Gas diffusion layer for fuel cell with improved bending characteristics

Abstract

The present invention relates to a gas diffusion layer for a fuel cell having high bending stiffness and high flexibility, which comprises at least one fiber material and a polymer mixture applied to and / or incorporated into the fiber material, a method for producing the gas diffusion layer, and a fuel cell equipped with the gas diffusion layer.

Description

Technical Field

[0001] The present invention relates to a gas diffusion layer having high bending rigidity and high flexibility, a method for manufacturing the gas diffusion layer, and a fuel cell including the gas diffusion layer.

[0002] Background Art A fuel cell generates electrical energy by utilizing the chemical reaction of a fuel, particularly hydrogen and oxygen, to produce water. In a hydrogen-oxygen fuel cell, hydrogen or a hydrogen-containing mixed gas is supplied to the positive electrode, where electrochemical oxidation occurs and electrons are released (H2 → 2H + + 2e - ). Protons are transported from the positive electrode chamber to the negative electrode chamber through a membrane that hermetically separates the reaction chambers and electrically insulates them. The electrons supplied to the positive electrode are supplied to the negative electrode via an external conductor circuit. Oxygen or an oxygen-containing mixed gas is supplied to the negative electrode, and oxygen reduction occurs by accepting electrons. The oxygen anions generated at that time react with the protons transported through the membrane to produce water (1 / 2O2 + 2H + + 2e - → H2O).

[0003] For many applications, particularly in automotive power trains, low-temperature proton exchange membrane fuel cells (PEMFCs, also called polymer electrolyte membrane fuel cells) are used, and the core of which is a polymer electrolyte membrane (PEM). This is a proton (or oxonium ion H3O +) It allows only water to permeate and generally spatially separates an oxidizing agent, which is usually oxygen in the atmosphere, from a reducing agent. Catalyst layers are provided on the positive electrode side and the negative electrode side of the membrane that is airtight, electrically insulating, and has proton conductivity. This catalyst layer forms an electrode and usually contains platinum as a catalytically active metal. In this catalyst layer, actual oxidation-reduction reactions and charge separation take place. The membrane and the catalyst layer form one unit, which is also called a CCM (catalyst coated membrane). Gas diffusion layers (GDLs) exist on both sides of the CCM, which stabilizes the cell structure and is responsible for the function of transporting and distributing reaction gases, water, heat, and electricity. A membrane electrode assembly (MEA) is formed by the membrane, the electrodes, and the gas diffusion layers. Bipolar plates (so-called bipolar plates) are arranged between these membrane electrode assemblies, which are provided with flow paths for supplying process gases to adjacent negative and positive electrodes and usually further internal cooling flow paths.

[0004] The gas diffusion layer located between the bipolar plate and the catalyst layer is very important for the function and performance of the fuel cell. It is necessary to transport the process components consumed and generated in the electrode reaction through the gas diffusion layer and distribute them homogeneously from the macrostructure of the bipolar plate / membrane electrode assembly to the microstructure of the catalyst layer. The electrons generated and consumed in the half-cell reaction need to be conducted to the bipolar plate with as little voltage loss as possible. Also, since the heat generated during the reaction needs to be released to the refrigerant by the bipolar plate, sufficient thermal conductivity is also required for the material of the GDL. Furthermore, the GDL must also function as a mechanical compensator between the macrostructured bipolar plate and the catalyst layer. For this purpose, the tolerances of the components need to be corrected and the compression pressure needs to be dispersed. Also, the GDL also serves as mechanical protection for the very thin membranes that are exposed to high loads in the fuel cell. Therefore, particularly high requirements are imposed on the mechanical properties of the GDL.

[0005] The gas diffusion layer for a fuel cell typically consists of a carbon fiber substrate that is usually hydrophobically finished with a fluorine-based polymer (e.g., PTFE), and then planar-coated with a microporous layer (MPL). The MPL usually consists of a fluorine-containing polymer (such as PTFE) as a binder and a porous and conductive carbon material (such as carbon black or graphite powder). Currently, the following three materials are used as the carbon fiber substrate of the GDL: - Carbon fiber paper (a carbon fiber non-woven fabric that has been chemically bonded through a wet lamination process, contains a chemical binder, and has been carbonized), - Carbon fiber woven fabric (e.g., a fabric made from yarns composed of polyacrylonitrile fibers that have been oxidized but not yet carbonized, and then carbonized or graphitized after weaving), - Carbon fiber non-woven fabric (e.g., a non-woven fabric composed of oxidized polyacrylonitrile, subjected to a dry lamination process, carding process, water jet strengthening, and then thickness adjustment and carbonization).

[0006] Carbon fiber paper has the technical advantage of having high strength against various types of stress (tensile, bending, shear). This improves the transmission of force from the web of the flow distribution plate / bipolar plate to the flow channel part, and makes the surface pressure and connection of the electrodes through the GDL homogeneous. However, these advantages are always accompanied by strong material embrittlement, which is shown by the paper breaking even under low bending stress. The factors for such behavior lie in the product design and manufacturing method. In particular, the chemical binder (usually a phenolic resin) used in the manufacture of carbon fiber paper becomes very brittle during carbonization, causing the material behavior as described above.

[0007] In strength theory, the types of stress are distinguished by the forces acting on a member. Even if the mechanical properties are equivalent, a material for a gas diffusion layer that exhibits favorable behavior with respect to shape changes (e.g., deflection, bending) that occur during bending stress is required. Here, the materials conventionally used still do not have an optimal combination of properties. Such materials are either (paper) showing bending rigidity and brittleness or (nonwoven fabric, woven fabric) showing flexibility and softness. It is desirable to have both high bending rigidity and high flexibility.

[0008] International Publication No. 2015 / 118323 (German Patent Application Publication No. 112015000657) describes the following components: (a) A porous nonwoven web containing carbon fibers, (b) Carbon-containing residues embedded in the porous nonwoven web, (c) A fluorinated polymer, and (d) Inert particles A porous gas diffusion base material containing the same, wherein at least a part of the carbon fibers of the porous nonwoven web has a coating containing a fluorinated polymer and inert particles, is described.

