Method for producing an electrode on a substrate material for an electrochemical cell, and coating device for carrying out the method

Abstract

The invention relates to a method for producing an electrode (8) on a substrate material (7) for an electrochemical cell (30). First, a strip-shaped substrate material (7) and an application paste (6) containing an electrode material (9) are provided. Subsequently, application paste (6) is applied onto the strip-shaped substrate material (7) in a roll-to-roll application method, in which the substrate material (7) is conveyed. Application paste (6) is applied onto the same strip of substrate material (7) in at least two tracks (11A, 11B) simultaneously, said tracks being guided parallel to each other and a coating distance (D) being set between two adjacent tracks (11A, 11B) such that an intermediate track (12) in which the substrate material (7) is uncoated is produced on the substrate material (7). The invention further relates to a roll-to-roll coating device (10) for carrying out the method and to correspondingly produced electrochemical cells (30).

Description

[0001] Description

[0002] Method for manufacturing an electrode on a substrate material for an electrochemical cell and coating device for carrying out the method

[0003] The present invention relates to a method for producing an electrode on a support material for an electrochemical cell, in particular for a PEM electrolysis cell with a polymer membrane as the support material. The invention further relates to a coating device configured for carrying out the method.

[0004] In various electrochemical conversion or storage technologies, such as fuel cells, electrolysis cells, batteries, or flow cells, electrodes and solid electrolytes are produced in coating systems. The electrodes can be applied directly to a solid electrolyte, a support substrate, or a functional substrate, e.g., a porous transport layer. Due to increasing demand, efficient and long-term stable cell components and manufacturing technologies for industrial-scale application need to be developed.

[0005] One example of a particularly interesting electrochemical conversion process is the so-called PEM electrolysis (PEM stands for "polymer electrolyte membrane" or "proton exchange").

[0006] Membrane). Due to its great potential for producing cost-effective green hydrogen, it is gaining increasing importance for industrial applications, as well as for use as a storage medium or component in energy storage systems. In the context of climate change, hydrogen and / or the possibility of producing H2 from renewable energy via PEM or water electrolysis has long since proven to be a key factor for the energy industry and related sectors. Even though most hydrogen is still produced today through steam reforming of methane, aggressive investments, regulations, and subsidies will certainly lead to a foreseeable trend toward renewable hydrogen production.

[0007] A particularly promising method for producing hydrogen (H2) is the electrolysis of water (H2O), especially when using renewable electricity. Hydrogen can serve as an energy storage medium, for example, by being used as a fuel to stabilize the electricity supply, particularly from renewable sources such as wind power, photovoltaics, and the like. Hydrogen can also be used in other processes that require a fuel or a reducing agent. The hydrogen produced by electrolysis can thus be used industrially, or electrical energy can be generated again electrochemically using fuel cells.

[0008] 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 method is the described PEM electrolysis, which—compared to alkaline electrolysis approaches—proves to be more load-dynamic and better suited for coupling fluctuating power sources due to its less complex peripherals. In particular, high current densities and power outputs can be achieved with PEM electrolysis even under higher load gradients, while the high quality or purity of the hydrogen product is advantageously maintained even under partial or overload operation.

[0009] Hydrogen is already used in countless industrial and technological applications. Its potential to produce large quantities of H2 in a climate-neutral way and / or to store or transport it "carbon-free" via hydrogen carriers such as ammonia opens up entirely new avenues for various industrial sectors, such as transportation, chemicals, and steel, to supply entire sectors with green energy or operate them in a climate-friendly manner. Furthermore, hydrogen is already highly interesting as a fuel or fuel additive, and will continue to be so in the future, due to its potential to produce no or fewer emissions.

[0010] In a PEM electrolysis cell, a membrane is provided which has a catalyst layer on each of its opposite surfaces (CCM, English: Catalyst-Coated Membrane or 3-Layer Membrane Electrode Assembly (MEA), English: Membrane Electrode Assembly). Adjacent to the catalyst layers are usually gas diffusion layers, which in turn are connected to electrically conductive contact plates, called bipolar plates, which serve, among other things, for electrical contacting. Preferably, these gas diffusion layers are also designed to enable the necessary substance transport during the intended operation of the electrolysis cell. The gas diffusion layer provides the necessary electrical conductivity to couple the contact plates and the catalyst layers electrically.This allows the desired electrochemical reaction to be achieved in the area of ​​the catalyst layers.

[0011] Hydrogen is produced electrolytically from water as a reactant. This is an electrochemical process in which water is separated into its chemical components, oxygen and hydrogen. The electrochemical cell reactions can be described and differentiated as follows:

[0012] In polymer electrolyte membrane electrolysis, the two partial reactions are spatially separated by an ion-conducting membrane, which must expediently be equipped with electrodes, in particular a cathodic catalyst and an anodic catalyst (CCM). Besides material improvements, significant cost reductions and substantial quality improvements can be achieved through improvements in manufacturing processes.

[0013] Since the production of PEM hydrogen electrolyzers (PEMWE) will increase significantly in terms of throughput and scale, and indeed must increase sharply to achieve agreed climate targets, there is an urgent need for technologies that make it possible to improve the throughput and manufacturing capacity of so-called corresponding CCMs.

[0014] A CCM comprises a membrane with a catalyst material on each of its two opposing surfaces. In many applications, particularly in PEM water electrolysis, very expensive and therefore very rare precious metals are used as catalyst materials.

