Gas diffusion layer with slight plastic deformation and high surface quality and method for manufacturing the same

Abstract

The present invention relates to a method for producing a gas diffusion layer for a fuel cell having low plastic deformation (low permanent deformation characteristics) and good surface quality, as well as to a gas diffusion layer obtained by this method and a fuel cell equipped with this gas diffusion layer.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a gas diffusion layer for a fuel cell with low plastic deformation (low permanent deformation properties) and good surface quality. The present invention further relates to a gas diffusion layer obtained by this method and to a fuel cell equipped with this gas diffusion layer.

[0002] <Background of the invention> Fuel cells utilize the chemical reaction of fuel, specifically hydrogen, with oxygen to produce water to generate electrical energy. In a hydrogen-oxygen fuel cell, hydrogen or a hydrogen-containing gas mixture is supplied to the anode, where it undergoes electrochemical oxidation with the release of electrons (H → 2H + +2e - ). Protons are transported from the anode compartment to the cathode compartment through a membrane that separates the reaction compartments gas-tightly from one another and electrically insulates them. Electrons provided at the anode are supplied to the cathode via an external conductor circuit. Oxygen or an oxygen-containing gas mixture is supplied to the cathode, whereby oxygen is reduced while absorbing electrons. The oxygen anions formed react with the protons transported through the membrane to form water (1 / 2O2 + 2H + +2e - →H2O).

[0003] Many applications, especially in automotive drivetrains, use low-temperature proton exchange membrane fuel cells (PEMFCs), whose core is the energy transfer of protons (or oxonium ions, HO) +The proton-conducting membrane is a polymer electrolyte membrane (PEM) that is permeable only to oxygen and water and spatially separates the oxidant, typically oxygen from the air, from the reductant. The gas-tight, electrically insulating proton-conducting membrane is coated on the anode and cathode sides with catalyst layers, which form electrodes and usually contain platinum as the catalytically active metal. The actual redox reactions and charge separation occur within the catalyst layers. The membrane and catalyst layers form a unit known as a catalyst-coated membrane (CCM). Gas diffusion layers (GDLs) are located on both sides of the CCM, stabilizing the cell structure and providing transport and distribution functions for reactant gases, water, heat, and electrical current. The membrane, electrodes, and gas diffusion layers form a membrane electrode assembly (MEA). Between the membrane electrode units, flow distribution plates (so-called bipolar plates) are arranged, which contain channels for supplying process gas to the adjacent cathodes and anodes and usually also contain internal cooling channels.

[0004] Gas diffusion layers for fuel cells typically consist of a carbon fiber substrate that has been hydrophobized with a fluoropolymer (e.g., PTFE) and then coated with a microporous layer (MPL). The MPL usually consists of a fluorine-containing polymer (e.g., PTFE) as a binder and an electrically conductive material, often a carbon material such as carbon black or graphite powder. The gas diffusion layer is crucial for the function and performance of the fuel cell. On the one hand, it transports the process components consumed and generated in the electrode reactions, and on the other hand, it guides the electrons formed and consumed in the half-cell reactions and the heat generated during the reactions to the flow distribution plate. Furthermore, the GDL also acts as a mechanical compensator between the macrostructured flow distribution plate and the catalyst layer. To this end, component manufacturing tolerances must be compensated for and compressive pressures must be distributed. The GDL also serves as mechanical protection for the extremely thin membranes that are subjected to high loads in fuel cells. The sensitive membranes should be as little damaged as possible by the gas diffusion layer and its components. Therefore, high demands are placed on the mechanical and surface properties of the GDL.

[0005] A major problem with fiber-based gas diffusion layers is that an uneven surface or protruding fibers in the gas diffusion layer can damage the fuel cell membrane. These fibers are typically very stiff and fragile. Furthermore, because the fiber thickness is often in the range of the fuel cell membrane's thickness, there is a risk that the membrane may be penetrated by the fibers, causing a short circuit. In the worst case scenario, a short circuit caused by a fiber penetrating the membrane can lead to the complete malfunction of the fuel cell stack. Another cause of defects that can lead to similar failures or a significant reduction in the stack's service life is, for example, an extremely rough MPL surface or impurities of various hardnesses that have become embedded in the MPL. Because the membrane can be subjected to significant mechanical stress during fuel cell operation, stack failure may not occur until later.

[0006] Fuel cell membranes are extremely thin, typically a few microns thick. Typical thicknesses vary between 8 and 50 microns, with some 5-micron-thick membranes already being tested. With the increasing use of fuel cells in automotive applications, a demand for further reduction in the thickness of all planar components (membrane, GDL / MPL, etc.) is expected. Internal short circuits, which can result from protruding fibers in the GDL placed on the membrane, cause significant performance problems. Therefore, there is a demand to avoid protruding fibers and / or smooth the MPL surface of the GDL.

[0007] When used in fuel cells, GDLs are typically subjected to strong pressure (compression). The properties of the GDL as a result of compression can be characterized by the ratio of elastic and plastic deformation. In the case of plastic deformation, the gas diffusion layer does not return to its original shape 100% after a load is applied, but remains a permanent shape change. The property of a material that permanently changes its shape when stress is applied, i.e., the deformability of the material, is also described by the term "permanent deformation." Materials with slight plastic deformation have slight permanent deformation properties. The permanent deformation properties of GDLs known from the prior art still need to be improved. If the GDL is subjected to inappropriate stress under high pressure in a fuel cell stack, permanent deformation will occur due to this stress and changes in dynamic forces during operation. This can lead to a loss of compression pressure in the fuel cell stack, which increases the material resistance of most components and, in particular, the transition resistance of the stack. Furthermore, adaptations to the stack design, such as the use of additional spring packages, may be required to compensate for the stress loss that occurs under permanent deformation. Therefore, the length of the stack and the space required for its installation may increase. Furthermore, additional measures may be required during stack assembly, such as stressing the stack multiple times during assembly and unloading it only afterwards, which increases production costs.

[0008] The development of fuel cells for everyday use is a key element in the energy transition from fossil fuels to sustainable fuels, and therefore there is currently a great demand for improved PEM fuel cells with respect to the complex property profiles described.

[0009] It is known to use a gas diffusion layer with a gradient in at least one physical or chemical property to adjust the application characteristics of a fuel cell. International Publication No. 2022 / 002932 describes a gas diffusion layer for a fuel cell in which at least one physical property selected from hydrophobicity and permeability varies in at least one direction along the maximum surface area. Specifically, it describes controlling hydrophobicity via the content of hydrophobic material (such as PTFE) and permeability via the porosity of the gas diffusion layer. If a microporous layer is applied, its thickness can be affected, which, among other things, results in a change in the local penetration depth into the support layer. The disclosure of this application lacks specificity and lacks both a description of how to implement the described concept and subsequently implementable examples and application data.

