Membrane-electrode assembly and manufacturing method therefor

Abstract

The present invention relates to a membrane-electrode assembly and a fuel cell including same. The membrane-electrode assembly has, by means of elongation, surface roughness only on the surface of a catalyst layer, such that interfacial bonding strength is increased by the surface roughness, the degree of contraction or expansion during cell operation is reduced such that durability may be improved, and furthermore, porosity is improved such that mass transfer and cell performance may also be improved.

Description

Membrane-electrode assembly and method for manufacturing the same

[0001] The present invention relates to a membrane-electrode assembly and a method for manufacturing the same.

[0002] A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbons such as methanol, ethanol, and natural gas into electrical energy. A representative example of this type of fuel cell is the polymer electrolyte membrane fuel cell (PEMFC). Due to its low operating temperature (<100°C), fast start-up and response characteristics, and excellent durability, the PEMFC is attracting attention as a power source for portable, automotive, and home use.

[0003] In the above fuel cell system, the membrane electrode assembly (MEA) that actually generates electricity has a structure in which an anode electrode (also called a fuel electrode or oxidation electrode) and a cathode electrode (also called an air electrode or reduction electrode) are positioned with a polymer electrolyte membrane in between.

[0004] Membrane-electrode assemblies are intended for use under the temperature conditions in which fuel cells operate, and will experience expansion and contraction depending on these conditions. Repeated expansion and contraction can create small pinholes in the membrane-electrode assembly, which can then lead to cracks, potentially reducing the durability and performance of the fuel cell.

[0005] Therefore, there is a need to improve the durability and performance of the fuel cell by preventing deterioration of the membrane-electrode assembly under the temperature conditions under which the fuel cell is operated.

[0006] The present invention provides a membrane-electrode assembly and a method for manufacturing the same, which enhance durability and implement improved performance by alleviating the degree of shrinkage and expansion due to use under temperature conditions in which a fuel cell is operated.

[0007] One embodiment of the present invention provides a membrane-electrode assembly comprising: a polymer electrolyte membrane; and a catalyst layer provided on at least one surface of the polymer electrolyte membrane; wherein the catalyst layer has surface roughness on the surface.

[0008] According to one embodiment of the present invention, the surface roughness of the catalyst layer can be formed by stretching the catalyst layer.

[0009] According to one embodiment of the present invention, the surface roughness of the catalyst layer may be 0.1 ㎛ or more and 6 ㎛ or less.

[0010] According to one embodiment of the present invention, the surface roughness of the catalyst layer may be provided in a negative shape.

[0011] According to one embodiment of the present invention, the depth of the surface roughness may be 20% or less with respect to the thickness of the catalyst layer.

[0012] According to one embodiment of the present invention, the surface roughness may be irregularly distributed on the surface of the catalyst layer.

[0013] According to one embodiment of the present invention, the area of ​​the surface roughness region of the catalyst layer may be 20% or more and 95% or less of the total active area of ​​the catalyst layer.

[0014] According to one embodiment of the present invention, the thickness of the polymer electrolyte membrane may be 5 ㎛ or more and 30 ㎛ or less, and the thickness of the catalyst layer may be 1 ㎛ or more and 30 ㎛ or less.

[0015] One embodiment of the present invention provides a method for manufacturing a membrane-electrode assembly, comprising: a step of manufacturing a polymer electrolyte membrane; a step of forming a catalyst layer on at least one surface of the polymer electrolyte membrane; a step of manufacturing a membrane-electrode assembly; and a step of forming surface roughness on the catalyst layer by stretching the membrane-electrode assembly.

[0016] According to one embodiment of the present invention, the stretching can be performed in the longitudinal direction (MD direction).

[0017] According to one embodiment of the present invention, the stretching can be performed at a stretching speed of 1.0 m / min or less.

[0018] According to one embodiment of the present invention, the stretching can be performed at a stretching tension of 30 N or less.

[0019] According to one embodiment of the present invention, the stretching can be performed so that the thickness reduction rate of the polymer electrolyte membrane becomes 5% or less.

[0020] According to one embodiment of the present invention, the stretching can be performed so that the change rate in length of the active area of ​​the catalyst layer is 8% or less.

[0021] According to one embodiment of the present invention, a membrane-electrode assembly can form surface roughness only on the surface of a catalyst layer while minimizing changes and damage to a polymer electrolyte membrane and a catalyst layer by controlling stretching and stretching conditions during the manufacture of the membrane-electrode assembly.

[0022] The effects of the present invention are not limited to the effects described above, and effects not mentioned will be clearly understood by those skilled in the art from the present specification and the attached drawings.

[0023] Figure 1 is a schematic diagram schematically illustrating the configuration of a membrane-electrode assembly before and after stretching, and shows the process of forming surface roughness due to the stretching.

[0024] Figure 2 is a photograph of the surface of the anode electrode and cathode electrode of the membrane-electrode assembly manufactured in the example before and after stretching.

[0025] Figure 3 is a surface photograph of a membrane-electrode assembly manufactured in Comparative Example 1.

[0026] Figure 4 is a photograph of the surface of the cathode electrode of the membrane-electrode assembly manufactured in Comparative Example 2 after stretching.

