Gas diffusion layer for polymer electrolyte membrane fuel cell with reduced contact resistance

Abstract

The present invention relates to a gas diffusion layer for a fuel cell, comprising: A) a planar conductive material, said planar conductive material comprising at least one fibrous material selected from the group consisting of carbon fiber nonwoven materials, carbon fiber papers, carbon fiber fabrics and mixtures thereof; and B) a microporous layer comprising electrically conductive carbon particles in a matrix consisting of a polymeric binder, wherein said electrically conductive carbon particles comprise carbon black and graphite, and the proportion of graphite is at least 50% by weight, based on the total weight of carbon black and graphite contained in the microporous layer, said microporous layer being applied on at least one side of the planar conductive material A). The present invention also relates to a method for manufacturing said gas diffusion layer, a fuel cell comprising said gas diffusion layer, and the use of said gas diffusion layer in a polymer electrolyte membrane fuel cell for reducing the contact resistance at the interface between the microporous layer of the gas diffusion layer and a catalyst layer applied on the polymer electrolyte membrane.

Description

Technical Field

[0001] This invention relates to a gas diffusion layer (GDL) for a polymer electrolyte membrane fuel cell, which reduces the contact resistance at the interface between the microporous layer (MPL) of the gas diffusion layer and a catalyst layer applied to the polymer electrolyte membrane. The invention also relates to a method for manufacturing the gas diffusion layer and a polymer electrolyte membrane fuel cell (PEM fuel cell) comprising the gas diffusion layer. Background Technology

[0002] Fuel cells generate electricity through the chemical reaction of fuel, particularly hydrogen, with oxygen to produce water. In a hydrogen-oxygen fuel cell, hydrogen or a hydrogen-containing gas mixture is supplied to the anode, where electrochemical oxidation occurs to release electrons (H2). 2 H + + 2 e - Protons are transported from the anode to the cathode chamber through a membrane that is airtight and electrically insulating to separate the reaction spaces. Electrons supplied at the anode are guided to the cathode via an external circuit. Oxygen or a mixture of oxygen-containing gases is supplied to the cathode, where oxygen reduction occurs to absorb electrons. The oxygen anions formed in this process react with the protons transported through the membrane to form water (1 / 2 O₂ + 2 H₂). + + 2 e - H2O).

[0003] For many applications, especially in automotive powertrains, low-temperature proton exchange membrane fuel cells (PEMFCs, also known as polymer electrolyte membrane fuel cells) are used. The core of these fuel cells is a polymer electrolyte membrane (PEM), which is sensitive only to protons (or oxonium ions H3O). +The membrane and water are permeable and spatially separate the oxidant (typically oxygen from the air) from the reductant. A catalyst layer is applied to the anode and cathode sides of a hermetically sealed, electrically insulating, proton-conducting membrane. This catalyst layer forms the electrode and typically contains platinum as the catalytically active metal. The actual redox reaction and charge separation occur within the catalyst layer. The membrane and catalyst layer form a unit, also known as a catalyst-coated membrane (CCM). Gas diffusion layers (GDLs) are located on both sides of the CCM, which stabilize the battery structure and facilitate the transport and distribution of reactant gases, water, heat, and current. The membrane, electrodes, and gas diffusion layers form a membrane electrode assembly (MEA). Fluid distribution plates (so-called bipolar plates) are arranged between the MEA assemblies. These fluid distribution plates have channels for supplying process gases to adjacent cathodes and anodes and typically also have internal cooling channels; that is, the GDLs are in direct contact with the bipolar plates in a PEM fuel cell.

[0004] These bipolar plates are mostly metal stamping plates or stamped graphite carbon fiber pads. In the battery, the ridge of the bipolar plate is placed directly on the fiber side (substrate side) of the GDL, which consists of a fiber substrate and a microporous layer, forming a direct contact point with the gas diffusion layer, through which electricity is conducted. Substances (reactant gases oxygen, hydrogen, and water) flow from the channels to the membrane and back from the membrane to the channels through the channels and the porous structure of the gas diffusion layer. Therefore, the gas diffusion layer located between the bipolar plate and the catalyst layer is crucial to the function and performance of the fuel cell. Process components consumed and generated in the electrode reactions must be transported through the gas diffusion layer and uniformly distributed from the macroscopic structure of the bipolar plate to the microscopic structure of the catalyst layer. Electrons generated and consumed in the half-cell reaction must be conducted to the bipolar plate with the smallest possible voltage loss. The heat generated in the reaction must be dissipated into the coolant of the bipolar plate, requiring the GDL material to also have sufficient thermal conductivity. Furthermore, the GDL must also act as mechanical compensation between the macroscopically structured bipolar plate and the catalyst layer. For this purpose, component tolerances must be compensated and compression pressure distributed. GDL also serves as mechanical protection for the electrode membranes that withstand high loads in fuel cells. Therefore, this places high demands on the mechanical properties of GDL.

[0005] Gas diffusion layers (GDLs) for fuel cells typically consist of a carbon fiber substrate, which is usually hydrophobically treated with a fluoropolymer (e.g., PTFE) and subsequently coated with a microporous layer (MPL). The MPL typically comprises a fluoropolymer (e.g., PTFE) as a binder and a porous, conductive carbon material (e.g., carbon black, graphite, graphene, carbon nanotubes (CNTs), carbon nanofibers, or mixtures thereof). Currently, the following three materials are used as carbon fiber substrates for GDLs: - Carbon fiber paper (a wet-laid and chemically bonded carbon fiber nonwoven material containing carbonized chemical binders). - Carbon fiber fabrics (e.g., made of yarns of polyacrylonitrile fibers that have been oxidized but not yet carbonized, which are then carbonized or graphitized after weaving). - Carbon fiber nonwoven materials (e.g., dry-laid, carded and hydroentangled nonwoven materials made of oxidized polyacrylonitrile, which are subsequently calibrated and carbonized).

[0006] DE 10 2021 215 036 A1 describes a polymer electrolyte membrane fuel cell having a GDL and an MPL located thereon, wherein the MPL contains carbon black particles in a polymer binder (such as PTFE). To prevent the non-conductive binder from migrating into the GDL substrate, the MPL has a carbon black content that is gradient along its thickness direction (z-axis).

[0007] JP200859917A describes a method for manufacturing a gas diffusion layer for a fuel cell, which can adjust the hydrophobicity of the fluid distribution plate side to prevent flooding or drying. For this purpose, an MPL coating comprising flake graphite is employed.

[0008] DE 10 2020 121 892 A1 describes a gas diffusion layer for a fuel cell comprising a planar conductive material selected from carbon fiber nonwoven materials, carbon fiber fabrics, and mixtures thereof, wherein the planar material comprises at least one fluoropolymer applied to and / or introduced into the planar material and at least one polymer different therefrom selected from polyetherketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co)polyamide, polyimide, polyamide-imide, polyetherimide, and mixtures thereof, and optionally a microporous layer is applied to one surface of the conductive material.

[0009] Since all components of a battery are typically assembled under pressure, the ridges of the bipolar plates can penetrate to varying degrees into the fiber layers of the gas diffusion layer, depending on the type of carbon fiber substrate, or the shape of the fiber layers can be mechanically altered to varying degrees, for example, by: - Infiltrates at the ridge-basement contact point (gas diffusion layer) and subsequently compresses the gas diffusion layer. - Bend or deform the gas diffusion layer into the channel of the bipolar plate. These two phenomena are directly caused by the mechanical properties of the gas diffusion layer.

[0010] Based on experience, the mechanical properties of the gas diffusion layer largely depend on the type of carbon fiber substrate, which varies between woven, paper, and nonwoven materials. In woven and dry-laid carbonized nonwoven materials, the fibers are mechanically bonded or interwoven by hydroentangling. In paper or wet-laid nonwoven materials, they are chemically bonded by additional resin and subsequently carbonized. While woven materials typically exhibit an ordered structure composed of filaments, nonwoven materials and paper utilize disordered and randomly oriented chopped fibers.

[0011] Therefore, the mechanical properties of the gas diffusion layer directly affect drainage efficiency and pressure distribution in the fuel cell stack. By assembling the gas diffusion layer in a fuel cell stack under pressure, the gas diffusion layer is compressed, particularly in the ridge region. Depending on the mechanical properties of the gas diffusion layer, this affects the contact between the MPL side of the gas diffusion layer and the carbon coating membrane (CCM). Compression of the gas diffusion layer in the ridge region typically causes wavy deformation and bending of the gas diffusion layer within the bipolar channel structure, leading to complete or partial delamination of the MPL side from the CCM, and consequently increasing the contact resistance with the CCM. This, in turn, affects the current density distribution on the surface and significantly reduces the performance and lifespan of the fuel cell (in cases where interlayer delamination extends into the ridge region).

[0012] By reducing the contact area between the gas diffusion layer and the CCM, in the worst case, "bubbles" are generated between these layers, which preferentially fill with water, resulting in what is known as "flooding".

[0013] The contact resistance between the gas diffusion layer (CCM) and the gas diffusion layer largely determines the performance of the fuel cell. A gas diffusion layer with ideal mechanical properties in terms of bending stiffness, compressibility, and maximum contact area with the CCM can significantly reduce the contact resistance between the CCM and the gas diffusion layer, and thus significantly improve the performance of the fuel cell.

[0014] Due to the characteristics of bipolar plates, the ridges are individually designed in terms of spacing, width, angle, and curvature according to the application. Gas diffusion layers with specific (mechanical) properties result in different performance characteristics under different ridge profiles. At the transition from the ridge to the channel, the substrate of the gas diffusion layer is particularly exposed to high pressure. This makes it especially vulnerable to damage to the microporous layer due to fiber breakage or other damage, depending on the radius and angle of the ridge. Broken fibers have particularly sharp edges at the break point and can cause short circuits by penetrating the microporous layer and membrane.

[0015] In existing technologies, solutions to the problem of excessive contact resistance between the CCM and the gas diffusion layer mainly rely on specific bipolar plate designs. However, the impact of such bipolar plate designs on contact with the CCM is largely ignored in existing technologies, i.e., not discussed.

[0016] Therefore, JP 2021 125356 A relates to a fuel cell separator with improved corrosion resistance and conductivity, comprising a substrate having a coating in contact with the fuel cell electrode. The coating comprises Fe3O4. The separator has an electrode-side surface roughness (Sa) of 5 to 100 μm, preferably 10 to 50 μm. The coating is, for example, an electroplated layer or a sintered layer. The substrate is, for example, stainless steel, titanium-based material, or aluminum-based material. The electrode surface in contact with the coating is, for example, made of a carbon-based material. In this case, the contact surface pressure acting between the coating and the electrode surface is 5 MPa or less, preferably 3 MPa or less. The fuel cell is, for example, a solid polymer fuel cell.

[0017] JP 2021 026909 A relates to a fuel cell for suppressing cathode-side pressure loss. The fuel cell includes a cathode separator, a cathode gas diffusion layer, a cathode catalyst electrode layer, an electrolyte layer, an anode catalyst electrode layer, an anode gas diffusion layer, and an anode separator, these components being laminated in this order. The cathode separator has channels allowing cathode gas to flow in the cathode gas diffusion layer. The anode separator has channels allowing anode gas to flow in the anode gas diffusion layer. The cathode gas diffusion layer has higher flexural strength and permeability per unit thickness in the planar direction compared to the anode gas diffusion layer.

[0018] DE 10 2018 202 561 A1 relates to a fuel cell having an ion-selective separator, a gas diffusion layer, and a separator. The separator, together with the gas diffusion layer, forms at least one flow field. At least one channel ridge of the separator separator has an end with a top side and an end face. The end face is configured to split fluid impinging on the end face of the channel ridge along a first direction into two sub-flows. The end face is configured to deflect liquid F impinging on the end face near the top side, such that the liquid F is farther from the top side after deflection than before deflection.

[0019] DE 10 2020 216 101 A1 relates to an electrochemical battery assembly comprising at least one gas diffusion layer (preferably having a microporous layer), a catalyst coating film with a frame, and a bipolar plate, wherein the gas diffusion layer is connected to the catalyst coating film and / or the bipolar plate respectively by means of a preferably conductive adhesive, the adhesive being disposed on the surface of the frame of the catalyst coating film, the bipolar plate, and / or optionally the microporous layer of the gas diffusion layer, and the surface being plasma-functionalized. Furthermore, the present invention relates to a vehicle comprising an electrochemical battery assembly and a method of manufacturing an electrochemical battery assembly. Covalent fixation of the adhesive on the frame of the film, the bipolar plate, or the microporous layer of the gas diffusion layer is achieved through surface plasma functionalization or by pretreatment of the surface by means of plasma, representing a stronger material bonding connection and thus enabling a more secure fixation of the gas diffusion layer to the bipolar plate or the catalyst coating film. Furthermore, the surface can be better wetted with the adhesive. By using the adhesive, the clamping force typically required in electrochemical battery assemblies (which, in particular, can damage the gas diffusion layer) can be significantly reduced, thereby improving gas distribution in the electrochemical battery. The conductive adhesive further improves the electrical contact between the bipolar plate and the gas diffusion layer, reducing contact resistance. Furthermore, the adhesive prevents displacement of the gas diffusion layer or catalyst coating on the bipolar plate during component stacking.