[0009] The production of this porous gas diffusion base material is as follows: (i) Providing a porous nonwoven web containing carbon fibers; (ii) Providing a dispersion containing a carbonizable resin; (iii) Impregnating the porous nonwoven web with the dispersion obtained in step (ii); (iv) Curing the carbonizable resin at a temperature of 100°C to 300°C; (v) Providing a gas diffusion base material precursor by heat-treating the carbonizable resin at a temperature of 900°C to 3000°C to carbonize / graphitize it; (vi) Providing a dispersion containing water, a fluorinated polymer, and inert particles; (vii) Treating the gas diffusion base material precursor with the dispersion produced in step (vi). (viii) A step of drying, and (ix) A step of heating to a temperature up to 400 °C to provide a gas diffusion substrate, and comprises.

[0010] When a porous nonwoven web is impregnated with a carbonizable resin and then carbonized, the material becomes brittle. Therefore, the resulting gas diffusion substrate has high flexural rigidity but poor flexibility.

[0011] WO 97 / 20358 relates to a gas diffusion electrode for a polymer electrolyte membrane fuel cell comprising a gas diffusion layer including a mechanically stable support material, wherein the support material may be a nonwoven fabric, a woven fabric or a paper containing fibers of carbon fiber, glass fiber or organic polymer. To manufacture the gas diffusion electrode, a suspension is applied to the support material or the support material is impregnated with a suspension containing a conductive material, such as carbon black, and a binder material. Suitable binder materials include, for example, temperature-stable polymers such as perfluorinated polymers, polyether ketones, polyether sulfones, polysulfones, polybenzimidazoles, polyphenylene sulfides, polyimides, polyamides and polyphenylene oxides. It is stated that a plurality of binders may be mixed depending on the desired hydrophobicity. The document does not teach the use of a combination of a specific fluorine-containing polymer and a specific high-performance polymer to optimize mechanical properties, particularly properties against bending stress.

[0012] An object of the present invention is to provide a planar conductive material and a gas diffusion layer for a fuel cell based thereon while avoiding the above-mentioned drawbacks.

[0013] Surprisingly, it has been found that when a carbon fiber substrate in the form of a nonwoven fabric or a woven fabric is treated with a hydrophobic fluoropolymer and a specific thermoplastic high-performance resin, a flexible and stiff composite material particularly suitable for the gas diffusion layer is obtained.

[0014] Summary of the Invention The first subject of the present invention is a gas diffusion layer for a fuel cell, the gas diffusion layer comprising: A) the following: a) at least one fibrous material selected from carbon fiber nonwoven fabrics, carbon fiber woven fabrics, and mixtures thereof which is a planar conductive material comprising, wherein the fibrous material b1) at least one fluorine-containing polymer, and b2) at least one polymer other than b1) selected from polyaryletherketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co) polyamide, polyimide, polyamideimide, polyetherimide, and mixtures thereof is included in a state applied onto the fibrous material and / or incorporated into the fibrous material, the conductive material, and / or a sintered body of A), B) optionally, a microporous layer on the surface of the conductive material A) and comprising a gas diffusion layer.

[0015] A specific embodiment is a gas diffusion layer which can be obtained by coating a planar conductive material A) with an aqueous composition comprising at least one fibrous material a) selected from carbon fiber nonwoven fabrics, carbon fiber woven fabrics, and mixtures thereof, at least one fluorine-containing polymer b1), and at least one polymer b2) other than b1) selected from polyaryletherketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co) polyamide, polyimide, polyamideimide, polyetherimide, and mixtures thereof, and / or impregnating the fibrous material a) with the aqueous composition, and then drying and / or sintering the treated fibrous material.

[0016] A further subject of the present invention is a method for manufacturing a gas diffusion layer for a fuel cell comprising a planar conductive material A), comprising: i) providing at least one fibrous material selected from carbon fiber nonwoven fabrics, carbon fiber woven fabrics, and mixtures thereof ii) Coating the fibrous material provided in step i) with a composition comprising at least one fluorine-containing polymer b1) and at least one polymer b2) other than b1), selected from polyether ketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co)polyamide, polyimide, polyamideimide, polyetherimide and mixtures thereof, and / or impregnating the fibrous material with the composition; iii) Subjecting the coated and / or impregnated fibrous material to drying and / or sintering; iv) Optionally, coating the dried and / or sintered fibrous material with a microporous layer A method comprising:

[0017] A further subject matter is a fuel cell comprising at least one gas diffusion layer defined above and below or obtainable by the method defined above and below.

[0018] A further subject matter of the present invention is the following: a) A planar conductive material A) comprising at least one fibrous material selected from carbon fiber non-woven fabric, carbon fiber woven fabric and mixtures thereof, wherein the fibrous material herein, the fibrous material b1) at least one fluorine-containing polymer, and b2) at least one polymer other than b1), selected from polyether ketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co)polyamide, polyimide, polyamideimide, polyetherimide and mixtures thereof, in a state applied on the fibrous material and / or incorporated in the fibrous material, the conductive material A), and / or use of a sintered body of A) as a gas diffusion layer for a fuel cell or in a gas diffusion layer for a fuel cell.

[0019] Description of the Invention The planar conductive material used according to the present invention and the gas diffusion layer based thereon have the following advantages: - The gas diffusion layer has good manufacturing characteristics and good processability in terms of application technology, - Compared with the rigid carbon fiber paper that has been preferably used before, it has equivalent mechanical properties while showing an improvement in bending behavior, - The gas diffusion layer realizes for the first time the characteristics of having both bending rigidity and flexibility, - In particular, in the three-point bending test, the maximum deflection amount (until the specimen breaks or slips off the support point) can be significantly larger, or the deflection angle can be significantly larger with equivalent bending rigidity and flexural modulus.