[0027] Figure 5 is a photograph of the surface of the cathode electrode of the membrane-electrode assembly manufactured in Comparative Example 3 after stretching.

[0028] Figure 6 shows the performance evaluation results of the membrane-electrode assemblies manufactured in Example 2 and Comparative Examples 1 to 3.

[0029] Figure 7 is a schematic diagram showing the overall configuration of a fuel cell according to one embodiment of the present invention.

[0030] Hereinafter, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0031] To clearly represent various layers and regions in the drawings, the thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there is another element in between. Conversely, when an element is said to be "directly over" another element, it means that there is no other element in between.

[0032] The terms "comprises" and "contains" as used herein are used to list materials, compositions, devices, and methods useful in the present invention, but are not limited to the listed examples.

[0033]

[0034] Hereinafter, a membrane-electrode assembly according to one embodiment of the present invention will be described with reference to the drawings.

[0035] Figure 1 is a schematic diagram schematically illustrating the configuration of a membrane-electrode assembly before (A) and after (B) stretching, and shows the process of forming surface roughness due to the stretching.

[0036] One embodiment of the present invention provides a membrane-electrode assembly (100) including a polymer electrolyte membrane (110); and a catalyst layer (120) provided on at least one surface of the polymer electrolyte membrane (110), wherein the catalyst layer (120) has a surface roughness (121) on the surface.

[0037] According to one embodiment of the present invention, a membrane-electrode assembly can form surface roughness only on the surface of the catalyst layer while minimizing changes and damages to the polymer electrolyte membrane and the catalyst layer by controlling stretching and stretching conditions during the manufacture of the membrane-electrode assembly. In addition, since the surface roughness is formed on the surface of the catalyst layer, the membrane-electrode assembly can mitigate changes due to shrinkage or expansion during operation of the fuel cell, thereby effectively improving the durability of the fuel cell. In addition, the membrane-electrode assembly can improve the bonding strength and interfacial durability due to the increased material transfer characteristics and interfacial bonding area by the surface roughness formed on the surface of the catalyst layer. In addition, by stretching the catalyst layer, the porosity within the catalyst layer is improved, thereby improving the performance of a fuel cell including the membrane-electrode assembly.

[0038] According to one embodiment of the present invention, the membrane-electrode assembly can exhibit excellent performance over a wide temperature range. For example, the membrane-electrode assembly can exhibit excellent performance under temperature conditions of 40°C or more and 130°C or less. As described above, the membrane-electrode assembly can mitigate changes due to shrinkage or expansion during operation of the fuel cell since the surface roughness is formed only on the surface of the catalyst layer. As a result, the membrane-electrode assembly can have excellent durability and electrochemical properties under the temperature conditions at which the fuel cell is operated.

[0039] According to one embodiment of the present invention, the polymer electrolyte membrane (110) may have an ion exchange function that moves hydrogen ions generated at the anode electrode to the cathode electrode. The polymer electrolyte membrane may be a hydrocarbon-based polymer electrolyte membrane, a fluorine-based polymer electrolyte membrane, or a mixture or copolymer of one or more thereof.

[0040] The above hydrocarbon polymer electrolyte membrane may include a hydrocarbon polymer, and the polymer may be selected from styrene, imide, sulfone, phosphazene, ether ether ketone, ethylene oxide, polyphenylene sulfide, or an aromatic group homopolymer or copolymer and derivatives thereof, and these polymers may be used alone or in combination. Manufacturing an electrolyte membrane using a hydrocarbon polymer is cheaper, easier to manufacture, and exhibits higher ionic conductivity than using a fluorinated polymer.

[0041] As the above suitable hydrocarbon membrane, more preferably, at least one selected from the group consisting of sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyetherketone, sulfonated polyetheretherketone, sulfonated poly ether ether ketone, sulfonated poly arylene ether ether ketone, sulfonated poly arylene ether sulfone, sulfonated poly arylene ether benzimidazole, and membranes into which an ion conductor is introduced may be used.

[0042] The above fluorinated polymer electrolyte membrane can be used without any particular restrictions as long as it has mechanical strength and high electrochemical stability sufficient to form a film as an ion-conducting membrane. Specific examples of the fluorinated polymer electrolyte membrane include perfluorosulfonic acid resins, copolymers of tetrafluoroethylene and fluorovinyl ether, etc. The fluorovinyl ether moiety may have the function of conducting hydrogen ions. The above copolymer is sold under the trade name Nafion by DuPont and is therefore commercially available.

[0043] According to one embodiment of the present invention, the thickness of the polymer electrolyte membrane may be 5 μm or more and 30 μm or less. As described below, the polymer electrolyte membrane may have a reduced thickness compared to before stretching due to stretching of the membrane-electrode assembly. That is, the thickness of the polymer electrolyte membrane may refer to the thickness after stretching the membrane-electrode assembly described below. By making the reduced thickness of the polymer electrolyte membrane after stretching fall within the above range, changes or damage to the polymer electrolyte membrane can be minimized, and accordingly, the performance and durability of the fuel cell can be maintained excellently.

[0044] According to one embodiment of the present invention, the polymer electrolyte membrane is not bent by the stretching described below and can have a substantially flat plane shape.