[0010] European Patent Application Publication No. 3957789 describes a gas diffusion layer that has high thermal conductivity, good handling properties, and good cell output despite its low density. The GDL has a carbon fiber felt containing carbon fibers with an average fiber diameter of 5 to 20 μm, and at least some of the carbon fibers forming the carbon fiber felt have flat portions, and in this flat portion, a maximum fiber diameter that is 10 to 50% larger than the average fiber diameter is observed in a plan view of the surface of the carbon fiber felt, and the frequency of these flat portions on the surface of the carbon fiber felt is 50 to 200 / mm 2 is.

[0011] WO 2020 / 165075 describes the following steps: a) preparing a carrier-binder paste comprising a solvent, a fluorinated binder, and conductive carrier particles; b) an adhesive composition, -solvent, fluorinated binders, and 0 to 15 wt. % conductive carrier particles, based on the total weight of the fluorinated binder and all conductive carrier particles preparing an adhesive composition comprising: c) combining a layer of support material, a layer of adhesive composition, and a layer of carrier-binder paste, wherein the layer of adhesive composition is applied between the layer of support material and the layer of carrier-binder paste; and pressing the combination of the support material, adhesive composition, and carrier-binder paste at a pressure of at least 15 kilopascals (0.15 bar) and / or heating the combination of the support material, adhesive composition, and carrier-binder paste to a temperature of at least 300°C; A method for manufacturing a gas diffusion layer is described, comprising:

[0012] The problem underlying this document is to provide a mechanically stable gas diffusion electrode in which a carrier / binder layer, preferably in the form of a microporous layer, is firmly bonded to the support material. This is achieved by an additional adhesive layer that contains no or only very small amounts of conductive particles. Pressing of the layer is carried out at a pressure of up to 2.5 MPa and a temperature of at least 300°C, with a long processing time of at least 15 minutes, preferably 1 to 4 hours. The separate binder layer between the substrate and the MPL increases the number of required process steps, and the long pressing time makes industrial applicability extremely difficult.

[0013] JP 2007-242378 A describes a gas diffusion layer composed of porous sintered carbon particles and water-repellent particles. To produce it, carbon particles and water-repellent particles are dispersed in water in the presence of a nonionic surfactant, concentrated using phase separation, and sintered. The sintered film is drawn out and re-ground, and the resulting sintered coarse particles are placed in a mold and hot-pressed to obtain a gas diffusion layer (GDL). This allows for the elimination of the fiber-based substrate in the final GDL, so that the GDL consists only of carbon-based coarse particles and water-repellent particles. This approach is expected to lead to drawbacks in further processing during cutting and manufacturing of the cell stack, as well as in stability within the cell.

[0014] EP 3276718 A1 describes a porous carbon electrode substrate that rarely causes short circuits when used in a fuel cell. In this case, carbon fibers that protrude or are forced to protrude from the substrate surface when the carbon fiber electrode substrate is placed under pressure, as well as short carbon fibers that are poorly bonded to the substrate surface, are substantially removed. For production, short carbon fibers and a binder resin containing at least 35% by weight of carbon and carbonized under heat are used. The resulting GDL substrate is therefore based on a fiber material that is completely impregnated with resin.

[0015] EP 3396753 describes a gas diffusion electrode that is less susceptible to short-circuit currents when used in a fuel cell. In this case, the GDL substrate contains short carbon fibers bound to a resin charcoal. The gas diffusion electrode preferably has a multilayer structure including at least two microporous layers, with different layer packing ratios. In this case, the microporous layers must be thick enough to withstand pressure. Several measures have been described to reduce the possibility of short circuits, such as pressurizing the precursor substrate before carbonizing the binder resin or increasing the temperature during the carbonization process. Only when further reduction is desired is post-treatment by calendering, followed by air blowing or suction, described. The disadvantages of this method are that pressurizing before carbonization requires additional effort, a resin binder in the fiber substrate is often undesirable, and the use of more than two MPL layers also increases the effort. Furthermore, the multilayer structure increases the risk of delamination during winding, distortion, stretching, or under pressure.

[0016] U.S. Patent Application Publication No. 2019 / 0344405 describes a bonding device for bonding gas diffusion layers in fuel cells. The device has a suction device to bond or remove loose or fuzzy fibers from the gas diffusion layer. The use of additional equipment increases manufacturing costs. Furthermore, it is doubtful that the use of this device will solve the problem of internal short circuits that may be caused by protruding fibers of the GDL placed on the membrane.

[0017] The problem underlying the present invention is to avoid or at least reduce the above-mentioned drawbacks.

[0018] It has now been surprisingly found that post-treatment of a gas diffusion layer at elevated pressure and temperature results in a gas diffusion layer with a favorable property profile, particularly excellent surface properties and significantly improved permanent deformation. Gas diffusion layers compressed at high temperatures are characterized by an extremely smooth surface, particularly on the side coated with the microporous layer. This significantly reduces the likelihood of short circuits due to protruding fibers, impurities on the MPL surface, other causes of roughness, or other effects that may occur during fuel cell operation and lead to membrane penetration. Furthermore, post-treatment at elevated pressure and temperature significantly reduces the rate of plastic deformation of the GDL. It has also been surprisingly found that such post-treatment can also control the transport properties of the GDL. Therefore, properties such as gas permeability and dry diffusion length can be controlled regardless of the material composition of the gas diffusion layer.

[0019] <Summary of the Invention> A first subject of the invention is a method for manufacturing a gas diffusion layer for a fuel cell, said gas diffusion layer comprising: A) a conductive textile material in the form of a sheet; and B) a microporous layer on at least one of the faces of the fibrous material, the microporous layer comprising conductive particles in a matrix of a polymeric binder; A method for manufacturing a gas diffusion layer comprising: i) preparing a planar conductive textile material A); ii) coating the fibrous material prepared in step i) with a precursor for forming a microporous layer; iii) subjecting the coated fiber material obtained in step ii) to a post-treatment at elevated pressure and optionally elevated temperature; The method has the following features.

[0020] Preferably, the method according to the invention, in particular the post-treatment in step iii), results in a gas diffusion layer having reduced plastic deformability compared to a non-post-treated gas diffusion layer, in particular a gas diffusion layer having reduced compression set values ​​compared to a non-post-treated gas diffusion layer.

[0021] Preferably, the method according to the invention, in particular the post-treatment in step iii), results in a gas diffusion layer with a smooth surface of at least one microporous layer.

[0022] In particular, the post-treatment in step iii) is carried out at an elevated pressure of at least 0.5 MPa and at an elevated temperature of at least 100°C.

