Electrode for fuel cell, membrane-electrode assembly, and method for manufacturing same

Abstract

The present invention relates to an electrode for a fuel cell, a membrane-electrode assembly including the same, and a method for manufacturing the same. More specifically, the electrode for a fuel cell of the present invention, specifically the anode, separates a water electrolysis catalyst from an electrode catalyst, and provides a gradient of hydrophobicity and water absorption in the catalyst layer, thereby allowing water to move easily in the water electrolysis catalyst layer. This significantly improves reverse voltage durability while maintaining the same output performance as conventional electrodes.

Description

[Technical Field]

[0001] The present invention relates to an electrode for a fuel cell, a membrane-electrode assembly, and a method for manufacturing the same. [Background technology]

[0002]

[0003] A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon materials such as methanol, ethanol, and natural gas into electrical energy. A representative example of such a fuel cell is the polymer electrolyte membrane fuel cell (PEMFC). Due to advantages such as a low operating temperature of less than 100°C, fast start-up and response characteristics, and excellent durability, the PEMFC is gaining attention as a power source for portable, vehicular, and home use.

[0004] The membrane electrode assembly (MEA), which actually generates electricity in the fuel cell system, 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 located on either side of an electrolyte membrane. The electrolyte is an electrically insulating but ionically conductive membrane, and protons generated at the anode pass through the membrane to the cathode, where they combine with oxygen to produce water.

[0005] Fuel cell systems can experience fuel starvation for various reasons during operation. When water or ice clogs the fuel cell channel or when there is a problem with the hydrogen supply system, the carbon support at the anode is oxidized and exposed to a reverse voltage. If this reverse voltage situation occurs repeatedly, the corrosion of the carbon support accelerates, severely damaging the electrode catalyst.

[0006] The reaction occurring in the anode catalyst layer is a hydrogen oxidation reaction (HOR), which is shown in Formula 1 below.

[0007] 2H2→4H + +4e - Formula (1)

[0008] When the supply of hydrogen is interrupted, a carbon oxidation reaction occurs as shown in the following formula 2, and the platinum supported on the carbon is lost, resulting in catalyst degradation.

[0009] C+H20→CO2+4H + +4e - , C + H20 → CO + 2H + +2e - Formula (2)

[0010] To solve this problem, a typical method is to protect the platinum catalyst by adding a catalyst that can induce an oxygen evolution reaction (OER) within the electrode so that a potential that accelerates corrosion of the carbon support does not form. The OER reaction is shown in Equation 3 below.

[0011] 2H2O→O2+4H + +4e - Formula (3)

[0012] [1] OER or water electrocatalysts are generally made of IrO2, RuO2, TiO2, Ir x Sn 1-x O2, PtIr, IrRu catalysts, etc. have been used. [2] In addition, a method has been proposed to improve durability by placing an OER reaction catalyst between the anode catalyst layer and the electrolyte membrane, or between the gas diffusion layer and the anode catalyst layer.

[0013] However, when an OER or water electrocatalyst is mixed with a platinum catalyst as in [1], the hydrogen oxidation reaction required for a fuel electrode catalyst is reduced. The presence of metals such as Ir or Ru around platinum, which has the highest hydrogen oxidation potential, can affect hydrogen oxidation activity. This can lead to increased overvoltage during hydrogen oxidation at the anode, resulting in reduced output performance. Furthermore, when oxides are used, they can cause lower electrical conductivity than a catalyst layer made solely of carbon, resulting in a decrease in overall cell output. Furthermore, when a separate catalyst layer made of an OER or water electrocatalyst is placed between the catalyst layer and the electrolyte membrane as in [2], the resistance to hydrogen proton transfer increases, resulting in reduced output, which needs to be addressed. Summary of the Invention [Problem to be solved by the invention]

[0014]

[0015] An object of the present invention is to provide an electrode for a fuel cell that has significantly improved reverse voltage durability without causing an increase in overvoltage or an increase in hydrogen proton transport resistance, a membrane-electrode assembly including the same, and a method for manufacturing the same. [Means for solving the problem]

[0016]

[0017] One embodiment of the present invention provides a fuel cell electrode comprising: a first catalyst layer containing a water electrolysis catalyst; a second catalyst layer provided on the first catalyst layer; and a third catalyst layer having water-absorbing properties provided on the second catalyst layer.

[0018] According to one embodiment of the present invention, the water electrolysis catalyst may include at least one oxygen evolution reaction catalyst selected from the group consisting of a metal selected from the group consisting of Li, Co, Ni, Zn, Fe, Ti, Na, Mn, Cu, Ga, Sn, Cr, W, Ru, Ir, Pt, Au, and alloys thereof, an oxide of the metal, a sulfide of the metal, and a carbide of the metal.

[0019] According to one embodiment of the present invention, the oxygen generation reaction catalyst is selected from the group consisting of IrO2, RuO2, TiO2, and Ir x Sn 1-x It may contain at least one selected from the group consisting of O2 (where x is a number greater than 0 and less than 1), PtIr, and IrRu.

[0020] According to one embodiment of the present invention, the first catalyst layer may further contain a water-repellent material.

[0021] According to one embodiment of the present invention, the water-repellent material may include at least one selected from the group consisting of a water-repellent resin, graphitized carbon, hydrophobically treated carbon, and hydrophobic silica.

[0022] According to one embodiment of the present invention, the water-repellent material may include hydrophobic silica surface-treated with at least one selected from the group consisting of methyl, difluoromethyl, ethyl, fluoroethyl, propyl, isopropyl, and 3-fluoropropyl.

[0023] According to one embodiment of the present invention, the content of the water repellent material may be 0.05 wt % to 3 wt % based on the total weight of the first catalyst layer.

[0024] According to one embodiment of the present invention, the first catalyst layer may have a surface contact angle of 70° or more and 160° or less, and the third catalyst layer may have a surface contact angle of 20° or more and 60° or less.

