Polymer electrolyte membrane and membrane-electrode assembly including the same

Abstract

The present invention relates to a polymer electrolyte membrane containing an ion conductor having ion conductivity, wherein the polymer electrolyte membrane has an initial storage modulus in the longitudinal direction (MD) of 500 MPa or more and an initial storage modulus in the transverse direction (TD) / initial storage modulus in the longitudinal direction (MD) of 0.5 to 1.0.

Description

[Technical Field]

[0001] The present invention relates to a polymer electrolyte membrane containing an ion conductor having ion conductivity, and the ratio of the storage modulus at the temperature when the fuel cell is operating to the temperature when it is not operating (resting) satisfies a certain range, thereby minimizing changes in dimensional stability and maintaining excellent adhesion to the electrodes, thereby maintaining excellent fuel cell performance for a long period of time, and a membrane-electrode assembly including the polymer electrolyte membrane. [Background technology]

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

[0003] A fuel cell generally has a structure in which an anode and a cathode are formed on either side of an 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 have been attracting attention as a power source for portable, vehicular, and home use due to their advantages such as a 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), which uses hydrogen gas as fuel.

[0006] To summarize the reactions that occur in a polymer electrolyte membrane fuel cell, first, when fuel such as hydrogen gas is supplied to the oxidizing electrode, hydrogen ions (H + ) and electrons (e - ) is produced. The hydrogen ions (H + ) is transferred to the reduction electrode through the polymer electrolyte membrane, and the generated electrons (e - ) is transferred to the reducing electrode via an external circuit. Oxygen is supplied to the reducing electrode, and the oxygen converts to hydrogen ions (H + ) and electrons (e - ) and produces water by oxygen reduction reaction.

[0007] The polymer electrolyte membrane absorbs hydrogen ions (H + ) to the reducing electrode, so basically hydrogen ions (H + In addition, the polymer electrolyte membrane must have excellent separation ability to separate hydrogen gas supplied to the oxidizing electrode from oxygen supplied to the reducing electrode, and other required properties include excellent mechanical strength, dimensional stability, and chemical resistance, as well as low ohmic loss at high current densities.

[0008] The polymer electrolyte membrane has ion channels that act as pathways through which hydrogen ions generated at the oxidizing electrode are transported to the reducing electrode. Functional groups that transport hydrogen ions, such as sulfonic acid groups and carboxyl groups, are located inside the channels to form ion clusters, which allow hydrogen ions to pass through the membrane and transport them.

[0009] In a fuel cell, the reactions at the oxidizing and reducing electrodes are different, resulting in different reactants and by-products, so that one side of the polymer electrolyte membrane and the other side are exposed to different environments during operation.Fuel cells have a structure in which electrode layers are transferred to both sides of the polymer electrolyte membrane to form a laminated membrane-electrode assembly, and bipolar plates are laminated on the surface of the membrane, with oxygen and fuel gas being injected through channels formed in the bipolar plates.

[0010] The electrode layers located on both sides of the polymer electrolyte membrane include a catalyst layer containing a catalyst and a fluorine-based binder, and an electrode substrate, and the catalyst layer is bonded to the surface of the polymer electrolyte membrane.

[0011] The moisture and heat generated during fuel cell operation can easily cause dimensional changes such as expansion and contraction of the ion conductor and porous support that make up the polymer electrolyte membrane, which can easily cause peeling from the catalyst layer.

[0012] If peeling from the catalyst layer occurs, deterioration of the fuel cell will be accelerated and its performance will be significantly reduced. Therefore, ensuring the dimensional stability of the polymer electrolyte membrane is a factor that has a significant impact on the performance and lifespan of the fuel cell.