[0023] A particular embodiment of the method for obtaining a gas diffusion layer has the following characteristics: -95~100g / m 2 Unit area weight and 15~22g / m 2 a compression set value of up to 5 μm at 1.0 MPa measured on a ring-shaped specimen having an inner diameter of 45 mm and an outer diameter of 56 mm in a GDL having an MPL load of 0.025 MPa to 1.0 MPa, wherein the specimen is subjected to three load cycles from 0.025 MPa to 1.0 MPa, the compression set value being obtained from the difference in thickness measured at 1.0 MPa in the first and third load cycles; - an arithmetic mean roughness R of at least 10% compared to the untreated gas diffusion layer, measured by the stylus method according to DIN EN ISO 4288:1998-04 a Decrease in - maximum height roughness R of at least 10% compared to the untreated gas diffusion layer, measured by the stylus method according to DIN EN ISO 4288:1998-04 z Decrease in -95g / m 2 unit area weight of 15g / m 2 Maximum 25% number of shorts measured by penetration measurement on the bottom GDL of 297 x 420 mm with an MPL load of Preferably, the compound has one, preferably two, particularly preferably three, and especially four of the above characteristics.

[0024] A further subject of the present invention is a gas diffusion layer obtainable by the method as described above and below.

[0025] A further subject of the present invention is a gas diffusion layer for a fuel cell, comprising: A) a conductive textile material in the form of a sheet; and B) a microporous layer on at least one of the faces of the fibrous material Including, In this case, the gas diffusion layer must have the following properties: -95~100g / m 2 Unit area weight and 15~22g / m 2 a compression set value of up to 5 μm at 1.0 MPa measured on a ring-shaped specimen having an inner diameter of 45 mm and an outer diameter of 56 mm in a GDL having an MPL load of 0.025 MPa to 1.0 MPa, wherein the specimen is subjected to three load cycles from 0.025 MPa to 1.0 MPa, the compression set value being obtained from the difference in thickness measured at 1.0 MPa in the first and third load cycles; - an arithmetic mean roughness R of at least 10% compared to the untreated gas diffusion layer, measured by the stylus method according to DIN EN ISO 4288:1998-04 a Decrease in - maximum height roughness R of at least 10% compared to the untreated gas diffusion layer, measured by the stylus method according to DIN EN ISO 4288:1998-04 z Decrease in -95g / m 2 unit area weight of 15g / m 2 Maximum 25% number of shorts measured by penetration measurement on the bottom GDL of 297 x 420 mm with an MPL load of It has at least one of the following characteristics:

[0026] A further subject of the present invention is a fuel cell comprising at least one gas diffusion layer as defined above and below.

[0027] A further subject of the present invention is the use of a gas diffusion layer as defined above and below or as obtained by a method as defined above and below in a proton exchange membrane fuel cell.

[0028] <Description of the Invention> The gas diffusion layer according to the invention and the gas diffusion layer obtainable by the method according to the invention have the following advantages: The resulting gas diffusion layer has very good surface properties. Gas diffusion layers that have been post-treated at elevated pressure and preferably at elevated temperature are distinguished by a very smooth surface, especially on the side coated with the microporous layer. The gas diffusion layer is highly unlikely to short circuit due to penetration of the proton exchange membrane, as may occur, in particular, due to protruding fibers, impurities on the surface of the MPL, or a rough surface of other origins. The gas diffusion layer has significantly improved permanent deformation properties. By the post-treatment according to the invention at elevated pressure and preferably at elevated temperature, the rate of plastic deformation of the GDL can be significantly reduced. Structural measures such as reducing the compression pressure or increasing the material resistance of the assembled components to adapt the fuel cell stack to the consequences associated with permanent deformation of the GDL and voltage losses can be reduced or completely eliminated. Surprisingly, it has been found that the transport properties of the gas diffusion layer can also be influenced in a targeted manner by the post-treatment according to the invention, so that properties such as gas permeability and dry diffusion length can be controlled regardless of the material composition of the gas diffusion layer. The gas diffusion layer according to the invention can be manufactured simply and cheaply.

[0029] The method according to the invention comprises the following steps: i) preparing a planar conductive textile material A); ii) coating the fibrous material prepared in step i) with a precursor for forming the microporous layer B), wherein the composition of the precursor is varied to create a gradient; iii) subjecting the coated fiber material obtained in step ii) to a post-treatment at elevated pressure and optionally elevated temperature; Includes:

[0030] With regard to the precursors and conditions for forming the fibrous material A) and the microporous layer B), reference is made to the full extent of the further embodiments below.

[0031] [iii) Post-treatment at elevated pressure and elevated temperature] In a particular embodiment, the treatment in step iii) is carried out at an elevated pressure of at least 0.5 MPa and at an elevated temperature of at least 100°C.

[0032] Preferably, the treatment in step iii) is carried out at a pressure in the range of 0.5 to 10.0 MPa (5 to 100 bar), particularly preferably 1.5 to 8.0 MPa.

[0033] Preferably, the treatment in step iii) is carried out at a temperature in the range of 100 to 350°C, particularly preferably 120 to 330°C, in particular 150 to 320°C.

[0034] Preferably, the treatment in step iii) is carried out in a press for a period of 5 seconds to 5 minutes, preferably 10 seconds to 2 minutes.

[0035] Preferably, the processing in step iii) is carried out in the calender machine for a period of more than 0 seconds to 10 seconds, preferably 0.1 seconds to 5 seconds.

[0036] For the post-treatment in step iii), conventional equipment such as a single-stage or multi-stage press, an endless belt press or a calender can be used. In a particular embodiment, at least one double-belt press is used for the post-treatment in step iii). In a more particular embodiment, at least one calender is used for the post-treatment in step iii).

[0037] Single- or multi-stage presses are particularly suitable for the intermittent post-processing of sectioned materials. Double-belt presses are suitable for both the processing of endless web-like materials and sectioned (plate) materials. Double-belt presses have two endless, circulating press belts between which the GDL web is transported in the feed direction and post-processed under pressure and, optionally, heat. The belts are oriented parallel to each other, with a gap between the upper and lower belts that can be opened or closed to accommodate the thickness of the GDL material and adjust the desired properties.

[0038] In a preferred embodiment, the treatment in step iii) is carried out in a double belt press, in particular at a pressure in the range of 1-8 MPa (10-80 bar) and a temperature in the range of 200-350°C.

[0039] In principle, known commercially available calenders can be used in step iii) of the method according to the present invention. Therefore, two, three, four, or five or more calender rolls may be used. In the simplest preferred embodiment, the calender used in the method according to the present invention is a two-roll calender. The gas diffusion layer can be guided through the calender once or repeatedly, for example, one, two, three, four, five, or six or more times. The calender rolls can be arranged in a geometry suitable for calendering the gas diffusion layer. Two-roll calenders can have a vertical, tilted, or horizontal roll arrangement. Three-roll calenders can have a vertical arrangement, an offset upper roll, or an offset lower roll. Four-roll calenders can have an L-shaped arrangement, an inverted L-shaped arrangement, an S-shaped arrangement, a Z-shaped arrangement, or other roll arrangements.