[0025] According to one embodiment of the present invention, the first catalyst layer includes a first catalyst and a first ion-conducting polymer, the second catalyst layer includes a second catalyst and a second ion-conducting polymer, and the third catalyst layer includes a third catalyst and a third ion-conducting polymer, and the first catalyst, second catalyst, and third catalyst may be the same as or different from one another, and the first ion-conducting polymer, second ion-conducting polymer, and third ion-conducting polymer may be the same as or different from one another.

[0026] According to one embodiment of the present invention, the first catalyst, the second catalyst, and the third catalyst may each independently include a platinum-based catalyst.

[0027] According to one embodiment of the present invention, the second catalyst layer may be thicker than the first catalyst layer and the third catalyst layer.

[0028] According to one embodiment of the present invention, the second catalyst layer may have a thickness of 5 μm or more and 20 μm or less.

[0029] According to one embodiment of the present invention, the third catalyst layer may further contain a water-absorbing material.

[0030] According to one embodiment of the present invention, the water-absorbing material may include at least one selected from the group consisting of hydrophilic resin, hydrophilically surface-treated carbon, hydrophilically surface-treated silica, large surface area carbon, and large surface area water-absorbing silica.

[0031] According to one embodiment of the present invention, the content of the water absorbing material may be 0.05 wt % or more and 5 wt % or less based on the total weight of the third catalyst layer.

[0032] According to one embodiment of the present invention, the electrode may be used as an anode of a fuel cell.

[0033] One embodiment of the present invention provides a method for manufacturing a membrane-electrode assembly including the electrode, the method including the steps of forming a second catalyst layer on a substrate, forming a third catalyst layer on the second catalyst layer, bonding the third catalyst layer to a polymer electrolyte membrane, removing the substrate, forming a first catalyst layer on the second catalyst layer, and bonding the first catalyst layer to a gas diffusion layer.

[0034] One embodiment of the present invention provides a membrane-electrode assembly including a polymer electrolyte membrane, an anode provided on one side of the polymer electrolyte membrane, a cathode provided on the other side of the polymer electrolyte membrane, and a gas diffusion layer provided on the anode and the cathode, wherein the anode is the electrode, the first catalyst layer of the anode is adjacent to the gas diffusion layer, and the third catalyst layer is adjacent to the polymer electrolyte membrane.

[0035] One embodiment of the present invention provides a fuel cell comprising the membrane-electrode assembly. [Effects of the Invention]

[0036]

[0037] In the present invention, the water electrolysis catalyst is separated from the electrode catalyst to form a fuel electrode structure, thereby suppressing an increase in overvoltage during hydrogen oxidation and forming a structure that does not affect the transport of hydrogen protons. In addition, an increase in electrical resistance and an increase in hydrogen oxidation overvoltage are suppressed, thereby preventing a decrease in output power.

[0038] In addition, by creating a gradient of hydrophobicity and water absorption in the catalyst layer and forming a structure that allows water to move easily in the water electrolysis catalyst layer, it is possible to significantly improve the reverse voltage durability of existing anode catalyst layers while achieving the same membrane-electrode assembly output performance as conventional catalyst layers.

[0039] The effects of the present invention are not limited to the effects described above, and effects not mentioned herein will be clearly understood by those skilled in the art from the present specification and the accompanying drawings. [Brief explanation of the drawings]

[0040]

[0041] [Figure 1] 1 is a cross-sectional view schematically illustrating a membrane-electrode assembly including an electrode according to one embodiment of the present invention.

[0042] [Figure 2] 1 is a schematic diagram showing the overall configuration of a fuel cell according to an embodiment of the present invention;

[0043] [Figure 3] The membrane-electrode assemblies produced in the comparative examples of the present invention are shown schematically, with (a), (b), and (c) of FIG. 3 showing Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0044]

[0045] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will now be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily understand and practice the present invention. However, as the present invention may be embodied in various different forms, it is not limited to the embodiments set forth herein.

[0046] In the drawings, the thickness of various layers and regions is exaggerated for clarity, and similar parts are designated by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is described as being "on" or "above" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part between them. Conversely, when a part is described as being "directly on" another part, it means that there is no other part between them.

[0047] As used herein, the terms "comprises" and "contains" are used to list materials, compositions, devices, and methods useful in the present invention, and are not intended to be limiting to the examples listed.

[0048]

[0049] Hereinafter, a fuel cell electrode according to one embodiment will be described with reference to FIG.

[0050] In one embodiment of the present invention, a fuel cell electrode is provided, which includes a first catalyst layer 21 containing a water electrolysis catalyst, a second catalyst layer 22 provided on the first catalyst layer 21, and a third catalyst layer 23 having water-absorbing properties and provided on the second catalyst layer 22.

[0051] According to one embodiment of the present invention, the first catalyst layer 21 may include a water electrolysis catalyst (first catalyst). When a fuel shortage occurs in a conventional fuel cell, a high potential is applied to the electrodes, particularly the anode. This can cause a carbon oxidation reaction at the anode, which can oxidize the catalyst and reduce durability. In contrast, in one embodiment of the present invention, the use of the first catalyst layer 21 allows a water splitting reaction to occur at the anode, protecting the catalyst and improving durability.

[0052] According to one embodiment of the present invention, the water electrolysis catalyst (first catalyst) may include an oxygen evolution reaction (OER) catalyst. Specifically, the oxygen evolution reaction catalyst (OER catalyst) may include at least one selected from the group consisting of a metal selected from the group consisting of Li, Co, Ni, Zn, Fe, Ti, Na, Mn, Cu, Ga, Sn, Cr, W, Ru, Ir, Pt, Au, and alloys thereof, an oxide of the metal, a sulfide of the metal, and a carbide of the metal, but is not limited thereto. More specifically, the OER catalyst may include a metal selected from the group consisting of Ir, Ru, Ti, Sn, Pt, and alloys thereof, or an oxide of the metal. For example, the OER catalyst may include IrO2, RuO2, TiO2, Ir x Sn 1-xThe metal oxide may include at least one selected from the group consisting of O2 (where x is a number greater than 0 and less than 1), PtIr, and IrRu. In this case, the metal oxide may have an average particle size of 1 nm or more and 6 nm or less.