[0020] WO 2022 / 094717 A1 relates to apparatus and methods for providing a desired contact pressure distribution between fuel cell components in a fuel cell stack. In some embodiments, the technology relates to a fuel cell bipolar plate structure and a compression system for a fuel cell stack, which can be used alone or in combination to provide a more uniform contact pressure distribution over the active regions of the fuel cells in the fuel cell stack.

[0021] DE 10 2020 209 811 A1 relates to a method for reducing the contact resistance between a metal separator (e.g., a monopolar or bipolar plate) and a gas diffusion layer of a fuel cell. The separator is at least partially provided with a carbon-based coating. According to the invention, to form the coating, at least one elastomer is added to the carbon as a binder.

[0022] DE 10 2011 006 651 A1 relates to a fuel cell stack with improved freeze-thaw durability. The fuel cell stack specifically includes a gas diffusion layer between the membrane electrode assembly and the bipolar plates. The gas diffusion layer here has a structure that reduces contact resistance in the fuel cell and is cut at a specific angle such that the machine direction (high stiffness direction) of the gas diffusion layer (GDL roll) is not parallel to the main current field direction of the bipolar plates, resulting in an increase in the stiffness of the GDL in the transverse direction perpendicular to the main current field direction of the bipolar plates.

[0023] DE 10 2010 002 392 A relates to a gas diffusion layer (GDL) for fuel cell applications that prevents intrusion into the channels of a bipolar plate. The gas diffusion layer is manufactured by cutting the GDL material at a specific angle such that the inherently high stiffness of the GDL material's machine orientation is not parallel to the main current field direction of the bipolar plate, thereby preventing GDL intrusion into the bipolar plate channels without altering existing gas diffusion layer manufacturing methods. The gas diffusion layer can improve the electrochemical performance of the fuel cell and improve the manufacturing process even with a small width of the wound GDL material.

[0024] US 2018 / 0006314 A1 relates to a bipolar plate for a battery that can improve battery efficiency by reducing contact resistance when in contact with an electrode, and to a redox flow battery comprising such a bipolar plate. According to at least one embodiment, a bipolar plate is provided comprising a conductive thermoplastic material portion formed on at least a portion of the plate for contact with an electrode, wherein the conductive thermoplastic material portion is morphologically matched to the electrode.

[0025] DE 10 2010 020 168 A1 relates to a bipolar plate for reducing the electrical contact resistance between a plate and a diffusion layer in a fuel cell. The opposing surfaces of the plates define flow channels through which upwardly projecting ridges are interspersed. The ridges of the plate form a conductive contact with the diffusion layer in the fuel cell. At least a portion of the conductive contact is composed of a nickel-based alloy, which reduces the contact resistance between the plate and the diffusion layer as a means of improving current density. In one embodiment, the alloy may be used as the primary material of the plate, while in another embodiment, it may be used as a coating deposited on a conventional stainless steel plate.

[0026] KR 101320786 B1 relates to an apparatus for measuring contact resistance and a method for measuring the contact resistance of a bipolar plate in a fuel cell, wherein the contact resistance of each region of the bipolar plate can be measured. This improves the accuracy of contact resistance measurement of the bipolar plate.

[0027] Furthermore, US 2023 / 0163314 A1 relates to a gas diffusion layer for an electrochemical device, comprising a) a first side in contact with a catalyst layer and b) a second side, wherein the first side in contact with the catalyst layer has an increased surface area. A gas diffusion layer with engineered surface roughness and thus an increased surface area improves the efficient diffusion of gaseous reactants in electrochemical devices such as polymer electrolyte membrane fuel cells.

[0028] DE 10 2020 202 433 A1 relates to a method for removing gas diffusion layer surface for a fuel cell, wherein the gas diffusion layer comprises: - A conductive network, - An electrically insulating hydrophobic material surrounding a conductive network for hydrophobicating the conductive network. - An electrode side facing the membrane of the fuel cell, and a bipolar plate side opposite the electrode side and facing the bipolar plate of the fuel cell, wherein the method comprises at least the following steps: a) Provide a gas diffusion layer, b) At least regionally, at least partially remove the electrically insulating hydrophobic material surrounding the conductive network on the bipolar plate side.

[0029] DE 10 2016 200 802 A1 relates to a channel-gas diffusion layer unit for a fuel cell, wherein the channel and gas diffusion layer are formed by a porous body, and the channel-gas diffusion layer unit is arranged between a membrane electrode assembly and a bipolar plate, wherein the porosity of the porous body in the region serving as the channel is greater than the porosity of the porous body in the region serving as the gas diffusion layer. This provides a layered structure for fuel cells that optimizes the contact resistance between components of the layered structure compared to the prior art.

[0030] EP 2722917 A1 relates to a gas diffusion layer for a fuel cell, which should possess high electrical conductivity and good gas permeability, thereby improving performance. The gas diffusion layer has a microporous layer on one surface, comprising a carbon material containing scale-like graphite. To further improve electrical performance and gas permeability, the MPL may further include carbon material embedded as spacers between the graphite layers. The additional carbon material used in the microporous layer can have a diameter of 1000 μm. 2 / g or higher specific surface area. In the embodiments, a coating material comprising flake graphite and carbon black was used to fabricate the microporous layer. To create the gas diffusion layer, the coating material used to form the microporous layer (i.e., the MPL slurry) was not applied directly to the GDL substrate, but rather applied to and cured onto a support. The resulting layered MPL substrate was peeled off from the support and laminated with the GDL substrate. This process is considered crucial to prevent the MPL layer from intruding into the GDL substrate and causing agglomeration. The contact resistance problem between the CCM and GDL and its solutions are not described in this document.

[0031] WO 2023 / 190153 A1 relates to a gas diffusion layer having a microporous layer on at least one side of a conductive porous substrate, wherein the microporous layer comprises carbon black and graphite particles with an aspect ratio of 10 or greater, and the conductive porous substrate is characterized in that the thickness of the portion of the conductive porous substrate in which the microporous layer is embedded is 5% to 20% (inclusive) of the thickness of the portion of the conductive porous substrate in which the microporous layer is not embedded. This reduces the resistance within the gas diffusion layer without impairing the gas diffusion capability. Using such a gas diffusion layer in a fuel cell can improve the power generation performance of the fuel cell.

[0032] The aforementioned existing technologies typically address the problem of high contact resistance by adjusting and optimizing the bipolar plates. For example, roughening the bipolar plates through mechanical methods or coatings to increase the surface area (contact surface with the substrate), bonding them to the GDL using special techniques, or milling the bipolar plates of the anode and cathode complementaryly.

[0033] Only DE 10 2020 202 433 A1, US 2023 / 0163314 A1, DE 10 2016 200 802 A1, and WO2023 / 190153 A1 attempted to resolve the issue by optimizing the GDL.

[0034] DE 10 2020 202 433 A1 and US 2023 / 0163314 A1 increase the surface area of ​​GDL through roughening. However, this does not prevent bending and interlayer delamination within the flow channel.

[0035] - DE 10 2016 200 802 A1 attempts to influence porosity, pore shape, pore size and thermal conductivity by using an additional raw material in another fiber form.

[0036] - WO 2023 / 190153 A1 describes reducing the resistance of GDL, but does not describe preventing GDL from bending into the flow channel or interlayer peeling of MPL.

[0037] Therefore, no solution has been attempted in fuel cells (especially PEMFCs) to address the problem of increased contact resistance between the GDL and CCM by specifically designing the microporous layer (MPL) of the GDL. This increased contact resistance is caused by the bulging and bending of the GDL into the bipolar channel structure and the resulting risk of the GDL peeling off from the CCM. Summary of the Invention

[0038] According to the present invention, this problem is solved by a gas diffusion layer for a fuel cell, the gas diffusion layer comprising: A) A planar conductive material, wherein the planar conductive material comprises at least one fibrous material, wherein the fibrous material is selected from carbon fiber nonwoven materials, carbon fiber paper, carbon fiber fabrics, and mixtures thereof. as well as B) A microporous layer comprising conductive carbon particles in a polymer binder matrix, wherein the conductive carbon particles comprise carbon black and graphite, and the graphite content is at least 50% by weight based on the total weight of carbon black and graphite contained in the microporous layer, the microporous layer being applied to at least one side of the planar conductive material A).

[0039] A preferred embodiment of the present invention is a gas diffusion layer for a fuel cell, the gas diffusion layer comprising: A) A planar conductive material comprising at least one fibrous material, wherein the fibrous material includes carbon fiber nonwoven material. as well as B) A microporous layer comprising conductive carbon particles in a polymer binder matrix, wherein the conductive carbon particles comprise carbon black and graphite, wherein the graphite content is at least 50% by weight based on the total weight of the carbon black and graphite contained in the microporous layer, and the microporous layer is applied to at least one side of the planar conductive material A).

[0040] In fuel cells, compared to prior art gas diffusion layers, the use of the gas diffusion layer according to the present invention results in a decrease in contact resistance at the microporous layer interface of the gas diffusion layer, particularly relative to the catalyst layer applied to the polymer electrolyte membrane of a polymer electrolyte membrane fuel cell, especially in the channel regions of the bipolar plates of the fuel cell, for example, particularly in the central channel region. Surprisingly, by using a combination of carbon black and graphite in the microporous layer, the contact resistance can be significantly improved. The GDL according to the present invention optimizes the mechanical and surface properties of the GDL to address the aforementioned problems.

[0041] Therefore, this invention solves the aforementioned problem by optimizing the ratio of carbon black to graphite in the microporous layer (MPL). This achieves unique mechanical properties in the MPL layer. For example, the incorporation of graphite particles makes the MPL particularly compressible, resulting in exceptionally low contact resistance between the microporous layer and the CCM due to adhesion to the CCM. This "compressible" characteristic can be particularly well described by compression set at 6.0 MPa. Without being bound by theory, it is hypothesized that when a combination of carbon black and graphite is used in the MPL of a GDL, similar to a conventional MPL, although the substrate of the GDL bulges into the bipolar channel after being compressed with other components to form a fuel cell, and the MPL bulges accordingly, the large graphite flakes can spatially compensate for and buffer this bulge while maintaining contact with the CCM.

[0042] In addition to the mechanical properties of the GDL substrate, the properties of the microporous layer can also significantly promote the interaction between the CCM and the MPL. The surface properties of the microporous layer, such as roughness, deformability and elasticity under pressure, and possible contact area, depend significantly on the properties of the materials used, such as carbon particles or binders (e.g., PTFE).

[0043] Depending on the ratio of carbon black to graphite, different properties of microporous layers can be achieved, such as different porosities, pore size distributions, permeability to gases and water, diffusion lengths, electrical and thermal conductivity, mechanical stability, surface roughness, and behavior under pressure (e.g., MPLs can be pressure-sensitive).

[0044] To describe the dependency between channel characteristics and the aforementioned mechanical properties of the GDL, a measurement method, known as fringe measurement, was also developed. This will be described in more detail below.

[0045] Rigidly compressed material bends into the bipolar plate channels along the Z-axis while maintaining its thickness. This can cause the MPL side to lose contact with the CCM or experience interlaminar delamination. Increased contact resistance is observed at this site (channel) in these materials. A further consequence may be a decrease in current density. Interlaminar delamination at the channel site can also progress to the entire surface, leading to a further accelerated performance degradation and a shortened fuel cell lifetime. Furthermore, the wavy deformation of the gas diffusion layer into the bipolar plate channels can reduce the contact area between the bipolar plate and the gas diffusion layer, potentially increasing the electrical contact resistance between these two components.

[0046] In contrast, the pressure-sensitive, compressible, and highly flexible gas diffusion layer can flexibly respond to different pressure conditions on its surface. Although the gas diffusion layer is also compressed at the contact point with the ridge and bends into the channel on the substrate side, it has sufficient flexibility to maintain contact with the CCM on the MPL side and prevent interlayer delamination at that location. This ensures sufficiently low contact resistance.

