Hollow fiber membrane for fuel cell humidifiers, humidifier and fuel cell system containing the same

Abstract

The present invention relates to a hollow fiber membrane for a fuel cell humidifier comprising a polymer and an antioxidant, wherein the antioxidant is disposed on the inner and / or outer surface, a method for producing the same, and a humidifier and fuel cell system comprising the same.

Description

Technical Field

[0001] The present invention relates to a hollow fiber membrane for a novel fuel cell humidifier, a humidifier including the same, and a fuel cell system.

Background Art

[0002] A fuel cell is a power generation type battery that converts the chemical energy of hydrogen and oxygen into electrical energy by an electrochemical reaction. Different from general chemical batteries such as dry batteries and storage batteries, a fuel cell continuously produces electricity as long as hydrogen and oxygen are supplied, and has the advantage that its efficiency is more than twice higher than that of an internal combustion engine because there is no heat loss. In addition, since hydrogen and oxygen are used as raw materials and water is generated as a product, it is an energy generation device friendly to an environment without pollutants. Therefore, a fuel cell has the advantage of not only being environmentally friendly but also reducing concerns about resource depletion due to an increase in energy consumption. Fuel cells can be classified into, for example, Polymer Electrolyte Membrane Fuel Cell (PEMFC), Phosphoric Acid Fuel Cell (PAFC), Molten Carbonate Fuel Cell (MCFC), Solid Oxide Fuel Cell (SOFC), and Alkaline Fuel Cell (AFC). Among these, a polymer electrolyte fuel cell is known to be suitable for use in a transportation system because it can operate at a low temperature and has a large output density compared to other fuel cells. On the other hand, in a polymer electrolyte fuel cell, generally, 2 moles of hydrogen and 1 mole of oxygen react in a fuel cell stack during driving to form water, but when an incomplete reaction proceeds, peroxide or a hydroxyl radical may be formed as a by-product. The peroxides or hydroxyl radicals generated in this way cause degradation of the polymer electrolyte membrane in the fuel cell stack. To prevent this degradation, techniques have been reported to include trace amounts of additives, such as inorganic materials, in the polymer electrolyte membrane. However, since polymer electrolyte membranes must have a certain level of pores distributed to allow ions to pass through, the content of inorganic materials, such as inorganic particles, required to improve durability is limited to below a specific value. As a result, there remains a demand for technologies that prevent the degradation of polymer electrolyte membranes even during long-term operation of fuel cells. [Overview of the project] [Problems that the invention aims to solve]

[0003] The present invention aims to protect polymer electrolyte membranes from peroxides and / or hydroxyl radicals that are continuously generated in the stack of fuel cell cells, thereby improving the durability of fuel cell systems. [Means for solving the problem]

[0004] In one aspect, a hollow fiber membrane for a fuel cell humidifier is provided, comprising a polymer and an antioxidant, wherein the antioxidant is disposed on the inner and / or outer surface of the hollow fiber membrane. In other aspects, the present invention provides a method for producing a hollow fiber membrane for a fuel cell humidifier, comprising the steps of: preparing a doping solution for forming a hollow fiber membrane containing a polymer and an antioxidant; discharging the doping solution into a solidification tank through a tubular spinning apparatus; and solidifying the spinning solution discharged into the solidification tank, then winding and drying to obtain a hollow fiber membrane, wherein the hollow fiber membrane has an antioxidant disposed on its inner and / or outer surface. In another aspect, a humidifier for a fuel cell, including the hollow fiber membrane, is provided. In other aspects, a fuel cell system is provided which includes a fuel cell stack comprising a fuel cell cell equipped with a polymer electrolyte membrane, and a fuel cell humidifier communicating with the fuel cell stack, wherein an antioxidant flows out from the humidifier and flows into the fuel cell stack at a rate of 1 μg / 1000hr or more. [Effects of the Invention]

[0005] In a one-sided hollow fiber membrane, the antioxidant is placed or dispersed on the inner and / or outer surface of the hollow fiber membrane. As the outside air is humidified through the hollow fiber membrane, the antioxidant flows out from the membrane and enters the fuel cell stack at a rate of 1 μg / 1000hr or more. This effectively prevents the degradation of the polymer electrolyte membrane contained in the fuel cell cells within the fuel cell stack, thereby improving durability. [Brief explanation of the drawing]

[0006] [Figure 1] This is an exploded perspective view of a fuel cell humidifier according to one embodiment of the present invention. [Figure 2] This is an exploded perspective view of a fuel cell humidifier according to one embodiment of the present invention. [Figure 3] This is an enlarged view of a cross-section of a hollow fiber membrane according to one embodiment of the present invention. [Figure 4] This is an enlarged view of a cross-section of a hollow fiber membrane according to one embodiment of the present invention. [Figure 5] This is an enlarged view of a cross-section of a hollow fiber membrane according to one embodiment of the present invention. [Figure 6] This is an enlarged view of a cross-section of a hollow fiber membrane according to one embodiment of the present invention. [Figure 7] This is a block diagram showing the configuration of a fuel cell system according to one embodiment of the present invention. [Figure 8] This is a block diagram showing the configuration of a fuel cell system according to one embodiment of the present invention. [Modes for carrying out the invention]

