Method for manufacturing a catalyst coating film for an electrochemical cell and an electrolytic cell manufactured therein

Abstract

A method for producing a catalyst coating film (25) for an electrochemical cell (25) is proposed. In this method, first, in step (S1), a powdered sulfonated nonfluorinated polymer (1) is prepared. In a further step (S2) of this method, the sulfonated nonfluorinated polymer (1) is dispersed in an anhydrous solvent (3) to form a plastisol (5). Then, in step (S3), a catalyst material (7) is mixed with the plastisol (5) to form a catalyst paste (9). Then, in step (S4), the catalyst paste (9) is applied to a film substrate (11).

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an electrochemically active cell, particularly a catalyst-coated membrane for a PEM electrolysis cell (hereinafter referred to as a catalyst-coated membrane). Furthermore, the present invention relates to a corresponding electrolysis cell and an electrolysis apparatus having such an electrolysis cell.

Background Art

[0002] So-called PEM electrolysis (where PEM stands for "polymer electrolyte membrane" or "proton exchange membrane") is becoming increasingly important as it holds great potential for producing cost-effective green hydrogen, not only for industrial applications but also as a storage medium or component in energy storage. From the perspective of climate change, the element hydrogen and / or the possibility of producing H2 from renewable energy through PEM electrolysis or water electrolysis has long been proven to be an important factor for the energy industry and related fields. Currently, most hydrogen is produced by steam reforming of methane, but with active investment, regulation, and support measures, a trend towards renewable hydrogen production will surely be brought about in the near future.

[0003] A particularly promising method for obtaining hydrogen (H2) is the electrolysis of water, especially by using renewable electrical energy. Hydrogen can serve as an energy storage medium, for example, by being used as a fuel to stabilize the power supply from renewable energy sources such as wind power and solar power. Hydrogen can also be used in other processes that require a fuel or reducing agent. Thus, the hydrogen obtained by electrolysis can also be used industrially, for example, or to generate electricity again electrochemically using a fuel cell.

[0004] Therefore, by using a suitable electrolysis cell, water can be separated into its chemical components, hydrogen (H2) and oxygen (O2). A particularly important method is the aforementioned PEM electrolysis. This method has proven to be more suitable for coupling with fluctuating power sources, especially compared to alkaline electrolysis, as it is very robust to load fluctuations and requires less complex peripheral equipment. In particular, PEM electrolysis can achieve high current density and high output even under relatively high load gradients, thus advantageously maintaining high quality or purity of hydrogen products, for example, during partial load or overload operation.

[0005] Hydrogen is already being applied in countless industrial and technological applications. The possibility of producing large quantities of H2 in a climate-neutral manner and / or storing or transporting it "carbon-free" using hydrogen carriers such as ammonia continues to open up entirely new avenues for supplying green energy and operating businesses in an environmentally friendly way across various industrial sectors such as transportation, chemicals, or steel. Furthermore, hydrogen as a fuel or fuel additive, which is already very interesting, has the potential to produce zero or minimal emissions in the long term.

[0006] In a PEM electrolytic cell, a membrane is provided, and this membrane has a catalyst-coated membrane (CCM) or a membrane-electrode assembly (MEA) on opposite sides. Each catalyst layer is typically adjacent to a gas diffusion layer, which is adjacent to a conductive contact plate called a bipolar plate. The bipolar plate, in particular, serves as an electrical contact. These gas diffusion layers are preferably formed simultaneously to allow the necessary mass transport during the intended operation of the electrolytic cell. The gas diffusion layers provide the "conductivity" necessary to electrically couple the contact plate and the catalyst layer to each other. This allows the desired electrochemical reaction to be realized in the region of the catalyst layer.

[0007] Hydrogen is produced by electrolysis using water as the starting material. This is an electrochemical process that separates water into its chemical components, oxygen and hydrogen. Electrochemical cell reactions can be described and distinguished as follows: [Table 1]

[0008] In electrolysis using polymer electrolyte membranes, each of the two partial reactions is spatially separated by an ion-conducting membrane, and this membrane must be appropriately equipped with electrodes, particularly cathode catalysts and anode catalysts (CCMs). Significant cost reductions can be achieved not only through improvements in materials but also through improvements in the manufacturing process.

[0009] The production volume of PEM (Percutaneous Emission Membrane) electrolysis units (PEMWEs) is expected to increase significantly in terms of processing capacity and scale (scalability), and will need to increase even more to meet the agreed climate targets. Therefore, there is an urgent need for technologies to improve the processing and production capacity of the corresponding CCMs.

[0010] A CCM comprises a film with catalytic material on two surfaces facing opposite each other. In many applications, particularly in PEM water electrolysis, precious metals, which are very expensive and therefore very rare, are used as catalytic materials.

[0011] Currently, the common method involves using catalyst pastes to fabricate catalyst layers or electrodes for anodes and cathodes. Here, the catalyst paste generally consists of the catalyst powder itself, an ionomer, possibly a polymer binder, and a solvent. After application, the solvent is generally removed thermally. If the catalyst layer is deposited on a thermally stable support film, the catalyst layer needs to be transferred to a film under pressure and temperature by a further process step ("decaling method"). This is intended to stably fix the electrodes to the film for a long period and to ensure good ionic contact between the catalyst material and the film. As an alternative to the decaling method, the catalyst paste can also be applied directly to the film ("direct coating" or "direct membrane coating").

[0012] Polymer electrolyte membrane electrolysis (PEMWE) is an industrially established technology for hydrogen production, deriving its name from the polymer membrane used as the electrolyte. Currently, both the membrane and electrode components are composed of polyfluorosulfonic acid (PFSA) ionomers. However, fluorinated polymers are suspected of being harmful to health due to their excellent chemical stability, which prevents their degradation in the environment and the human body. In light of these findings, the European Chemicals Agency (ECHA) recently proposed a nationwide ban on polyfluoroalkyl compounds (PFAS), including PFSA polymers, across Europe. The imminent ban, along with the separate announcement by a major polymer manufacturer of its intention to phase out all fluorinated materials in the near future, highlight the urgent need for the development of long-term stable, commercially available, fluorine-free alternatives to ensure the continuation of PEMWE electrolysis using environmentally friendly alternatives in the future. [Overview of the Initiative]

[0013] Therefore, the present invention is based on the problem of providing a significantly improved manufacturing method that is particularly preferable from an environmental standpoint for manufacturing catalyst coating films (CCMs) and corresponding PEM electrolytic cells and / or cell stacks.