[0015] Today's common methods utilize a catalyst paste to create the catalyst layers or electrodes for the anode and cathode. The catalyst paste typically consists of the catalyst powder itself, an ionomer, optionally a polymeric binder, and a solvent. After application, the solvent is usually thermally removed. If the catalyst layer is deposited on a thermally stable support film, it must be transferred to the membrane in a further process step under pressure and temperature ("decaling 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 decaling process, the catalyst paste can also be applied directly to the membrane ("direct coating").(Direct membrane coating), which is of particular interest for industrial production in coating systems for direct coating. A number of technical coating methods based on water / alcohol ionomer dispersions are known from the literature. These methods are hardly suitable for direct coating because the dispersion medium, water or alcohols, leads to strong swelling behavior of the membrane substrate, thus impairing the dimensional stability of the membrane or the CCM. Catalyst inks based on water / alcohol ionomer dispersions have a very low viscosity and tend to separate after only a few minutes. The viscosity is often increased by the addition of thickeners such as methyl ethylcellulose; however, such auxiliary substances must also be thermally decomposed or burned off at temperatures above 300 °C. This would again decompose the membrane.Catalysts are structurally damaged. To avoid this, the decal process described above is frequently used in the prior art. The high number of process steps results in long throughput times and higher process costs compared to the often preferred direct membrane deposition.

[0016] Alternative manufacturing processes, which are part of the present invention, are available for further development.

[0017] The parametric requirements for a MEA for PEM water electrolysis are typically complex and difficult to represent and control using conventional methods involving multiple steps. A current density in the cell should be between or up to 4 A / cm². 2The temperature range must be between 60°C and 80°C. Furthermore, low swelling behavior and high mechanical and chemical stability are required. High electrical and ionic conductivity of the catalyst layer, low contact resistance, and a cost-effective material base are also necessary. All these requirements must be met in the future for significantly larger, industrial-scale production.

[0018] The invention is therefore based on the objective of providing a significantly improved manufacturing approach for producing an electrode on a substrate material, which forms a particularly important functional component of an electrochemical cell. Furthermore, it is an objective of the invention to provide a corresponding coating device designed for carrying out the process.

[0019] The problem directed towards a manufacturing process is solved according to the invention by a process for producing an electrode on a support material for an electrochemical cell, which manufacturing process comprises the following steps:

[0020] - Providing a ribbon-shaped support material,

[0021] - Providing an application paste containing an electrode material,

[0022] - Application of coating paste to the ribbon-shaped carrier material in a roll-to-roll application process, whereby the carrier material is conveyed;

[0023] - Simultaneous application of coating paste in at least two parallel paths onto the same strip of carrier material, whereby a coating distance is set between two adjacent paths, so that an intermediate path with uncoated carrier material is produced on the carrier material.

[0024] The invention is based on the understanding that existing manufacturing processes for electrode layers on a substrate, as well as coating systems that implement roll-to-roll deposition processes, are limited in terms of production flexibility and scalability. Currently, electrodes and solid electrolytes for various electrochemical conversion or storage technologies, such as fuel cells, electrolysis, batteries, and flow cells, are manufactured in coating systems. Production often takes place in a roll-to-roll process. In this process, the electrodes are applied either directly to a solid electrolyte, a substrate material, or a functional substrate, such as a porous transport layer. A significant disadvantage of this method is that only one lane of electrodes can be produced per coating system or line.

[0025] Currently, expanding production capacity, for example for electrodes, can be achieved by increasing the utilization of the existing system and / or the system speed. However, both options are limited. It is foreseeable that significantly more production capacity will be needed. Known solutions involve procuring and commissioning additional coating systems of the same design, i.e., simply duplicating them. This, however, entails a correspondingly high multiple investment requirement for equipment costs, installation space, and increased operating costs, such as electricity costs for running multiple coating systems. Furthermore, an increased need for personnel for operation and maintenance is anticipated.

[0026] The invention departs from the previously established standard single-lane solutions by designing the manufacturing process for the first time as a multi-lane roll-to-roll (R2R) process on a single carrier strip. This multi-lane manufacturing process can advantageously be integrated and carried out in a single coating unit. Thus, the electrode deposition on the strip-shaped carrier material is performed in several parallel lanes on one and the same strip, so that a suitably designed coating unit can produce two or more lanes simultaneously and in parallel, instead of just one lane, by applying the deposition paste in at least two parallel lanes onto the same strip of carrier material. This can be achieved, in particular, via one or more application rollers with multiple metering units for the deposition paste and the electrode material.With multiple rollers, these can be arranged offset from each other in the conveying direction. The coating rollers can also be arranged and operated in the opposite direction (reverse-roll (coating)). By specifying a coating distance between the adjacent lanes of a first lane and a second lane, it is possible to double the throughput of electrode layers on the carrier film or substrate tape without providing and operating a second coating unit. A significantly smaller footprint is required.

[0027] A significant advantage is the concept of incorporating an uncoated intermediate layer on the substrate during manufacturing. This allows the parallel layers to be precisely defined and spaced apart, meaning each layer can be coated with adhesive paste. Mixing is prevented because the intermediate layer separates the electrode layers on adjacent layers. This enables targeted post-treatment or specific cutting of the electrodes. The intermediate layer and substrate can simultaneously function as an inert frame for the active central section containing the electrode layer and serve as a fastening element during installation in an electrochemical cell.

[0028] It is possible, for example, for the electrode to be applied as an electrode layer with a catalyst material on a polymer membrane as a support material, with the polymer membrane being provided as a ribbon-shaped support material. Thus, a catalyst-coated polymer membrane (CCM) can be produced, such as that which can be provided as a CCM (catalyst-coated membrane) in corresponding PEM electrolysis cells and / or cell stacks. The invention specifically describes the manufacturing process and corresponding means that solve the problems described above and demonstrate simple, novel ways of producing corresponding electrodes for various applications on a support material in large volumes and throughputs. The merits of the present invention thus significantly improve the entire manufacturing process and productivity, and therefore the scaling up of, for example,This enables electrolyzers and electrolysis or power-to-X power plants to achieve ever higher hydrogen yields. In particular, existing coating facilities can be upgraded, expanded, and retrofitted for multi-lane operation according to the proposed manufacturing process, without requiring and installing a second plant.

[0029] It has proven advantageous that, in a particularly preferred embodiment of the process, a coating distance of 10%-20% of the coating width of a web is set.