[0007] The present inventive concept described below is capable of various transformations and has many embodiments; therefore, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this should be understood not as limiting the present inventive concept to specific embodiments, but rather as encompassing all transformations, equivalents, or substitutes that fall within the technical scope of the present inventive concept. The terms used below are used solely to describe specific embodiments and are not intended to limit the concepts of the present invention. A singular expression includes plural expressions unless the context clearly indicates otherwise. Hereafter, terms such as “includes” or “having” are used to indicate the presence of features, numbers, steps, operations, components, parts, ingredients, materials, or combinations thereof described in the specification, and should not be understood to preemptively exclude the presence or possibility of adding one or more other features, numbers, steps, operations, components, parts, ingredients, materials, or combinations thereof. When it is mentioned that one component is “connected” or “joined” with another component, it should be understood that the first component may be directly connected or joined to the other component, but that there may also be other components between the first component and the other component. On the other hand, when it is mentioned that one component is “directly connected” or “directly joined” with another component, it should be understood that there are no other components between the first component and the other component. Throughout the specification, when a part such as a layer, film, region, or plate is described as being "on top of" or "on" another part, this includes not only cases where it is directly above another part, but also cases where there are other parts in between. Throughout the specification, terms such as "first," "second," etc., are used to describe various components, but components should not be limited by these terms. The terms are used solely for the purpose of distinguishing one component from another. As used throughout this specification, the term "polymer" means a polymer formed by the polymerization of one or more monomer units, and includes polymer resins and polymer macromolecules. The embodiments described below are merely illustrative, and various modifications are possible from these embodiments. In one aspect, a hollow fiber membrane is provided comprising a polymer and an antioxidant, wherein the antioxidant is disposed on the inner and / or outer surfaces. The antioxidant may be arranged on at least one of the inner and outer surfaces of the hollow fiber membrane, come into contact with the outside air passing through the humidifying membrane, and be configured so that a portion of the antioxidant is released. According to one example, the hollow fiber membrane has a mesh structure made of a polymer, and the mesh structure may further contain an antioxidant.

[0008] In one example, the antioxidant is dispersed within the polymer constituting the hollow fiber membrane. For example, the antioxidant is particulate and dispersed within the polymer in an embedded structure. That is, the antioxidant does not form bonds with the polymer forming the skeleton of the hollow fiber membrane, but is dispersed within the mesh structure. Because the antioxidant does not form a bond with the hollow fiber membrane, the antioxidant can be released as outside air passes through the hollow portion of the hollow fiber membrane and transmitted to the fuel cell stack along with the humidified air. According to one example, the antioxidant may be configured to leak out of the hollow fiber at a rate of 1 μg / 1000hr or more. By leaking out the antioxidant at a concentration of 1 μg / 1000hr or more, chemical degradation of the polymer electrolyte membrane in the fuel cell stack from oxidizing substances can be suppressed. According to one example, the antioxidant is incorporated into the hollow fiber membrane by a manufacturing process described later. For example, the antioxidant is mixed with a dope solution and incorporated into the hollow fiber membrane during the film-forming process, or the antioxidant is contained in the core solution and discharged and incorporated into the interior of the hollow fiber membrane during the phase transition process, or an antioxidant solution is injected into the hollow portion after the manufacturing of the hollow fiber membrane to form an antioxidant coating layer on the inner surface of the hollow fiber membrane and thus incorporated into the hollow fiber membrane. In one embodiment, the antioxidant is dispersed on at least one of the inner and outer surfaces of the hollow fiber or in the form of a coating layer. For example, the antioxidant can be attached in particulate form to at least one of the inner and outer surfaces of the hollow fiber, or a plurality of particles can form a coating layer. For example, the antioxidant particles can be uniformly distributed across the entire surface so as not to block the pores of the hollow fibers. According to one example, the antioxidant is present in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the polymer. According to one example, the antioxidant can form an antioxidant coating layer disposed on at least one of the inner and outer surfaces of the hollow fiber. In this case, the antioxidant coating layer may be configured to flow out in a certain amount when in contact with the outside air. For the antioxidant to flow out in a certain amount, it is desirable that there is no chemical bond between the antioxidant and the main polymer of the film and that it is located on the inner surface of the film. Therefore, when forming a humidifying film, crosslinking agents or additives that cause crosslinking between the antioxidant and the main polymer must be excluded.

[0009] For example, the antioxidant coating layer can be 1 to 50 μm thick so that a certain amount of antioxidant is released. If the thickness of the antioxidant coating layer is less than 1 μm, it is difficult to obtain a sufficient amount of antioxidant release due to contact with the outside air, and if the thickness exceeds 50 μm, it acts as a resistance layer against the passage of outside air, making it difficult for sufficient moisture exchange with the outside air to occur. According to one example, the antioxidant particles or antioxidant coating layer can cover all or part of the inner or outer surface of the hollow fiber. According to one example, the antioxidant may be present in an amount of 0.01 to 5 parts by weight per 100 parts by weight of the polymer forming the hollow fiber film. When the antioxidant is contained in an amount less than 0.01 part by weight, it is insufficient to prevent the deterioration of the hollow fiber membrane caused by peroxides or hydroxyl radicals generated in the reaction of the fuel cell. When the amount exceeds 5 parts by weight, the pores of the hollow fiber membrane are blocked, the moisture exchange ability decreases, and the function of the membrane humidifier decreases.

[0010] According to one embodiment, the antioxidant may include a phenolic antioxidant, an amine antioxidant, a metal antioxidant, an organometallic antioxidant, a sulfur-based, a phosphorus-based antioxidant, or a combination thereof. For example, the phenolic antioxidants include Irganox 1010 (Irganox 1010: pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], manufactured by BASF Ltd.), Irganox 1076 (Irganox 1076: octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, manufactured by BASF Ltd.), Irganox 1330 (Irganox 1330: 3,3',3”,5,5',5”-hexa-t-butyl-a,a',a”-( Methylene-2,4,6-triyl)tri-p-cresol (manufactured by BASF Ltd.), Irganox 3114 (1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (manufactured by BASF Ltd.), Irganox 3790 (1,3,5-tris((4-t-butyl-3-hydroxy-2,6-xilyl)methyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (manufactured by B Corporation) (Manufactured by ASF), Irganox 1035 (Irganox1035: Thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], (Manufactured by BASF Ltd.), Irganox 1135 (Irganox1135: Benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-C7-C9 side-chain alkyl ester, (Manufactured by BASF Ltd.), Irganox 1520L (Irganox1520L: 4,6-bis(octylthiomethyl-o-cresol, (Manufactured by BASF Ltd.)), Irganox 3125 (manufactured by BASF Ltd.), Irganox 565 (2,4-bis(n-octylthio)-6-(4-hydroxy-3',5'-di-t-butylanilino)-1,3,5-triazine, manufactured by BASF Ltd.), Adekastab® AO-80 (3,9-bis(2-(3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy)-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro(5,5) May contain undecane (manufactured by ADEKA Corporation), Sumirizer® BHT, copper GA-80, copper GS (all manufactured by Sumitomo Chemical Co., Ltd.), Cyanox® 1790 (manufactured by Cytech Co., Ltd.), and vitamin E (manufactured by Eisai Co., Ltd.), or any combination thereof. Amine-based antioxidants may include phenyl-α-naphthylamine, phenyl-β-naphthylamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-naphthyl-p-phenylenediamine, HALS compounds, or combinations thereof. For example, phosphorus-based antioxidants include tris(2,4-di-t-butylphenyl) phosphite (Irgafos 168), tris[2-[[2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosfepin-6-yl]oxy]ethyl]amine (Irgafos 12), bis(2,4-bis(1,1-dimethylethyl-6-methylphenyl)ethyl phosphite (Irgafos 38), Adekastab 329K, Adekastab PEP36, Adekastab PEP-8, Sandstab P-EPQ, Weston 618, Weston 619G, and Ultranox. 626, (6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosfepine) (Smilizer GP), or combinations thereof may be included.