[0013] Therefore, there is a need to develop technology for polymer electrolyte membranes that not only undergo minimal dimensional change even with the heat and moisture generated by the operation of fuel cells, but also have excellent physical and mechanical properties and excellent ionic conductivity. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Registration No. 4734279 (November 6, 2008) [Patent Document 2] Japanese Patent Registration No. 3978668 (2004.08.12) [Patent Document 3] Japanese Patent Publication No. 2011-145588 (November 24, 2011) Summary of the Invention [Problem to be solved by the invention]

[0015] An object of the present invention is to provide a polymer electrolyte membrane that is prevented from being deformed by heat and moisture generated during operation of a fuel cell.

[0016] The present invention aims to provide a polymer electrolyte membrane that is free from the problem of separation of the polymer electrolyte membrane from the electrodes due to deformation of the polymer electrolyte membrane during operation and at rest of the fuel cell, has excellent adhesion to the electrodes, and prevents deterioration of the cell performance.

[0017] Another object of the present invention is to provide a membrane-electrode assembly comprising said polymer electrolyte membrane. [Means for solving the problem]

[0018] According to one aspect of the present invention, there is provided a polymer electrolyte membrane comprising an ion conductor having ion conductivity, wherein the polymer electrolyte membrane has an initial storage modulus in a longitudinal direction (MD) of 500 MPa or more, and an initial storage modulus (S) in the direction with the smaller initial storage modulus out of the transverse direction (TD) and the longitudinal direction (MD) / initial storage modulus (L) in the direction with the larger initial storage modulus is 0.5 to 1.0.

[0019] According to one embodiment, the polymer electrolyte membrane may include a porous support and an ion conductor filled in pores of the porous support.

[0020] According to another embodiment, the porous support may include any one selected from the group consisting of nylon, polyimide, polybenzoxazole, polyethylene terephthalate, polyethylene, polypropylene, polytetrafluoroethylene, polyarylene ether sulfone, polyether ether ketone, copolymers thereof, and combinations thereof.

[0021] According to another embodiment, the porous support may include a perfluorinated polymer sheet having a large number of voids due to the microstructure of polymer fibrils, or a nanoweb in which nanofibers are accumulated in the form of a nonwoven fabric having a large number of voids.

[0022] According to another embodiment, the ionic conductor may be one selected from a hydrocarbon-based ionic conductor, a fluorine-based ionic conductor, an anionic conductor, or a mixture thereof.

[0023] According to another embodiment, the ion conductor may have an ion exchange capacity (equivalent weight, EW) of 500 to 1100 g / eq.

[0024] According to another embodiment, the ion conductor includes a hydrocarbon-based ion conductor, and the hydrocarbon-based ion conductor is selected from the group consisting of sulfonated polyimide (S-PI), sulfonated polyarylethersulfone (S-PAES), sulfonated polyetheretherketone (SPEEK), sulfonated polybenzimidazole (SPBI), sulfonated polysulfone (S-PSU), sulfonated polystyrene (S-PS), sulfonated polyphosphazene, sulfonated polyquinoxaline, sulfonated polyketone, sulfonated polyphenylene oxide, and sulfonated polyethersulfone. polyether sulfone, 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 ether nitrile), sulfonated polyarylene ether ether nitrile, sulfonated polyarylene ether sulfone ketone ether sulfone ketone), and mixtures thereof.

[0025] According to another embodiment, the ionic conductor comprises a fluoro-based ionic conductor, which may be poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), a copolymer of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, defluorinated sulfurized polyether ketone, or a mixture thereof.

[0026] According to another aspect of the present invention, there is provided a membrane-electrode assembly including the above-mentioned polymer electrolyte membrane, the membrane-electrode assembly including an anode electrode and a cathode electrode positioned opposite each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode.

[0027] According to another aspect of the present invention, there is provided a fuel cell comprising a membrane-electrode assembly including the polymer electrolyte membrane described above. [Effects of the Invention]

[0028] The polymer electrolyte membrane according to the present invention is inhibited from being deformed by heat and moisture generated during the operation of the fuel cell, and has excellent dimensional stability and mechanical durability, as well as excellent ionic conductivity.

