Membrane-electrode assembly and fuel cell including the same

Abstract

A membrane-electrode assembly with improved durability is provided. One embodiment of the present invention provides a membrane-electrode assembly comprising a polymer electrolyte membrane having an uneven portion on at least one surface thereof and a catalyst layer disposed on the polymer electrolyte membrane, the catalyst layer comprising a first catalyst layer filling the inside of the uneven portion and a second catalyst layer disposed on the polymer electrolyte membrane, the first catalyst layer being interposed between the polymer electrolyte membrane and the second catalyst layer.

Description

[Technical Field]

[0001] The present invention relates to a membrane-electrode assembly and a fuel cell including the same, and more particularly to a membrane-electrode assembly with improved durability 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. 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). 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. 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. 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. Conventional membrane-electrode assemblies have been manufactured using flat films to provide a polymer electrolyte membrane, which can result in poor interfacial adhesion between the electrolyte membrane and the electrodes, resulting in poor performance or a shortened lifespan for the polymer electrolyte membrane fuel cell. Meanwhile, Korean Patent Publication KR10-1715447B1 (published on December 24, 2014) is an invention relating to a membrane electrode assembly including an electrolyte membrane with recesses on its surface and electrodes with protrusions on their surfaces, a manufacturing method thereof, and a fuel cell including the same. However, the Korean Patent Publication only discloses a polymer electrolyte membrane with protrusions, and there is still a problem in that the interfacial adhesion between the electrode and the electrolyte membrane is insufficient, resulting in reduced electrode durability. Summary of the Invention [Problem to be solved by the invention]

[0003] SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a membrane-electrode assembly which improves the interfacial bonding between the polymer electrolyte membrane and the catalyst layer. Another object of the present invention is to solve the above problems and to provide a membrane-electrode assembly having improved durability by improving the interfacial adhesion between catalyst layers. It is still another object of the present invention to provide a fuel cell comprising the membrane-electrode assembly. 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]

[0004] One embodiment of the present invention to achieve the above object provides a membrane-electrode assembly including a polymer electrolyte membrane having a concave-convex portion on at least one surface thereof and a catalyst layer disposed on the polymer electrolyte membrane, the catalyst layer including a first catalyst layer filling the concave-convex portion and a second catalyst layer disposed on the polymer electrolyte membrane, the first catalyst layer being interposed between the polymer electrolyte membrane and the second catalyst layer. Specifically, the first catalyst layer may be different from the second catalyst layer. According to yet another embodiment of the present invention, the first catalyst layer comprises a first ionomer, and the second catalyst layer comprises a second ionomer. The weight of the first ionomer relative to the total weight of the first catalyst layer may be the same as or different from the weight of the second ionomer relative to the total weight of the second catalyst layer. Specifically, the weight of the first ionomer relative to the total weight of the first catalyst layer may be greater than the weight of the second ionomer relative to the total weight of the second catalyst layer. More specifically, the weight of the first ionomer relative to the total weight of the first catalyst layer may be greater than 35 wt %, and the weight of the second ionomer relative to the total weight of the second catalyst layer may be less than 35 wt %. Specifically, the first ionomer and the second ionomer may each independently be any one selected from the group consisting of hydrocarbon-based ionomers, fluorine-based ionomers, and mixtures thereof. Specifically, the uneven portion may include first recesses and first protrusions arranged alternately with the first recesses. According to yet another embodiment of the present invention, the first catalyst layer may be filled to 80% (v / v) or more of the total volume of the first recess. According to yet another embodiment of the present invention, the first catalyst layer may fill the entire volume of the first recess. According to one specific example, the first catalyst layer may include a first central portion and a sidewall portion including a first sidewall portion and a second sidewall portion disposed opposite each other across the first central portion. The first sidewall portion may include a first side surface and a first curved surface extending from the first side surface to the top surface of the first central portion. The second sidewall portion may include a second side surface and a second curved surface extending from the second side surface to the top surface of the first central portion. According to one specific example, the thickness H of the first central portion may be greater than 0 μm and less than 1 μm. According to another specific example, the minimum thickness I of the first sidewall portion may be greater than 0 and less than 0.8 times the thickness H of the first central portion, or greater than 0 and less than 0.5 times the thickness H of the first central portion. According to one specific example, the maximum width B of the first side wall portion can be less than 0.2 times the width A between the first side surface and the second side surface. According to one specific example, the curvature R of the first curved surface can be equal to or less than the difference HI between the thickness H of the first central portion and the minimum thickness I of the first side wall portion. According to yet another embodiment of the present invention, the first catalyst layer may further include a functional additive. Yet another embodiment of the present invention provides a fuel cell including the membrane-electrode assembly. [Effects of the Invention]