[0053] According to one embodiment of the present invention, the water electrocatalyst may be supported on a conductive support. Supporting the water electrocatalyst on a support may further improve catalytic activity and stability. The conductive support for the water electrocatalyst may be a carbon-based support such as graphite, denka black, ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, carbon nanowires, activated carbon, etc.

[0054] According to one embodiment of the present invention, the water electrolysis catalyst (first catalyst) has a metal concentration of 0.001 mg / cm 3 from the water electrolysis catalyst in the first catalyst layer 21. 2 More than 0.3mg / cm 2 Below, 0.005mg / cm 2 More than 0.25mg / cm 2 Below, 0.01mg / cm 2 More than 0.2mg / cm 2 Below, 0.01mg / cm 2 More than 0.1mg / cm 2 Below, 0.01mg / cm 2 More than 0.05mg / cm 2 Below, 0.001mg / cm 2 More than 0.01mg / cm 2 or less, or 0.005 to 0.1 mg / cm 2 By setting the amount of the water electrolysis catalyst within the above range, it is possible to improve the reverse voltage durability without deteriorating the performance of the fuel cell.

[0055] According to one embodiment of the present invention, the first catalytic layer 21 may further contain a water-repellent material. Since it is necessary to suppress water penetration to some extent so that water is preferentially decomposed in the first catalytic layer including the water electrolysis catalyst, the first catalytic layer 21 may contain a water-repellent material.

[0056] According to one embodiment of the present invention, the water-repellent material may specifically include at least one selected from the group consisting of a water-repellent resin, graphitized carbon, hydrophobically treated carbon, and hydrophobic silica, but is not necessarily limited thereto.

[0057] The water-repellent resin may be at least one selected from the group consisting of fluorine-based resins, such as polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, fluorinated ethylene propylene, polychlorotrifluoroethylene, and copolymers thereof.

[0058] According to one embodiment of the present invention, the hydrophobically treated carbon and the hydrophobic silica may be carbon and silica surface-treated with a hydrophobic functional group, which may be one or more functional groups selected from the group consisting of alkyl groups, haloalkyl groups, halo groups, alkenyl groups, phenyl groups, organosilicon groups, and combinations thereof, but is not limited thereto.

[0059] The alkyl group may be a linear or branched alkyl group having 1 to 10 carbon atoms. The halo group may be a chloro group, a fluoro group, a bromo group, or an iodo group. The haloalkyl group may be a linear or branched alkyl group having 1 to 10 carbon atoms and containing one or more halogen atoms, such as chlorine, fluorine, or bromine. The alkenyl group may be a linear or branched alkenyl group having 2 to 10 carbon atoms. The organosilicon group may contain at least one group selected from the group consisting of an alkyl group, a haloalkyl group, a halo group, an alkenyl group, and a phenyl group. For example, the hydrophobically treated carbon or hydrophobic silica may be surface-treated with at least one group selected from the group consisting of methyl, difluoromethyl, ethyl, fluoroethyl, propyl, isopropyl, 3-fluoropropyl, methylsilyl, dimethylsilyl, and trimethylsilyl. Using the surface-treated hydrophobic silica as the water-repellent material can further improve the reverse voltage durability of the electrode.

[0060] According to one embodiment of the present invention, the content of the water-repellent material may be 0.05 wt % to 3 wt %, 0.1 wt % to 3 wt %, 0.1 wt % to 2 wt %, 0.1 wt % to 1 wt %, 0.1 wt % to 0.5 wt %, 0.5 wt % to 1 wt %, 0.4 wt % to 3 wt %, or 0.45 wt % to 2 wt %, based on the total weight of the first catalytic layer. By adding the water-repellent material in an amount within this range, it is possible to strike an appropriate balance between preventing water penetration so that water splitting can occur preferentially in the first catalytic layer 21 and preventing the first catalytic layer 21 from being unable to retain water and preventing water splitting from occurring.

[0061] According to one embodiment of the present invention, the first catalyst layer 21 may contain a catalyst and an ion-conducting polymer contained in a catalyst layer of a typical fuel cell electrode for a cell reaction. The first catalyst and the first ion-conducting polymer used in the first catalyst layer 21 may be the same as or different from those used in the second catalyst layer 22 and the third catalyst layer 23 described below. For an explanation of the first catalyst and the first ion-conducting polymer, please refer to the description of the second catalyst layer 22 described below.

[0062] According to one embodiment of the present invention, the first catalytic layer 21 may further contain a water-repellent material, thereby becoming a catalytic layer with relatively higher hydrophobicity than the second and third catalytic layers. However, the inclusion of the water-repellent material does not necessarily mean that the first catalytic layer 21 itself is hydrophobic. Depending on the type and content of the water-repellent material, the first catalytic layer 21 itself may become hydrophobic or approach hydrophobic.

[0063] According to one embodiment of the present invention, the first catalyst layer 21 may have a surface contact angle of 70° to 160°, 70° to 140°, 70° to 120°, 70° to 110°, 70° to 100°, or 95° to 110°. The contact angle is the water contact angle at room temperature, measured by dropping a water droplet on a substrate such as the first catalyst layer and then analyzing the image to determine the end point of the water droplet curve and the contact point with the substrate surface. A surface with a surface contact angle of 90° or more is a hydrophobic surface, and a surface contact angle of less than 90° is a hydrophilic surface.

[0064] According to one embodiment of the present invention, the first catalyst layer 21 may have a thickness of 0.1 μm to 5 μm, 0.5 μm to 3 μm, 1 μm to 2 μm, 0.5 μm to 2 μm, or 3 μm to 5 μm. By setting the thickness within the above range, it is possible to improve the reverse voltage durability without degrading the performance of the fuel cell.

[0065]

[0066] According to one embodiment of the present invention, the second catalyst layer 22 may be a catalyst layer commonly used in fuel cell electrodes. The second catalyst layer 22 may contain a second catalyst and a second ion-conducting polymer. The second catalyst may be the same as or different from the first catalyst or a third catalyst described below. The second ion-conducting polymer may be the same as or different from the first ion-conducting polymer or a third ion-conducting polymer described below.