[0040] Preferably, the treatment in step iii) is carried out in a calender machine at a linear pressure in the range of 5 to 500 N / mm, preferably 10 to 100 N / mm.

[0041] Preferably, the calendering in step iii) is carried out at a speed of between 0.05 m / min and 30 m / min.

[0042] In a preferred embodiment, the treatment in step iii) is carried out in a calender, particularly at a roll temperature in the range of 130 to 220°C, a linear pressure in the range of 8 to 80 N / mm, and a web speed of 1 to 10 m / min.

[0043] [Conductive planar fiber material A and gas diffusion layer (GDL)] In the context of the present invention, nonwoven fabrics generally refer to sheet-like structures that consist primarily of individualized fibers, the cohesion of which is essentially provided solely by their inherent adhesive forces. The conversion of nonwoven fabrics into nonwoven materials, which is achieved by creating stronger bonds between the fibers than exist in the nonwoven fabric, is achieved by nonwoven fixing processes, which are primarily divided into mechanical, chemical, and thermal methods. Nonwoven fabrics, nonwoven materials, and methods for their production are described in "Vliesstoffe", 2nd Edition, edited by H. Fuchs and W. Albrecht (Wiley-VCH GmbH, Weinheim, Germany).

[0044] The planar conductive material A) and gas diffusion layer used in accordance with the present invention are planar structures having a substantially two-dimensional planar extent and a relatively small thickness. The gas diffusion layer according to the present invention typically has a bottom surface that substantially corresponds to the bottom surface of the adjacent membrane with the catalyst layer and the bottom surface of the adjacent flow distribution plate. The shape of the bottom surface of the gas diffusion layer may be, for example, a polygon (n-gonal, where n≧3, e.g., triangular, square, pentagonal, hexagonal, etc.), a circle, a sector (e.g., semicircular), an ellipse, or an elliptical sector. Preferably, the bottom surface is rectangular or circular. A Cartesian coordinate system can be used to describe the GDL, in which the bottom surface of the GDL lies in a plane defined by the x- and y-axes (also referred to as the x-y plane). The perpendicular z-axis is used to describe the material thickness. According to the usual description for fiber composite materials, the x-axis is also referred to as the machine direction (MD), and the y-axis is also referred to as the cross-machine direction (CMD). In the direction of the z-axis, material transport occurs essentially between the flow distribution plate and the membrane.

[0045] The gas diffusion layer comprises, as component A), at least one electrically conductive planar fibrous material. Preferably, component A) comprises a fibrous material selected from nonwoven fabrics, paper, woven fabrics, and combinations thereof. Suitable substrate materials are fibrous materials that are electrically conductive themselves or that are made electrically conductive by adding conductive additives such as carbon or metal particles. Suitable substrate materials are, in principle, carbon fibers, glass fibers, fibers of organic polymers such as polypropylene, polyester, polyphenylene sulfide, polyether ketone, and mixtures thereof. The fibers contained in fibrous material A) preferably comprise or consist of carbon fibers. Such fibrous materials particularly advantageously meet the requirements for gas diffusion rate, liquid and water permeability, electrical conductivity, and thermal conductivity of the GDL. The fibrous material A) is preferably selected from woven carbon fiber fabrics, carbon fiber paper, and nonwoven carbon fiber materials. In a preferred embodiment, the fibrous material A) comprises at least one carbon fiber nonwoven material or consists of a carbon fiber nonwoven material.

[0046] Carbon fibers can be produced by conventional methods, preferably using polyacrylonitrile fibers (PAN fibers) as the starting material. PAN fibers are produced by radical polymerization of a monomer composition containing preferably at least 90% by weight of acrylonitrile, based on the total weight of the monomers used for polymerization. The resulting polymer solution is spun, for example, by wet spinning and coagulation to form filaments, which are then assembled into a rope. Before the PAN precursor is converted into carbon fibers at elevated temperatures, it is usually subjected to oxidative cyclization (also referred to as oxidation for short) in an oxygen-containing atmosphere at elevated temperatures of about 180-300°C. The resulting chemical crosslinking improves the dimensional stability of the fibers. This is followed by actual pyrolysis at a temperature of at least 1200°C to obtain the carbon fibers. For this pyrolysis, starting fibers or already planar fiber materials can be used, depending on the desired fiber shape. Depending on the pyrolysis temperature, a distinction is made between carbonization and graphitization. Carbonization refers to treatment at approximately 1200-1500°C under an inert gas atmosphere, which results in the elimination of volatile products. Graphitization, i.e., heating at approximately 2000-3000°C under an inert gas, results in so-called high-modulus fibers or graphite fibers. These fibers are highly pure, lightweight, strong, and have excellent electrical and thermal conductivity.

[0047] The fibrous material A) is preferably selected from woven carbon fiber fabrics, carbon fiber papers and nonwoven carbon fiber materials.

[0048] In carbon fiber woven fabrics, two fiber systems, namely warp and weft, are intertwined to produce a planar fibrous material. As in textiles, the fiber bundles are flexibly but inseparably bonded to one another. To produce carbon fiber woven fabrics, PAN fibers that have been oxidized but not yet carbonized or graphitized are preferably used. Carbonization or graphitization to impart electrical conductivity to the planar fibrous material is carried out after knitting.

[0049] As mentioned at the beginning, oxidized PAN fibers are typically used to produce carbon fiber paper. As is known per se, the PAN fibers are milled into fiber fragments, suspended, and, similar to papermaking, screened to produce fiber sheets and dried. In a preferred embodiment, at least one binder is additionally incorporated into the paper. Suitable binders include, for example, phenolic resins, furan resins, polyimide resins, etc. To incorporate the binder, the paper can be impregnated with the binder, which can then be cured. After impregnation and curing, the carbon fiber paper is further carbonized / graphitized, thereby converting the binder into a compound with improved electrical conductivity. In a further preferred embodiment, filled carbon fiber paper is used to provide the fiber material A). This is first carried out as described above, but instead of incorporating the binder and carbonizing / graphitizing, a filler consisting of a carbon material in a polymer binder is incorporated into the still-wet paper. In particular, a carbon-PTFE filler is used for this purpose. Such filling increases the thermal and electrical conductivity, and as a result carbonization / graphitization can be omitted.

