Gas diffusion layer having low plastability and high surface quality

Abstract

The present invention relates to a method for manufacturing a gas diffusion layer for a fuel cell having low plastic deformation (low permanent deformation) and good surface properties, to a gas diffusion layer obtained according to the method, and to a fuel cell comprising such a gas diffusion layer.

Description

Field of the Invention

[0001] The present invention relates to a method for producing a gas diffusion layer for a fuel cell, the gas diffusion layer having low plastic deformability (low permanent deformation) and good surface properties. The present invention also relates to a gas diffusion layer obtained according to the method, and a fuel cell comprising such a gas diffusion layer. Background Art

[0002] Fuel cells use a fuel (especially hydrogen) to react with oxygen to produce water to generate electricity. In a hydrogen-oxygen fuel cell, hydrogen or a gas mixture containing hydrogen is supplied to the anode, where it undergoes electrochemical oxidation and releases electrons (H2→2H + +2e - ). The protons are transported from the anode region to the cathode region via a membrane, which separates the reaction chambers from one another in a gas-tight manner and electrically insulates them. The electrons provided at the anode are transported to the cathode via an external conductor circuit. Oxygen or a gas mixture containing oxygen is supplied to the cathode, where the oxygen is reduced by absorbing electrons. The oxygen anions formed in the process react with the protons transported via the membrane and form water (1 / 2O2 + 2H + +2e - →H2O).

[0003] Many applications (especially automotive powertrains) use low-temperature proton exchange membrane fuel cells (PEMFCs), which are core components that allow only protons (or hydronium ions H3O + ) and water pass through and spatially separate the oxidant (generally atmospheric oxygen) from the reductant. Catalyst layers are applied on the anode and cathode sides of the gas-tight electrically insulating proton-conducting membrane, which form electrodes and usually contain platinum as a catalytically active metal. The actual redox reaction and charge separation take place in the catalyst layers. The membrane and the catalyst layer form a unit also known as CCM (catalyst coated membrane). Gas diffusion layers (GDL) are provided on both sides of the CCM, which stabilize the cell structure and assume the transport and distribution functions of the reaction gases, water, heat and current. The membrane, electrodes and gas diffusion layers form a membrane electrode unit (MEA). Distribution plates (so-called bipolar plates) are provided between the membrane electrode units. These distribution plates have channels for supplying process gases to the adjacent cathodes and anodes, and usually also have internal cooling channels.

[0004] The gas diffusion layer used in fuel cells is generally composed of a carbon fiber substrate, which is made hydrophobic with a fluoropolymer (such as PTFE) and then flatly coated with a microporous layer (MPL). The MPL is usually composed of a fluoropolymer (such as PTFE) as a binder and a conductive material, wherein carbon materials such as carbon black or graphite powder are usually used. The gas diffusion layer plays a vital role in the function and performance of the fuel cell. On the one hand, the gas diffusion layer is used to transport the process components consumed and generated in the electrode reaction, and on the other hand, the electrons formed and consumed in the half-cell reaction and the heat formed in the reaction are conducted to the distribution plate. In addition, the GDL also plays a mechanical compensation role between the macro-structured distribution plate and the catalyst layer. To this end, component tolerances must be compensated and compression pressures must be distributed. The GDL also provides mechanical protection for very thin membranes exposed to high loads in fuel cells. The sensitive membrane should be as free as possible from damage by the gas diffusion layer and its components. This places high demands on the mechanical properties and surface properties of the GDL.

[0005] A big problem with fiber-based gas diffusion layers is that the inhomogeneous surface of the gas diffusion layer or protruding fibers may damage the membrane of the fuel cell. These fibers are usually very hard and brittle. In addition, the fiber thickness usually varies within the thickness range of the fuel cell membrane, so there is a risk that the membrane is penetrated by the fibers and causes a short circuit. In the worst case, a short circuit caused by the fiber puncturing the membrane may cause the entire fuel cell stack to fail. Other sources of failure that may cause similar failures or significantly shorten the life of the stack include, for example, a very rough surface of the MPL or impurities of different hardness in the MPL. Since the membrane may be subjected to huge mechanical stresses during the operation of the fuel cell, the stack may also fail at a later point in time.

[0006] Fuel cell membranes are very thin, typically a few microns thick. Typical thicknesses range from 8 μm to 50 μm, with membranes of 5 μm thickness having been tested in some cases. It is foreseeable that as fuel cells are increasingly used in automobiles, there is a need to further reduce the thickness of all planar components (membranes, GDL / MPL, etc.). Internal short circuits caused by protruding fibers of the GDL lying flat on the membrane can cause very large performance problems. Therefore, it is necessary to prevent fiber protrusions and / or smooth the MPL surface of the GDL.

[0007] When used in fuel cells, the GDL is usually pressed (compressed) with high strength. Due to the compression, the properties of the GDL can be characterized by the ratio of elastic to plastic deformation. In plastic deformation, the gas diffusion layer cannot return to its original shape 100% after loading, and its shape is permanently changed. The property of a material to permanently change its shape when stress is applied, that is, deformability, is also expressed by the term "permanent deformation". Materials with low plastic deformability have low permanent deformation performance. The permanent deformation of the GDL known in the prior art still needs to be improved. If the GDL in the fuel cell stack is tensioned under high pressure, permanent deformation will occur due to the tension force and dynamic force changes in operation. This may lead to compression pressure losses in the fuel cell stack, thereby increasing the material resistance of most components in the stack, mainly its transition resistance. In addition, it may be necessary to adjust the stack design, such as using additional spring groups to compensate for the tension losses that occur during permanent deformation. As a result, the length of the stack and the required installation space may increase. In addition, additional measures may be required when installing the stack, such as tightening and loosening the stack several times during assembly before fixing it, which increases the manufacturing difficulty.

[0008] The development of fuel cells suitable for everyday use makes an important contribution to the energy transition from fossil fuels to sustainable fuels. Therefore, there is currently a great demand for PEM fuel cells that have improved aspects of the above-mentioned complex characteristics.

[0009] A known solution is to use a gas diffusion layer with a gradient in at least one chemical and / or physical property to set the application characteristics of a fuel cell. WO 2022 / 002932 A1 describes a gas diffusion layer for a fuel cell, wherein at least one physical property (selected from hydrophobicity and permeability) changes along the maximum planar extension in at least one direction. Specifically, for example, hydrophobicity is controlled by the content of hydrophobic material (such as PTFE), and permeability is controlled by the porosity of the gas diffusion layer. For the applied microporous layer, its thickness may be affected, which mainly leads to changes in the local penetration depth of the support layer. The disclosure of this application is not very specific, and lacks both instructions for implementing the described scheme and repeatable embodiments and application data.