[0067] According to one embodiment of the present invention, the second catalyst can be any catalyst that participates in the cell reaction and is generally usable as a catalyst for a fuel cell, preferably a platinum-based metal.

[0068] According to one embodiment of the present invention, the platinum-based metal is platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), osmium (Os), platinum-M alloy (wherein M is 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), or the like. The platinum-based catalytic metal may include one selected from the group consisting of one or more metals selected from the group consisting of platinum (Zn), tin (Sn), molybdenum (Mo), tungsten (W), lanthanum (La), and rhodium (Rh), non-platinum alloys, and combinations thereof. More preferably, a combination of two or more metals selected from the platinum-based catalytic metal group may be used, but is not limited thereto, and any platinum-based catalytic metal usable in the art may be used without limitation.

[0069] Specifically, the platinum alloy may be selected from the group consisting of Pt-Pd, Pt-Sn, Pt-Mo, Pt-Cr, Pt-W, Pt-Ru, Pt-Ru-W, Pt-Ru-Mo, Pt-Ru-Rh-Ni, Pt-Ru-Sn-W, Pt-Co, Pt-Co-Ni, Pt-Co-Fe, Pt-Co-Ir, Pt-Co-S, Pt-Co-P, Pt-Fe, Pt-Fe-Ir, Pt-Fe-S, Pt-Fe-P, Pt-Au-Co, Pt-Au-Fe, Pt-Au-Ni, Pt-Ni, Pt-Ni-Ir, Pt-Cr, Pt-Cr-Ir, and combinations thereof, and may be used alone or in combination of two or more.

[0070] In addition, the non-platinum alloy may be selected from the group consisting of Ir-Fe, Ir-Ru, Ir-Os, Co-Fe, Co-Ru, Co-Os, Rh-Fe, Rh-Ru, Rh-Os, Ir-Ru-Fe, Ir-Ru-Os, Rh-Ru-Fe, Rh-Ru-Os, and combinations thereof, and may be used alone or in combination of two or more.

[0071] Such a catalyst can be used as a catalyst black or can be supported on a carrier.

[0072] According to one embodiment of the present invention, the support may be selected from carbon-based supports, porous inorganic oxides such as zirconia, alumina, titania, silica, and ceria, zeolites, etc. The carbon-based support may be selected from graphite, super P, carbon fiber, carbon sheet, carbon black, Ketjen Black, Denka Black, acetylene black, carbon nanotubes (CNTs), carbon spheres, carbon ribbons, fullerenes, activated carbon, carbon nanofibers, carbon nanowires, carbon nanoballs, carbon nanohorns, carbon nanocages, carbon nanorings, ordered nano- / meso-porous 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.

[0073] According to one embodiment of the present invention, the catalyst may be located on the surface of the support, or may penetrate into the support while filling the pores inside the support. When a metal supported on a support is used as the catalyst, a commercially available product may be used, or a metal may be prepared by supporting the metal on a support.

[0074] According to one embodiment of the present invention, the content of the second catalyst may be 20 wt % or more and 80 wt % or less based on the total weight of the second catalyst layer. Alternatively, the second catalyst may be present in the second catalyst layer 22 in a concentration of 0.05 mg / cm of metal from the second catalyst. 2 More than 1mg / cm 2 Below, for example, 0.1 mg / cm 2 More than 0.8mg / cm 2 The catalyst may be used in an amount falling within the range below. By setting the amount of the catalyst within the above range, the catalytic activity can be effectively exhibited.

[0075] According to one embodiment of the present invention, the second ion-conducting polymer is for hydrogen ion transport and can also function as a binder. The ion-conducting polymer that can be used as the second ion-conducting polymer may be a cation conductor having at least one proton exchange group selected from the group consisting of a sulfonic acid group, a carboxyl group, a boronic acid group, a phosphate group, an imide group, a sulfonimide group, a sulfonamide group, a sulfonyl fluoride group, and combinations thereof.

[0076] The ion-conducting polymer may be a fluorine-based cation conductor, a hydrocarbon-based cation conductor, or a mixture thereof. Specifically, the ion-conducting polymer may be a fluorine-based cation conductor having a sulfonic acid group and / or a carboxyl group, a hydrocarbon-based cation conductor having a sulfonic acid group and / or a carboxyl group, or a mixture thereof.

[0077] Examples of the fluorine-based cation conductor include Nafion, Aciplex, Flemion, polyvinylidene fluoride, hexafluoropropylene, trifluoroethylene, polytetrafluoroethylene, and copolymers thereof.

[0078] Examples of the hydrocarbon-based cation conductor include hydrocarbon-based polymers having the cation exchange group on their side chains, such as sulfonated polyimide (S-PI), sulfonated polyarylethersulfone (SPAES), sulfonated polyetheretherketone (SPEEK), sulfonated polybenzimidazole (SPBI), sulfonated polysulfone (S-PSU), sulfonated polystyrene (S-PSU), and sulfonated polyimide (S-PI). polystyrene (S-PS), sulfonated polyphosphazene, sulfonated polyquinoxaline, sulfonated polyketone, sulfonated polyphenylene oxide, sulfonated polyether sulfone, sulfonated polyether ketone, sulfonated polyphenylene sulfone, sulfonated polyphenylene sulfide, sulfonated polyphenylene sulfide sulfone, sulfonated polyphenylene sulfide sulfone nitrile, sulfonated polyarylene ether, sulfonated polyarylene ether nitrile, sulfonated polyarylene ether ether nitrile, polyarylene ether sulfone ketone, and the like may also be used.

[0079] According to one embodiment of the present invention, the second catalyst layer 22 may be thicker than the first catalyst layer 21 and the third catalyst layer 23. For example, the second catalyst layer 22 may have a thickness of 5 μm to 20 μm. When the thickness of the second catalyst layer is within the above range, it is possible to prevent problems such as a small reaction area resulting in reduced activity and an increase in the travel distance of ions and electrons resulting in increased resistance.