[0005] According to the present invention, it is possible to provide a membrane-electrode assembly that not only improves the interfacial adhesion between the polymer electrolyte membrane and the catalyst layer but also improves both the chemical and mechanical durability, thereby improving both the performance and lifespan of the fuel cell. 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]

[0006] [Figure 1] 1 is a cross-sectional view showing a membrane-electrode assembly according to one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the uneven portion of FIG. 1. [Figure 3] FIG. 4 is a cross-sectional view showing a membrane-electrode assembly according to another embodiment of the present invention. [Figure 4] FIG. 10 is a cross-sectional view showing a membrane-electrode assembly according to yet another embodiment of the present invention. [Figure 5] FIG. 10 is a schematic diagram illustrating a fuel cell according to still another embodiment of the present invention. [Figure 6] 1 shows a photograph of a membrane-electrode assembly according to Example 1-1. DETAILED DESCRIPTION OF THE INVENTION

[0007] 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. One embodiment of the present invention provides a membrane-electrode assembly including a polymer electrolyte membrane having a concave-convex portion on at least one surface and a catalyst layer disposed on the polymer electrolyte membrane, the catalyst layer including a first catalyst layer filling the concave-convex portion and a second catalyst layer disposed on the polymer electrolyte membrane, the first catalyst layer being interposed between the polymer electrolyte membrane and the second catalyst layer. Specifically, the first catalyst layer may be different from the second catalyst layer. According to one aspect of the present invention, by interposing the first catalyst layer between the polymer electrolyte membrane and the second catalyst layer, it is possible to provide a membrane-electrode assembly having improved interfacial adhesion between the polymer electrolyte membrane and the catalyst layer as well as improved chemical and mechanical durability. This may result in improved fuel cell performance and lifespan. The configuration of the present invention will be described in more detail below with reference to the drawings. 1. Membrane-electrode Assembly FIG. 1 is a cross-sectional view showing a membrane-electrode assembly according to one embodiment of the present invention. As shown in FIG. 1, a membrane-electrode assembly 100 according to the present invention comprises a polymer electrolyte membrane 10 and a catalyst layer 20 . The polymer electrolyte membrane 10 according to the present invention may have at least one surface with the uneven portion 15. Therefore, the polymer electrolyte membrane 10 may have the uneven portion 15 on one or both surfaces thereof. One surface of the polymer electrolyte membrane 10 may have a plurality of concave and convex portions 15 . The concave-convex portion 15 according to the present invention can include first concave portions and first convex portions alternately arranged with the first concave portions. For example, the first concave portions can be individual concave portions forming the concave-convex portion, and the first convex portions can be individual convex portions forming the concave-convex portion. Although FIG. 1 illustrates the first catalyst layer 20a filling the entire volume of the first recess, according to an embodiment of the present invention, the first catalyst layer 20a may be filled at 80% (v / v) or more of the entire volume of the first recess, preferably 80-95% (v / v), and more preferably 85-95% (v / v). If the first catalyst layer 20a fills less than 80% (v / v) of the entire volume of the first recess, the interfacial adhesion between the polymer electrolyte membrane and the catalyst layer may not be sufficiently strong, resulting in a failure to significantly improve interfacial durability. For example, the volume ratio of the first catalyst layer 20a to the entire volume of the first recess can be calculated by measuring the entire volume of the first recess and the volume of the first catalyst layer using a scanning electron microscope (SEM). The casting method, which has been used to manufacture polymer electrolyte membranes in the past, involves casting a solution containing a solute dissolved in a solvent into a mold of a certain shape and evaporating the solvent with heat to produce a film. This casting and drying process takes some time, and since the drying state of each part varies due to the heat used to form the unevenness, it can be difficult to manufacture a uniform shape of various shapes.