[0014] According to the present invention, this problem is solved by a method for producing a catalyst coating film for an electrochemical cell. This method involves the following steps: A step of preparing a powdered sulfonated fluorine-free polymer (hereinafter referred to as "non-fluorine-based"), A step of forming a plastisol by dispersing a sulfonated nonfluorine polymer in an anhydrous solvent (also called a non-aqueous solvent), A process of mixing a catalyst material with a plastisol to form a catalyst paste, A step of applying catalyst paste to a film substrate, Includes.

[0015] This invention is based on the understanding that the formulation of the catalyst paste is extremely important in the production of catalyst coating films. This has a significant impact on the formation of the catalyst layer on the film substrate and on long-term stable bonding. Relying on known formulations and application methods of catalyst pastes from PFSA technology has been shown to have very limited applicability to the development and bonding of non-fluorinated polymers in coating methods.

[0016] Therefore, industrial coating methods based on water / alcohol ionomer dispersions have also been proposed for non-fluorinated polymers. However, these methods are largely unsuitable for direct coating because the dispersant, water or alcohol, causes significant swelling of the film substrate, severely hindering the dimensional stability of the film or CCM. Furthermore, catalyst inks based on water / alcohol ionomer dispersions have very low viscosity and tend to separate after only a few minutes. Viscosity can often be increased by adding additives such as thickeners like methyl ethyl cellulose, but such additives must be thermally decomposed or burned at temperatures above 300°C again after the catalyst paste is applied. This can cause the film to decompose again or structurally damage the catalyst material. Therefore, to avoid this, the decal method described above is frequently used in the prior art. Unfortunately, the increased number of process steps results in longer lead times and higher process costs compared to direct film coating.

[0017] On the other hand, in addition to environmental advantages or future requirements, fluorine-free (hereinafter referred to as non-fluorinated) ionomers have been shown to offer further technical advantages compared to the use of PFSA, such as higher processing temperatures and reduced gas transfer through the film. [Modes for carrying out the invention]

[0018] One aspect of the present invention relates to a method for producing a catalyst coating film for electrochemical cells, particularly electrolytic cells. In contrast to a film having a film substrate itself, a catalyst coating film (CCM) comprises at least one porous electrode, which is realized by coating and bonding a catalytically active porous layer. Here, the combination of solvent selection and non-fluorinated polymer selection is very important in the formulation of the paste. Compared with known coating methods, the present invention proposes applying an anhydrous solvent to the catalyst paste in the production of a CCM.

[0019] In contrast to conventional practices of treating non-fluorinated ionomers with water / alcohol mixtures based on methanol, ethanol, or isopropanol, the electrode compositions described herein form a more stable “intervening layer,” i.e., an intermediate or bonding layer, between the film substrate and the electrode, thereby improving electrochemical stability when applied to the electrolysis of water and consequently extending the service life. By selecting a suitable non-fluorinated film substrate (also known as a fluorine-free film substrate, etc.) containing a sulfonated non-fluorinated polymer, the material is adapted to be nearly identical to the corresponding non-fluorinated polymer in the catalyst paste, resulting in the formation of this adhesion promoter layer as an “intervening layer” in combination with an anhydrous solvent.

[0020] This method includes, in the first step, preparing a sulfonated non-fluorinated polymer in solid or powder form, that is, preferably undissolved or not in solution.

[0021] This method further includes dispersing the starting material or sulfonated nonfluorinated polymer in an anhydrous solvent, particularly a high-boiling polar solvent such as 2-pyrrolidone or γ-butyrolactam, to form a plastisol.

[0022] This method further includes homogeneously mixing or blending a catalyst starting material, particularly a metallic catalyst, in solid or powder form, with a plastisol to form a catalyst paste as a coating paste, and subsequently, preferably, directly coating the catalyst paste onto a corresponding film substrate (direct film coating). The catalyst pastes described above can be used very advantageously in the direct film coating method. This has far greater applicability compared to the decal method.

[0023] Therefore, the present invention advantageously enables the cost-effective and easy scaling up of large-area catalyst coating films for PEM water electrolysis.

[0024] In particular, due to the advantages of the present invention, the application of the catalyst can be advantageously significantly improved as the hydrogen evolution reaction (HER) described above on the cathode side or as the oxygen evolution reaction (OER) on the anode side, so that the use of a fluorine-free catalyst-coated membrane (CCM) in HER and OER in an electrolytic cell becomes possible.

[0025] Furthermore, the present invention has found that a catalyst-coated fluorine-free membrane (CCM) in roll-to-roll coating technology can be produced on an industrial scale, thereby advantageously making it possible to shorten the throughput time of related components of an electrolysis device. Furthermore, the presented method can advantageously significantly improve both the ionic and mechanical bonding of the catalyst material to the membrane substrate for a fluorine-free membrane electrode assembly (MEA). Furthermore, in addition to the advantageously high material compatibility and extremely good paste stability of the catalyst paste, the improvement of the sedimentation behavior and coating characteristics of this paste formulation should also be noted. Furthermore, from a technical and economic perspective, complicated pressing methods and post-treatment processes are also unnecessary.

[0026] In a particularly advantageous configuration of this method, the aprotic solvent, particularly the highly 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. The use of one of the solvents selected from the above-mentioned group of aprotic solvents promotes, in a specific manner, the formation of an intermediate layer ("intervening layer") as a functional layer for good and long-term stable adhesion of the catalyst to the membrane substrate by interaction with a sulfonated non-fluorine-based polymer, that is, it has been shown that connection by material bonding occurs. This is achieved by selectively dissolving more of the surface of the membrane substrate and comparing it with an aqueous solvent. Therefore, in particular, the electrochemical stability of the catalyst-coated membrane and the high long-term stability during application in an electrolytic cell are promoted.

[0027] In a more preferred configuration of this method, the anhydrous solvent is a mixture containing N-methyl-2-pyrrolidone and a component selected from N-ethyl-2-pyrrolidone, γ-butyrolactone or diethylene glycol monoethyl ether in a specific ratio. By adopting a mixed solvent, the compatibility during the production of the catalyst paste is further enhanced. As a result, depending on the coating system of the catalyst layer, a sufficiently high degree of dissolution of the surface of the membrane substrate and a tight material bond in the region of the intermediate layer are achieved.

[0028] Preferably, the catalyst material contains iridium Ir provided as a so-called "iridium black" in solid or powder form, especially for coating the anode side of the membrane substrate. According to this design, a particularly efficient OER catalyst for the catalyst coating film in the membrane structure or CCM is further provided. Alternatively, or in addition to this, the anode-side catalyst material may contain IrOOH, IrO2, IrRuO2, or a variant (modified form) supported on TiO2, NbO2 or SnO2 of the aforementioned catalyst or the corresponding material system.

[0029] In a preferred design for the cathode, the catalyst material contains platinum, especially in the form of a so-called "platinum black" in solid or powder form for HER catalyst. Alternatively, or in addition to this, palladium, ruthenium, or a carbon-supported variant (modified form) or mixture of the aforementioned catalyst may also be contained.