[0045] According to one embodiment of the present invention, an anode electrode may be provided on one surface of the polymer electrolyte membrane (110), and a cathode electrode may be provided on the other surface. An electrode disposed on one surface of the electrolyte membrane (110) that causes an oxidation reaction to generate hydrogen ions and electrons from fuel is called an anode electrode, and an electrode that causes a reduction reaction to generate water from hydrogen ions supplied through the electrolyte membrane (110) and an oxidizing agent of the electrode is called a cathode electrode.

[0046] According to one embodiment of the present invention, the electrode may include a catalyst layer (120). The catalyst layer (120) contains a catalyst. The catalyst may include any metal catalyst particle that can participate in the reaction of the fuel cell and be used as a catalyst. Specifically, the catalyst may include platinum-based catalyst particles. As the platinum-based catalyst, any metal particle selected from the group consisting of platinum, ruthenium, osmium, a platinum-M alloy (wherein M is any transition metal selected from the group consisting of Pd, Ir, Os, Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Mo, W, Rh, Ru, and alloys thereof), and mixtures thereof may be used. For example, the platinum-based catalyst is Pt, Pt-Pd, Pt-Mn, Pt-Sn, Pt-Mo, Pt-Cr, Pt-W, Pt-Ru, Pt-Ni, Pt-Co, Pt-Y, Pt-Ru-W, Pt-Ru-Ir, Pt-Ru-Ni, Pt-Ru-Mo, Pt-Ru-Rh-Ni, Pt-Ru-Sn-W, Pt-Ru-Ir-Ni, Pt-Ru-Ir-Y, 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, It can be Pt-Ni-Ir, Pt-Cr, or Pt-Cr-Ir.

[0047] According to one embodiment of the present invention, based on 100 parts by weight of the catalyst layer, the content of the catalyst may be 30 parts by weight or more and 85 parts by weight or less. At this time, the catalyst may include the above-described catalyst particles and the carrier. The weight ratio of the catalyst particles and the carrier included in the catalyst may be 1:0.5 to 1:1.5. When the content of the catalyst included in the catalyst layer is within the above-described range, the performance of the membrane-electrode assembly can be effectively improved, and a decrease in durability can be suppressed.

[0048] According to one embodiment of the present invention, the catalyst may be a catalyst particle supported on a catalyst carrier. Any catalyst carrier that can be used as a carrier in the field of fuel cell technology may be used. The catalyst carrier may preferably be a carbon-based carrier having excellent electrical conductivity, and the carbon-based carrier may be selected from the group consisting of 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- / meso-porous carbon, carbon aerogel, mesoporous carbon, graphene, stabilized carbon, activated carbon, and a combination of two or more thereof.

[0049] According to one embodiment of the present invention, the catalyst layer may include an ionomer. Any ionomer that can be used in the field of fuel cell technology may be used. The ionomer is intended for hydrogen ion transport and may also function as a binder.

[0050] The ionomer may be a cation conductor having at least one cation exchange group selected from the group consisting of a sulfonic acid group, a carboxyl group, a boronic acid group, a phosphoric acid group, an imide group, a sulfonimide group, a sulfonamide group, a sulfonic acid fluoride group, and combinations thereof. Specifically, the ionomer according to one embodiment of the present invention may be a fluorinated cation conductor having a sulfonic acid group and / or a carboxyl group, a hydrocarbon cation conductor having a sulfonic acid group and / or a carboxyl group, or a mixture thereof. More specifically, the ionomer may be a fluorinated ionomer.

[0051] According to one embodiment of the present invention, the catalyst layer can be manufactured using a catalyst composition. The catalyst composition can include the catalyst and the ionomer. Based on 100 parts by weight of the catalyst composition, the content of the catalyst can be 30 parts by weight or more and 85 parts by weight or less, and the content of the ionomer can be 15 parts by weight or more and 70 parts by weight or less. In this case, the catalyst can include the above-described catalyst particles and the carrier. The weight ratio of the catalyst particles and the carrier included in the catalyst can be 1:0.5 to 1:1.5.

[0052] According to one embodiment of the present invention, the thickness of the catalyst layer may be 1 ㎛ or more and 30 ㎛ or less, 1 ㎛ or more and 25 ㎛ or less, 1 ㎛ or more and 20 ㎛ or less, 1 ㎛ or more and 15 ㎛ or less, or 1 ㎛ or more and 10 ㎛ or less. When the thickness of the catalyst layer is within the above-mentioned range, the reaction area can be prevented from being small and the activity can be prevented from being reduced, and the movement distance of ions and electrons can be suppressed from increasing the resistance.

[0053] According to one embodiment of the present invention, the catalyst layer may have surface roughness. Specifically, the surface of the catalyst layer exposed to the outside may have surface roughness. One side of the catalyst layer may be in contact with the polymer electrolyte membrane, and the other side of the catalyst layer may be exposed to the outside. In this case, the one side and the other side of the catalyst layer may be opposite sides. In other words, the other side of the catalyst layer exposed to the outside may have surface roughness.