[0050] For the production of carbon fiber nonwoven materials, either unoxidized or oxidized PAN fibers can be used. In a first step, the PAN fibers are laid in a dry state (carded) and then consolidated to form a nonwoven material. This can be done, for example, by hydroentangling, in which the carbon fibers are oriented, entangled, and thus mechanically stabilized. In some cases, the thickness of the consolidated nonwoven material can be calibrated to a desired value. Nonwoven materials based on nonoxidized PAN fibers are first oxidized in an oxygen atmosphere at elevated temperature after nonwoven fabric formation and solidification, and then carbonized / graphitized in an inert gas atmosphere. Nonwoven materials based on oxidized PAN fibers are only carbonized / graphitized after nonwoven fabric formation and solidification. Optionally, the nonwoven can additionally contain at least one binder, which can then be cured if necessary. Suitable binders are those mentioned for carbon fiber paper, especially phenolic resins. The incorporation of a binder may, for example, be carried out following carbonization / graphitization, and the resulting impregnated nonwoven may finally be carbonized / graphitized again.

[0051] In a particular embodiment, the areal conductive fiber material A) comprises at least one carbon fiber nonwoven material, which is particularly advantageous since it is compressively elastic and can be easily produced industrially, for example by roll-to-roll processes.

[0052] The fibrous materials A) are usually: a1) carbon fiber, a2) optionally at least one polymeric binder and / or its thermal decomposition products, a3) optionally at least one further additive different from a2); A fiber composite material comprising:

[0053] The fibrous material A) contained in the gas diffusion layer can contain common additives a3), which are preferably selected from hydrophobizing agents, conductivity-improving additives, surface-active substances and mixtures thereof.

[0054] To improve the transport process through the GDL and the interface, it may be advantageous to increase the hydrophobicity of the fiber material A). Suitable hydrophobizing agents are fluorine-containing polymers such as polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). PTFE is preferably used as the hydrophobizing agent. The fiber material can be impregnated with the hydrophobizing agent by conventional impregnation methods. For this purpose, a PTFE dispersion is added to an immersion bath, the solvent is evaporated, and the treated fiber material can be sintered at elevated temperatures, typically at least 300°C.

[0055] Preferably, the fiber material A) has a content of hydrophobizing agent of 3 to 40% by weight, based on the total weight of the fiber material A). In a particular embodiment, the fiber material has a content of PTFE of 3 to 40% by weight, based on the total weight of the fiber material A).

[0056] To improve electrical and thermal conductivity, at least one additive for improving conductivity can be added to the fiber material A). Suitable additives for improving conductivity include, for example, metal particles, carbon particles, etc. Preferably, the additive for improving conductivity is selected from carbon black, graphite, graphene, carbon nanotubes (CNTs), carbon nanofibers, and mixtures thereof. The addition of at least one additive for improving conductivity to the fiber material A) can be carried out, for example, together with a hydrophobizing agent, in particular a PTFE dispersion. In many cases, the fiber material A) has good electrical and thermal conductivity even without the additive for improving conductivity, depending on the carbon fiber used.

[0057] Preferably, the fiber material A) has a content of conductivity-improving additives of 0 to 40% by weight, based on the total weight of the fiber material A). If the fiber material A) comprises a conductivity-improving additive, it is preferably in an amount of 0.1 to 40% by weight, particularly preferably 0.5 to 30% by weight, based on the total weight of the fiber material A).

[0058] The fiber material A) preferably has a thickness in the range of 50 to 750 μm, particularly preferably 100 to 500 μm, in the uncompressed state of the fiber material A), i.e. before further treatment in step iii) and before the incorporation of the GDL into the fuel cell.

[0059] The fibrous material A) preferably has a porosity, measured by mercury porosimetry according to DIN ISO 15901-1:2019-03, in the range from 10 to 90%, particularly preferably from 20 to 85%.

[0060] The average pore diameter of the fibrous material A) is preferably in the range of 5 to 60 μm, particularly preferably 8 to 50 μm, in particular 10 to 40 μm. The average pore diameter is determined by mercury porosimetry according to DIN ISO 15901-1:2019-03.

[0061] Microporous layer B) The gas diffusion layer according to the invention consists of a two or more layer composite based on an areal electrically conductive fibrous material A) and at least one microporous layer (MPL) B) provided on at least one of the surfaces of the fibrous material A).

[0062] According to the present invention, the microporous layer B) comprises conductive particles in a matrix of a polymer binder. The conductive particles are preferably selected from conductive carbon particles, in particular carbon black, graphite, graphene, carbon nanotubes (CNTs), carbon nanofibers, and mixtures thereof. Preferably, carbon black, graphite, or mixtures thereof are used.

[0063] In particular, the polymer binder comprises at least one fluorine-containing polymer. The fluorine-containing polymer is preferably selected from polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, perfluoroalkoxy polymer, and mixtures thereof. Preferably, polytetrafluoroethylene (PTFE) is used.

[0064] Preferably, to produce the microporous layer B), 0.5 to 50% by weight, particularly preferably 1.0 to 40% by weight, in particular 10 to 25% by weight of polymer binder is used, based on the total weight of polymer binder and conductive particles.

[0065] In contrast to the macroporous fibrous material A), the MPL B) is usually microporous, with pore diameters that are significantly smaller than the micrometer, preferably 900 nm or less, particularly preferably 500 nm or less, in particular 300 nm or less. The average pore diameter of the MPL B) is preferably in the range from 5 to 200 nm, particularly preferably 10 to 100 nm.

[0066] Porosity and pore size distribution can be measured by mercury intrusion porosimetry, as described in DIN ISO 15901-1:2019-03: Mercury intrusion porosimetry. The latter average pore diameter applies, in particular, when carbon black is used as the conductive particle in the MPL. Significantly larger MPL pores can also be produced by using graphite as the conductive particle in the MPL or by using a pore-forming agent. In this case, depending on the composition, the average pore diameter can be, for example, greater than 1 μm. When various conductive particles are used, the pore diameters may have a bimodal or multimodal distribution curve. Thus, when a mixture of carbon black and graphite is used, a pore diameter distribution containing two pore peaks (a carbon black peak and a graphite peak) can result.

[0067] The microporous layer B) preferably has a thickness in the range of 5 to 150 μm, particularly preferably 10 to 100 μm, in the uncompressed state of the microporous layer B), i.e. before the post-treatment in step iii) and before the incorporation of the GDL into the fuel cell.

[0068] The presence of MPL has a significant impact on the water content of the fuel cell: the high proportion of PTFE and the smaller pores of the MPL make it difficult for the GDL and electrodes to become waterlogged, as the MPL acts as a liquid water barrier, thus facilitating mass transport of gaseous reactants to the catalyst.

[0069] The gas diffusion layer according to the invention preferably has a thickness (total thickness consisting of the fiber material A) and the MPL B) in the range of 50 to 1000 μm, particularly preferably 75 to 500 μm. This thickness relates to the uncompressed state of the GDL, i.e. before the post-treatment in step iii) and before the GDL is incorporated into the fuel cell.