[0047] This invention relates to a method for manufacturing such a gas diffusion layer, wherein... i) The fibrous material is coated and / or impregnated with a preferably aqueous composition, and subsequently dried and / or sintered to obtain the planar conductive material A), wherein the composition comprises the at least one polymer and optionally further components, and the sintering is achieved by heat treatment at a temperature of 250°C to 500°C, preferably 300°C to 450°C, especially 350°C to 450°C, and subsequently... ii) The planar conductive material A) is coated with a preferably water-based composition, and then dried and / or sintered to obtain the microporous layer, wherein the composition comprises the conductive carbon particles and the polymer binder, and the sintering is achieved by heat treatment at a temperature of 250°C to 500°C, preferably 300°C to 450°C, and especially 350°C to 450°C.

[0048] In this application, the terms "sintering" and "performing sintering" are used synonymously.

[0049] The present invention also relates to a fuel cell comprising at least one such gas diffusion layer, wherein the fuel cell is typically a polymer electrolyte membrane fuel cell.

[0050] Accordingly, the present invention also relates to the use of such gas diffusion layers in fuel cells (preferably polymer electrolyte membrane fuel cells).

[0051] Furthermore, the present invention relates to the use of such a gas diffusion layer in a polymer electrolyte membrane fuel cell for reducing the contact resistance at the interface between the microporous layer of the gas diffusion layer and the catalyst layer applied to the polymer electrolyte membrane, particularly in the channel region of the bipolar plate of the fuel cell, especially at the interface in the central region of the channel.

[0052] Furthermore, the present invention relates to the use of conductive carbon particles comprising carbon black and graphite in the microporous layer of a gas diffusion layer, preferably as defined above, for reducing the contact resistance at the interface between the microporous layer of the gas diffusion layer and the catalyst layer applied to the polymer electrolyte membrane of a polymer electrolyte membrane fuel cell, particularly in the channel region of the bipolar plate of the fuel cell, especially at the interface in the central region of the channel.

[0053] Furthermore, the present invention relates to the use of polymers selected from polyaryletherketones, polyphenylene sulfides, polysulfones, polyethersulfones, semi-aromatic (co)polyamides, polyimides, polyamide-imides, polyetherimides, and mixtures thereof (preferably polyaryletherketones such as polyetheretherketones) in and / or on the fibrous material of the gas diffusion layer for reducing the contact resistance at the interface between the gas diffusion layer (if present, its MPL) and the catalyst layer applied to the polymer electrolyte membrane of a polymer electrolyte membrane fuel cell, particularly in the channel region of the bipolar plate of the fuel cell, for example, particularly at the interface in the central region of the channel. The fibrous material preferably comprises carbon fiber nonwoven fabric. Particularly preferably, the gas diffusion layer is defined as described above.

[0054] Surprisingly, when such polymers are used in and / or on the fibrous material of the gas diffusion layer (GDL), the GDL bulges less or not at all into the channels of the bipolar plate. This improves the adhesion of the GDL to the CCM and, in particular, prevents or at least mitigates the interlayer peeling of the GDL (i.e., its MPL, if present) from the CCM. This results in a lower contact resistance at the interface between the GDL and the CCM. Therefore, by impregnating and / or coating the fibrous material with such polymers, the adhesion behavior of the GDL can also be suitably adapted to specific channel geometries.

[0055] Preferred embodiments of the gas diffusion layer and fuel cell according to the invention, the method for manufacturing the gas diffusion layer according to the invention, and the uses according to the invention are described in the dependent claims. Unless otherwise stated, preferred embodiments of any of the above inventions are also preferred embodiments of other inventions.

[0056] Gas diffusion layer The planar conductive material and gas diffusion layer used in this invention are planar structures having a substantially two-dimensional planar extension and a relatively smaller thickness. The gas diffusion layer has a bottom surface, which typically largely corresponds to the bottom surface of the adjacent membrane with the catalyst layer and the bottom surface of the adjacent bipolar plate of the fuel cell. The shape of the bottom surface of the gas diffusion layer can be, for example, a polygon (n-sided, where n ≥ 3, such as a triangle, square, pentagon, hexagon, etc.), a circle, a segmented circle (e.g., a semicircle), an ellipse, or a segmented ellipse. Preferably, the bottom surface is rectangular or circular.

[0057] The gas diffusion layer for fuel cells according to the present invention comprises A) a planar conductive material comprising at least one fibrous material, wherein the fibrous material comprises carbon fiber nonwoven fabric, and B) a microporous layer comprising conductive carbon particles in a polymer binder matrix, wherein the conductive carbon particles comprise carbon black and graphite, and the graphite content is at least 50% by weight based on the total weight of the carbon black and graphite contained in the microporous layer. Carbon fiber nonwoven fabric is advantageous, one reason being its compressive elasticity and its ease of manufacture on a large industrial scale (e.g., in roll-to-roll processes).

[0058] The conductive carbon particles used vary significantly. Carbon particles in the form of carbon black largely have a disordered structure. These particles typically consist of aggregates of extremely small, spherical primary particles, with diameters typically in the lower nanometer range of 5 to several hundred nm, for example, above 10 nm to about 100 nm, depending on the production conditions. Such aggregates, typically with diameters of at most a few μm, can be at least partially broken up during processing (e.g., dispersion in water) due to shear forces, resulting in smaller particles. Carbon black powder typically has particles (aggregates) with D90 values ​​of at most a few μm (especially up to 500 nm), which are determined by static light scattering at 25 °C using a Mastersizer 2000 instrument from Malvern Instruments (where wet measurement in distilled water can be performed, or preferably dry measurement). In this application, the D90 value of the integral volume distribution is defined as the particle diameter, where 90% (by volume) of the particles have a diameter smaller than the diameter corresponding to the D90 value. In dispersions, the measured particle size is usually significantly smaller due to the breakup of agglomerates.

[0059] Graphite is a natural form of carbon with a unique hexagonal crystal structure arranged in multiple parallel planes (i.e., graphene layers). Therefore, graphite is sheet-like. This anisotropic structure endows graphite with special properties, such as electrical conductivity and exceptional strength along the layers, as well as easy separability and good sliding and lubrication properties. Therefore, graphite is relatively stable during processing. Graphite is further classified into natural and synthetic forms. In graphite powder, graphite typically exists primarily in the form of basic particles. The particles present in the powder typically have a particle size greater than 500 nm, preferably in the µm range. The D90 value is typically significantly higher than 1 µm, each determined by static light scattering at 25 °C using a Mastersizer 2000 instrument from Malvern Instruments (where wet measurements in distilled water can be performed, or preferably dry measurements). In this application, the D90 value of the integral volume distribution is defined as the particle size, where 90% (by volume) of the particles have a diameter smaller than the diameter corresponding to the D90 value.

[0060] According to the present invention, the fuel cell preferably includes a polymer electrolyte membrane on which a catalyst layer is applied, wherein the catalyst layer can be in contact with the surface of the microporous layer of the gas diffusion layer.

[0061] Planar conductive material A) According to the present invention, the fiber material preferably has a content of 15 to 400 g / m². 2Preferred concentration: 20 to 300 g / m 2 More preferably 30 to 150 g / m 2 And especially 40 to 120 g / m 2 (e.g., 50 to 100 g / m) 2 The weight per unit area of ​​the fiber material. In this application, the mass or total weight of the fiber material refers to the untreated fiber material, i.e., the mass or total weight of components that do not contain any polymers or other additives.

[0062] The fiber material preferably has a thickness in the range of 50 to 500 µm, and particularly preferably in the range of 100 to 400 µm. This thickness refers to the unprocessed, uncompressed state of the fiber material, i.e., before the GDL is installed into the fuel cell.

[0063] The fibers contained in the fibrous material include carbon fibers (carbon fibers), which include carbon fiber nonwoven materials, and optionally various other fibers, preferably selected from glass fibers, fibers of organic polymers (e.g., polypropylene, polyester, polyphenylene sulfide, polyetherketone), and mixtures thereof. In particular, the fibers contained in the fibrous material consist only of carbon fibers.

[0064] The carbon fibers can be manufactured using conventional methods, preferably using polyacrylonitrile fibers (PAN fibers) as the starting material. PAN fibers are prepared by free radical polymerization of a monomer composition, preferably containing at least 90% by weight of acrylonitrile based on the total weight of the monomers used for polymerization. The resulting polymer solution is spun into filaments and bundled into tows, for example, by wet spinning and coagulation. Before converting the PAN precursor into carbon fibers at high temperatures, the PAN precursor is typically subjected to oxidative cyclization (also simply called oxidation) in an oxygen-containing atmosphere at elevated temperatures of about 180 to 300 °C. The resulting chemical crosslinking improves the steric stability of the fibers. Subsequent actual pyrolysis is carried out at a temperature of at least 1200 °C to form carbon fibers. For the pyrolysis process, starting fibers or pre-formed planar fiber materials can be used depending on the shape of the target fiber material. Carbonization and graphitization can be distinguished based on the temperature during pyrolysis. Carbonization refers to treatment in an inert gas atmosphere at about 1200 to 1500 °C to release volatile products. So-called high-modulus fibers or graphite fibers are obtained by graphitization (i.e., heating to approximately 2000 to 3000 °C under an inert gas). These fibers are characterized by high purity, light weight, high strength, and very good electrical and thermal conductivity.

[0065] According to the present invention, the fibrous material is selected from carbon fiber nonwoven materials, carbon fiber paper, carbon fiber fabrics, and mixtures thereof. Preferably, the fibrous material is a carbon fiber nonwoven material (i.e., the fibrous material is composed of the carbon fiber nonwoven material). More preferably, the fibrous material is composed of carbon fiber paper. In an alternative embodiment, the fibrous material is a combination of carbon fiber nonwoven material and carbon fiber fabric or carbon fiber paper.

[0066] Carbon fiber fabrics are manufactured by interlacing two sets of yarn systems: warp yarns and weft yarns. As with textiles, the fiber bundles are flexibly but non-detachably connected to each other. Carbon fiber fabrics are preferably made from PAN fibers that have been oxidized but not yet carbonized or graphitized. To impart electrical conductivity to the fiber material, carbonization or graphitization is performed after weaving.

[0067] Carbon fiber paper is typically manufactured using oxidized PAN fibers. The oxidized PAN fibers are pulverized into fiber fragments in a manner known per se, forming a pulp, and then, analogous to papermaking, are sieved (handmade papermaking) to create a fiber layup and dried. In a preferred embodiment, at least one binder is additionally introduced into the paper. Suitable binders include, for example, phenolic resins, furan resins, and polyimide resins. To introduce the binder, the paper can be impregnated with the binder, and subsequently cured, if appropriate. After impregnation and curing, the carbon fiber paper is carbonized / graphitized again to also convert the binder into a compound with improved conductivity. In another suitable embodiment, a filled carbon fiber paper is used to provide the fiber material. The manufacturing process is initially carried out as described above; however, instead of introducing the binder and performing carbonization / graphitization, a filler consisting of carbon materials is introduced into the still-wet paper in a polymer binder. In particular, a carbon-PTFE filler is used for this purpose. This filler increases thermal and electrical conductivity to the point that carbonization / graphitization can be omitted.

[0068] To manufacture carbon fiber nonwoven materials, unoxidized or oxidized PAN fibers can be used. In a first preferred embodiment, the fibers are dry-laid into a fiber web (already combed) in a first step and then cured into a nonwoven material. This can be done, for example, by hydroentangling, where the carbon fibers are oriented, entangled, and thus mechanically stabilized. If necessary, the thickness of the cured nonwoven material can be calibrated to the desired value. Nonwoven materials based on unoxidized PAN fibers are first oxidized at elevated temperatures and in an oxygen atmosphere after web laying and curing, and then carbonized / graphitized in an inert gas atmosphere. Nonwoven materials based on oxidized PAN fibers are only carbonized / graphitized after web laying and curing. The carbon fiber nonwoven material manufactured by dry-laying the fibers into a fiber web in the first step is a preferred embodiment of the invention.

[0069] In a preferred embodiment, the fibrous material contains at least one polymer applied to and / or introduced into the fibrous material. For this purpose, the fibrous material can be equipped with the polymer component and, where appropriate, further additives using common application and impregnation processes.

[0070] Preferably, the polymer a1) comprises at least one fluoropolymer, preferably selected from polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), perfluoroalkoxy polymer (PFA), and mixtures thereof. The perfluoroalkoxy polymer is, for example, a copolymer of tetrafluoroethylene (TFE) and perfluoroalkoxy vinyl ether (such as perfluorovinyl propyl ether). Particularly preferably, the fluoropolymer a1) comprises (especially the fluoropolymer a1) polytetrafluoroethylene. Component a1) can be used to increase the hydrophobicity of the fibrous material.