[0008] According to the present invention, protrusions are formed on the surface of a roll press, and a polymer electrolyte membrane without protrusions is passed between upper and lower rolls, whereby protrusions are pressed to form protrusions on one or both sides of the polymer electrolyte membrane. The number of protrusions on the polymer electrolyte membrane may vary depending on the type of roll press. The thickness of the polymer electrolyte membrane before the concave-convex portions are formed may be, for example, 5 to 20 μm, although the thickness of the polymer electrolyte membrane may vary depending on the purpose. The polymer electrolyte membrane 10 may include an ion conductor. The ion conductor may be one selected from the group consisting of a fluorine-based ionomer, a hydrocarbon-based ionomer, and a mixture thereof. A detailed description thereof will be given later, as it overlaps with the first and second ionomers described below. The catalyst layer 20 according to the present invention may be disposed on the polymer electrolyte membrane 10. Specifically, the catalyst layer 20 may include a first catalyst layer 20a filling the interior of the uneven portion 15 and a second catalyst layer 20b disposed on the polymer electrolyte membrane 10. The first catalyst layer 20a may be interposed between the polymer electrolyte membrane 10 and the second catalyst layer 20b. The first catalyst layer 20a may comprise a first ionomer acting as a binder, and the second catalyst layer 20b may comprise a second ionomer acting as a binder. Specifically, the first ionomer may be the same as or different from the second ionomer. For example, the weight of the first ionomer relative to the total weight of the first catalyst layer may be the same as or different from the weight of the second ionomer relative to the total weight of the second catalyst layer.

[0009] Preferably, the weight of the first ionomer relative to the total weight of the first catalyst layer may be greater than the weight of the second ionomer relative to the total weight of the second catalyst layer. For example, the weight of the first ionomer relative to the total weight of the first catalyst layer may be greater than 35 wt %, and the weight of the second ionomer relative to the total weight of the second catalyst layer may be less than 35 wt %. Conventionally, when a catalyst layer is formed by coating one type of catalyst slurry on both sides of a polymer electrolyte membrane having a concave-convex portion and then drying it, there is a problem that the bonding between the flat surfaces results in poor adhesion at the interface between the polymer electrolyte membrane and the catalyst layer, and overall chemical and mechanical durability is not improved. According to the present invention, the chemical and mechanical durability of the interface can be improved by forming the concave-convex portion, forming a first catalyst layer with a high ionomer content on the concave-convex portion, and then forming a second catalyst layer. By increasing the weight of the first ionomer relative to the weight of the second ionomer, interfacial adhesion between the polymer electrolyte membrane and the catalyst layer can be improved, and overall durability between the catalyst layers can be improved. Furthermore, by reducing the ionomer content of the second catalyst layer, performance can be improved through smooth mass transfer. The first ionomer and the second ionomer may each independently be any one selected from the group consisting of hydrocarbon-based ionomers, fluorine-based ionomers, and mixtures thereof. The fluorine-based ionomer may be a fluoropolymer containing fluorine in the main chain having a cation exchange group or an anion exchange group, or a partially fluorinated polymer such as polystyrene-graft-ethylene tetrafluoroethylene copolymer, polystyrene-graft-polytetrafluoroethylene copolymer, etc. The fluorine-based ionomer may be a fluorine-based polymer including, for example, 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.

[0010] The cation exchange group is a functional group capable of transferring cations such as hydrogen ions, and may be, for example, an acidic group such as a sulfonic acid group, a carboxyl group, a boronic acid group, a phosphate group, an imide group, a sulfonimide group, or a sulfonamide group, and generally may be a sulfonic acid group or a carboxyl group. The anion exchange group is a polymer capable of transporting anions such as hydroxide ions, carbonate ions, or bicarbonate ions. The anion exchange group is commercially available in the form of hydroxide or halide (generally chloride). The anion exchange group can be used in industrial water purification, metal separation, catalytic processes, etc. The polymer containing the anion exchange group 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. The hydrocarbon ionomer may be a hydrocarbon polymer having a cation exchange group or an anion exchange group, for example, a hydrocarbon polymer having at least one selected from the group consisting of imidazole, benzimidazole, polyamide, polyamideimide, polyimide, polyacetal, polyethylene, polypropylene, acrylic resin, polyester, polysulfone, polyether, polyetherimide, polyester, polyethersulfone, polyetherimide, polycarbonate, polystyrene, polyphenylene sulfide, polyetheretherketone, polyetherketone, polyarylethersulfone, polyphosphazene, and polyphenylquinoxaline in its main chain. Examples of the hydrocarbon ionomer include 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, and sulfonated polyethersulfone. 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 nitrilenitrile, sulfonated polyarylene ether ether nitrile, sulfonated polyarylene ether sulfone ketone, and hydrocarbon polymers including mixtures thereof, but the technical concept of the present invention is not limited thereto.