[0030] In a particularly preferred configuration of this method, the material of the membrane substrate is composed of a fluorine-free sulfonated polymer, and the sulfonated non-fluorine-based polymer of the catalyst paste is adapted to this.

[0031] In this design, the sulfonated non-fluorinated polymer is selectively fitted to be of the same type or similar to the film substrate material. This configuration significantly improves the bonding of the catalyst layer to the film substrate. In other words, the catalyst paste with an anhydrous solvent can simultaneously function as a highly effective binder or adhesive for bonding, essentially facilitating the formation of an intermediate layer for adhesion promotion. Thus, by partially dissolving the film substrate material through the coating method, a very stable intervening layer is formed by creating and optimizing a permanent and tight bond at the boundary region to the catalyst layer.

[0032] The terms "similar type" or "similar" mean, for example, that both materials mentioned above are at least non-fluorinated polymers, but they do not necessarily have to be the same type of polymer. Both polymers may also be sulfonated. In this context, one of the polymers may be, for example, a hydrocarbon polymer.

[0033] In one configuration, this method causes little, no, or almost no adverse precipitation and / or phase separation of sulfonated nonfluorinated polymers and / or catalyst materials in the catalyst paste, for example.

[0034] In a preferred configuration, the sulfonated non-fluorinated polymer is provided by a fluorine-free hydrocarbon compound having a cationic conductive group. This can be achieved, for example, by an aromatic hydrocarbon compound having a cationic conductive group.

[0035] Here, more preferably, a polycyclic aromatic ionomer having a sulfonated side chain as a cation-conducting group is provided as a sulfonated nonfluorine polymer.

[0036] In this case, in a preferred configuration, the polycyclic aromatic ionomer is selected from the group of sulfonated polyether ketones (sPEEK), sulfonated polyphenylenes (sPPX), and sulfonated polyimides (sPI). These can also be called fluorine-free "hydrocarbons," and are preferred as a type of non-fluorinated polymer for catalyst pastes and film substrates, in contrast to perfluoroionsomers, which have long been common and are still widely used for PEM electrolysis.

[0037] In principle, various non-fluorinated polymers can be selected for the functionalization of ionsomers to provide catalyst coatings (CCMs) or membrane electrode assemblies (MEAs). For PEM water electrolysis, polycyclic aromatic ionsomers are particularly important due to the high demands on chemical, thermal, and mechanical properties. The largest group of hydrocarbons preferred here for PEM electrolysis are poly(arylene ethers), polyphenylenes, and polyimides. These all share the common characteristic of low gas crossover (gas leakage). The largest group is poly(arylene ether)-based hydrocarbons, which include sulfonated polyether ether ketones (sPEEK). The biggest advantage is that they are readily available and low-cost compared to PFSAs. Furthermore, they have high mechanical strength and high thermal stability. Another group is sulfonated polyphenylenes (sPPX), which have similar properties. A major advantage is the high stability of the main chain against chemical decomposition. Furthermore, there are sulfonated polyimides (sPIs), which also possess high thermal stability, high mechanical strength, and good film-forming properties. The biggest challenge with sPIs is the hydrolysis of the imide ring in the hydrated state at operating temperatures related to PEMWE. The same applies to hydrocarbons with aliphatic main chains that have low oxidation resistance.

[0038] Preferably, in this method, the catalyst paste is tightly mixed to form a paste mixture, and the solid content of the catalyst material and sulfonated nonfluorinated polymer in this paste mixture is set to 35% to 60% by weight, particularly 45% to 55% by weight.

[0039] As a general trend, it has been found that a relatively higher solids content is advantageous compared to PFSA-based systems for producing fluorine-free catalyst coatings (CCMs) with the properties required for application in PEM electrolytic cells. This can be adjusted and adapted to the paste formulation for each selected specific application, including the solvent, non-fluorinated sulfonated polymer, and catalyst material system. Therefore, when mixing the catalyst paste, the solvent-to-solids ratio (LMA) is preferably adjusted, for example, by weight, to 40 / 60, 45 / 55, or 50 / 50, depending on the requirements.

[0040] The compounding or manufacturing of the paste is divided into the following steps: the preparation of an ionomer dispersion and the subsequent mixing step with particulate catalyst material. Particular attention must be paid to the interactions between each component, as these significantly influence the material properties of the catalyst paste. Rheological properties play a crucial role in the coating step following paste compounding, for example, by influencing electrode structure, electrode thickness, and electrode weight. Preferably, a balance is required between the disadvantages of low-viscosity pastes (thickness variation, separation) and the disadvantages of high-viscosity pastes (clogging of coating equipment, mixing step problems). In general, when applying catalyst paste to a film substrate using fluorine-free CCS, higher viscosity catalyst pastes are preferred to prioritize a good structure of the CCS, as well as particularly tight, uniform, and long-term stable bonding of the catalyst material to the film substrate, and the formation of a stable intermediate layer.

[0041] In a preferred design, the catalyst paste is directly applied to the film substrate, which is done by doctor blade application or optionally by using a vacuum plate adapted to hold the film substrate. With a configuration using a vacuum plate, the method according to the present invention can be carried out on a laboratory scale or a small industrial scale, for example, for testing or for small-batch industrial production of catalyst coating films.

[0042] In a particularly preferred design of this method, the direct application of the catalyst paste to the film substrate is carried out by a roll-to-roll application method, and in particular, by using a heat treatment oven during paste application to eliminate the solvent.

[0043] This design allows for significant expansion of processing volume and production batches, as the manufacturing method itself is largely unrestricted, for example, regarding coating width. This greatly improves the overall manufacturing capacity for electrolytic cells. In particular, these advantages mean that the manufacturing process is no longer constrained by the ratio of limitations imposed by conventional technologies.

[0044] In one design, the catalyst paste is properly heat-treated by an oven, such as a multi-chamber oven in the case of double-sided coating of the film substrate, during the direct application of the catalyst paste to the film substrate, and after the application of the catalyst paste, the solvent and / or binder optionally introduced into the catalyst paste are removed.

[0045] In a preferred configuration, the catalyst paste is further applied to the film substrate by a slot nozzle or slot nozzle coating, particularly a so-called wide slot nozzle, i.e., roll-to-roll application. This design advantageously allows for control of the required wet film layer thickness during application by a measured mass flow rate and a predetermined substrate speed.

[0046] On the other hand, in one configuration, the catalyst paste is applied to the film substrate by a coating roll, a metering roll, or a screen roll. This configuration allows the coating to be carried out advantageously in a simple and automated metering and dispensing manner, and intermittently, i.e., interrupted as needed.

