Semipermeable membrane for membrane humidifier

Abstract

The present invention relates to a semipermeable membrane (10), particularly for use in a membrane humidifier for a fuel cell system, comprising: (a) a support layer (12) comprising a composite material including at least one plastic and at least one silicon-containing porous filler embedded in the plastic; and (b) a coating layer (14) disposed on the support layer (12) and comprising at least one organosilicon compound.

Description

[Technical Field]

[0001] The present invention relates to semipermeable membranes, membrane humidifiers including the corresponding semipermeable membranes, fuel cell systems including the corresponding membrane humidifiers, and methods for manufacturing the corresponding semipermeable membranes. [Background technology]

[0002] For the past few years, the use of fuel cells in vehicle technology has been seen as a promising way to reduce dependence on fossil fuels such as crude oil. Fuel cells are one of the most important alternatives to the use of batteries, such as lithium-ion batteries. Compared to battery technology, fuel cell technology offers specific advantages, particularly the practical handling of fuel compared to electrochemical storage, the possibility of storability of fuel and the possibility of short replenishment times, thus avoiding long charging times, and the possibility of using existing lines and storage infrastructure for conventional fuel supplies instead of building battery charging infrastructure. These advantages are particularly important for use in sectors where long charging processes need to be avoided, especially in the aviation sector and in heavily used commercial vehicle fleets.

[0003] In a fuel cell, the conversion of oxygen by a fuel (e.g., hydrogen, methane, or methanol) to water and possibly other reaction products occurs under controlled reaction conditions, and the reaction steps of the redox reaction are spatially separated. To this end, a fuel cell consists of an anode and a cathode separated from each other by an electrolyte (e.g., an electrolyte membrane).

[0004] Reactants are typically supplied continuously to a fuel cell during operation. During operation, fuel cells, especially polymer electrolyte membrane fuel cells (PEM fuel cells), place high demands on the purity of the process gases used and on optimal humidity settings to prevent the electrolyte membrane from drying out even at high operating temperatures. This typically requires complex management and control of fluid flows and the use of sophisticated filter technology.

[0005] To ensure sufficient humidification of the electrolyte membrane even at high operating temperatures, it is generally advantageous to humidify the process gas being supplied, especially the cathode-side process gas. This moisture can be supplied to the process gas from a reservoir, such as humidified air, via a suitable humidification device. Since water is produced during fuel cell operation, the exhaust gas from the fuel cell can also serve as a reservoir for moisture, for example. During humidification, the goal is usually to eliminate or minimize contact between the process gas and the reservoir, except for moisture exchange. This can prevent contamination of the process gas, for example, by the exhaust gas.

[0006] In theory, a variety of humidifiers can be used as humidification devices, however so-called membrane humidifiers, which use one or more moisture-permeable membranes, such as hollow fiber membranes, that are permeable to water vapor but largely prevent further exchange of materials, are generally recognized as a particularly efficient and advantageous form of humidification device.

[0007] When humidified and dry gas streams are separated by such a semipermeable membrane, the difference in water partial pressure in the two gas streams will cause diffusion-driven permeation of water from the humidified gas stream to the dry gas stream.

[0008] PEM fuel cell systems, their design and the use of membrane humidifiers in these PEM fuel cell systems are comprehensively known to the person skilled in the art from the prior art and are described, for example, in DE 102015202089 A1, DE 102015224202 A1 or DE 102016224478 A1.

[0009] While slight permeation of other components of the storage fluid, i.e. in addition to the desired moisture permeation, is usually not considered problematic for applications in the field of air management in buildings, for example, for applications in the field of fuel cells, it is generally desired to prevent as reliably as possible any mixing of the supply and exhaust air streams that would exceed the moisture exchange. In addition to the structural aspects of the membrane humidifier, this is usually highly dependent on the properties of the membranes used, and there is always a need to further improve these membranes.

[0010] In the field of building air management, membrane humidifiers have been proposed that use semipermeable membranes as water transport membranes, as disclosed in EP 2435171. The semipermeable membranes comprise a porous polyethylene substrate impregnated with silicon dioxide, the surface of which is coated with a cross-linked, water-permeable, nonionic polyurethane-polyether polymer. EP 2435171 shows that these water transport membranes have high permeability to water (vapor and liquid) while exhibiting low or almost no permeability to gases and impurities.

[0011] The inventors tested water transport membranes known from the building air management field, as described in EP 2435171, and evaluated their performance in the context of membrane humidifier applications for fuel cells. They found that the water transport membranes known from the prior art were unable to fully meet the application-specific requirements in all areas. The inventors suspect that this is at least in part due to the high temperature and / or humidity actually present in the fuel cell exhaust stream compared to building air conditioning. In addition to the achievable water permeation and the observed leakage of exhaust or impurities under process conditions, the durability of the water transport membranes, particularly in fuel cell systems, was found to be insufficient. In particular, the high temperature or humidity environments proved insufficient to ensure sufficient durability under the mechanical loads expected in vehicle use. This durability, which the inventors consider inadequate for fuel cell applications, is primarily related to the adhesive strength between the substrate and the polyurethane-polyether polymer coating. This effect, which may result in the coating peeling off upon prolonged exposure to warm and humid environments, may be acceptable for building climate control applications, but in the inventor's assessment has already been clearly documented in EP 2435171 (see paragraph

[0063] ). Summary of the Invention [Problem to be solved by the invention]

[0012] SUMMARY OF THE INVENTION The main object of the present invention is to overcome or at least mitigate the above-mentioned drawbacks of the prior art.