[0011] The catalyst layer 20 according to the present invention may be made of any material that can be used as a catalyst in a hydrogen gas oxidation reaction and / or an oxygen gas reduction reaction, and preferably, a platinum-based metal or a non-platinum-based metal can be used. The platinum-based metal may be platinum (Pt) and / or a Pt-M alloy, where M may be any 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 Pt-M alloy may be Pt-Pd, Pt-Sn, Pt-Mo, Pt-Cr, Pt-W, Pt-Ru, Pt-Ni, Pt-Co, Pt-Y, Pt-Ru-W, Pt-Ru-Ni, Pt-Ru-Mo, Pt-Ru-Rh-Ni, Pt-Ru-Sn-W, Pt-Ru-Ir-Ni, Pt-Co-Mn, 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, or a mixture of two or more thereof. The non-platinum based metal may be one selected from the group consisting of palladium (Pd), ruthenium (Ru), iridium (Ir), osmium (Os), and a non-platinum based alloy. The non-platinum alloy may be 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, Fe-N, Fe-P, Co-N, or a mixture of two or more thereof. In yet another embodiment of the present invention, the catalyst layer 20 can include catalysts in which metal nanoparticles fill the surface or internal pores of the support. The support can be, for example, a carbon-based support, a porous inorganic oxide such as zirconia, alumina, titania, silica, ceria, or a zeolite.

[0012] The carbon-based support may be selected from graphite, Super P, carbon fiber, carbon sheet, carbon black, Ketjen black, Denka black, acetylene black, carbon nanotube (CNT), carbon sphere, carbon ribbon, fullerene, activated carbon, carbon nanofiber, carbon nanowire, carbon nanoball, carbon nanohorn, carbon nanocage, carbon nanoring, ordered nano / mesoporous carbon, carbon aerogel, mesoporous carbon, graphene, stabilized carbon, activated carbon, and combinations of one or more thereof, but is not limited thereto. Any support available in the art may be used without limitation. The surface area of ​​the carrier is 50 m2 / g or more, and the average particle size preferably falls within the range of 10 to 300 nm. If the surface area of ​​the carrier is less than the above range, it is not possible to obtain a uniform distribution of the metal particles. FIG. 2 is an enlarged cross-sectional view of the uneven portion of FIG. As shown in FIG. 2, the first catalyst layer 20a according to the present invention can fill the entire volume of the first recess. The first catalyst layer 20a may include a first center portion cp and sidewall portions swp. The sidewall portions swp may refer to members on both sides of the first center portion cp. Specifically, the sidewall portions swp may include a first sidewall portion swp1 and a second sidewall portion swp2 disposed opposite each other with the first center portion cp in between. The first side wall portion swp1 may have a first side surface ss1 and a first curved surface cs1 extending from the first side surface ss1 to an upper surface cpus of the first central portion cp. The first curved surface cs1 may be essentially formed because the catalyst layer disposed on the polymer electrolyte membrane in the process of forming the first catalyst layer has an overall concave shape due to the influence of surface tension, etc. The upper surface cpus of the first central portion cp may be, for example, a flat surface. The second side wall portion swp2 may have a second side surface ss2 and a second curved surface cs2 extending from the second side surface ss2 to an upper surface cpus of the first center portion cp. Since the catalyst layer disposed on the polymer electrolyte membrane in the process of forming the first catalyst layer has an overall concave shape due to the influence of surface tension, etc., the second curved surface cs2 may be essentially formed.