[0011] For example, metallic antioxidants may include cerium, nickel, tungsten, ruthenium, palladium, silver, rhodium, cesium, zirconium, cobalt, chromium, yttrium, manganese, iron, molybdenum, lead, vanadium, titanium, niobium, lanthanum, their ions, their oxides, their salts, or any mixture thereof. For example, organometallic antioxidants may include Ce-crown complexes, Ce-phosphoric acid complexes, Ce-bypyridine, or any mixture thereof. For example, sulfur-based antioxidants may include dilauryl thiodipropionate (DLTDP), distearyl thiodipropionate (DSTDP), ditridecyl thiodipropionate (DMTDP), bis(2-methyl-4-(3-alkylthio)-propionyloxy)-5-tert-butylphenol sulfide, tetrakis(methylene-3-(laurylthio)propionate)methane, or a combination thereof. According to one embodiment, the hollow fiber membrane contains a polymer, and the polymer is selected and used from known polymers suitable for forming a hollow fiber membrane. For example, polyvinylidene fluoride (PVDF)-based polymers, polysulfone-based polymers, sulfonated polysulfone, cellulose acetate, cellulose triacetate, polymethyl methacrylate, nafion, polystyrene (PS)-based polymers, polytetrafluoroethylene (PTFE)-based polymers, perfluorosulfonic acid (PFSA)-based polymers, polyphenylsulfone-based polymers, polyethersulfone (PES)-based polymers, polyacrylonitrile (PAN)-based polymers, polyetherimide (PEI)-based polymers, polyimide (PI)-based polymers, or any combination of the aforementioned polymers may be included. For example, the polymer may include a polystyrene-based polymer. The hollow fiber membrane contains one or more of the aforementioned polymers as the main polymer, and may further contain an auxiliary polymer in consideration of the desired physical properties of the hollow fiber membrane. For example, the auxiliary polymer includes polyvinylpyrrolidone.

[0012] According to one embodiment, the polymer is contained in an amount of 90 parts by weight or more and less than 100 parts by weight, or 95 to 99.999 parts by weight based on 100 parts by weight of the hollow fiber membrane. According to one embodiment, the auxiliary polymer is contained in an amount of 5 to 20 parts by weight based on 100 parts by weight of the hollow fiber membrane. According to one example, the thickness of the hollow fiber membrane is 0.5 nm to 1 mm. According to one example, the hollow fiber membrane may further contain additives such as surfactants, hydrophilic organic compounds, hydrophilic polymers, or crosslinking agents. For example, the additive may include at least one of polyethylene glycol, glycerin, diethyl glycol, triethylene glycol, ethanol, polyvinylpyrrolidone, water, zinc chloride, and lithium chloride. Such additives can be added in appropriate amounts, within a range that does not impair the inherent properties of the hollow fiber membrane. Furthermore, it is obvious to those skilled in the art that known materials used in the manufacture of hollow fiber membranes may also be used. In one aspect, a method for manufacturing a hollow fiber membrane for a fuel cell humidifier is provided, comprising the step of providing a hollow fiber membrane configured to allow an antioxidant to flow out. Humidifiers for fuel cells provide humidified air to the fuel cell stack. However, if the humidified air contains impurities, it can reduce the lifespan of the fuel cell. Therefore, it is necessary to suppress the leaching of impurities caused by the decomposition of hollow fiber materials. Since hollow fibers are essentially formed from organic polymers, when exposed to the hot, humid air generated from the stack during fuel cell operation, the polymer may deform or short-circuit, or various impurity ions may be formed due to polymer decomposition. Such impurities can be transmitted into the stack, potentially causing a decrease in the performance of the fuel cell stack. To address these problems, attempts have been made to enhance the durability of hollow fiber membranes by adding fluorine-based materials as polymers or by providing a durable coating layer on the surface of the hollow fiber membrane. However, the addition of fluorine-based materials and the provision of a durable coating layer still have limitations that either inhibit the moisture exchange properties of the hollow fiber membrane or reduce its heat resistance.