[0013] In particular, the objective of the present invention was to identify a semipermeable membrane that has excellent water permeability while simultaneously preventing air and other impurities from passing through the membrane as much as possible. At the same time, the disclosed semipermeable membrane is required to have high mechanical strength and durability compared to the prior art, especially under high temperature or humidity conditions. Furthermore, the disclosed semipermeable membrane is required to be producible as quickly and cost-effectively as possible, and it is desirable to minimize the use of materials harmful to health and / or the environment during its manufacture, in particular to avoid the use of perfluorinated compounds.

[0014] A further object of the present invention was to provide a method for producing a corresponding semipermeable membrane.

[0015] A second object of the present invention was to provide an efficient membrane humidifier for use in a fuel cell system and a corresponding fuel cell system.

[0016] The inventors of the present invention have realized that the above problems can surprisingly be solved by a semipermeable membrane as claimed, comprising a support layer comprising a particular composite material and a coating layer comprising an organosilicon compound disposed on the support layer, thereby providing a semipermeable membrane that is also well suited for many other applications requiring the transfer of moisture and / or enthalpy from a humidified compartment to a dry compartment.

[0017] Therefore, the above-mentioned problem is solved by the object of the invention as defined in the claims. Preferred embodiments according to the invention are derived from the dependent claims and the following description.

[0018] In particularly preferred embodiments, the embodiments identified below as preferred are combined with features of other preferred embodiments. Thus, combinations of two or more of the embodiments described below as particularly preferred are particularly preferred. Also preferred are embodiments in which features of some preferred embodiments are combined with one or more features of other some preferred embodiments. Features of preferred membrane humidifiers, methods, and fuel cell systems follow from features of preferred semipermeable membranes. [Means for solving the problem]

[0019] The present invention provides (a) a support layer comprising a composite material including at least one plastic and at least one silicon-containing porous filler embedded in the plastic; (b) a coating layer disposed on the support layer and comprising at least one organosilicon compound, the coating layer being particularly suitable for use in a membrane humidifier for a fuel cell system. DETAILED DESCRIPTION OF THE INVENTION

[0020] The semipermeable membrane of the present invention is particularly suitable for use in a membrane humidifier in a fuel cell system, particularly in a fluid conduit system. This suitability is due in particular to the excellent properties of the semipermeable membrane of the present invention, such as its excellent durability even in high-temperature environments of 80°C or higher, and its adaptability to the high humidity environment that occurs in the exhaust stream of a fuel cell system. Furthermore, because the semipermeable membrane of the present invention has excellent water permeability and the ability to reliably inhibit the permeation of air and other impurities, it is also highly suitable for other applications, such as modules for transferring moisture and / or enthalpy from a gas with a high water partial pressure to a drier gas.

[0021] Compared to prior art, such as that disclosed in EP 2435171, the semipermeable membranes of the present invention achieve advantageous properties, particularly excellent durability and strong interlayer adhesive strength, without the need for additional chemical crosslinking. Furthermore, the excellent transport properties of the semipermeable membranes of the present invention are achieved without the need for additional post-coating processing steps, particularly compared to PVA-based coatings. In particular, since there is no need to create intentional defects or intentional peeling in the top layer, a continuous, highly functional, and durable coating layer can be obtained in the manufacture of the semipermeable membranes of the present invention using only a single coating step and a single coating device.

[0022] As understood by those skilled in the art, the term "semipermeable" means that the semipermeable membrane of the present invention does not have the same permeability to all substances. The permeability of individual molecules or substances may depend on their aggregation state and / or particle form, and in some cases, the permeability may be so low that certain components may not substantially pass through the semipermeable membrane. Those skilled in the art will understand that the semipermeable membrane of the present invention is a water transport membrane that is permeable to at least gaseous water, preferably gaseous and condensed water. In other words, the semipermeable membrane of the present invention is permeable to water.

[0023] The objective of the semipermeable membrane of the present invention is to prevent the permeation of other components, particularly air and other gases, and particulate impurities, in addition to transporting water. Therefore, the semipermeable membrane of the present invention has reduced permeability to these components. A preferred semipermeable membrane of the present invention is one having an air permeability of 2.0 cm when a pressure difference of 20 kPa is applied between the sides of the membrane. 3 / (cm 2 min) or less, preferably 1.0 cm 3 / (cm 2 min) or less, preferably 0.5 cm 3 / (cm 2 ·min) or less. Particularly preferred semipermeable membranes of the present invention are those that are substantially impermeable to air, and in particular those that are substantially impermeable to oxygen, nitrogen, carbon dioxide, and mixtures thereof. Therefore, semipermeable membranes that are substantially impermeable to particulate impurities are also particularly preferred.

