, curing and an optional multi-stage thermal aftertreatment of the catalyst-coated membrane 25. In this way, a good surface structure of the catalytically active porous layer and long-term stable and uniform bonding to the membrane substrate 11 is achieved.

[0086] Depending on the application method, an appropriate viscosity range can be advantageously adjusted via the solvent combination. Furthermore, the achievable paste viscosity is also largely determined by the anhydrous solvent 3 or the solids content in the catalyst paste, as well as the solids ratio. The solids ratio indicates the ratio of the ionomer content to the proportion of catalyst material in the catalyst paste 9.

[0087] A 10 to 20 wt%, especially 9 wt%, plastisol made from the combination of Pemion™ as a fluorine-free ionomer and 2-pyrrolidone (500 mPas) has proven particularly advantageous for coating with a wet film thickness of approximately 30 to 70 μm, especially 50 μm, and using a reverse roll or roller application process. Similarly good results can be achieved with the fluorine-free ionomer TS 00X and the solvent content of N-methyl-2-pyrrolidone (NMP) of 5 to 12 wt%, especially 7 wt%.

[0088] The aim is, in particular, to provide a catalyst paste 9 that enables efficient coating of the catalyst particles with fluorine-free ionomer and a highly 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.

[0089] Further important aspects are the film formation in the drying step S5 of the catalyst paste 9, for example, by means of an oven 15 shown in FIGS. 3 to 5 and used in conjunction with corresponding roll-to-roll processes. It is also important that the layer dries as quickly as possible and that the coating exhibits good adhesion properties to the (membrane) substrate, thus promoting the formation of the intermediate layer 33. This is explained further below with reference to FIG. 8.

[0090] By means of the proposed method, in particular a characteristic intermediate layer 33 (see FIG. 8) as an important functional layer ("interlayer") is not achieved by reaching the glass transition temperature of the membrane substrate under increased pressure, but in the present case this is achieved instead by a targeted and sufficient dissolution of the membrane substrate 11 in the boundary region to the applied layer with the catalyst material 7. In other words, the fluorine-free ionomer 1 from the class of hydrocarbons is selected such that it expediently has the same material as a material of the membrane substrate 11 itself. By means of this adaptation by means of the application of the catalyst paste 9, the function of a binder or adhesive for the catalyst material 7 is advantageously achieved at the same time.The advantageous effect of selecting an anhydrous solvent 3 for the catalyst paste 9 has been shown , which promotes this dissolution process in the boundary layer and the formation of the intermediate layer .

[0091] A possible embodiment for producing a described plastisol 5 as a stock solution comprises, for example, providing 5 g of a fluorine-free polymer, for example Pemion™ in powder form, which is stirred into 30 g of 2-pyrrolidone solution. Complete dissolution occurs after several hours. To produce a catalyst paste 9 for cathode electrodes to catalyze the HER reaction, for example, 10 g of Pt-black can be provided and mixed with 10 g of a 10 to 20 percent fluorine-free hydrocarbon plastisol stock solution and then thoroughly mixed with ZrCh grinding balls in a paste mixer. Settling or agglomeration of the particles is not observed, so that an HER catalyst is formed on the cathode side.

[0092] For the preparation of a catalyst paste 9 for anode electrodes using 10g Ir-black with 10g together with 10g of a comparable fluorine-free hydrocarbon plastisol stock solution, good results can be achieved in a corresponding manner.

[0093] As alternatives to the aforementioned HER catalyst, palladium, ruthenium, or carbon-supported variants and mixtures of the aforementioned catalysts can also be used as catalyst materials in the catalyst paste 9 for the cathode. As alternative embodiments for the OER catalyst, optionally IrOOH, IrCh, IrRuCh, or TiCh-, NbCh-, or SnCh-supported variants of the aforementioned catalysts can be used as catalyst materials in the corresponding catalyst paste 9 for the anode.