[0054] According to one embodiment of the present invention, the surface roughness of the catalyst layer can be formed by stretching the catalyst layer. As described below, by stretching the membrane-electrode assembly including the polymer electrolyte membrane and the catalyst layer in a certain direction, the surface roughness can be formed in the catalyst layer. When using a method of stretching the catalyst layer, the physical properties of the catalyst layer can be easily controlled by linking the thickness and surface roughness of the catalyst layer, compared to when forming the surface roughness by a method such as etching, printing, or embossing. Meanwhile, when using a method such as etching, printing, or embossing, the surface roughness can be formed regularly. In contrast, when using a method of stretching the catalyst layer, a more random surface roughness can be formed in the catalyst layer. When a more random surface roughness is formed on the surface of the catalyst layer, the manufacturing cost and time of the catalyst layer can be effectively reduced, and the physical properties of the catalyst layer can be effectively improved, compared to when forming a regular surface roughness.

[0055] According to one embodiment of the present invention, the surface roughness of the catalyst layer may be provided in a negative shape. When the surface roughness is provided in a negative shape on one surface of the catalyst layer exposed to the outside, deformation, pinholes, and cracks due to shrinkage or expansion of the membrane-electrode assembly can be reduced, and the interfacial adhesion can be improved, while maintaining excellent electrical characteristics of the catalyst layer.

[0056] According to one embodiment of the present invention, the surface roughness of the catalyst layer may be 0.1 ㎛ or more and 6 ㎛ or less. Specifically, the depth of the surface roughness of the catalyst layer may be 0.1 ㎛ or more and 6 ㎛ or less, 0.5 ㎛ or more and 5 ㎛ or less, 0.5 ㎛ or more and 3.5 ㎛ or less, 0.5 ㎛ or more and 2 ㎛ or less, or 0.1 ㎛ or more and 1.5 ㎛ or less. By setting the surface roughness within the above range, deformation or occurrence of pinholes or cracks due to shrinkage or expansion of the membrane-electrode assembly can be reduced, and interfacial adhesion can be improved, while maintaining excellent electrical characteristics of the catalyst layer.

[0057] According to one embodiment of the present invention, the surface roughness of the catalyst layer can be provided in various forms. The form of the surface roughness can vary depending on the thickness and composition of the catalyst layer, the thickness and composition of the polymer electrolyte membrane, and the form and conditions of the stretching. Meanwhile, the surface roughness may have a wave shape. However, the surface roughness may have a form with only concave portions, rather than a form in which both convex and concave portions of the wave appear.

[0058] According to one embodiment of the present invention, the depth of the surface roughness may be 20% or less, 15% or less, or 11% or less with respect to the thickness of the catalyst layer. In addition, the depth of the surface roughness may be 5% or more, 7% or more, or 10% or more with respect to the thickness of the catalyst layer. Referring to FIG. 1, one surface of the catalyst layer (120) is in contact with the polymer electrolyte membrane (110), and the other surface opposite to the one surface of the catalyst layer (120) is exposed to the outside. At this time, the surface roughness (121) may be provided in a negative shape along the direction from the other surface of the catalyst layer (120) toward the one surface. When the ratio of the depth of the surface roughness to the thickness of the catalyst layer is within the above-mentioned range, deformation or occurrence of pinholes or cracks due to shrinkage or expansion of the membrane-electrode assembly can be reduced, and interfacial adhesion can be improved, while the electrical characteristics of the catalyst layer can be maintained excellently.

[0059] According to one embodiment of the present invention, the surface roughness may be irregularly distributed on the surface of the catalyst layer. Here, irregularly distributed may mean that the surface roughness is formed only in a part of the surface of the catalyst layer or is irregularly distributed in several parts of the surface of the catalyst layer. In addition, the depth or shape of each of the plurality of surface roughnesses may be independent of each other. For example, some surface roughnesses may be formed at a depth of 20% of the catalyst layer thickness, and other surface roughnesses may be formed at a depth of 15% of the catalyst layer thickness. In addition, as illustrated in Fig. 1, a plurality of surface roughnesses may be formed on a catalyst layer provided on one side of a polymer electrolyte membrane, and a fewer number of surface roughnesses may be formed on a catalyst layer provided on the other side. The distribution or shape of the surface roughnesses formed on the catalyst layers provided on both sides of the polymer electrolyte membrane may be similar or identical to each other.

[0060] According to one embodiment of the present invention, the area of ​​the surface roughness region of the catalyst layer may be 20% or more and 95% or less of the total active area of ​​the catalyst layer. Specifically, the ratio of the area occupied by the surface roughness region based on the total active area of ​​the catalyst layer may be 20% or more and 90% or less, 30% or more and 90% or less, or 40% or more and 80% or less. By setting the area ratio of the surface roughness region within the above range, deformation or the occurrence of pinholes or cracks due to shrinkage or expansion of the membrane-electrode assembly can be reduced, and the interfacial adhesion can be improved, while the electrical characteristics of the catalyst layer can be maintained excellently.

[0061] The shape of the surface roughness, the depth of the surface roughness, the ratio of the depth of the surface roughness to the thickness of the catalyst layer, the ratio of the area of ​​the surface roughness region to the total active area of ​​the catalyst layer, etc., described above can be calculated through images taken using SME or an optical microscope.

[0062] According to one embodiment of the present invention, a gas diffusion layer (not shown) may be formed on the catalyst layer (120). The gas diffusion layer is arranged between the membrane-electrode assembly and the separator of the fuel cell, and requires high gas diffusivity for diffusing gas supplied from the separator to the catalyst layer, high drainage for discharging water generated along with the electrochemical reaction to the separator, and high conductivity for extracting the generated current. For this reason, a conductive porous substrate having a pore diameter in a range of typically 10 μm to 100 μm is used for the gas diffusion layer.