[0020] Bending test The measurement of the bending characteristics can be carried out according to a general method known to those skilled in the art, such as described in DIN EN ISO 178:2019-08 (Plastics - Determination of flexural properties). The principle of the bending test is based on a bending device that places the specimen as a bending beam on two supports and applies a load in the center by an internal support (three-point bending test). This test is performed by measuring the central deflection amount (= the maximum deflection amount until the specimen breaks or slips off the support) until a predetermined strain occurs at a constant speed or until a defect occurs in the specimen.

[0021] As a result of the bending test, the bending rigidity [N / mm] can be obtained as the slope of the initial straight line portion of the stress-strain curve. This can be read from the load-displacement curve, that is, the formula shown below: (X H -X L ) / D L The bending rigidity is an index indicating the resistance of a member subjected to bending stress to strain.

[0022] Furthermore, the flexural modulus E [N / mm 2 or MPa] can be obtained. Here, the flexural modulus is calculated as follows: E=(lv 3 (X H -X L )) / (4D L ba 3 ) Here, E: Flexural modulus (kN / mm 2 ) l v : Support width (mm) X H : End of flexural modulus measurement (kN) X L : Start of flexural modulus measurement (kN) D L : X H ~X L Deflection amount at (mm) b: Specimen width (mm) a: Specimen thickness (mm) is.

[0023] Furthermore, the maximum deflection angle α can be calculated from the maximum deflection amount and half of the distance between the two support points: α = arctan(maximum deflection amount / half of the support width)

[0024] Preferably, in the planar conductive material A) or its sintered body, for a rectangular test body with a width of 50 mm, a thickness of 0.13 mm, and a length of 100 mm, the flexural rigidity determined by the central stress in a three-point bending test conforming to DIN EN ISO 178:2019-08 with a support width of 32 mm and a test speed of 2 mm / min is 0.05 to 0.08 N / mm.

[0025] Preferably, in the planar conductive material A) or its sintered body, for a rectangular test body with a width of 50 mm, a thickness of 0.13 mm, and a length of 100 mm, the maximum deflection angle α determined by the central stress in a three-point bending test conforming to DIN EN ISO 178:2019-08 with a support width of 32 mm and a test speed of 2 mm / min is 50 to 60°.

[0026] Preferably, in the planar conductive material A) or its sintered body, for a rectangular test piece with a width of 50 mm, a thickness of 0.13 mm, and a length of 100 mm, the flexural modulus determined by the central stress in a three-point bending test conducted in accordance with DIN EN ISO 178:2019-08 at a support width of 32 mm and a test speed of 2 mm / min is 3000 to 6000 N / mm 2 is as follows.

[0027] Preferably, in the gas diffusion layer according to the present invention including a planar conductive material and a microporous layer, for a rectangular test piece with a width of 50 mm, a thickness of 0.16 mm, and a length of 100 mm, the flexural rigidity determined by the central stress in a three-point bending test conducted in accordance with DIN EN ISO 178:2019-08 at a support width of 32 mm and a test speed of 2 mm / min is 0.08 to 0.12 N / mm.

[0028] Preferably, in the gas diffusion layer according to the present invention including a planar conductive material and a microporous layer, for a rectangular test piece with a width of 50 mm, a thickness of 0.16 mm, and a length of 100 mm, the maximum deflection angle α determined by the central stress in a three-point bending test conducted in accordance with DIN EN ISO 178:2019-08 at a support width of 32 mm and a test speed of 2 mm / min is 50 to 60°.

[0029] Preferably, in the gas diffusion layer according to the present invention including a planar conductive material and a microporous layer, for a rectangular test piece with a width of 50 mm, a thickness of 0.16 mm, and a length of 100 mm, the flexural modulus determined by the central stress in a three-point bending test conducted in accordance with DIN EN ISO 178:2019-08 at a support width of 32 mm and a test speed of 2 mm / min is 3000 to 6000 N / mm 2 is as follows.

[0030] Gas diffusion layer The planar conductive material and the gas diffusion layer used according to the present invention are planar structures that are substantially two-dimensional and have a planar spread, but have a small thickness. The gas diffusion layer usually has a bottom surface that substantially corresponds to the bottom surface of the adjacent membrane having the catalyst layer and the bottom surface of the adjacent current collector plate of the fuel cell. The shape of the bottom surface of the gas diffusion layer may be, for example, polygonal (n-sided polygon where n ≧ 3, for example, triangle, quadrilateral, pentagon, hexagon, etc.), circular, circular segment (for example, semi-circular), elliptical, or elliptical segment. Preferably, the bottom surface is rectangular or circular.

[0031] The gas diffusion layer comprises, as component A), a fiber composite material composed of at least one planar conductive carbon fiber material a), at least one fluorine-containing polymer b1), and at least one polymer b2) other than b1) selected from polyether ketone, polyphenylene sulfide, polysulfone, polyether sulfone, semi-aromatic (co) polyamide, polyimide, polyamideimide, polyetherimide, and mixtures thereof. As will be explained in more detail below, component b1) can serve to enhance the hydrophobicity of the fiber material a). Component b2) can serve to stiffen the planar conductive material or the gas diffusion layer. By the combination of component a), b1), and b2), the advantageous mechanical properties described above, in particular the advantageous bending behavior, are achieved. For this purpose, at least one fiber material a) can be treated with the polymer components b1) and b2) and optionally further additives by conventional application and impregnation processes. Such processes will be described in detail below.

[0032] At least one fiber material a) is selected from carbon fiber nonwovens, carbon fiber woven fabrics, and mixtures thereof, including those in a state where the polymer components b1) and b2) are applied thereon and / or incorporated therein. Preferably, the fiber material a) comprises at least one carbon fiber nonwoven. In a particular embodiment, the fiber material a) consists of a carbon fiber nonwoven.

[0033] The fibers contained in the fiber material a) are carbon fibers (carbon fiber, carbon fiber) and optionally other fibers, preferably selected from glass fibers, organic polymers such as polypropylene, polyester, polyphenylene sulfide, polyether ketone and mixtures thereof. In particular, the fibers contained in the fiber material a) consist only of carbon fibers.