[0030] Moreover, it has been shown that the process is also very advantageously applicable, in principle, to direct-membrane coating processes. Furthermore, the process is advantageously applicable to the application of a catalyst layer to a gas diffusion layer as a support material, whereby the multi-layer application method is used on the support material. Thus, the production of gas diffusion electrodes (GDEs) and the application of a corresponding layer to a porous, planar support material is also possible with this process.

[0031] The intermediate layer creates a free area or strip on the substrate material, free of the coating paste, across the coating spacing. This allows conveying of the strip-shaped substrate material without affecting the electrode layer by means of conveying devices engaging the free area of ​​the intermediate layer. Furthermore, in a subsequent manufacturing step, cutting is possible without affecting the electrode layer of the membrane electrode assembly (MEA), with the intermediate layer simultaneously providing an electrode-free mounting area. The coating width of adjacent layers on the substrate material can preferably be set identically.However, it is also possible that - depending on the application - the cell structure and the active area with the electrode layer require different dimensions and thus coating widths, so that a flexible adaptation and individual adjustment of the coating width of a track can be provided.

[0032] In a preferred embodiment of the method, the coating paste is applied intermittently to a web, so that separate rectangular areas with coating paste are formed within a web on the carrier material, which are surrounded by a circumferential strip of uncoated carrier material, so that a coating gap is formed.

[0033] Intermittent processes (from Latin *intermittere* = to interrupt / suspend) are characterized by interruptions or alternating states. The opposite is continuous, meaning uninterrupted or without interruption. The invention allows for both operating modes of the process, as well as combinations thereof. Intermittent deposition offers the advantage of forming distinct, surface-defined cell elements with a substantially rectangular active electrode layer on the ribbon-like carrier material. These active surface areas with the electrode are surrounded by uncoated carrier material, facilitating transport, cutting, further processing, and treatment of the carrier material locally coated with the deposition paste.

[0034] Preferably, an electrode unit produced in this way, consisting of a carrier material and optionally electrodes coated on both sides, is cut out from the ribbon-shaped carrier material using a cutting tool along the uncoated intermediate layer or the enclosing edge of an electrode unit. This allows for the production of a large number of electrode units.

[0035] In a particularly preferred embodiment of the method, coating paste is applied to the adjacent webs by means of a respective coating and metering roller, wherein the coating and metering rollers are arranged spaced apart from each other on a shaft.

[0036] It is possible to use a single-shaft arrangement or a two- or multi-shaft arrangement. In a single-shaft arrangement, a first application and metering roller and a second application and metering roller are arranged and aligned side-by-side on the same shaft, perpendicular to the belt and conveying direction. In a two-shaft arrangement, a first application and metering roller and a second application and metering roller are mounted on separate shafts, offset from one another when viewed in the belt or conveying direction of the carrier material. The first and second application and metering rollers each ensure a uniform application of the coating paste to their respective webs, spaced apart from each other by the intermediate web, on the endless carrier belt.

[0037] Preferably, in this process the coating and metering rollers are arranged on a common shaft.

[0038] Therefore, a single-shaft system can be advantageous and cost-effective for many applications, as it eliminates the need for components such as additional shafts and drive units for the metering and application device compared to two- or multi-shaft systems. However, this depends on the available installation space in the coating system, its adaptability, and the specific coating task on the respective substrate material.

[0039] The method is advantageously applicable for applying an electrode to various substrate materials using a viscous coating paste. Depending on the requirements, a suitably selected electrode material is incorporated into the coating paste. Applications of the invention are therefore, in principle, possible in fuel cells, electrolysis cells, batteries, flow cells, etc., where electrodes and solid electrolytes are produced in coating systems.

[0040] Particular attention is paid to the manufacturing process for the paste formulation of the application paste, i.e., to the recipe and preparation of a viscous mass or paste containing the electrode material, which is prepared for application and adhesion to a respective carrier material, the carrier film or the substrate, and is suitable for processing in the application process of the invention.

[0041] A particular aspect and especially preferred embodiment of the method of the present invention relates to a method for producing a catalyst-coated polymer membrane for an electrochemical cell, in particular an electrolysis cell. In this process, a catalyst material is incorporated into the coating paste used to produce the electrode. In contrast to the polymer membrane as such, a catalyst-coated membrane (CCM) comprises at least one porous electrode to ensure media transport in the three-phase system of the electrode, as is required for a PEM electrolysis cell.

[0042] In this preferred embodiment of the manufacturing process, a polymer membrane is provided as the carrier material, and the application paste containing the electrode material is provided by subsequent process steps that precede the application of the application paste:

[0043] The process first comprises providing a solid or powdered, preferably undissolved or in solution, sulfonated polymer (PFSA). The material in question can also be a sulfonated fluoropolymer, a perfluorinated copolymer with a sulfone group, or a hydrocarbon polymer. Alternatively, a fluorine-free polymer, such as a hydrocarbon, can be used.

[0044] The process further includes dispersing this starting material or polymer in a, in particular high-boiling, polar solvent, such as 2-pyrrolidone (butyrolactam), to form a plastisol.

[0045] The process further includes mixing or blending a catalyst material, in particular a metallic one, for example in solid form or in powder form, with the plastisol to form an application paste for the subsequent production of the electrode layer.

[0046] The application paste prepared in this way is then applied, preferably directly, to a suitable polymer membrane as a substrate. A direct membrane coating is performed.

[0047] In a preferred embodiment of the process, the application paste is thus carried out on the substrate, whereby an electrode containing catalyst material is formed on the polymer membrane.

[0048] In this embodiment, which is particularly advantageous for industrial production, the application of the coating paste to the polymer membrane as a substrate is not carried out by a transfer printing or a comparable (indirect) process, but via a direct coating.

[0049] The significantly greater potential lies in the direct membrane coating process, but the application is not limited to this in principle.