[0010] EP 3957789 A1 describes a gas diffusion layer having high thermal conductivity despite its low density, and having good operability and battery performance. The GDL comprises a carbon fiber felt containing carbon fibers having an average fiber diameter of 5 μm to 20 μm, wherein at least a portion of the carbon fibers forming the carbon fiber felt has a flat portion, wherein a maximum value of the fiber diameter observed from a plan view of the surface of the carbon fiber felt is 10% to 50% greater than the average fiber diameter, and a frequency of occurrence of the flat portion on the surface of the carbon fiber felt is 50 / mm 2 Up to 200 / mm2 .

[0011] WO 2020 / 165075 A1 describes a method for producing a gas diffusion layer, the method comprising the following steps:

[0012] a) preparing a carrier-binder coating comprising a solvent, a fluorinated binder and conductive carrier particles,

[0013] b) making a viscous composition comprising

[0014] - solvent,

[0015] - fluorinated binders, and

[0016] - substantially no or equal to or less than 15 wt. % conductive support particles relative to the total weight of the fluorinated binder and all conductive support particles; and

[0017] c) a combination of a carrier material layer, an adhesive composition layer and a carrier-adhesive coating layer, wherein the adhesive composition layer is applied between the carrier material layer and the carrier-adhesive coating layer, and

[0018] The carrier material, viscous composition and carrier-binder coating combination is pressed under a pressure of at least 15 kilopascals (0.15 bar) and / or heated to at least 300°C.

[0019] The object of this document is to provide a mechanically stable gas diffusion electrode in which a support-adhesive layer, preferably formed by a microporous layer, is firmly connected to the support material. This is achieved by an additional adhesive layer which contains no or only a small amount of conductive particles. The layers are pressed at a pressure of up to 2.5 MPa and a temperature of at least 300° C., with a relatively long processing time of at least 15 minutes, preferably 1 to 4 hours, being used. The additional adhesive layer between substrate and MPL increases the number of required process steps and, moreover, the relatively long pressing times make industrial applications very difficult.

[0020] JP 2007242378 A describes a gas diffusion layer consisting of sintered porous carbon particles and hydrophobic particles. To produce this gas diffusion layer, carbon particles and hydrophobic particles are dispersed in water in the presence of a non-ionic surfactant, concentrated and sintered under phase inversion. The sintered film is removed, crushed into powder again, and the resulting sintered coarse particles are hot-pressed into a GDL in a mold. This makes it possible, if desired, to dispense with the use of a fiber-based substrate in the final GDL, which consists only of carbon-based coarse particles and hydrophobic particles. This treatment can have an adverse effect on further processing during cutting and manufacturing of the cell stack and on the stability of the cell.

[0021] EP 3276718 A1 describes a porous carbon electrode substrate which hardly causes short circuits when used in fuel cells. In this case, carbon fibers protruding from the substrate surface or protruding when the carbon electrode substrate is subjected to pressure and short carbon fibers not tightly attached to the substrate surface are fully removed. The substrate is manufactured using short carbon fibers and a binding resin having a carbon content of at least 35% by weight and carbonized when heated. Thus, the resulting GDL substrate is based on a completely resin-impregnated fiber material.

[0022] EP 3396753 A1 describes a gas diffusion electrode that is not prone to short-circuit current when applied to a fuel cell. The GDL substrate comprises short carbon fibers bonded to a carbon resin, wherein the gas diffusion electrode has a multilayer structure preferably comprising at least two microporous layers, the two microporous layers being different from each other in terms of layer filling rate, and wherein the microporous layer must have sufficient thickness under pressure load. To reduce the possibility of short circuits, a large number of measures are described, such as pressurizing the precursor substrate before carbonizing the bonding resin, and increasing the temperature in the carbonization step. Only when further reduction is desired, post-treatment is performed by calendering, followed by blowing and suction with air. The disadvantage of this method is that pressurization before carbonization requires additional costs, resin binders are generally not desired in the fiber substrate, and the use of two or more MPL layers also increases costs. The multilayer structure also increases the risk of delamination when winding, bending, stretching or under pressure.

[0023] US2019 / 0344405 describes a gluing device for gluing gas diffusion layers inside fuel cells. This device has a suction device and is intended to glue together or remove fluffy or loose fibers of the gas diffusion layer. The use of additional equipment increases manufacturing costs. In addition, it is questionable whether the use of this device solves the problem of internal short circuits that may be caused by protruding fibers of the GDL lying flat on the membrane.

[0024] The object of the present invention is to avoid or at least reduce the aforementioned disadvantages.

[0025] It has now surprisingly been found that if the gas diffusion layer is post-treated at high pressure and temperature, a gas diffusion layer with good properties and in particular excellent surface properties and significantly improved permanent deformation can be obtained. The hot compressed gas diffusion layer is characterized by a significantly smoother surface on the side coated with the microporous layer. As a result, the possibility of short circuits caused by protruding fibers and impurities on the surface of the MPL, as well as other surface roughness reasons, or other effects that occur during fuel cell operation and may lead to membrane penetration is greatly reduced. In addition, by post-treatment at high pressure and temperature, the proportion of plastic deformation of the GDL can be significantly reduced. In addition, it has been surprisingly found that the transport characteristics of the GDL can also be controlled by post-treatment. Therefore, it is possible to control properties such as permeability and dry diffusion length independently of the composition of the gas diffusion layer material. Summary of the invention

[0026] A first subject of the invention is a method for producing a gas diffusion layer for a fuel cell, the gas diffusion layer comprising

[0027] A) a planar conductive fiber material, and

[0028] B) a microporous layer on at least one of the surfaces of the fibrous material, the microporous layer comprising electrically conductive particles in a matrix consisting of a polymer binder,

[0029] in

[0030] i) providing a planar conductive fiber material A),

[0031] ii) coating the fiber material provided in step i) with a precursor for forming a microporous layer,

[0032] iii) post-treating the coated fiber material obtained in step ii) at high pressure and optionally high temperature.

[0033] Preferably, the method of the present invention, especially the post-treatment in step iii), reduces the plastic deformability of the gas diffusion layer relative to the untreated gas diffusion layer. In particular, the compression set value of the gas diffusion layer is reduced relative to the untreated gas diffusion layer.

[0034] Preferably, through the method of the present invention, especially the post-treatment in step iii), the surface of at least one microporous layer of the gas diffusion layer is smoother.

[0035] In particular, the post-treatment in step iii) is carried out at a high pressure of at least 0.5 MPa and a high temperature of at least 100°C.

