Ion conductor dispersion, polymer electrolyte membrane prepared therefrom, membrane-electrode assembly and fuel cell

Abstract

An ion conductor dispersion capable of improving the chemical and mechanical durability of a polymer electrolyte membrane is provided. The ion conductor dispersion according to the present invention comprises an ion conductor, a crosslinking agent, and a solvent, and has a contact angle of 135° or less with respect to a PTFE (Polytetrafluoroethylene) porous membrane. Here, the contact angle is the contact angle measured after 1 second has elapsed since the ion conductor composition was dropped onto the PTFE (Polytetrafluoroethylene) porous membrane under conditions of 25°C and 60% relative humidity.

Description

Technology Field

[0001] The present invention relates to an ion-conducting dispersion, a polymer electrolyte membrane prepared therefrom, a membrane-electrode assembly, and a fuel cell, and more specifically, to an ion-conducting dispersion that improves the mechanical and chemical durability of a polymer electrolyte membrane, a polymer electrolyte membrane prepared therefrom, a membrane-electrode assembly, and a fuel cell. Background Technology

[0002] Fuel cells are batteries equipped with a power generation system that directly converts chemical reaction energy, such as the oxidation / reduction reaction of hydrogen and oxygen contained in hydrocarbon-based fuel materials like methanol, ethanol, and natural gas, into electrical energy. Due to their high energy efficiency and eco-friendly characteristics, including low pollutant emissions, they are gaining attention as a next-generation clean energy source capable of replacing fossil fuels.

[0003] These fuel cells have the advantage of being able to produce a wide range of outputs through a stack configuration formed by stacking unit cells, and are attracting attention as small and portable power sources because they exhibit an energy density 4 to 10 times that of small lithium batteries.

[0004] The stack that actually generates electricity in a fuel cell has a structure in which several to tens of unit cells, each consisting of a membrane-electrode assembly (MEA) and a separator (also called a bipolar plate), are stacked. The membrane-electrode assembly generally has a structure in which an anode (or fuel electrode) and a cathode (or air electrode) are formed on opposite sides of an electrolyte membrane.

[0005] Fuel cells can be classified into alkaline electrolyte membrane fuel cells and polymer electrolyte membrane fuel cells (PEMFC) depending on the state and type of electrolyte. Among these, polymer electrolyte membrane fuel cells are gaining popularity as portable, automotive, and home power devices due to their advantages, such as a low operating temperature of less than 100°C, fast start-up and response characteristics, and excellent durability.

[0006] Representative examples of polymer electrolyte membrane fuel cells include proton exchange membrane fuel cells (PEMFCs) that use hydrogen gas as fuel and direct methanol fuel cells (DMFCs) that use liquid methanol as fuel.

[0007] To summarize the reactions occurring in a polymer electrolyte membrane fuel cell, first, when a fuel such as hydrogen gas is supplied to the anode, hydrogen ions (H₂) are produced at the anode through the oxidation reaction of the hydrogen gas. + ) and electrons (e - ) is generated. The generated hydrogen ions are transferred to the reduction electrode through the polymer electrolyte membrane, and the generated electrons are transferred to the reduction electrode through the external circuit. At the reduction electrode, oxygen gas is supplied, and oxygen combines with hydrogen ions and electrons to produce water through the reduction reaction of oxygen.

[0008] Meanwhile, there are still many technical barriers to overcome to realize the commercialization of polymer electrolyte membrane fuel cells, and essential improvements include achieving high performance, long lifespan, and low cost. The membrane-electrode assembly is the component that has the greatest impact on this, and among them, the polymer electrolyte membrane is one of the key factors that most significantly affects the performance and price of the MEA.

[0009] The requirements for the polymer electrolyte membrane necessary for the operation of the above-mentioned polymer electrolyte membrane fuel cell include high hydrogen ion conductivity, chemical stability, low fuel permeability, high mechanical strength, low water content, and excellent dimensional stability.

[0010] In the conventional process of preparing ion conductor dispersions for manufacturing polymer electrolyte membranes, crosslinking agents were not introduced, resulting in a decrease in the chemical and mechanical durability of the polymer electrolyte membrane during fuel cell operation. Even if crosslinking agents were introduced, crosslinking agents such as hexamethylenediamine and oxydianiline did not mix well with the PFSA polymer. In particular, under high temperature and low humidity conditions, perfluorosulfonic acid polymers such as PFSA easily undergo a change in physical properties into a rubbery form at high temperatures, and hydrogen ion conductivity decreases rapidly at low relative humidity. The problem to be solved

[0011] The object of the present invention is to provide an ion-conducting dispersion that improves the chemical and mechanical durability of a polymer electrolyte membrane.

