Reinforced composite membrane, membrane-electrode assembly comprising the same, and fuel battery

Abstract

To provide a reinforced composite membrane having improved moisture retention and ionic conductivity while maintaining dimensional stability, and also provide a reinforced composite membrane that directs water produced at a cathode to an anode for reaction or wetting purposes.SOLUTION: An embodiment of the present invention is a reinforced composite membrane comprising a porous support and an ionomer layer comprising an ion conductor filling an internal pore of the porous support. The porous support comprises a first surface and a second surface opposite to the first surface, and the first surface is modified to contain a first hydrophilic active group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a reinforced composite membrane, a membrane-electrode assembly including the same, and a fuel cell, and more particularly to a reinforced composite membrane in which one surface of a porous support is modified to contain hydrophilic functional groups, thereby improving ionic conductivity and water retention, and a membrane-electrode assembly and a fuel cell including the same. [Background technology]

[0002] 2. Description of the Related Art Fuel cells are cells that directly convert chemical energy generated by the oxidation of fuel into electrical energy, and are attracting attention as a next-generation energy source due to their high energy efficiency and environmentally friendly characteristics such as low pollutant emissions.

[0003] A fuel cell generally has a structure in which an anode and a cathode are formed on either side of a polymer electrolyte membrane, and this structure is called a membrane electrode assembly (MEA).

[0004] Fuel cells can be classified into alkaline electrolyte fuel cells, polymer electrolyte membrane fuel cells (PEMFC), etc. depending on the type of electrolyte membrane. Among them, polymer electrolyte membrane fuel cells are gaining attention as portable, vehicular, and home power sources due to their advantages such as low operating temperature of less than 100°C, fast start-up and response characteristics, and excellent durability.

[0005] A typical example of such a polymer electrolyte membrane fuel cell is a proton exchange membrane fuel cell (PEMFC) that uses hydrogen gas as fuel.

[0006] To summarize the reactions that occur in a polymer electrolyte membrane fuel cell, first, when a fuel such as hydrogen gas is supplied to the oxidizing electrode (or anode), hydrogen ions and electrons are generated at the oxidizing electrode through an oxidation reaction of the hydrogen gas. The generated hydrogen ions are transferred to the reducing electrode through the polymer electrolyte membrane, and the generated electrons are transferred to the reducing electrode (or cathode) through an external circuit. Oxygen gas is supplied to the reducing electrode, and the oxygen gas combines with the hydrogen ions and electrons to generate water through a reduction reaction.

[0007] The polymer electrolyte membrane is the path through which hydrogen ions generated at the oxidizing electrode are transferred to the reducing electrode, so it must have excellent hydrogen ion conductivity. It must also have excellent separation ability between hydrogen gas supplied to the oxidizing electrode and oxygen supplied to the reducing electrode. It must also have excellent mechanical strength, dimensional stability, chemical resistance, and low ohmic loss at high current densities.

[0008] On the other hand, the porous support used in conventional reinforced composite membranes does not have hydrophilic functional groups on its surface, which means that water generated at the cathode does not diffuse well to the anode, resulting in a decrease in the water retention capacity of the reinforced composite membrane. This leads to an additional problem of a decrease in the conductivity of protons, which must move through water. Furthermore, it is very difficult to uniformly impregnate a hydrophilic ion conductor into the interior of a superhydrophobic porous support, and even if impregnation is successful, there is a problem of the ion conductor and the porous support separating from each other. Summary of the Invention [Problem to be solved by the invention]

[0009] SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide a reinforced composite membrane having improved water retention capacity and ionic conductivity while maintaining dimensional stability.

[0010] Another object of the present invention is to provide a reinforced composite membrane that overcomes the above problems by directing water produced at the cathode to the anode for reaction or wetting purposes.

[0011] It is yet another object of the present invention to provide a reinforced composite membrane in which the hydrophilic ion conductor and the hydrophobic porous support are not separated, thereby solving the above problems.

[0012] It is yet another object of the present invention to provide a membrane-electrode assembly comprising the reinforced composite membrane.

[0013] It is still another object of the present invention to provide a fuel cell comprising the membrane-electrode assembly.

[0014] The objects of the present invention are not limited to the objects mentioned above, and other objects and advantages of the present invention not mentioned above can be understood from the following description and will be more clearly understood from the embodiments of the present invention. Furthermore, it will be easily understood that the objects and advantages of the present invention can be realized by the means and combinations thereof recited in the claims. [Means for solving the problem]

[0015] To achieve the above object, one embodiment of the present invention provides a reinforced composite membrane comprising a porous support and an ionomer layer containing an ion conductor filling the internal pores of the porous support, wherein the porous support has a first surface and a second surface opposite to the first surface, and the first surface is modified to contain a first hydrophilic functional group. [Effects of the Invention]

[0016] According to the present invention, water produced at the cathode can be returned to the anode for reaction or wetting purposes, thereby increasing water retention capacity and ionic conductivity. In addition, the present invention solves the problem of separation between the hydrophilic ion conductor and the superhydrophobic porous support.