[0013] As a result, the inventors, in the process of focusing their research on substances that cause the decomposition of hollow fiber membranes, studied ways to essentially remove oxidizing substances that flow from the fuel cell stack into the membrane humidifier along with high-temperature, high-humidity air. In this regard, the inventors found that injecting large amounts of antioxidants into the fuel cell stack to remove oxidizing substances generated from the fuel cell stack would interact with impurities in the fuel cell stack and reduce its efficiency. Therefore, they concluded that if the hollow fiber membrane contained in the fuel cell humidifier is configured to allow a constant amount of antioxidant to flow out over a long period of time, the antioxidant will be continuously supplied to the fuel cell stack, contributing to the removal of oxidizing substances. Based on this finding, the inventors completed the present invention. According to one embodiment, the step of providing a hollow fiber membrane configured to allow the antioxidant to flow out may include the step of preparing a doping solution for forming a hollow fiber membrane. In one embodiment, the doping solution may include the step of mixing a polymer and an antioxidant in an organic solvent, wherein the antioxidant is mixed in an amount of 0.01 to 5 parts by weight per 100 parts by weight of polymer to obtain a spinning stock. In this case, the organic solvent used in the production of the doping solution may be a third solvent described later, such as N-methyl-2-methylpyrrolidone. The solvent may include at least one of the first solvent, the second solvent, and the third solvent. For example, the solvent is a mixed solvent containing two of the first solvent, the second solvent, and the third solvent. The first solvent may include butanol, isobutanol, octanol, pentanol, isopentanol, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, polyoxyethylene octylphenyl ether, or combinations thereof, as a solvent that does not dissolve the polymer at room temperature (e.g., 23-25°C) but dissolves it at high temperatures (e.g., 80°C or higher). The second solvent may include water, methanol, ethanol, isopropanol, acetone, hexane, pentane, benzene, toluene, carbon tetrachloride, o-dichlorobenzene, polyethylene glycol, or a combination thereof, as a solvent that does not dissolve the polymer. The third solvent may include N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, tetrahydrofuran, tetramethylurea, or trimethyl phosphate as a solvent that dissolves the polymer even at room temperature.

[0014] A typical technician can use a mixture of one or more of the first, second, and third solvents, taking into consideration the characteristics of the polymer raw materials and the production of a hollow fiber membrane having the desired physical properties. According to one example, when the solvent is a mixed solvent of two types of solvents, the mixing ratio of the solvents is 1:9 to 9:1 by weight, but is not limited to this, and can be selected within an appropriate range by an ordinary technician considering the polymer and antioxidant content, the viscosity of the spinning solution, the porosity of the hollow fiber membrane, and the physical properties of the final hollow fiber membrane. In one embodiment, the spinning solution contains a polymer that forms the backbone of the hollow fiber membrane, an antioxidant, and a solvent, and optionally contains additional additives. During the process of forming the hollow fiber membrane, the solvent is removed from the spinning solution, and the final product has a structure in which the antioxidant is included in the polymer backbone. According to one example, the polymer content in the spinning solution is 15 to 25 parts by weight per 100 parts by weight of the total spinning solution. For example, the polymer content in the spinning solution is 16 to 24 parts by weight, 17 to 23 parts by weight, 18 to 22 parts by weight, or 19 to 21 parts by weight. According to one example, the content of the antioxidant contained in the spinning solution is greater than 0 and less than or equal to 5 parts by weight, or 0.001 to 5 parts by weight, per 100 parts by weight of polymer constituting the skeleton of the hollow fiber membrane. According to one example, in the step of obtaining the spinning solution, the temperature at which the polymer, antioxidant, and optionally additives are mixed in the solvent can be appropriately selected from room temperature or high temperature, taking into consideration the polymer, antioxidant, additives, and solvent used. According to one example, the time for mixing the spinning solution is sufficient to allow the polymer, antioxidant, and any additives to dissolve and / or disperse sufficiently in the solvent. According to one example, the viscosity of the spinning solution is 5,000 to 50,000 cps at 35°C. When the viscosity of the spinning solution satisfies this range, the spinning solution can be smoothly discharged through the die without clogging.

[0015] To maintain the viscosity of the spinning solution within the aforementioned range, the temperature of the spinning nozzle can be adjusted to a certain temperature or higher. Alternatively, the spinning solution may further contain a viscosity modifier to adjust the viscosity as needed. According to one example, the spinning solution may further contain additives, taking into consideration the film-forming properties and porosity of the hollow fiber membrane, the dispersibility of the antioxidant, and the viscosity of the spinning solution. For example, the additive may include at least one of polyethylene glycol, glycerin, diethyl glycol, triethylene glycol, ethanol, polyvinylpyrrolidone, water, zinc chloride, and lithium chloride. In one embodiment, the step of spinning the spinning stock into a coagulation tank includes the step of spinning the discharged liquid using a tubular spinning apparatus, such as a double-tubular spinning apparatus or a triple-tubular spinning apparatus. However, it is not limited to such a tubular shape, and any discharge method that forms a hollow shape can be used without limitation. According to one example, when the spinning solution is discharged into a coagulation tank through a double-tube spinning apparatus, the composition of the spinning solution discharged from each tube of the double tubular structure is either the same or different from each other. For example, when the spinning solution is discharged using a triple-tube spinning apparatus, the composition of the spinning solution passing through each tube is either the same or different. For example, when using a triple-tube spinning apparatus, the composition of the spinning solution passing through the tubes located on the inside and outside of the tubular structure is the same, and only the composition of the spinning solution passing through the intermediate tube between the inside and outside is different. According to one example, in the step of spinning the spinning solution into a coagulation tank, the spinning temperature can be set to the same temperature as or higher than the mixing temperature of the spinning solution. In this case, when using a multi-tubular die, by setting the temperature of each die differently, it is possible to discharge the preferred spinning solution at the appropriate temperature. According to one example, in the step of spinning the spinning solution into a coagulation tank, the discharge rate is 5 to 100 g / min. In one embodiment, when the spinning stock is discharged through a tubular nozzle, the core liquid can be discharged together with it into the hollow part inside the tubular nozzle. The core liquid may contain a mixed solution of the second solvent and the third solvent.