[0012] Another objective of the present invention is to provide a polymer electrolyte membrane prepared from the ion-conducting dispersion.

[0013] Another objective of the present invention is to provide a membrane-electrode assembly comprising the polymer electrolyte membrane having improved chemical and mechanical durability under high temperature and low humidity conditions.

[0014] Another objective of the present invention is to provide a fuel cell comprising the membrane-electrode assembly.

[0015] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims. means of solving the problem

[0016] According to a first aspect of the present invention for achieving the above objective, an ion conductor dispersion comprising an ion conductor, a crosslinking agent, and a solvent is provided, wherein the contact angle with respect to a PTFE (Polytetrafluoroethylene) porous membrane is 135° or less. Herein, the contact angle is the contact angle measured after 1 second has elapsed since the ion conductor composition was dropped onto the PTFE (Polytetrafluoroethylene) porous membrane under conditions of 25°C and 60% relative humidity.

[0017] According to a second aspect of the present invention, the ion conductor in the first aspect may be any one selected from the group consisting of fluorine-based ion conductors, partially fluorine-based ion conductors, hydrocarbon-based ion conductors, and mixtures thereof.

[0018] According to a third aspect of the present invention, the crosslinking agent in the first or second aspect may comprise any one selected from the group consisting of salicylic acid-based compounds, coumaric acid-based compounds, terephthalic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, and combinations thereof.

[0019] According to the fourth aspect of the present invention, the salicylic acid-based compound in the third aspect may include any one selected from the group consisting of salicylsalicylic acid, acetylsalicylic acid, and combinations thereof.

[0020] According to the fifth aspect of the present invention, in any one of the first to fourth aspects, the crosslinking agent may be included in an amount of 0.05 to 20 parts by weight based on 100 parts by weight of the ion conductor.

[0021] According to the sixth aspect of the present invention, in any one of the first to fifth aspects, the solvent may be selected from the group consisting of polar solvents, non-polar solvents, and mixtures thereof.

[0022] According to the seventh aspect of the present invention, the polar solvent in the sixth aspect may be any one selected from the group consisting of distilled water, alcohol solvents, tetrahydrofuran, 1,4-dioxane, dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, methylene chloride, and mixtures thereof.

[0023] According to the eighth aspect of the present invention, the nonpolar solvent in the sixth aspect may be any one selected from the group consisting of n-hexane, 1,1,2,2-tetrachloroethane, 1,2-dichloroethane, chloroform, and mixtures thereof.

[0024] According to the ninth aspect of the present invention, in any one of the first to eighth aspects, the solubility of the crosslinking agent in the solvent may be 0.5 to 400 g / L under conditions of 20 to 30°C and 50 to 70% relative humidity.

[0025] According to the 10th aspect of the present invention, in any one of the 1st to 9th aspects, the dielectric constant of the solvent may be 48 or less.

[0026] According to the 11th aspect of the present invention, in any one of the 1st to 10th aspects, the contact angle of the ion-conducting dispersion with respect to the PTFE porous membrane may be 10 to 130°.

[0027] According to the 12th aspect of the present invention, a polymer electrolyte membrane prepared from an ion-conducting dispersion according to any one of the 1st to 11th aspects may be provided.

[0028] According to the 13th aspect of the present invention, the polymer electrolyte membrane in the 12th aspect comprises a porous support, and the porous support may be impregnated with the ion conductor dispersion.

[0029] According to the 14th aspect of the present invention, a membrane-electrode assembly comprising a polymer electrolyte membrane according to the 12th or 13th aspect and a catalyst layer disposed on at least one surface of the polymer electrolyte membrane may be provided.

[0030] According to the 15th aspect of the present invention, a fuel cell comprising a membrane-electrode assembly according to the 14th aspect can be provided. Effects of the invention

[0031] According to one embodiment of the present invention, not only can the chemical and mechanical durability of a polymer electrolyte membrane be improved, but the polymer electrolyte membrane can also be easily applied to the manufacturing process, thereby promoting process efficiency and economic feasibility. In particular, according to one embodiment of the present invention, a polymer electrolyte membrane with improved durability under high temperature and low humidity conditions can be provided.

[0032] In addition to the effects described above, the specific effects of the present invention are described together with the following explanation of the specific details for implementing the invention. Brief explanation of the drawing

[0033] FIG. 1 is a cross-sectional view showing a polymer electrolyte membrane according to one embodiment of the present invention. FIG. 2 is a cross-sectional view showing a membrane-electrode assembly according to one embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a fuel cell according to one embodiment of the present invention. Specific details for implementing the invention

[0034] Hereinafter, each component of the present invention is described in more detail so that a person skilled in the art to which the present invention pertains can easily implement it; however, this is merely an example, and the scope of the rights of the present invention is not limited by the following.