[0036] A special embodiment is a method for realizing a gas diffusion layer having one, preferably two, particularly preferably three, in particular four of the following properties:

[0037] The maximum compression set value under -1.0MPa is 5μm, and its unit area weight is 95g / m 2 Up to 100g / m 2 And the MPL load is 15g / m 2 Up to 22g / m 2 The compression set value is measured on a GDL of 45 mm using a ring sample with an inner diameter of 45 mm and an outer diameter of 56 mm, wherein the sample is subjected to three loading cycles from 0.025 MPa to 1.0 MPa, and the compression set value is obtained by measuring the thickness difference at 1.0 MPa in the first loading cycle and the third loading cycle,

[0038] -Arithmetic mean roughness R a Compared to an untreated gas diffusion layer, the arithmetic mean roughness is reduced by at least 10%, the arithmetic mean roughness being measured by the stylus method in accordance with DIN EN ISO 4288:1998-04,

[0039] - Roughness depth R Z Compared to an untreated gas diffusion layer, the roughness depth is reduced by at least 10%, the roughness depth being measured by the stylus method according to DIN EN ISO 4288:1998-04,

[0040] - The number of short circuits is a maximum of 25%, the short circuit number is measured by puncture on a surface area of ​​297 mm×420 mm and a unit area weight of 95 g / m 2 And the MPL load is 15g / m 2 Measured on the GDL.

[0041] Another subject of the invention is a gas diffusion layer obtained by a process as described above and below.

[0042] Another subject of the invention is a gas diffusion layer for a fuel cell, the gas diffusion layer comprising:

[0043] A) a planar conductive fiber material, and

[0044] B) a microporous layer on at least one of the surfaces of the fiber material,

[0045] The gas diffusion layer has at least one of the following characteristics:

[0046] The maximum compression set value under -1.0MPa is 5μm, and its unit area weight is 95g / m 2 Up to 100g / m 2And the MPL load is 15g / m 2 Up to 22g / m 2 The compression set value is measured on a GDL of 45 mm using a ring sample with an inner diameter of 45 mm and an outer diameter of 56 mm, wherein the sample is subjected to three loading cycles from 0.025 MPa to 1.0 MPa, and the compression set value is obtained by measuring the thickness difference at 1.0 MPa in the first loading cycle and the third loading cycle,

[0047] -Arithmetic mean roughness R a Compared to an untreated gas diffusion layer, the arithmetic mean roughness is reduced by at least 10%, the arithmetic mean roughness being measured by the stylus method in accordance with DIN EN ISO 4288:1998-04,

[0048] - Roughness depth R Z Compared to an untreated gas diffusion layer, the roughness depth is reduced by at least 10%, the roughness depth being measured by the stylus method according to DIN EN ISO 4288:1998-04,

[0049] - The number of short circuits is a maximum of 25%, the short circuit number is measured by puncture on a surface area of ​​297 mm×420 mm and a unit area weight of 95 g / m 2 And the MPL load is 15g / m 2 Measured on the GDL.

[0050] Another subject matter of the invention is a fuel cell comprising at least one gas diffusion layer as described above and below.

[0051] Another subject of the present invention is the use of a gas diffusion layer as described above and below or obtained by a process as described above and below in a proton exchange membrane fuel cell.

[0052] Description of the invention

[0053] The gas diffusion layer of the present invention obtained by the method of the present invention has the following advantages:

[0054] The obtained gas diffusion layer has very good surface properties. The gas diffusion layer which has been post-treated at high pressure and preferably at high temperature is characterized by a significantly smoother surface on the side coated with the microporous layer.

[0055] The probability of the gas diffusion layer short-circuiting due to penetration of the proton exchange membrane is greatly reduced, especially penetration that may be caused by protruding fibers, impurities on the MPL surface or other causes of surface roughness.

[0056] - The gas diffusion layer has a significantly improved permanent deformation. By carrying out the post-treatment according to the invention at high pressure and preferably at high temperature, the plastic deformation proportion of the GDL can be drastically reduced.

[0057] Design measures for adjusting the fuel cell stack to the consequences associated with permanent deformation of the GDL, such as reduced compression pressure, increased material resistance of installed components and voltage losses, can be reduced or can be omitted entirely.

[0058] Surprisingly, it has been found that the transport properties of the gas diffusion layer can also be influenced in a targeted manner by the post-treatment according to the invention. Thus, properties such as permeability and dry diffusion length can be controlled independently of the composition of the gas diffusion layer material.

[0059] The gas diffusion layer according to the invention can be produced simply and cost-effectively.

[0060] The method of the present invention comprises the following steps:

[0061] i) providing a planar conductive fiber material A),

[0062] ii) coating the fiber material provided in step i) with a precursor for forming the microporous layer B), wherein the composition of the precursor is varied to produce a gradient,

[0063] iii) post-treating the coated fiber material obtained in step ii) at high pressure and optionally high temperature.

[0064] With regard to the fiber material A) and the precursors and conditions for forming the microporous layer B), please fully refer to the following description.

[0065] iii) Post-treatment under high pressure and high temperature

[0066] In a particular embodiment, the treatment in step iii) is carried out at an elevated pressure of at least 0.5 MPa and an elevated temperature of at least 100°C.

[0067] The treatment in step iii) is preferably carried out in a pressure range of 0.5 MPa to 10.0 MPa (5 bar to 100 bar), particularly preferably 1.5 MPa to 8.0 MPa.

[0068] Preferably, the treatment in step iii) is carried out in a temperature range of 100°C to 350°C, particularly preferably 120°C to 330°C, in particular 150°C to 320°C.

[0069] Preferably, said treatment in step iii) is carried out in a press for a period of time ranging from 5 seconds to 5 minutes, preferably from 10 seconds to 2 minutes.

[0070] Preferably, said treatment in step iii) is carried out in a calender for a period of time of more than 0 seconds to 10 seconds, preferably 0.1 seconds to 5 seconds.

[0071] Conventional equipment, such as a single-layer press or a multilayer press, a continuous belt press or a calender can be used for the post-treatment in step iii). In a particular embodiment, at least one double belt press is used for the post-treatment in step iii). In another particular embodiment, at least one calender is used for the post-treatment in step iii).

[0072] Single-layer or multi-layer presses are particularly suitable for discontinuous post-processing of segmented materials. Double-belt presses are suitable for processing both continuous web materials and segmented materials (sheets). Double-belt presses have two continuously circulating press belts between which the GDL web is post-processed while being transported in the forward direction under pressure and, if necessary, heat. The belts are parallel to each other and there is a gap between the upper and lower belts, which can be opened and closed to adjust to the thickness of the GDL material and to set the desired properties.

[0073] In a preferred embodiment, the treatment in step iii) is carried out in a double belt press. In particular, the treatment in step iii) is carried out in a double belt press at a pressure range of 1 MPa to 8 MPa (10 bar to 80 bar) and a temperature range of 200° C. to 350° C.

[0074] In principle, known commercial calenders can be used in step iii) of the method of the present invention. Therefore, a calender with 2, 3, 4 or more calendering rollers can be used. In a simplest preferred embodiment, the calender used in the method of the present invention is a 2-roll calender. The gas diffusion layer can pass through the calender once or repeatedly, for example 1 time, 2 times, 3 times, 4 times, 5 times or more than 5 times. The calendering rollers can be arranged into a geometric shape suitable for calendering of the gas diffusion layer. A two-roll calender can have rollers with a vertical, inclined or horizontal layout. A three-roll calender can have a vertical layout, a staggered upper roller or a staggered lower roller. A four-roll calender can have rollers with an L layout, an inverted L layout, an S layout, a Z layout or other layouts.