[0029] By using such a polymer electrolyte membrane according to the present invention, the present invention has the advantage that the problem of the polymer electrolyte membrane being separated from the electrodes due to deformation of the polymer electrolyte membrane during operation and at rest of the fuel cell is not caused, and the performance of the fuel cell is maintained in an excellent state. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a vertical cross-sectional view of a polymer electrolyte membrane according to the present invention. [Figure 2] 1 is a vertical cross-sectional view of a membrane-electrode assembly including a polymer electrolyte membrane according to the present invention. [Figure 3] 1 is a schematic diagram showing the overall configuration of a fuel cell according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0031] 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 by the following content.

[0032] As used herein, the terms "preferred" or "preferably" refer to embodiments of the invention that have certain advantages under certain conditions. However, other embodiments may also be preferred under the same or different conditions. Furthermore, the presence of one or more preferred embodiments does not imply that other embodiments are not useful, nor does it exclude other embodiments within the scope of the invention.

[0033] As used herein, the term "comprising" is used in listing materials, compositions, devices, and methods useful in the present invention, without limiting the listed examples.

[0034] A polymer electrolyte membrane according to one embodiment of the present invention is a polymer electrolyte membrane containing an ion conductor having ion conductivity, characterized in that the polymer electrolyte membrane has an initial storage modulus in a longitudinal direction (MD) of 500 MPa or more, and an initial storage modulus (S) in the direction with the smaller initial storage modulus out of a transverse direction (TD) and a longitudinal direction (MD) / an initial storage modulus (L) in the direction with the larger initial storage modulus is 0.5 to 1.0.

[0035] The storage modulus refers to the ratio of elastic energy of a material, and the higher the storage modulus, the more elastic the material. The initial storage modulus refers to the storage modulus of a polymer electrolyte membrane after its preparation and before its use.

[0036] The MD direction is the production direction during roll-to-roll manufacturing, and the TD direction is the perpendicular direction. When viewed on a surface, the MD direction and the TD direction can be seen as the X and Y axes.

[0037] If the initial storage modulus of the MD is less than 500 MPa or the S / L ratio is less than 0.5, the dimensional change rate along both the X and Y axes is different, resulting in anisotropic properties. This can lead to pinholes or tearing in the electrolyte membrane due to stress caused by contraction / expansion in humid / dry environments during fuel cell operation, causing delamination and reduced durability. Furthermore, the increased dimensional change can lead to a decrease in adhesion to the electrodes, which can accelerate battery degradation in environments with severe temperature changes or with increased battery operation cycles, resulting in a significant decrease in battery performance. If the S / L ratio exceeds 1.0, the rigidity of the electrolyte membrane can decrease, resulting in reduced physical and mechanical properties.

[0038] A polymer electrolyte membrane having the above-mentioned initial storage modulus and S / L ratio can be realized by stacking multiple polymer electrolyte membranes or porous supports whose storage moduli have been measured, or by adjusting physical properties such as the equivalent weight (EW) and content of the ion conductor and the thickness of the support.

[0039] Meanwhile, the polymer electrolyte membrane according to the present invention may be a single membrane or a reinforced composite membrane.

[0040] More preferably, the polymer electrolyte membrane may be a reinforced composite membrane including a porous support and an ion conductor filled in the voids of the porous support.

[0041] By using a reinforced composite membrane that has relatively excellent dimensional stability and physical and mechanical properties, even if the resistance of the polymer electrolyte membrane itself increases slightly, the deterioration of the cell performance is prevented, and therefore the performance and lifespan of the fuel cell itself are maintained in excellent condition.

[0042] More specifically, the porous support includes a number of pores, and the ion conductor is a polymer electrolyte membrane in the form of a reinforced composite membrane that fills the pores of the porous support.

[0043] The porous support may have a form including a perfluorinated polymer sheet having a large number of voids due to the microstructure of polymer fibrils, or a nanoweb in which nanofibers are accumulated in the form of a nonwoven fabric having a large number of voids.