[0035] An ion conductor dispersion according to one embodiment of the present invention comprises an ion conductor, a crosslinking agent, and a solvent, and may have a contact angle of 135° or less with respect to a PTFE (Polytetrafluoroethylene) porous membrane. The contact angle of the ion conductor dispersion with respect to the PTFE porous membrane is measured after 1 second has elapsed since the ion conductor dispersion was dropped onto the PTFE porous membrane under conditions of 25°C and 60% relative humidity.

[0036] The configuration of the present invention will be described in more detail below.

[0037] 1. Ion conductor dispersion

[0038] The ion conductor dispersion according to the present invention comprises an ion conductor, a crosslinking agent, and a solvent.

[0039] The ion conductor according to the present invention may be any one selected from the group consisting of fluorine-based ion conductors, partially fluorine-based ion conductors, hydrocarbon-based ion conductors, and mixtures thereof.

[0040] The above fluorine-based ion conductor may be any one selected from the group consisting of, for example, poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, and mixtures thereof, as fluorine-based polymers containing fluorine in the main chain.

[0041] The above-mentioned partially fluorinated ion conductor may be, for example, a polystyrene-graft-ethylene tetrafluoroethylene copolymer or a polystyrene-graft-polytetrafluoroethylene copolymer.

[0042] The above hydrocarbon-based ion conductor is, for example, sulfonated polyimide (S-PI), sulfonated polyarylethersulfone (S-PAES), sulfonated polyetheretherketone (S-PEEK), sulfonated polybenzimidazole (S-PBI), sulfonated polysulfone (S-PSU), sulfonated polystyrene (S-PS), sulfonated polyphosphazene, sulfonated polyquinoxaline, sulfonated polyketone, sulfonated polyphenylene oxide, sulfonated polyethersulfone, sulfonated Sulfonated polyether ketone, sulfonated polyphenylene sulfone, sulfonated polyphenylene sulfide, sulfonated polyphenylene sulfide sulfone, sulfonated polyphenylene sulfide sulfone nitrile, sulfonated polyarylene ether, sulfonated polyarylene ether nitrile, sulfonated polyarylene ether ether nitrile,It may be any one selected from the group consisting of sulfonated polyarylene ether sulfone ketones and mixtures thereof.

[0043] The crosslinking agent according to the present invention may include any one selected from the group consisting of salicylic acid compounds, coumaric acid compounds, terephthalic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, and combinations thereof. Specifically, the salicylic acid compound may include, for example, any one selected from the group consisting of salicylsalicylic acid, acetylsalicylic acid, and combinations thereof. The coumaric acid compound may be, for example, any one selected from the group consisting of ortho-coumaric acid, meta-coumaric acid, para-coumaric acid, and combinations thereof.

[0044] In the conventional process of preparing ion conductor dispersions, salicylic acid-based compounds were not introduced as crosslinking agents, resulting in a problem where the chemical and mechanical durability of the polymer electrolyte membrane prepared from the ion conductor dispersion was reduced. Even if a crosslinking agent was introduced into the ion conductor dispersion, crosslinking agents such as hexamethylenediamine and oxydianiline did not mix well with the PFSA polymer. In particular, under high temperature and low humidity conditions, perfluorosulfonic acid polymers such as PFSA exhibited problems such as easily changing their physical properties into a rubbery form at high temperatures and a rapid decrease in hydrogen ion conductivity at low relative humidity. According to one embodiment of the present invention, by introducing a salicylic acid-based compound as a crosslinking agent, it can exhibit a unique effect of being well soluble in a solvent as well as being well soluble with the PFSA polymer. Accordingly, the mechanical durability of the polymer electrolyte membrane can be improved while minimizing the decrease in hydrogen ion conductivity by promoting the crosslinking reaction between the ion conductor compounds. In addition to the salicylic acid compounds mentioned above, each coumaric acid compound, terephthalic acid, 3-hydroxybenzoic acid, and 4-hydroxybenzoic acid compound can also perform the same function as the salicylic acid compounds mentioned above.

[0045] The crosslinking agent according to the present invention may be included in an amount of 0.05 to 20 parts by weight, preferably 0.1 to 5 parts by weight, and more preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the ion conductor. If the content of the crosslinking agent is less than the above numerical range, the chemical and mechanical durability of the polymer electrolyte membrane may not be sufficiently improved, and if it exceeds the above numerical range, the hydrogen ion conductivity becomes too low, and some may precipitate and act as foreign substances.