[0075] Preferably, the treatment in step iii) is carried out in a calender at a line pressure ranging from 5 N / mm to 500 N / mm, preferably from 10 N / mm to 100 N / mm.

[0076] Preferably, the calendering in step iii) is carried out at a speed of 0.05 m / min to 30 m / min.

[0077] In a preferred embodiment, the treatment in step iii) is carried out in a calender. In particular, the treatment in step iii) is carried out in a calender at a roller temperature range of 130° C. to 220° C., a line pressure range of 8 N / mm to 80 N / mm, and a web speed of 1 m / min to 10 m / min.

[0078] Planar conductive fiber material A) and gas diffusion layer (GDL)

[0079] In the context of the present invention, nonwoven fabrics / webs are generally understood to mean fabrics which consist largely of individual fibers, the cohesion of which is provided essentially only by their own adhesion. The conversion of a web into a nonwoven by forming stronger bonds between the fibers than are present in the web is carried out by web consolidation processes, which are generally divided into mechanical, chemical and thermal processes. Webs, nonwovens and their production are described in H. Fuchs, W. Albrecht, "Nonwovens", 2nd edition (Wiley-VCH Publishers, Weinheim, Germany).

[0080] The planar conductive material A) and the gas diffusion layer used in the present invention are planar structures that are basically two-dimensionally extended and relatively thin. The base surface of the gas diffusion layer of the present invention generally corresponds to the base surface of the adjacent membrane with a catalyst layer and the base surface of the adjacent distribution plate in the fuel cell. The shape of the base surface of the gas diffusion layer can be, for example, a polygon (n-gon, n≥3, such as a triangle, a quadrilateral, a pentagon, a hexagon, etc.), a circle, a circle segment (such as a semicircle), an ellipse or an ellipse segment. The base surface is preferably rectangular or circular. An orthogonal coordinate system can be used to describe the GDL, wherein the base surface of the GDL is located in a plane described by the x-axis and the y-axis (also known as the xy plane). The z-axis orthogonal thereto is used to describe the material thickness. According to the conventional description applicable to fiber composite materials, the x-axis is also referred to as the rolling direction (machine direction, machine direction, MD), and the y-axis is also referred to as the rolling opposite direction (machine transverse direction, cross machine direction, CMD). Along the z-axis direction, material transmission is basically carried out between the distribution plate and the membrane.

[0081] The gas diffusion layer comprises at least one planar conductive material as component A). Component A) preferably comprises a fiber material selected from a fiber mesh, paper, fabric and a combination thereof. Suitable substrate materials are fiber materials that are conductive themselves or that are made conductive by adding conductive additives (such as carbon particles or metal particles). In principle, fibers of carbon fibers, glass fibers, and organic polymers (such as polypropylene, polyester, polyphenylene sulfide, polyether ketone and mixtures thereof) are all suitable for use as substrate materials. The fibers contained in the fiber material A) preferably include carbon fibers or consist of carbon fibers (carbon fibers). Such carbon fibers are particularly advantageous in meeting the requirements for gas diffusion, liquid water permeability, electrical conductivity and thermal conductivity of the GDL. The fiber material A) is preferably selected from carbon fiber fabrics, carbon fiber paper and carbon fiber nonwovens. In a preferred embodiment, the fiber material A) includes at least one carbon fiber nonwoven, or the fiber material A) consists of a carbon fiber nonwoven.

[0082] Carbon fibers can be manufactured by conventional methods, wherein polyacrylonitrile fibers (PAN fibers) are preferably used as starting materials. PAN fibers are made by free radical polymerization of a monomer composition, which preferably contains at least 90% by weight of acrylonitrile, with reference to the total weight of the monomers used for polymerization. The resulting polymer solution is spun into filaments, for example, by wet spinning and coagulation spinning, and combined into ropes. Before the PAN precursor is converted into carbon fibers at high temperatures, the PAN precursor is usually subjected to oxidative cyclization (also referred to as oxidation for short) in an oxygen-containing atmosphere at elevated temperatures of about 180° C. to 300° C. The chemical crosslinking thus produced helps to improve the dimensional stability of the fibers. Subsequently, the actual pyrolysis into carbon fibers is carried out at a temperature of at least 1200° C. Depending on the shape of the desired fiber material, the initial fibers or the already planar fiber material can be used for this pyrolysis. Depending on the temperature during pyrolysis, a distinction is made between carbonization and graphitization. Carbonization refers to treatment under conditions of about 1200° C. to 1500° C. in an inert atmosphere to eliminate volatile products. So-called high modulus fibers or graphite fibers can be obtained by graphitization (i.e. heating to about 2000°C to 3000°C in an inert gas). These fibers are high in purity, light in weight, strong, and have excellent electrical and thermal conductivity.

[0083] The fiber material A) is preferably selected from the group consisting of carbon fiber woven fabrics, carbon fiber papers and carbon fiber nonwovens.

[0084] In the case of carbon fiber fabrics, the planar fiber material is made by interweaving two thread systems, warp (warp yarns) and weft (weft yarns). As in textiles, the fiber bundles are flexibly but inseparable. The carbon fiber fabric is preferably made of oxidized but not yet carbonized or graphitized PAN fibers. Carbonization or graphitization is carried out after weaving to make the planar fiber material conductive.

[0085] As mentioned at the beginning of this article, carbon fiber paper is usually produced from oxidized PAN fibers. These oxidized PAN fibers are comminuted into fiber fragments in a known manner, pulped, and formed into a fiber-based cloth by screening (pulpwood trough) in a manner similar to paper production and dried. In a preferred embodiment, at least one binder is additionally introduced into the paper. Suitable binders are, for example, phenolic resins, furan resins, polyimide resins, etc. In order to introduce the binder, the paper can be impregnated with this binder, and then, if necessary, the binder is cured. After impregnation and curing, the carbon fiber paper is carbonized / graphitized again in order to also convert the binder into a more conductive compound. In another suitable embodiment, the fiber material A is provided with filled carbon fiber paper. First, the production is carried out as described above, but instead of introducing the binder and carbonizing / graphitizing, a filler formed by a carbon material in a polymer binder is introduced into the still wet paper. For this purpose, in particular a carbon-PTFE filler is used. This filling increases the thermal conductivity and electrical conductivity, so that carbonization / graphitization can be omitted.