[0080]

[0081] According to one embodiment of the present invention, the third catalyst layer 23 is a catalyst layer that contacts the electrolyte membrane and may be a catalyst layer that has relatively higher water absorption than the first catalyst layer 21 and the second catalyst layer 22.

[0082] Because the first catalytic layer 21 has relatively high water repellency, a structure in which a gradient of hydrophobicity and water absorption is formed in the catalytic layers from the first catalytic layer 21 to the third catalytic layer 23 may be provided. When water generated at the cathode flows through the electrolyte membrane to the anode, the third catalytic layer 23 allows the water to be rapidly transferred to the first catalytic layer 21 via the second catalytic layer 22. In addition, in a situation where fuel is scarce, a water electrolysis reaction occurs in the first catalytic layer 21, preventing catalyst deterioration in the second catalytic layer 22.

[0083] According to one embodiment of the present invention, in order to increase the water absorption of the third catalytic layer 23, the third catalytic layer 23 may have a relatively higher content of ion-conductive polymer than the first catalytic layer 21 and the second catalytic layer 22. In addition, the third catalytic layer 23 may have a higher loading of catalyst particles than the first catalytic layer 21 and the second catalytic layer 22.

[0084] According to one embodiment of the present invention, the third catalyst layer 23 may contain a water-absorbing material, which may include at least one material selected from the group consisting of hydrophilic resin, hydrophilically surface-treated carbon, hydrophilically surface-treated silica, large surface area carbon, and large surface area water-absorbing silica, but is not limited thereto.

[0085] The hydrophilic resin may be a resin containing a hydrophilic functional group. The hydrophilically surface-treated carbon and the hydrophilically surface-treated silica may be carbon and silica surface-treated with a hydrophilic functional group. The hydrophilic functional group may be selected from the group consisting of a hydroxyl group (-OH), a carboxyl group (-COOH), an amine group (-NH), a sulfonic acid group (-SO3H), an ether group (-CO-), a nitrate group (-NO3), an alkoxy group (-OR, where R may be an alkyl group having 1 to 10 carbon atoms), and combinations thereof, but is not limited thereto. Examples of the hydrophilic resin include polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, carboxymethyl ether sodium salt, polyvinyl methyl ether, hydroxyethyl ether, methylhydroxyethyl ether, hydroxyethyl cellulose, carboxymethyl cellulose, and glycerol propoxylate. The carbon and silica surface-treated with a hydrophilic functional group may be carbon surface-treated with a hydroxyl group and silica surface-treated with a hydroxyl group.

[0086] The high surface area carbon and the high surface area water-absorbing silica may be carbon or silica that is highly porous, has a large surface area, and has a high ability to absorb water, etc. The high surface area silica may have a BET specific surface area of, for example, 200 m 2 / g or more, specifically, 200m 2 / g or more 800m 2 / g or less, e.g., 300m 2 / g or more 600m 2 / g or less.

[0087] According to one embodiment of the present invention, the content of the water-absorbing material may be 0.05 wt % to 5 wt %, 0.1 wt % to 4 wt %, 0.5 wt % to 3 wt %, 0.5 wt % to 1.5 wt %, 1.5 wt % to 3 wt %, 0.05 wt % to 3 wt %, or 1 wt % to 5 wt %, based on the total weight of the third catalytic layer. When the content of the water-absorbing material is within the above range, it can facilitate the transfer of water generated at the cathode without affecting battery performance.

[0088] According to one embodiment of the present invention, the third catalyst layer 23 may contain a catalyst and an ion-conducting polymer contained in a catalyst layer of a typical fuel cell electrode for a cell reaction. The third catalyst and the third ion-conducting polymer used in the third catalyst layer 23 may be the same as or different from those used in the first catalyst layer 21 and the second catalyst layer 22. For an explanation of the third catalyst and the third ion-conducting polymer, please refer to the description of the second catalyst layer 22.

[0089] According to one embodiment of the present invention, the third catalyst has a metal content of 0.001 mg / cm 3 from the third catalyst in the third catalyst layer 23. 2 More than 0.3mg / cm 2 Below, 0.005mg / cm 2 More than 0.25mg / cm 2 Below, 0.01mg / cm 2 More than 0.2mg / cm 2 Below, 0.03mg / cm 2 More than 0.1mg / cm 2 Below, 0.03mg / cm 2 More than 0.05mg / cm 2 Below, 0.001mg / cm 2 More than 0.03mg / cm 2 or less, or 0.005 to 0.3 mg / cm 2 By setting the amount of the third catalyst within the above range, it is possible to improve the reverse voltage durability without deteriorating the performance of the fuel cell.

[0090] According to one embodiment of the present invention, the third catalyst layer 23 may contain a water-absorbing material, thereby having a relatively higher hydrophilicity than the first and second catalyst layers. According to one realization example of the present invention, the third catalyst layer 23 may have a surface contact angle of 20° to 60°, 30° to 60°, 30° to 50°, or 45° to 60°. As described above, a surface with a surface contact angle of 90° or more is a hydrophobic surface, and a surface with a surface contact angle of less than 90° is a hydrophilic surface. A third catalyst layer 23 with a surface contact angle of less than 90° is hydrophilic.

[0091] According to one embodiment of the present invention, the third catalyst layer 23 may have a thickness of 0.1 μm to 5 μm. When the thickness of the third catalyst layer is within the above range, the reverse voltage durability can be improved without deteriorating the performance of the fuel cell.

[0092]

[0093] Meanwhile, the membrane-electrode assembly according to the present invention can be manufactured using a conventional method known in the art.

[0094] One embodiment of the present invention provides a method for manufacturing a membrane-electrode assembly including the electrode, the method including the steps of forming a second catalyst layer 22 on a substrate, forming a third catalyst layer 23 on the second catalyst layer 22, bonding the third catalyst layer 23 to a polymer electrolyte membrane 30, removing the substrate, forming a first catalyst layer 21 on the second catalyst layer 22, and bonding the first catalyst layer 21 to a gas diffusion layer 10.