[0063] The gas diffusion layer may be formed by a conductive porous substrate alone or may further include a conductive porous substrate and a microporous layer formed on one surface of the conductive porous substrate.

[0064] The materials for the conductive porous substrate and microporous layer constituting the gas diffusion layer can be used without limitation as long as they satisfy the porosity or hydrophobicity conditions according to the positions of the electrode segments described above. For example, the conductive porous substrate can be selected from the group consisting of carbon fiber paper, carbon cloth, carbon fiber non-woven fabric, and carbon felt. The conductive porous substrate can be hydrophobic-treated by further including a hydrophobic resin. The hydrophobic resin can be a fluorine-based resin or a silicone-based resin, and examples thereof include PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (perfluoroalkoxyfluorinated resin), ETFA (ethylenetetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), etc. The above microporous layer can be formed by including carbon-based materials such as carbon black, acetylene black, and carbon nanotubes, and fluorine-based resins such as polytetrafluoroethylene and polyvinylidene fluoride (PVdF).

[0065] According to one embodiment of the present invention, as the catalyst layer (120) is provided with surface roughness, the interfacial adhesive force between the catalyst layer and the gas diffusion layer can be increased.

[0066]

[0067] One embodiment of the present invention provides a method for manufacturing a membrane-electrode assembly, comprising: a step of manufacturing a polymer electrolyte membrane; a step of forming a catalyst layer on at least one surface of the polymer electrolyte membrane; a step of manufacturing a membrane-electrode assembly; and a step of forming surface roughness on the catalyst layer by stretching the membrane-electrode assembly.

[0068] Through the manufacturing method of the membrane-electrode assembly according to the present embodiment, the membrane-electrode assembly according to the above-described embodiment can be manufactured. That is, the polymer electrolyte membrane, catalyst layer, surface roughness, catalyst composition, etc. in the membrane-electrode assembly according to the present embodiment may be the same as the polymer electrolyte membrane, catalyst layer, surface roughness, catalyst composition, etc. in the membrane-electrode assembly according to the above-described embodiment.

[0069] According to one embodiment of the present invention, the step of manufacturing the polymer electrolyte membrane can be performed using materials and methods commonly used in the art. For example, the polymer electrolyte membrane can be manufactured using a method of casting a hydrocarbon ionomer dispersion, a fluorinated polymer dispersion, or the like.

[0070] According to one embodiment of the present invention, the step of forming a catalyst layer may include forming a catalyst layer on one side of the polymer electrolyte membrane using a catalyst composition. At this time, the catalyst composition may include the aforementioned catalyst and ionomer. Through a method of transferring a catalyst layer prepared from the catalyst composition, the catalyst layer may be provided on one side, the other side, or both sides of the polymer electrolyte membrane.

[0071] According to one embodiment of the present invention, before the step of performing stretching, a membrane-electrode assembly including a polymer electrolyte membrane and a catalyst layer can be manufactured. The manufacturing of the membrane-electrode assembly can be performed by any of the general membrane-electrode assembly manufacturing methods, specifically, a batch or roll-to-roll decal transfer method or a direct coating method.

[0072] According to one embodiment of the present invention, the stretching is performed after the manufacturing of the membrane-electrode assembly, and can be applied to either a roll-type membrane-electrode assembly or a sheet-type membrane-electrode assembly. Specifically, in the case of a roll-type membrane-electrode assembly, stretching can be performed by winding the electrolyte membrane having the catalyst layer formed thereon while applying tension in an arbitrary stretching direction after manufacturing the membrane-electrode assembly, and in the case of a sheet-type membrane-electrode assembly, stretching can be performed by pulling the electrolyte membrane in an arbitrary stretching direction while the electrolyte membrane having the catalyst layer formed thereon.

[0073] According to one embodiment of the present invention, the stretching may be in the longitudinal (MD), transverse (TD), or biaxial stretching in the longitudinal / transverse directions. In order to minimize changes and damage to the polymer electrolyte membrane and the catalyst layer during stretching, stretching in one direction is preferred, and longitudinal (MD) stretching is more preferred than transverse stretching in terms of processability. Referring to Fig. 1, the X direction may correspond to the longitudinal (MD) direction, and the longitudinal direction may mean the length direction of the membrane-electrode assembly. For example, when the width is longer than the length of the membrane-electrode assembly, the transverse direction may correspond to the longitudinal direction.

[0074] According to one embodiment of the present invention, the stretching may be performed at a stretching speed of 1.0 m / min or less. Specifically, the stretching speed may be 0.9 m / min or less, 0.8 m / min or less, or 0.5 m / min or less. In addition, the stretching speed may be 0.05 m / min or more, 0.1 m / min or more, or 0.3 m / min or more. By performing the stretching under the stretching conditions described above, it may be easy to control the surface roughness to be formed in a negative shape only on the surface of the catalyst layer.