[0034] Carbon fibers can be produced by conventional methods, preferably using polyacrylonitrile fibers (PAN fibers) as starting materials. PAN fibers are produced by radical polymerization of a monomer composition containing preferably at least 90% by weight of acrylonitrile based on the total weight of the monomers used in the polymerization. The resulting polymer solution is made into filaments, for example, by wet spinning or coagulation, and then made into a cord. This PAN precursor is usually subjected to oxidative cyclization (also abbreviated as oxidation) at a high temperature of about 180 to 300 °C in an atmosphere containing oxygen before being converted into carbon fibers at a high temperature. The chemical cross-linking that occurs during this process improves the dimensional stability of the fibers. Subsequently, the actual pyrolysis to carbon fibers is carried out at a temperature of at least 1200 °C. For this pyrolysis, depending on the shape of the target fiber material, either fibrils or already planar fiber materials can be used. Depending on the temperature during pyrolysis, it is distinguished between carbonization and graphitization. Carbonization means treatment at about 1200 to 1500 °C in an inert gas atmosphere, where volatile products are decomposed. Graphitization, that is, heating to about 2000 to 3000 °C under an inert gas, yields so-called highly elastic fibers or graphite fibers. These fibers are highly pure, lightweight, high-strength, and have very good electrical and thermal conductivity.

[0035] In the case of carbon fiber fabrics, a planar fiber material is produced by interlacing two systems of yarns, the warp and the weft. Similar to textiles, the bundles of fibers are joined to each other in a flexible but inseparable manner. For the production of carbon fiber fabrics, preferably oxidized but uncarbonized or ungraphitized PAN fibers are used. Carbonization and graphitization for imparting conductivity to the planar fiber material are carried out after weaving.

[0036] For the production of carbon fiber nonwoven fabrics, non-oxidized or oxidized PAN fibers can be used. In a first preferred embodiment, the fibers are laminated in a dry state in a first step to form a web (carding process), and then this is strengthened to form a nonwoven fabric. This can be done, for example, by hydroentanglement, whereby the carbon fibers are oriented, intertwined, and mechanically stabilized. If necessary, the thickness of the strengthened nonwoven fabric can be calibrated to a desired value. Non-oxidized PAN fiber-based nonwoven fabrics are first subjected to oxidation in an oxygen atmosphere at a high temperature after web lamination and strengthening, and then to carbonization / graphitization in an inert gas atmosphere. Oxidized PAN fiber-based nonwoven fabrics are only subjected to carbonization / graphitization after web lamination and strengthening. A carbon fiber nonwoven fabric in which the fibers are laminated in a dry state in a first step to form a web during its production is a preferred embodiment of the present invention.

[0037] When using a bonded fiber material as the fiber material a), this is particularly selected from mechanically bonded fiber materials. Chemical bonding, especially chemical bonding by a carbonizable polymer binder, can have an adverse effect on the bending properties of the gas diffusion layer. Specifically, the fiber material used according to the present invention does not contain polymers other than polymers b1) and b2) as binders.

[0038] In a further suitable embodiment, the fibers are wet-laminated in a first step. In this case, in the present embodiment, the term carbon fiber nonwoven fabric includes, for example, wet-laminating materials composed of chopped carbon fibers, carbon black, at least one polymer b1), in particular PTFE, and at least one polymer b2), in particular PEEK. In contrast to the carbon fiber paper known from the prior art, the wet-laminated fiber material used according to the present invention contains no or only a very small proportion of phenolic resin as a binder. Preferably, the mass ratio of the phenolic resin is 0 to 10%, preferably 0 to 5%, in particular 0 to 1% with respect to the mass of the fiber material a). In particular, the wet-laminated fiber material used according to the present invention does not contain phenolic resin as a binder. More particularly, the wet-laminated fiber material used according to the present invention does not contain polymers other than polymers b1) and b2) as binders.

[0039] In a particular embodiment, the planar conductive fiber material a) comprises at least one carbon fiber nonwoven fabric. These are particularly advantageous because they have compressive elasticity and can be easily manufactured on a large scale, for example, in a roll-to-roll process.

[0040] According to the present invention, the fiber material a) comprises at least one fluorine-containing polymer b1), at least one polymer b2) other than b1) and optionally at least one further additive.

[0041] In particular, the fiber material a) - at least one fluorine-containing polymer b1), - at least one polymer b2) other than b1), selected from polyaryletherketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co)polyamide, polyimide, polyamideimide, polyetherimide and mixtures thereof, - optionally at least one conductivity-improving additive b3), - optionally the following: - a polymer binder b41) other than b1) and b2), - surfactant b42), - further additive substances and auxiliary substances b43) at least one further additive b4) selected from is included in a state applied onto the fiber material and / or in a state incorporated into the fiber material.

[0042] Hereinafter, the mass or total weight of the fiber material a) relates to the untreated fiber material, i.e., the one that does not contain components b1), b2) and, if present, b3) and b4).

[0043] In a specific embodiment, the fiber material a) does not contain the added polymer binder b41). This particularly corresponds to the polymer binder b41) that is carbonized under the manufacturing conditions of the planar conductive material A).

[0044] Polymer b1) Preferably, the fluorine-containing polymer b1) is 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 a perfluoroalkoxy vinyl ether such as perfluorovinyl propyl ether. Preferably, polytetrafluoroethylene is used as the polymer b1).

[0045] Preferably, the mass ratio of the fluorine-containing polymer b1) is 0.5 to 40%, preferably 1 to 20%, particularly 1 to 10% based on the mass of the fiber material a). In a specific embodiment, the fluorine-containing polymer b1) is PTFE, and the mass ratio is 0.5 to 40%, preferably 1 to 20%, particularly 1 to 10% based on the mass of the fiber material a).

[0046] Polymer b2) In a preferred embodiment, polymer b2) is selected from so-called high-performance plastics characterized by properties such as a high glass transition temperature, a high melting temperature, good heat resistance, good chemical resistance, and good mechanical properties. Preferably, polymer b2) has a continuous use temperature (permanent operating temperature) of at least 150 °C.