[0050] The present invention thus advantageously enables a particularly cost-effective and easily scalable production of large-area catalyst-coated polymer membranes, for example for PEM water electrolysis, wherein a multi-lane coating is carried out in at least two parallel lanes on the same polymer ribbon as substrate.

[0051] In particular, the application of the catalysts, whether as a so-called HER (English for: "hydrogen evolution reaction") for the hydrogen evolution reaction described above at the cathode, or as an OER (English for: "oxygen evolution reaction") for an anode-side oxygen evolution reaction, can be advantageously significantly improved by the advantages of the present invention.

[0052] Furthermore, the invention enables the mass production of CCMs using roll-to-roll application technology, thus advantageously allowing for faster throughput times of corresponding electrolyzer components. The presented method according to the invention also advantageously makes it possible to improve both the ionic and mechanical bonding of the catalyst material to the polymer membrane.

[0053] Furthermore, the advantageously high material compatibility and very good paste stability of the coating paste (see below) are particularly noteworthy, as is the improved sedimentation behavior of the preferred approach for paste formulation and multi-lane application chosen within the scope of the invention. From a technical and economic perspective, complex pressing processes and post-treatment procedures are also eliminated, as a high quality can be achieved.

[0054] In one embodiment of the patent formulation, the solvent is a solvent, in particular a polar and high-boiling solvent, selected from N-octylpyrrolidone, N-methyl-2-pyrrolidone, 2-pyrrolidone (γ-butyrolactam), or 2-methyl-2,4-pentanediol. In one embodiment, the catalyst material for the anode electrode comprises iridium (Ir), in particular as a solid or powdered form, so-called "iridium black." According to this embodiment, a particularly efficient OER catalyst for the membrane assembly is provided. Alternatively or additionally, the catalyst material can contain IrOOH, IrCy, IrRuCy, or TiCf-, NbCy-, or SnCy-supported variants of the aforementioned catalysts or corresponding material systems.

[0055] In one embodiment for the cathode electrode, the catalyst material comprises platinum, in particular solid or powdered so-called "platinum black" for the HER catalyst. Alternatively or additionally, it can contain palladium, ruthenium, or carbon-supported variants and mixtures of the aforementioned catalyst materials.

[0056] In one embodiment, the process leads to hardly, not at all, or almost not at all to adverse sedimentation and / or demixing effects, for example of the sulfonated polymer and / or the catalyst starting material in the application paste.

[0057] In one embodiment, the sulfonated polymer is similar or identical to a material of the polymer membrane as a substrate. As has been shown, this embodiment significantly improves the bonding of the electrode layer containing the catalyst particles to the polymer membrane as a substrate. In other words, the application paste can act as a binder or adhesive for the bonding and inherently form a kind of intermediate layer, in which the support material provided by the polymer membrane is partially dissolved by the application process, thus optimizing the bond at the interface with the catalyst-containing electrode layer.

[0058] The term "similar" is intended to mean, for example, that both materials mentioned are at least polymeric, but do not necessarily refer to the same type of polymer. In this context, one polymer could be, for example, a hydrocarbon-based polymer, and the other a fluoropolymer.

[0059] According to the invention, the application paste thus provided is applied to a polymer membrane as a substrate by means of a so-called roll-to-roll application process (R2R process), whereby a multi-lane application onto the same polymer membrane is implemented, as described above. According to this embodiment, the manufacturing process itself is subject to virtually no limitations, for example, with regard to the coating width of a lane and the coating distance between adjacent lanes, and can thus be scaled up to ever larger throughputs or production batches, thereby significantly increasing the overall production capacity for electrolysis cells through the multi-lane implementation. In particular, these advantages mean that one is no longer bound by the procedural limitations of the prior art.

[0060] In one embodiment, during the direct application of the paste to the polymer membrane as a carrier material, a heat treatment is expediently carried out 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 after the paste application.

[0061] In one embodiment, the application of the coating paste to the substrate material, i.e., for example by roll-to-roll coating, is carried out via a slot nozzle or slot nozzle coating, in particular via so-called wide-slot nozzles. This embodiment advantageously offers the possibility of controlling the desired wet film thickness of the coating by means of the measured mass flow rate and a predetermined substrate velocity.

[0062] In a particularly advantageous embodiment, the paste is applied to the membrane substrate using an application, metering, or anilox roller. This embodiment advantageously allows for simple, self-metering, and intermittent (intermittent) coating.

[0063] In a particularly preferred embodiment, the coating paste is applied to the support material, in particular to a polymer membrane, on both sides, especially in the case of a polymer membrane for PEM electrolysis with differently selected and adapted catalyst materials on the opposite surfaces of the polymer membrane, so that an anode electrode and a cathode electrode are formed. Due to the described requirements of the electrolysis reaction at the cathode side and at the anode, it is usually necessary to apply different catalyst coatings to the cathode and anode.

[0064] In principle, however, it is possible that in one embodiment of the invention the application of the coating paste is carried out only on one side of the substrate material, for example to produce a specifically designed functional or transport layer of an electrochemical cell. According to this embodiment, the invention can thus advantageously also be used for "one-sided" coating systems.

[0065] It is particularly advantageous to be able to process each of the at least two tracks individually, i.e., to coat the substrate material or track with a pre-prepared coating paste. For example, an anode and a cathode can be produced side-by-side on the same substrate in a simultaneous, parallel process. This involves using an anodic coating paste and a cathodic coating paste in parallel operation, each individually prepared and applied to the substrate. This allows, for example, a cathode electrode and an anode electrode to be produced on adjacent, parallel tracks on the substrate. A polymer membrane is typically used as the substrate material.

[0066] Another aspect of the present invention relates to a catalyst-coated membrane (CCM) for PEM electrolysis or a membrane electrode assembly (MEA) which is produced or can be produced by the described method.

[0067] Such a PEM membrane electrode arrangement therefore comprises a polymer membrane coated with an electrode having a catalyst material, which is produced according to the method of the invention.