[0017] The specific effects of the present invention, together with the above-mentioned effects, will be described below while explaining specific details for carrying out the invention. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view showing a reinforced composite membrane according to one embodiment of the present invention.

[0019] [Figure 2] 1 is a cross-sectional view showing a reinforced composite membrane according to another embodiment of the present invention.

[0020] [Figure 3] 1 is a cross-sectional view showing a membrane-electrode assembly according to one embodiment of the present invention.

[0021] [Figure 4] 1 is a schematic diagram illustrating a fuel cell according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, each component of the present invention will be described in more detail so that a person having ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited to the following content.

[0023] The reinforced composite membrane of the present invention comprises a porous support and an ionomer layer containing an ion conductor filling the internal pores of the porous support. The porous support has a first surface and a second surface opposite the first surface, and the first surface is modified to contain a first hydrophilic functional group. The porous support used in conventional reinforced composite membranes lacks hydrophilic functional groups on its surface, which prevents water generated at the cathode from diffusing toward the anode, resulting in a decrease in the water retention capacity of the reinforced composite membrane. This leads to an additional problem of reduced hydrogen ion conductivity, which must be transported through water. Furthermore, it is extremely difficult to uniformly impregnate a hydrophilic ion conductor into a superhydrophobic porous support, and even if impregnation is achieved, separation of the ion conductor from the porous support is a common problem. According to one aspect of the present invention, the first surface is modified to contain a first hydrophilic functional group, thereby allowing water produced at the cathode to be returned to the anode for reaction or wetting purposes, thereby improving water retention and ionic conductivity. According to another aspect of the present invention, the first surface is modified to contain a first hydrophilic functional group, thereby solving the problem of separation between the hydrophilic ion conductor and the superhydrophobic porous support.

[0024] The configuration of the present invention will be described in more detail below with reference to the drawings.

[0025] 1. Reinforced composite membrane 50

[0026] FIG. 1 is a cross-sectional view showing a reinforced composite membrane according to one embodiment of the present invention.

[0027] As shown in FIG. 1, a reinforced composite membrane 50 according to the present invention can include a porous support 52 and an ionomer layer 55 .

[0028] The porous support 52 according to the present invention may have a first surface 52a and a second surface 52b opposite to the first surface 52a.

[0029] Specifically, the first surface 52a of the porous support 52 may be modified to include a first hydrophilic functional group. Specifically, the first surface may be modified by any one of the following methods: irradiation with radiation such as plasma, UV, ion beam, gamma ray, or electron beam; and reaction with a chemical agent. A plasma method is preferred. For example, the first hydrophilic functional group introduced into the first surface 52a of the porous support 52 may be analyzed by infrared spectroscopy or by measuring the contact angle of deionized water with the first surface of the porous support.

[0030] The first hydrophilic functional group may be any one selected from the group consisting of a hydroxyl group, a carboxyl group, a sulfate group, and a phosphate group. By modifying the first surface 52a of the porous support 52 with the hydrophilic functional group, the wettability of the reinforced composite membrane may be improved, and the ionic conductivity of hydrogen ions may be increased.

[0031] To introduce hydroxyl groups to the first surface, for example, a dry air (oxygen) / moisture supply method can be used; to introduce carboxyl groups to the first surface, for example, a carbon dioxide supply method can be used; to introduce sulfate groups to the first surface, for example, a sulfur dioxide (SO2) supply method can be used; and to introduce phosphate groups to the first surface, for example, a solution spray method containing a compound containing a phosphate group can be used.

[0032] In one embodiment of the present invention, the second surface 52b of the porous support 52 may not be modified to contain hydrophilic functional groups. Therefore, only the first surface 52a is selectively modified to contain hydrophilic functional groups, which facilitates the migration of water generated at the cathode to the anode, thereby improving the water retention capacity and ionic conductivity of the reinforced composite membrane. Furthermore, the bonding strength between the hydrophilic ion conductor and the porous support is improved, thereby solving the problem of separation between the ion conductor and the porous support.

[0033] The contact angle of the first solvent with respect to the first surface 52 a may be lower than the contact angle of the first solvent with respect to the second surface 52 b. The first solvent may be any one selected from the group consisting of water, ethylene glycol, and mixtures thereof, and may preferably be distilled water.

[0034] Since the contact angle of the first solvent on the first surface 52a is smaller than the contact angle of the first solvent on the second surface 52b, the wettability of the reinforced composite membrane can be improved, increasing the ionic conductivity of hydrogen ions, and the water generated at the cathode can be easily transported to the anode.