[0047] The application of the catalyst paste to the film substrate is preferably a double-sided coating, and in particular, different catalyst materials are used on opposite sides or surfaces of the film substrate. Due to the aforementioned requirements of the electrolytic reaction at the cathode and anode, it is usually necessary to provide different catalyst coatings at the cathode and anode.

[0048] In possible configurations, the catalyst paste is applied to only one side of the film substrate or film, and the opposite side, i.e., the functional film surface, is coated, for example, using a so-called decal method. With this configuration, the present invention can be advantageously utilized with "single-sided" coating equipment as needed. However, greater advantages for industrial applications are obtained by direct coating for producing fluorine-free coated films having catalyst layers corresponding to the anode and cathode sides, as previously described.

[0049] In a particularly preferred configuration of this method, after applying the catalyst paste to the film substrate, a drying step is performed to dry, cure, and optionally perform a heat post-treatment of the catalyst material on the coated film substrate.

[0050] Typically, drying is carried out using a circulating air dryer at a drying temperature of, for example, 60-80°C or up to 100°C.

[0051] Drying in the drying process is a crucial step in MEA production by the method described herein, as it affects the evaporation rate and volume reduction of the solvent, and consequently contributes significantly to the formation of the electrode structure. In the case of catalyst pastes with a high solid content, evaporation is dominant in this drying process.

[0052] The drying process can be divided into three stages: liquid, gel, and solid. First, the paste film shrinks to the final electrode thickness before the pores become empty due to the evaporation of the solvent. Generally, high drying temperatures result in high porosity, and the ionomer migrates to the upper free surface. However, this leads to a decrease in the adhesive strength of the electrode in the film, which can result in delamination. Therefore, especially in the case of fluorine-free CCM according to the present invention, a moderate drying temperature is preferred, and thus 70°C to 80°C is preferred. The drying process may include a adapted heat post-treatment of the laminated structure, so-called "curing." This curing is carried out by a precisely controlled heat input, preferably monitored, and repeated as necessary until the desired structural properties of the film and the electrode applied to the CCM are achieved.

[0053] In a particularly preferred configuration of this method, the ionomer content on the anode and / or cathode side of the layer coated on the film substrate and containing the catalyst material is set to 6% to 15% by weight, particularly 9% to 12.5% ​​by weight.

[0054] The ionomer content can be adjusted in the catalyst paste formulation by changing the solid weight ratio of the added powdered sulfonated fluoropolymer in the catalyst paste, i.e., in the dispersion or paste-like mixture of the anhydrous solvent, catalyst material, and non-fluorinated polymer, thereby obtaining a correspondingly preferred ionomer content after the drying process. Ionomer content with the aforementioned preferred weight ratio has been shown to be particularly advantageous for the function and desired transport properties of fluorine-free CCM. Sufficient porosity is required for the removal of water and gas, which is typically around 60%. Insufficient gas transport can lead to increased gas pressure, which can result in gas crossover through the membrane. Therefore, gas crossover is related to the ionomer content. Thus, the preferred operating point for the ionomer content in the catalyst paste formulation and the CCM after drying is a compromise between the following: In other words, it is a compromise between small pore volume and mass transport loss that occurs when the ionomer content is relatively high, and a compromise between insufficient proton conductivity and ionic ohmic loss (voltage loss) that occurs when the ionomer content is relatively low.

[0055] The ionomer content depends on the constituent components and their respective applications in the anode or cathode, and can take higher values, up to 30% by weight, compared to the generally preferred somewhat lower ionomer content. Finally, the final microstructure is influenced by the type of coating and drying process.

[0056] Further aspects of the present invention relate to catalyst-coated PEM membranes or membrane devices manufactured or that can be manufactured by the methods described.

[0057] Another further aspect of the present invention relates to an electrolytic cell utilizing a modified form of the CCM described above, for example, having double-sided electrodes or single-sided electrodes.

[0058] A further advantageous aspect of the present invention involves configuring multiple such electrolytic cells that are stacked and electrically connected in series. These form a cell stack or electrolytic stack that is expandable to accommodate large electrolytic outputs.

[0059] Therefore, in a particularly preferred configuration of the present invention, an electrolysis apparatus comprising such a cell stack is proposed.

[0060] Therefore, the benefits of the present invention are evident not only in small or minimal product units such as membranes or CCMs, but also, through scaling effects, in electrolytic cells and, correspondingly, in cell stacks, electrolytic apparatuses, or electrolytic systems having said electrolytic cells, which also relate to further aspects of the present invention. This enables, from an environmental standpoint, future manufacturing approaches for fluorine-free CCMs for water electrolysis and their application on an industrial scale.

[0061] In particular, the present invention relates to a PEM electrolytic apparatus, and more particularly to an entire electrolytic power plant or Power-to-X plant comprising the electrolytic equipment described herein.

[0062] Therefore, the configurations, features, and / or advantages related to the method here also apply to the manufactured product itself, namely the membrane structure, as well as to the electrolytic cell, cell stack, electrolytic equipment, and / or the entire Power-to-X plant, and vice versa.

[0063] When the expressions "and / or" or "or" used herein are used in the enumeration of two or more elements, it means that each element listed can be used individually, or any combination of two or more of the listed elements can be used.

[0064] Embodiments of the present invention will be described in more detail with reference to the drawings. Hereinafter, the following are shown in a schematic and greatly simplified manner. [Brief explanation of the drawing]

[0065] [Figure 1] Figure 1 shows the function of a cell for water electrolysis, particularly PEM electrolysis, and the catalyst coating film used therein. [Figure 2] Figure 2 shows a schematic flowchart that generalizes the steps of the method according to the present invention. [Figure 3] Figure 3 shows a coating method for manufacturing a catalyst coating film by coating a film substrate. [Figure 4] Figure 4 shows a modified form of the coating method for coating the film substrate shown in Figure 3. [Figure 5] Figure 5 shows an alternative coating method for coating a film substrate. [Figure 6] Figure 6 illustrates the electrochemical properties of a fluorine-free catalyst-coated membrane (Catalyst-Coated-Membrane: CCM) manufactured by direct coating of catalyst material onto a membrane substrate, based on polarization curves. [Figure 7] Figure 7 illustrates the long-term stability of two different fluorine-free CCMs at a given current density. [Figure 8] Figure 8 is a simplified diagram showing the intermediate layer ("intervening layer") formed between the film substrate and the catalyst layer during the coating process, for CCM.

[0066] In the examples and figures, elements having the same or equivalent function may be given the same reference numeral. The illustrated elements and their relative size ratios should not be considered to be to scale in principle; rather, individual elements may be exaggerated, thicker, or larger in size for better visualization and / or better understanding.