[0016] According to one embodiment, the core solution can be a mixture of the second solvent and the third solvent in a volume ratio of 3:7 to 7:3. When the core solution satisfies the volume ratio within the above range, antioxidants contained in the spinning solution can be encapsulated within the hollow fiber membrane during the phase transition process of the spun product. According to one example, the core solution may further contain an antioxidant. By further including an antioxidant in the core solution, the antioxidant can be dispersed on the inner surface of the hollow fiber membrane by phase separation during the hollow fiber membrane formation process. As a result, the antioxidant can be dispersed and present at a high concentration on the inner surface of the hollow fiber membrane. As mentioned above, when a core solution containing an antioxidant is discharged together, the spinning solution contains only a small amount of antioxidant or none at all. According to one example, the spun material discharged from the spinning apparatus can come into contact with the coagulation liquid in the coagulation tank via an air gap. The air gap is the region in which the spun material comes into contact with air, and artificial cooling air can be flowed through it, taking into account the physical properties of the spun material. For example, the length of the air gap can be set to 0.1 to 50 cm. The air gap is the section where primary phase transition occurs, and the water vapor in the atmosphere is exchanged with the organic solvent in the spinning solution to carry out the phase transition. When the length of the air gap satisfies the above range, sufficient phase transition occurs, and a hollow fiber membrane having the desired porosity structure can be obtained. The spun material solidifies upon contact with the coagulation liquid contained in the coagulation tank via an air gap, thereby forming a porous hollow fiber membrane. According to one example, the solidification tank consists of one unit, but is not limited to this; two or more solidification tanks may be arranged in sequence. When there are two or more solidification tanks, the solidifying liquid used in each tank may be the same or different. According to one example, the coagulation liquid contained in the coagulation tank plays the role of solidifying the discharged liquid, which is discharged through the nozzle, into the shape of a hollow fiber membrane. The coagulation liquid used in this process can be appropriately selected by an ordinary technician from among known coagulation liquids, taking into consideration the porosity and pore structure of the hollow fiber membrane. For example, an acidic solution or a second solvent such as water may be used as the coagulation solution. According to one example, the hollow fiber membrane obtained through the coagulation tank can undergo a post-processing step. According to one example, the post-treatment step may include a step of performing a chemical treatment and / or a physical treatment.

[0017] For example, the chemical treatment in the post-treatment step is performed to remove and dry the coagulated liquid contained in the pores after the formation of the hollow fiber membrane, and includes washing with water, washing, and hot water treatment, and if necessary, the solution used for washing with water, washing, and hot water treatment may further contain an antioxidant. For example, the physical processing in the post-processing step may further include stretching and shrinking processes to control the size and shape of the pores inside the hollow fiber membrane and to improve the strength and durability of the hollow fiber membrane. According to one example, after forming a hollow fiber membrane, a post-treatment can be performed in which a solution of an antioxidant dissolved in a second solvent is injected into the hollow portion of the hollow fiber, followed by drying. Through such post-treatment, an antioxidant coating layer can be provided on the inner surface of the hollow fiber membrane. This post-treatment to provide an antioxidant coating layer on the inner surface of the hollow fiber membrane can be performed in addition to the aforementioned process, or it can be performed for the purpose of selectively producing an antioxidant coating layer only on the inner surface of a hollow fiber membrane that contains or does not contain an antioxidant after its manufacture. In the hollow fiber membranes for fuel cell humidifiers manufactured using the aforementioned process, the antioxidant is not bound to the hollow fibers via a crosslinking agent or binder. Instead, it is dispersed within the hollow fiber membrane or forms a coating layer on the inner surface of the hollow fiber membrane, making it easy for the antioxidant to leach into the outside air during the moisture exchange process of the hollow fiber membrane. In another aspect, a humidifier including the hollow fiber membrane is provided. The information regarding hollow fiber membranes is as described above, and the humidifier will be explained below with reference to Figures 1 and 2. Figures 1 and 2 are perspective views showing a fuel cell humidifier 100 according to one embodiment of the present invention. As shown in Figures 1 and 2, the fuel cell humidifier 100 of the present invention includes a middle case 110, a cap case 120, a fixing part 130, and a hollow fiber membrane bundle 200. Here, the hollow fiber membrane bundle 200 may have antioxidant particles distributed on each surface of the hollow fiber membrane, or it may include an antioxidant coating layer on its surface. See Figures 3 and 4 for an enlarged view of the hollow fiber membrane surface.

[0018] The middle case 110 is combined with the cap case 120 to form the outer shape of the membrane humidifier 100. The middle case 110 and the cap case 120 are made of hard plastic such as polycarbonate or metal. The middle case 110 and the cap case 120 have a circular cross-sectional shape in the width direction, as shown in Figure 1, or a polygonal cross-sectional shape in the width direction, as shown in Figure 2. The polygon can be a quadrilateral, square, trapezoid, parallelogram, pentagon, hexagon, etc., and the polygon can also have rounded corners. The circular shape can also be an ellipse. The middle case 110 has a second fluid inlet 112 through which the second fluid is supplied and a second fluid outlet 113 through which the second fluid is discharged. Figures 1 and 2 illustrate an example in which multiple hollow fiber membranes 210 are arranged in the middle case 110 in the shape of a single hollow fiber membrane bundle 200. However, the hollow fiber membranes 210 may also be arranged in the middle case 110 in a state where they are divided and housed in two or more cartridges. A fluid inlet / outlet 121 is formed in the cap case 120. One of the cap cases 120, which are connected to both ends of the middle case 110, has a fluid inlet / outlet 121 that serves as the first fluid inlet, and the other cap case 121 has a fluid inlet / outlet 121 that serves as the first fluid outlet. The first fluid that flows in through the fluid inlet / outlet 121 that functions as the first fluid inlet passes through the internal conduit [i.e., the lumens] of the hollow fiber membrane 210 housed inside the middle case 110, and then flows out to the fluid inlet / outlet 121 that functions as the first fluid outlet. The ends of the hollow fiber membranes 210 are potted to the fixing parts 130. The fixing parts 130 bind the hollow fiber membranes 210 together while filling the gaps between the hollow fiber membranes 210 and the gap between the hollow fiber membranes 210 and the middle case 110. As a result, both ends of the middle case 110 are closed by the fixing parts 130, and a flow path for the second fluid is formed inside. The material of the fixing parts 130 is known and will not be described in detail in this specification. Figures 3 to 6 are enlarged views showing a cross-section of one of the hollow fibers in a hollow fiber membrane bundle according to one embodiment of the present invention. The enlarged views in Figures 3 to 5 show one configuration in which antioxidant particles or an antioxidant coating layer are arranged only on the outer surface of the hollow fiber according to one embodiment of the present invention, but are not necessarily limited to this configuration. Configurations in which antioxidant particles or an antioxidant coating layer are provided on the inner surface of the hollow fiber, or on both the inner and outer surfaces simultaneously, also constitute an embodiment of the present invention.