[0035] The contact angle of the first solvent with respect to the first surface 52a may be 75 to 105°, and the contact angle of the first solvent with respect to the second surface 52b may be 110 to 145°. Preferably, the contact angle of the first solvent with respect to the first surface 52a may be 80 to 100°, and the contact angle of the first solvent with respect to the second surface 52b may be 120 to 140°.

[0036] In another embodiment of the present invention, the second surface 52b of the porous support 52 may be modified to include a second hydrophilic functional group. Specifically, the second hydrophilic functional group may be any one selected from the group consisting of a hydroxyl group, a carboxyl group, a sulfate group, and a phosphate group. The first hydrophilic functional group and the second hydrophilic functional group may be the same or different.

[0037] However, the degree to which the second surface 52b of the porous support 52 is modified may be less than that of the first surface 52a, and a method for achieving this may be to adjust the output of an electrode in a plasma-based method.

[0038] As in the above-described embodiment, the contact angle of the second solvent with respect to the first surface 52a may be smaller than the contact angle of the second solvent with respect to the second surface 52b. Specifically, the contact angle of the second solvent with respect to the first surface 52a may be 75 to 105°, and the contact angle of the second solvent with respect to the second surface 52b may be 108 to 120°. Preferably, the contact angle of the second solvent with respect to the first surface 52a may be 80 to 100°, and the contact angle of the second solvent with respect to the second surface 52b may be 108 to 118°, and more preferably, the contact angle of the second solvent with respect to the first surface 52a may be 85 to 95°, and the contact angle of the second solvent with respect to the second surface 52b may be 110 to 115°.

[0039] The second solvent can be the same as or different from the first solvent, preferably the same.

[0040] The porous support 52 according to one embodiment of the present invention may include a highly fluorinated polymer, preferably a perfluorinated polymer, which has excellent resistance to thermal and chemical decomposition. For example, polytetrafluoroethylene (PTFE) or tetrafluoroethylene and CF₂=CFC. n F 2n+1 (n is a real number between 1 and 5) or CF2 = CFO-(CF2CF(CF3)O) m C n F 2n+1 (m is a real number of 0 to 15, and n is a real number of 1 to 15).

[0041] In another embodiment of the present invention, the porous support 52 may be expanded polytetrafluoroethylene (e-PTFE) having a microstructure of polymer fibrils or a microstructure in which nodes are connected to each other by fibrils. Also, a film having a microstructure of polymer fibrils without nodes may be used as the porous support 52.

[0042] In yet another embodiment of the present invention, the porous support 52 may comprise a perfluorinated polymer. The porous support 52 may be formed by extruding dispersion-polymerized PTFE into a tape in the presence of a lubricant and then stretching the resulting material to form a more porous and stronger porous support.

[0043] The amorphous content of PTFE can also be increased by heat-treating the e-PTFE at a temperature exceeding the melting point of PTFE (approximately 342°C). The e-PTFE film produced by the above method can have micropores with various diameters and porosity. The e-PTFE film produced by the above method can have at least 35% pores, and the diameter of the micropores can be approximately 0.01 to 1 μm.

[0044] According to one embodiment of the present invention, the porous substrate 52 may be a nonwoven fibrous web made of randomly oriented fibers. The nonwoven fibrous web refers to a sheet having a structure of individual fibers or filaments that are interlaid but not in the same manner as a woven fabric. The nonwoven fibrous web may be manufactured by any one method selected from the group consisting of carding, garneting, air-laying, wet-laying, meltblowing, spunbonding, and stitchbonding.

[0045] The fibers may comprise one or more polymeric materials. Generally, any fiber-forming polymeric material may be used. Specifically, hydrocarbon-based fiber-forming polymeric materials may be used. For example, the fiber-forming polymeric material may be any one selected from the group consisting of polyolefins (e.g., polybutylene, polypropylene, and polyethylene), polyesters (e.g., polyethylene terephthalate and polybutylene terephthalate), polyamides (nylon-6 and nylon-6,6), polyurethane, polybutene, polylactic acid, polyvinyl alcohol, polyphenylene sulfide, polysulfone, fluid crystalline polymers, polyethylene-co-vinyl acetate, polyacrylonitrile, cyclic polyolefins, polyoxymethylene, polyolefin-based thermoplastic elastomers, and combinations thereof. However, the technical concept of the present invention is not limited thereto.

[0046] The porous support 52 according to one embodiment of the present invention may include a nanoweb in which nanofibers are accumulated in the form of a nonwoven fabric having a plurality of pores.