[0071] Preferably, based on the mass of the fiber material, the mass fraction of the fluoropolymer a1) is 0.5 to 40%, preferably 1 to 20%, and particularly 1 to 10%. In a particular embodiment, the fluoropolymer a1) is PTFE, and based on the mass of the fiber material, the mass fraction of the PTFE is 0.5 to 40%, preferably 1 to 20%, and particularly 1 to 10%.

[0072] Preferably, the polymer a1) comprises various polymers a2) selected from the following: polyaryletherketone (PAEK), polyphenylene sulfide (PPS), polysulfone (PSU), polyethersulfone (PES), semi-aromatic (co)polyamide (high-temperature polyamide, HTPA), polyimide (PI), polyamide-imide (PAI), polyether-imide (PEI), and mixtures thereof (blends). Using this component a2) in and / or on a fibrous material of a gas diffusion layer can result in a reduction in the contact resistance at the interface between the gas diffusion layer and a catalyst layer applied to the polymer electrolyte membrane of a polymer electrolyte membrane fuel cell, particularly in the channel region of the bipolar plate of the fuel cell, for example, particularly in the region at the center of the channel.

[0073] Specifically, polymer component a2) comprises at least one polyaryletherketone. Polyaryletherketones are semi-crystalline thermoplastics having an alternating structure in which an aryl group is followed by either a ketone (carbonyl) or an ether group, wherein the ratio of ketone to ether groups is variable and may differ in terms of the substitution pattern on the aromatic ring. Suitable polyaryletherketones a2) are polyetherketones (PEK), polyetheretherketones (PEEK), polyetherketoneketones (PEKK), etc. Preferably, polymer component a1) comprises at least one polyetheretherketone, and in particular, polymer component a1) is composed of at least one polyetheretherketone.

[0074] Suitable semi-aromatic (co)polyamides (a2) are polymers particularly known as high-temperature polyamides (HTPA). These are semi-crystalline or amorphous, thermoplastic, semi-aromatic polyamides. Preferably, these contain at least one copolymerized aromatic dicarboxylic acid, particularly selected from terephthalic acid, isophthalic acid, and mixtures of terephthalic acid and isophthalic acid. Preferred semi-aromatic (co)polyamides (a2) are selected from PA6.T, PA10.T, PA12.T, PA6.I, PA10.I, PA12.I, PA6.T / 6.I, PA6.T / 6, PA6.T / 10T, PA10.T / 6.T, PA6.T / 12T, PA12.T / 6.T, and mixtures thereof. Another particular embodiment of polyamide (a2) is polyphthalamide (PPA).

[0075] Suitable polyimides (a2) are polysuccinimide (PSI), polybismaleimide (PBMI), polyimide sulfone (PISO), and polymethacrylimide (PMI).

[0076] Suitable polymers (a2) can also be (semi)aromatic polyesters (such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT)), polycarbonate (PC), and heat-resistant melamine (such as melamine foam filled with nanoporous SiO2 aerogel).

[0077] Preferably, polymer a2) as defined above is selected from so-called high-performance plastics, which are characterized by properties such as high glass transition temperature, high melting temperature, good temperature resistance, good chemical resistance, and good mechanical properties. Preferably, polymer a2) has a continuous operating temperature (sustained use temperature) of at least 150 °C. Preferably, polymer a2) is a semi-aromatic or aromatic polymer. Preferably, polymer a2) is a thermoplastic.

[0078] Preferably, based on the mass of the fiber material a), the mass fraction of the polymer a2) is 0.5% to 40%, preferably 1% to 20%. In a particular embodiment, the polymer a2) is PEEK, and based on the mass of the fiber material, the mass fraction of the PEEK a2) is 0.5% to 40%, preferably 1% to 20%.

[0079] In a particularly preferred embodiment, the polymer a1) comprises at least one fluoropolymer and / or at least one polymer a2) different from a1) (as defined above) in order to simultaneously achieve suitable hydrophobicity of the fibrous material and the reduced contact resistance as described above.

[0080] Preferably, based on the total weight of the fluoropolymer a1) and the polymer a2) which is different from a1), the proportion of the fluoropolymer a1) is 10 to 100% by weight, preferably 20 to 90% by weight, more preferably 30 to 80% by weight, still more preferably 40 to 75% by weight, for example, particularly 40 to 60% by weight or 60 to 75% by weight.

[0081] If a bonded fiber material is used as the fiber material, the bonded fiber material is specifically selected from mechanically bonded fiber materials. Chemical bonding (especially using carbonizable polymer binders) may adversely affect the bending properties of the gas diffusion layer. In particular, the fiber material used according to the invention does not contain polymers other than polymers a1) and a2) added as binders.

[0082] In one embodiment of the invention, the fibers are wet-laid in a first step. In this embodiment, the concept of carbon fiber nonwoven material subsequently also includes, for example, a wet-laid material composed of chopped carbon fibers, carbon black, at least one polymer (a1) (particularly PTFE), and at least one polymer (a2) (particularly PEEK). Unlike carbon fiber paper known in the prior art, the wet-laid fiber material used according to the invention contains no or only a very low proportion of phenolic resin as a binder. Preferably, the mass fraction of phenolic resin, based on the weight of the fiber material, is 0 to 10%, preferably 0 to 5%, and particularly 0 to 1%.

[0083] In many cases, the fibrous material already possesses good electrical and thermal conductivity even without additives to improve conductivity, due to the use of carbon fibers. However, to further improve electrical and thermal conductivity, the fibrous material can be additionally equipped with at least one conductivity-enhancing additive (a3). Preferably, the conductivity-enhancing additive (a3) ​​is selected from metal particles, carbon black, graphite, graphene, carbon nanotubes (CNTs), carbon nanofibers, and mixtures thereof. Preferably, the conductivity-enhancing additive (a3) ​​comprises or is composed of carbon black. The fibrous material can be equipped with at least one conductivity-enhancing additive (a3), for example, together with a polymer (e.g., polymer a1 and / or a2) and / or other additives. Preferably, an aqueous dispersion is used to equip the fibrous material.

[0084] Preferably, the conductivity-enhancing additive a3) has a mass fraction of 0.5% to 45%, more preferably 1% to 25%, based on the mass of the fiber material. In a particular embodiment, the conductivity-enhancing additive a3) comprises or is composed of carbon black, and the mass fraction is 0.5% to 45%, more preferably 1% to 25%, based on the mass of the fiber material.

[0085] In a preferred embodiment, the fiber material contains, by weight of components a1), a2), and a3), at least 10 to 50 wt%, preferably 20 to 40 wt%, of at least one fluoropolymer a1), 0 to 40 wt%, of at least one polymer a2 different from a1), and at least 20 to 90 wt%, preferably 50 to 80 wt%, of at least one conductive additive a3. Here, by weight of the fiber material, the total weight of components a1), a2), (if present), and a3) is 3 to 50 wt%, preferably 5 to 35 wt%, particularly 10 to 25 wt%.

[0086] In one embodiment, the fiber material further comprises at least one additive a4) applied to and / or introduced into the fiber material, said additive a4) being selected, for example, from polymer binders a41 (such as furan resins, polyimide resins), surfactants a42, and further additives and auxiliaries a43, which are different from polymers a1) and a2) as defined above.

[0087] The fibrous material may be prepared with at least one further additive a4, for example, together with a polymer (such as polymer a1) and / or a2) and / or other additives. If necessary, the binder a41) may then be cured. This may be done, for example, together with drying and / or sintering after the fibrous material is prepared with a polymer (such as polymer a1) and / or a2), or it may be done separately from the drying and / or sintering.

[0088] Preferably, the total mass fraction of the further additive a4) is 0 to 80%, preferably 0 to 50%, based on the mass of the fiber material. If the fiber material further contains at least one other additive a4), the total mass fraction of the further additive a4) is 0.1 to 80%, preferably 0.5 to 50%, based on the mass of the fiber material.

[0089] Specifically, in addition to the fluoropolymer a1) and the polymer a2), the fibrous material comprises a variety of other polymers a41), which are applied thereon and / or introduced therein at a weight ratio of up to 5%, preferably up to 1%, particularly preferably up to 0.5%, and especially up to 0.1% (based on the total weight of the fibrous material). More specifically, the fibrous material does not contain any other polymers a41 different from the fluoropolymer a1) and the polymer a2). This is particularly applicable to the polymer binder a41), which undergoes carbonization under the manufacturing conditions of the planar conductive material A).

[0090] The fibrous material can be coated with polymer components such as polymers a1) and / or a2) and, depending on the circumstances, other components such as a3) and / or a4) by common methods. Suitable coating and impregnation processes are described in more detail below. To manufacture the planar conductive material A) according to the invention, the coated and / or impregnated fibrous material is subsequently dried and / or sintered, preferably dried and sintered, which is also described in more detail below. The bonding effect of the polymer is achieved by the sintering. The sintering step can also be carried out without a pre-drying step. However, a pre-drying step is preferred, as it promotes a more uniform distribution of binder in the sintered product of the planar conductive material A).

[0091] Accordingly, this application also relates to a gas diffusion layer according to the invention as defined above, wherein the planar conductive material A) is obtained by coating and / or impregnating the fibrous material with a preferably aqueous composition, and subsequently drying and / or sintering the coated and / or impregnated fibrous material, preferably drying and sintering, wherein the composition contains at least one polymer and, if applicable, other components, wherein the sintering is performed by heat treatment at a temperature of 250 °C to 500 °C, preferably 300 °C to 450 °C, and particularly 350 °C to 450 °C. Accordingly, the gas diffusion layer preferably comprises a planar conductive material A) obtained by drying the coated and / or impregnated fibrous material. Also preferably, the gas diffusion layer comprises a sintered product of the planar conductive material A) obtained by heat treatment at a temperature of 250 °C to 500 °C, preferably 300 °C to 450 °C, and particularly 350 °C to 450 °C. The finished weight of the preferred aqueous composition, i.e., the mass of solid material used based on the mass of the unfinished fibrous material, is typically 5 to 25%, preferably 10 to 20%, for example about 15%.

[0092] Method for manufacturing planar conductive material A) In the first step of the method according to the invention, at least one fibrous material is provided, said fibrous material comprising carbon fiber nonwoven fabric. Preferably, said fibrous material is composed of carbon fiber nonwoven fabric. In an alternative embodiment, said fibrous material is a combination of carbon fiber nonwoven fabric and carbon fiber woven fabric or carbon fiber paper. The foregoing statements refer entirely to suitable and preferred fibrous materials.

[0093] In the second step, the fibrous material provided in the first step is coated and / or impregnated with a preferred aqueous composition containing a polymer, such as at least one fluoropolymer a1) and / or at least one polymer a2 different from a1) (each as defined above), and other additives as appropriate. The preferred aqueous composition may be present in the form of a dispersion or a solution. Typically, it is present in the form of an aqueous dispersion.

[0094] The fibrous material is coated and / or impregnated using common application methods known to those skilled in the art. Preferably, the fibrous material is coated and / or impregnated using a method selected from padding, scraping, spraying, smearing, and combinations thereof.

[0095] During the impregnation process, the fibrous material is passed through an impregnation mill (impregnation tank) containing a solution or dispersion of additives, and then extruded through a pair of pressure-adjustable and, depending on the situation, gap-adjustable rollers to apply the required amount of additives.

[0096] In the coating method, gravure printing and screen printing are distinguished. In gravure printing, a steel strip with or without a supporting squeegee is used as a squeegee. It is used to scrape off excess solution or dispersion containing additives from the squeegee of the printing roller (i.e., scraping). In contrast, in screen printing, the squeegee is typically made of rubber or plastic with sharp or rounded ground edges.

[0097] In spray application, the solution or dispersion containing the additive is applied to the fibrous material to be treated using a slit nozzle.

[0098] The kiss-roll method is used to coat the underside of a horizontally running web of fabric. The coating medium can be applied to the fabric web in either the reverse or forward direction. Indirect coating with a small application amount can be achieved using a transfer roller.

[0099] In one particular embodiment, according to the invention, the padding method is used to finish cleaning products.

[0100] In the third step of the process according to the invention, the coated and / or impregnated fibrous material is dried and / or sintered, preferably dried and sintered, to obtain the planar conductive material A. Suitable methods for drying fibrous materials such as nonwoven materials or fabrics coated and / or impregnated with solutions or dispersions containing additives are known in principle. For example, after applying the method, at least a portion of the solvent, particularly water, can be drawn out of the fibrous material by passing it, for example, through a suction opening, and the liquid can be discharged from the suction opening by an applied negative pressure. Alternatively or supplementarily, the fibrous material can be dried at an increased temperature. Furthermore, the drying can be carried out under reduced pressure. Preferably, the drying of the fibrous material is carried out at a temperature in the range of 20 to 250 °C, particularly preferably 40 to 200 °C.