[0019] Referring to Figures 3 to 6, the hollow fibers 30, 40, 50, and 60 include cavities 300, 400, 500, and 600, which serve as air passages and locations for moisture exchange. The hollow fiber membrane includes an inner surface S2, which is the cavity-side surface, and an outer surface S1, which faces outward. The hollow fibers have thickness regions 310, 410, 510, and 610 between the inner surface S2 and the outer surface S1, and these thickness regions 310, 410, 510, and 610 have a porous structure, although these are not shown. The porosity of these thickness regions can be configured to allow moisture exchange between humid air supplied from the fuel cell stack and dry air from the outside air. The outer surface S1 or inner surface S2 of the hollow fibers 30, 40, 50, and 60 are provided with antioxidant particles 320, and 520, or antioxidant coating layers 420, and 620 containing antioxidant particles. In this case, the antioxidant particles 320, 520 and the antioxidant coating layers 420, 620 may be provided in an amount that does not clog the pores located in the thickness regions 310, 410, 510, and 610. Furthermore, the antioxidant particles 320, 520 and the antioxidant coating layers 420, 620 may be arranged so as not to clog the gaps between adjacent hollow fiber membranes when the hollow fibers 30, 40, 50, and 60 form a bundle. That is, the thickness of the antioxidant coating layers 420, 620 is configured not to exceed half the width of the gaps between the hollow fiber membranes in the hollow fiber membrane bundle, and the antioxidant particles 320, 520 are provided so as to be uniformly dispersed on the surface. Although not shown in Figures 3 through 6, structures in which antioxidant particles and antioxidant coating layers are mixed on the inner or outer surface can also be understood by technicians in the relevant field, so no further explanation is provided in this application. In another aspect, a fuel cell system is provided which includes a fuel cell stack comprising a fuel cell cell having a polymer electrolyte membrane, and a humidifier communicating with the fuel cell stack, wherein an antioxidant flows out from the humidifier and flows into the fuel cell stack at a rate of 1 μg / 1000hr or more.

[0020] Referring to Figure 7, a fuel cell system according to one embodiment of the present invention includes a fuel cell stack 1000, a hydrogen supply unit 2000, and an air supply unit 3000. The fuel cell stack 1000 reacts hydrogen supplied from the hydrogen supply unit 2000 with oxygen supplied from the air supply unit 3000 to generate heat and steam. The fuel cell stack 1000 consists of a membrane electrode assembly, an electrolyte membrane, a catalyst layer, cathode and anode electrodes, a gas diffusion layer, a separation plate, and a gasket, and each component can be manufactured using known materials and by known methods. The fuel cell stack 1000 generates electricity through a hydrogen-oxygen bonding reaction. Specifically, hydrogen is supplied to the anode side and oxygen to the cathode side. On the anode side, hydrogen ions are generated by the oxidation reaction of hydrogen, and the electrons generated at this time move to the cathode side through the wire. The hydrogen ions move to the cathode side through the electrolyte membrane and come into contact with oxygen to form water vapor. In a polymer electrolyte fuel cell, the reduction reaction of oxygen at the cathode electrode proceeds with the formation of hydrogen peroxide as an intermediate reaction; therefore, hydrogen peroxide or hydroxide radicals can be generated at the cathode electrode. Furthermore, at the anode electrode of the same polymer electrolyte fuel cell, hydrogen peroxide or hydroxide radicals can also be generated as oxygen molecules permeate through the polymer electrolyte membrane. These generated hydrogen peroxide or hydroxide radicals cause degradation of the polymer electrolyte membrane, which is vulnerable to oxidizing substances. As an attempt to prevent the degradation of such polymer electrolyte membranes, a method of introducing radical scavengers to the surface of the polymer electrolyte membrane has been proposed. However, when excessive radical scavengers are used to improve durability, there is a problem of reduced ion exchange due to pore blockage of the ion exchange membrane. Furthermore, during fuel cell operation, the radical scavengers present on the surface of the polymer electrolyte membrane are lost, which reduces the durability of the polymer electrolyte membrane and makes it difficult to obtain sufficient durability and lifespan characteristics. The inventors of this invention have conducted extensive research to address the issue of reduced fuel cell durability due to hydrogen peroxide or hydroxide radicals generated in the fuel cell stack. Based on the finding that fuel cell durability characteristics can be obtained when air containing an antioxidant is continuously supplied from a humidifier 3200 contained within an air supply unit 300 provided upstream of the fuel cell stack, the inventors completed this invention.