[0067] Figure 1 shows an electrolytic cell 25, specifically a PEM electrolytic cell for water electrolysis, in the image area on the left. An important functional element of such a polymer electrolyte membrane electrolytic cell 25 is generally formed by a catalyst coating membrane 23, also known as a catalyst-coated electrolyte membrane or simply CCM. Such a membrane 23 or CCM is shown in more detail on the right side of the electrolytic cell 25 in Figure 1.

[0068] The catalyst coating film 25 comprises a film substrate 11 coated on both sides with catalyst material 7. For this purpose, the film substrate 11 is typically coated on two surfaces facing opposite directions, both on the anode and cathode sides, with layers of each catalyst material 7. Each cell reaction of electrolysis takes place in the region of the layer formed by each catalyst material 7. During the specified operation, electrons are delivered to the contact plate or bipolar plate 29 via the respective catalyst material 7 and a carrier structure or channel structure that may be formed by or provided by the gas diffusion layer 27 (see electrolytic cell 25 on the left side of the figure).

[0069] Furthermore, it can be seen that the desalted raw water H2O is usually supplied to the anode side and then to the PEM electrolytic cell 25. The raw water H2O is decomposed into oxygen O2 and hydrogen H2 through the electrolysis process. Here, oxygen O2 is formed as the electrolytic product at the anode and hydrogen H2 at the cathode, and these are recovered separately and discharged from the PEM electrolytic cell 25.

[0070] The catalyst coating film 23 includes a film substrate 11 made of a film material, and is coated with a paste-like, highly viscous catalyst paste 9 as a coating material during the production of the coating film 23. Here, the catalyst paste contains the catalyst material 7. The film substrate 11 is fluorine-free and contains, or is formed from, a sulfonated hydrocarbon polymer, so-called hydrocarbon, as an ionomer for proton conduction. Here, as the non-fluorine polymer for the film substrate, a material from sulfonated polycyclic aromatics is selected. For example, as illustrated in Figure 2, so-called sPEEK or sPPX can be applied to the film substrate 11, or the film substrate 11 may be formed from these. The largest group is poly(arylene ether)-based hydrocarbons, which include sulfonated polyether ether ketones (sPEEK). A further group is sulfonated polyphenylene (sPPX), which has similar properties. Their major advantage is their high stability against chemical degradation.

[0071] Ionomers are polymers that have ionic groups that confer characteristic proton-conducting properties to them. In the case of PEM water electrolysis, the ionic group is a sulfonic acid group (-SO3H). These can be randomly distributed or fixed in position. In PEM water electrolysis, ionomers are used as film materials in the film substrate 11 and in electrodes coated on the film substrate 11, i.e., in layers having the catalyst material 7, mainly due to their proton conductivity and simultaneous electrical insulation properties. Therefore, here, material suitability is intended, in particular for fluorine-free catalyst coating films 23.

[0072] The provision of coating materials will be described in more detail with reference to Figure 2. Figure 2 shows the method steps according to the present invention based on a schematic flowchart, particularly to illustrate the paste formulation for catalyst paste 9. The method according to the present invention is a process for producing a catalyst coating film 23 for an electrochemical cell, in this case an electrolytic cell 25 for water electrolysis.

[0073] This method first includes, in step S1, providing a non-fluorinated ionomer as a starting material in solid form, i.e., the starting material is preferably in the form of a fine powder rather than a solution. As the ionomer, a powdered sulfonated polymer 1 from the group of hydrocarbons is selected, here for example, a sulfonated polyether ether ketone having sPEEK.

[0074] For providing the powdered non-fluorinated polymer 1 in step S1, commercially available packaged dispersions already containing the non-fluorinated polymer to be applied can be used, for example. These can be converted to the desired powder beforehand by, for example, a spray-drying step to obtain or separate the powdered non-fluorinated polymer from the dispersion. Such spray drying or atomization drying is a method from process engineering for drying solutions or, for example, suspensions. Here, the material to be dried is introduced into a high-temperature gas stream or atomized in it, thereby drying it in a short time to a fine powder.

[0075] The drying process can be carried out, for example, with the following parameters or conditions: injection temperature of 120°C, injection pressure of 10 bar, nozzle size of 0.5 mm, jacket or wall temperature of 250°C, gas temperature of 380°C, and / or gas flow rate of approximately 50 l / min. Alternatively, for example, vacuum spray drying can be carried out by a one-component or two-component nozzle (Ein-oder Zweistoffduese (ue with u umlaut)) with the following parameters: for example, a pressure of 100 mbar, a nozzle hole of approximately 0.3 mm, an injection temperature of 130°C, a jacket temperature of 200°C, and for example, a nozzle pressure of 10 bar.

[0076] This method further comprises, in step S2, dispersing, introducing, or treating a non-fluorinated polymer 1 in an anhydrous solvent 3 to form a plastisol 5. The term "plastisol" here generally refers to a dispersion or heterogeneous mixture. [Table 2]

[0077] For example, the anhydrous solvents 3 or solvent combinations listed in the table summary shown earlier can be used in further described specifications, particularly with respect to possible ionomer proportions. These described value ranges for ionomer proportions and paste viscosity are generally preferred ranges for formulation and can be adapted to specific requirements. A two-component mixture of two of the listed solvents 3, for example, N-methyl-2-pyrrolidone and N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, γ-butyrolactone, or diethylene glycol monoethyl ether, has been proven effective. Here, depending on the application example and material composition of the catalyst paste 9 to each film substrate 11, relatively high viscosities of over 500 mPas, for example up to 1000 mPas, are also possible.

[0078] The method according to the present invention further comprises, in step S3, tightly and homogeneously mixing the catalyst material 7 with the plastisol 5. From step S3 of this method, a paste-like, generally viscous, or highly viscous coating material is obtained, thereby forming a catalyst paste 9. Here, the catalyst paste 9, which is a paste mixture, is prepared to have a generally high solid content of catalyst material 7 and sulfonated non-fluorinated polymer 1, with solid content of 35% to 60% by weight, particularly 45% to 55% by weight.

[0079] Furthermore, this method further includes, in step S4, directly coating the catalyst paste 9 onto a film substrate 11 from the same type of material, a corresponding non-fluorinated polymer 1 such as sPEEK. A direct coating method is applied to the coating of the catalyst paste 9 obtained in method step S3 onto the film substrate 11. Thus, the present invention particularly advantageously enables the cost-effective and scalable production of large fluorine-free catalyst coating films 23. Such catalyst coating films (CCMs) are particularly environmentally friendly and applicable to PEM water electrolysis. Due to the intended paste formulation and the resulting suitable viscosity properties (rheology), the fluorine-free catalyst paste 9 described herein further enables and facilitates the use of industrially standardized R2R (roll-to-roll) coating methods for direct film coating, and optionally further coating methods, as illustrated below in Figures 3 and 4. Following the coating of the catalyst paste 9 onto the film substrate 11, a drying step S4 is performed. This drying step involves drying, curing, and optionally multi-stage heat post-treatment of the catalyst coating film 25. In this way, a good surface structure for the catalytically active porous layer and uniform bonding with long-term stability to the film substrate 11 can be obtained.