[0024] In technical terms, a membrane refers to a thin planar structure whose extent in the XY plane is significantly greater than its Z direction (thickness), i.e., whose length and width are much greater than its thickness.

[0025] The semipermeable membrane of the present invention includes a support layer. This support layer includes a composite material. As understood in the art, a composite material refers to a material composed of two or more components combined together, which exhibits different physicochemical properties than when the components are present alone. Such a composite material may also be called a composite.

[0026] According to the present invention, since the support layer comprises a composite material, the support layer may be at least partially formed of other materials. However, as will be appreciated by those skilled in the art, it is preferred that the support layer not only be composed partially of a composite material, but also be composed at least predominantly, and preferably substantially entirely, of a composite material. In the inventors' view, embodiments in which the support layer is substantially entirely formed of a composite material are preferred for substantially all applications.

[0027] The composite material itself is formed by at least one kind of plastic and at least one kind of silicon-containing porous filler, and the silicon-containing porous filler is embedded in the plastic so as to be at least partially dispersed.The semipermeable membrane of the present invention relates to almost all embodiments, in which the silicon-containing porous filler is present in the composite material as a plurality of particles dispersed in the plastic.Although it is conceivable that the silicon-containing porous filler is distributed unevenly in the plastic matrix, it is preferred that the silicon-containing porous filler in the composite material is substantially uniformly dispersed in the plastic in the semipermeable membrane of the present invention.

[0028] The plastic forming the carrier matrix that embeds the silicon-containing porous filler within the composite can in principle be any conventional polymeric material, since the chemistry of the plastic matrix itself is not believed to be the determining factor for application-relevant properties, and the actual choice of plastic is based primarily on the desired mechanical properties.

[0029] According to the present invention, the fillers associated with plastics contain silicon, which, as understood by those skilled in the art, means that the fillers consist of compounds that contain silicon atoms in their molecular and / or crystalline structure.

[0030] However, the filler used in the composite material not only contains silicon, but is also porous, which means that the ratio of the volume of voids inside the porous filler to the total volume of the porous filler is greater than zero, which means that the porous filler or the particles of the porous filler have voids inside that can be connected to each other.The so-called open porosity or effective porosity is determined by the total volume of voids that are connected to each other and connected to the external environment.Those skilled in the art will understand that for the silicon-containing porous filler used in the present invention, the porosity should be at least partially open porosity, such as in the case of many zeolite materials and many industrial fillers made from amorphous silicon dioxide (also known as "silica").The semipermeable membrane of the present invention relates to almost all embodiments in which the silicon-containing porous filler is micropores and / or mesopores and / or macropores. Preferred semipermeable membranes of the present invention are those in which the silicon-containing porous filler has mesopores and / or macropores, and particularly preferably the silicon-containing porous filler is designed as a hierarchical porous filler, i.e., has a hierarchically structured pore system in which the mesopores are located at the edges of the macropores.

[0031] Those skilled in the art will understand that the porosity of the silicon-containing porous filler creates or promotes the porosity of the composite material, which in turn creates or promotes water permeability. Thus, the semipermeable membrane of the present invention is relevant to almost all embodiments in which the composite material is a porous composite material, preferably a microporous composite material. Preferred semipermeable membranes of the present invention are those in which the porosity of the composite material is in the range of 30 to 90%, preferably in the range of 40 to 80%, and particularly preferably in the range of 50 to 60%.

[0032] In addition to the support layer, the semipermeable membrane of the present invention also includes a coating layer. This coating layer is disposed on the support layer and at least partially covers the support layer, so the coating layer can be understood as a coating of the support layer. Unlike the prior art, this coating layer includes at least one organosilicon compound. According to the understanding in the art, silicon compounds, also called organosilicon compounds, are compounds containing at least silicon atoms and carbon atoms, and carbon can be bonded to silicon directly or via heteroatoms, particularly oxygen, as in the case of siloxanes and polysiloxanes. Corresponding starting materials suitable for producing the coating layer are commercially available from many manufacturers, such as Evonik, Hubei, and Wacker Chemie, although some of them are also used for other purposes, such as adhesion promoters. Examples of commercially available products include those sold by Evonik under the trade name "Dynasylan," such as SIVO 110, SIVO 418, SIVO 850, VPS SIVO 608, Hydrosil 2909, and Triamo.

[0033] In principle, it is possible to use additional layers in the semipermeable membrane of the present invention. However, in consideration of the performance characteristics of the membrane and the achievable membrane thickness, it is often preferable to form the semipermeable membrane with only the above two layers. Therefore, the semipermeable membrane of the present invention is preferably composed of a support layer and a coating layer.

[0034] As mentioned above, composite materials can contain a wide variety of plastics, and those skilled in the art can select the plastic to be used, taking into particular consideration the mechanical requirements of the semipermeable membrane and the available materials. However, the inventors have succeeded in identifying plastics that are particularly suitable for use in the semipermeable membrane of the present invention in terms of processing characteristics and mechanical properties. Preferred semipermeable membranes of the present invention are those in which the plastic is selected from the group consisting of thermoplastic resins, preferably selected from the group consisting of polyvinyl chloride and polyolefins, particularly preferably selected from the group consisting of polyolefins, in particular polyethylene and polypropylene, and particularly preferably polyethylene, in particular ultra-high molecular weight polyethylene.