[0095] According to one embodiment of the present invention, the first catalyst layer, the second catalyst layer, or the third catalyst layer may be formed by any method known in the art, such as electroplating, spray coating, bar coating, inkjet printing, roll-to-roll printing, screen printing, etc., and preferably by spray coating. Specific manufacturing conditions for manufacturing the optional catalyst layer, such as electroplating conditions, spray pressure, drying temperature, drying time, etc., may be appropriately selected by those skilled in the art.

[0096]

[0097] In one embodiment of the present invention, a membrane-electrode assembly 100 is provided, which includes a polymer electrolyte membrane 30, an anode provided on one side of the polymer electrolyte membrane 30, a cathode provided on the other side of the polymer electrolyte membrane 30, and a gas diffusion layer 10 provided on the anode and the cathode, the anode being an electrode according to the above-described embodiment, with a first catalyst layer 21 of the electrode adjacent to the gas diffusion layer 10 and a third catalyst layer 23 adjacent to the polymer electrolyte membrane 30.

[0098] According to one embodiment of the present invention, the gas diffusion layer 10 is disposed between the membrane-electrode assembly and the separator of the fuel cell. Any gas diffusion layer commonly used in the art may be used. For example, the gas diffusion layer 10 may be formed of a conductive substrate selected from the group consisting of carbon paper, carbon fiber, and carbon felt. The gas diffusion layer may further include a microporous layer formed on one side of the conductive substrate. The microporous layer may be formed of a carbon-based material such as carbon black or carbon nanotubes, or a fluorine-based resin such as polytetrafluoroethylene or polyvinylidene fluoride (PVdF).

[0099] In the membrane-electrode assembly 100, an electrode disposed on one side of the polymer electrolyte membrane 30 and causing an oxidation reaction to generate hydrogen ions and electrons from fuel is called a fuel electrode (anode electrode), and an electrode causing a reduction reaction to generate water from hydrogen ions supplied through the polymer electrolyte membrane 30 and an oxidant at the electrode is called an air electrode (cathode electrode).

[0100] Of the anode and cathode, the anode is preferably the fuel cell electrode 20 of the present invention described above, but is not necessarily limited thereto, and the cathode may also include the fuel cell electrode 20 of the present invention.

[0101] According to one embodiment of the present invention, the anode can include a first catalyst layer 21 containing a water electrolysis catalyst, a second catalyst layer 22 provided on the first catalyst layer 21, and a third catalyst layer 23 having high water absorption properties and provided on the second catalyst layer 22.

[0102] According to one embodiment of the present invention, the first catalyst layer 21 of the anode may be adjacent to the gas diffusion layer 10, and the third catalyst layer 23 of the anode may be adjacent to the polymer electrolyte membrane 30. Here, the term "adjacent" means adjacent to each other, and does not exclude a case where a layer other than the first to third catalyst layers exists between the adjacent first catalyst layer 21 and the gas diffusion layer 10, or a case where a layer other than the first to third catalyst layers exists between the adjacent third catalyst layer 23 and the polymer electrolyte membrane 30.

[0103] According to one embodiment of the present invention, the polymer electrolyte membrane 30 is a solid polymer electrolyte and has an ion exchange function of transferring protons generated at the anode to the cathode. The polymer electrolyte membrane 30 may be a hydrocarbon-based polymer electrolyte membrane, a fluorine-based polymer electrolyte membrane, or a mixture or copolymer of one or more of these.

[0104] The hydrocarbon-based polymer electrolyte membrane may include a hydrocarbon-based polymer, which may be selected from styrene, imide, sulfone, phosphazene, ether ether ketone, ethylene oxide, polyphenylene sulfide, or aromatic homopolymers or copolymers and derivatives thereof, and these polymers may be used alone or in combination. Manufacturing an electrolyte membrane using a hydrocarbon-based polymer is cheaper and easier to manufacture than using a fluorine-based polymer, and exhibits high ionic conductivity.

[0105] The suitable hydrocarbon membrane may more preferably be one or more selected from the group consisting of sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyetherketone, sulfonated polyetheretherketone, sulfonated polyaryleneetheretherketone, sulfonated polyaryleneethersulfone, sulfonated polyaryleneetherbenzimidazole, and a membrane incorporating an ion conductor.

[0106] The fluorine-based polymer electrolyte membrane can be any material that is an ion-conductive membrane and has sufficient mechanical strength and electrochemical stability to form a film. Specific examples of the fluorine-based polymer electrolyte membrane include perfluorosulfonic acid resin and a copolymer of tetrafluoroethylene and fluorovinyl ether. The fluorovinyl ether moiety has the function of conducting hydrogen ions. The copolymer is commercially available under the trade name Nafion from DuPont.

[0107]

[0108] 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.

[0109] FIG. 2 is a schematic diagram showing the overall configuration of a fuel cell according to one embodiment of the present invention.

[0110] As shown in FIG. 2, the fuel cell 200 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.

[0111] The stack 230 may include a plurality of unit cells that generate electrical energy by inducing an oxidation / reduction reaction between the reformed gas, including hydrogen gas, supplied from the reforming unit 220 and the oxidant supplied from the oxidant supplying unit 240.

[0112] Each unit cell refers to a unit cell that generates electricity and includes the membrane-electrode assembly that oxidizes / reduces oxygen in the reformed gas containing hydrogen gas and the oxidant, and a separator plate (also called a bipolar plate, hereinafter referred to as "separator plate") that supplies the reformed gas containing hydrogen gas and the oxidant to the membrane-electrode assembly. The separator plates may be disposed on both sides of the membrane-electrode assembly, with the membrane-electrode assembly at the center. In this case, the separator plates located at the outermost periphery of the stack may be referred to as end plates.

[0113] 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.

[0114]

[0115] Specific examples of the present invention will be presented below. However, the examples described below are merely for the purpose of specifically illustrating and explaining the present invention, and are not intended to limit the present invention. Furthermore, content not described herein can be fully inferred by a person skilled in the art, and therefore, a description thereof will be omitted.