[0070] Furthermore, the gas diffusion layer preferably has a high total porosity, preferably in the range of 20% to 80%, as measured by mercury porosimetry according to DIN ISO 15901-1:2019-03, as described above.

[0071] [Method for manufacturing a gas diffusion layer] [Step i)] With regard to suitable preferred fibre materials A) used in step i), reference is made in full scope to the embodiments described above.

[0072] [Step ii)] The precursor used in step ii) preferably comprises at least one fluorine-containing polymer, at least one carbon material, and optionally at least one pore-forming agent. The fluorine-containing polymer is preferably selected from polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). PTFE is preferably used. The carbon material is preferably selected from carbon black, graphite, graphene, carbon nanotubes (CNTs), carbon nanofibers, and mixtures thereof. Carbon black or graphite is preferably used. In a particular embodiment, the precursor used in step b) comprises at least one pore-forming agent. Suitable pore-forming agents are, for example, commercially available plastic particles made of polymethyl methacrylate (PMMA). Suitable particle sizes are in the range of 10 to 100 μm.

[0073] Preferably, the volume fraction of pores in the finished microporous layer resulting from the use of the pore-forming agent is 0 to 70 volume % based on the total volume of pores in the finished microporous layer.

[0074] The application of MPL to fiber materials can be carried out in various ways. For intermittent production, spraying, screen printing, or Mayer rod methods are frequently used, while for continuous coating, doctor blade, slit nozzle, and gravure roller processes are preferred. The MPL layer thickness and indentation depth can be influenced by the coating process parameters and the viscosity of the coating. Finally, a new heat treatment is carried out, for example, in a drying and sintering furnace. This can involve first drying at a temperature of 100-200°C, followed by sintering at a temperature of 300-500°C.

[0075] Post-processing step iii) has already been comprehensively described above, to which reference is now made.

[0076] [Compression set value] When a material such as a gas diffusion layer is subjected to a load, it is said to be plastically deformed if it does not return to its original shape 100% but is left with a permanent change in shape. Part of the deformation is elastic and therefore reversible, while only a certain part is plastic and remains permanent. The property of a material to permanently change its shape when stress is applied, i.e., the deformability of the material, is also described by the term "permanent set." A material with slight plastic deformability has slight permanent set properties.

[0077] The compression set value is a measure of how a material, in this case a GDL, behaves when subjected to pressure deformation and then released. When used in a fuel cell, a GDL is usually subjected to strong compression (compression). To characterize the properties of a GDL under compression, the proportions of elastic and plastic deformation can be considered. Compression set is the permanent deformation that remains after the applied force is removed. A gas diffusion layer with low compression set properties is characterized by a low compression set value. The compression set value can be measured in the following manner: At the same time, the values ​​of other physical quantities, such as thickness, gas permeability, and electrical resistance, can be measured, each under a specific compression force and after one or more force applications.

[0078] Three samples (left, right and center) are taken across the full width of the GDL to be examined and an average value is calculated from these samples. If the material has a machine direction due to its manufacture, the samples are taken perpendicular to the machine direction (CMD). The samples are ring-shaped with an inner diameter of 45 mm and an outer diameter of 56 mm. The sample area is 8.72577 cm 2In the testing machine, the sample is subjected to a time-varying compressive force acting perpendicular to the sample surface. A sensor measures the change in GDL thickness over time under each applied force. The sample is placed on a device for measuring elastic and plastic deformation using a force sensor; the movement is transmitted to the sample via a spring. The distance traveled until the maximum compressive force is reached is measured by a distance sensor. Since the sample deformation is nonlinear, the measurement curve is adapted to the relative change. One measurement cycle, i.e., one load to the maximum pressure followed by unloading, takes one minute. The sample is subjected to three load cycles. The initial value, at which only a small force is applied to the sample, is 0.025 MPa. Typical pressure values ​​for measuring compression set values ​​(and other physical quantities such as thickness, electrical conductivity or surface resistance, gas permeability, etc.) are, for example, 0.6 MPa, 1.0 MPa, and 2.4 MPa.

[0079] The compression set value at a given pressure is obtained from the difference between the thickness measured at that pressure on the first load cycle and the thickness measured at that pressure on the third load cycle.

[0080] Preferably, the GDL according to the present invention has a density of 90 to 95 g / m 2 Unit area weight and 15.0~22.0g / m 2 In ring-shaped samples having an inner diameter of 45 mm and an outer diameter of 56 mm in a GDL with an MPL load of 10 bar (1 MPa) by the method described above, the maximum compression set value is 5 μm.

[0081] Roughness The roughness can be measured by the usual stylus method known to those skilled in the art, which is described, for example, in DIN 4768-1:1974-08 as "Roughness measurements R with electrical stylus instruments" a , R z , R max The calculation of the basis for the calculation of the

[0082] Arithmetic mean roughness R a(average distance from the measurement point on the surface to the center line) and the average maximum height roughness R z was measured. The measurements were carried out using a Mahrsurf XCR20 measuring instrument equipped with a Mahr free probe MFW-250. Each value is the average of six measurements: three in the machine direction (MD) and three in the cross-machine direction (CD). Specific measurement conditions are described in the Examples section, for which reference is made.

[0083] [Penetration measurement, number of short circuits] FIG. 1 shows an apparatus for penetration measurements to measure the number of short circuits as a measurement for characterizing the probability of short circuits.

[0084] In the penetration measurement, a PP film (4 μm thick) is attached between two GDL samples (GDL layers) and a distance layer with a specified thickness (0.1–1.0 mm) and a specified spacing. The material is placed on a conductive, smooth metal plate. During the measurement, a metal stamp (12.7 mm diameter) slowly presses the upper GDL into the spacing between the spacer layers and onto the PP film. The conductive pressure stamp and metal plate are connected to a resistance measuring device. When the maximum pressure is reached, the measurement at the test point is terminated. If the resistance falls below a threshold resistance of 10 kΩ, penetration of the PP film has occurred. The corresponding pressure is recorded. Since the GDL itself is conductive, this measurement detects damage to the PP film caused by the pressed GDL. During one measurement run, typically 117 measurement points are measured over an area of ​​approximately 300 × 400 mm.

[0085] Furthermore, tests with PP films of various thicknesses (4-14 μm) have shown that for a given number of measurements for the same material / measurement parameter combination, a decrease in the PP film thickness increases the probability of film / membrane penetration, or the number of penetrations. For each combination, at least 117 measurements were performed (standard: 4 replicates of 117 measurements each).

[0086] The number of shorts as a measure to characterize the probability of a short circuit is defined as follows: Number of short circuits = (number of measurement points with penetrations / total number of measurement points) x 100

[0087] In other words, the percentage ratio between the number of measurements below the threshold resistance and the total number of measurements is defined as the number of shorts. The fewer the number of measurements below the threshold resistance, the smaller the number of shorts and the smaller the possibility of membrane puncture.