[0094] The coating of the membrane substrate 11 comprising a similar or identical fluorine-free hydrocarbon with the catalyst paste 9 containing the catalyst material 7 is finally carried out according to process step S4 using a direct application. Direct application is carried out without any transfer, transfer, or pressing steps. This advantageously applicable coating method is also referred to as direct membrane deposition (DMD).

[0095] For this purpose, for example, a simple doctor blade application can be carried out, wherein the catalyst paste 9 is distributed and / or applied with a doctor blade onto the membrane substrate 11, which is held and / or moved, for example, by a vacuum plate - not explicitly shown in the figures. This embodiment is particularly useful for test batches or laboratory samples in relatively small quantities. With or without a short drying time, the membrane 23 (CCM) catalyst-coated on one side with the catalyst paste 9 can be dried, for example, in an oven 15 (see further below) between 50 and 100 °C. The back of this thus fully coated half-membrane can then be coated in a similar way until, for example, final drying or tempering takes place, preferably at temperatures well above 100 °C.

[0096] FIG. 3 shows a preferred application method for coating a membrane substrate 9 for producing a catalyst-coated membrane 23. FIG. 3 shows a merely schematic side or sectional view of a coating device 17 which uses the general roll-to-roll principle and has corresponding rollers 21 for fixing and conveying the membrane substrate 11. Specifically, the catalyst paste 9 is preferably applied via so-called slot dies 19 which are arranged and positioned on both sides of the coating device 17. The slot die 19 shown on the right is designed to coat a first active side of the membrane substrate 11, as described above, for example with a catalyst material 5 comprising platinum Pt contained in the catalyst paste 9.The layer application can then be dried or pre-dried in a multi-zone oven 15 - not explicitly shown in FIG 3 -. The ribbon-shaped membrane substrate 1, which has already been coated on one side, can then be conveyed further via the rollers 21. A second side of the membrane substrate 11, facing away from the first side of the same, can now be coated with a catalyst paste 9 which contains iridium Ir as catalyst material 5, until the membrane substrate 11, which has been coated on both sides in this way, passes through the oven 15 again, in particular in order to expel the solvent 3 or any residues or binders from the catalyst paste 9. The drying step S5 is therefore already at least partially, i.e. as a sub-step, integrated in the coating device 17 by the oven 15. However, further heat treatment steps can still follow.

[0097] For the formation of a porous surface structure with good catalytic properties and a particularly long service life of a fluorine-free catalyst-coated membrane 23 and bonding to the membrane substrate 11, in addition to the selection of the fluorine-free hydrocarbon as the ionomer, a corresponding selection of the solvent in the manufacturing process of the catalyst paste 9 has proven particularly advantageous. Contrary to previous practice, anhydrous solvents 3 have surprisingly proven to be very useful for dissolving the interfaces, forming an interlayer, and ensuring long-term stable bonding in the patent formulation to form a colloidal dispersion, such as the use of the solvents N-methyl-2-pyrrolidone or 2-pyrrolidone (γ-butyrolactam).

[0098] Media dosing during the slot die application of the catalyst paste 9 can be carried out, for example, via so-called eccentric screw pumps. The coating device 17 has a pay-off reel with brake, a belt tension (e.g. 50 Nm), a double-sided slot die coater with a passage width of approximately 10 cm and a design for a substrate thickness of approximately up to 90 μm. During application, a belt speed of between 0.8 and 1.2 m / min is set and an application thickness (wet film) of less than 50 μm is used. A viscosity range of, for example, 200 to 1000 mPas for the catalyst paste 9 is expedient, with a "wet loading" of the membrane substrate 11 of approximately 30 mg / cm 2 and is carried out under drying in a circulating air dryer (drying temperature, for example, 80 to 100 ° C). In general, a high solids content in weight percent is

[0099] (wt%) of the processable fluorine-free catalyst paste 9 of 35 to 65 wt%, in particular 45 to 55 wt%, is provided. Coating via slot dies 19 advantageously offers the possibility of controlling the desired wet film thickness of the application by means of the measured mass flow and a predetermined substrate speed. The embodiments of a coating device 17 based on a roll-to-roll conveyor technology shown in FIGS. 3 and 4 advantageously allow simultaneous double-sided dosing and application of two different and accordingly specifically adapted catalyst materials 7 in a catalyst paste 9 on a fluorine-free hydrocarbon-based membrane substrate 11 provided in strip form.