[0086] Non-oxidized or oxidized PAN fibers can be used to produce carbon fiber nonwovens. These fibers can be made into yarns (combed) in a dry-laid manner in a first step and then consolidated into a nonwoven. For example, this can be done by hydroentangling, in which the carbon fibers are oriented, entangled, and thus mechanically stabilized. The thickness of the cured nonwoven can be calibrated to the desired value as required. The nonwoven based on non-oxidized PAN fibers is first oxidized at elevated temperature and in an oxygen atmosphere after the nonwoven is webbed and cured, and then carbonized / graphitized in an inert atmosphere. The nonwoven based on oxidized PAN fibers is only carbonized / graphitized after the nonwoven is webbed and cured. Optionally, at least one binder can be additionally introduced into the fiber web, and then, as appropriate, this binder is hardened. Suitable binders are those mentioned for carbon fiber paper, in particular phenolic resins. For example, a binder can be introduced immediately after carbonization / graphitization, and finally the resulting impregnated fiber web is carbonized / graphitized again.

[0087] In a specific embodiment, the planar conductive fiber material A) comprises at least one carbon fiber nonwoven fabric. Advantages of carbon fiber nonwoven fabrics include, but are not limited to, compression elasticity, and are convenient for large-scale production, such as in a roll-to-roll process.

[0088] Fibrous materials A) generally refer to fiber composite materials, including:

[0089] a1) Carbon fiber,

[0090] a2) optionally at least one polymer binder and / or a pyrolysis product thereof,

[0091] a3) optionally at least one further additive different from a2).

[0092] The fiber material A) contained in the gas diffusion layer may contain customary additives a3). The additives are preferably selected from the group consisting of hydrophobizing agents, conductivity-improving additives, surface-active substances and mixtures thereof.

[0093] To improve the transport process through the GDL and at the interface, the hydrophobicity of the fiber material A) can advantageously be increased. Suitable hydrophobes are fluoropolymers, such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymers (FEP). Preferably, PTFE is used as a hydrophobic agent. The fiber material can be finished with a hydrophobic agent by conventional impregnation methods. For this purpose, a PTFE dispersion is applied in an immersion tank, the solvent is evaporated, and the treated fiber material is sintered at a high temperature, usually at least 300° C.

[0094] Preferably, the hydrophobizing agent content of the fibrous material A) is 3 to 40 wt % relative to the total weight of the fibrous material A). In a specific embodiment, the hydrophobizing agent content of the fibrous material is 3 to 40 wt % relative to the total weight of the fibrous material A).

[0095] In order to improve the electrical and thermal conductivity, the fiber material A) can be finished with at least one conductivity-improving additive. The conductivity-improving additive is, for example, metal particles, carbon particles, etc. Preferably, the conductivity-improving additive is selected from carbon black, graphite, graphene, carbon nanotubes (CNT), carbon nanofibers and mixtures thereof. For example, the finishing of the fiber material A) with at least one conductivity-improving additive can be carried out together with the finishing with a hydrophobic agent, in particular a PTFE dispersion. Even without the conductivity-improving additive, the fiber material A) tends to have good electrical and thermal conductivity due to the carbon fibers used.

[0096] Preferably, the content of the conductivity-improving additive of the fiber material A) is 0% to 40% by weight, relative to the total weight of the fiber material A). If the fiber material A) contains a conductivity-improving additive, the content is preferably 0.1% to 40% by weight, particularly preferably 0.5% to 30% by weight, relative to the total weight of the fiber material A).

[0097] The fiber material A) preferably has a thickness in the range of 50 μm to 750 μm, particularly preferably 100 μm to 500 μm. This thickness relates to the uncompressed state of the fiber material A), ie before the post-treatment in step iii) and before the GDL is installed in a fuel cell.

[0098] The fiber material A) preferably has a porosity in the range of 10% to 90%, particularly preferably 20% to 85%, measured by means of mercury porosimetry in accordance with DIN ISO 15901-1:2019-03.

[0099] The average pore size of the fiber material A) is preferably in the range of 5 μm to 60 μm, particularly preferably 8 μm to 50 μm, in particular 10 μm to 40 μm. The average pore size can be determined by mercury porosimetry according to DIN ISO 15901-1:2019-03.

[0100] Microporous layer B)

[0101] The gas diffusion layer of the present invention is composed of a two-layer or multi-layered composite based on a planar electrically conductive fiber material A) and at least one microporous layer (MPL) B) on at least one surface of the fiber material A).

[0102] According to the invention, the microporous layer B) comprises conductive particles in a matrix consisting of a polymer binder. The conductive particles are preferably selected from conductive carbon particles, in particular carbon black, graphite, graphene, carbon nanotubes (CNT), carbon nanofibers and mixtures thereof. Preferably, carbon black, graphite or mixtures thereof are used.

[0103] The polymer binder comprises in particular at least one fluorine-containing polymer. The fluorine-containing polymer is preferably selected from polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymers, perfluoroalkoxy polymers and mixtures thereof. Polytetrafluoroethylene (PTFE) is preferably used.

[0104] The microporous layer B) is preferably produced with 0.5 to 50 wt %, particularly preferably 1.0 to 40 wt %, particularly preferably 10 to 25 wt % of polymer binder, relative to the total weight of polymer binder and conductive particles.

[0105] Compared to the macroporous fiber material A), the MPL B) is microporous, with a pore size generally well below one micrometer, preferably a maximum of 900 nm, particularly preferably a maximum of 500 nm, in particular a maximum of 300 nm. The average pore size of the MPL B) is preferably in the range of 5 nm to 200 nm, particularly preferably 10 nm to 100 nm.

[0106] The determination of the porosity and the pore size distribution can be carried out with the aid of mercury porosimetry, as described in DIN ISO 15901-1:2019-03: Mercury porosimetry. The last-mentioned average pore size applies primarily to the case where carbon black is used as conductive particle in the MPL. By using graphite as conductive particle in the MPL or by using pore formers, significantly larger MPL pores can also be produced. In this case, depending on the specific composition, the average pore diameter is, for example, greater than 1 μm. When using different conductive particles, the pore size can have a bimodal or multimodal distribution curve. Thus, when a mixture of carbon black and graphite is used, a pore size distribution with two pore size peaks (carbon black peak and graphite peak) can be obtained.

[0107] The microporous layer B) preferably has a thickness in the range of 5 to 150 μm, particularly preferably 10 to 100 μm. This thickness relates to the uncompressed state of the microporous layer B), ie before the post-treatment in step iii) and before the GDL is installed in a fuel cell.

[0108] The presence of MPL has a significant impact on the water balance of the fuel cell. Due to the high PTFE ratio and small pores of MPL, it becomes difficult for water to flow into the GDL and electrodes because the MPL acts as a liquid barrier, thereby facilitating the bulk transport of gaseous reactants to the catalyst.

[0109] The gas diffusion layer according to the invention preferably has a thickness (total thickness of fiber material A) and MPL B) in the range of 50 μm to 1000 μm, particularly preferably 75 μm to 500 μm. This thickness relates to the uncompressed state of the GDL, i.e. before post-treatment in step iii) and before installation in a fuel cell.