[0047] Preferred as polymer b2) are semi-aromatic polymers and aromatic polymers. Preferably, polymer b2) is a thermoplastic resin.

[0048] Preferably, polymer b2) is selected from polyaryl ether ketones (PAEK), polyphenylene sulfides (PPS), polysulfones (PSU), polyether sulfones (PES), semi-aromatic (co) polyamides (high-temperature polyamides, HTPA), polyimides (PI), polyamide-imides (PAI), polyether imides (PEI), and mixtures (blends) thereof. (Semi) aromatic polyesters such as PET and PBT, polycarbonates (PC), and heat-resistant melamines such as melamine foam filled with nanoporous SiO2 aerogel are also suitable as polymer b2).

[0049] In a preferred embodiment, polymer component b2) contains at least one polyaryl ether ketone. In particular, polymer component b2) consists of at least one polyaryl ether ketone. Polyaryl ether ketone (PAEK) is a semi-crystalline thermoplastic resin having an alternating structure in which a ketone group (carbonyl group) or an ether group follows each aryl group, and the ratio of the ketone group and the ether group may vary and there may be a difference in the substitution pattern on the aryl ring. Suitable polyaryl ether ketones b2) are polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), etc. Preferably, polymer component b1) contains at least one polyether ether ketone or consists of at least one polyether ether ketone.

[0050] A suitable semi-aromatic (co)polyamide b2) is a polymer called high-temperature polyamide (HTPA). This is a semi-crystalline or amorphous thermoplastic semi-aromatic polyamide. Preferably, it includes at least one aromatic dicarboxylic acid polymerized from those particularly selected from terephthalic acid, isophthalic acid, and a mixture of terephthalic acid and isophthalic acid. Preferred semi-aromatic (co)polyamides b2) 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 / 12.T, PA12.T / 6.T and mixtures thereof. A further specific embodiment of polyamide b2) is polyphthalamide (PPA).

[0051] Suitable polyimides b2) are polysuccinimide (PSI), polybismaleimide (PBMI), polyimide sulfone (PISO) and polymethacrylimide (PMI).

[0052] Preferably, the mass ratio of the polymer b2) is 0.5 to 40%, preferably 1 to 20% based on the mass of the fiber material a). In a specific embodiment, the polymer b2) is selected from PEEK, PPS and mixtures thereof, and the mass ratio of the polymer b2) is 0.5 to 40%, preferably 1 to 20% based on the mass of the fiber material a).

[0053] Other additives In many cases, the fiber material a) already has good electrical conductivity and thermal conductivity due to the carbon fibers used, even without conductivity-improving additives. However, in order to improve the electrical conductivity and thermal conductivity, at least one conductivity-improving additive b3) can be further included in the fiber material a). Preferably, the conductivity-improving additive b3) is selected from metal particles, carbon black, graphite, graphene, carbon nanotubes (CNT), carbon nanofibers, and mixtures thereof. Preferably, the conductivity-improving additive b3) contains or consists of carbon black. The treatment of the fiber material a) with at least one conductivity-improving additive b3) can be carried out, for example, together with the polymer b1) and / or b2) and / or further additives. Preferably, an aqueous dispersion is used for the treatment of the fiber material a).

[0054] Preferably, the mass ratio of the conductivity-improving additive b3) is 0.5 to 45%, preferably 1 to 25%, based on the mass of the fiber material a). In a specific embodiment, the conductivity-improving additive b3) contains or consists of carbon black, and the mass ratio is 0.5 to 45%, preferably 1 to 25%, based on the mass of the fiber material a).

[0055] Preferably, the total weight of the components b1), b2) and b3) is 3 to 50% by weight, preferably 5 to 35% by weight, based on the total weight of the (untreated) fiber material a).

[0056] Preferably, the fiber material a) contains, in a state applied onto the fiber material a) and / or incorporated into the fiber material a), - at least one fluorine-containing polymer b1) 10 to 50% by weight - at least one polymer b2) other than b1) 5 to 40% by weight, and - at least one conductivity-improving additive b3) 20 to 80% by weight in this state.

[0057] The fibrous material a) may further contain at least one additional additive b4). These include, for example, a polymer binder b41) other than the components b1) and b2), a surfactant b42), etc. Suitable binders b41) are, for example, furan resins, polyimide resins, etc. The treatment of the fibrous material a) with at least one additional additive b4) can be carried out together with the polymers b1) and / or b2) and / or other additives. The binder b41) can be cured afterwards if necessary. This can be carried out either together with the drying and / or sintering after the treatment with the polymers b1) and b2) or separately therefrom.

[0058] Preferably, the total mass ratio of the additional additive b4) is 0 to 80%, preferably 0 to 50% based on the mass of the fibrous material a). When the fibrous material a) further contains at least one additional additive b4), the total mass ratio of the additional additive b4) is 0.1 to 80%, preferably 0.5 to 50% based on the mass of the fibrous material a).

[0059] In particular, the fibrous material a) contains an additional polymer b41) other than the fluorine-containing polymer b1) and the polymer b2) in a weight ratio of at most 5%, preferably at most 1%, particularly preferably at most 0.5%, and most particularly preferably at most 0.1% based on the total weight of the fibrous material a), in a state applied onto the fibrous material a) and / or incorporated into the fibrous material a). Even more particularly, the fibrous material a) does not contain an additive of an additional polymer b41) other than the fluorine-containing polymer b1) and the polymer b2).

[0060] The fibrous material a) preferably has a thickness in the range of 50 to 500 μm, particularly preferably 100 to 400 μm. This thickness relates to the untreated and uncompressed state of the fibrous material a), i.e., the state before the GDL is incorporated into the fuel cell.

[0061] The fibrous material a) can be treated with components b1), b2) and optionally b3) and / or b4) by conventional processes. Suitable coating and impregnation processes will be described in detail below.

[0062] In a specific embodiment, the fibrous material a) treated with components b1), b2) and optionally b3) and / or b4) is subjected to a heat treatment (sintering).