[0100] FIG. 4 shows an alternative embodiment of a double-sided direct coating of a membrane substrate 11. Here, the coating device 17 is equipped with application or metering rollers 13, by means of which the coating can advantageously be applied very easily and in a self-metering manner. Otherwise, the process can be carried out essentially analogously to the description of FIG. 3. This type of coating - also referred to as reverse-roll coating - is particularly useful for producing a particularly uniformly coated catalyst-coated membrane 23, i.e. CCMs of particularly high quality. Here, too, a double-chamber oven 15 with spatial dimensions of significantly more than 1 m can be used for a drying step S5, as well as corresponding circulating air or floating dryers in order to implement the application as evenly and as extensively as possible on the fluorine-free membrane substrate 11.The drying step S5 may comprise further sub-steps, such as a multi-stage post-heat treatment, the so-called "curing", which is not explained in more detail here.

[0101] An alternative application method to the coating of a membrane substrate 11 shown in FIGS. 3 and 4 is shown in FIG. 5. Here, the application of the catalyst paste 9 according to step S4 in the coating device 17 sketched in FIG. 5 is carried out only on one side of the membrane substrate 11. The side facing away from this one side can, if required, be coated using a transfer printing process. In particular, the catalyst paste 9 is first applied directly to a polyimide film - not explicitly identified here - and then laminated by transfer printing. More precisely, a catalyst layer made of the catalyst paste 9 can be applied in particular to an FEP-coated, hydrophobicized Kapton film (type Dupont 300 FN 929) using application rollers. The coating is then preferably carried out in segmented fields.The resulting so-called "decal films" can then be laminated to the back of the directly coated membrane using a hot-pressing process. Hydrophobizing the Kapton film improves the release properties of the "decal," allowing even strongly adherent plastisol layers to be transferred.

[0102] FIG. 6 also shows the result of an electrochemical characterization of the fluorine-free catalyst-layered membrane (23) directly coated according to the invention. Electrochemical characterizations were carried out on the fluorine-free CCMs from the TS 00X and Pemion™ test series in order to validate the system efficiency (polarization curves and impedance spectroscopy), long-term stability and system reliability (gas chromatography). In order to electrochemically characterize the fluorine-free CCMs, U-I characteristic curves were measured. The prepared MEA samples contained different electrode combinations in order to separate the factors influencing the properties on the anode and cathode. In particular, FIG. 6 shows, as an example, a corresponding polarization curve - a U-I characteristic curve - with a cell voltage U, plotted against the respective current density I, which provides proof of functionality in the present case.In FIG. 6, two characteristic curves Ti (A) and Ti (B) show exemplary results from a test series using the TS O OX ionomer as a fluorine-free hydrocarbon. The results from a test series using Pemion™ ionomer are shown for comparison in characteristic curve T2 (A).

[0103] Corresponding endurance tests at a constant current density of 2 A / cm 2were carried out in order to draw conclusions about the long-term stability of the samples. A known degradation effect in endurance tests is the increase in voltage at constant current density, which can be attributed to various causes of degradation, such as catalyst passivation, loss of contact between the components, ionomer degradation. As an example, FIG 7 shows an investigation of the long-term stability of a fluorine-free catalyst-coated membrane 23, where T1 shows the long-term behavior of a CCM with a TS O OX ionomer and T2 shows the long-term behavior of a CCM with a Pemion™ ionomer. In each case, the temporal progression of the cell voltage U is plotted against time t. A largely and almost constant voltage level could be demonstrated for both fluorine-free CCMs for a long investigation period of at least 72 h.The economic potential for the future use of fluorine-free catalyst-coated membranes 23 produced by the process of the invention is demonstrated.