[0013] The first central portion cp and the side wall portion swp may be in contact with the polymer electrolyte membrane 10. Specifically, the first central portion cp and the side wall portion swp may be disposed directly on the polymer electrolyte membrane 10. The thickness H of the first central portion cp may be more than 0 μm and less than 1 μm, preferably 0.1 to 0.9 μm. If the thickness H of the first central portion cp exceeds the above range, problems may occur such as reduced interfacial durability and interfacial bonding strength. The minimum thickness I of the first side wall portion swp1 may be greater than 0 and less than 0.8 times the thickness H of the first central portion, and preferably greater than 0 and less than 0.5 times the thickness H of the first central portion. If the minimum thickness I of the first side wall portion swp1 is less than this range, problems may occur such that the bending of the concave-convex portions is weak and the interfacial bonding strength is reduced, resulting in reduced durability. If it exceeds this range, the thickness H exceeds 1 μm, resulting in problems such as reduced interfacial durability and interfacial bonding strength. The maximum width B of the first side wall portion swp1 may be less than 0.2 times, and preferably 0.02 to 0.18 times, the width A between the first side surface ss1 and the second side surface ss2. If the maximum width B of the first side wall portion swp1 exceeds this range, the curvature of the concave-convex portion may be weak, and the interfacial bonding strength may be reduced, resulting in a decrease in durability. The curvature R of the first curved surface cs1 may be less than or equal to the difference HI between the thickness H of the first central portion and the minimum thickness I of the first side wall portion. If the curvature of the first curved surface cs1 exceeds the difference HI between the thickness H of the first central portion and the minimum thickness I of the first side wall portion, the maximum width B of the first side wall portion swp1 increases, weakening the curvature of the concave-convex portion, reducing the interfacial bonding strength and reducing durability. The curvature of the first curved surface cs1 can be measured, for example, by comparing a circle whose radius is the maximum width B of the first side wall portion swp1 with a circle whose radius is the difference HI between the thickness H of the first central portion cp and the minimum thickness I of the first side wall portion swp1. In other words, the curvature can be calculated by calculating the inverse of the radii of curvature defined by the two circles. For example, the thickness H of the first central portion cp, the minimum thickness I of the first side wall portion swp1, the maximum width B of the first side wall portion swp1, and the curvature R of the first curved surface cs1 can all be measured or calculated through cross-sectional analysis using a scanning electron microscope (SEM).

[0014] Unlike the configuration shown in FIG. 1, according to another embodiment of the present invention, the first catalytic layer 20a may fill the entire volume of the first recess and may extend to a portion of the upper surface of the first protrusion disposed on one side of the first recess. Therefore, the width A between the first side surface ss1 and the second side surface ss2 may be 90 to 110%, preferably 95 to 105%, based on the electrode active area of ​​the individual protrusion / convex portion. If the width A between the first side surface ss1 and the second side surface ss2 is outside the above range, the first catalytic layer may not fill the protrusion / convex portion by 80% or may fill more than 120%, which may result in poor interface durability and a reduced specific gravity of the second catalytic layer, resulting in degraded performance. For example, the width A between the first side surface ss1 and the second side surface ss2 may be measured through cross-sectional analysis using a scanning electron microscope (SEM). According to yet another embodiment of the present invention, the first catalyst layer 20a may further include a functional additive. The functional additive may include any one selected from the group consisting of a radical scavenger, a heat dissipating material, a chelating agent, a hygroscopic material, and combinations thereof, and preferably includes all of them. The content of the functional additive is preferably 5 to 67 wt % based on the total solid content of the first catalyst layer. If the content of the functional additive is less than this range, the heat dissipation effect and oxygen radical scavenging effect may not be sufficiently improved, and if it exceeds this range, the coating operation of the catalyst slurry may be difficult. The radical scavenger may be, for example, any one selected from the group consisting of transition metals, transition metal ions, transition metal oxides, transition metal complexes, noble metals, noble metal ions, noble metal oxides, noble metal complexes, and combinations thereof, although the technical concept of the present invention is not limited thereto and any particulate form capable of capturing oxygen radicals may be applied. The transition metal may be any one selected from the group consisting of cerium (Ce), manganese (Mn), tungsten (W), cobalt (Co), vanadium (V), nickel (Ni), chromium (Cr), zirconium (Zr), yttrium (Y), iridium (Ir), iron (Fe), titanium (Ti), molybdenum (Mo), lanthanum (La), and neodymium (Nd). The noble metal can be any one selected from the group consisting of silver (Ag), platinum (Pt), ruthenium (Ru), palladium (Pd), and rhodium (Rh). The first catalyst layer according to the present invention includes a radical scavenger, which can effectively capture oxygen radicals generated during fuel cell operation, thereby effectively preventing the oxygen radicals from changing the structure of the ion conductor compound that corresponds to the hydrogen ion channel.