[0047] The nanofibers are preferably made of hydrocarbon-based polymers that exhibit excellent chemical resistance, are hydrophobic, and are not susceptible to deformation due to moisture in a humid environment. Specifically, the hydrocarbon-based polymer may be selected from the group consisting of nylon, polyimide, polyaramid, polyetherimide, polyacrylonitrile, polyaniline, polyethylene oxide, polyethylene naphthalate, polybutylene terephthalate, styrene butadiene rubber, polystyrene, polyvinyl chloride, polyvinyl alcohol, polyvinylidene fluoride, polyvinyl butylene, polyurethane, polybenzoxazole, polybenzimidazole, polyamide imide, polyethylene terephthalate, polyphenylene sulfide, polyethylene, polypropylene, copolymers thereof, and mixtures thereof. Among these, polyimide is preferably used because of its excellent heat resistance, chemical resistance, and dimensional stability.

[0048] The nanoweb is an aggregate of randomly arranged nanofibers produced by electrospray irradiation, and preferably has an average diameter of 40 to 5,000 nm, calculated from the average of 50 fiber diameters measured using a scanning electron microscope (JSM6700F, JEOL), taking into account the porosity and thickness of the nanoweb.

[0049] If the average diameter of the nanofibers is less than the above range, the mechanical strength of the porous support may be reduced, and if the average diameter of the nanofibers is greater than the above range, the porosity may be significantly reduced and the thickness may be increased.

[0050] The thickness of the nonwoven fibrous web may be 10 to 50 μm, specifically 15 to 43 μm. If the thickness of the nonwoven fibrous web is less than this range, the mechanical strength may be reduced, and if it exceeds this range, the resistance loss may increase, and the weight and integration may be reduced.

[0051] The nonwoven fibrous web has a basic weight of 5 to 30 mg / cm 2 If the basis weight of the nonwoven fibrous web is less than the above range, visible pores may be formed, making it difficult to function as a porous support, whereas if the basis weight exceeds the above range, it may be manufactured in the form of paper or fabric with almost no pores.

[0052] The porosity can be calculated as the ratio of the air volume in the porous support to the total volume of the porous support according to the following mathematical formula 1. Here, the total volume is calculated by preparing a rectangular sample and measuring its width, length, and thickness, and the air volume can be obtained by measuring the mass of the sample and then subtracting the polymer volume, which is calculated back from the density, from the total volume.

[0053] [Mathematical formula 1]

[0054] Porosity (%) = (air volume in the porous support / total volume of the porous support) × 100

[0055] The porosity of the porous support according to the present invention may be 30 to 90%, and preferably 60 to 85%. If the porosity of the porous support is below this range, the impregnation of the ion conductor may be reduced, and if it exceeds this range, the dimensional stability may be reduced, which may hinder smooth subsequent processes.

[0056] The ionomer layer 55 according to the present invention may include an ion conductor that fills the internal pores of the porous support 52 .

[0057] The ion conductor according to the present invention may be a cation conductor having a cation exchange functional group such as a hydrogen ion, or an anion conductor having an anion exchange functional group such as a hydroxyl ion, carbonate, or bicarbonate. The cation exchange functional group may be any one selected from the group consisting of a sulfonic acid group, a carboxyl group, a boronic acid group, a phosphate group, an imide group, a sulfonimide group, a sulfonamide group, a sulfonyl fluoride group, and combinations thereof, and is generally a sulfonic acid group or a carboxyl group.

[0058] Examples of the cation conductor include a fluorine-based polymer containing the cation exchange functional group and fluorine in the main chain, a hydrocarbon polymer such as benzimidazole, polyamide, polyamideimide, polyimide, polyacetal, polyethylene, polypropylene, acrylic resin, polyester, polysulfone, polyether, polyetherimide, polyester, polyethersulfone, polyetherimide, polycarbonate, polystyrene, polyphenylene sulfide, polyetheretherketone, polyetherketone, polyarylethersulfone, polyphosphazene, or polyphenylquinoxaline, a partially fluorinated polymer such as polystyrene-graft-ethylenetetrafluoroethylene copolymer or polystyrene-graft-polytetrafluoroethylene copolymer, sulfonimide, or a mixture thereof.

[0059] More specifically, when the cation conductor is a hydrogen ion cation conductor, the polymer may have a cation exchange group in a side chain selected from the group consisting of a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a phosphonic acid group, and derivatives thereof. Specific examples thereof include poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), a copolymer of tetrafluoroethylene and fluorovinyl ether containing a sulfonic acid group, a fluorine-based polymer containing defluorinated sulfonated polyether ketone, or a mixture thereof, sulfonated polyimide (S-PI), sulfonated polyarylethersulfone (S-PAES), sulfonated polyetheretherketone (S-PEEK), sulfonated polybenzimidazole (S-PBI), sulfonated polysulfone (S-PSU), sulfonated polystyrene (S-PEEK), and the like. polystyrene (S-PS), sulfonated polyphosphazene, sulfonated polyquinoxaline, sulfonated polyketone, sulfonated polyphenylene oxide, sulfonated polyether sulfone, sulfonated polyether ketone, sulfonated polyphenylene sulfone, sulfonated polyphenylene sulfide, sulfonated polyphenylene sulfideExamples of the hydrocarbon polymer include sulfonated polyphenylene sulfide sulfone nitrile, sulfonated polyarylene ether, sulfonated polyarylene ether nitrile, sulfonated polyarylene ether ether nitrile, sulfonated polyarylene ether sulfone ketone, and mixtures thereof, but the technical concept of the present invention is not limited thereto.