[0046] The solvent according to the present invention may be any one selected from the group consisting of polar solvents, non-polar solvents, and mixtures thereof.

[0047] The polar solvent may be any one selected from the group consisting of distilled water, alcohol solvents, tetrahydrofuran, 1,4-dioxane, dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, methylene chloride, and mixtures thereof.

[0048] The above alcohol solvent may be, for example, any one selected from the group consisting of methanol, ethanol, propanol, and butanol.

[0049] The above nonpolar solvent may be any one selected from the group consisting of n-hexane, 1,1,2,2-tetrachloroethane, 1,2-dichloroethane, chloroform, and mixtures thereof.

[0050] The solubility of the crosslinking agent in the solvent may be 0.5 to 400 g / L under conditions of 20 to 30°C and relative humidity (RH) of 50 to 70%, preferably 1 to 300 g / L, and more preferably 2 to 150 g / L. If the solubility of the crosslinking agent in the solvent is below the above numerical range, it may precipitate upon introduction into the polymer electrolyte membrane and not function as a crosslinking agent, and if it exceeds the above numerical range, it may be lost during fuel cell operation and exhibit a lower degree of crosslinking compared to what was intended.

[0051] In other words, the dielectric constant of the solvent may be, for example, 48 or less at 20 to 25°C, specifically 1 to 48, and more specifically 5 to 48.

[0052] The contact angle of the ion conductor dispersion to the PTFE (Polytetrafluoroethylene) porous membrane according to the present invention may be 135° or less, preferably 10 to 130°, more preferably 20 to 125°, 80 to 120°, or 86 to 118°. The contact angle of the ion conductor dispersion to the PTFE porous membrane may be measured after 0.001 to 120 seconds have elapsed since the ion conductor dispersion was dropped onto the PTFE porous membrane under conditions of 20 to 30°C and 30 to 70% relative humidity, preferably after 0.005 to 60 seconds, more preferably after 0.01 to 20 seconds, and specifically after 1 second has elapsed under conditions of 25°C and 60% relative humidity. For example, the contact angle of the above ion conductor dispersion can be comprehensively influenced by the types of ion conductor and solvent, the presence or absence of a crosslinking agent, and the content of the crosslinking agent. Therefore, by appropriately controlling the composition and content of the ion conductor, solvent, and crosslinking agent, respectively, it is possible to derive a contact angle of the ion conductor dispersion that improves the mechanical properties of the polymer electrolyte membrane while simultaneously improving the chemical durability of the membrane-electrode assembly.

[0053] The above PTFE porous membrane may correspond to, for example, a Teflon porous membrane. Since the contact angle of the ion conductor dispersion with respect to the PTFE porous membrane satisfies the above numerical range, the cross-linking reaction can be effectively carried out.

[0054] 2. Polymer electrolyte membrane

[0055] Another embodiment of the present invention is a polymer electrolyte membrane prepared from the ion conductor dispersion. Here, the polymer electrolyte membrane prepared from the ion conductor dispersion may be a membrane in which the ion conductor dispersion is dried to remove the solvent, and a crosslinking reaction is carried out to form a crosslinking matrix between the ion conductor and the crosslinking agent. According to another aspect of the present invention, the polymer electrolyte membrane may include repeating units derived from the ion conductor and repeating units derived from the crosslinking agent. For example, the crosslinking matrix may include a first ion conductor chain, a second ion conductor chain different from the first ion conductor chain, and a molecular structure derived from a crosslinking agent that crosslinks the first and second ion conductor chains. Here, through the molecular structure derived from the crosslinking agent, the first and second ion conductor chains may be connected to each other. For example, as a method for analyzing the polymer electrolyte membrane 1 H-NMR, 13 Various known analytical methods such as C-NMR and FT-IR can be used.

[0056] Meanwhile, the first and second ion conductor chains may include a crosslinking functional group in the side chain capable of crosslinking with a crosslinking agent. Here, the crosslinking functional group may react with the crosslinking agent. For example, the crosslinking functional group may include -SO2-OH.

[0057] According to another embodiment of the present invention, the polymer electrolyte membrane may be a polymer electrolyte membrane in the form of a single membrane.

[0058] A polymer electrolyte membrane according to another embodiment of the present invention comprises a porous support, and the porous support may be impregnated with the ion-conducting dispersion. The polymer electrolyte membrane may be a reinforced composite membrane in the form of a composite membrane. In this specification, "impregnation" is defined as the ion-conducting dispersion penetrating into the internal pores of the porous support. Hereinafter, the configuration of the present invention will be described in detail with reference to FIG. 1.

[0059] FIG. 1 is a cross-sectional view showing a polymer electrolyte membrane according to one embodiment of the present invention.