[0015] The heat dissipation material may be, for example, hexagonal boron nitride (h-BN), AlN, Al2O3, TiO2, ZnO, ZrO, SiO2, etc. The heat dissipation material can improve the performance of the fuel cell by dissipating heat generated during operation of the fuel cell to the outside. The chelating agent may be, for example, citric acid, which has the purpose of capturing dissolved metal ions and may have the effect of improving durability. The hygroscopic material may be, for example, an acrylic resin having acrylic acid as a monomer or a silicate compound. By including the hygroscopic material, the first catalyst layer according to the present invention can have the effect of improving low humidification performance. 3 is a cross-sectional view showing a membrane-electrode assembly according to another embodiment of the present invention. The repeated explanations of the above-mentioned parts will be simplified or omitted. 3, a first catalyst layer 20a according to the present invention can be disposed on the surface of the first convex portion while filling the interior of the concave-convex portion 15. The thickness of the first catalyst layer disposed on the surface of the first convex portion is preferably 1 μm or less. The second catalyst layer 20b may be interposed between different portions of the first catalyst layer 20a disposed on the surface of the first convex portion. In other words, the second catalyst layer 20b may be inserted into an accommodation space defined by the first catalyst layer. The accommodation space is defined as a space between different portions of the first catalyst layer 20a disposed on the surface of the first convex portion. In the membrane-electrode assembly according to the present invention, the first catalyst layer 20a is disposed on the surface of the first protrusion, which can further improve the interfacial adhesion between the polymer electrolyte membrane and the catalyst layer, thereby improving the durability of the membrane-electrode assembly. 4 is a cross-sectional view showing a membrane-electrode assembly according to another embodiment of the present invention. The repeated descriptions of the above-mentioned parts will be simplified or omitted. As shown in FIG. 4, the first catalyst layer 20a according to the present invention may be disposed directly above the polymer electrolyte membrane 10, and more specifically, may be disposed on both the surfaces of the first recess and the first protrusion. The maximum thickness of the first catalyst layer 20a is preferably 2 μm or less. In this specification, the "maximum thickness of the first catalyst layer 20a" is defined as the height from the surface where the first catalyst layer 20a and the polymer electrolyte membrane 10 contact each other to the surface where the first catalyst layer 20a and the second catalyst layer 20b contact each other.

[0016] 2.Fuel cell Yet another embodiment of the present invention provides a fuel cell comprising the membrane-electrode assembly. FIG. 5 is a schematic diagram illustrating a fuel cell according to still another embodiment of the present invention. As shown in FIG. 5, 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. 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. 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. 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. 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. Hereinafter, the embodiments of the present invention will be 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 to the following content.