[0035] Similarly, the inventors have succeeded in identifying particularly advantageous silicon-containing porous fillers that, when used in the semipermeable membrane of the present invention, can result in particularly advantageous composite materials. These silicon-containing porous fillers can be particularly well dispersed uniformly in conventional plastics, are available with suitable porosities, and exhibit advantageous interactions with the organosilicon compounds of the coating layer. Preferred semipermeable membranes of the present invention are those in which the silicon-containing porous filler is selected from the group consisting of silicon-aluminum-phosphorus-oxygen compounds, silicon-containing metal organic framework compounds, zeolites, and amorphous silicon dioxide, preferably selected from the group consisting of amorphous silicon dioxide, more preferably selected from the group consisting of zeolites and amorphous silica, particularly preferably selected from the group consisting of amorphous silica, in particular aerogel, precipitated silica, and fumed silica, and most preferably selected from the group consisting of aerogel and precipitated silica, in particular precipitated silica.

[0036] Those skilled in the art will understand that silicon-containing porous fillers, particularly the silicon-containing porous fillers preferred above, typically have hygroscopic properties, which may not only affect porosity but also promote water permeation through the composite material and may advantageously give the composite material a high water absorption capacity. The semipermeable membrane of the present invention relates to almost all embodiments in which the silicon-containing porous filler is a desiccant.

[0037] In this regard, the inventors have succeeded in identifying particularly advantageous mass fractions of the above two components of the composite material. A preferred semipermeable membrane of the present invention is one in which the total mass fraction of the silicon-containing porous filler in the composite material is in the range of 25 to 85%, preferably 45 to 80%, and particularly preferably 60 to 75%, based on the mass of the composite material. Additionally or alternatively, a preferred semipermeable membrane of the present invention is one in which the total mass fraction of the plastic in the composite material is in the range of 15 to 75%, preferably 20 to 55%, and particularly preferably 25 to 40%, based on the mass of the composite material.

[0038] The present inventors have also succeeded in identifying organosilicon compounds that are particularly suitable for obtaining a particularly efficient semipermeable membrane according to the present invention. These compounds have particularly excellent water permeability and, furthermore, are highly compatible with the preferred silicon-containing porous filler described above. That is, preferred for the semipermeable membrane of the present invention are organosilicon compounds selected from the group consisting of silyl ethers, silanes, siloxanes, and polysiloxanes, preferably selected from the group consisting of silyl ethers, siloxanes, and polysiloxanes, more preferably selected from the group consisting of siloxanes and polysiloxanes, and most preferably selected from the group consisting of siloxanes and polysiloxanes.

[0039] In this regard, those skilled in the art will understand that although other compounds such as binders may be contained in the coating layer in addition to the organosilicon compounds provided in the present invention, it is preferable that the coating layer be composed solely of organosilicon compounds as much as possible. Therefore, the semipermeable membrane of the present invention is preferably one in which the total mass fraction of the organosilicon compounds in the coating layer is in the range of 50 to 100%, preferably 70 to 100%, particularly preferably 90 to 100%, and very preferably 95 to 100% relative to the mass of the coating layer, and the coating layer is almost completely composed of organosilicon compounds.

[0040] Furthermore, for certain applications, it may be preferable for the coating layer to contain one or more additives to precisely adapt its physicochemical properties to the respective requirements of the application. In particular, antioxidants can be considered for use to improve resistance to degradation. Furthermore, the top coat can be specifically physicochemically modified to improve properties such as water wettability, oxidative stability, and / or mechanical stability, selectivity, permeability, or to reduce the susceptibility to fouling. This can be achieved by the use of ionizing radiation, such as electron beams, ion beams, or gamma rays, or by the introduction of appropriate organic or inorganic components. While the semipermeable membrane of the present invention has the advantage of being highly durable even without additional crosslinking, it may be useful, particularly in mechanically demanding applications, to additionally chemically crosslink the coating layer by thermal or radiation-induced crosslinking. For this purpose, crosslinking agents and / or corresponding initiators can be added to the coating layer as additives. Furthermore, coupling agents can also be considered as additives. For example, they can be used to further strengthen the bond between the coating layer and the support layer.

[0041] The semipermeable membranes of the present invention have a high resistance to permeation of air and other impurities, allowing them to be designed to be particularly thin without introducing undesirable levels of impurities into the gas stream being humidified. Designing the semipermeable membranes of the present invention as thin films is particularly advantageous in terms of water permeability, material requirements, and manufacturing costs, making it reasonable to design them to be particularly thin while taking advantage of their favorable properties. An advantage of the semipermeable membranes of the present invention is that by having a specific coating layer, their advantageous properties regarding the permeation of air and other foreign substances can be fully achieved even with a relatively thin coating layer. Because a thin coating layer can lead to material savings and improved water permeability, the inventors believe that it is particularly advantageous to make the coating layer as thin as possible. In this regard, preferred semipermeable membranes of the present invention have a coating layer with an average thickness in the range of 0.1 to 10 μm, preferably 0.5 to 8 μm, and particularly preferably 1 to 5 μm. Additionally or alternatively, preferred semipermeable membranes of the present invention have a support layer having an average thickness in the range of 10 to 500 μm, preferably in the range of 20 to 250 μm, particularly preferably in the range of 40 to 190 μm, and most preferably in the range of 80 to 160 μm.