[0060] The anion conductor is a polymer capable of transporting anions such as hydroxide ions, carbonate ions, or bicarbonate ions. Anion conductors are commercially available in hydroxide or halide (generally chloride) forms, and can be used in industrial water purification, metal separation, catalytic processes, and the like.

[0061] The anion conductor may generally be a polymer doped with a metal hydroxide. Specifically, metal hydroxide-doped poly(ether sulfone), polystyrene, vinyl polymer, poly(vinyl chloride), poly(vinylidene fluoride), poly(tetrafluoroethylene), poly(benzimidazole), or poly(ethylene glycol) may be used.

[0062] The ionomer layer 55 according to the present invention may include a first resin layer 54 and a second resin layer 56 facing the first resin layer 54. Specifically, the first resin layer 54 may be disposed on the first surface 52a, and the second resin layer 56 may be disposed on the second surface 52b. Therefore, the ionomer layer 55 may be formed on the surface of the porous support 52.

[0063] 2 is a cross-sectional view showing a reinforced composite membrane according to another embodiment of the present invention. The repeated explanations of the above-mentioned parts will be simplified or omitted.

[0064] 2, the porous support 52 according to the present invention may include at least two sub-porous supports. Specifically, the porous support 52 may include a first sub-porous support 52_1 and a second sub-porous support 52_2 disposed on the first sub-porous support 52_1.

[0065] The first sub-porous support 52_1 and the second sub-porous support 52_2 may be the same as or different from the above-described porous supports, independently of each other.

[0066] The thickness of the first sub-porous support 52_1 may be, for example, 1 to 50 μm, and the thickness of the second sub-porous support 52_2 may be, for example, 1 to 50 μm.

[0067] The porosity of each of the first sub-porous support 52_1 and the second sub-porous support 52_2 may be the same as or different from the above-mentioned porous supports, and the configuration may be the same as or different from the above-mentioned porous supports.

[0068] The first sub-porous support 52_1 may have the first surface 52a, and the second sub-porous support 52_2 may have the second surface 52b.

[0069] Unlike the above-described embodiment, the ionomer layer 55 according to the present invention may further include a third resin layer 58. The third resin layer 58 may be disposed between the first sub-porous support 52_1 and the second sub-porous support 52_2.

[0070] The equivalent weights of the ion conductors constituting the first to third resin layers 54, 56, and 58 may be the same or different from each other. The ion conductor constituting the resin layers may be any one selected from the group consisting of a fluorine-based ion conductor, a hydrocarbon-based ion conductor, and a mixture thereof, similar to the above-mentioned ion conductors.

[0071] 2. Membrane-electrode assembly 100

[0072] 3 is a cross-sectional view showing a membrane-electrode assembly according to one embodiment of the present invention. The repeated explanations of the above-mentioned parts will be simplified or omitted.

[0073] As shown in FIG. 3, the membrane-electrode assembly 100 according to the present invention includes the reinforced composite membrane 50 and the fuel cell electrodes 20 and 20 ′ disposed on both sides of the reinforced composite membrane 50 , respectively.

[0074] The membrane-electrode assembly 100 according to one embodiment of the present invention may include the reinforced composite membrane 50, the anode 20 disposed on the first surface (not shown), and the cathode 20' disposed on the second surface (not shown). The ionomer layer (not shown) according to the present invention may include a first resin layer and a second resin layer facing the first resin layer.

[0075] The electrodes 20, 20′ include electrode substrates 40, 40′ and catalyst layers 30, 30′ formed on the surfaces of the electrode substrates 40, 40′. A microporous layer (not shown) containing conductive fine particles such as carbon powder or carbon black may be further provided between the electrode substrates 40, 40′ and the catalyst layers 30, 30′ to facilitate material diffusion in the electrode substrates 40, 40′.

[0076] In the membrane-electrode assembly 100, the electrode 20 disposed on one side of the reinforced composite membrane 50 and causing an oxidation reaction to generate hydrogen ions and electrons from the fuel transferred to the catalyst layer 30 via the electrode substrate 40 is called the anode.

[0077] The electrode 20′ disposed on the other side of the reinforced composite membrane 50 and causing a reduction reaction to generate water from the hydrogen ions supplied through the reinforced composite membrane 50 and the oxidant transferred to the catalyst layer 30′ via the electrode substrate 40′ is called the cathode electrode.