[0101] Furthermore, either after drying or as an alternative to drying, the coated and / or impregnated fibrous material may be sintered in a third step. The sintering is preferably carried out by heat treatment at a temperature of 250 °C to 500 °C, preferably 300 °C to 450 °C, and particularly 350 °C to 450 °C.

[0102] Microporous layer B): According to the invention, the microporous layer (MPL) contains conductive carbon particles in a matrix composed of a polymer binder. To reduce contact resistance, as described above, the conductive carbon particles comprise carbon black and graphite, wherein the graphite proportion is at least 50% by weight based on the total weight of the carbon black and graphite contained in the microporous layer. It is applied to at least one surface of the planar conductive material A), i.e., applied to at least one side. In a preferred embodiment, it is applied to only one surface of the planar conductive material A). In another alternative embodiment, it is applied to both surfaces of the planar conductive material A. Alternatively, an MPL according to the invention may be applied to one surface of the planar conductive material A, and a non-invention MPL may be applied to the other surface of the planar conductive material A. The non-invention MPL contains conductive particles, typically conductive carbon particles, preferably carbon black and / or graphite, in a polymer binder matrix (such as the aforementioned preferred fluoropolymer, particularly polytetrafluoroethylene (PTFE)). Typically, only one MPL is applied to one surface of the planar conductive material A, because this creates a porosity gradient within the resulting GDL. This facilitates both the supply of fuel gas to the catalyst layer in a fine distribution and the discharge of combustion gases (in the form of water).

[0103] In a further alternative embodiment, an MPL according to the invention may be combined with an MPL not according to the invention on at least one surface of the planar conductive material A).

[0104] The microporous layer according to the invention may further contain conductive particles, preferably carbon particles, such as graphene, carbon nanotubes (CNTs), carbon nanofibers or mixtures thereof.

[0105] In a preferred embodiment of the MPL according to the invention, the total weight of carbon black and graphite contained in the microporous layer is at least 50%, preferably at least 90%, more preferably at least 95%, and particularly 100%, based on the total weight of the conductive carbon particles contained in the MPL.

[0106] The polymer binder of the MPL preferably comprises at least one fluoropolymer. The fluoropolymer is preferably selected from polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer, perfluoroalkoxy polymers, and mixtures thereof. Polytetrafluoroethylene (PTFE) is preferred.

[0107] In a preferred embodiment, the graphite content of the microporous layer is 50 to 90 wt%, more preferably 60 to 85 wt%, and particularly 65 to 80 wt%, for example 70 to 75 wt%, based on the total weight of carbon black and graphite contained in the microporous layer. As the graphite content of the MPL increases, as described above, the contact resistance at the interface between the MPL of the gas diffusion layer and the catalyst layer applied to the polymer electrolyte membrane further decreases. However, when the graphite content in the MPL is very high, its thermal conductivity and electrical conductivity, as well as the permeability of the GDL according to the Gurley method, typically deteriorate.

[0108] Preferably, the microporous layer contains 10 to 45% by weight, preferably 15 to 40% by weight, of carbon black, based on the total weight of the microporous layer. Preferably, the microporous layer contains 30 to 80% by weight, preferably 40 to 70% by weight, of graphite, based on the total weight of the microporous layer. Preferably, the microporous layer contains 10 to 45% by weight, preferably 15 to 40% by weight, of carbon black and 30 to 80% by weight, preferably 40 to 70% by weight, respectively, based on the total weight of the microporous layer.

[0109] In another preferred embodiment, the microporous layer contains 5 to 50% by weight, preferably 15 to 30% by weight, and particularly 20 to 25% by weight, of the polymer binder, based on the total weight of the microporous layer. In another preferred embodiment, the microporous layer contains a total of 40 to 95% by weight, preferably 60 to 90% by weight, and particularly 70 to 80% by weight, of carbon black and graphite, based on the total weight of the microporous layer. In another preferred embodiment, the microporous layer contains 5 to 50% by weight, preferably 15 to 30% by weight, and particularly 20 to 25% by weight, of the polymer binder, and a total of 40 to 95% by weight, preferably 60 to 90% by weight, and particularly 70 to 80% by weight, of carbon black and graphite, based on the total weight of the microporous layer.

[0110] In one particular embodiment, the MPL contains at least one pore-forming agent. Suitable pore-forming agents are commercially available plastic granules, such as those made of polymethyl methacrylate (PMMA). Suitable particle sizes are in the range of 10 to 100 μm.

[0111] The loading amount of the microporous layer is preferably 10 to 50 g / m 2 More preferably 10 to 30 g / m 2 And especially 15 to 25 g / m 2 .

[0112] Accordingly, the microporous layer B) preferably has a thickness of 5 to 150 µm, particularly preferably in the range of 10 to 100 µm. This thickness refers to the uncompressed state of the microporous layer B), i.e., before the GDL is installed into the fuel cell.

[0113] In contrast to the macroporous planar conductive material A), the MPL B) is microporous, with a pore size typically significantly smaller than 5 micrometers, preferably up to 900 nm, particularly preferably up to 500 nm, and especially up to 300 nm. The pore size distribution can be determined using a mercury porosimeter, as described in DIN ISO 15901-1:2019-03: Mercury Porosimeter. The pore size can have a bimodal or multimodal distribution curve. Therefore, when using a mixture of carbon black and graphite, a pore size distribution with multiple peaks can be obtained.

[0114] The presence of the MPL has a significant impact on the water balance of the fuel cell. Due to the high proportion of polymer binders such as PTFE and the small pore size of the MPL, the MPL acts as a liquid water barrier, making it difficult to submerge the GDL and the electrode, thereby facilitating the mass transfer of gaseous reactants to the catalyst.

[0115] The microporous layer, as measured according to DIN 4768-1:1974-08, preferably has an arithmetic mean roughness R of up to 10 μm, more preferably up to 5 µm. a .

[0116] Furthermore, the microporous layer, as measured according to DIN 4768-1:1974-08, preferably has an average roughness depth R of up to 60 μm, more preferably up to 30 µm. z .

[0117] Methods for manufacturing microporous layers B) According to the present invention, in order to manufacture the microporous layer B), the planar conductive material A) is typically coated with a preferred aqueous composition containing the conductive carbon particles and the polymer binder, and then the coated material A) is dried and / or sintered, preferably dried and sintered.

[0118] The MPL (B) can be coated onto the planar conductive material (A) in various ways. While spraying, screen printing, or the Meyer-Rod method is frequently used in batch manufacturing, scraping, slit nozzle, and roller processes are preferred for continuous coating.

[0119] Suitable drying methods are known in principle. For example, drying can be carried out at elevated temperatures. Furthermore, the drying can be performed under reduced pressure. Preferably, the drying is carried out at temperatures ranging from 20 to 250 °C, particularly preferably from 40 to 200 °C, for example, in the range of 100 to 200 °C.

[0120] The sintering is performed by heat treatment at temperatures ranging from 250 °C to 500 °C, preferably from 300 °C to 450 °C, and particularly from 350 °C to 450 °C. The binding of the polymer is achieved through sintering. The sintering step can also be performed without a pre-drying step. However, a pre-drying step is preferred, as it promotes a more uniform distribution of the binder in the sintered MPL (B) product.

[0121] Therefore, this application also relates to a gas diffusion layer as defined above according to the invention, wherein the microporous layer B) can be obtained by coating the planar conductive material A) with a preferred aqueous composition containing the conductive carbon particles and the polymer binder, and subsequently drying and / or sintering the coated material A), wherein the sintering is performed by heat treatment at a temperature of 250 °C to 500 °C, preferably 300 °C to 450 °C, and particularly 350 °C to 450 °C.

[0122] The particle size values ​​D10, D50, and D90 for graphite and carbon black can be determined according to ISO 13320:2020-01 (particle size analysis – laser diffraction). In a preferred embodiment, the particle size value D10 of the graphite is typically 0.5 to 15 μm, preferably 1 to 10 μm, and especially 3 to 7 μm, and the D10 value is determined by static light scattering at 25 °C using a Mastersizer 2000 instrument from Malvern Instruments. In another preferred embodiment, the particle size value D50 of the graphite is typically 1 to 50 μm, preferably 2 to 30 μm, and especially 10 to 25 μm, and the D50 value is determined by static light scattering at 25 °C using the Mastersizer 2000 instrument. In another preferred embodiment, the graphite particle size D90 is typically 2 to 100 μm, preferably 5 to 70 μm, and especially 30 to 60 μm, and is determined by static light scattering at 25 °C using the Mastersizer 2000 device. The determination of the particle size using static light scattering at 25 °C using the Mastersizer 2000 device is performed by a wet method, typically with the addition of distilled water. In this application, the D10, D50, or D90 values ​​of the integral volume distribution are defined as the diameter of particles representing 10%, 50%, or 90% of the volume percentage that is smaller than the diameter corresponding to the D10, D50, or D90 values.

[0123] Preferably, the graphite has a density of 0.5 to 50 μm as determined according to ISO 9277:2010. 2 Within the range of / g, preferably from 1.0 to 25 m 2 BET specific surface area within the range of / g.

[0124] In another preferred embodiment, the carbon black has a particle size D10 that is typically 5 to 50 nm, preferably 10 to 30 nm, and the D10 value is determined by static light scattering at 25 °C using the Mastersizer 2000 instrument. In another preferred embodiment, the carbon black has a particle size D50 that is typically 20 to 200 nm, preferably 50 to 150 nm, and the D50 value is determined by static light scattering at 25 °C using the Mastersizer 2000 instrument. In another preferred embodiment, the carbon black has a particle size D90 that is typically 40 to 500 nm, preferably 80 to 300 nm, and the D90 value is determined by static light scattering at 25 °C using the Mastersizer 2000 instrument. The determination of the particle size using static light scattering at 25 °C using the Mastersizer 2000 instrument is performed using a wet method, typically with the addition of distilled water.

[0125] Preferably, the carbon black has a viscosity of 10 to 600 μm as determined according to ISO 9277:2010. 2 Within the range of / g, preferably between 20 and 400 m 2 BET specific surface area within the range of / g.

[0126] According to the present invention, a single type of carbon black or a combination thereof with at least one other carbon black can be used as the carbon black. Therefore, the particle size distribution of the carbon black in the preferably aqueous composition can be unimodal or multimodal, such as bimodal. Similarly, a single type of graphite or a combination thereof with at least one other graphite can be used as the graphite. Accordingly, the particle size distribution of the graphite in the preferably aqueous composition can be unimodal or multimodal, such as bimodal.

[0127] Accordingly, the microporous layer B according to the invention is preferably obtained from a composition that is preferably aqueous, wherein the graphite and / or the carbon black has such a particle size.

[0128] Characteristics of gas diffusion layer The gas diffusion layer according to the invention preferably has a thickness in the range of 100 to 300 μm, more preferably in the range of 130 to 250 μm, and especially in the range of 150 to 200 μm at a pressure of 0.025 MPa.

[0129] As previously stated, according to the present invention, a high compressive permanent deformation value is beneficial for reducing the contact resistance at the GDL interface.

[0130] Plastic deformation refers to the situation where a material (e.g., a gas diffusion layer) cannot fully recover its original shape after being subjected to stress, but instead suffers permanent deformation. Part of the deformation is elastic and therefore reversible, while only a specific portion is plastic and persistent. The property of a material to permanently change its shape when stress is applied (i.e., its deformability) is also referred to by the term "settling." Materials with lower plastic deformation properties exhibit lower settlement behavior. The compression settling value measures the performance of a material (in this application, a GDL) under pressure deformation and subsequent relaxation. GDLs used in fuel cells are typically subjected to strong compression. The ratio of elastic deformation to plastic deformation can be used to characterize the properties of the GDL due to compression. The compression settling is the permanent deformation remaining after the force is removed. Gas diffusion layers with low settlement behavior are characterized by low compression settling values. The compression settling value can be determined in a manner described in detail in the test methods below. Other physical quantities (e.g., thickness, gas permeability, and electrical resistance) can be measured simultaneously under their respective specific pressures and after single or multiple applications of force.

[0131] Preferably, the gas diffusion layer has a compression set value of at least 4.0 μm, preferably at least 5.0 μm, more preferably at least 7.0 μm, and especially at least 10.0 μm (e.g., at least 20 μm) at 1.0 MPa, the compression set value being measured on a ring-shaped sample with an inner diameter of 45 mm and an outer diameter of 56 mm, wherein the sample has undergone three load cycles from 0.025 MPa to 1.0 MPa, and the compression set value is derived from the difference in thickness measured at 1.0 MPa in the first and third load cycles.