[0110] Furthermore, the gas diffusion layer preferably has a high total porosity. This total porosity is preferably in the range of 20% to 80%, as described above, and is measured by mercury porosimetry according to DIN ISO 15901-1:2019-03.

[0111] Method for manufacturing a gas diffusion layer

[0112] Step i)

[0113] With regard to suitable and preferred fiber materials A) used in step i), reference is made to the above explanations.

[0114] Step ii)

[0115] The precursor used in step ii) preferably comprises at least one fluoropolymer, at least one carbon material and optionally comprises at least one pore former. Fluoropolymer is preferably selected from carbon polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). PTFE is preferably used. Preferably, the carbon material is selected from carbon black, graphite, graphene, carbon nanotube (CNT), carbon nanofiber and mixture thereof. Carbon black or graphite is preferably used. In a particular embodiment, the precursor used in step b) comprises at least one pore former. Suitable pore formers are commercially available plastic particles, for example, formed by polymethyl methacrylate (PMMA). Suitable particle size is within the range of 10 μm to 100 μm.

[0116] Preferably, the volume ratio of the pores in the manufactured microporous layer is 0 t volume % to 70 t volume % due to the use of the pore former relative to the total volume of the pores in the manufactured microporous layer.

[0117] MPL can be applied to the fiber material in different ways. Spraying, screen printing or Meyer-Rod processes are usually used in discontinuous production, while doctor blade, slot nozzle and gravure roller processes are preferably used in continuous coating. The MPL layer thickness and penetration depth may be affected by the coating process parameters and the viscosity of the coating. Finally, heat treatment is performed again, for example in a drying furnace or sintering furnace. Drying is first carried out at a temperature of 100°C to 200°C and then sintering is carried out at a temperature of 300°C to 500°C.

[0118] The post-processing step iii) has been described in detail above, please refer to the above content.

[0119] Compression set value:

[0120] Plastic deformation refers to the inability of a material (such as a gas diffusion layer) to return to 100% of its original shape after being loaded, but rather a permanent change in shape. Part of the deformation is elastic and therefore reversible, and only part is plastic and remains permanent. The property of a material to permanently change its shape when a stress is applied, i.e. deformability, is also referred to by the term "permanent deformation". Materials with low plastic deformability exhibit low permanent deformation.

[0121] The compression set value is a measure of how a material (here the GDL) behaves during deformation under pressure and subsequent pressure relief. When used in fuel cells, the GDL is usually pressed (compressed) at high intensity. The compression-based properties of the GDL can be characterized by the ratio of elastic to plastic deformation. Compression set is an irreversible deformation that remains after the applied force has disappeared. Gas diffusion layers with low permanent deformation are characterized by low compression set values. The compression set value can be determined as follows. The values ​​of other physical variables (such as thickness, permeability, electrical resistance) can be determined at a specific pressure and after single or multiple loading.

[0122] Take three samples (left, right and center) across the width of the GDL to be tested and average them. If the material has a machine direction during manufacture, take the sample perpendicular to the machine direction (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 cm 2 . The sample is exposed to a time-varying pressure in a testing machine, which acts perpendicularly on the sample surface. The sensor determines the change in thickness of the GDL over time under the corresponding force. The sample is placed on a device for determining elastic and plastic deformations by means of a force sensor, wherein the movement is transmitted to the sample via a spring. The distance moved until the maximum pressure is reached is measured by a displacement sensor. Since the deformation of the sample is nonlinear, the measurement curve is adapted to the relative change. A measuring cycle, i.e. a loading to the maximum pressure and the subsequent pressure relief, lasts for 1 min. The sample undergoes three loading cycles. The initial value, to which only a small force is applied to the sample, is 0.025 MPa. Typical pressure values ​​for determining compression set values ​​(and other physical variables such as thickness, conductivity or resistivity per unit area, air permeability, etc.) are, for example, 0.6 MPa, 1.0 MPa and 2.4 MPa.

[0123] The compression set value for a certain pressure is obtained from the difference between the thickness measured at this pressure in the first loading cycle and the thickness measured at this pressure in the third loading cycle.

[0124] Preferably, the GDL of the present invention has a compression set value of at most 5 μm at 10 bar (1 MPa), and the compression set value is 90 g / m2 according to the above method. 2 Up to 95g / m 2 And the MPL load is 15.0g / m 2 Up to 22.0g / m 2 The GDL is measured using a ring sample with an inner diameter of 45 mm and an outer diameter of 56 mm.

[0125] Roughness:

[0126] The roughness measurement is carried out according to the conventional stylus method known to the person skilled in the art and described, for example, in DIN 4768-1:1974-08, entitled "Determination of the roughness measurement variable R by means of an electric stylus instrument" a , R z , R max ; Basic Principles.

[0127] Determine the arithmetic mean roughness value R a (average distance from the measuring point on the surface to the center line) and the arithmetic mean roughness depth R z The measurements were carried out with a Marsurf XCR 20 with a free stylus MFW-250. The values ​​are the average of 6 measurements: 3 in the machine direction (MD) and 3 perpendicular to the machine direction (CD). The specific measurement conditions are described in the Examples section, to which reference is made.

[0128] Puncture measurement, number of short circuits:

[0129] Figure 1 A device for penetration measurement is shown in order to determine the number of short circuits as a measured value characterizing the probability of a short circuit.

[0130] In the puncture measurement, a PP film (PP foil, thickness 4 μm) is installed between two GDL samples (GDL sheets) and a distance layer (Distance layer) with a defined thickness (0.1 mm to 1.0 mm) and a defined gap. The material is located on a conductive and smooth metal plate. During the measurement, a metal stamp (diameter 12.7 mm) slowly presses the upper GDL into the gap between the distance layers and onto the PP film. The conductive pressure stamp and the metal plate are connected to a resistance measuring device. When the maximum pressure is reached, the measurement at the test site ends. If the threshold resistance is below 10 kΩ, the PP film is punctured. The corresponding pressure is recorded. Since the GDL itself is conductive, this measurement can determine the damage to the PP film caused by the pressed GDL. In one measurement cycle, usually 117 measurement points are passed in an area of ​​about 300 mm × 400 mm.

[0131] Furthermore, tests with PP films of different thicknesses (4 μm-14 μm) showed that as the thickness of the PP film decreases, the probability of the film / membrane being punctured increases, or the number of punctures increases when a certain number of measurements are performed under the same material / measurement parameter combination. At least 117 measurements were performed for each combination (standard: 4 cycles, 117 measurements each).

[0132] The short circuit number is a measurement used to characterize the possibility of a short circuit and is defined as follows:

[0133] Number of short circuits =

[0134] (Number of pierced measuring points / Total number of measuring points)×100

[0135] In other words, the percentage of the number of measurements below the threshold resistance to the total number of measurements is defined as the number of short circuits. The fewer the number of measurements below the threshold resistance, the smaller the number of short circuits, and the smaller the possibility of membrane penetration.