[0044] The perfluorinated polymer sheet having a large number of voids due to the microstructure of polymer fibrils may have a large number of voids due to a microstructure consisting of nodes interconnected by fibrils. Since the perfluorinated polymer sheet has a large number of voids due to the microstructure, it may be an expanded perfluorinated polymer sheet.

[0045] The perfluorinated polymer may comprise a highly fluorinated polymer, preferably a perfluorinated polymer, having excellent resistance to thermal and chemical degradation, such as polytetrafluoroethylene (PTFE) or tetrafluoroethylene and CF₂=CFC. n F 2n+1 (n is an integer from 1 to 5) or CF2=CFO-(CF2CF(CF3)O) m C n F 2n+1 (m is an integer of 0 to 15, and n is an integer of 1 to 15).

[0046] PTFE, which is commercially available, can be preferably used as the porous support. Expanded polytetrafluoroethylene (e-PTFE) sheets having a microstructure of polymer fibrils or a microstructure in which nodes are connected to each other by fibrils can also be preferably used as the porous support. PTFE having a microstructure of polymer fibrils without nodes can also be preferably used as the porous support. The e-PTFE sheet can have a void ratio of at least 35%, and the diameter of the micropores can be about 0.01 μm to 1 μm.

[0047] Meanwhile, the nanoweb may be a nanoweb in which nanofibers are accumulated in the form of a nonwoven fabric containing a large number of voids.

[0048] The nanoweb has a basic weight of 5 g / m 2 ~30g / m 2 The nanoweb may have a basis weight of 5 g / m 2 If the thickness is less than 30 g / m, visible pores may be formed and the porous support may not function properly. 2 If the thickness exceeds 100 μm, the product may be produced in the form of paper or fabric with few pores formed.

[0049] The porosity of the porous support may be 45% or more, specifically 60% or more. Meanwhile, the porous support preferably has a porosity of 90% or less. If the porosity of the porous support exceeds 90%, the dimensional stability may be reduced, which may hinder smooth subsequent processes. The porosity can be calculated as the ratio of the air volume to the total volume of the porous support according to the following equation (1): Here, the total volume is calculated by preparing a rectangular sample and measuring its width, length, and thickness. The air volume can be calculated by measuring the mass of the sample and then subtracting the volume of the polymer, calculated from the density, from the total volume.

number

[0050] The polymer electrolyte membrane may be a reinforced composite membrane in which pores of the porous support are filled with an ion conductor, and may include a first ion conductor layer located on one side of the porous support and a second ion conductor layer located on the other side of the porous support. The first ion conductor layer and the second ion conductor layer may be formed by filling the pores of the porous support with the ion conductor remaining thereon to form a thin film on the surface of the porous support.

[0051] The porous support is composed of an aggregate of nanofibers that are three-dimensionally irregularly and discontinuously connected, thereby containing a large number of uniformly distributed pores. The porous support, which has a large number of uniformly distributed pores, has excellent porosity and properties (e.g., dimensional stability) that complement the physical properties of ion conductors.

[0052] The pore size, which is the diameter of the pores formed in the porous support, may be in the range of 0.05 to 30 μm. If the pore size is less than 0.05 μm, the ionic conductivity of the polymer electrolyte may be reduced, and if the pore size exceeds 30 μm, the mechanical strength of the polymer electrolyte may be reduced.

[0053] The porosity of the porous support, which indicates the degree of pore formation, can be formed within the range of 50 to 98%.

[0054] If the porosity of the porous support is less than 50%, the ionic conductivity of the polymer electrolyte may be reduced, and if the porosity is more than 98%, the mechanical strength and dimensional stability of the polymer electrolyte may be reduced.

[0055] The porosity (%) can be calculated by the ratio of the air volume to the total volume of the porous support, as shown in the following formula (2).

number

[0056] In this case, the total volume of the porous support can be calculated by preparing a rectangular porous support sample and measuring its width, length, and thickness. The air volume of the porous support can be calculated by measuring the mass of the porous support sample and then subtracting the volume of the polymer, which is calculated back from the density, from the total volume of the porous support.