[0132] Also preferably, the gas diffusion layer has a compression set value of at least 4.0 μm, preferably at least 5.0 μm, more preferably at least 7.0 μm, and especially at least 10.0 μm (e.g., at least 20 μm) at 2.0 MPa, the compression set value being measured on a ring-shaped sample with an inner diameter of 45 mm and an outer diameter of 56 mm, wherein the sample has undergone three loading cycles from 0.025 MPa to 2.0 MPa, and the compression set value is derived from the difference in thickness measured at 2.0 MPa in the first loading cycle and the third loading cycle.

[0133] Also preferably, the gas diffusion layer has a compression set value of at least 5.0 μm, preferably at least 10.0 μm, more preferably at least 15.0 μm, and especially at least 20.0 μm at 6.0 MPa, the compression set value being measured on a ring-shaped sample with an inner diameter of 45 mm and an outer diameter of 56 mm, wherein the sample has undergone three load cycles from 0.025 MPa to 6.0 MPa, and the compression set value is derived from the difference in thickness measured at 6.0 MPa in the first load cycle and the third load cycle.

[0134] In a preferred embodiment, the gas diffusion layer also has a permeability of 1 to 50 seconds, preferably 5 to 25 seconds, more preferably 10 to 20 seconds, as determined by the Gurley method according to ISO 5636-5:2013-11, also referred to as gas permeability or gas permeability.

[0135] In another preferred embodiment, the gas diffusion layer has a dry-state diffusion length of 250 μm to 900 μm, preferably 300 to 800 μm. The dry-state diffusion length refers to the actual distance (in μm) that gas molecules travel through the planar conductive material A) and the microporous layer B). It is measured using a steady-state Wicke-Kallenbach cell.

[0136] fuel cells The present invention also relates to a fuel cell comprising at least one gas diffusion layer as described above according to the present invention.

[0137] In principle, the gas diffusion layer according to the invention is suitable for all common fuel cell types. The invention preferably relates to a polymer electrolyte membrane fuel cell. In this case, the fuel cell according to the invention comprises a polymer electrolyte membrane on which a catalyst layer is applied, wherein the catalyst layer is in contact with the surface of the microporous layer of the gas diffusion layer according to the invention.

[0138] As described above, compared to prior art gas diffusion layers, the gas diffusion layer according to the present invention is suitable for use in a polymer electrolyte membrane fuel cell to reduce the contact resistance at the interface between the microporous layer of the gas diffusion layer and the catalyst layer applied to the polymer electrolyte membrane, particularly in the channel region of the bipolar plate of the fuel cell, especially at the interface in the central region of the channel.

[0139] In a fuel cell according to the invention, the channels K of the bipolar plates can have different geometries, particularly in terms of the width B and radius R of the fillet (wherein the channels K on the bipolar plates can be arranged linearly and parallel, for example). Geometries (B1, R1), (B1, R2), (B2, R1), and (B2, R2) are mentioned here as examples, where “B” represents the width, “R” represents the fillet radius of the channel K, and the channel K is followed by a ridge S (see...). Figure 1 The diagram schematically shows a cut (cross-section) of a bipolar plate in the prior art. "B1" here represents a channel width of 0.3 mm, and "B2" represents a channel width of 0.6 mm. "R1" represents a channel fillet radius of 0.13 mm, and "R2" represents a channel fillet radius of 0.26 mm.

[0140] The contact resistance of a gas-displaced polymer (GDL) plate disposed on a bipolar plate at its interface with a catalyst layer applied to a polymer electrolyte membrane can be simulated by test method F (stripe measurement). This applies to both the channel regions (especially the central region of the channel) and the ridge regions of the bipolar plate of the fuel cell. The contact resistance is simulated by measuring the contact resistance of the GDL plate disposed on the bipolar plate at the interface with the measuring electrode in the corresponding region. For details of test method F (including the measuring apparatus), please refer to the subsequent measurement methods section.

[0141] Because the pressure exerted on the GDL (Gas Diffusion Layer) in the bipolar plate channel region (especially in the central region of the channel) is reduced compared to the ridge region after the various components of the fuel cell are compressed, the contact resistance at the interface with the catalyst layer is relatively high. Surprisingly, compared to GDLs in the prior art, the gas diffusion layer of the present invention significantly reduces the contact resistance at the interface with the catalyst layer in the compressed fuel cell. This is particularly effective in the channel region, especially the central region of the channel.

[0142] In the fuel cell according to the invention, when using bipolar plates with relatively small channel widths (e.g., in geometry (B1, R1) or (B1, R2), wherein the channels on the bipolar plates can be arranged linearly and parallel, for example), at a compression pressure of 1.0 MPa, the contact resistance of the interface between the GDL and the catalyst layer in the central region of the channel of the bipolar plate is as follows: - If the GDL is arranged on the bipolar plate such that the machine direction of the GDL extends parallel to the main field direction of the bipolar plate, then typically < 15 mOhm*cm 2 Preferred size < 10 mOhm*cm2 .

[0143] - If the arrangement of the GDL on the bipolar plate such that the machine direction of the GDL extends at a 90° angle to the main field direction of the bipolar plate (i.e., the machine direction of the GDL extends laterally parallel to the main field direction of the bipolar plate), then it is usually < 15 mOhm*cm 2 Preferred size < 10 mOhm*cm 2 The contact resistance therein is typically relatively low.

[0144] The gas diffusion layer has a machine direction (MD) that extends parallel to the production direction of the roll and thus extends along the winding direction; and a cross-machine direction (CMD) that extends laterally to the production direction, i.e. at a 90° angle to the production direction and thus laterally to the winding direction.

[0145] If the channel of a bipolar plate used in a fuel cell is anisotropic (e.g., when it extends linearly and parallel), the contact resistance between the GDL and the CCM in the channel region can be minimized through proper arrangement of the GDL on the bipolar plate. Preferably, the arrangement of the GDL on the bipolar plate should not such that the machine direction of the GDL extends parallel to the mainstream field direction of the bipolar plate. Particularly preferably, the arrangement of the GDL on the bipolar plate is such that the machine direction of the GDL forms an angle of 25° to 90°, preferably 45° to 90°, with particular emphasis on 90°, with respect to the mainstream field direction of the bipolar plate. The machine direction of the GDL typically has relatively high bending stiffness, so when it is not arranged parallel to the bipolar plate and is particularly preferably at a 90° angle to the mainstream field direction of the bipolar plate, the intrusion of the GDL into the bipolar plate channel can be minimized, thereby minimizing the contact resistance between the GDL and the CCM in the channel region.

[0146] Furthermore, in the fuel cell according to the invention, when using bipolar plates with relatively large channel widths (e.g., existing in geometries (B2, R1) or (B2, R2), wherein the channels on the bipolar plates can be arranged linearly and parallel, for example), under a compression pressure of 1.0 MPa, the contact resistance of the interface between the GDL and the catalyst layer in the central region of the channel of the bipolar plate is as follows: - If the GDL is arranged on the bipolar plate such that the machine direction of the GDL extends parallel to the main field direction of the bipolar plate, then typically < 40 mOhm*cm 2 Preferred size < 25 mOhm*cm 2And especially < 15mOhm*cm 2 .

[0147] - If the arrangement of the GDL on the bipolar plate such that the machine direction of the GDL extends at a 90° angle to the mainstream field direction of the bipolar plate (i.e., the machine direction of the GDL extends laterally parallel to the mainstream field direction of the bipolar plate), then typically < 30 mOhm*cm 2 Preferred size < 20 mOhm*cm 2 And especially < 10 mOhm*cm 2 .

[0148] As previously mentioned, due to the compressibility of the MPL, the gas diffusion layer of the present invention exhibits a relatively high compression set value. The compression set at 2.0 MPa and at 6.0 MPa is particularly preferably greater than 20 μm; in such gas diffusion layers, the contact resistance at the interface between the MPL and the catalyst layer in the channel region of the bipolar plate is typically significantly reduced, such that this contact resistance differs at most slightly from that in the ridge region. This means that the adhesion and conductivity between the channel region and the ridge region differ only slightly.

[0149] The present invention is illustrated by the following non-limiting embodiments.

[0150] Measurement methods The following details this application, particularly the test methods used to evaluate the (comparative) embodiments: Roughness (Test Method A) Roughness (e.g., the roughness of a microporous layer) can be measured using a commonly used stylus method known to those skilled in the art, such as the one titled "Determination of Roughness Measurement R by an Electrical Stylus Instrument". a R z R max As described in DIN 4768-1:1974-08, "Basic".

[0151] Determining the arithmetic mean roughness R a (Average distance from the measurement point on the surface to the centerline) and average roughness depth R z Measurements were performed using a Mahrsurf XCR20 Mahr measuring instrument equipped with an MFW-250 free stylus. The values ​​are the average of six measurements: three in the machine direction (MD) and three in the perpendicular direction (CD).

[0152] Thickness (Test Method B) The thickness under uncompressed conditions can be determined according to DIN 53855-1:1993-08 "Determination of thickness of textile fabrics" (Test Method B1).

[0153] The thickness of the GDL at a specific pressure (e.g., at 0.025 MPa) can be determined using a device that measures compressive deformation, as described in detail below (Test Method B2).

[0154] Compression set (Test Method C) Three samples (left, right, and middle) were taken from the entire width of the GDL to be tested, and the average value was calculated. If the material has a machine orientation due to manufacturing reasons, the sample should be taken perpendicular to the machine orientation (CMD). The sample is annular with an inner diameter of 45 mm and an outer diameter of 56 mm. The sample area is 8.72577 cm². 2 In the testing machine, the sample is subjected to a time-varying pressure, which acts perpendicularly to the sample surface. Sensors measure the change in GDL thickness over time under their respective applied pressures. The sample is supported on a device that measures elastic and plastic deformation using force sensors, where motion is transmitted to the sample via springs. Displacement sensors measure the distance traveled until the maximum pressure is reached. Because the deformation of the sample is non-linear, adjustments must be made to the relative changes in the measurement process. One measurement cycle, i.e., a single loading to the maximum pressure followed by unloading, lasts for 1 minute. The sample undergoes three loading cycles. The initial value is 0.025 MPa, at which point only a small force is applied to the sample. Typical pressure values ​​used to determine compressive permanent deformation (and other physical quantities such as thickness, conductivity or surface resistivity, gas permeability, etc.) are, for example, 0.6 MPa, 1.0 MPa, 2.0 MPa, 2.4 MPa, and 6.0 MPa.

[0155] The compressive permanent deformation value for a specific pressure is derived from the difference between the thickness measured under that pressure in the first loading cycle and the thickness measured under that pressure in the third loading cycle.

[0156] According to the Gurley method, air permeability (gas permeability, gas permeability) (Test Method D) Gas permeability perpendicular to the material plane can be determined using the Gurley measurement method, which can be performed using an automated Gurley permeability meter from Gurley Precision Instruments. Measurements are taken over time, measured in seconds, up to 100 cm⁻¹. 3 Air flows vertically through a point with a pressure difference of 6.42 cm under constant pressure. 2 The flow area of ​​the GDL sample. The method for determining air permeability according to the Gurley method is described in ISO 5636-5.

[0157] Dry diffusion length (test method E) The dry-state diffusion length of GDL was determined using a static Wicke-Kallenbach cell.

[0158] Strip measurement (Test Method F) The contact resistance at the interface between the GDL applied to the bipolar plate and the catalyst layer applied to the polymer electrolyte membrane can be simulated by strip measurements. This applies to both the channel region (especially the central region of the channel) and the ridge region of the bipolar plate of the fuel cell. Here, the contact resistance is simulated by measuring the contact resistance at the interface between a circular sample of GDL applied to the channel structure of the respective bipolar plate and the measuring electrode (i.e., in the desired region, such as in the central region of the channel and / or in the ridge region). For this purpose, a circular GDL sample is clamped between the corresponding upper channel structure and the lower measuring electrodes 1 to 20 under a compressive pressure of 1.0 MPa, specifically at a predetermined angle to the mainstream field direction of the channel structure. Here, the 20 measuring electrodes are arranged perpendicular to the mainstream field direction of the channel. The channel can have, for example, the geometry defined above (B1, R1), (B1, R2), (B2, R1), or (B2, R2). Here, the circular GDL sample is large enough that it covers at least one channel and two adjacent ridges at its maximum width. Measuring electrodes 1 and 2, and 19 and 20, are disposed in the ridge region of the GDL sample; additionally, measuring electrodes 10 and 11 are disposed in the channel center region of the GDL sample. Further details of the measurement method (including the measuring apparatus) can be found in the *Journal of The Electrochemical Society*, 159 (6) B709-B713 (2012), which, by reference, forms part of the disclosure. Particular attention is paid to the experimental portion of the disclosure, including the figures referenced therein (such as those in particular the accompanying drawings). Figure 1 (and in particular the statement under “Measurement of Contact Resistance”).