[0042] In this regard, the inventors have also identified an appropriate basis weight for coating the covering layer on the support layer. In fact, the semipermeable membrane of the present invention is preferably one in which the basis weight of the covering layer is 0.25 to 15 g / m 2 in the range of 0.5 to 5 g / m 2 The range is as follows:

[0043] The ability of a particular coating layer to prevent the permeation of air and other undesirable impurities allows the semipermeable membrane to have an asymmetric structure. In this asymmetric structure, only one coating layer is provided, and it is applied to only one side of the support layer, eliminating the need for coating layers on both sides of the support layer, thereby saving material, reducing weight, and simplifying manufacturing. Therefore, a preferred semipermeable membrane of the present invention has a coating layer disposed on only one side of the support layer.

[0044] As mentioned above, it is possible and reasonable to provide a coating layer on only one side of the support layer, but in the opinion of the inventors, for the intended use, it is preferable to cover one side of the support layer as completely as possible with the coating layer so as to avoid the formation of areas within the semipermeable membrane that are excessively permeable to air and unwanted contaminants.Preferred semipermeable membranes of the present invention have a support layer that is more than 60% covered on one side with the coating layer, preferably more than 75%, particularly preferably more than 90%, and most preferably almost completely covered with the coating layer.In particular, when the coverage of the support layer with the coating layer is low, it is advantageous to instead apply a sealing coating, i.e., a coating that is impermeable to both air and water, to the uncovered surface area.

[0045] To further prevent unintended permeable areas of the semipermeable membrane, it is preferable to apply a coating that is as uniform as possible. Thus, preferred semipermeable membranes of the present invention are those in which the thickness of the coating layer varies by no more than 50%, preferably no more than 25%, particularly preferably no more than 10%, and very particularly preferably no more than 5% over the entire area of ​​the support layer covered by the coating layer.

[0046] According to the inventors, one of the outstanding advantages of the semipermeable membrane of the present invention is the particularly high adhesive strength between the coating layer and the support layer, which allows the semipermeable membrane of the present invention to maintain long-term durability even in high-temperature and high-humidity environments. According to the inventors, this effect is particularly pronounced when the organosilicon compound of the coating layer is at least partially covalently bonded to the composite. This bond is suitably formed on the silicon-containing porous filler of the composite, which is substantially uniformly distributed within the plastic matrix and also present on the surface of the support layer. Such covalent bonds can be formed by chemically and / or thermally induced reactions between the organosilicon compound and the silicon-containing porous filler, and the use of so-called "crosslinking agents" may be required to promote the covalent bond. A particular advantage here is that the silicon-containing porous filler present on the surface of the composite, due to its high porosity, provides a large internal surface area available for the binding of the organosilicon compound. Particularly preferred semipermeable membranes of the present invention are those in which at least a portion of the organosilicon compound of the coating layer is covalently bonded to the silicon-containing porous filler of the composite.

[0047] In a particularly preferred embodiment, the organosilicon compound is covalently bonded to the silicon-containing porous filler by condensation reaction between the Si-OR group (wherein R represents hydrogen or an organic radical) of the organosilicon compound and the silanol group present on the surface of the silicon-containing porous filler.For example, this is also the case on the surface of amorphous silica.For this purpose, the semipermeable membrane of the present invention is preferably one in which the organosilicon compound is selected from the group consisting of organosilicon compounds having at least one Si-OR group (wherein R represents hydrogen or an organic radical, preferably an alkyl radical, particularly preferably an alkyl radical having 1 to 10 carbon atoms).In this regard, in addition or alternatively, it is also preferred to use one in which the silicon-containing porous filler contains Si-OH groups on its surface.

[0048] In other words, a preferred semipermeable membrane of the present invention is one in which a coating layer can be formed by coating a support layer with one or more organosilicon compounds selected from the group consisting of organosilicon compounds having at least one Si—OR group (wherein R represents hydrogen or an organic radical, preferably an alkyl radical, particularly preferably an alkyl radical having 1 to 10 carbon atoms).

[0049] While mechanical stress often causes undesirable peeling of the coating layer in semipermeable membranes, which not only adversely affects performance but may even call into question their fundamental suitability in particularly sensitive fuel cell systems, the semipermeable membranes of the present invention, especially when at least partially covalently bonded, have excellent composite strength, and based on experiments by the inventors, the semipermeable membranes of the present invention can even be folded. In this way, significant advantages can be achieved in terms of space utilization and effective usable surface area, making the semipermeable membranes of the present invention particularly suitable for use in fuel cell systems. Therefore, the semipermeable membranes of the present invention are also preferably folded in a flat pleated configuration, as is known, for example, from flat pleated filters.