[0136] Preferably, the gas diffusion layer of the present invention has a short circuit number of at most 15% and a weight per unit area of ​​95 g / m2 measured by puncture on a base surface of 297 mm×420 mm. 2 And the MPL load is 15g / m 2 Measured on the GDL.

[0137] The specific measurement conditions are described in the Examples section, please refer to the content there.

[0138] Other physical variables

[0139] The air permeability perpendicular to the plane of the material can be determined by Gurley measurement. For this purpose, an automated Gurley densitometer from Gurley Precision Instruments can be used. The measurement time is measured in seconds up to 100 cm 3 The air flows vertically through the sample at a constant pressure difference, with a flow area of ​​6.42 cm 2 The determination of air permeability according to the Gurley method is described in ISO 5636-5.

[0140] The dry diffusion length indicates the actual distance a gas molecule travels through the planar fiber material A) and / or the microporous layer B) in μm. The dry diffusion length is determined with the aid of a stationary Wicke-Kallenbach cell.

[0141] The thickness of the gas diffusion layer can be determined according to DIN 53855-1:1993-08 "Determination of thickness of textile fabrics". The thickness at a certain pressure (eg 0.025 MPa or 1.0 MPa) can be determined in an apparatus for measuring compression set as described in detail above.

[0142] The mass per unit area can be determined according to EN 29073-1:1992 in g / m 2 As unit.

[0143] The porosity of the GDL can be determined by means of mercury porosimetry as described in DIN ISO 15901-1:2019-03: Mercury porosimetry.

[0144] Fuel Cells

[0145] Another subject of the invention is a fuel cell comprising at least one gas diffusion layer as described above or at least one gas diffusion layer obtained by a method as described above.

[0146] In principle, the gas diffusion layer of the present invention is applicable to all common fuel cell types. The fuel cell of the present invention preferably refers to a proton exchange membrane fuel cell (PEMFC) in particular. A proton exchange membrane fuel cell is also known as a polymer electrolyte fuel cell (PEFC) or a low temperature polymer electrolyte membrane fuel cell (LT-PEMFC). A specific embodiment of the present invention is a hydrogen and oxygen fuel cell in the form of a low temperature proton exchange membrane fuel cell (PEMFC). Please fully refer to the description of the structure of the fuel cell in the foregoing text.

[0147] The fuel cell of the present invention preferably comprises a polymer electrolyte membrane, to which a catalyst layer is applied on the anode side and the cathode side, the catalyst layer forming an electrode. Preferably, a gas diffusion layer (GDL) in contact with the catalyst layer is provided on the anode and / or cathode side. The fuel cell in particular has a polymer electrolyte membrane, to which a catalyst layer is applied, the catalyst being in contact with the surface of the microporous layer B) of the gas diffusion layer of the present invention. In particular, the fuel cell has the gas diffusion layer of the present invention on the cathode side, wherein the catalyst layer is in contact with the surface of the microporous layer B) of the gas diffusion layer. More particularly, the fuel cell has the gas diffusion layer of the present invention on the cathode side and on the anode side, wherein both the cathode layer and the anode layer are in contact with the surface of the microporous layer B) of the gas diffusion layer of the present invention.

[0148] One advantage of the invention is that the transport process through the gas diffusion layer can be specifically adapted to the gradient of the working medium flowing through the fuel cell and / or the operating parameters of the fuel cell. To this end, at least one characteristic gradient of the gas diffusion layer generally corresponds to at least one characteristic gradient of the working medium flowing through the fuel cell and / or the operating parameters of the fuel cell.

[0149] Another subject of the present invention is the use of a gas diffusion layer as described above or obtained by a method as described above in a proton exchange membrane fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0150] Figure 1 A device for penetration measurement is shown in order to determine the number of short circuits as a measured value characterizing the probability of a short circuit.

[0151] Figure 2 The plastic deformation properties (permanent set performance) at compression set values ​​at 1 MPa are shown for 5 pairs consisting of a comparative GDL (left column) and a GDL according to the invention (right column), respectively.

[0152] Figure 3a The arithmetic mean roughness values ​​R of two pairs consisting of a comparative GDL (left column) and a GDL according to the invention (right column) are shown. a (MD), the arithmetic mean roughness value is measured according to the stylus method described in DIN 4768-1:1974-08.

[0153] Figure 3b The arithmetic mean roughness values ​​R of two pairs consisting of a comparative GDL (left column) and a GDL according to the invention (right column) are shown. a (CD), the arithmetic mean roughness value is measured according to the stylus method described in DIN 4768-1:1974-08.

[0154] Figure 4a The arithmetic mean roughness depth R of two pairs consisting of a comparative GDL (left column) and a GDL according to the invention (right column) are shown. Z (MD), the arithmetic mean roughness depth is measured according to the stylus method described in DIN 4768-1:1974-08.

[0155] Figure 4b The arithmetic mean roughness depth R of two pairs consisting of a comparative GDL (left column) and a GDL according to the invention (right column) are shown. Z (CD), the arithmetic mean roughness depth is measured according to the stylus method described in DIN 4768-1:1974-08.

[0156] The following examples are used to illustrate the present invention in detail, but these examples do not limit the present invention in any way. DETAILED DESCRIPTION

[0157] I) Fabrication of Gas Diffusion Layer

[0158] Manufacturing Example 1:

[0159] Production of a gas diffusion layer without the aftertreatment according to the invention (Example V1) and a gas diffusion layer after the aftertreatment according to the invention at high pressure and high temperature (Example 1)

[0160] Made of 100% carbon fiber with a unit area weight of 100g / m2 The nonwoven fabric is sized by mixing an impregnation composition, which contains 80% carbon black and 20% PTFE in terms of solid matter. The sizing is performed by padding with an aqueous dispersion, and the sizing weight is 15% of the mass of the GDL substrate (equivalent to 15 g / m 2 ). Subsequently, it was dried at 80°C for 2 minutes and sintered at 400°C for 2 minutes. Subsequently, MPL was also applied to the substrate obtained in this way to produce the gas diffusion layer of the present invention. In order to coat the MPL, an MPL coating containing 2.0 wt% PTFE and 7.8 wt% carbon in distilled water was applied to the fiber material. Subsequently, the fiber material was dried at 160°C for 2 minutes and sintered at 400°C for 2 minutes. The resulting MPL loading was 15 g / m 2 The GDL of the invention was post-treated in a double belt press at a pressure of 25 bar and a temperature of 320° C. for 20 seconds. A GDL without post-treatment was used as a comparison.

[0161] II) Examples of applied technology

[0162] The following materials were used to determine the technical application properties:

[0163] 1) Instance 1 / V1

[0164] GDL in Manufacturing Example 1

[0165] 2) Instance 2 / V2

[0166] Similar to the manufacturing example 1, the unit area weight is 100 g / m 2 GDL.