[0080] Depending on the application method, the appropriate viscosity range can be advantageously adjusted by the solvent combination. Furthermore, the obtainable paste viscosity is still largely determined by the anhydrous solvent 3 or solid content ratio and the solid content ratio in the catalyst paste. The solid content ratio represents the ratio of the ionomer content to the catalytic material content in the catalyst paste 9.

[0081] A 10-20% by weight, particularly 9% by weight, plastisol from a combination of Pemion® as a non-fluorinated ionomer and 2-pyrrolidone (500 mPas) has proven particularly advantageous for coatings with a wet film thickness of approximately 30-70 μm, especially 50 μm, and when using a reverse roll or coating roller method. Similar good results can be obtained with the non-fluorinated ionomer TS00X and 5-12% by weight, particularly 7% by weight, of N-methyl-2-pyrrolidone (NMP) in a solvent ratio.

[0082] In particular, the objective is to efficiently encapsulate catalyst particles with a non-fluorinated ionomer and to provide a catalyst paste 9 that enables a highly stable paste for industrial-scale applications, exhibiting little to no separation or sedimentation. This has been proven successful under the conditions described herein.

[0083] A further important aspect is the film formation in the drying step S5 of the catalyst paste 9, for example, by using an oven 15 applied in the corresponding roll-to-roll process, as shown in Figures 3 to 5. Here, it is even more important that the layer is dried as quickly as possible and that good adhesion properties for coating the (film) onto the substrate are adjusted so as to facilitate the formation of the intermediate layer 33. This will be further explained below with reference to Figure 8.

[0084] In the proposed method, the characteristic intermediate layer 33 (see Figure 8), in particular as an important functional layer ("intervening layer"), is not achieved by reaching the glass transition temperature of the film substrate under pressure, but rather by selectively and thoroughly dissolving the film substrate 11 in the boundary region to the coated layer having the catalyst material 7. In other words, a non-fluorinated ionomer 1 from the class of hydrocarbons is selected so that it appropriately contains the same material as the film substrate 11 itself. This adaptation by coating the catalyst paste 9 advantageously provides simultaneous functionality as a binder or adhesive for the catalyst material 7. Here, the advantageous effect of selecting an anhydrous solvent 3 for the catalyst paste 9 is demonstrated, thereby promoting this dissolution process in the boundary layer and the formation of the intermediate layer.

[0085] One possible example for preparing Plastisol 5 as described in stock solution includes, for example, providing 5 g of a non-fluorinated polymer, e.g., Pemion®, in powder form, which is introduced by stirring into 30 g of a 2-pyrrolidone solution. Complete dissolution occurs after several hours.

[0086] For the preparation of catalyst paste 9 for the cathode electrode for catalysis of the HER reaction, for example, 10 g of Pt black can be provided and mixed with 10-20 percent of fluorine-free hydrocarbon plastisol stock solution of 10 g, and then tightly mixed in a paste mixer with ZrO2 grinding balls. Here, no sedimentation or aggregation of particles is observed, and thus the HER catalyst is formed on the cathode side.

[0087] When 10 g of Ir Black is used together with 10 g of an equivalent fluorine-free hydrocarbon plastisol stock solution to produce a catalyst paste 9 for the anode electrode, correspondingly good results can be achieved.

[0088] As alternatives to the HER catalysts mentioned above, palladium, ruthenium, or carbon-supported variants and mixtures thereof can also be used as catalytic materials in the catalyst paste 9 for the cathode. As alternative configurations for the OER catalysts, IrOOH, IrO2, IrRuO2, or TiO2-supported, NbO2-supported, or SnO2-supported variants of the aforementioned catalysts can be optionally used as catalytic materials in the corresponding catalyst paste 9 for the anode.

[0089] Finally, coating of a film substrate 11 having the same type or the same fluorine-free hydrocarbon with a catalyst paste 9 containing catalyst material 7 is carried out by direct coating according to method step S4. In the case of direct coating, it is applied without any transfer, copying, or pressing steps. This advantageously applicable coating method is also called direct film deposition (DMD).

[0090] To this end, for example, a simple doctor blade application can be performed, in which the catalyst paste 9 is distributed and / or applied using a doctor blade onto a film substrate 11 which is held and / or moved by a vacuum plate, which is not explicitly shown in the figure. This configuration is particularly reasonable for relatively small test lots or laboratory samples. With or without a short drying time, the catalyst coating film 23 (CCM) with catalyst paste 9 on one side can be dried, for example, in an oven 15 (see further below) at 50-100°C. Subsequently, the other side of this half-film, with the coating thus completed, can be similarly coated, for example, at a temperature preferably well above 100°C until final drying or temperature adjustment is performed.

[0091] Figure 3 illustrates a preferred coating method for coating a film substrate 9 for producing a catalyst coating film 23. Here, Figure 3 shows a schematic side or cross-sectional view of a coating apparatus 17 having corresponding rollers 21 for fixing and conveying the film substrate 11 using a general roll-to-roll principle. Specifically, the application of the catalyst paste 9 is preferably carried out by so-called wide-slot nozzles 19 arranged and positioned on both sides of the coating apparatus 17. The wide-slot nozzle 19 shown on the right is constructed to coat the first active side of the film substrate 11 with a catalyst material 5 having, for example, platinum Pt contained in the catalyst paste 9, as previously described. Subsequently, although not explicitly shown in Figure 3, the layered coating can be dried or pre-dried in a multi-zone oven 15. Thereafter, the ribbon-shaped film substrate 1, already coated on one side, is further conveyed by the rollers 21. Here, the second side opposite the first side of the film substrate 11 can be coated with a catalyst paste 9 containing iridium Ir as the catalyst material 5, until the film substrate 11, thus coated on both sides, passes through the oven 15 again, in particular, until the solvent 3 or any residue or binder present in the catalyst paste 9 is removed. Thus, the drying step S5 is already at least partially, i.e., as a sub-step, integrated into the coating equipment 17 by the oven 15. However, a post-heat treatment step may still follow.

[0092] For the formation of a porous surface structure with good catalytic properties and particularly long lifespan for the fluorine-free catalyst coating film 23, and for bonding to the film substrate 11, it has been found that not only the selection of a fluorine-free hydrocarbon as the ionomer, but also the selection of a solvent in the manufacturing process of the catalyst paste 9 that is compatible with this is particularly advantageous. Surprisingly, in contrast to previous practices, the anhydrous solvent 3 has been found to be very reasonable for bonding with interfacial dissolution, intervening layer formation, and long-term stability in paste formulation into colloidal dispersions, for example, by applying the solvent N-methyl-2-pyrrolidone or 2-pyrrolidone (γ-butyrolactam).