[0159] The present invention will be described below through examples that are not intended to be limiting. Attached Figure Description

[0160] Figure 1 A cutout (cross-sectional view) of a bipolar plate in the prior art is shown, which can also be used in the fuel cell of the present invention. Here, "B" represents the width of the channel K shown, "R" represents the fillet radius, and ridges S connect the two sides of the channel K. Detailed Implementation

[0161] I) Manufacturing of gas diffusion layer As described below, gas diffusion layers according to the present invention and comparative gas diffusion layers have been fabricated, each of which comprises a planar conductive material A) and a microporous layer B). In GDL fabrication, aqueous dispersions are used as impregnation compositions and MPL slurries, respectively. In this application, additives such as surfactants are not considered as solid components of the impregnation composition or MPL slurry, particularly since these additives typically decompose during sintering.

[0162] Comparative Example 1 (VB1) To manufacture a planar conductive material, a material composed of 100% carbon fiber with a unit area weight of 40 g / m² was used. 2 Nonwoven fabric I. To treat the nonwoven material, an impregnation composition was prepared, comprising 70 wt% carbon black and 30 wt% PTFE based on the solids. Treatment was carried out by pad impregnation, using a treatment weight of 15% (based on the mass of the GDL substrate (i.e., nonwoven fabric I), which corresponds to 6.0 g / m²). 2 The aqueous dispersion (processed) was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. MPL was then coated. For the MPL coating, an MPL slurry containing 20 wt% PTFE and 80 wt% carbon black (by solids) in distilled water was coated onto the fiber material. The fiber material was then dried at 130 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 15 g / m³. 2 .

[0163] Example 2 (B2) The only difference between the gas diffusion layer of Example 2 and that of Comparative Example 1 lies in the MPL slurry used. For the MPL coating, an MPL slurry containing 20 wt% PTFE, 40 wt% carbon black, and 40 wt% graphite (by solids content) in distilled water was coated onto the fibrous material. The fibrous material was then dried at 130 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 15 g / m³. 2 .

[0164] Example 3 (B3) The only difference between the gas diffusion layer of Example 3 and that of Comparative Example 1 lies in the MPL slurry used. Therefore, for the MPL coating, an MPL slurry containing 20 wt% PTFE, 20 wt% carbon black, and 60 wt% graphite (by solids content) in distilled water was coated onto the fibrous material. The fibrous material was then dried at 130 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 20 g / m³. 2 .

[0165] Example 4 (B4) The difference between the fabrication of the gas diffusion layer in Example 4 and that in Comparative Example 1 is that: (i) in order to fabricate the planar conductive material, a material composed of 100% carbon fiber with a unit area weight of 63 g / m² was used. 2 The amount of the impregnation composition used is also 15% of the weight of the GDL substrate (i.e., the nonwoven fabric II) (equivalent to 9.5 g / m²). 2 (i) the weight of the material; and (ii) the MPL slurry used. For the MPL coating, an MPL slurry containing 20 wt% PTFE, 20 wt% carbon black, and 60 wt% graphite (by solids content) in distilled water was coated onto the fiber material. The fiber material was then dried at 130 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 13 g / m³. 2 .

[0166] Example 5 (B5) The difference between the fabrication of the gas diffusion layer in Example 5 and that in Comparative Example 1 is that: (i) in order to fabricate the planar conductive material, a material composed of 100% carbon fiber with a unit area weight of 63 g / m² was used. 2 The nonwoven fabric II (the amount of the impregnation composition is also 15% of the weight of the GDL substrate (i.e., the nonwoven fabric II); and (ii) the MPL slurry used. For the MPL coating, an MPL slurry containing 20 wt% PTFE, 40 wt% carbon black and 40 wt% graphite (by solids content) in distilled water was coated onto the fiber material. The fiber material was then dried at 130 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading value was 25 g / m. 2 .

[0167] Comparative Example 6 (VB6) To manufacture a planar conductive material, a material composed of 100% carbon fiber with a unit area weight of 63 g / m² was used. 2 Nonwoven fabric III. To treat the nonwoven fabric, an impregnation composition was prepared, comprising 70% by weight carbon black and 30% by weight PTFE, based on solids content. The treatment was carried out by pad impregnation using a treatment weight of 15% (equivalent to 9.5 g / m² based on the mass of the GDL substrate (i.e., nonwoven fabric III)). 2 An aqueous dispersion (by weight of the processed material) was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. An MPL coating was then applied. For the MPL coating, an MPL slurry containing 20 wt% PTFE and 80 wt% carbon black (by weight, based on solids) in distilled water was coated onto the fibrous material. The fibrous material was then dried at 160 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 23 g / m³. 2 .

[0168] Comparative Example 7 (VB7) The only difference between the gas diffusion layer of Comparative Example 7 and that of Comparative Example 6 lies in the impregnation composition used. For treating the nonwoven fabric III, an impregnation composition was prepared, comprising 60 wt% carbon black, 22 wt% PTFE, and 18 wt% PEEK, based on solids content. The treatment was carried out by pad impregnation using an aqueous dispersion having 15% of the treatment weight (based on the mass of the GDL substrate, i.e., the nonwoven fabric III). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes.

[0169] Example 8 (B8) The only difference between the gas diffusion layer of Example 8 and that of Comparative Example 6 lies in the MPL slurry used. For the MPL coating, a slurry comprising 20 wt% PTFE, 40 wt% carbon black, and 40 wt% graphite (by solids content) was coated onto the fibrous material. The fibrous material was then dried at 160 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 15 g / m³. 2 .

[0170] Example 9 (B9) The difference between the fabrication of the gas diffusion layer in Example 9 and that in Comparative Example 6 lies in: (i) the impregnation composition used. For treating the nonwoven fabric III, an impregnation composition comprising 60% carbon black, 22% PTFE, and 18% PEEK (by solids content) was prepared. The treatment was performed by pad impregnation using an aqueous dispersion having 15% of the treatment weight (by the mass of the GDL substrate, i.e., the nonwoven fabric III). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. The difference between the fabrication of the gas diffusion layer in Example 9 and that in Comparative Example 6 also lies in: (ii) the MPL slurry used. For the MPL coating, an MPL slurry comprising 20% ​​PTFE, 40% carbon black, and 40% graphite (by solids content) in distilled water was applied to the fibrous material. The fiber material was then dried at 160 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 15 g / m². 2 .

[0171] Example 10 (B10) The only difference between the gas diffusion layer of Example 10 and that of Comparative Example 6 lies in the MPL slurry used. For the MPL coating, an MPL slurry containing 20 wt% PTFE, 20 wt% carbon black, and 60 wt% graphite (by solids content) in distilled water was coated onto the fibrous material. The fibrous material was then dried at 160 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 20 g / m³. 2 .

[0172] Example 11 (B11) The difference between the fabrication of the gas diffusion layer in Example 11 and that in Comparative Example 6 lies in: (i) the impregnation composition used. For treating the nonwoven fabric III, an impregnation composition comprising 60 wt% carbon black, 22 wt% PTFE, and 18 wt% PEEK (based on solids content) was prepared. The treatment was performed by pad impregnation using an aqueous dispersion having 15% of the treatment weight (based on the mass of the GDL substrate (i.e., the nonwoven fabric III)). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. The difference between the fabrication of the gas diffusion layer in Example 11 and that in Comparative Example 6 also lies in: (ii) the MPL slurry used. For the MPL coating, an MPL slurry comprising 20 wt% PTFE, 20 wt% carbon black, and 60 wt% graphite (based on solids content) in distilled water was applied to the fibrous material. The fiber material was then dried at 160 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 20 g / m². 2 .

[0173] Comparative Example 12 (VB12) The only difference between the gas diffusion layer of Comparative Example 12 and that of Comparative Example 1 lies in the impregnation composition used. For the nonwoven step I treatment, an impregnation composition comprising 60 wt% carbon black, 28 wt% PTFE, and 12 wt% PEEK (based on solids content) was prepared. The treatment was carried out by pad impregnation using an aqueous dispersion having 15% of the treatment weight (based on the mass of the GDL substrate (i.e., the nonwoven fabric I)). Subsequently, it was dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes.

[0174] Comparative Example 13 (VB13) The only difference between the gas diffusion layer of Comparative Example 13 and that of Comparative Example 1 lies in the impregnation composition used. For treating the nonwoven fabric I, an impregnation composition comprising 50 wt% carbon black, 26 wt% PTFE, and 24 wt% PEEK (based on solids content) was prepared. The treatment was carried out by pad impregnation using an aqueous dispersion having 15% of the treatment weight (based on the mass of the GDL substrate (i.e., the nonwoven fabric I)). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes.

[0175] Example 14 (B14) The difference between the fabrication of the gas diffusion layer in Example 14 and that in Comparative Example 1 lies in: (i) the impregnation composition used. For treating the nonwoven fabric I, an impregnation composition comprising 60 wt% carbon black, 28 wt% PTFE, and 12 wt% PEEK (based on solids content) was prepared. The treatment was performed by pad impregnation using an aqueous dispersion having 15% of the treatment weight (based on the mass of the GDL substrate (i.e., the nonwoven fabric I)). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. The difference between the fabrication of the gas diffusion layer in Example 14 and that in Comparative Example 1 also lies in the MPL slurry used. For the MPL coating, an MPL slurry containing 20 wt% PTFE, 40 wt% carbon black, and 40 wt% graphite in distilled water was applied to the fibrous material. The fiber material was then dried at 130 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 15 g / m². 2 .

[0176] Example 15 (B15) The difference between the fabrication of the gas diffusion layer in Example 15 and that in Comparative Example 1 lies in: (i) the impregnation composition used. Therefore, to treat the nonwoven fabric, an impregnation composition comprising 50 wt% carbon black, 26 wt% PTFE, and 24 wt% PEEK (based on solids content) was prepared. The treatment was performed by pad impregnation using an aqueous dispersion having 15% of the treatment weight (based on the mass of the GDL substrate (i.e., the nonwoven fabric I)). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. The difference between the fabrication of the gas diffusion layer in Example 15 and that in Comparative Example 1 also lies in the MPL slurry used. For the MPL coating, a slurry containing 20 wt% PTFE, 40 wt% carbon black, and 40 wt% graphite (based on solids content) in distilled water was coated onto the fibrous material. The fiber material was then dried at 130 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 15 g / m². 2 .

[0177] Example 16 (B16) The difference between the fabrication of the gas diffusion layer in Example 16 and that in Comparative Example 1 lies in: (i) the impregnation composition used. Therefore, to treat the nonwoven fabric, an impregnation composition comprising 60 wt% carbon black, 28 wt% PTFE, and 12 wt% PEEK (based on solids content) was prepared. The treatment was performed by pad impregnation using an aqueous dispersion having 15% of the treatment weight (based on the mass of the GDL substrate (i.e., the nonwoven fabric I)). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. The difference between the fabrication of the gas diffusion layer in Example 16 and that in Comparative Example 1 also lies in the MPL slurry used. For the MPL coating, an MPL slurry containing 20 wt% PTFE, 20 wt% carbon black, and 60 wt% graphite in distilled water was applied to the fibrous material. The fiber material was then dried at 130 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 20 g / m². 2 .

[0178] Example 17 (B17) The difference between the fabrication of the gas diffusion layer in Example 17 and that in Comparative Example 1 lies in: (i) the impregnation composition used. For treating the nonwoven fabric I, an impregnation composition comprising 50 wt% carbon black, 26 wt% PTFE, and 24 wt% PEEK (based on solids content) was prepared. The treatment was performed by pad impregnation using an aqueous dispersion having 15% of the treatment weight (based on the mass of the GDL substrate (i.e., the nonwoven fabric I)). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. The difference between the fabrication of the gas diffusion layer in Example 17 and that in Comparative Example 1 also lies in the MPL slurry used. For the MPL coating, an MPL slurry comprising 20 wt% PTFE, 20 wt% carbon black, and 60 wt% graphite (based on solids content) in distilled water was applied to the fibrous material. The fiber material was then dried at 130 °C and sintered at 400 °C to produce the desired gas diffusion layer. The resulting MPL loading was 20 g / m². 2 .