[0017] [Production Preparation Example 1: Production of Polymer Electrolyte Membrane] <Comparative Preparation Example 1: Production of a polymer electrolyte membrane without uneven portions> A polymer electrolyte membrane was fabricated by applying a polymer solution, which was a mixture of a solvent (water and isopropanol) in a 1:1 weight ratio and perfluorosulfonic acid, to a glass substrate using a doctor blade, gradually heating the applied solution to 80°C, and then drying it for 4 hours. <Preparatory Example 1: Production of a polymer electrolyte membrane having uneven portions> A polymer electrolyte membrane was fabricated by applying a polymer solution, which was a mixture of a solvent (a 1:1 weight ratio of water and isopropanol) and perfluorosulfonic acid, to a glass substrate using a doctor blade, gradually increasing the temperature of the applied polymer solution to 80°C, and then drying it for 4 hours. The glass substrate was then removed, and a roll press (roll temperature: 120-160°C) with concave-convex portions was used to press both sides of the polymer electrolyte membrane, fabricating a polymer electrolyte membrane with a first concave-convex portion having a depth of 2 μm. [Production Example 1: Production of membrane-electrode assembly] When manufacturing the membrane-electrode assembly according to the embodiment, the volume of the first recess formed in the polymer electrolyte membrane according to Preparation Example 1 was calculated in advance, and the content of the catalyst slurry was adjusted accordingly. <Comparative Example 1-1: Membrane-electrode assembly manufactured using a polymer electrolyte membrane without unevenness> A catalyst slurry (3.5 mL) of Tanaka's commercial Pt / C catalyst and binder (Nafion D-521) mixed at a weight ratio of 1:0.48 was directly coated on both sides of the polymer electrolyte membrane prepared in Comparative Preparation Example 1, and then dried at 80°C for 5 minutes to prepare a membrane-electrode assembly. <Comparative Example 1-2: Membrane-electrode assembly manufactured using a polymer electrolyte membrane having uneven portions, in which a catalyst layer was formed using only one type of catalyst slurry> A first catalyst layer was formed by coating both sides of the polymer electrolyte membrane of Example 1 with a first catalyst slurry (3.5 mL) in which a commercial Pt / C catalyst from Tanaka and a first ionomer (Nafion D-521) were mixed in a weight ratio of 1:0.48. <Example 1-1: Membrane-electrode assembly in which the first catalyst layer fills 80% or more of the total volume of the first recess> A first catalyst slurry (0.7 mL) containing a Tanaka Corporation commercial Pt / C catalyst and a first ionomer (Nafion D-521) in a weight ratio of 1:0.56 was coated on both sides of the polymer electrolyte membrane prepared in Example 1 and dried at 80°C for 2 minutes to fill 90% (v / v) of the first recessed portion with the first catalyst layer. A second catalyst slurry (3.0 mL) containing a commercial Pt / C catalyst and a second ionomer (Nafion D-521) in a weight ratio of 1:0.48 was then applied to the remaining 10% (v / v) of the first recessed portion and directly coated onto the surfaces of the first protrusions alternately arranged with the first recessed portion using a slot-die method. The second catalyst slurry was then dried at 80°C for 4 minutes to form a second catalyst layer. <Example 1-2: Different from Example 1-1, but with the same binder content> A membrane-electrode assembly was prepared in the same manner as in Example 1-1, except that the first catalyst slurry and the second catalyst slurry were prepared by mixing a commercial Pt / C catalyst and an ionomer (Nafion D-521) in a weight ratio of 1:3. <Example 1-3: Unlike Example 1-1, when the binder type is hydrocarbon-based ionomer> A membrane-electrode assembly was manufactured in the same manner as in Example 1-1, except that sulfonated poly(arylene ether sulfone); sPAES (degree of sulfonation: 17%), which is a hydrocarbon-based ionomer, was used as the first catalyst slurry and the second catalyst slurry instead of the fluorine-based ionomer (Nafion D-521). <Example 1-4: When functional additives were included in the first catalyst slurry> A membrane-electrode assembly was prepared in the same manner as in Example 1-1, except that a catalyst slurry was prepared by mixing 100 parts by weight of a first catalyst slurry in which a commercial Pt / C catalyst and a first ionomer (Nafion D-521) were mixed in a weight ratio of 1:3 based on the total weight of the first catalyst slurry, and 7 parts by weight of radical scavenger particles (CeO). <Example 2-1: Membrane-electrode assembly in which the first catalyst layer fills less than 80% of the total volume of the first recess> A membrane-electrode assembly was manufactured in the same manner as in Example 1-1, except that the first catalyst slurry (0.59 mL) and the second catalyst slurry (3.11 mL) were used to adjust the first catalyst layer to fill 75% (v / v) of the total volume of the first recess. <Example 3-1: Case where the first catalyst layer is completely filled based on the entire volume of the first recess> The membrane-electrode assembly was manufactured in the same manner as in Example 1-1, except that the first catalyst slurry (0.85 mL) was used and the first catalyst layer was adjusted to fill the entire volume of the first recess. Specifically, the thickness H of the first central portion constituting the first catalyst layer was 0.8 μm, the width A between the first side surface and the second side surface was 3 μm, the minimum thickness I of the first side wall portion was 0.3 μm, the maximum width B of the first side wall portion was 0.5 μm, and the curvature of the first curved surface was 0.4 μm. -1 It was adjusted so that Thereafter, the second catalyst slurry (2.85 mL) according to Example 1-1 was coated onto the first convex portions and the surface of the first catalyst layer to form a second catalyst layer with a thickness of 9 μm. <Example 4-1: Unlike Example 3-1, when parameters are not satisfied> A membrane-electrode assembly was produced in the same manner as in Example 3-1, except that the first catalyst slurry (1.0 mL) and the second catalyst slurry (2.7 mL) were used, and the thickness H of the first central portion constituting the first catalyst layer was 1.2 μm, the width A between the first side surface and the second side surface was 3 μm, the minimum value I of the thickness of the first side wall portion was 1.0 μm, the maximum value B of the width of the first side wall portion was 0.8 μm, and the curvature of the first curved surface was 0.3 μm. -1 It was adjusted so that