[0021] Specifically, the hollow fiber membrane contained in humidifier 3200 releases antioxidants at concentrations of 1 μg / 1000hr or higher, and these antioxidants are then incorporated into the air flowing into the fuel cell stack. The hydrogen supply unit 2000 supplies the stored hydrogen to the fuel cell stack 1000. Any hydrogen supply unit that supplies hydrogen to the fuel cell stack can be used without restriction. The air supply unit 3000 includes an air compression unit 3100 that compresses outside air to generate a first fluid and a humidifier 3200 that humidifies the first fluid and transmits it to the fuel cell stack. The air compression unit 3100 supplies a first fluid, which is compressed by receiving outside air, into the humidifier. The air compression unit 3100 is a device for compressing a fluid such as air, and may include, for example, a blower, a compressor, etc. If necessary, an additional filter may be installed in front of the air compression unit inlet to block the entry of contaminants, or a separate air filter may be provided. The humidifier 3200 receives compressed air from the air compressor 3100, humidifies it, and then supplies it to the fuel cell stack. The humidifier 3200 facilitates moisture exchange between outside air and steam generated from the fuel cell stack 1000, and supplies humidified air into the fuel cell stack 1000. A further aspect of the fuel cell system is a fuel cell stack 1000, a hydrogen supply unit 2000 for supplying hydrogen to the stack, and an air supply unit 3000 for supplying air to the stack, wherein the air supply unit includes an air compressor 3100 and a humidifier 3200, and includes a filter unit positioned on the path through which outside air that has passed through the humidifier 3200 moves to the fuel cell stack, and configured to remove peroxides and / or hydroxide radicals. Such a fuel cell system will be explained with reference to Figure 8. In the system shown in Figure 8, the fuel cell stack 1000 and hydrogen supply unit 2000 are as described in Figure 7, and the air supply unit 3000 is similar to the humidifier 3200 described in Figure 5, except that the hollow fiber membrane contained within the humidifier 3200 does not contain an antioxidant. The filter unit 4000 may be positioned between the humidifier 3200 and the fuel cell stack 1000. Specifically, the filter unit 4000 may be positioned adjacent to the outlet of the outside air (i.e., the first fluid) that has passed through the humidifier, adjacent to the inlet where the first fluid flows into the fuel cell stack, or in the path through which the first fluid moves between the humidifier and the fuel cell stack.

[0022] The filter portion 4000 may include a porous substrate and an antioxidant provided on the surface of the porous substrate. The porous substrate is a porous nonwoven fabric. For example, the porous substrate includes a film on its surface having an average void size of 50 nm to 10 μm. The porous substrate may selectively include either a hydrophilic film or a hydrophobic film. For example, but not limited to, the porous substrate may include a film containing a thermoplastic polymer including polyethylene, polypropylene, 1-octene, styrene, polyolefin (co)polymer, polyamide, poly-1-butene, poly-4-methyl-1-pentene, polyethersulfone, ethylenetetrafluoroethylene, polyvinylidene fluoride, polysulfone, polyacrylonitrile, polyamide, cellulose acetate, cellulose nitrate, regenerated cellulose, polyvinyl chloride, polycarbonate, polyethylene terephthalate, polyimide, polytetrafluoroethylene, ethylene chlorotrifluoroethylene, or a combination thereof. The porous substrate may include all known substrates having a mesh-like structure. The antioxidant may be provided on one or both sides of the porous substrate. For example, the antioxidant may be provided on both sides of the porous substrate, but the concentration of the antioxidant provided on the first side facing the fuel cell stack 1000 is higher than the concentration of the antioxidant provided on the second side opposite the first side. For details regarding the aforementioned antioxidants, please refer to the previously mentioned section. In the following, an embodiment of the present invention will be described through examples and comparative examples, and there is no intention to limit the scope of the present invention to these examples.

[0023] (Examples) Example 1 A dope stock solution was prepared by mixing 20% ​​by weight of polystyrene (PS), 6% of polyvinylpyrrolidone (PVP), and 1% of the antioxidant Irganox 1010 with 73% of the solvent N-methylpyrrolidone (NMP). The core solution was prepared by mixing N-methylpyrrolidone and ethanol in a volume ratio of 6:4. The dope stock solution was discharged from the outer tube of a double-tubular nozzle, and the core solution was discharged from the inner tube, thereby immersing the spun material in a coagulation tank containing a coagulation solution. The spun material came into contact with the coagulation solution in the coagulation tank and formed a hollow fiber membrane. The coagulation solution used was water and polyethylene glycol (PEG) in a 1:1 ratio, and the temperature was adjusted to 40°C. The hollow fiber membrane that passed through the coagulation tank was washed with 40°C water in a washing tank and then dried to obtain a hollow fiber membrane. The thickness of the hollow fiber membrane was set to 150 μm. Comparative Example 1 A dope stock solution was prepared by mixing 20% ​​by weight of polystyrene (PS), 6% of polyvinylpyrrolidone (PVP), and 1% of the antioxidant Irganox 1010 with 73% of the solvent N-methylpyrrolidone (NMP). The core solution was prepared by mixing N-methylpyrrolidone and ethanol in a volume ratio of 75:25. The dope stock solution was discharged from the outer tube of a double-tubular nozzle, and the core solution was discharged from the inner tube, immersing the spun material in a coagulation tank containing a coagulation solution. The spun material came into contact with the coagulation solution in the coagulation tank and formed a hollow fiber membrane. The coagulation solution used was water and polyethylene glycol (PEG) in a 1:1 ratio, and the temperature was adjusted to 40°C. The hollow fiber membrane that passed through the coagulation tank was washed with 40°C water in a washing tank and then dried to obtain a hollow fiber membrane. The thickness of the hollow fiber membrane was set to 150 μm. Comparative Example 2 A dope stock solution was prepared by mixing 20% ​​by weight of polystyrene (PS), 6% of polyvinylpyrrolidone (PVP), and 74% of the solvent N-methylpyrrolidone (NMP). The core solution was prepared by mixing N-methylpyrrolidone and ethanol in a volume ratio of 6:4. The dope stock solution was discharged from the outer tube of a double-tubular nozzle, and the core solution was discharged from the inner tube, thereby immersing the spun material in a coagulation tank containing a coagulation solution. The spun material came into contact with the coagulation solution in the coagulation tank and formed a hollow fiber membrane. The coagulation solution used was water and polyethylene glycol (PEG) in a 1:1 ratio, and the temperature was adjusted to 40°C. The hollow fiber membrane that passed through the coagulation tank was washed with 40°C water in a washing tank and then dried to obtain a hollow fiber membrane. The thickness of the hollow fiber membrane was set to 150 μm.