[0063] A preferred embodiment is a gas diffusion layer comprising a sintered body of A) obtained by heat treatment at a temperature in the range of at least 250 °C, preferably at least 300 °C, particularly 300 - 450 °C, especially 350 - 450 °C.

[0064] In a preferred embodiment, the gas diffusion layer according to the invention consists of a two-layered layer composite based on a planar conductive material A) or its sintered body and a microporous layer (MPL) B) provided on one surface of the fibrous material a).

[0065] In contrast to the macroporous fibrous material a), the MPL is usually microporous with a pore diameter clearly below 1 micrometer, preferably at most 900 nm, particularly preferably at most 500 nm, especially at most 300 nm. The average pore diameter of the MPL B) is preferably in the range of 5 - 200 nm, particularly preferably 10 - 100 nm. The measurement of the average pore diameter can also be carried out by mercury porosimetry in this case. The MPL contains conductive carbon particles, preferably carbon black or graphite, in a matrix of a polymer binder. A preferred binder is the fluorine-containing polymer mentioned above, particularly polytetrafluoroethylene (PTFE).

[0066] The microporous layer B) preferably has a thickness in the range of 10 - 100 μm, particularly preferably 20 - 50 μm. This thickness relates to the non-compressed state of the microporous layer B), i.e., the state before the GDL is incorporated into the fuel cell.

[0067] The gas diffusion layer according to the present invention preferably has a total thickness (the sum of the fiber material a and the MPL B) in the range of 80 to 1000 μm, particularly preferably 100 to 500 μm. This thickness relates to the non-compressed state of the GDL, that is, the state before the GDL is incorporated into the fuel cell.

[0068] Manufacturing method In step i) of the method according to the present invention, at least one fiber material selected from carbon fiber non-woven fabrics, carbon fiber woven fabrics, and mixtures thereof is provided. For suitable and preferred fiber materials, the description given above is fully incorporated by reference.

[0069] In step ii), the fiber material provided in step i) is coated with an aqueous composition containing at least one fluorine-containing polymer b1) and at least one polymer other than b2) selected from polyaryletherketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co) polyamide, polyimide, polyamideimide, polyetherimide, and mixtures thereof, and / or the fiber material is impregnated with the composition.

[0070] For suitable and preferred polymers b1) and b2), the description given above is fully incorporated by reference.

[0071] The treatment of the fiber material by coating and / or impregnation is carried out according to conventional application methods known to those skilled in the art. Preferably, for the coating and / or impregnation of the fiber material, a method selected from padding, doctor blade processing, spraying, slope padding, and combinations thereof is used.

[0072] In the padding process, the fiber material is passed through a pad (dipping tank) together with a solution or dispersion containing an additive, and then squeezed with a pair of rollers capable of adjusting pressure and, if necessary, the gap, to obtain the desired dosage of the additive.

[0073] In the process using a doctor blade, gravure printing and screen printing are distinguished. In gravure printing, as the doctor blade, for example, a polished blade-shaped steel plate with or without a backup blade is used. This is used to scrape off the excess solution or dispersion containing additives adhering to the web of the impression cylinder (removal by the doctor blade). On the other hand, in screen printing, the doctor blade is usually made of rubber or plastic, and the edge is polished to be sharp or rounded.

[0074] In spray coating, a solution or dispersion containing an additive is applied to the fiber material to be treated by a slot nozzle.

[0075] The slope padding process (kiss roll) is used to coat the lower side of the horizontally extending web material. The coating medium can be applied in the opposite direction or the same direction with respect to the web. Indirect coating can be achieved with a small amount of application by a transfer roller.

[0076] In a particular embodiment, the padding process is used for the treatment of the purification article according to the present invention.

[0077] In step iii) of the method according to the present invention, the coated and / or impregnated fiber material is subjected to drying and / or sintering. Suitable processes for drying a non-woven fabric or a woven fabric coated and / or impregnated with a solution or dispersion containing an additive are known in principle. After application, for example, at least a part of the solvent, particularly water, can be removed from the fiber material by suction, which can be done, for example, by passing the fiber material through a suction port and applying a negative pressure to discharge the liquid from this suction port. Instead of this, or in addition to this, the fiber material can be dried at a high temperature. Further, drying can also be carried out under reduced pressure. Preferably, the drying of the fiber material is carried out at a temperature in the range of 20 to 250 °C, more preferably 40 to 200 °C.

[0078] In addition to, or in place of, drying, the coated and / or impregnated fibrous material can be subjected to sintering in step iii). Sintering is preferably carried out by heat treatment at a temperature in the range of at least 250 °C, preferably at least 300 °C, particularly 300 - 450 °C, especially 350 - 450 °C.

[0079] Finally, the treated and dried and / or sintered fibrous material can be coated with a microporous layer in step iv). For suitable and preferred embodiments of the microporous layer, the description given above is fully incorporated by reference.

[0080] Fuel cell A further subject of the present invention is a fuel cell comprising at least one gas diffusion layer as defined above or obtainable by the method defined above.

[0081] In principle, the gas diffusion layer according to the present invention is suitable for all conventional types of fuel cells, and is particularly suitable for low-temperature proton exchange membrane fuel cells (PEMFC). The above-described embodiments regarding the structure of the fuel cell are fully incorporated by reference.

[0082] One advantage of the present invention is that the gas diffusion layer can be tailored to the structural conditions of the fuel cell, the operating medium flowing through the gas diffusion layer and / or the operating parameters of the fuel cell.

[0083] The present invention will be illustrated by the following examples, which are to be understood as non-limiting examples.

Brief Description of the Drawings

[0084]

Figure 1

Figure 2

Figure 3

Figure 4

[0085] Example The measurement of the bending properties was carried out in accordance with DIN EN ISO 178:2019-08. As described later, a planar conductive material according to the present invention and a planar conductive material for comparison were manufactured. Further, a microporous layer (MPL) was provided on some of the materials. From these materials, specimens with a specimen width of 50 mm and a specimen length of 100 mm were obtained.