[0050] In the opinion of the inventors, the semipermeable membrane used in the membrane humidifier for the fuel cell system is aa) a support layer comprising a composite material comprising at least one plastic and at least one silicon-containing porous filler embedded in the plastic, wherein the silicon-containing porous filler is selected from the group consisting of zeolite and amorphous silica, in particular amorphous silica, and the total mass fraction of the plastics in the composite material is in the range of 15-75% and the total mass fraction of the silicon-containing porous filler in the composite material is in the range of 25-85% (both based on the mass of the composite material); and bb) a coating layer disposed on the support layer, the coating layer comprising at least one organosilicon compound selected from the group consisting of siloxanes and polysiloxanes, the total mass fraction of the organosilicon compound in the coating layer being in the range of 50 to 100% (based on the mass of the coating layer).

[0051] Those skilled in the art will further appreciate that the present invention also relates to membrane humidifiers, particularly those used in fuel cell systems, said humidifiers comprising at least one, and preferably two or more, semipermeable membranes of the present invention.

[0052] The present invention also relates to a fuel cell system, in particular a polymer electrolyte membrane fuel cell system, comprising at least one fuel cell and at least one membrane humidifier of the present invention.

[0053] In this case, the membrane humidifier of the present invention is disposed in the fluid line system of the fuel cell, preferably in the fluid line system on the cathode side, and is preferably disposed simultaneously in the fluid supply line and the fluid discharge line, thereby allowing the supplied process gas and the discharged process gas to flow so as to be partially separated by the semipermeable membrane of the present invention.

[0054] The present invention also provides (u) manufacturing or preparing a support layer from a composite material comprising at least one plastic and at least one silicon-containing porous filler embedded in said plastic; (v) applying a coating composition comprising at least one organosilicon compound and at least one solvent to the surface of the substrate; and (w) evaporating the solvent to obtain a coating layer disposed on the support layer, the coating layer comprising at least one organosilicon compound.

[0055] A preferred method of the present invention is to produce the support layer by extruding a plastic mixture containing a silicon-containing porous filler, preferably using an extruder.

[0056] In terms of the achievable quality of the coating, particularly when partial covalent bonding of the coating layer and the support layer occurs, the method of the present invention is preferably carried out at a temperature of 40 to 120° C., preferably 50 to 100° C., and particularly preferably 60 to 90° C. In another preferred method of the present invention, the solvent is evaporated so that at least a portion of the organosilicon compound of the coating layer is covalently bonded to the silicon-containing porous filler of the composite material.

[0057] From the viewpoint of efficient process control, in a preferred method according to the invention, the solvent is preferably selected from the group consisting of water, alcohols (especially methanol, ethanol and isopropanol), aqueous acids, aqueous bases and mixtures of these solvents, particularly preferably selected from the group consisting of water, aqueous bases (especially aqueous solutions of alcoholates or hydroxides) and mixtures of these solvents, and preferably the solvent comprises water, an alcohol and a base. [Brief explanation of the drawings]

[0058] In the following, the invention and preferred embodiments thereof will be explained in more detail with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a schematic cross-sectional view of a semipermeable membrane of the present invention in a preferred embodiment. [Figure 2] FIG. 2 shows four cross-sectional scanning electron microscope images of a semipermeable membrane of the present invention after storage in boiling water for 10 days. [Figure 3] FIG. 3 shows two cross-sectional scanning electron microscope images of a semipermeable membrane of the present invention after storage in a drying oven at 105° C. for 10 days.

[0059] FIG. 1 shows a schematic cross-sectional view of a semipermeable membrane 10 of the present invention in a preferred embodiment. The exemplary semipermeable membrane 10 is intended for use in a membrane humidifier used in a polymer electrolyte membrane fuel cell system. The semipermeable membrane 10 of FIG. 1 includes a support layer 12 and a coating layer 14 disposed on one side of the support layer 12 and substantially completely covering the surface of the support layer 12 on that side. The support layer 12 is formed entirely from a composite material containing polyethylene as a plastic matrix in which porous amorphous silicon dioxide, i.e., precipitated silicon dioxide, is substantially uniformly dispersed. The support layer 12 has a substantially uniform thickness of approximately 120 μm, and the coating layer 14 has a substantially uniform thickness of approximately 3 μm.

[0060] The presence of the silicon-containing porous filler within the plastic matrix of the composite is visualized by the asterisks shown in the support layer 12 in FIG.

[0061] As a result, the semipermeable membrane 10 shown in FIG. 1 is permeable to water but is substantially impermeable to air and can be considered air-impermeable according to practically applicable standards.

[0062] Because the silicon-containing porous filler has mesopores and macropores, the composite material itself becomes a porous material with mesopores and macropores due to the effect of the embedded porous filler. In the composite material of the carrier layer 12, the mass fraction of the silicon-containing porous filler is approximately 65%, and the remaining mass fraction is composed of polyethylene.

[0063] In the example shown, the top layer 14 is composed substantially entirely of polysiloxane having Si—OR groups (R=H or alkyl) that are at least partially covalently bonded to the silicon-containing porous filler of the composite material, i.e., by reaction of the Si—OR groups with silanol groups located on the surface of the filler particles.