[0093] Metering and dispensing of the medium in the wide-slot nozzle coating of catalyst paste 9 can be performed, for example, by a so-called eccentric screw pump. The coating equipment 17 has a brake, a belt tension (e.g., 50 Nm), and a rewind reel having a double-slot nozzle coater with a passage width of approximately 10 cm, and is designed for substrate thicknesses up to approximately 90 μm. During coating, the belt speed is adjusted to 0.8 to 1.2 m / min, and the coating thickness (wet film) is adjusted to less than 50 μm. A viscosity range of, for example, 200 to 1000 mPas for catalyst paste 9 is reasonable, and the "wet filling" of the film substrate 11 is carried out at approximately 30 mg / cm2 and under drying in a circulating air dryer (drying temperature is, for example, 80 to 100°C). Herein, a high solids content in weight percent (wt%) of the processable fluorine-free catalyst paste 9 is generally provided, of 35 to 65 wt%, and especially 45 to 55 wt%. Coating with the slot nozzle 19 offers the advantage of being able to control the desired wet film thickness of the coating by the measured mass flow rate and predetermined substrate speed.

[0094] The configuration of the coating apparatus 17, based on roll-to-roll conveying technology as shown in Figures 3 and 4, advantageously allows for the simultaneous metering, dispensing, and coating of two different correspondingly specific catalyst materials 7 in a catalyst paste 9 onto a ribbon-shaped fluorine-free hydrocarbon-based film substrate 11 on both sides.

[0095] Figure 4 illustrates an alternative configuration for double-sided direct coating of the film substrate 11. Here, the coating apparatus 17 is equipped with a coating roller or a metering roller 13, which allows for very easy and automated coating. Otherwise, this process can be carried out substantially the same as described in Figure 3. This coating method, also called reverse roll coating, is particularly suitable for producing a uniformly coated catalyst coating film 23, i.e., a CCM of extremely high quality. Here again, for the drying process S5, a double-chamber oven 15 with a spatial dimension well over 1 m, and a corresponding circulating air dryer or flotation dryer can be used to perform coating on the fluorine-free film substrate 11 as uniformly and over a large area as possible. The drying process S5 may include further sub-processes such as multi-stage heat post-treatment, known as "curing," but these will not be described in detail here.

[0096] An alternative coating method for the film substrate 11, shown in Figures 3 and 4, is illustrated in Figure 5. Here, the application of the catalyst paste 9 by step S4 in the coating apparatus 17 depicted in Figure 5 is intended for only one side of the film substrate 11. The opposite side of this one side can be coated by a transfer printing method as needed. In particular, the catalyst paste 9 is first applied directly to a polyimide foil (not explicitly described here) and then laminated via a transfer printing route. More precisely, the catalyst layer from the catalyst paste 9 can be applied to an FEP-coated hydrophobic Kapton foil (of the Dupont 300 FN 929 type), in particular, by a coating roller. The coating is then preferably carried out in segmented areas. Furthermore, the resulting so-called "decal foil" can be laminated on the back of the directly coated film by a hot press method. Hydrophobization of the Kapton foil provides improved separation characteristics of the "decal," thereby allowing for the transfer of a strongly adhesive plastisol layer as well.

[0097] Figure 6 further illustrates the results of electrochemical characterization of the directly coated fluorine-free catalyst coating film (23) according to the present invention. Here, electrochemical characterization was performed on fluorine-free CCMs in an experimental series of TS00X and Pemion® to verify system efficiency (polarization curve and impedance spectroscopy), long-term stability, and system safety (gas chromatography). UI characteristic curves were measured to electrochemically characterize the fluorine-free CCMs. The provided MEA samples included various electrode combinations to isolate the influencing factors at the anode and cathode for the characteristics. Specifically, exemplary, Figure 6 shows the UI characteristic curve, which is the corresponding polarization curve, with the cell voltage U plotted against the respective current density I, thereby providing proof of functionality. Here, exemplary, two characteristic curves T1(A) and T1(B) in Figure 6 show the results for a series of tests using TS00X ionomer as a fluorine-free hydrocarbon. The results of a series of tests using Pemion® ionomer are shown in characteristic curve T2(A) for comparison.

[0098] To conclude on the long-term stability of the samples, corresponding long-term experiments were conducted at a constant current density of 2 A / cm². The known degradation effect in long-term experiments is a voltage rise at a constant current density, which can be due to various degradation causes such as catalyst passivation, component contact losses, and ionomer degradation. Exemplarily, Figure 7 shows an investigation of the long-term stability of fluorine-free catalyst coating films 23, where T1 shows the long-term behavior of a CCM using TS00X ionomer and T2 shows the long-term behavior of a CCM using Pemion® ionomer. In this case, the time course of the cell voltage U against time t is plotted against time t for each. Over a long investigation period of at least 72 hours, approximately and nearly constant voltage levels were demonstrated for both fluorine-free CCMs. The economic potential for future use of the fluorine-free catalyst coating films 23 produced by the method of the present invention is demonstrated.

[0099] Figure 8 shows CCM23 in a simplified diagram. A selective dissolution process is initiated by the selected paste composition and application method, and this dissolution process, through solvent selection and ionomer material compatibility, results in the formation of an intermediate layer 33 as a crucial functional layer in the manufacturing process. This intermediate layer 33 provides good adhesion and long-term stability of the catalyst layer 31, which has a catalyst material 7 and a non-fluorinated polymer 1, on the film substrate 11. The catalyst layer 31 has a non-fluorinated polymer 1, for example, sulfonated polyetherketone sPEEK. Similarly, the film substrate 11 has a similar or identical non-fluorinated polymer 1, preferably also sulfonated polyetherketone sPEEK. The intermediate layer 33 has a layer thickness D of approximately 3-10 μm, so that a strong, long-term stable material bond connection between the catalyst layer 31 and the film substrate 11 is formed by the dissolution of a similar ionomer.