[0068] Another aspect of the present invention relates to an electrolysis cell which efficiently utilizes a variant of the previously described CCMs with double- or single-sided electrodes.

[0069] The merits of the present invention are therefore not only evident in the small or minimal product unit, such as the membrane or the CCM, but also significantly through the scale effect in the electrolysis cell and a cell stack, electrolyzer or electrolysis system comprising the electrolysis cell, which relates to further aspects of the present invention.

[0070] In particular, the present invention relates to PEM electrolyzers and, furthermore, to complete electrolysis or power-to-X power plants with the electrolysis system described herein. Generally, the manufacturing process is applicable to the production of electrodes for various electrochemical cells. The coating equipment required for this purpose can be newly designed or existing equipment can be retrofitted and configured, expanded, and operated for a two-lane operation for a roll-to-roll (R2R) process with direct coating. A further particular aspect of the invention therefore relates to a roll-to-roll coating device for carrying out the manufacturing process according to the invention. This coating device has a roller arrangement with at least two application and metering rollers for a coating paste and a central inlet for a ribbon-shaped carrier material.The roller arrangement is set up in such a way that simultaneous application of the coating paste in at least two parallel tracks onto the same strip of carrier material is possible, whereby a coating distance between two adjacent tracks can be adjusted so that an intermediate track with uncoated carrier material can be produced on the carrier material.

[0071] In a preferred embodiment of the roll-to-roll coating device, the application and metering rollers (14A, 14B) are arranged on a common shaft and / or are offset from each other on a respective shaft in the transport direction and of the belt.

[0072] The features, characteristics and / or advantages relating to the manufacturing process and the R2R coating device also apply to the manufactured product itself or the membrane electrode assembly (MEA), as well as to the electrolysis cell, the cell stack, the electrolysis system and / or the entire power plant, and vice versa.

[0073] The expression “and / or” or “or” used here, when used in a series of two or more elements, means that each of the listed elements can be used alone, or any combination of two or more of the listed elements can be used.

[0074] Further details of the invention are described below with reference to the exemplary embodiments shown in the FIG. FIG. 1 shows in a schematic representation the basic structure and operation of a PEM electrolysis cell which has a catalyst-coated membrane (CCM) as the cell element;

[0075] FIG 2 in a schematic flowchart process steps for providing an application paste for the manufacture of an electrode;

[0076] FIG 3A shows a simplified side view of a coating device for the production of an electrode, set up for conventional process control;

[0077] FIG 3B shows a simplified top view of the coating device shown in FIG 3A for producing an electrode in a known manner;

[0078] FIG 4 shows a basic representation of a coating device for the production of an electrode, which is set up for improved process control;

[0079] FIG 5 shows an alternative embodiment of a suitably enhanced coating device for the production of an electrode compared to FIG 4;

[0080] FIG 6 shows a schematic side or sectional view of a coating device for applying an electrode to a substrate material;

[0081] FIG 7 shows a schematic side or section view of a modification of the coating device shown in FIG 7;

[0082] FIG. 8 shows a schematic side or sectional view of a modification compared to the coating device shown in FIG. 6 and FIG. 7. In the exemplary embodiments and figures, identical or equivalent elements may be designated with the same reference numerals. The depicted elements and their relative sizes are generally not to be considered to scale; rather, individual elements may be exaggerated in thickness or size for better clarity and / or understanding.

[0083] FIG 1 shows on the left an electrolysis cell 30, in particular a PEM electrolysis cell for water electrolysis. An essential functional element of such a polymer electrolyte membrane electrolysis cell 30 is generally formed by a catalyst-coated membrane 20, which is shown isolated and enlarged on the right in the illustration.

[0084] The catalyst-coated membrane 20, also referred to as CCM, has an electrode 8 made of an electrode material 9 on both the anode and cathode sides, which in this case is applied to a polymer membrane 1 as a support material 7. The electrode material 9 contains a specific catalyst material 5, which is adapted to the anode-side and cathode-side function of the electrolysis cell 30. For this purpose, the polymer membrane 1 is typically provided with a layer of the respective electrode material 9 on both the anode-side and cathode-side surfaces facing away from each other. The respective cell reaction of electrolysis takes place in the region formed by the respective electrode material 9 and is catalytically supported by the catalyst material 5.During normal operation, electrons are conducted via the respective catalyst material and a support structure, which can be formed by or provided by the gas diffusion layer 31, to the contact or bipolar plates 32 (see left in the illustration). It is also evident that reactant water (H₂O) is generally supplied on the anode side, which is decomposed by electrolysis into oxygen (O₂) at the anode and hydrogen (H₂) at the cathode, and the product gases can be obtained separately.

[0085] The polymer membrane 1 or a support material 7 as a starting material, which is usually to be coated for the coating of the polymer membrane 1 with the catalyst material 5, contains, for example, a sulfonated fluoropolymer 2 PFSA: perfluorosulfonic acid ) or a sulfonated hydrocarbon polymer .

[0086] The preparation and setup of a typical coating material for the support material 7 is explained in more detail with reference to FIG. 2. FIG. 2 merely indicates, by means of a schematic flowchart, the necessary process steps for paste formulation to obtain a coating paste 6 that serves as an electrode layer. The process shows, by way of example, a process for producing a catalyst-coated polymer membrane 1, such as can be used in an electrochemical cell, in this case an electrolysis cell 30.

[0087] The process comprises in step a) providing a fluoropolymer 2 as a starting material in solid form, i.e., preferably not in solution. It can be provided in the form of a fine-granular PFSA powder and prepared accordingly.

[0088] For this purpose, commercially available water-alcohol dispersions can be used, which are first converted into powder, for example, by a spray-drying step. Such spray or atomization drying is a method from process engineering for drying solutions or, for example, suspensions. In this process, the material to be dried is introduced into or atomized in a hot gas stream, which dries it into a fine powder in a short time.