[0057] The porous support is composed of an aggregate of nanofibers that are three-dimensionally irregularly and discontinuously connected, and the average diameter of the nanofibers may be in the range of 0.005 to 5 μm. If the average diameter of the nanofibers is less than 0.005 μm, the mechanical strength of the porous support may be reduced, and if the average diameter of the nanofibers is more than 5 μm, it may be difficult to adjust the porosity of the porous support.

[0058] The nanofibers may be any one selected from the group consisting of nylon, polyimide, polybenzoxazole, polyethylene terephthalate, polyethylene, polypropylene, polytetrafluoroethylene, polyarylene ether sulfone, polyether ether ketone, copolymers thereof, and combinations thereof, but the present invention is not limited thereto.

[0059] The porous support may be formed to a thickness of 5 to 30 μm. If the thickness of the porous support is less than 5 μm, the mechanical strength and dimensional stability of the polymer electrolyte may be reduced, and if the thickness of the porous support is more than 30 μm, the resistance loss of the polymer electrolyte may be increased.

[0060] The ion conductors may each independently be a cation conductor having a cation exchange group such as a proton, or an anion conductor having an anion exchange group such as a hydroxy ion, carbonate, or bicarbonate.

[0061] The cation exchange 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 may generally be a sulfonic acid group or a carboxyl group.

[0062] Examples of the cation conductor include: a fluoropolymer containing the cation exchange 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; and sulfonimide.

[0063] More specifically, when the cation conductor is a hydrogen ion cation conductor, the polymer may have a cation exchange group in the 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, and specific examples thereof include fluoropolymers including poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), a copolymer of tetrafluoroethylene and fluorovinyl ether containing a sulfonic acid group, defluorinated sulfurized polyether ketone, or a mixture thereof;Sulfonated polyimide (S-PI), sulfonated polyarylethersulfone (S-PAES), sulfonated polyetheretherketone (SPEEK), sulfonated polybenzimidazole (SPBI), sulfonated polysulfone (S-PSU), sulfonated polystyrene (S-PS), sulfonated polyphosphazene, sulfonated polyquinoxaline, sulfonated polyketone, sulfonated polyphenylene oxide, sulfonated polyether sulfone, sulfonated polyether ketone ketone), sulfonated polyphenylene sulfone, sulfonated polyphenylene sulfide, sulfonated polyphenylene sulfide sulfone, sulfonated polyphenylene sulfide sulfone nitrile, sulfonated polyarylene ether, sulfonated polyarylene ether nitrile; ether nitrile), sulfonated polyarylene ether ether nitrile, sulfonated polyarylene ether sulfone ketone and hydrocarbon-based polymers including, but not limited to, ether sulfone ketone, and mixtures thereof.

[0064] The anion conductor is a polymer capable of transporting anions such as hydroxide ions, carbonate ions, or bicarbonates. Anion conductors are commercially available in the form of hydroxides or halides (generally chlorides). The anion conductors can be used in industrial water purification, metal separation, catalytic processes, and the like.

[0065] 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.

[0066] Among the ion conductors, fluorine-based polymers can be used. The fluorine-based polymers can be, for example, perfluorosulfonic acid (PFSA)-based polymers or perfluorocarboxylic acid (PFCA)-based polymers, but are not limited thereto. Nafion (Dupont) can be used as the perfluorosulfonic acid-based polymer, and Flemion (Asahi Glass) can be used as the perfluorocarboxylic acid-based polymer.

[0067] The weight average molecular weight of the ionic conductor may be 240 g / mol to 200,000 g / mol, specifically 240 g / mol to 10,000 g / mol.

[0068] In particular, in the present invention, the ion conductor may have an ion exchange capacity (equivalent weight, EW) of 500 to 1100 g / eq, more preferably -600 to 1000 g / eq.