[0060] Referring to FIG. 1, the porous support (52) according to the present invention may be a fluorine-based support or a nanoweb support.

[0061] The above-mentioned fluorine-based support may correspond, for example, to expanded polytetrafluoroethylene (e-PTFE) having a microstructure of polymer fibrils or a microstructure in which nodes are connected to each other by fibrils. Additionally, a film having a microstructure of polymer fibrils in which nodes are not present may also be used as the above-mentioned porous support (52).

[0062] The above fluorine-based support may include a perfluorinated polymer. The porous support (52) may correspond to a more porous and stronger porous support by extruding dispersed polymerized PTFE onto a tape in the presence of a lubricant and stretching the material obtained thereby.

[0063] In addition, the amorphous content of the PTFE may be increased by heat-treating the e-PTFE at a temperature exceeding the melting point (approx. 342°C) of the PTFE. The e-PTFE film produced by the above method may have micropores of various diameters and porosity. The e-PTFE film produced by the above method may have at least 35% porosity, and the diameter of the micropores may be approximately 0.01 to 1 μm (micrometer).

[0064] A nano web support according to one embodiment of the present invention may be a non-woven fibrous web composed of a plurality of randomly oriented fibers. The non-woven fibrous web refers to a sheet having the structure of individual fibers or filaments, which is interlaid but not in the same manner as a woven fabric. The non-woven fibrous web may be manufactured by any one method selected from the group consisting of carding, garneting, air-laying, wet-laying, melt blowing, spun bonding, and stitch bonding.

[0065] The above fiber may comprise one or more polymer materials, and any material generally used as a fiber-forming polymer material may be used; specifically, hydrocarbon-based fiber-forming polymer materials may be used. For example, the fiber-forming polymer material may comprise 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); polyurethanes, 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.

[0066] A nano web support according to one embodiment of the present invention may be a support in which nanofibers are integrated in the form of a nonwoven fabric having a plurality of pores.

[0067] The above nanofibers may preferably be hydrocarbon-based polymers that exhibit excellent chemical resistance and hydrophobicity, so there is no concern about shape deformation due to moisture in high-humidity environments. Specifically, the above 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, polyamideimide, polyethylene terephthalate, polyphenylene sulfide, polyethylene, polypropylene, copolymers thereof, and mixtures thereof.

[0068] The above nanoweb support is an aggregate of nanofibers in which nanofibers manufactured by electrospinning are randomly arranged. In this case, considering the porosity and thickness of the nanoweb, it is preferable that the nanofibers have an average diameter of 40 to 5000 nm (nanometers) when 50 fiber diameters are measured using a scanning electron microscope (JSM6700F, JEOL) and calculated from the average.

[0069] If the average diameter of the nanofiber is less than the above numerical range, the mechanical strength of the porous support may be reduced, and if the average diameter of the nanofiber exceeds the above numerical range, the porosity may be significantly reduced and the thickness may be increased.

[0070] The thickness of the nonwoven fiber web may be 10 to 50 μm (micrometers), specifically 15 to 43 μm (micrometers). If the thickness of the nonwoven fiber web is less than the above numerical range, the mechanical strength may decrease, and if it exceeds the above numerical range, the resistance loss increases, and the lightweighting and integration may decrease.

[0071] The above nonwoven fibrous web has a basic weight of 5 to 30 mg / cm² 2 It may be. If the basis weight of the above nonwoven fibrous web is less than the above numerical range, visible pores may be formed, making it difficult to function as a porous support, and if it exceeds the above numerical range, it may be manufactured in the form of paper or fabric in which pores are hardly formed.

[0072] The above porosity can be calculated by the ratio of the volume of air within the porous support to the total volume of the porous support according to the following mathematical formula 1. At this time, the total volume is calculated by manufacturing a rectangular sample and measuring its width, length, and thickness, and the volume of air can be obtained by measuring the mass of the sample and subtracting the volume of the polymer, which is inversely calculated from the density, from the total volume.

[0073] [Mathematical Formula 1]

[0074] Porosity (%) = (Volume of air in porous support / Total volume of porous support) X 100

[0075] The porosity of the porous support (52) according to the present invention may be 30 to 90%, and preferably 60 to 85%. If the porosity of the porous support (52) is less than the above numerical range, a problem of reduced impregnation of the ion conductor may occur, and if it exceeds the above numerical range, shape stability may be reduced, which may prevent the subsequent process from proceeding smoothly.

[0076] The polymer electrolyte membrane (50) 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 a first surface (52a) of the porous support (52), and the second resin layer (56) may be disposed on a second surface (52b) facing the first surface (52a). Accordingly, the ion conductor layer (55) may be formed on the surface of the porous support (52) and may include the aforementioned ion conductor.