[0104] FIG 8 shows a CCM 23 in a simplified representation. The selected paste composition and the application method specifically initiate a dissolving process which, through the choice of solvent and the material adaptation of the ionomer, leads to the formation of an intermediate layer 33 as an important functional layer in the manufacturing process. This intermediate layer 33 ensures good adhesion and long-term stable bonding of the catalyst layer 31 comprising the catalyst material 7 and the fluorine-free polymer 1 to the membrane substrate 11. The catalyst layer 31 comprises the fluorine-free polymer 1, for example a sulfonated polyether ketone sPEEK. The membrane substrate 11 also comprises a similar or identical fluorine-free polymer 1, preferably also a sulfonated polyether ketone sPEEK.The intermediate layer 33 has a layer thickness D of approximately 3-10 pm, so that a firm and long-term stable material bond is formed between the catalyst layer 31 and the membrane substrate 11 via dissolution of the similar ionomer.

[0105] Through the catalyst layer 31 on the membrane substrate

[0106] 11 an electrode is provided, in the enlarged detail of FIG 8 an anode electrode with platinum Pt as catalyst material 7. In an analogous way a cathode electrode is formed on the opposite side of the membrane substrate 11, which has iridium as catalyst material 7. The microstructure of the electrode is a three-dimensional network made up of the ionomer, i.e. the fluorine-free hydrocarbon, the catalyst material 7 and pores. Due to the porous structure the electrode is permeable to diffusion for the transport of the reactants and the electrolysis products. The intersection point of the three components is called the three-phase boundary (TPB). This is where the electrochemical reaction takes place locally and microscopically, since in addition to the availability of the catalyst material 7 the provision of the reactants, i.e. Water H2O, is crucial for the reaction.Thus, a gas diffusion electrode or gas diffusion layer is formed on the CCM 23. In the case of platinum Pt as the catalyst material 7, the platinum catalyst can be supported on carbon. The carbon forms agglomerates which are partially enclosed by the ionomer. A further distinction can be made between primary and secondary pores. Primary pores are located within an agglomerate and secondary pores are located between agglomerates. They also differ in that the ionomer is mainly present in the secondary pores, thus creating an increased ionic resistance in the primary pores.

[0107] The present invention enables the production of fluorine-free catalyst-coated membranes for PEM water electrolysis on an industrial scale. This counteracts the impending Europe-wide ban on PFSA. In addition, the targeted use of fluorine-free ionomers and the production of fluorine-free membrane electrode assemblies (MEAs) for PEM water electrolysis and electrolysis plants is possible. Good system efficiency and long-term stability of the fluorine-free MEAs are achieved through the advantageous paste formulation and the choice of materials. Fluorine-free MEAs offer a number of advantages over fluorine-containing ionomers. First of all, technical advantages such as higher operating temperatures due to the higher thermal resistance of hydrocarbons for PEM water electrolysis should be mentioned.Furthermore, an alternative technology is proposed in the event of an EU ban on PFAS materials, which is generally expected. The process of the invention and the CCMs produced according to the process thus ensure that no environmentally harmful fluorine compounds, which could enter the environment along the process chain, need to be treated. Finally, a downstream recycling process is also considerably simplified, since there is no risk of hydrogen fluoride being produced during thermal reprocessing in an MEA combustion process. This eliminates the previously necessary, very complex gas scrubbing of the combustion products. Fewer corrosion problems induced by fluorine ions during operation of an electrolysis plant, which lead to adverse degradation, are also expected.

[0108] The formulation of catalyst paste 9 allows for the ionomer / catalyst ratio to be adjusted very precisely and adapted to the respective anhydrous solvent. Furthermore, known or standardized production dimensions can be easily scaled up, for example, to significantly increase the production capacity of high-purity hydrogen.

Claims

Patent claims 1. A method for producing a catalyst-coated membrane (25) for an electrochemical cell (25), comprising the steps: - Sl: Providing a powdered sulfonated fluorine-free polymer (1) , - S2 dispersing the sulfonated fluorine-free polymer (1) in an anhydrous solvent (3) to form a plastisol (5), - S3: Mixing a catalyst material (7) with the plastisol (5) to form a catalyst paste (9), and - S4: Application of the catalyst paste (9) to a membrane substrate (11).