[0089] The drying process can be carried out, for example, with the following parameters or specifications: injection temperature 120 °C, injection pressure of 10 bar, nozzle dimension 0.5 mm, jacket or wall temperature of 250 °C, a gas temperature of 380 °C and / or a gas flow of approximately 50 1 / min.

[0090] Alternatively, for example, vacuum spray drying with a single or dual nozzle can be used 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.

[0091] The process further comprises in step b) the dispersion, introduction, or processing of the fine-granular or powdered polymer 2 in a solvent 3 to form a plastisol 4. The term "plastisol" shall generally refer to a dispersion or a heterogeneous mixture.

[0092] The following solvents or solvent combinations with the further specifications given have proven suitable and can be used in particular:

[0093] The inventive method further comprises in step c) the mixing of a catalyst material 5 with the plastisol 4 to form an application paste 6 .

[0094] Finally, in step d), the process further comprises the direct application of the coating paste 6 to a support material 7, for example, a polymer membrane 1 as a substrate, preferably via direct coating of the support material 7 or the polymer membrane. The present invention particularly advantageously enables cost-effective and scalable production of large-format CCMs, especially for PEM water electrolysis. The PFSA plastisol pastes described here, as coating paste 6, enable processing in an improved roll-to-roll application process for direct membrane coating to produce an electrode 8 on a support material 7, as described later in FIGS. 4 to 8.

[0095] Depending on the application method, the required viscosity range can be advantageously adjusted via the solvent combination. Furthermore, the achievable viscosity of the application paste 6 is still significantly determined by the solvent-to-solid ratio in the paste.

[0096] A 10- to 20-wt plastisol consisting of the combination of 3M PFSA EW 825 and 2-pyrrolidone (500 mPas) has proven particularly advantageous for coating with a wet film thickness of approximately 30 to 70 pm, especially 50 pm, using a reverse roll or coating roller process. The primary objective is to provide a coating paste 6 that enables efficient encapsulation of the catalyst particles with ionomer or PFSA and a highly stable coating paste 6 for industrial-scale applications and processing, exhibiting little to no segregation or sedimentation. This has been successfully achieved with the specifications described herein.

[0097] Other important aspects include film formation during the drying step of the coating paste 6, for example by an oven 15 as shown in FIGS. 6 to 8 and used in conjunction with appropriate roll-to-roll processes. It is also important that the applied layer dries as quickly as possible and that good adhesion properties of the coating to the substrate are achieved.

[0098] The inventive process enables the formation of a characteristic interlayer during production. This is achieved by partially dissolving the polymer membrane 1 at the interface with the layer containing the catalyst material 5. In other words, the PFSA ionomer in the coating paste 6 is advantageously selected from the same or a similar material as the polymer membrane 1. This material matching allows the coating paste 6 to advantageously function as a binder or adhesive for the catalyst material 5, resulting in particularly good adhesion and electrode function.

[0099] A specific example of how to prepare the described plastisol 4 as a stock solution includes, for example, providing 5g of PFSA powder (e.g., 3M EW 825), which is stirred into 30g of 2-pyrrolidone solution. Complete dissolution occurs after several hours.

[0100] For the production of an application paste 6 for an electrode 8 for the cathode with a catalyst material 5 for a HER reaction (“HER catalyst”), for example, 10 g of Pt-black can be provided and mixed with 10 g of a 10 to 20% PFSA plastisol stock solution and then thoroughly mixed with ZrCg grinding spheres in a paste mixer. No settling or agglomeration of the particles is observed.

[0101] Very good results can be achieved in an analogous manner for the production of an application paste 6 of an electrode 8 for the anode (“OER catalyst”) using 10 g of Ir-black with 10 g of a comparable PFSA plastisol stock solution.

[0102] As an alternative to the aforementioned HER catalyst, palladium, ruthenium, or carbon-supported variants / mixtures of the aforementioned catalysts can be used as catalyst material 5 for the cathode. For the anode OER catalyst, a catalyst material 5 such as IrOOH, IrO2, IrRuO2, or TiO2, NbO2, or SnO2-supported variants of the aforementioned catalysts can be used.

[0103] The respective anode-side and cathode-side coating of the polymer membrane 1 with the paste 6 containing the catalyst material 5 is carried out according to step d) according to the invention finally with an improved R2R direct application, i.e. without any further transfer, transfer or pressing steps, as is explained below.

[0104] Figure 3A shows a simplified side view of typical functional elements of a known coating device 10 for producing an electrode 8, which is set up and prepared for a conventional R2R process. The coating device 10 has a central roller 14 which integrates or is encompassed at its periphery by an application and metering device 21, so that an application paste 6 can be applied to a carrier material 5 as a substrate. A ribbon-shaped carrier material 7 is inserted into or placed in the coating device 10, so that a uniform advance 19 of the carrier material 7 can be carried out at a certain advance rate during operation.Simultaneously, the application paste 6 is metered and released onto the carrier material 7 by the application and metering device 21 and applied in a thin and uniform layer or web, so that an electrode 8 is continuously produced on the carrier material 7. The roller 14 is rotatably mounted and stationary above the carrier material 7, so that a desired layer thickness can be adjusted.

[0105] FIG. 3B shows a simplified top view of the coating unit 10 shown in FIG. 3A for producing an electrode 8 in a known manner. It can be seen that only a single-lane electrode layer with an electrode 8 is produced in a single lane 11. The electrode 8 can be applied directly to a solid electrolyte, a support substrate, or a functional substrate, e.g., a porous transport layer, as a support material 7. The problem here is that only a single lane 11 of, for example, electrodes 8 can be produced per coating unit 10 or line, and only a single electrode type. Currently, expanding the production capacity of, for example, electrodes 8 can only be achieved by increasing the utilization of the coating unit 10 and / or the system speed. However, both of these options are limited.Should additional production capacity be required, another coating unit (10) would have to be procured and put into operation. This would entail a corresponding CAPEX requirement (equipment, space requirements, possibly a new building) as well as an increased OPEX requirement (e.g., electricity costs), but also an increased need for personnel for operation and maintenance, which is very disadvantageous.