[0077] According to one embodiment of the present invention, the tensile strength of the polymer electrolyte membrane (50) may be 25 to 90 MPa, 30 to 85 MPa, 35 to 82 MPa, 40 to 82 MPa, or 50 to 82 MPa. For example, a method of measuring the tensile strength of the polymer electrolyte membrane may be used by utilizing a universal testing machine (SHM-C-500, Shamhan Tech, Korea) according to the ASTM D882 method. Specifically, the means for achieving the tensile strength of the polymer electrolyte membrane may vary depending on the composition of the ion conductor dispersion.

[0078] 3. Membrane-electrode assembly

[0079] FIG. 2 is a cross-sectional view showing a membrane-electrode assembly according to one embodiment of the present invention. The above-mentioned parts and repeated descriptions are briefly described or omitted.

[0080] Referring to FIG. 2, the membrane-electrode assembly (100) according to the present invention is a membrane-electrode assembly comprising the polymer electrolyte membrane (50), wherein the anode electrode (20) and the cathode electrode (20') are positioned opposite each other, and the polymer electrolyte membrane (50) is positioned between the anode electrode (20) and the cathode electrode (20').

[0081] The anode and cathode electrodes (20, 20') include an electrode substrate (40, 40') and a catalyst layer (30, 30') formed on the surface of the electrode substrate (40, 40'), and may further include a microporous layer (not shown) containing conductive fine particles such as carbon powder or carbon black between the electrode substrate (40, 40') and the catalyst layer (30, 30') to facilitate material diffusion from the electrode substrate (40, 40').

[0082] The catalyst layer (30, 30') of the anode and cathode electrodes (20, 20') comprises a catalyst. Any catalyst that participates in the reaction of the cell and can be used as a catalyst for a fuel cell can be used. Preferably, a platinum-based metal can be used.

[0083] The above 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, and more preferably, a combination of two or more metals selected from the group of platinum-based catalyst metals may be used, but is not limited thereto, and any platinum-based catalyst metal available in the field of the present technology may be used without limitation.

[0084] The above M may correspond to one or more 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 mentioned above may be used alone or in a mixture of two or more 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.

[0085] In addition, the above-mentioned non-platinum alloy may be used alone or in a mixture of two or more 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.

[0086] The above catalyst may be used as the catalyst itself (black) or supported on a carrier.

[0087] 4. Fuel cell

[0088] FIG. 3 is a schematic diagram illustrating a fuel cell according to one embodiment of the present invention.

[0089] Another embodiment of the present invention is a fuel cell comprising the membrane-electrode assembly.

[0090] Referring to FIG. 3, the fuel cell (200) according to the present invention may include a fuel supply unit (210) that supplies a mixed fuel in which fuel and water are mixed, 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 causing an electrochemical reaction between the reformed gas containing hydrogen gas supplied from the reforming unit (220) and an oxidizing agent supply unit (240) that supplies an oxidizing agent to the reforming unit (220) and the stack (230).

[0091] The stack (230) may be equipped with a plurality of unit cells that generate electrical energy by inducing an oxidation / reduction reaction between a reforming gas containing hydrogen gas supplied from the reforming unit (220) and an oxidizing agent supplied from the oxidizing agent supply unit (240).

[0092] Each unit cell refers to a unit cell that generates electricity and may include a membrane-electrode assembly that oxidizes / reduces oxygen in an oxidant and a reforming gas containing hydrogen gas, and a separator (also called a bipolar plate, hereinafter referred to as a 'separator') for supplying the reforming gas containing hydrogen gas and the oxidant to the membrane-electrode assembly. The separator is positioned on both sides of the membrane-electrode assembly with the membrane-electrode assembly at the center. At this time, the separator located at the outermost side of the stack is specifically referred to as an end plate.

[0093] Among the above separator plates, the end plate is provided with a pipe-shaped first supply pipe (231) for injecting a reforming gas containing hydrogen gas supplied from the reforming unit (220) and a pipe-shaped second supply pipe (232) for injecting oxygen gas, and the other end plate may be provided with a first discharge pipe (233) for discharging to the outside a reforming gas containing hydrogen gas that is finally unreacted and remaining in a plurality of unit cells and a second discharge pipe (234) for discharging to the outside an oxidizing agent that is finally unreacted and remaining in the above unit cells.

[0094] In the above fuel cell, the separator, fuel supply unit, and oxidant supply unit constituting the electricity generation unit are used in conventional fuel cells, so a detailed description is omitted in this specification.