2. Process according to claim 1, wherein the anhydrous solvent (3), in particular a polar, high-boiling solvent, is selected from: dimethyl sulfoxide, N,N-dimethylformamide, N,N-diethylformamide, 2-pyrrolidone or γ-butyrolactam, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone.

3. The process according to claim 1, wherein the anhydrous solvent (3) used is a mixture of N-methyl-2-pyrrolidone and a portion selected from N-ethyl-2-pyrrolidone, γ-butyrolactone or diethylene glycol monoethyl ether.

4. The method according to claim 1, 2 or 3, wherein the catalyst material (7) comprises iridium (Ir), in particular solid or powdered iridium black.

5. Method according to one of the preceding claims, wherein the catalyst material (7) comprises platinum (Pt), in particular solid or powdered platinum black.

6. Method according to one of the preceding claims, wherein the material of the membrane substrate (11) is composed of a fluorine-free sulfonated polymer (1), wherein the sul- fonated fluorine-free polymer (1) of the catalyst paste (9) is adapted thereto.

7. The method according to any one of the preceding claims, wherein sulfonated fluorine-free polymer (1) is provided by a fluorine-free hydrocarbon compound, in particular an aromatic hydrocarbon compound having a cation-conducting group.

8. The method according to claim 7, wherein the sulfonated fluorine-free polymer (1) provided is a polyaromatic ionomer having a sulfonated side group as a cation-conducting group.

9. The method according to claim 8, wherein the polyaromatic ionomer is selected from the group of sulfonated polyether ketones (sPEEK), sulfonated polyphenylenes (sPPX) and sulfonated polyimides (sPI).

10. The method according to any one of the preceding claims, wherein the catalyst paste (9) is intimately mixed to form a paste mixture, wherein a high solids content of catalyst material (7) and sulfonated fluorine-free polymer (1) of 35 wt% to 60 wt%, in particular of 45 wt% to 55 wt%, is set in the paste mixture.

11. Method according to one of the preceding claims, wherein a direct application (S4) of the catalyst paste (7) onto the membrane substrate (11) is carried out by means of a doctor blade application and optionally with the aid of a vacuum plate which is designed to hold the membrane substrate (11).

12. The method according to any one of claims 1 to 10, wherein the direct application of the catalyst paste (7) to the membrane substrate (11) in method step (S4) is carried out by means of a roll-to-roll application method, in particular using an oven (15) for a heat treatment during the paste application to drive off the solvent (3).

13. The method according to claim 12, wherein the application of the catalyst paste (7) to the membrane substrate (11) is further carried out via a nozzle coating.

14. The method according to claim 12, wherein the catalyst paste (7) is applied to the membrane substrate (1) via an application roller (13).

15. The method according to any one of claims 1 to 10, wherein the application of the catalyst paste (11) to the membrane substrate (11) is carried out on both sides, in particular with different catalyst materials (7) on the opposite sides of the membrane substrate (11).

16. Method according to one of the preceding claims, wherein after the application (S4) of the catalyst paste (7) to the membrane substrate (11), a drying step (S5) is carried out in which drying, curing and thermal aftertreatment of the catalyst material (7) on the coated membrane substrate (11) is brought about.

17. The method according to claim 16, wherein an ionomer content of 6 wt% to 15 wt%, in particular of 9 wt% to 12.5 wt%, is set on the anode side and / or cathode side in the layer applied to the membrane substrate (11) and comprising the catalyst material (7).

18. PEM membrane assembly comprising a catalyst-coated membrane (23) manufactured according to the method of any one of the preceding claims.

19. Electrolysis cell (25) comprising a PEM membrane arrangement according to claim 18.

20. A cell stack comprising a plurality of electrolysis cells (25) according to claim 19.

21. Electrolysis plant with a cell stack according to claim 19.

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