[0075] According to one embodiment of the present invention, the stretching may be performed at a stretching tension of 30 N or less. Specifically, the stretching tension may be 28 N or less, 25 N or less, or 23 N or less. In addition, the stretching tension may be 6 N or more, 10 N or more, 15 N or more, or 18 N or more. At this time, the stretching tension conditions may be conditions during stretching using a roll-to-roll process. By performing the stretching under the stretching conditions described above, it may be easy to control the surface roughness to be formed in an engraved shape only on the surface of the catalyst layer.

[0076] According to one embodiment of the present invention, the stretching may be performed so that the thickness reduction rate of the polymer electrolyte membrane becomes 5% or less. As the membrane-electrode assembly is stretched, the thickness of the polymer electrolyte membrane may be reduced. That is, the thickness reduction rate refers to the rate at which the thickness of the polymer electrolyte membrane is reduced after stretching, based on the thickness of the polymer electrolyte membrane before stretching. The thickness reduction rate of the polymer electrolyte membrane may be 1% or more and 5% or less, 1% or more and 3% or less, or 1% or more and 2% or less. When stretching is performed so that the thickness reduction rate of the polymer electrolyte membrane satisfies the above-mentioned range, the polymer electrolyte membrane can be prevented from being damaged or changed during the stretching process.

[0077] According to one embodiment of the present invention, the stretching may be performed so that the thickness reduction rate of the catalyst layer becomes 5% or less. The thickness reduction rate refers to the ratio of the thickness of the catalyst layer reduced after stretching based on the thickness of the catalyst layer before stretching. The thickness reduction rate of the catalyst layer may be 1% or more and 5% or less, 1% or more and 3% or less, or 1% or more and 2% or less. When stretching is performed so that the thickness reduction rate of the catalyst layer satisfies the above-mentioned range, the catalyst layer can be prevented from being damaged or changed during the stretching process.

[0078] According to one embodiment of the present invention, the stretching may be performed so that the length change rate of the active area of ​​the catalyst layer is 8% or less. Specifically, the length change rate of the active area of ​​the catalyst layer may refer to a length increase rate. In addition, the length change rate of the active area of ​​the catalyst layer may be 1% or more and 8% or less, 3% or more and 7% or less, or 5% or more and 7% or less. Here, the length change rate of the active area may refer to a length change of a longer axis or a length change in a longitudinal direction among the active areas. By making the length change rate of the active area of ​​the catalyst layer within the above range, the catalyst layer can be prevented from being damaged or changed during the stretching process.

[0079]

[0080] A fuel cell according to one embodiment of the present invention includes the membrane-electrode assembly and may be, for example, a fuel cell that uses hydrogen gas as fuel.

[0081] Figure 7 is a schematic diagram showing the overall configuration of a fuel cell.

[0082] Referring to FIG. 7, a fuel cell (200) includes a fuel supply unit (210) that supplies a mixed fuel in which fuel and water are mixed, a reformer 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 reformer unit (220) and an oxidizer, and an oxidizer supply unit (240) that supplies an oxidizer to the reformer unit (220) and the stack (230).

[0083] The stack (230) has a plurality of unit cells that generate electrical energy by inducing an oxidation / reduction reaction of a reforming gas containing hydrogen gas supplied from a reforming unit (220) and an oxidizing agent supplied from an oxidizing agent supply unit (240).

[0084] Each unit cell refers to a unit cell that generates electricity, and includes a membrane-electrode assembly that oxidizes / reduces oxygen in a reformed gas containing hydrogen gas and an oxidizer, and a separator (also called a bipolar plate, hereinafter referred to as a "separator") for supplying the reformed gas containing hydrogen gas and the oxidizer 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 plates located at the outermost sides of the stack are also specifically referred to as end plates.

[0085] Among the separators, the end plate is provided with a first supply pipe (231) in the shape of a pipe for injecting reformed gas containing hydrogen gas supplied from a reforming unit (220), and a second supply pipe (232) in the shape of a pipe for injecting oxygen gas, and the other end plate is provided with a first discharge pipe (233) for discharging reformed gas containing hydrogen gas that is ultimately unreacted and remaining in a plurality of unit cells to the outside, and a second discharge pipe (234) for discharging oxidant that is ultimately unreacted and remaining in the unit cells to the outside.

[0086] In the above fuel cell, except that the membrane-electrode assembly (100) according to one embodiment of the present invention is used, the separator, fuel supply unit, and oxidant supply unit constituting the electricity generation unit are used in a typical fuel cell, and therefore, a detailed description thereof is omitted herein.

[0087] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0088]

[0089] [Example 1]

[0090] 1-(1): Fabrication of membrane-electrode assembly

[0091] A catalyst was prepared in which Pt catalyst particles with a particle size of approximately 30 to 200 nm were supported on a carrier (carbon black) at a loading ratio of 50 wt%. The catalyst was mixed with a fluorinated ionomer (Nafion D2020) to prepare a catalyst composition. At this time, based on 100 wt% of the catalyst composition, the content of the catalyst (50% Pt / C) was 50 wt%, and the content of the fluorinated ionomer was 50 wt%.

[0092] Thereafter, the above catalyst composition was applied to the transfer substrate to a thickness of 7 μm.

[0093] A hydrocarbon-based polymer electrolyte membrane (thickness: 20 ㎛) was manufactured by casting a hydrocarbon-based ionomer (polyphenylene-based) dispersion.