[0095] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the present invention; however, this is merely an example, and the scope of the present invention is not limited by the following.

[0096] [Preparation Example 1: Preparation of Ion Conductor Dispersion]

[0097] An ion conductor dispersion as shown in Table 1 below was prepared.

[0098] Unit: parts by weight Manufacturing Comparative Example 1 Comparative Manufacturing Example 2 Manufacturing Example 1 Manufacturing Example 2 Manufacturing Example 3 Manufacturing Example 4 Fluorine-based ion conductors 1) 100 - 100 100 - - Hydrocarbon-based ion conductors 2) - 100 - - 100 100 salicylic acid - - 1 - 1 - Acetyl salicylic acid - - - 1 - 1 Propan-1-ol : Ethanol : Distilled water (1:1:1 weight ratio) 300 - 300 300 - - Dimethylacetamide (DMAc) - 650 - - 650 650 1) PFSA (perfluorosulfonic acid) 2) S-PES (Sulfonated poly(ether sulfone)) with a degree of sulfonation of 60% and an ion exchange capacity of 1.6 meq / g

[0099] [Experimental Example 1: Contact Angle for PTFE (Polytetrafluoroethylene) Porous Membrane]

[0100] The contact angle of the ion conductor dispersion according to Preparation Example 1 above was measured on a PTFE (Polytetrafluoroethylene) porous membrane (product name: PTFE substrate of Teflon).

[0101] While maintaining 25°C and RH 60%, the ion conductor dispersion according to Preparation Example 1 was filled into a syringe, and a liquid droplet with a volume of 5 µl was dropped onto the PTFE porous membrane. After waiting for 1 second for the liquid droplet to spread, the contact angle formed between the PTFE porous membrane and the liquid droplet was measured using a contact angle measuring instrument (measuring instrument: Model 190 of Technox Co., Ltd.).

[0102] Sample Manufacturing Comparative Example 1 Comparative Manufacturing Example 2 Manufacturing Example 1 Manufacturing Example 2 Manufacturing Example 3 Manufacturing Example 4 Contact angle (°) 118 87 117 118 88 86

[0103] [Preparation Example 2: Preparation of Polymer Electrolyte Membrane]

[0104] A polymer electrolyte membrane as described below was prepared using the ion conductor dispersion according to Preparation Example 1 above. In the following comparative examples and examples, drying and crosslinking proceeded simultaneously.

[0105] <Comparative Example 1>

[0106] A polymer electrolyte membrane was prepared by forming an ion conductor dispersion according to Comparative Example 1 of Table 1 above onto a glass substrate and then drying it at 90°C for 12 hours.

[0107] <Comparative Example 2>

[0108] A polymer electrolyte membrane was prepared by forming an ion conductor dispersion according to Comparative Example 2 above onto a glass substrate and then drying it at 90°C for 24 hours.

[0109] <Comparative Example 3>

[0110] A polymer electrolyte membrane (or reinforced composite membrane) was prepared by impregnating an e-PTFE (expanded-polytetrafluoroethylene) support having an average pore size of 0.2 μm and a porosity of 75% with an ion conductor dispersion according to Comparative Example 1 above, and then drying the impregnated PTFE (polytetrafluoroethylene) support at 90°C for 12 hours.

[0111] <Comparative Example 4>

[0112] The ion conductor dispersion according to Comparative Example 2 above was impregnated into a PPS (polyphenylene sulfide) support having an average pore size of 0.2 μm and a porosity of 70%, and then the impregnated product was dried at 90°C for 24 hours to produce a polymer electrolyte membrane (or reinforced composite membrane).

[0113] <Examples 1, 2>

[0114] After forming the ion conductor dispersions according to Manufacturing Examples 1 and 2 above onto a glass substrate, the polymer electrolyte membranes were each prepared by drying them at 90°C for 12 hours.

[0115] <Examples 3, 4>

[0116] After forming the ion conductor dispersions according to Manufacturing Examples 3 and 4 above onto a glass substrate, the polymer electrolyte membranes were each prepared by drying them at 90°C for 24 hours.

[0117] <Example 5>

[0118] A polymer electrolyte membrane (or reinforced composite membrane) was prepared in the same manner as Comparative Example 3, but instead of the ion conductor dispersion according to Comparative Example 1, the ion conductor dispersion according to Example 1 was used.

[0119] <Example 6>

[0120] A polymer electrolyte membrane (or reinforced composite membrane) was prepared in the same manner as Comparative Example 3, but instead of the ion conductor dispersion according to Comparative Example 1, the ion conductor dispersion according to Example 2 was used.