[0018] [Experimental Example 1: Evaluation of mechanical durability of membrane-electrode assembly] The chemical durability of the membrane-electrode assembly of Preparation Example 1 was evaluated in accordance with the durability evaluation protocol of the U.S. Department of Energy (DOE). Specifically, to evaluate the chemical durability of the membrane-electrode assembly, wet-dry cycling was performed for 20,000 cycles under air / air conditions at 80°C with repeated cycles of 2 minutes wet and 2 minutes dry, and then hydrogen gas crossover was measured. The measured values ​​are shown in Table 1 below. [Table 1] Referring to Table 1, when the amount of hydrogen gas was measured at the cathode, it was confirmed that the amount of hydrogen gas permeating the polymer electrolyte membrane in the Example was significantly less than that in the Comparative Example. It can be inferred that the chemical durability of the membrane-electrode assembly is significantly improved according to an Example of the present invention, thereby extending the performance and lifespan of the fuel cell. Comparing Example 1-1 and Example 1-2 in terms of the content of the ionomer acting as a binder, it can be seen that when the content of the ionomer in the first catalyst slurry is higher than the content of the ionomer in the second catalyst slurry, the amount of hydrogen gas permeating the polymer electrolyte membrane is significantly lower. Comparing Example 1-1 and Example 2-1 in terms of the content of the first catalyst layer based on the total volume of the first recess, it can be inferred that when the first catalyst layer is filled to 80% (v / v) or more of the total volume of the first recess, the amount of hydrogen gas permeating the polymer electrolyte membrane is significantly reduced, resulting in a significant improvement in chemical durability.

[0019] [Experimental Example 2: Photograph of membrane-electrode assembly according to Example 1-1] FIG. 6 shows a photograph of the membrane-electrode assembly according to Example 1-1. As shown in FIG. 6, it can be inferred that the membrane-electrode assembly according to Example 1-1 was realized. 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 membrane-electrode assembly comprising a polymer electrolyte membrane having an uneven portion on at least one surface thereof, and a catalyst layer disposed on the polymer electrolyte membrane, the catalyst layer includes a first catalyst layer filling the interior of the uneven portion and a second catalyst layer disposed on the polymer electrolyte membrane, the first catalyst layer is interposed between the polymer electrolyte membrane and the second catalyst layer; the first catalyst layer comprises a first ionomer; the second catalyst layer comprises a second ionomer; the weight of the first ionomer relative to the total weight of the first catalyst layer is greater than the weight of the second ionomer relative to the total weight of the second catalyst layer; The maximum thickness of the first catalyst layer is 2 μm or less. Membrane-electrode assembly.

2. the weight of the first ionomer relative to the total weight of the first catalyst layer is more than 35 wt %; 2. The membrane-electrode assembly according to claim 1, wherein the weight of the second ionomer relative to the total weight of the second catalyst layer is less than 35% by weight.

3. The first ionomer and the second ionomer each independently comprise:

2. The membrane-electrode assembly according to claim 1, wherein the ionomer is any one selected from the group consisting of hydrocarbon-based ionomers, fluorine-based ionomers, and mixtures thereof.

4. The uneven portion is a first recess; and a first protrusion arranged alternately with the first recess, The first catalyst layer comprises:

2. The membrane-electrode assembly according to claim 1, wherein the first recess is filled to 80% (v / v) or more of its total volume.

5. The first catalyst layer comprises: filling the entire volume of the first recess; The first catalyst layer comprises: a first central portion; and a sidewall portion including a first sidewall portion and a second sidewall portion disposed opposite each other with the first central portion therebetween; The first side wall portion The first aspect and a first curved surface extending from the first side surface to a top surface of the first central portion; The second side wall portion The second aspect; and 5. The membrane-electrode assembly according to claim 4, further comprising a second curved surface extending from the second side surface to the top surface of the first central portion.

6. The thickness H of the first central portion is The membrane-electrode assembly according to claim 5, wherein the thickness is more than 0 μm and less than 1 μm.

7. The minimum thickness I of the first side wall portion is 6. The membrane-electrode assembly according to claim 5, wherein the thickness H of the first central portion is greater than 0 and less than 0.8 times the thickness H of the first central portion.

8. The minimum thickness I of the first side wall portion is 8. The membrane-electrode assembly according to claim 7, wherein the thickness H of the first central portion is greater than 0 and less than 0.5 times the thickness H of the first central portion.

9. The maximum width B of the first side wall portion is 6. The membrane-electrode assembly according to claim 5, wherein the width A between the first side and the second side is less than 0.2 times the width A between the first side and the second side.

10. The curvature R of the first curved surface is 6. The membrane-electrode assembly according to claim 5, wherein the difference between the thickness H of said first central portion and the minimum value I of the thickness of said first side wall portion is equal to or less than HI.

11. The first catalyst layer comprises:

10. The membrane-electrode assembly according to claim 1, further comprising a functional additive.

12. A fuel cell comprising the membrane-electrode assembly according to claim 1.

Images