[0064] The corresponding semipermeable membrane 10 can be produced using a support layer 12 as a substrate. The composite material is composed of a plastic and a silicon-containing porous filler, and can be produced, for example, by extruding a plastic mixture containing these two components. A coating composition containing an organosilicon compound and at least one solvent (e.g., an aqueous solution of an alcoholate prepared by mixing water, an alcohol, and a base) is then applied to the support layer 12. The coating layer 14 disposed on the support layer 12 is then formed by evaporating the solvent in a high-temperature environment, for example, at 80°C. The conditions in this process are preferably set to promote covalent bonding between the organosilicon compound of the coating layer 12 and the silicon-containing porous filler of the support layer 14.

[0065] Figures 2 and 3 show cross-sectional scanning electron micrographs of semipermeable membranes of the present invention (see below for manufacturing details) after different degradation conditions. Figure 2 shows the membrane after 10 days of storage in flowing boiling water (100°C), while Figure 3 shows the membrane after 10 days of storage in a dry oven at 105°C. To obtain a fracture surface and ensure a representative image, the samples were immersed in liquid nitrogen and analyzed by scanning electron microscopy (SEM) immediately after temperature-induced fracture ("cryofracture"). The SEM images clearly show the structure of the composite material in the support layer, revealing a clear dispersion of particulate porous amorphous silicon dioxide within the polyolefin support matrix. In all SEM images, the respective coating layers, located below the support layer in Figure 2 and above the support layer in Figure 3, are clearly identifiable even after degradation tests equivalent to the loads expected in a fuel cell, and show that a defect-free, continuous coating is substantially maintained.

[0066] In the following, the present invention and preferred embodiments thereof will be further explained and described with reference to experiments.

[0067] A. Preparation of the Semipermeable Membrane of the Present Invention: Four semipermeable membranes (E1 to E4) of the present invention were produced. For this purpose, a support layer was prepared made of a composite material commercially available from PPG Industries under the trade name Teslin SP600. The support layer consisted of a polyolefin support matrix in which granular porous amorphous silicon dioxide was dispersed. The support layer had an average thickness of about 150 μm and an average basis weight of about 97 g / m 2 It was decided.

[0068] The coating layer was applied to the substrate by coating using an Easycoater coating device manufactured by Coatema. To prepare the coating composition, an organofunctionalized siloxane oligomer commercially available from Evonik Operations under the trade name Dynasylan Hydrosil 2909 was prepared. The organofunctionalized siloxane oligomer was diluted with a suitable solvent to obtain a coating composition (mass fraction of siloxane oligomer: approximately 10%), which was then uniformly applied to the substrate. A solid coating layer was obtained from the coating composition by evaporating the solvent (temperature: 70°C, time: 5 minutes). For film E1, the coating composition was applied to an average layer thickness of approximately 22 μm. For film E2, a substrate prepared similarly to E1 was again coated, and the coating composition was again applied to an average layer thickness of approximately 22 μm. For film E3, a one-step coating process was again selected, and the coating composition was applied to an average layer thickness of approximately 44 μm. Membrane E4 was prepared in a manner similar to that of membrane E1, except that the vacuum fixation of the coating equipment was not used and the substrate was fixed with adhesive strips instead to eliminate the effect of vacuum fixation on the penetration of the coating composition into the substrate. The coating thickness of the dry coating layer was calculated to be 2.2 μm (E1, E4) and 4.4 μm (E2, E3).

[0069] B. Reference membrane: The uncoated substrate used in Membranes E1–E4 was initially used as reference membrane V1. In addition, commercial membranes currently used in fuel cell applications were used as reference membranes: V2 (Nafion 110; Chemours; a chemically stabilized copolymer of perfluorosulfonic acid and polytetrafluoroethylene; average thickness: approximately 127 μm), V3 (Fumasep F10120-PK; Fumatech; a perfluorosulfonic acid-based membrane with long side chains (LSC) and reinforced with PEEK fibers; average thickness: approximately 120 μm), and V4 (Fumasep F-950; Fumatech; an unreinforced perfluorosulfonic acid-based membrane with long side chains (LSC); average thickness: approximately 50 μm).

[0070] C. Experiment: For the tested membranes, the water permeability (WTR, kg / m 2 / day) was measured. The experimental setup was based on the device disclosed for this purpose in EP 2435171 and comprised two fluid conduit paths Z and A separated by a membrane to be tested, each with an inlet and an outlet, allowing the properties of the test gas (air) introduced into the fluid conduit paths to be controlled and their changes analyzed. In the configuration used, the area of ​​each membrane between the fluid conduit paths was 0.04 m 2 The gas introduced into both fluid conduit paths had a pressure of 200 kPa and a temperature of approximately 80°C. The first gas stream Z was dried to approximately 0% humidity, while the humidity of the second gas stream A was set to approximately 90%, which corresponds to typical conditions for downstream saturated air flow in fuel cell applications. The volumetric flow rate of the test gas used has a significant effect on the measured water permeability. Since EP 2435171 does not specify the volumetric flow rate, the inventors set the volumetric flow rate of the test gas used to Q = 20 NL / min, which they believed would provide reliable results. The measured values ​​were calculated as the average value obtained from each of three measurements.