[0100] An electrode is provided on the film substrate 11 by a catalyst layer 31, and in the partially enlarged view of Figure 8, an anode electrode having platinum Pt as the catalyst material 7 is provided. Similarly, on the opposite side of the film substrate 11, a cathode electrode having iridium as the catalyst material 7 is formed. Here, the microstructure of the electrode is a three-dimensional network of ionomer, i.e., fluorine-free hydrocarbon, catalyst material 7, and pores. Due to the porous structure, the electrode is diffused for the transport of reactants and electrolysis products. The intersection of the three components is called the triple-phase boundary (TPB). Here, an electrochemical reaction is occurring, observed locally and microscopically, because not only the availability of the catalyst material 7 but also the supply of reactants, i.e., water H2O, is equally crucial to the reaction. Therefore, a gas diffusion electrode or gas diffusion layer is formed on the CCM23. In the case of platinum (Pt) as the catalyst material 7, the platinum catalyst may exist supported on carbon. Carbon forms aggregates, and these aggregates are partially surrounded by ionomers. Furthermore, they can be distinguished into primary and secondary pores. Primary pores are located inside the aggregates, while secondary pores are located between the aggregates. Moreover, they differ in that the ionomers are mainly present in the secondary pores, and therefore an increase in ionic resistance occurs in the primary pores.

[0101] This invention makes it possible to manufacture fluorine-free catalyst coatings for PEM water electrolysis on an industrial scale, thereby addressing the impending PFSA ban across Europe. Furthermore, the selective use of fluorine-free ionomers and the manufacturing process proposed herein enables fluorine-free membrane electrode assemblies (MEAs) for PEM water electrolysis and electrolysis equipment. Here, good system efficiency and long-term stability of the fluorine-free MEA are achieved through favorable paste formulations and material selections.

[0102] Fluorine-free MEA offers a number of advantages compared to fluorine-containing ionomers. First, there are technical advantages, such as higher operating temperatures due to the relatively high heat resistance of hydrocarbons for PEM water electrolysis. Furthermore, alternative technologies are proposed in case the EU ban on PFAS materials is announced, as is generally expected. Thus, the method of the present invention and the CCM produced by this method ensure that no environmentally harmful fluorine compounds that could enter the environment along the process chain are treated. Finally, downstream recycling processes are considerably simplified because there is no concern about the generation of hydrogen fluoride during thermal aftertreatment in the MEA combustion process. This eliminates the need for the very cumbersome gas washing of combustion products that was previously required. A reduction in corrosion problems that lead to unfavorable degradation caused by fluoride ions during the operation of electrolysis equipment is also expected.

[0103] Furthermore, the formulation of catalyst paste 9 allows for particularly precise adjustment of the ionomer / catalyst ratio to suit each anhydrous solvent. Additionally, known or standardized fabrication dimensions can be easily expanded to a high degree, similarly significantly increasing, for example, the production capacity of high-purity hydrogen. [Explanation of symbols]

[0104] 1...Sulfonated non-fluorinated polymer, 3...Anhydrous solvent, 5...Plastisol, 7...Catalyst material, 9...Catalyst paste, 11...Membrane substrate, 13...Coating roller, 15...Oven, 17...Coating equipment, 19...Wide slot nozzle, 21...Roller, 23...Catalyst coating film, 25...Electrochemical cell, 27...Gas diffusion layer, 29...Contact plate or bipolar plate, 31...Catalyst layer, 33...Intermediate layer, D...Layer thickness, S1...Process, S2...Process, S3...Process, S4...Process, S5...Drying process

Claims

1. A method for producing a catalyst coating film (25) for an electrochemical cell (25), comprising the following steps: -S1: A step of providing a powdered sulfonated nonfluorine polymer (1), -S2: A step of dispersing the sulfonated nonfluorine polymer (1) in an anhydrous solvent (3) to form a plastisol (5), - S3: A step of mixing the catalyst material (7) with the plastisol (5) to make a catalyst paste (9), -S4: A step of applying the catalyst paste (9) to the film substrate (11), Methods that include...

2. The method according to claim 1, wherein the anhydrous solvent (3) is selected from dimethyl sulfoxide, N,N-dimethylformamide, N,N-diethylformamide, 2-pyrrolidone, or γ-butyrolactam, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone.

3. The method according to claim 1, wherein the anhydrous solvent (3) is a mixture of N-methyl-2-pyrrolidone and a component 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), particularly solid or powdered iridium black.

5. The method according to any one of claims 1 to 4, wherein the catalyst material (7) includes platinum (Pt), particularly solid or powdered platinum black.

6. The method according to any one of claims 1 to 5, wherein the material of the film substrate (11) is composed of a fluorine-free sulfonated polymer (1), and the sulfonated non-fluorinated polymer (1) of the catalyst paste (9) is adapted thereto.

7. The method according to any one of claims 1 to 6, wherein a sulfonated nonfluorinated polymer (1) is provided by a fluorine-free hydrocarbon compound, in particular an aromatic hydrocarbon compound having a cationic conductive group.

8. The method according to claim 7, which provides a polycyclic aromatic ionomer having a sulfonated side chain as a cation-conducting group as a sulfonated nonfluorinated polymer (1).

9. The method according to claim 8, wherein the polycyclic aromatic ionomer is selected from the group consisting of sulfonated polyether ketone (sPEEK), sulfonated polyphenylene (sPPX), and sulfonated polyimide (sPI).

10. The method according to any one of claims 1 to 9, wherein the catalyst paste (9) is tightly mixed to form a paste mixture, and in the paste mixture, a high solid content of 35% to 60% by weight, particularly 45% to 55% by weight, of the catalyst material (7) and the sulfonated nonfluorinated polymer (1) is set.

11. The method according to any one of claims 1 to 10, wherein the direct application (S4) of the catalyst paste (7) to the film substrate (11) is performed by doctor blade application, and optionally, the application is performed using a vacuum plate configured to hold the film 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 film substrate (11) in the method step (S4) is performed by a roll-to-roll application method, and in particular by using the heat treatment oven (15) during application to remove the solvent (3).

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

14. The method according to claim 12, wherein the application of the catalyst paste (7) to the film substrate (1) is performed by a coating roller (13).

15. The method according to any one of claims 1 to 10, wherein the application of the catalyst paste (11) to the film substrate (11) is performed on both sides, and in particular, different catalyst materials (7) are applied to opposite sides of the film substrate (11).

16. The method according to any one of claims 1 to 15, wherein after the application of the catalyst paste (7) to the film substrate (11) (S4), a drying step (S5) is performed in which the catalyst material (7) on the coated film substrate (11) is dried, cured, and subjected to thermal post-treatment.

17. The method according to claim 16, wherein in the layer having the catalyst material (7) applied to the film substrate (11), the ionomer content on the anode side and / or cathode side is set to 6% to 15% by weight, particularly 9% to 12.5% ​​by weight.

18. A PEM membrane structure comprising a catalyst coating film (23) manufactured by the method described in any one of claims 1 to 17.

19. An electrolytic cell (25) comprising the PEM membrane structure described in claim 18.

20. A cell stack comprising a plurality of electrolytic cells (25) as described in claim 19.

21. An electrolytic apparatus having the cell stack described in claim 19.

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