[0078] The catalyst layers 30, 30' of the anode and cathode electrodes 20, 20' contain a catalyst. The catalyst participates in the cell reaction and can be any catalyst that is generally usable as a catalyst for fuel cells. Preferably, a platinum-based metal can be used.

[0079] The platinum-based metal may include one selected from the group consisting of platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), osmium (Os), platinum-M alloys, non-platinum alloys, and combinations thereof. More preferably, a combination of two or more metals selected from the platinum-based catalytic metal group may be used, but is not limited thereto, and any platinum-based catalytic metal usable in the art may be used without limitation.

[0080] The M may be at least one selected from the group consisting of palladium (Pd), ruthenium (Ru), iridium (Ir), osmium (Os), gallium (Ga), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), silver (Ag), gold (Au), zinc (Zn), tin (Sn), molybdenum (Mo), tungsten (W), lanthanum (La), and rhodium (Rh). Specifically, the platinum alloy may be selected from the group consisting of Pt-Pd, Pt-Sn, Pt-Mo, Pt-Cr, Pt-W, Pt-Ru, Pt-Ru-W, Pt-Ru-Mo, Pt-Ru-Rh-Ni, Pt-Ru-Sn-W, Pt-Co, Pt-Co-Ni, Pt-Co-Fe, Pt-Co-Ir, Pt-Co-S, Pt-Co-P, Pt-Fe, Pt-Fe-Ir, Pt-Fe-S, Pt-Fe-P, Pt-Au-Co, Pt-Au-Fe, Pt-Au-Ni, Pt-Ni, Pt-Ni-Ir, Pt-Cr, Pt-Cr-Ir, and combinations thereof, and may be used alone or in combination of two or more.

[0081] Furthermore, the non-platinum alloy may be selected from the group consisting of Ir-Fe, Ir-Ru, Ir-Os, Co-Fe, Co-Ru, Co-Os, Rh-Fe, Rh-Ru, Rh-Os, Ir-Ru-Fe, Ir-Ru-Os, Rh-Ru-Fe, Rh-Ru-Os, and combinations thereof, and may be used alone or in combination of two or more.

[0082] The catalyst may be used as a catalyst itself (black) or may be supported on a carrier.

[0083] 3.Fuel cell 200

[0084] FIG. 4 is a schematic diagram illustrating a fuel cell according to one embodiment of the present invention.

[0085] One embodiment of the present invention relates to a fuel cell comprising the membrane-electrode assembly.

[0086] As shown in FIG. 4, a fuel cell 200 according to the present invention may include a fuel supply unit 210 that supplies a mixed fuel obtained by mixing fuel and water, a reforming unit 220 that reforms the mixed fuel to generate a reformed gas containing hydrogen gas, a stack 230 that generates electrical energy by electrochemically reacting the reformed gas containing hydrogen gas supplied from the reforming unit 220 with an oxidant, and an oxidant supply unit 240 that supplies an oxidant to the reforming unit 220 and the stack 230.

[0087] The stack 230 may include a plurality of unit cells that generate electrical energy by conducting an oxidation / reduction reaction between the reformed gas containing hydrogen gas supplied from the reforming unit 220 and the oxidant supplied from the oxidant supplying unit 240.

[0088] Each unit cell refers to a unit cell that generates electricity and may include the membrane-electrode assembly that oxidizes / reduces oxygen in the reformed gas containing hydrogen gas and the oxidant, and a separator plate (also called a bipolar plate, hereinafter referred to as "separator plate") that supplies the reformed gas containing hydrogen gas and the oxidant to the membrane-electrode assembly. The separator plates are disposed on both sides of the membrane-electrode assembly. In this case, the separator plates located at the outermost sides of the stack are also referred to as end plates.

[0089] Of the separation plates, the end plate may be provided with a pipe-shaped first supply pipe 231 for injecting the reformed gas containing hydrogen gas supplied from the reforming section 220 and a pipe-shaped second supply pipe 232 for injecting oxygen gas, and the other end plate may be provided with a first exhaust pipe 233 for discharging the reformed gas containing hydrogen gas that is ultimately left unreacted in the plurality of unit cells to the outside, and a second exhaust pipe 234 for discharging the oxidant that is ultimately left unreacted in the unit cells to the outside.

[0090] In the fuel cell, the separator, fuel supply section, and oxidant supply section that constitute the electricity generating section are the same as those used in ordinary fuel cells, and therefore detailed description thereof will be omitted in this specification.

[0091] Hereinafter, the embodiments of the present invention will be described in detail so that a person having ordinary skill in the art to which the present invention pertains can easily carry out the present invention. However, this is merely an example, and the scope of the present invention is not limited to the following content.

[0092] [Example of manufacturing preparation: manufacturing of porous support]

[0093] Porous supports were prepared according to the following working examples, comparative examples, and reference examples.