[0121] <Example 7>

[0122] A polymer electrolyte membrane (or reinforced composite membrane) was prepared in the same manner as Comparative Example 4, but instead of the ion conductor dispersion according to Comparative Example 2, the ion conductor dispersion according to Example 3 was used.

[0123] <Example 8>

[0124] A polymer electrolyte membrane (or reinforced composite membrane) was prepared in the same manner as Comparative Example 4, but instead of the ion conductor dispersion according to Comparative Example 2, the ion conductor dispersion according to Example 4 was used.

[0125] [Experimental Example 2: Evaluation of Tensile Strength of Polymer Electrolyte Membrane]

[0126] The tensile strength of the polymer electrolyte membrane according to the above Preparation Example 2 was measured according to the ASTM D882 method using a universal testing machine (SHM-C-500, Shamhan Tech, Korea).

[0127] Tensile strength (MPa) Comparative Example 1 23.7 Comparative Example 2 47.9 Comparative Example 3 50.1 Comparative Example 4 71.2 Example 1 28.5 Example 2 27.2 Example 3 54.9 Example 4 55.3 Example 5 53.6 Example 6 54.6 Example 7 80.6 Example 8 81.0

[0128] Referring to Table 3 above, it can be seen that the tensile strength of the examples is significantly improved compared to the comparative example. Through this, it can be inferred that the mechanical durability of the polymer electrolyte membrane or reinforced composite membrane is significantly improved by the introduction of a crosslinking agent.

[0129] [Experimental Example 3: OCV Reduction Rate from DOE Chemical Durability Evaluation of Membrane-Electrode Assembly]

[0130] Electrodes prepared by the decal method are attached to both sides of the polymer electrolyte membrane (or reinforced composite membrane) according to Preparation Example 2 above, and an electrode slurry (catalyst: Pt / C, Pt loading content: 0.4 mg / cm²) 2 A membrane-electrode assembly was fabricated by directly coating the material. The chemical durability of the membrane-electrode assembly was evaluated based on the durability evaluation protocol of the U.S. Department of Energy (DOE). Specifically, voltage loss was measured after performing the OCV hold method for 500 hours under conditions of 120°C and 20% RH, and the measured values ​​are shown in Table 4 below.

[0131] OCV Voltage Loss (%) Comparative Example 1 23.7 Comparative Example 2 30.8 Comparative Example 3 20.5 Comparative Example 4 24.4 Example 1 19.2 Example 2 19.1 Example 3 17.6 Example 4 17.8 Example 5 15.6 Example 6 15.4 Example 7 19.4 Example 8 20.2

[0132] Referring to Table 4 above, it can be inferred that the examples have relatively lower OCV voltage loss compared to the comparative example, and that the chemical durability is generally improved.

[0133] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also included within the scope of the present invention. Explanation of the symbols

[0134] 50: Polymer electrolyte membrane 52: Porous support 54: First resin layer 55: Ion conductor layer 56: Second resin layer 100: Membrane-electrode assembly 200: Fuel cell

Claims

Claim 1 An ion conductor dispersion comprising an ion conductor; a crosslinking agent; and a solvent, wherein the contact angle measured after 1 second has elapsed after the ion conductor dispersion is dropped onto a PTFE (Polytetrafluoroethylene) porous membrane under conditions of 25°C and 60% relative humidity is 86 to 118°, the crosslinking agent comprises acetylsalicylic acid, and the solvent comprises distilled water and an alcohol solvent. Claim 2 In claim 1, the ion conductor is an ion conductor dispersion selected from the group consisting of fluorine-based ion conductors, partially fluorine-based ion conductors, hydrocarbon-based ion conductors, and mixtures thereof. Claim 3 delete Claim 4 delete Claim 5 In claim 1, the crosslinking agent is an ion conductor dispersion containing 0.05 to 20 parts by weight based on 100 parts by weight of the ion conductor. Claim 6 In claim 1, the above alcohol solvent is an ion-conducting dispersion comprising propan-1-ol and ethanol. Claim 7 An ion-conducting dispersion according to claim 6, wherein the weight ratio of the propan-1-ol, the ethanol, and the distilled water is 1:1:

1. Claim 8 delete Claim 9 delete Claim 10 delete Claim 11 A polymer electrolyte membrane in which the ion conductor dispersion according to claim 1 is dried. Claim 12 In claim 11, the polymer electrolyte membrane comprises a porous support, and the porous support is impregnated with the ion conductor dispersion. Claim 13 A membrane-electrode assembly comprising: a polymer electrolyte membrane according to claim 11; and a catalyst layer disposed on at least one surface of the polymer electrolyte membrane. Claim 14 A fuel cell comprising a membrane-electrode assembly according to paragraph 13.

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