[0088] Preferably, the gas diffusion layer according to the present invention has a density of 95 g / m 2 unit area weight of 15g / m 2 The maximum number of short circuits was 15% as measured by penetration measurement in the GDL of the bottom surface of 297 x 420 mm with an MPL load of 1000.

[0089] Specific measurement conditions are described in the Examples section, for reference.

[0090] [Other physical quantities] The gas permeability perpendicular to the plane of the material can be determined via Gurley measurements, using an automated Gurley densometer from Gurley Precision Instruments. The measurements are performed at a constant differential pressure of 100 cm in the vertical direction. 3 of air, 6.42 cm 2 The time it takes for air to flow through a GDL sample with a flow area of ​​100 mm is measured in seconds. Measurement of air permeability by the Gurley method is described in ISO 5636-5.

[0091] The dry diffusion length is the actual length in μm that gas molecules travel through a surface fibrous material A) and / or a microporous layer B) and is measured by a stationary Wicke-Kallenbach cell.

[0092] The thickness of the gas diffusion length can be measured according to DIN 53855-1:1993-08 "Measurement of the thickness of fibrous sheet structures." The thickness measurement under a predetermined pressure (e.g., 0.025 MPa or 1.0 MPa) can be performed in an apparatus for measuring compression set, as described in detail above.

[0093] Mass over area in g / m 2 Measurements at can be made in accordance with EN29073-1:1992.

[0094] The porosity of the GDL can be measured by mercury intrusion as described in DIN ISO 15901-1:2019-03: Mercury intrusion.

[0095] [Fuel cell] Another subject of the present invention is a fuel cell comprising at least one gas diffusion layer as defined above or at least one gas diffusion layer obtainable by the method as defined above.

[0096] In principle, the gas diffusion layer according to the invention is suitable for all common fuel cell types. Preferably, the fuel cell according to the invention is a proton exchange membrane fuel cell (PEMFC), also called a polymer electrolyte fuel cell (PEFC) or a low temperature polymer electrolyte membrane fuel cell (LT-PEMFC). A particular embodiment of the invention is a water-oxygen fuel cell in the form of a low temperature proton exchange membrane fuel cell (PEMFC). Reference is made in its entirety to the above-mentioned embodiments for constructing the fuel cell.

[0097] The fuel cell according to the invention preferably comprises a polymer electrolyte membrane on the anode side and the cathode side, on which are deposited catalyst layers forming the electrodes. Preferably, on the anode side and / or the cathode side, a gas diffusion layer (GDL) is in contact with the catalyst layer. The fuel cell in particular has a polymer electrolyte membrane on which a catalyst layer is deposited, which is in contact with the surface of the microporous layer B) of the gas diffusion layer according to the invention. In particular, the fuel cell has a gas diffusion layer according to the invention on the cathode side, which catalyst layer is in contact with the surface of the microporous layer B) of the gas diffusion layer. In particular, the fuel cell has a gas diffusion layer according to the invention on the cathode side and the anode side, where the cathode layer and the anode layer are each in contact with the surface of the microporous layer B) of the gas diffusion layer according to the invention.

[0098] An advantage of the present invention is that the transport process through the gas diffusion layer can be appropriately adapted to the gradient of the working medium flowing through the fuel cell and / or to the gradient of the operating parameters of the fuel cell, for which at least one property gradient of the gas diffusion layer typically corresponds to at least one property gradient of the working medium flowing through the fuel cell and / or to at least one operating parameter of the fuel cell.

[0099] Another subject of the present invention is the use of a gas diffusion layer as defined above or a gas diffusion layer obtainable by the method as defined above in a proton exchange membrane fuel cell. [Brief explanation of the drawings]

[0100] [Figure 1] FIG. 1 shows an apparatus for penetration measurements to measure the number of short circuits as a measurement for characterizing the probability of short circuits. [Figure 2] FIG. 1 shows the plastic deformation properties (set properties) based on compression set values ​​at 1 MPa for five sets each consisting of one comparative GDL (left bar) and one GDL according to the invention (right bar). [Figure 3a]1 shows the arithmetic mean roughness Ra(MD) measured according to the stylus method as described in DIN 4768-1:1974-08 for two sets of one comparative GDL (left bar) and one GDL according to the invention (right bar). [Figure 3b] 1 shows the arithmetic mean roughness Ra(CD) measured according to the stylus method as described in DIN 4768-1:1974-08 for two sets of one comparative GDL (left bar) and one GDL according to the invention (right bar). [Figure 4a] 1 shows the average maximum height roughness Rz(MD) measured according to the stylus method as described in DIN 4768-1:1974-08 for two sets each consisting of one comparative GDL (left bar) and one GDL according to the invention (right bar). [Figure 4b] FIG. 1 shows the average maximum height roughness Rz(CD) measured according to the stylus method as described in DIN 4768-1:1974-08 for two sets of one comparative GDL (left bar) and one GDL according to the invention (right bar).

[0101] The following examples are used to illustrate the present invention without limiting it in any way.

[0102] <Example> [I) Production of gas diffusion layer] Example 1: Preparation of gas diffusion layers without post-treatment according to the invention (Example V1) and with post-treatment according to the invention (Example 1) at elevated pressure and elevated temperature To produce a sheet of conductive material, 100 g / m 2 A nonwoven material consisting of 100% carbon fiber with a unit area weight of 15 g / m was used. For the loading of the nonwoven material, an impregnation composition containing 80% carbon black and 20% PTFE in terms of solids was mixed. The loading was determined by the mass of the GDL substrate (15 g / m). 2This was done by Foulard impregnation with an aqueous dispersion having a loading weight of 15% relative to the total mass of the fiber (corresponding to 10 ... 2 The GDL according to the invention was post-treated in a double belt press for 20 seconds at a pressure of 25 bar and a temperature of 320° C. As a comparison, a GDL that was not post-treated was used.

[0103] [II) Examples of applied technologies] The following materials were used to measure the application properties: 1) Example 1 / V1 GDL according to Manufacturing Example 1 2) Example 2 / V2 100g / m 2 The same GDL as in Preparation Example 1, having a unit area weight of 3) Example 3 / V3 132g / m 2 The same GDL as in Preparation Example 1, having a unit area weight of 4) Example 4 / V4 135g / m 2 The same GDL as in Preparation Example 1, having a unit area weight of 5) Example 5 / V5 96.5g / m 2 The same GDL as in Preparation Example 1, having a unit area weight of 6) Example 6 / V6 94g / m 2 The same GDL as in Preparation Example 1, having a unit area weight of

[0104] [Compression set] Compression set values ​​and thickness were calculated according to the methods detailed above, and are shown in Table 1 below.

[0105] Roughness The roughness measurements were carried out according to the stylus method as described in DIN 4768-1:1974-08.