[0094] <Example 1: When only the first surface is modified>

[0095] The oxygen gas flow rate was set to 20 sccm, the plasma power was set to 2 W, and the plasma treatment time was set to 5 seconds. The first surface of the porous support (e-PTFE) was modified to have hydroxyl groups (-OH) using an RF (radio frequency) plasma method, while the second surface opposite the first surface was not modified. The porous support of Preparative Example 1 had a porosity of 70%, a thickness of 10 μm, and a pore size of 0.2 μm.

[0096] <Preparation Example 2: Second surface modified less than the first surface>

[0097] A porous support was produced in the same manner as in Preparative Example 1, but the second surface was additionally modified by setting the oxygen gas flow rate to 20 sccm, the plasma power to 2 W, and the plasma treatment time to 2 seconds, so that the concentration of hydroxy groups per unit area of ​​the first surface was greater than that of the second surface.

[0098] <Preparation Example 3: Porous support having two sub-porous supports>

[0099] A porous support was prepared in the same manner as in Preparative Example 1, except that a second subporous support (e-PTFE) was formed on a first subporous support (e-PTFE) to produce a final porous support. The first subporous support had a porosity of 65%, a thickness of 5 μm, and a pore size of 0.15 μm, while the second subporous support had a porosity of 75%, a thickness of 5 μm, and a pore size of 0.2 μm. The first surface of the first subporous support (e-PTFE) was modified to have hydroxyl groups (-OH) using a radio frequency (RF) plasma method. Specifically, the method of forming the second subporous support on the first subporous support involved spraying alcohol onto the surface of the first subporous support, followed by a thermocompression process using a roll press.

[0100] Comparative Preparation Example 1: Unmodified Porous Support

[0101] A porous support (e-PTFE) with an unmodified surface and a porosity of 70%, a thickness of 10 μm, and a pore size of 0.2 μm was prepared.

[0102] <Reference Preparation Example 1: Porous Support Having Both First and Second Surfaces Modified Identical to Each Other>

[0103] A porous support was manufactured using the same method as in Preparatory Example 2, but both the first and second surfaces were modified using the same oxygen gas flow rate of 100 sccm, plasma power of 3 W, and plasma treatment time of 5 seconds.

[0104] [Experimental Example 1: Contact angle measurement]

[0105] A porous support was prepared according to the above Preparation Example, and the contact angles of distilled water on each of the first and second surfaces were measured.

[0106] 1) Contact angle measurement method

[0107] Distilled water was filled into a syringe at 25°C and 40% RH, and a 3mm diameter water droplet was dropped onto the surface of the porous support. After 5 minutes, the water droplet was allowed to spread, and the contact angle between the surface of the porous support and the water droplet was measured. A smaller contact angle indicates that the surface of the porous support was more hydrophilically modified.

[0108] [Table 1]

[0109] [Manufacturing example: Manufacturing of reinforced composite membrane]

[0110] Reinforced composite membranes were prepared according to the following examples and comparative examples.

[0111] Example 1: Reinforced composite membrane with porous support of Preparatory Example 1

[0112] The porous support prepared in Preparation Example 1 was placed in a reaction vessel containing isopropyl alcohol at room temperature for 5 minutes for pretreatment. The pretreated porous support was then immersed in a 10 wt.% solution of Nafion dispersed in an emulsion state (product name: Nafion D1021) for 5 minutes and then dried at 60°C for 4 hours to prepare a reinforced composite membrane.

[0113] Example 2: Reinforced composite membrane with porous support of Preparation Example 2

[0114] A reinforced composite membrane was produced in the same manner as in Example 1, but the porous support of Preparative Example 2 was used instead of the porous support of Preparative Example 1.

[0115] Example 3: Reinforced composite membrane with porous support of Preparation Example 3

[0116] A reinforced composite membrane was produced in the same manner as in Example 1, but the porous support of Preparative Example 3 was used instead of the porous support of Preparative Example 1.

[0117] Example 4: Different from Example 1, in which the ionic conductor was different

[0118] A reinforced composite membrane was prepared in the same manner as in Example 1, except that a sulfonated poly(ether sulfone) having an ion exchange capacity of 1.7 meq / g was used instead of the 10 wt % Nafion solution used in Preparative Example 1.

[0119] <Comparative Example 1: Reinforced composite membrane with porous support of Comparative Preparation Example 1>

[0120] A reinforced composite membrane was produced in the same manner as in Example 1, but the porous support of Comparative Preparation Example 1 was used instead of the porous support of Working Preparation Example 1.

[0121] <Reference Example 1: Reinforced composite membrane with porous support of Reference Preparation Example 1>

[0122] A reinforced composite membrane was produced in the same manner as in Example 1, but the porous support of Reference Preparation Example 1 was used instead of the porous support of Working Preparation Example 1.