[0106] In contrast, FIG. 4 shows a schematic top view of a coating device 10 for producing a thin electrode 8 on a substrate 7, designed for significantly improved process control and production flexibility. The coating device 10 is designed with multiple lanes and is equipped with a first lane 11A and a second lane 11B, which are guided parallel to each other on the same ribbon-shaped substrate. Instead of just one lane 11 as in the prior art process shown in FIG. 3A and FIG. 3B, two or more lanes 11A, 11B are provided simultaneously and in parallel for applying the coating paste 6, and the coating device 10 is configured accordingly.This is achieved by means of several application and metering rollers 14A, 14B, which, in the embodiment of FIG. 4, are rotatably mounted and positioned on a single common shaft 17 above the strip-shaped carrier material, whereby a predefinable coating distance D is set, which separates the webs 11A, 11B, so that an intermediate web 12 is formed. In addition to the paste-free intermediate web 12 achieved by the coating distance D, an edge strip 22 is provided on both sides of the strip-shaped carrier material 7, which is also not coated with the application paste 6. The edge strip 22 and the coating distance D facilitate further processing. With the composition and formulation of the application paste 6, which contains an electrode material 9, an electrode 8 can be produced on the carrier material 7.

[0107] In the case of multiple coating and metering rollers 14A, 14B, these can also be arranged offset from one another in the conveying direction, as illustrated in FIG. 5. FIG. 5 shows an alternative embodiment compared to FIG. 4 of a correspondingly modified coating device 10 for the production of an electrode 8. Here, a first coating and metering roller 14A and a second coating and metering roller 14B are guided individually via a respective shaft 17 and positioned parallel to each other over the carrier material 7, with an offset 23 in the conveying direction of the belt. It is therefore a two-shaft arrangement of a coating device 10. During operation of the coating device 10, an electrode 8 is applied to the carrier material 7. The belt-shaped carrier material 7 is provided, as well as a coating paste 6 containing an electrode material 9.The coating paste 6 can be formulated and provided according to the method described in FIG. 2. The coating paste 6 is applied to the ribbon-shaped carrier material 7 in a roll-to-roll application process, whereby the carrier material 7 is conveyed. Simultaneously, coating paste 6 is applied in at least two parallel webs 11A, 11B onto the same ribbon of carrier material 7, with a coating gap D being set between two adjacent webs 11A, 11B, so that an intermediate web 12 with uncoated carrier material 7 is produced on the carrier material 7. The coating gap D is set to approximately 10%–20% of the coating width B of a web 11A, 11B. It is also possible to apply the coating paste 6 intermittently to a track 11A, 11B, so that separate rectangular areas with coating paste 6 are formed on the carrier material 7 within a track 11A, 11B.Thus, individual electrode units can be manufactured.

[0108] In a multi-lane coating system 10 designed and upgraded in this way, it is also possible for the application and metering rollers 14A, 14B to rotate in the opposite direction (reverse-roll coating), which is not described in detail here.

[0109] Various plant designs and concepts for coating equipment 10 are possible, which advantageously apply and integrate the multi-lane coating concept of the invention described above. For example, FIG. 6 shows a schematic side or sectional view of a coating equipment 10, which utilizes the general roll-to-roll principle, with numerous rollers 16 provided for transporting and deflecting the ribbon-shaped carrier material 7. The carrier material 7b is a polymer membrane 1. The uniform, multi-lane application of the coating paste 6 in a process step d is carried out via so-called slot nozzles 13, which are shown in simplified form on both sides of the illustration in FIG. 6. The nozzle 13 shown on the right is configured to coat a first active side of the polymer membrane 1 in a multi-lane parallel operation as described above.A plastisol containing fine-grained or powdered platinum (Pt) as catalyst material 5 is used as the anode-side coating paste 6. The coating layer, in its thin wet film (not explicitly shown in FIG. 6), can then be dried or pre-dried in a multi-zone oven 15. The polymer membrane 1 is then conveyed as a substrate over rollers 16 and coated with the catalyst material 5, containing iridium (Ir), on a second side of the polymer membrane 1, the side facing away from the first. The polymer membrane 1, now coated on both sides, passes through the oven 15 again. There, in addition to drying, any remaining solvents or binders are driven off from the coating paste 6, resulting in a catalytically active electrode layer.

[0110] Media dosing during the slot die application of the coating paste 6 can be carried out, for example, via so-called progressive cavity pumps, provided that the system 10 has a winding reel with brake, a belt tension (e.g., 50 Nm), a double-sided slot die coater with a passage width of approximately 10 cm, a substrate thickness of approximately 90 µm, a belt speed between 0.8 and 1.2 m / min, a coating thickness (wet film) of less than 50 µm, in a viscosity range of 500 to 1000 mPas, and a "wet loading" of 30 mg / cm². 2 and drying takes place in a circulating air dryer (drying temperature, for example, 80 to 100 °C) with a solids content of the processable paste of 20 to 50 wt%. Coating via slot nozzles advantageously offers the possibility of controlling the desired wet film thickness of the application by means of the measured mass flow rate and a predetermined substrate velocity.

[0111] The embodiments of the roll-to-roll based coating device 10 shown in FIGS. 6 and FIGS. 7 advantageously allow simultaneous, i.e. double-sided, dosing and application of two different catalyst materials 5 in a multi-lane coating process carried out over a ribbon-shaped support material 7.

[0112] FIG. 7 shows a schematic side or sectional view of a modification of the coating device 10 shown in FIG. 6. The alternative embodiment of FIG. 8 shows a coating device 10 with a number of application or metering rollers 14, via which the coating with the electrode material 9 can be carried out efficiently, particularly simply, and automatically. The process can otherwise be carried out essentially analogously to the description in FIG. 6. This type of coating shown – also known as reverse roll coating – is particularly suitable for producing uniformly coated CCMs. Here, a double-chamber oven 15 with spatial dimensions of well over 1 m can also be used, as well as appropriate circulating air or suspended air dryers to ensure that the coating is applied as uniformly and over as large an area as possible on the polymer membrane 1.