[0071] Gas permeation ("gas crossover") was also measured for selected membranes, requiring only a slight adjustment to the experimental setup described above. Other conditions remained the same, but the inlet of the second fluid line path was closed and the test gas was supplied only through the first fluid line path (Q = 70 NL / min). In this configuration, gas flow could be measured as the volumetric flow rate at the outlet of the second fluid line path.

[0072] D. Results The water permeability (WTR) of the membranes of the present invention and the reference membrane was measured as described above, and the results are shown in Table 1. [Table 1]

[0073] The data shown in Table 1 clearly demonstrate that the semipermeable membranes of the present invention exhibit excellent water permeability, achieving higher water permeability than some comparable membranes of the prior art, even at increased layer thicknesses. Because water permeability is comparable to that of the most efficient membranes of the prior art without having to rely on perfluorosulfonic acid-based materials, especially when using a one-step coating process, the semipermeable membranes of the present invention may be a promising alternative to perfluorosulfonic acid-based systems without the drawbacks of perfluorinated materials, particularly those related to environmental and health aspects.

[0074] The air permeability of the reference sample V1 was 1.3 NL / min. The membrane of the present invention, even at the thinnest coating thickness (E1), exhibited an air permeability of 0.01 NL / min, which corresponds to practically 0% within the measurement uncertainty and is in any case significantly higher than the typical market specification of 0.5 NL / min.

[0075] To simulate the degradation behavior of the membranes of the present invention, they were subjected to various degradation conditions according to E1. The water permeability (WTR) of each aged membrane was then evaluated in comparison with that of an uncoated substrate. Notably, no peeling of the top layer was observed in any of the degradation tests, indicating excellent durability.

[0076] In the aging test A1, the samples were subjected to a functional aging process, where the aging conditions were adjusted to match the loads expected in a fuel cell. For this purpose, a sample container filled with water was sealed with the membrane and heated in an oven at 90 °C during the aging process. The results confirmed that the membrane maintained a constant water vapor permeation rate at temperatures corresponding to the operating temperatures of a fuel cell. The results are shown in Table 2. [Table 2]

[0077] In aging test A2, the samples were aged at a high temperature of 110° C. without the presence of water vapor. The results are shown in Table 3. [Table 3]

[0078] In degradation test A3, samples were stored in a boiling water bath (temperature approximately 100°C) to test the ease of peeling of the coating disclosed in particular in EP 2435171. The results are shown in Table 4. [Table 4]

[0079] The results of the aging tests clearly show that the favorable water permeability is maintained over a long period of time even under aging conditions, but at the same time the difference in water permeability compared to the uncoated substrate is also maintained, which, together with the absence of observed delamination of the top layer, leads to the conclusion of high durability and exceptional longevity of the coating.

[0080] The excellent durability under mechanical load was also demonstrated by a folding test. For this purpose, the membrane was folded into a flat fold configuration and then tested for water permeability. The water permeability was 51 (kg / (m 2* d) to 54 (kg / (m 2* d), which is within the range of measurement accuracy. [Explanation of symbols]

[0081] 10 Semi-permeable membrane 12 Support layer 14 Covering layer

Claims

1. (a) a support layer (12) comprising a composite material including at least one plastic and at least one silicon-containing porous filler embedded in said plastic; (b) a coating layer (14) disposed on said support layer (12) and comprising at least one organosilicon compound, said semipermeable membrane (10) being particularly suitable for use in a membrane humidifier for a fuel cell system.

2. 2. The semipermeable membrane (10) of claim 1, wherein the plastic is selected from the group consisting of thermoplastics, preferably polyvinyl chloride and polyolefins.

3. 3. The semipermeable membrane (10) of claim 1 or 2, wherein the silicon-containing porous filler is selected from the group consisting of silicon-aluminum-phosphorus-oxygen compounds, silicon-containing metal organic framework compounds, zeolites, and amorphous silicon dioxide.

4. The semipermeable membrane (10) of any one of claims 1 to 3, wherein the organosilicon compound is selected from the group consisting of silyl ethers, silanes, siloxanes, and polysiloxanes.

5. The semipermeable membrane (10) of any one of claims 1 to 4, wherein at least a portion of the organosilicon compound of the coating layer (14) is covalently bonded to the silicon-containing porous filler of the composite material.

6. The semipermeable membrane (10) according to any one of claims 1 to 5, wherein the coating layer (14) has an average thickness in the range of 0.1 to 10 μm.

7. A membrane humidifier, in particular for use in a fuel cell system, comprising at least one semipermeable membrane (10) according to any one of claims 1 to 6.

8. A fuel cell system, in particular a polymer electrolyte membrane fuel cell system, comprising at least one fuel cell and at least one membrane humidifier according to claim 7.

9. (u) manufacturing or preparing a support layer (12) from a composite material comprising at least one plastic and at least one silicon-containing porous filler embedded in said plastic; (v) applying a coating composition comprising at least one organosilicon compound and at least one solvent to the surface of the support layer (12); (w) evaporating the solvent to obtain a coating layer (14) disposed on the support layer (12) comprising at least one organosilicon compound.

10. 10. The method of claim 9, wherein evaporation of the solvent is performed such that at least a portion of the organosilicon compound of the coating layer (14) is covalently bonded to the silicon-containing porous filler of the composite material.

Images