[0123] <Comparative Example 2: Different from Example 4, in which a different porous support was used>

[0124] A reinforced composite membrane was produced in the same manner as in Example 4, but the porous support of Comparative Preparation Example 1 was used instead of the porous support of Working Preparation Example 1.

[0125] [Experimental Example 2: Measurement of water absorption rate and dimensional change rate of reinforced composite membrane]

[0126] The water absorption rate and dimensional change rate of the reinforced composite membrane according to the above Preparation Example were measured.

[0127] 1) Water absorption rate

[0128] The reinforced composite membrane according to the above Preparation Example was washed several times with deionized water, and the washed reinforced composite membrane was dried in a vacuum oven at 120°C for 24 hours, and then weighed (W dry The same membrane was then immersed in deionized water for 24 hours, removed, and reweighed (W wet The water absorption rate was calculated using the following mathematical formula 2.

[0129] [Mathematical formula 2]

[0130]

number

[0131] 4) Dimensional change rate

[0132] The dimensional change rate of the reinforced composite membrane according to the above Preparation Example was measured in the same manner as the water absorption rate measurement method, but instead of measuring the weight, the volume change of the reinforced composite membrane was measured and calculated using the following Equation 3.

[0133] [Mathematical formula 3]

[0134]

number

[0135] [Table 2]

[0136] Referring to Table 2, it can be seen that the Examples have a lower water absorption rate and a significantly lower dimensional change rate than the Reference Example. This confirms the problem of reduced dimensional stability when both sides of a porous support are modified in the same way, and that modifying one side of the porous support as in the Examples, or modifying both sides differently by adjusting the plasma treatment time, is a factor in improving dimensional stability.

[0137] [Experimental Example 3: Performance evaluation of membrane-electrode assembly]

[0138] The electrode slurry was directly coated on both sides of the reinforced composite membrane according to the above Preparation Example and then dried to prepare a membrane-electrode assembly. The ionic conductivity of the membrane-electrode assembly including the reinforced composite membrane according to the above Preparation Example was measured by the following method.

[0139] 1) Ionic conductivity (experimental conditions: 80°C / 50%RH)

[0140] The ionic conductivity of the membrane-electrode assembly including the reinforced composite membrane according to the above Preparation Example was measured using a measuring device (Solatron-1280 Impedance / Gain-Phase analyzer) at a measurement temperature of 80° C. Specifically, the ohmic resistance or bulk resistance was measured using the four-point probe AC ​​impedance spectroscopic method, and then the ionic conductivity was calculated using the following Equation 4.

[0141] [Mathematical formula 4]

[0142]

number

[0143] In the above mathematical formula 4, σ is the ionic conductivity (S / cm), R is the ohmic resistance of the electrolyte membrane (Ω), L is the distance between the electrodes (cm), and S is the area in the electrolyte through which a certain current flows (cm 2 ) applies.

[0144] [Table 3]

[0145] Referring to Table 3, it can be seen that the Examples have higher ionic conductivity than the Comparative Examples. Reference Example 1 had high ionic conductivity, but had a problem of significantly reduced dimensional stability, as seen in Experimental Example 2. The present invention provides a membrane-electrode assembly with high ionic conductivity while satisfying an appropriate range of dimensional stability.

[0146] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

Claims

1. a porous support; an ionomer layer containing an ion conductor that fills the internal pores of the porous support; 1. A reinforced composite membrane comprising: The porous support includes: A first surface; a second surface opposite to the first surface; Equipped with the first surface is modified to contain a first hydrophilic functional group; The porous support includes: At least two or more sub-porous supports; Reinforced composite membrane.

2. The porous support is made of expanded polytetrafluoroethylene (e-PTFE). The reinforced composite membrane of claim 1.

3. a contact angle of the first solvent with the first surface at 25° C. and 40% RH is lower than a contact angle of the first solvent with the second surface; The first solvent is any one selected from the group consisting of water, ethylene glycol, and a mixture thereof. The reinforced composite membrane of claim 1.

4. The porous support includes: a first sub-porous support; a second sub-porous support disposed on the first sub-porous support; 10. The reinforced composite membrane of claim 1, comprising:

5. The first sub-porous support comprises: the first surface, The second sub-porous support comprises: The reinforced composite membrane of claim 4 comprising said second surface.

6. The ionic conductor is 2. The reinforced composite membrane according to claim 1, wherein the ion conductor is any one selected from the group consisting of a fluorine-based ion conductor, a hydrocarbon-based ion conductor, and a mixture thereof.

7. The reinforced composite membrane of claim 1; an anode disposed on the first surface; a cathode disposed on the second surface; A membrane-electrode assembly comprising:

8. The ionomer layer is a first resin layer; a second resin layer facing the first resin layer; The membrane-electrode assembly according to claim 7, comprising:

9. A fuel cell comprising the membrane-electrode assembly according to claim 7.

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