[0106] Arithmetic mean roughness R a (average distance from the measurement point on the surface to the center line) and the average maximum height roughness R z was measured. Measurements were made using a Mahrsurf XCR20 equipped with a Mahr free probe MFW-250. Each value is the average of six measurements: three in the machine direction (MD) and three in the cross-machine direction (CD).

[0107] The following conditions were selected for the measurements: Probe = MFW-250. Probe diamond radius 2 μm, cone angle 60° LC(GS)=2.5mm=Cutoff=LT+LM LT = 17.5 mm = probe measurement distance = 2.5 mm. The front measurement distance is 2.5 mm and the back measurement distance is 2.5 mm for turning the Gaussian filter on and off. This 2 x 2.5 mm distance is not taken into account in the measurement. LM = 12.5 mm = measurement section leading to calculation of roughness value Z=5=R z The number of individual measurements of the value. In this case, the measurement path (profile) is divided into five symmetrical individual sections (=LM / 5). The mean value is calculated from each individual section. From the five mean values, R z Average the values. VB = +-250μm = Probe measurement range Profile resolution per measurement section = 100,000 steps Linearity=<1% Probe force (measuring force) = 0.8 mN Probe speed 0.5mm / sec

[0108] [Penetration measurement, number of short circuits] The penetration measurements to determine the number of short circuits were performed as described above. During one measurement run, 117 measurement points were measured over an area of ​​approximately 300 x 400 mm. The results are listed in Table 1.

[0109] The Gurley gas permeability was measured in the direction perpendicular to the plane of the material by a Gurley densometer manufactured by Gurley Precision Instruments in accordance with ISO 5636-5. The results are also shown in Table 1.

[0110] Dry diffusion lengths were measured using a stationary Wicke-Kallenbach cell, and the results are also reported in Table 1.

[0111] [Table 1]

Claims

1. 1. A method for manufacturing a gas diffusion layer for a fuel cell, the gas diffusion layer comprising: A) a planar conductive textile material; and B) a microporous layer on at least one of the faces of the fibrous material, the microporous layer comprising conductive particles in a matrix of a polymeric binder. A method for manufacturing a gas diffusion layer comprising: i) providing a planar conductive textile material A); ii) coating the fibrous material prepared in step i) with a precursor for forming a microporous layer; iii) subjecting the coated fiber material obtained in step ii) to a post-treatment at elevated pressure and optionally elevated temperature, The method has the following features:

2. The following properties: -95~100g / m 2 and 15 to 22 g / m 2 a compression set value of up to 5 μm at 1.0 MPa measured on a ring-shaped sample having an inner diameter of 45 mm and an outer diameter of 56 mm in a GDL having an MPL load of 0.025 MPa to 1.0 MPa, wherein the sample is subjected to three load cycles from 0.025 MPa to 1.0 MPa, and the compression set value is obtained from the difference in thickness measured at 1.0 MPa at the first load cycle and the third load cycle; an arithmetic mean roughness R of at least 10% compared to the non-post-treated gas diffusion layer, measured by the stylus method according to DIN EN ISO 4288:1998-04 a Decrease in a maximum height roughness R of at least 10% compared to the non-post-treated gas diffusion layer, measured by the stylus method according to DIN EN ISO 4288:1998-04 z Decrease in -95 g / m 2 and 15 g / m 2 Maximum 25% number of shorts measured by penetration measurement on the bottom GDL of 297 x 420 mm with an MPL load of 2. A method according to claim 1 for obtaining a gas diffusion layer having one or more of the following properties:

3. 3. The method according to claim 1, wherein the fiber material A) is selected from nonwoven carbon fiber materials, woven carbon fiber materials, and mixtures thereof.

4. 4. The method according to claim 1, wherein the treatment in step iii) is carried out at a pressure in the range of 0.5 to 10.0 MPa, preferably 1.5 to 8.0 MPa.

5. 5. The process according to claim 1, wherein the treatment in step iii) is carried out at a temperature in the range from 100 to 350°C, preferably from 120 to 330°C, particularly preferably from 150 to 320°C.

6. 6. The method according to claim 1, wherein for the treatment in step iii) an apparatus selected from a single-stage press, a multi-stage press, an endless belt press, a calender, and combinations thereof is used, preferably a double-belt press, a calender, and combinations thereof.

7. 7. The method according to claim 1, wherein the treatment in step iii) is carried out in a press for a period of 5 seconds to 5 minutes, preferably 10 seconds to 2 minutes.

8. Method according to any one of the preceding claims, wherein the treatment in step iii) is carried out in a calender machine for a period of more than 0 seconds to 10 seconds, preferably 0.1 seconds to 5 seconds.

9. 9. The method according to any one of claims 1 to 8, wherein the treatment in step iii) is carried out in a calender at a linear pressure in the range of 5 to 500 N / mm, preferably 10 to 100 N / mm.

10. A gas diffusion layer obtained by the method according to any one of claims 1 to 9.

11. A gas diffusion layer for a fuel cell, the gas diffusion layer comprising: A) a planar conductive textile material; and B) a microporous layer on at least one of the faces of the fibrous material. Including, The gas diffusion layer has the following properties: -95~100g / m 2 and 15 to 22 g / m 2 a compression set value of up to 5 μm at 1.0 MPa measured on a ring-shaped sample having an inner diameter of 45 mm and an outer diameter of 56 mm in a GDL having an MPL load of 0.025 MPa to 1.0 MPa, wherein the sample is subjected to three load cycles from 0.025 MPa to 1.0 MPa, and the compression set value is obtained from the difference in thickness measured at 1.0 MPa at the first load cycle and the third load cycle; an arithmetic mean roughness R of at least 10% compared to the non-post-treated gas diffusion layer, measured by the stylus method according to DIN EN ISO 4288:1998-04 a Decrease in a maximum height roughness R of at least 10% compared to the non-post-treated gas diffusion layer, measured by the stylus method according to DIN EN ISO 4288:1998-04 z Decrease in -95 g / m 2 and 15 g / m 2 Maximum 25% number of shorts measured by penetration measurement on the bottom GDL of 297 x 420 mm with an MPL load of A gas diffusion layer having at least one of the following properties:

12. A fuel cell comprising at least one gas diffusion layer according to claim 10 or 11 or at least one gas diffusion layer obtainable by the method according to any one of claims 1 to 9.

13. 13. The fuel cell according to claim 12, further comprising a polymer electrolyte membrane, the polymer electrolyte membrane being coated with a catalyst layer, the catalyst layer being in contact with the surface of the microporous layer B) of the gas diffusion layer.

14. Use of a gas diffusion layer according to claim 10 or 11 or a gas diffusion layer obtainable by the method according to any one of claims 1 to 9 in a proton exchange membrane fuel cell.

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