[0069] If the ion exchange capacity is smaller than the above range, there is a possibility that a problem of a decrease in battery performance at low temperatures may occur, whereas if the ion exchange capacity is larger than the above range, there is a possibility that a problem of a decrease in dimensional stability and a decrease in durability of the polymer electrolyte membrane may occur.

[0070] The invention will now be explained in more detail on the basis of the drawings.

[0071] However, this is merely an example for explaining the present invention, and the scope of the present invention is not limited by the following description.

[0072] FIG. 1 is a vertical cross-sectional view of a polymer electrolyte membrane according to the present invention.

[0073] Referring to FIG. 1, a polymer electrolyte membrane according to an embodiment of the present invention shows a vertical cross section of a porous support 21 having a number of voids and a reinforced composite membrane in which an ion conductor (not shown) is impregnated into the voids of the porous support, and may further include ion conductor layers 31 and 32 on one and the other sides of the porous support impregnated with the ion conductor, respectively.

[0074] 2 is a schematic cross-sectional view of a membrane-electrode assembly including a polymer electrolyte membrane according to the present invention. Referring to FIG. 2, the membrane-electrode assembly 100 includes the polymer electrolyte membrane 50 and electrodes 20, 20' disposed on both sides of the polymer electrolyte membrane 50. 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 included between the electrode substrates 40, 40' and the catalyst layers 30, 30' to facilitate diffusion of materials in the electrode substrates 40, 40'.

[0075] In the membrane-electrode assembly 100, the electrode 20 disposed on one side of the ion exchange membrane 50 and causing an oxidation reaction to generate hydrogen ions and electrons from the fuel that has passed through the electrode substrate 40 and been transferred to the catalyst layer 30 is called the anode electrode, and the electrode 20' disposed on the other side of the ion exchange membrane 50 and causing a reduction reaction to generate water from the hydrogen ions supplied through the ion exchange membrane 50 and the oxidant that has passed through the electrode substrate 40' and been transferred to the catalyst layer 30' is called the cathode electrode.

[0076] The electrode substrates 40 and 40' may be porous conductive substrates to ensure smooth supply of hydrogen or oxygen. Representative examples include, but are not limited to, carbon paper, carbon cloth, carbon felt, and metal cloth (a porous film made of fibrous metal cloth or a metal film formed on the surface of a polymer fiber cloth). Furthermore, the electrode substrates 40 and 40' are preferably treated with a fluorine-based resin for water repellency, since this prevents a decrease in the diffusion efficiency of reactants due to water generated during fuel cell operation. Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, fluorinated ethylene propylene, polychlorotrifluoroethylene, and copolymers thereof.

[0077] A fuel cell according to an embodiment of the present invention includes the membrane-electrode assembly, and may be, for example, a fuel cell that uses hydrogen gas as fuel.

[0078] FIG. 3 is a schematic diagram showing the overall configuration of the fuel cell.

[0079] Referring to FIG. 3, the fuel cell 200 includes a fuel supply unit 210 that supplies a mixed fuel obtained by mixing fuel and water, a reformer 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 reformer 220 with an oxidant, and an oxidant supply unit 240 that supplies an oxidant to the reformer 220 and the stack 230.

[0080] The stack 230 includes a plurality of unit cells that generate electrical energy by inducing an oxidation / reduction reaction between the reformed gas, including hydrogen gas, supplied from the reforming unit 220 and an oxidant supplied from the oxidant supplying unit 240.

[0081] Each unit cell refers to a unit cell that generates electricity and includes 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 located on both sides of the membrane-electrode assembly, with the membrane-electrode assembly at the center. In this case, the separator plates located at the outermost sides of the stack are sometimes referred to as end plates.

[0082] Among the separator plates, the end plate is provided with a first pipe-shaped supply pipe 231 for injecting the reformed gas containing hydrogen gas supplied from the reforming section 220 and a second pipe-shaped supply pipe 232 for injecting oxygen gas, and the other end plate is 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.