[0086] The flexural stress was measured by a three-point bending test with a support width of 32 mm, an initial test speed of 2 mm / min, and a subsequent test speed of 50 mm / min until the specimen reached breakage or slipped off the support points. The flexural rigidity [N / mm] and the flexural modulus E [N / mm 2 were determined from the measurement of the central deflection amount.

[0087] The maximum deflection angle α was calculated from the maximum deflection amount and half of the distance between the two support points: α = arctan(maximum deflection amount / half of the support width)

[0088] I) Manufacture of gas diffusion layer Production Example 1 For the production of the planar conductive material, a basis weight of 63 g / m 2A non-woven fabric made of 100% carbon fiber was used. To treat this non-woven fabric, an impregnating composition containing 60% carbon black, 22% PTFE, and 18% PEEK based on solids was mixed. The treatment was carried out by pad-impregnating an aqueous dispersion so that the treatment weight was 15% of the mass of the GDL substrate (corresponding to 9.5 g / m 2 ). Then, it was further dried at 160 °C for 5 minutes and sintered at 400 °C for 10 minutes. Next, the stiffened substrate thus obtained was further given MPL for the production of Materials 2) and 3) according to the present invention, and then the application technical characteristics were measured.

[0089] Production Example 2 For the production of a planar conductive material, a non-woven fabric made of 100% carbon fiber with a basis weight of 40 g / m 2 was used. To treat this non-woven fabric, an impregnating composition containing 40% carbon black, 20% PTFE, and 40% PPS (Fortron® 0205B4 manufactured by Celanese) based on solids was mixed. The treatment was carried out by pad-impregnating an aqueous dispersion so that the treatment weight was 15% of the mass of the GDL substrate (corresponding to 6.0 g / m 2 ). Then, it was further dried at 150 °C for 5 minutes and sintered at 400 °C for 10 minutes.

[0090] II) Measurement of bending characteristics: For measuring the application technical characteristics, the following materials were used. 1) The GDL according to the present invention obtained in Production Example 1 without MPL applied 2) The GDL according to the present invention similar to Production Example 1 with MPL applied For MPL coating, an MPL paste containing 2% by weight of FEP (tetrafluoroethylene-hexafluoropropylene copolymer) and 7.8% by weight of carbon in distilled water was applied to the fibrous material. Then, this fibrous material was dried at 160 °C and sintered at 400 °C. The supported amount of the obtained MPL was 21 g / m 2 . 3) The GDL according to the present invention obtained in Production Example 1 with MPL applied For MPL coating, an MPL paste containing 2.7 wt% of PTFE and 10.8 wt% of carbon in distilled water was applied to the fibrous material. Then, this fibrous material was dried at 160 °C and sintered at 400 °C. The obtained MPL loading was 15 g / m 2 was obtained. V4) Comparative example: A non-impregnated 100% carbon fiber nonwoven fabric with a basis weight of 63 g / m according to Production Example 1 2 V5) Comparative example: A 100% carbon fiber nonwoven fabric with a basis weight of 63 g / m according to Production Example 1, impregnated with PTFE / carbon black without polymer stiffening 2 V6) Comparative example: An MPL-coated carbon fiber paper GDL Total thickness 120 μm, basis weight 103 g / m 2 CeTech GDL 120 (CeTech Co., Ltd., Taiwan) V7) Comparative example: A carbon fiber paper GDL, without PTFE impregnation and MPL coating, a sheet product instead of a wound product Total thickness 120 μm, Toray TGP-H030 (Toray Industries, Inc., Japan) V8) Comparative example: A carbon fiber paper GDL, with MPL coating and PTFE impregnation, a sheet product instead of a wound product Total thickness 220 μm, basis weight 91 g / m 2 SGL 29BC (SGL Carbon SE, Germany) V9) Comparative example: A carbon fiber paper GDL, with MPL coating and PTFE impregnation, a sheet product instead of a wound product Total thickness 215 μm, basis weight: 74 g / m 2 SGL 22BB (SGL Carbon SE, Germany) V10) Comparative example: A carbon fiber paper GDL, with MPL coating and PTFE impregnation, a sheet product instead of a wound product Total thickness 190 μm, basis weight: 56 g / m 2 AVCarb MB030 (AvCarb Material Solutions, USA) ​​

[0091] The results of the applied technical measurements are shown in FIGS. 1 to 4. It has been shown that the gas diffusion layer treated according to the present invention has an optimal combination of properties of high bending stiffness and high flexibility. The maximum amount of deflection of the GDL according to the present invention is caused by the slipping off of the end from the support point, rather than by the breakage of the material. The gas diffusion layer treated according to the present invention has a bending stiffness and a flexural modulus that are at least equivalent to, and often exceed, those of the carbon fiber paper known in the prior art. As shown in the examples of polyether ketone and polyphenylene sulfide, non-woven fabrics that have not been treated at all and GDLs that have not been subjected to additional polymer stiffening have low bending stiffness. In particular, the absence of "brittle fracture behavior" and the significantly larger maximum deflection angle constitute a particularly advantageous combination of properties.

Claims

1. A gas diffusion layer for a fuel cell, wherein the gas diffusion layer is A) a planar conductive material composed of the following components a), b1), b2) and b3), a) at least one fiber material selected from carbon fiber non-woven fabric, carbon fiber woven fabric and mixtures thereof, The fiber material is b1) at least one fluorine-containing polymer, b2) at least one polymer other than b1) selected from polyaryletherketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co) polyamide, polyimide, polyamideimide, polyetherimide and mixtures thereof, and b3) at least one conductivity-improving additive, The planar conductive material is to be included in a state applied onto the fiber material and / or incorporated into the fiber material, and / or a sintered body of A) A gas diffusion layer comprising.

2. The gas diffusion layer is B) a microporous layer on one surface of the conductive material A) The gas diffusion layer according to claim 1, further comprising.