[0167] 3) Instance 3 / V3

[0168] Similar to the manufacturing example 1, the unit area weight is 132 g / m 2 GDL.

[0169] 4) Instance 4 / V4

[0170] Similar to the manufacturing example 1, the unit area weight is 135 g / m 2 GDL.

[0171] 5) Instance 5 / V5

[0172] Similar to the manufacturing example 1, the unit area weight is 96.5 g / m 2 GDL.

[0173] 6) Example 6 / V6

[0174] Similar to the manufacturing example 1, the unit area weight is 94 g / m2 GDL.

[0175] Compression Set:

[0176] The compression set values ​​and thickness were determined according to the methods described in detail above. The values ​​are given in Table 1 below.

[0177] Roughness

[0178] The roughness determination was carried out according to the stylus method described in DIN 4768-1:1974-08.

[0179] Determine the arithmetic mean roughness value R a (average distance from the measuring point on the surface to the center line) and the arithmetic mean roughness depth R z The measurements were carried out with a Marsurf XCR 20 with a free stylus MFW-250. The values ​​are the average of 6 determinations: 3 in the machine direction (MD) and 3 perpendicular to the machine direction (CD).

[0180] The measurement conditions are as follows:

[0181] Stylus = MFW-250. Stylus diamond radius 2μm, cone angle 60°

[0182] LC(GS)=2.5mm=cutoff value=LT+LM

[0183] LT = 17.5 mm = stylus path = 2.5 mm lead and 2.5 mm lag for the onset / attenuation of the Gaussian filter. This 2×2.5 mm path is not taken into account in the measurement.

[0184] LM = 12.5 mm = measuring distance, used to determine the roughness value

[0185] Z=5=number of individual measurements of the Rz value. The measurement path (profile) is decomposed into 5 symmetrical individual distances (=LM / 5). The average value is calculated from each individual distance. The Rz value is obtained by averaging the 5 average values.

[0186] VB=+-250μm=Stylus measurement range

[0187]

[0188] Linearity = <1%

[0189] Detection force (measurement force) = 0.8mN

[0190] Detection speed 0.5mm / sec

[0191] Puncture measurement, number of short circuits:

[0192] As described above, the penetration measurement was carried out to determine the number of short circuits. In one measurement cycle, 117 measurement points were passed over an area of ​​approximately 300 mm×400 mm. The results are shown in Table 1.

[0193] The Gurley air permeability was measured perpendicular to the plane of the material using a Gurley densitometer from Gurley Precision Instruments according to ISO 5636-5. The results are also shown in Table 1.

[0194] The dry diffusion length was determined with the aid of a stationary Wicke-Kallenbach cell. The results are also shown in Table 1.

[0195] Table 1

[0196]

[0197] (MD) = along the machine direction, (CD) cross the machine direction

Claims

1. A method for manufacturing a gas diffusion layer for a fuel cell, the gas diffusion layer comprising A) a planar conductive fiber material, and B) a microporous layer on at least one of the surfaces of the fibrous material, the microporous layer comprising conductive particles in a matrix consisting of a polymer binder, in i) providing a planar conductive fiber material A), ii) coating the fiber material provided in step i) with a precursor for forming a microporous layer, iii) post-treating the coated fiber material obtained in step ii) at high pressure and optionally high temperature.

2. The method for realizing a gas diffusion layer according to claim 1, wherein the gas diffusion layer has one or more of the following characteristics: The maximum compression set value under -1.0MPa is 5μm, and its unit area weight is 95g / m 2 Up to 100g / m 2 And the MPL load is 15g / m 2 Up to 22g / m 2 The compression set value is measured on a GDL of 45 mm using a ring sample with an inner diameter of 45 mm and an outer diameter of 56 mm, wherein the sample is subjected to three loading cycles from 0.025 MPa to 1.0 MPa, and the compression set value is obtained by measuring the thickness difference at 1.0 MPa in the first loading cycle and the third loading cycle, -Arithmetic mean roughness R a Compared to an untreated gas diffusion layer, the arithmetic mean roughness is reduced by at least 10%, the arithmetic mean roughness being measured by the stylus method in accordance with DIN EN ISO 4288:1998-04, - Roughness depth R Z Compared to an untreated gas diffusion layer, the roughness depth is reduced by at least 10%, the roughness depth being measured by the stylus method according to DIN EN ISO 4288:1998-04, - The number of short circuits is a maximum of 25%, the short circuit number is measured by puncture on a surface area of ​​297 mm×420 mm and a unit area weight of 95 g / m 2 And the MPL load is 15g / m 2 Measured on the GDL.

3. The method according to claim 1 or 2, wherein the fiber material A) is selected from the group consisting of carbon fiber nonwovens, carbon fiber fabrics, and mixtures thereof.

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

5. The method according to any of the preceding claims, wherein the treatment in step iii) is carried out in a temperature range of 100°C to 350°C, preferably 120°C to 330°C, particularly preferably 150°C to 320°C.

6. The method according to any one of the preceding claims, wherein the treatment in step iii) is carried out using an apparatus selected from a single-layer press, a multi-layer press, a continuous belt press, a calender and a combination thereof, preferably selected from a double-belt press, a calender and a combination thereof.

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

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

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

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

11. A gas diffusion layer for a fuel cell, the gas diffusion layer comprising: A) a planar conductive fiber material, and B) a microporous layer on at least one of the surfaces of the fiber material, The gas diffusion layer has at least one of the following characteristics: The maximum compression set value under -1.0MPa is 5μm, and its unit area weight is 95g / m 2 Up to 100g / m 2 And the MPL load is 15g / m 2 Up to 22g / m 2 The compression set value is measured on a GDL of 45 mm using a ring sample with an inner diameter of 45 mm and an outer diameter of 56 mm, wherein the sample is subjected to three loading cycles from 0.025 MPa to 1.0 MPa, and the compression set value is obtained by measuring the thickness difference at 1.0 MPa in the first loading cycle and the third loading cycle, -Arithmetic mean roughness R a Compared to an untreated gas diffusion layer, the arithmetic mean roughness is reduced by at least 10%, the arithmetic mean roughness being measured by the stylus method in accordance with DIN EN ISO 4288:1998-04, - Roughness depth R Z Compared to an untreated gas diffusion layer, the roughness depth is reduced by at least 10%, the roughness depth being measured by the stylus method according to DIN EN ISO 4288:1998-04, - The number of short circuits is a maximum of 25%, the short circuit number is measured by puncture on a surface area of ​​297 mm×420 mm and a unit area weight of 95 g / m 2 And the MPL load is 15g / m 2 Measured on the GDL.

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

13. The fuel cell according to claim 12, comprising a polymer electrolyte membrane on which a catalyst layer is applied, wherein the catalyst layer is in contact with a surface of the microporous layer B) of the gas diffusion layer.

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

Images