[0179] Example 18 (B18) The difference between the preparation of the gas diffusion layer in Example 18 and that in Example 2 lies in the choice of carbon layer. In Example 18, a carbonized carbon fiber paper with a density of 44.5 g / m³ was used. 2The carbon fiber paper had a unit area weight and a thickness of 192 µm (at 0.25 bar). It was impregnated with a PTFE dispersion containing 10% by weight (based on the GDL substrate mass). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. For MPL coating, an MPL slurry containing 20% ​​by weight PTFE, 40% by weight carbon black, and 40% by weight graphite (based on solids content) in distilled water was coated onto the fiber material. The fiber material was then dried at 160 °C and sintered at 400 °C to produce the desired gas diffusion layer. The MPL loading was similar to that of Example 2.

[0180] Example 19 (B19) The difference between the preparation of the gas diffusion layer in Example 19 and that in Example 4 lies in the choice of carbon layer. In Example 19, a carbonized carbon fiber paper with a density of 44.5 g / m³ was used. 2 The carbon fiber paper had a unit area weight and a thickness of 192 µm (at 0.25 bar). It was impregnated with a PTFE dispersion at a finishing weight of 10% (based on the mass of the GDL substrate). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. The fiber material was subsequently dried at 130 °C and sintered at 400 °C to obtain the desired gas diffusion layer. The MPL loading was similar to that of Example 4.

[0181] Example 20 (B20) The difference between the preparation of the gas diffusion layer in Example 20 and that in Example 3 lies in the choice of carbon layer. In Example 20, a carbonized carbon fiber paper with a density of 44.5 g / m³ was used. 2 The carbon fiber paper had a unit area weight and a thickness of 192 µm (at 0.25 bar). It was impregnated with a PTFE dispersion at a finishing weight of 10% (based on the mass of the GDL substrate). It was then dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. The MPL loading was similar to that of Example 3.

[0182] II) Characteristics of gas diffusion layer Table 1 below shows the contact resistance at the interface between the microporous layer (MPL) of the gas diffusion layer in the (comparative) embodiment, simulated by test method F (strip measurement), and the catalyst layer applied to the polymer electrolyte membrane. In the strip measurement, bipolar plates with linearly and parallelly arranged channels of different channel geometries, namely (B1, R1), (B1, R2), (B2, R1), and (B2, R2), were used. Table 1 also shows the compression set values ​​of the gas diffusion layer of the (comparative) embodiment under different pressures: For example, as shown by comparing Embodiments 2 and 3 of the present invention with Comparative Example 1, Embodiments 8 and 10 of the present invention with Comparative Example 6, Embodiments 14 and 16 of the present invention with Comparative Example 12, Embodiments 15 and 17 of the present invention with Comparative Example 13, and Embodiments 4 and 5 of the present invention, the additional use of graphite in a carbon black-containing MPL (particularly in the channel region) results in a significant reduction in contact resistance at the interface between the MPL and the CCM of the corresponding gas diffusion layer, especially when the graphite-to-carbon black ratio is high (e.g., 3:1), excellent contact resistance can be achieved. As shown by the compression set values ​​of the corresponding gas diffusion layers, the MPL of the gas diffusion layer in the embodiments of the present invention is relatively "compression-soft".

[0183] The results also indicate that the arrangement of the GDL sample on the bipolar plate affects the contact resistance due to the anisotropic channel arrangement. Therefore, in the presence of this anisotropic channel arrangement, particularly low contact resistance can be obtained if the GDL is arranged on the bipolar plate with its machine orientation (MD) at a 90° angle to the mainstream field direction of the bipolar plate. Furthermore, the contact resistance at the center of the channel can be reduced by selecting a relatively small channel width, for example, in the cases of geometries (B1, R1) or (B1, R2) (compare with the contact resistance under geometries (B2, R1) or (B2, R2).

[0184] Furthermore, as shown by comparisons between Examples 6 and 7, Examples 8 and 9, Examples 10 and 11, Examples 12 and 13 with Example 1, Examples 14 and 15 with Example 2, and Examples 16 and 17 with Example 3, the use of polyetheretherketone (PEEK) in the fibrous material of the sheet-like conductive material of the gas diffusion layer and / or thereon results in a significant reduction in the contact resistance at its interface with the CCM. The contact resistance is also affected by the weight ratio of PEEK to PTFE in the impregnation composition used. Therefore, by selecting a suitable fibrous material for impregnation, the contact resistance of the gas diffusion layer according to the invention at the interface between its MPL (containing carbon black and graphite) and the CCM can be further reduced.

Claims

1. A gas diffusion layer for a fuel cell, comprising: A) A planar conductive material comprising at least one fibrous material, wherein the fibrous material is selected from carbon fiber nonwoven materials, carbon fiber paper, carbon fiber fabrics, and mixtures thereof. as well as B) A microporous layer comprising conductive carbon particles in a polymer binder matrix, wherein the conductive carbon particles comprise carbon black and graphite, and the graphite content is at least 50% by weight based on the total weight of carbon black and graphite contained in the microporous layer, the microporous layer being applied to at least one side of the planar conductive material A).

2. A gas diffusion layer for a fuel cell, comprising: A) A planar conductive material comprising at least one fibrous material, wherein the fibrous material includes carbon fiber nonwoven material. as well as B) A microporous layer comprising conductive carbon particles in a polymer binder matrix, wherein the conductive carbon particles comprise carbon black and graphite, wherein the graphite content is at least 50% by weight based on the total weight of the carbon black and graphite contained in the microporous layer, and the microporous layer is applied to at least one side of the planar conductive material A).

3. The gas diffusion layer according to claim 1 or 2, having one or more of the following characteristics: - The graphite has a particle size D10 of 0.5 to 15 µm, preferably 1 to 10 µm, and especially 3 to 7 µm, as determined by static light scattering at 25°C according to ISO 13320:2020-01. - The graphite has a particle size D50 of 1 to 50 µm, preferably 2 to 30 µm, and especially 10 to 25 µm, as determined by static light scattering at 25°C according to ISO 13320:2020-01. - The graphite has a particle size D90 of 2 to 100 µm, preferably 5 to 70 µm, and especially 30 to 60 µm, as determined by static light scattering at 25°C according to ISO 13320:2020-01.

4. The gas diffusion layer according to any one of claims 1 to 3, having one or more of the following characteristics: - The carbon black has a particle size D10 of 5 to 50 nm, preferably 10 to 30 nm, as determined by static light scattering at 25°C according to ISO 13320:2020-01. - The carbon black has a particle size D50 of 20 to 200 nm, preferably 50 to 150 nm, as determined by static light scattering at 25°C according to ISO 13320:2020-01. - The carbon black has a particle size D90 of 40 to 500 nm, preferably 80 to 300 nm, as determined by static light scattering at 25°C according to ISO 13320:2020-01.

5. The gas diffusion layer according to any one of claims 1 to 4, wherein the carbon black has a BET specific surface area in the range of 10 to 600 m2 / g, preferably in the range of 20 to 400 m2 / g, determined according to ISO 9277:2010. 2 2 / g, determined according to ISO 9277:2010.​ 6. The gas diffusion layer according to any one of claims 1 to 5, wherein the graphite has a density of 0.5 to 50 m as determined by ISO 9277:2010. 2 Within the range of / g, preferably from 1.0 to 25 m 2 BET specific surface area within the range of / g.

7. The gas diffusion layer according to any one of the preceding claims, wherein the fiber material is carbon fiber nonwoven fabric.

8. The gas diffusion layer according to any one of the preceding claims, wherein the fibrous material comprises at least one polymer applied thereon and / or introduced therein.

9. The gas diffusion layer according to claim 8, wherein the polymer comprises: a1) At least one fluoropolymer, preferably selected from polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymers, perfluoroalkoxy polymers and mixtures thereof, and especially polytetrafluoroethylene, and / or a2) At least one polymer different from a1), selected from polyaryletherketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co)polyamide, polyimide, polyamide-imide, polyetherimide and mixtures thereof, preferably selected from polyaryletherketone, such as polyetheretherketone.

10. The gas diffusion layer according to claim 8 or 9, wherein the fibrous material comprises at least one conductive reinforcing additive (a3) ​​applied thereon and / or introduced therein, wherein the conductive reinforcing additive (a3) ​​is preferably selected from metal particles, carbon black, graphite, graphene, carbon nanotubes (CNTs), carbon nanofibers and mixtures thereof, and especially carbon black.

11. The gas diffusion layer according to any one of claims 8 to 10, wherein the planar conductive material A) can be obtained by coating and / or impregnating the fibrous material with a preferably aqueous composition, and subsequently drying and / or sintering the coated and / or impregnated fibrous material, wherein the composition comprises the at least one polymer and optionally further components, and the sintering is achieved by heat treatment at a temperature of 250°C to 500°C, preferably 300°C to 450°C, and especially 350°C to 450°C.

12. The gas diffusion layer according to any one of the preceding claims, wherein the graphite content of the microporous layer is 50 to 90% by weight, more preferably 60 to 85% by weight, and especially 65 to 80% by weight, for example 70 to 75% by weight, based on the total weight of carbon black and graphite contained in the microporous layer.

13. The gas diffusion layer according to any one of the preceding claims, wherein the microporous layer contains 10 to 45% by weight, preferably 15 to 40% by weight, of carbon black based on the total weight of the microporous layer.

14. The gas diffusion layer according to any one of the preceding claims, wherein the microporous layer comprises 30 to 80% by weight, preferably 40 to 70% by weight, of graphite based on the total weight of the microporous layer.

15. The gas diffusion layer according to any one of the preceding claims, wherein the microporous layer contains 5 to 50% by weight, preferably 15 to 30% by weight, and especially 20 to 25% by weight of the polymer binder, based on the total weight of the microporous layer.

16. The gas diffusion layer according to any one of the preceding claims, wherein the polymer binder of the microporous layer comprises, and is preferably, a fluoropolymer, such as polytetrafluoroethylene.

17. The gas diffusion layer according to any one of the preceding claims, wherein the microporous layer B) can be obtained by coating the planar conductive material A) with a preferably aqueous composition, and subsequently drying and / or sintering the coated material A), wherein the composition comprises the conductive carbon particles and the polymer binder, and the sintering is achieved by heat treatment at a temperature of 250°C to 500°C, preferably 300°C to 450°C, and especially 350°C to 450°C.

18. A method for manufacturing a gas diffusion layer for a fuel cell according to any one of claims 8 to 17, comprising: i) The fibrous material is coated and / or impregnated with a preferably aqueous composition, and subsequently dried and / or sintered to obtain the planar conductive material A), wherein the composition comprises the at least one polymer and optionally further components, and the sintering is achieved by heat treatment at a temperature of 250°C to 500°C, preferably 300°C to 450°C, especially 350°C to 450°C, and subsequently... ii) The planar conductive material A) is coated with a preferably water-based composition, and then dried and / or sintered to obtain the microporous layer, wherein the composition comprises the conductive carbon particles and the polymer binder, and the sintering is achieved by heat treatment at a temperature of 250°C to 500°C, preferably 300°C to 450°C, and especially 350°C to 450°C.

19. A fuel cell comprising at least one gas diffusion layer according to any one of claims 1 to 17.

20. The fuel cell of claim 19, comprising a polymer electrolyte membrane on which a catalyst layer is applied, wherein the catalyst layer is in contact with the surface of the microporous layer of the gas diffusion layer.

21. Use of a gas diffusion layer according to any one of claims 1 to 17 in a fuel cell, wherein the fuel cell is preferably a polymer electrolyte membrane fuel cell.

22. Use of a gas diffusion layer according to any one of claims 1 to 17 in a polymer electrolyte membrane fuel cell for reducing the contact resistance at the interface between the microporous layer of the gas diffusion layer and the catalyst layer applied to the polymer electrolyte membrane, particularly in the channel region of the bipolar plate of the fuel cell, especially at the interface in the central region of the channel.

23. Use of conductive carbon particles comprising carbon black and graphite in the microporous layer of the gas diffusion layer, preferably as defined in any one of claims 1 to 17, for reducing the contact resistance at the interface between the microporous layer of the gas diffusion layer and the catalyst layer applied to the polymer electrolyte membrane of a polymer electrolyte membrane fuel cell, particularly in the channel region of the bipolar plate of the fuel cell, especially at the interface in the central region of the channel.

24. Use of a polymer selected from polyaryletherketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co)polyamide, polyimide, polyamide-imide, polyetherimide, and mixtures thereof, preferably polyaryletherketone such as polyetheretherketone, in and / or on the fibrous material of the gas diffusion layer as defined in any one of claims 1 to 17, for reducing the contact resistance at the interface between the gas diffusion layer and the catalyst layer applied to the polymer electrolyte membrane of a polymer electrolyte membrane fuel cell, particularly at the interface in the channel region of the bipolar plate of the fuel cell, especially in the central region of the channel.

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