[0024] Evaluation Example 1 Humidifier modules containing the hollow fiber membranes prepared in Example 1 and Comparative Example 1 were fabricated, and when these modules were installed in a fuel cell system and operated, and after 1000 hours, the content of antioxidants remaining in the hollow fiber membranes was measured by the method described below and is shown in Table 1 below. [Method for measuring the content of antioxidants] The antioxidant content was measured using 1H-NMR. The fabricated hollow fiber film was dissolved in DMSO-D6 and measured. The total content was calculated by comparing the integral ratio of the proton peaks of the main polymer and the antioxidant. [Table 1] As shown in Table 1 above, the membrane humidifier containing the hollow fiber membrane in Example 1 showed a decrease in antioxidant content after 1000 hours of fuel cell operation, suggesting that the antioxidant was transferred from the membrane humidifier to the fuel cell stack. Comparative Example 1 confirmed that, despite containing antioxidant in the dope stock, no antioxidant was present inside the final manufactured membrane humidifier, suggesting that the mixing ratio of the core liquid is important for retaining antioxidant inside the hollow fiber membrane during the membrane formation process. Evaluation Example 2 Humidifier modules containing the hollow fiber membranes produced in Example 1 and Comparative Example 2 were fabricated and installed in a fuel cell system. After 1000 hours, the gas permeability of the polymer electrolyte membrane in the stack was measured using the following method and is shown in Table 2. [Method for measuring gas permeability of polymer electrolyte membranes] The gas permeability of a polymer electrolyte membrane is measured by cutting the membrane into a 50 mm diameter circle, mounting it in a measuring jig, and applying hydrogen gas at a pressure of 0.5 bar, then measuring the amount of hydrogen that permeates through the membrane. [Table 2] As shown in Table 2 above, the polymer electrolyte membrane in the fuel cell stack supplied with antioxidant from the membrane humidifier showed suppressed chemical degradation due to oxidizing substances, resulting in a gas permeability reduction of approximately 30% compared to Comparative Example 2, where antioxidant was not replenished. It was confirmed that when the hollow fiber membrane produced by Example 1 is applied to a membrane humidifier and used in a fuel cell system, the membrane humidifier plays a role in supplying antioxidants to the fuel cell stack, thereby preventing the chemical degradation of the polymer electrolyte membrane in the fuel cell stack.

Claims

1. Containing polymers and antioxidants, A hollow fiber membrane for a fuel cell humidifier, wherein the antioxidant is disposed on the inner and / or outer surface.

2. The hollow fiber membrane for a fuel cell humidifier according to claim 1, wherein the polymer forms a mesh structure and the antioxidant is dispersed within the mesh structure.

3. The hollow fiber membrane for a fuel cell humidifier according to claim 1, wherein the antioxidant is configured to flow out of the hollow fiber membrane in an amount of 1 μg or more for 1,000 hours when the fuel cell is in operation.

4. The hollow fiber membrane for a fuel cell humidifier according to claim 1, wherein the polymer comprises polyvinylidene fluoride (PVDF) polymers, polysulfone polymers, sulfonated polysulfone, cellulose acetate, cellulose triacetate, polymethyl methacrylate, nafion, polystyrene (PS) polymers, polytetrafluoroethylene (PTFE) polymers, perfluorosulfonic acid (PFSA) polymers, polyphenylsulfone polymers, polyethersulfone (PES) polymers, polyacrylonitrile (PAN) polymers, polyetherimide (PEI) polymers, polyimide (PI) polymers, or any combination thereof.

5. The hollow fiber membrane for a fuel cell humidifier according to claim 4, wherein the polymer includes a polysulfone polymer, a sulfonated polysulfone, a polystyrene (PS) polymer, a polyethersulfone (PES) polymer, or any combination thereof.

6. The hollow fiber membrane for a fuel cell humidifier according to claim 1, wherein the polymer is contained in an amount of 90 parts by weight or more and less than 100 parts by weight per 100 parts by weight of the hollow fiber membrane.

7. The hollow fiber membrane for a fuel cell humidifier according to claim 1, wherein the antioxidant comprises a phenolic antioxidant, an amine antioxidant, a metal antioxidant, an organometallic antioxidant, a sulfur-based antioxidant, a phosphorus-based antioxidant, or a combination thereof.

8. The hollow fiber membrane for a fuel cell humidifier according to claim 1, wherein the antioxidant is contained in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the polymer.

9. The hollow fiber membrane for a fuel cell humidifier according to claim 1, further comprising polyvinylpyrrolidone.

10. The steps include preparing a doping solution for forming hollow fiber membranes containing polymers and antioxidants, The steps include: discharging the dope solution into a coagulation tank through a tubular spinning apparatus; The process includes the step of solidifying the spinning solution discharged into the solidification tank in the solidification tank, and then winding and drying it to obtain a hollow fiber membrane. A method for manufacturing a hollow fiber membrane for a fuel cell humidifier, wherein the hollow fiber membrane has an antioxidant disposed on its inner and / or outer surface.

11. The method for producing a hollow fiber membrane for a fuel cell humidifier according to claim 10, wherein the doping solution is obtained by mixing a polymer and an antioxidant in an organic solvent, and the antioxidant is mixed in an amount of 0.01 to 5 parts by weight per 100 parts by weight of polymer to obtain a spinning doping solution.

12. The tubular spinning apparatus contains a mixed solution of a second solvent and a third solvent in a volume ratio of 3:7 to 7:3 as a core liquid in the hollow section. The second solvent includes water, methanol, ethanol, isopropanol, acetone, hexane, pentane, benzene, toluene, carbon tetrachloride, o-dichlorobenzene, polyethylene glycol, or a combination thereof. The method for producing a hollow fiber membrane for a fuel cell humidifier according to claim 10, wherein the third solvent includes N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, tetrahydrofuran, tetramethylurea, trimethyl phosphate, or a combination thereof.

13. The method for producing a hollow fiber membrane for a fuel cell humidifier according to claim 12, wherein the core liquid further comprises an antioxidant.

14. A fuel cell humidifier comprising a hollow fiber membrane according to any one of claims 1 to 9.

15. A fuel cell stack including a fuel cell cell equipped with a polymer electrolyte membrane, The humidifier according to claim 14, which communicates with the fuel cell stack, A fuel cell system in which an antioxidant is discharged from the humidifier and flows into the fuel cell stack at a rate of 1 μg / 1000hr or more.

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