[0116]

[0117] [Comparative Example 1] Anode made of second catalyst layer containing platinum-supported catalyst

[0118] Anode and cathode slurries were prepared using a Pt / carbon catalyst by conventional methods.

[0119] Electrode area 25cm 2 The fuel electrode has a platinum content of 0.1 mg. Pt / cm 2 , and the air electrode is 0.4 mg Pt / cm 2 The mixture was coated onto a release film and dried in an oven at 60°C for 8 hours.

[0120] A commonly used perfluorosulfonic acid-based polymer electrolyte membrane was positioned in the center, and a positive electrode catalyst layer and a negative electrode catalyst layer were laminated on both sides. The fuel cell membrane-electrode assembly (MEA) was completed using the decal transfer method at 180°C and 4 MPa.

[0121]

[0122] [Comparative Example 2] Anode including a polymer electrolyte membrane and a first catalyst layer adjacent to the polymer electrolyte membrane

[0123] IrO2 as a water electrolysis catalyst was dispersed in 1-propanol in an amount of 5 wt % together with Nafion ion-conductive polymer to prepare a dispersion solution.

[0124] The anode prepared in Comparative Example 1 was placed on a heating plate, and the dispersion solution prepared was sprayed under pressure to deposit Ir at a concentration of 0.01 mg / cm. 2 In the same manner as in Comparative Example 1, the perfluorosulfonic acid-based polymer electrolyte membrane was positioned in the center, and a membrane-electrode assembly for a fuel cell was obtained by a decal transfer method.

[0125]

[0126] [Comparative Example 3] Anode including a first catalyst layer adjacent to a gas diffusion layer

[0127] The membrane-electrode assembly prepared in Comparative Example 1 was placed on a heating plate, and the aqueous electrolysis catalyst-containing dispersion solution of Comparative Example 2 was sprayed under pressure onto the fuel electrode side to adjust the amount of Ir to 0.01 mg / cm 2 After drying, a decal was applied to obtain an MEA.

[0128]

[0129] [Example 1]

[0130] Example 1-1

[0131] The same anode slurry as in Comparative Example 1 was used to form the second catalyst layer at 0.07 mg / cm 2 The film was coated with the solution and dried.

[0132] The third catalyst layer is a Pt / C catalyst with 350 m 2 A solution was prepared by dispersing water-absorbing porous silica with a large specific surface area of ​​0.5 wt% in water and 1-propanol. The dried second catalyst layer was placed on a heating plate, and the prepared solution was sprayed under pressure to a Pt content of 0.03 mg / cm. 2 The third catalyst layer was produced by coating the catalyst so that the thickness of the catalyst layer was 1 / 3.

[0133] A commonly used perfluorosulfonic acid-based polymer electrolyte membrane was placed in the center, and the prepared anode catalyst layer and the cathode catalyst layer of Comparative Example 1 were applied in the same manner, and a fuel cell MEA was completed by decal transfer method under conditions of 180°C and 4 MPa.

[0134] The first catalyst layer was a catalyst for water electrolysis, and a small amount of IrO2 was added and dispersed in IPA (isopropyl alcohol) to prepare a solution. The MEA was placed on a heating plate, and the prepared solution was sprayed under pressure to prepare a solution containing 0.01 mg / cm of Ir. 2 The coating was carried out so that the thickness was 1 / 4 of that of the coated film.

[0135]

[0136] Example 1-2

[0137] A membrane-electrode assembly (MEA) was prepared in the same manner as in Example 1-1, except that the amount of water-absorbing porous silica was adjusted to 1.5 wt % when preparing the third catalyst layer.

[0138]

[0139] Examples 1-3

[0140] An electrode and a membrane-electrode assembly (MEA) were prepared in the same manner as in Example 1-1, except that the amount of water-absorbing porous silica was adjusted to 3.0 wt % when preparing the third catalyst layer.

[0141]

[0142] [Example 2]

[0143] Example 2-1

[0144] The first catalyst layer was a water electrolysis catalyst (first catalyst) and was formed by preparing a dispersion solution by adding 0.1 wt% of hydrophobic silica surface-treated with CH groups to IrO2. An MEA was fabricated in the same manner as in Example 1.

[0145]

[0146] Example 2-2

[0147] An MEA was prepared in the same manner as in Example 2-1, except that a dispersion solution was prepared by adding 0.5 wt % of hydrophobic silica surface-treated with CH groups.

[0148]

[0149] Example 2-3

[0150] An MEA was prepared in the same manner as in Example 2-1, except that a dispersion solution was prepared by adding 1.0 wt % of hydrophobic silica surface-treated with CH groups.

[0151]

[0152] [Experimental Example 1] Evaluation of output performance and reverse voltage durability

[0153] A cell reversal test was conducted on the membrane-electrode assemblies of the examples and comparative examples under fuel starvation conditions at the anode. Specifically, the unit cell temperature was maintained at 65°C, and hydrogen and air with 100% relative humidity were supplied to the cathode and anode in amounts that matched stoichiometry 1.5 / 2.0, respectively, while a back pressure of 150 kPa was applied. The current density was 1.0 A / cm. 2 The potential was measured and maintained for 10 minutes. After that, nitrogen was supplied to the anode, and 0.2 A / cm 2 The potential was measured while applying a current of 100 kJ / s, and the cell reversal time (TCR) is shown in Tables 1 to 6. CR , -2.0V is 0.2A / cm 2 is the time it takes for the voltage to drop to -2.0 V when a current of CR , the longer the voltage is at -2.0V, the higher the durability.

[0154]

[0155] [Table 1]

[0156] [Table 2]

[0157] Referring to Tables 1 and 2, Comparative Example 1, which does not contain an OER catalyst, exhibits poor durability, with a reverse potential maintenance time of less than 2 minutes. However, Comparative Examples 2 and 3, which contain an OER catalyst, exhibit differences in durability due to the structural differences in the location of the OER catalyst used in the anode, despite the same amount of OER catalyst. Comparative Example 2 exhibits excellent reverse voltage durability, but exhibits a decrease in output voltage due to resistance caused by the third catalyst layer when hydrogen ions generated at the anode are transferred to the electrolyte membrane. Conversely, when the OER catalyst is included in the first catalyst layer, durability is lower than that of Comparative Example 2 due to the relatively low water distribution caused by the distance that moisture from the cathode must travel.