[0094] Thereafter, the manufactured catalyst layer was transferred to each of the two surfaces (upper and lower surfaces) of the manufactured polymer electrolyte membrane to obtain a membrane-electrode assembly. At this time, the thickness of the catalyst layer was approximately 6.8 μm.

[0095]

[0096] 1-(2): Manufacturing of membrane-electrode assembly (formation of surface roughness)

[0097] The membrane-electrode assembly manufactured in the above 1-(1) was stretched in the longitudinal direction (length direction) at a stretching speed of 0.3 m / min until the length of the catalyst layer increased by 5% compared to the original length. Through this, a membrane-electrode assembly including a catalyst layer having surface roughness was finally obtained.

[0098] At this time, the change rate in the thickness of the polymer electrolyte membrane was 1%, the change rate in the thickness of the catalyst layer was 1%, the change rate in the length of the active area of ​​the catalyst layer was 5%, and the depth of the surface roughness was 0.75 ㎛ on average, which was 11% of the total thickness of the catalyst layer.

[0099]

[0100] [Example 2]

[0101] A membrane-electrode assembly was manufactured in the same manner as in Example 1, except that a fluorinated polymer (Nafion D2020) dispersion was used instead of a hydrocarbon ionomer dispersion to manufacture a fluorinated polymer electrolyte membrane (thickness: 15 μm). At this time, the thickness of the catalyst layer was approximately 6.9 μm.

[0102] Thereafter, the manufactured membrane-electrode assembly was stretched in a roll state at a stretching speed of 0.3 m / min and a stretching tension of 20 N until the length of the catalyst layer increased by 7% compared to the original length. Through this, a membrane-electrode assembly including a catalyst layer with surface roughness was finally obtained.

[0103] At this time, the change rate of the thickness of the polymer electrolyte membrane was 2%, the change rate of the thickness of the catalyst layer was 2%, the change rate of the active area length of the catalyst layer was 7%, and the depth of the surface roughness was 1.03 ㎛ on average, which was 15% of the total thickness of the catalyst layer.

[0104]

[0105] [Comparative Example 1]

[0106] In the above Example 1, the membrane-electrode assembly of 1-(1) was used as is without performing the surface roughness formation step of 1-(2).

[0107]

[0108] [Comparative Example 2]

[0109] In the above Example 2, a membrane-electrode assembly was manufactured in the same manner as in the above Example 2, except that the stretching tension condition was changed from 20 N to 35 N.

[0110] At this time, the change rate of the thickness of the polymer electrolyte membrane was 4%, the change rate of the thickness of the catalyst layer was 4%, the change rate of the active area length of the catalyst layer was 9%, and the depth of the surface roughness was 3.9 ㎛ on average, which was 50% of the total thickness of the catalyst layer.

[0111]

[0112] [Comparative Example 3]

[0113] In the above Example 2, a membrane-electrode assembly was manufactured in the same manner as in the above Example 2, except that the stretching tension condition was changed from 20 N to 45 N.

[0114] At this time, the change rate in the thickness of the polymer electrolyte membrane was 6%, the change rate in the thickness of the catalyst layer was 7%, the change rate in the length of the active area of ​​the catalyst layer was 11%, and the depth of the surface roughness was 6.8 ㎛ on average, which was 98% of the total thickness of the catalyst layer.

[0115]

[0116] [Experimental Example 1] Surface and Characteristic Observation

[0117] Figure 2 is a photograph of the surface of the anode electrode and cathode electrode of the membrane-electrode assembly manufactured in the example before and after stretching.

[0118] In order to observe the electrode surface before and after each stretching in Examples 1 and 2, the surface was photographed using an optical microscope, and the results are shown in Fig. 2. At this time, (A) of Fig. 2 corresponds to Example 1, and (B) of Fig. 2 corresponds to Example 2. Referring to Fig. 2, it was confirmed that a large number of surface roughnesses were generated in the catalyst layer after stretching compared to before stretching.

[0119]

[0120] Fig. 3 is a surface photograph of a membrane-electrode assembly manufactured in Comparative Example 1, Fig. 4 is a surface photograph of a cathode electrode of a membrane-electrode assembly manufactured in Comparative Example 2 after stretching, and Fig. 5 is a surface photograph of a cathode electrode of a membrane-electrode assembly manufactured in Comparative Example 3 after stretching.

[0121] In order to observe the surface roughness of the catalyst layer in the membrane-electrode assembly manufactured in Example 1, Example 2, and Comparative Examples 1 to 3, surface images were taken using an optical microscope.

[0122] Referring to Fig. 2, it was confirmed that in the cases of Examples 1 and 2, engraved portions were irregularly formed on the surface. Specifically, in the case of Example 1, it was confirmed that a shape in which flat rhombus shapes were irregularly intersected with a small surface roughness was formed. In the case of Example 2, it was confirmed that triangular prisms with a larger roughness were irregularly intersected.

[0123] Meanwhile, referring to Fig. 3, it was confirmed that in the case of Comparative Example 1, no surface roughness was formed on the catalyst layer. Referring to Fig. 4, it was confirmed that in Comparative Example 2, the surface roughness had a shape in which triangular prisms intersected irregularly with a deeper depth, and some of the surface roughness had cracks that reached the surface of the polymer electrolyte membrane. Referring to Fig. 5, it was confirmed that in Comparative Example 3, the surface roughness had cracks that reached the surface of the polymer electrolyte membrane, and some of them had fallen off from the electrode.