[0113] In contrast, Figure 8 schematically illustrates the application of the coating paste 6 according to step d) of the invention only to one side of the polymer membrane 1 as a substrate, wherein the side facing away from this one side can be coated using a transfer printing process. In particular, it is possible that the coating paste 6 is first applied directly to a polyimide film as a carrier material 7, which is not explicitly characterized here. Subsequently, the coated polyimide film is laminated by means of transfer printing. More precisely, an electrode layer made of the coating paste 6 can be applied, in particular, to an FEP-coated hydrophobic Kapton film (type Dupont 300 FN 929) using coating rollers. The coating is then preferably carried out in segmented fields. The resulting decal films can further be laminated onto the back of the directly coated membrane by means of a hot-pressing process.Hydrophobing the Kapton film improves the release properties of the "decal", allowing even strongly adhering plastisol layers to be transferred.

[0114] The present invention exhibits high process robustness, a broad range of applications, and efficiency. Further fundamental advantages include the ability to implement and improve simple and efficient roll-to-roll coating processes, thereby significantly reducing the number of complex and scalability-prone sub-steps, or upgrading and retrofitting existing coating equipment. Furthermore, manual process steps are no longer required; the process can run essentially fully automatically, as required for an industrially designed manufacturing process. This also results in shorter cycle times for the CCM (coating control unit) and the MEA (machine output equipment), and a significantly higher throughput.

Claims

Patent claims 1. Method for producing an electrode (8) on a support material (7) for an electrochemical cell (30) , comprising: - Providing a ribbon-shaped support material (7) , - Providing an application paste (6) containing an electrode material (9) , - Application of coating paste (6) to the ribbon-shaped carrier material (7) in a roll-to-roll application process, wherein the carrier material (7) is conveyed; - Simultaneous application of coating paste (6) in at least two parallel tracks (11A, 11B) onto the same strip of carrier material (7), wherein a coating distance (D) is set between two adjacent tracks (11A, 11B) so that an intermediate track (12) with uncoated carrier material (7) is produced on the carrier material (7).

2. Method according to claim 1, wherein a coating distance (D) of 10%-20% of the coating width (B) of a web (11A, 11B) is set.

3. Method according to claim 1 or 2, wherein the application paste (6) is applied intermittently to a web (11A, 11B) such that separate rectangular areas with application paste (6) are formed on the carrier material (7) within a web (11A, 11B).

4. Method according to one of the preceding claims, wherein the application paste (6) is applied to the adjacent webs (11A, 11B) by means of a respective application and metering roller (14A, 14B), wherein the application and metering rollers (14A, 14B) are arranged spaced apart from each other on a shaft (17).

5. Method according to claim 4, wherein the application and metering roller (14A, 14B) are arranged on a common shaft (17) or roller.

6. Method according to one of the preceding claims, wherein a polymer membrane (1) is provided as a substrate as the carrier material (7) and the application paste is provided (6) is carried out according to the following steps: - a) Providing a solid or powdered sulfonated polymer (2) , - b) Dispersing the sulfonated polymer (2) in a solvent (3) to form a plastisol (4) , - c) Mixing a catalyst material (5) with the plastisol (4) to form the application paste (6) .

7. Method according to claim 6, wherein in step d) the application paste (6) is applied to the substrate, forming an electrode (8) containing a catalyst material (5) on the polymer membrane (1).

8. Method according to claim 6 or 7, wherein the solvent (3) , in particular a polar, high-boiling solvent , is selected from: N-octylpyrrolidone, N-methyl-2-pyrrolidone, 2-pyrrolidone or γ-butyrolactam or 2-methyl-2,4-pentanediol .

9. Method according to claim 6, 7 or 8, wherein the catalyst material (5) comprises iridium (Ir), in particular solid or powdered iridium black.

10. Method according to any one of claims 6 to 9, wherein the catalyst material (5) comprises platinum (Pt), in particular solid or powdered platinum black.

11. Method according to any one of claims 6 to 10, wherein the sulfonated polymer (2) is selected to be similar to the carrier material (7) of the polymer membrane (1).

12. Method according to one of the preceding claims, wherein the application of the coating paste (6) to the carrier material (7) is further carried out via a nozzle coating.

13. Method according to one of the preceding claims, wherein the application of the coating paste (6) to the carrier material (7) is carried out on both sides, wherein different materials for the electrodes (8) are provided in the coating paste (6) on the opposite sides of the ribbon-shaped carrier material (7).

14. Roll-to-roll coating device (10) for carrying out the method according to one of the preceding claims, comprising a roller arrangement (18) with at least two application and metering rollers (14A, 14B) for an application paste (6) and a central inlet for a ribbon-shaped carrier material (7), wherein the roller arrangement (18) is configured such that the application paste (6) is applied simultaneously in at least two parallel webs (11A, 11B) onto the same ribbon of carrier material. (7) is feasible, wherein a coating distance (D) can be adjusted between two adjacent webs (11A, 11B) so that an intermediate web (12) with uncoated carrier material (7) can be produced on the carrier material (7).

15. Roll-to-roll coating device (10) according to claim 14, wherein the application and metering rollers (14A, 14B) are arranged on a common shaft (17) or on a respective shaft (17) and offset from each other in the transport direction (19) of the belt.

16. PEM membrane electrode arrangement (20) comprising a polymer membrane (1) with an electrode (8) comprising a catalyst material (5) which is manufactured according to the method of any one of claims 1 to 13.

17. Electrolysis cell (30) comprising a PEM membrane electrode arrangement (20) according to claim 16.

18. Cell stack (40) comprising an electrolysis cell (30) according to claim 17.

Images