3. A gas diffusion layer for a fuel cell, wherein the gas diffusion layer is A) a planar conductive material composed of the following components a), b1), b2), b3) and b4), a) at least one fiber material selected from carbon fiber non-woven fabric, carbon fiber woven fabric and mixtures thereof, The fiber material a) is - at least one fluorine-containing polymer b1), - at least one polymer b2) other than b1) selected from polyaryletherketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co) polyamide, polyimide, polyamideimide, polyetherimide and mixtures thereof, - at least one conductivity-improving additive b3), - the following: - a polymer binder b41) other than b1) and b2), - a surfactant b42), - at least one further additive b4) selected from further additive substances and auxiliary substances b43) The planar conductive material is to be included in a state applied onto the fiber material and / or incorporated into the fiber material, and / or a sintered body of A) A gas diffusion layer comprising.

4. ​ The fluorine-containing polymer b1) is selected from polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, perfluoroalkoxy polymer, and mixtures thereof, and the gas diffusion layer according to any one of claims 1 to 3.

5. The polymer b2) is selected from polyaryl ether ketone, polyphenylene sulfide, polysulfone, polyether sulfone, and mixtures thereof, and the gas diffusion layer according to any one of claims 1 to 4.

6. The fiber material a) b3) at least one conductivity-improving additive selected from metal particles, carbon black, graphite, graphene, carbon nanotubes (CNT), carbon nanofibers, and mixtures thereof is included in a state where it is applied onto the fiber material a) and / or in a state where it is incorporated into the fiber material a), and the gas diffusion layer according to any one of claims 1 to 5.

7. The fiber material a) is based on the total weight of the components b1), b2), and b3) - at least one fluorine-containing polymer b1) 10 to 50% by weight, - at least one polymer b2) other than b1) 5 to 40% by weight, and - at least one conductivity-improving additive b3) 20 to 80% by weight is included in a state where it is applied onto the fiber material a) and / or in a state where it is incorporated into the fiber material a), and the gas diffusion layer according to any one of claims 1 to 6.

8. The total weight of the components b1), b2), and b3) is 3 to 50% by weight based on the total weight of the fiber material a), and the gas diffusion layer according to any one of claims 1 to 7.

9. The fiber material a) contains an additional polymer b41) other than the fluorine-containing polymer b1) and the polymer b2) in a weight ratio of at most 5% based on the total weight of the fiber material a), in a state where it is applied onto the fiber material a) and / or in a state where it is incorporated into the fiber material a), and the gas diffusion layer according to claim 3.

10. A method for manufacturing a gas diffusion layer for a fuel cell including the planar conductive material A) according to any one of claims 1 to 9, i) providing at least one fiber material selected from carbon fiber nonwoven fabric, carbon fiber woven fabric, and mixtures thereof ii) coating the fibrous material provided in step i) with a composition comprising at least one fluorine-containing polymer b1), at least one polymer b2) other than b1) selected from polyaryletherketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co)polyamide, polyimide, polyamideimide, polyetherimide and mixtures thereof, and at least one conductivity-improving additive b3), and / or impregnating the fibrous material with the composition; iii) subjecting the coated and / or impregnated fibrous material to a heat treatment; A method comprising the steps of. [

11. ] The method according to claim 10, further comprising iv) coating the heat-treated fibrous material with a microporous layer. [

12. ] The method according to claim 10 or 11, wherein in step iii), the coated and / or impregnated fibrous material is subjected to sintering by heat treatment at a temperature of at least 250°C. [

13. ] A fuel cell comprising at least one gas diffusion layer according to any one of claims 1 to 9. [

14. ] A planar conductive material A) comprising the following components a), b1), b2) and b3), a) at least one fibrous material selected from carbon fiber nonwoven fabric, carbon fiber woven fabric and mixtures thereof, wherein the fibrous material b1) at least one fluorine-containing polymer, b2) at least one polymer other than b1) selected from polyether ketone, polyphenylene sulfide, polysulfone, polyethersulfone, semi-aromatic (co)polyamide, polyimide, polyamideimide, polyetherimide and mixtures thereof, and b3) at least one conductivity-improving additive, wherein the planar conductive material A) is in a state applied on the fibrous material and / or incorporated in the fibrous material, and / or a sintered body of A), for use as a gas diffusion layer for a fuel cell or in a gas diffusion layer for a fuel cell. [

15. ] A planar conductive material A) comprising the following components a), b1), b2), b3) and b4), a) at least one fibrous material selected from carbon fiber nonwoven fabric, carbon fiber woven fabric and mixtures thereof, wherein the fibrous material b1) at least one fluorine-containing polymer, b2) at least one polymer other than b1), selected from polyether ketone, polyphenylene sulfide, polysulfone, polyether sulfone, semi-aromatic (co) polyamide, polyimide, polyamideimide, polyetherimide, and mixtures thereof, and b3) at least one conductivity-improving additive, - as follows: - a polymer binder b41) other than b1) and b2), - a surfactant b42), - further additive substances and auxiliary substances b43) at least one further additive b4) selected from shall be included in a state applied onto the fiber material and / or incorporated into the fiber material, the planar conductive material A), and / or a sintered body of A), for use as a gas diffusion layer for a fuel cell or in a gas diffusion layer for a fuel cell.

16. The planar conductive material A) or the sintered body of A) has the following properties: - For a rectangular test piece with a width of 50 mm, a thickness of 0.13 mm, and a length of 100 mm, the flexural rigidity determined by the central stress in a three-point bending test conforming to DIN EN ISO 178:2019-08 with a support width of 32 mm and a test speed of 2 mm / min is 0.05 to 0.08 N / mm, - For a rectangular test piece with a width of 50 mm, a thickness of 0.13 mm, and a length of 100 mm, the maximum deflection angle α determined by the central stress in a three-point bending test conforming to DIN EN ISO 178:2019-08 with a support width of 32 mm and a test speed of 2 mm / min is 50 to 60°, - For a rectangular specimen with a width of 50 mm, a thickness of 0.13 mm, and a length of 100 mm, the flexural modulus determined by the central stress in a three-point bending test conducted in accordance with DIN EN ISO 178:2019-08 at a support width of 32 mm and a test speed of 2 mm / min is 3000 to 6000 N / mm ２ is The use according to claim 14 or 15, having at least one of the above.

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