[0124]

[0125] [Experimental Example 2] Performance Evaluation of Membrane-Electrode Assembly (80℃, 50RH Conditions)

[0126] Figure 6 shows the performance evaluation results of the membrane-electrode assemblies manufactured in Example 2 and Comparative Examples 1 to 3.

[0127] The membrane-electrode assemblies manufactured in the above comparative examples and examples were evaluated for output performance through IV measurements. Specifically, to confirm the output performance under actual fuel cell operating conditions, the membrane-electrode assembly was used in a fuel cell unit cell evaluation device (Scribner 850 fuel cell test system). At this time, hydrogen (50% RH) and air (50% RH) were supplied to the anode and cathode in amounts corresponding to the stoichiometry of 1.2 / 2.0 at a temperature of 80°C. The current density was measured when the voltage was 0.6 V, and the results are shown in Fig. 6.

[0128] Referring to Fig. 6, it was confirmed that the membrane-electrode assembly manufactured in Example 2 exhibited superior output performance compared to Comparative Examples 1 to 3.

[0129]

[0130] [Experimental Example 3] Durability Evaluation of Membrane-Electrode Assembly (Wet-Dry Durability)

[0131] The physical durability of each membrane-electrode assembly was evaluated based on the durability assessment protocol of the U.S. Department of Energy (DOE). Specifically, to evaluate the physical durability of the membrane-electrode assembly, the H2 crossover was measured after 20,000 wet / dry cycles were performed, and the measured values ​​are shown in Table 1 below.

[0132]

[0133] wet / dry cycle(20,000 cycles)H2crossover @0.2V(mA / cm 2 ) Example 13.4 Example 24.3 Comparative Example 15.5 Comparative Example 210.3 Comparative Example 325.5

[0134] Referring to Table 1 above, it can be seen that the membrane-electrode assemblies manufactured in Examples 1 and 2 have superior physical durability compared to Comparative Examples 1 to 3.

[0135]

[0136] Although the preferred embodiments of the present invention have been described in detail above, the above-described embodiments are presented as specific examples of the present invention, and the present invention is not limited thereby, and the scope of the present invention includes various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the claims to be described later.

[0137] [Explanation of symbols]

[0138] 100: Membrane-electrode assembly

[0139] 110: Polymer electrolyte membrane

[0140] 120: Catalyst layer 121: Surface roughness

[0141] 200: Fuel cell

[0142] 210: Fuel supply section 220: Reforming section

[0143] 230: Stack 231: First supply pipe

[0144] 232: Second supply pipe 233: First discharge pipe

[0145] 234: Second discharge pipe 240: Oxidizer supply section

Claims

1. Polymer electrolyte membrane; and A catalyst layer provided on at least one surface of the polymer electrolyte membrane; The above catalyst layer is a membrane-electrode assembly having a surface roughness on the surface.

2. In paragraph 1, A membrane-electrode assembly in which the surface roughness of the catalyst layer is formed by stretching the catalyst layer.

3. In paragraph 1, A membrane-electrode assembly wherein the surface roughness of the catalyst layer is 0.1 ㎛ or more and 6 ㎛ or less.

4. In paragraph 1, A membrane-electrode assembly in which the surface roughness of the above catalyst layer is provided in a negative shape.

5. In paragraph 4, A membrane-electrode assembly wherein the depth of the surface roughness is 20% or less of the thickness of the catalyst layer.

6. In paragraph 4, A membrane-electrode assembly wherein the above surface roughness is irregularly distributed on the surface of the catalyst layer.

7. In paragraph 1, A membrane-electrode assembly, wherein the area of ​​the surface roughness region of the catalyst layer is 20% or more and 95% or less of the total active area of ​​the catalyst layer.

8. In paragraph 1, The thickness of the polymer electrolyte membrane is 5 ㎛ or more and 30 ㎛ or less, A membrane-electrode assembly wherein the thickness of the catalyst layer is 1 ㎛ or more and 30 ㎛ or less.

9. Step of manufacturing a polymer electrolyte membrane; A step of manufacturing a membrane-electrode assembly by forming a catalyst layer on at least one surface of the polymer electrolyte membrane; A method for manufacturing a membrane-electrode assembly, comprising: a step of forming surface roughness on the catalyst layer by stretching the membrane-electrode assembly.

10. In paragraph 9, A method for manufacturing a membrane-electrode assembly, wherein the above stretching is performed in the longitudinal direction (MD direction).

11. In paragraph 9, A method for manufacturing a membrane-electrode assembly, wherein the above stretching is performed at a stretching speed of 1.0 m / min or less.

12. In paragraph 9, A method for manufacturing a membrane-electrode assembly, wherein the above stretching is performed at a stretching tension of 30 N or less.

13. In paragraph 9, A method for manufacturing a membrane-electrode assembly, wherein the above stretching is performed so that the thickness reduction rate of the polymer electrolyte membrane is 5% or less.

14. In paragraph 9, A method for manufacturing a membrane-electrode assembly, wherein the above stretching is performed so that the length change rate of the active area of ​​the catalyst layer is 8% or less.

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