[0083] The present invention will be described in more detail below based on examples. However, this is merely an illustrative description for understanding the present invention, and the scope of the present invention is not limited to or constrained by the following examples.

[0084] Example 1 A first ionomer dispersion containing 20 wt% of a highly fluorinated polymer with an equivalent weight (EW) of 600 g / eq was prepared. Two porous sub-supports (e-PTFE, pore size: 0.10 μm to 0.2 μm, thickness: 3 μm, MD / TD tensile elongation ratio: 0.4) were laminated with their MD and TD directions perpendicular to each other and then immersed in the ionomer solution. The resulting composite membrane was dried at 80°C for 4 hours in a convection oven, cooled, and then heat-treated at 190°C for 20 minutes. The thickness of the reinforced composite membrane was 20 μm, with an initial MD storage modulus of 1000 MPa and an initial storage modulus ratio (S / L) of 0.7.

[0085] Example 2 A first ionomer dispersion containing 15 wt% of a highly fluorinated polymer with an equivalent weight (EW) of 700 g / eq was prepared. One porous sub-substrate (e-PTFE, pore size: 0.10 μm–0.2 μm, thickness: 6 μm, MD / TD tensile elongation ratio: 0.3–0.5) with different tensile elongations and two porous sub-substrates (e-PTFE, pore size: 0.10 μm–0.2 μm, thickness: 6 μm, MD / TD tensile elongation ratio: 0.2–0.4) were laminated in the same direction and then immersed in the ionomer solution. The composites were dried in a convection oven at 80°C for 4 hours, cooled, and then heat-treated at 160°C for 20 minutes. The reinforced composite membrane had a thickness of 20 μm, an initial MD storage modulus of 550 MPa, and an initial storage modulus ratio (S / L) of 0.5.

[0086] (Comparative Example 1) A first ionomer dispersion containing 15 wt% of a highly fluorinated polymer with an equivalent weight (EW) of 700 g / eq was prepared. A porous sub-support (e-PTFE, pore size: 0.10 μm-0.2 μm, thickness: 3 μm, MD / TD tensile elongation ratio: 0.3-0.5) was immersed in the ionomer solution. It was then dried in a convection oven at 80°C for 4 hours and then heat-treated at 140°C for 20 minutes. The reinforced composite membrane had a thickness of 20 μm, an initial MD storage modulus of 392 MPa, and an initial storage modulus ratio (S / L) of 0.4.

[0087] [Measurement method] 1) Measurement of initial storage modulus The initial storage modulus was measured using a TA-Instruments Q800 under the following conditions: room temperature, frequency = 1 Hz, strain = 0.1%, preload force = 0.25 N, isothermal = 3 minutes.

[0088] 2) Evaluation of dimensional stability The MD / TD directions of a sample cut into a 10 x 10 cm size were marked with a blue name pen. A 500 ml beaker was filled with 300 ml of distilled water and heated on a hot plate at room temperature and humidity (23°C, 50% R). Once the water reached 100°C, the sample was placed in the beaker and immersed for 10 minutes. The sample was then removed and drained. The changes in length, both horizontal and vertical, were measured using graph paper and a ruler. The changes in length before and after immersion were recorded, and the dimensional change rate was calculated using the following formula: The dimensional change of the reinforced composite membrane was calculated as the average of the MD / TD values.

number

[0089] 3) Measurement of ionic conductivity Ionic conductivity was measured as in-plane conductivity using a 4-probe DC method using a Scribner Associates Model 740 MTS. The sample size was 1 × 3 cm, and the temperature and humidity during the ionic conductivity measurement were 80°C and 50% RH.