[0158]

[0159] [Table 3]

[0160] [Table 4]

[0161] Referring to Tables 3 and 4, it can be seen that when the amount of water-absorbing silica contained in the third catalytic layer is increased, the amount of water passing through from the cathode increases, and the overall water vapor distribution in the anode increases, thereby improving reverse potential durability. However, the increased silica in the third catalytic layer increases proton transport resistance, resulting in a decrease in output voltage.

[0162]

[0163] [Table 5]

[0164] [Table 6]

[0165] Referring to Tables 5 and 6, when the third catalytic layer contains an appropriate amount of water-absorbent silica and the first catalytic layer contains water-repellent silica, water vapor is guided toward the gas diffusion layer, allowing for smooth supply of water vapor to the first catalytic layer. The stronger the water repellency, the greater the improvement in reverse potential durability. However, as in the previous experiment, as the silica content increases, resistance occurs in the transfer of electrons generated by the oxidation of hydrogen to the gas diffusion layer, resulting in a decrease in output voltage.

[0166] 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 are not intended to limit the present invention. The scope of the present invention also includes various modifications and improvements made by those skilled in the art using the basic concept of the present invention as defined in the claims below. [Explanation of symbols]

[0167] 100: Membrane-electrode assembly 10: Gas diffusion layer 20: Electrode 21: First catalyst layer 22: Second catalyst layer 23: Third catalyst layer 30:Polymer electrolyte membrane 200: Fuel cell 210: Fuel supply unit 220: Reforming unit 230: Stack 231: First supply pipe 232: Second supply pipe 233: First discharge pipe 234: Second discharge pipe 240: Oxidizer supply section

Claims

1. a first catalyst layer containing a water electrocatalyst; a second catalyst layer provided on the first catalyst layer; a third catalyst layer provided on the second catalyst layer and having water absorption properties; An electrode for a fuel cell comprising:

2. 2. The electrode according to claim 1, wherein the water electrolysis catalyst comprises at least one oxygen evolution reaction catalyst selected from the group consisting of a metal selected from the group consisting of Li, Co, Ni, Zn, Fe, Ti, Na, Mn, Cu, Ga, Sn, Cr, W, Ru, Ir, Pt, Au, and alloys thereof, an oxide of the metal, a sulfide of the metal, and a carbide of the metal.

3. The oxygen generation reaction catalyst is IrO ２ , RuO ２ , TiO ２ , Ir ｘ Sn １－ｘ O ２ 3. The electrode according to claim 2, comprising at least one selected from the group consisting of PtIr and IrRu (where x is a number greater than 0 and less than 1).

4. The electrode according to claim 1 , wherein the first catalyst layer further contains a water-repellent material.

5. 5. The electrode according to claim 4, wherein the water-repellent material comprises at least one selected from the group consisting of a water-repellent resin, graphitized carbon, hydrophobically treated carbon, and hydrophobic silica.

6. 5. The electrode according to claim 4, wherein the water-repellent substance comprises hydrophobic silica that has been surface-treated with at least one selected from the group consisting of methyl, difluoromethyl, ethyl, fluoroethyl, propyl, isopropyl, and 3-fluoropropyl.

7. The electrode of claim 4 , wherein the content of the water-repellent material is 0.05 wt % to 3 wt % based on the total weight of the first catalyst layer.

8. 5. The electrode according to claim 4, wherein the first catalyst layer has a surface contact angle of 70° or more and 160° or less, and the third catalyst layer has a surface contact angle of 20° or more and 60° or less.

9. the first catalyst layer includes a first catalyst and a first ion-conducting polymer, the second catalyst layer includes a second catalyst and a second ion-conducting polymer, and the third catalyst layer includes a third catalyst and a third ion-conducting polymer; the first catalyst, the second catalyst, and the third catalyst are the same as or different from one another; 2. The electrode of claim 1, wherein the first ion-conducting polymer, the second ion-conducting polymer, and the third ion-conducting polymer are the same as or different from one another.

10. 10. The electrode of claim 9, wherein the first catalyst, the second catalyst, and the third catalyst each independently comprise a platinum-based catalyst.

11. 2. The electrode according to claim 1, wherein the second catalyst layer is thicker than the first catalyst layer and the third catalyst layer.

12. The electrode according to claim 11 , wherein the second catalyst layer has a thickness of 5 μm or more and 20 μm or less.

13. The electrode according to claim 1 , wherein the third catalyst layer further contains a water-absorbing material.

14. 14. The electrode according to claim 13, wherein the water-absorbing material comprises at least one selected from the group consisting of hydrophilic resin, hydrophilically surface-treated carbon, hydrophilically surface-treated silica, large surface area carbon, and large surface area water-absorbing silica.

15. The electrode of claim 13 , wherein the content of the water-absorbing material is 0.05 wt % to 5 wt % based on the total weight of the third catalyst layer.

16. 2. The electrode according to claim 1, which is used as a fuel electrode in a fuel cell.

17. forming a second catalyst layer on the substrate; forming a third catalyst layer on the second catalyst layer; bonding the third catalyst layer to a polymer electrolyte membrane; removing the substrate; forming a first catalyst layer on the second catalyst layer; bonding the first catalyst layer to a gas diffusion layer; A method for producing a membrane-electrode assembly comprising an electrode according to claim 1, comprising:

18. a polymer electrolyte membrane; a fuel electrode provided on one surface of the polymer electrolyte membrane; an air electrode provided on the other surface of the polymer electrolyte membrane; a gas diffusion layer provided on the anode and the cathode; Including, The anode is an electrode according to claim 1, a membrane-electrode assembly in which the first catalyst layer of the anode is adjacent to the gas diffusion layer, and the third catalyst layer is adjacent to the polymer electrolyte membrane;

19. A fuel cell comprising a membrane-electrode assembly according to claim 18.

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