[0090] 4) Wet / dry cycling evaluation (mechanical durability evaluation) The accelerated durability test method for measuring the mechanical durability of fuel cell polymer electrolyte membranes was based on a standard test method (NEDO protocol, Humidity Cycle Test Method) developed by NEDO (Japan). The cell temperature was 80°C, the wet cycle was Tda = Tdc = 90°C (RH 150%) for 2 minutes, and the dry cycle was Tda = Tdc = dry (RH 0%) for 2 minutes. The test was terminated when the hydrogen leakage amount exceeded 10 times the initial amount, or when 20,000 cycles were completed, whichever came first.

[0091] Membrane-electrode assemblies were manufactured using the polymer electrolyte membranes of the Examples and Comparative Examples, and the battery performance, dimensional stability, and peel strength between the electrode and polymer electrolyte membrane were evaluated. The results are shown in the table below. [Table 1]

[0092] Referring to Table 1, it can be seen that the polymer electrolyte membrane of Example 1, which satisfies the ratio of the initial storage modulus of MD and the initial storage modulus of S / L according to the present invention, has little dimensional change and is excellent in durability.

Claims

1. A polymer electrolyte membrane containing an ion conductor having ion conductivity, The polymer electrolyte membrane has an initial storage modulus in the longitudinal direction (MD) of 500 MPa or more, A polymer electrolyte membrane, wherein the ratio of initial storage modulus (S) in the direction having a smaller initial storage modulus, either in a width direction (TD) or a longitudinal direction (MD), to initial storage modulus (L) in the direction having a larger initial storage modulus, is 0.5 to 1.

0.

2. The polymer electrolyte membrane is 2. The polymer electrolyte membrane according to claim 1, comprising a porous support and an ion conductor filled in the voids of the porous support.

3. 3. The polymer electrolyte membrane of claim 2, wherein the porous support comprises any one selected from the group consisting of nylon, polyimide, polybenzoxazole, polyethylene terephthalate, polyethylene, polypropylene, polytetrafluoroethylene, polyarylene ether sulfone, polyether ether ketone, copolymers thereof, and combinations thereof.

4. 3. The polymer electrolyte membrane of claim 2, wherein the porous support comprises a perfluorinated polymer sheet having a large number of voids due to a microstructure of polymer fibrils, or a nanoweb in which nanofibers are accumulated in the form of a nonwoven fabric having a large number of voids.

5. 3. The polymer electrolyte membrane according to claim 2, wherein the ion conductor is one selected from the group consisting of hydrocarbon-based ion conductors, fluorine-based ion conductors, anion conductors, and mixtures thereof.

6. 6. The polymer electrolyte membrane according to claim 5, wherein the ion conductor has an ion exchange capacity (equivalent weight, E.W.) of 500 to 1100 g / eq.

7. the ionic conductor includes a hydrocarbon-based ionic conductor, The hydrocarbon-based ion conductor may be sulfonated polyimide (S-PI), sulfonated polyarylethersulfone (S-PAES), sulfonated polyetheretherketone (SPEEK), sulfonated polybenzimidazole (SPBI), sulfonated polysulfone (S-PSU), sulfonated polystyrene (S-PS), sulfonated polyphosphazene (S-PS), sulfonated polyisobutylene ... polyphosphazene, sulfonated polyquinoxaline, sulfonated polyketone, sulfonated polyphenylene oxide, sulfonated polyether sulfone, 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 ether nitrile, sulfonated polyarylene ether ether nitrile, sulfonated polyarylene ether sulfone ketone 6. The polymer electrolyte membrane according to claim 5, wherein the polymer electrolyte membrane is any one selected from the group consisting of: ether sulfone ketone, and mixtures thereof.

8. the ionic conductor includes a fluoro-based ionic conductor, 2. The polymer electrolyte membrane according to claim 1, wherein the fluorine-based ion conductor is poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), a copolymer of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, defluorinated sulfurized polyether ketone, or a mixture thereof.

9. A membrane-electrode assembly comprising the polymer electrolyte membrane of claim 1, an anode electrode and a cathode electrode positioned opposite each other; and a membrane-electrode assembly including a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode;

10. A fuel cell comprising the membrane-electrode assembly of claim 9.

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