Membrane electrode assembly for fuel cell containing plate-shaped porous silica and fuel cell containing the same

Abstract

The present invention relates to a membrane electrode assembly for a fuel cell and a fuel cell including the same, and more particularly, to a membrane electrode assembly for a fuel cell and a fuel cell including the same, in which plate-shaped porous silica is included in a catalyst layer, thereby improving fuel cell performance in a low humidification environment.

Description

[Technical Field]

[0001] The present invention relates to a membrane electrode assembly for a fuel cell with improved performance in low-humidity environments. [Background technology]

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

[0003] Fuel cells have the advantage of being able to produce a wide range of output power due to their stack structure made up of stacked unit cells, and they are attracting attention as a small and portable power source because they exhibit an energy density that is 4 to 10 times that of small lithium batteries.

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

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

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

[0007] To summarize the reactions that occur in a polymer electrolyte fuel cell, first, when fuel such as hydrogen gas is supplied to the oxidizing electrode, hydrogen ions (H+) and electrons (e-) are generated through an oxidation reaction at the oxidizing electrode. The generated hydrogen ions are transported to the reducing electrode through the polymer electrolyte membrane, and the generated electrons are transported to the reducing electrode through an external circuit. Oxygen is supplied to the reducing electrode, and the oxygen combines with the hydrogen ions and electrons to generate water through an oxygen reduction reaction.

[0008] Meanwhile, in order to apply fuel cells to FCVs (Fuel Cell Vehicles), the fuel cell system must be miniaturized. To achieve this, it is necessary to develop a membrane electrode assembly (MEA) that can exhibit excellent power density per unit area. In particular, the durability of the MEA catalyst layer must be improved for practical operation of FCVs. Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a membrane electrode assembly with improved mass transfer efficiency, performance in low-humidity environments, and durability by introducing nanostructured porous silica into a portion of the electrode layer.

[0010] Another object of the present invention is to provide a fuel cell to which the membrane electrode assembly structure is applied, which has improved performance and durability in a low-humidity environment. [Means for solving the problem]

[0011] To achieve the above object, a membrane electrode assembly for a fuel cell according to one embodiment of the present invention includes a first catalyst layer including plate-shaped porous silica and a polymer electrolyte membrane.

[0012] The plate-like porous silica may include mesopores perpendicular to the plate-like shape.

[0013] The plate-like porous silica may have pores with a diameter of 2 to 40 nm.

[0014] The plate-like porous silica may have a size of 50 to 2000 nm and a thickness of 30 to 300 nm.

[0015] In the first catalytic layer, the plate-shaped porous silica may be included in an amount of 1 to 20 wt % based on the total weight of the first catalytic layer.

[0016] The ionomer content of the first catalyst layer may be 34 to 40 wt % based on the total weight of the first catalyst layer.

[0017] The first catalyst layer may have a thickness of 0.2 to 5 μm.

[0018] The first catalyst layer may be located between the polymer electrolyte membrane and a second catalyst layer that does not contain or contains a smaller amount of plate-shaped porous silica.

[0019] The ionomer content of the first catalyst layer may be greater than the ionomer content of the second catalyst layer.

[0020] A fuel cell according to another embodiment of the present invention includes the above-described membrane electrode assembly for a fuel cell. [Effects of the Invention]

[0021] The membrane electrode assembly of the present invention can solve the problem of decreased ionic conductivity that occurs when the electrolyte membrane dries out in a low-humidity environment, because the catalyst layer can effectively absorb moisture discharged from the electrolyte membrane through the pores of the plate-shaped porous silica. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing one shape of plate-like porous silica.

[0023] [Figure 2] FIG. 1 is a diagram schematically illustrating a structure in which plate-shaped porous silica is contained in a first catalyst layer.

[0024] [Figure 3] FIG. 2 is a schematic diagram showing the overall configuration of the fuel cell.

[0025] [Figure 4] 1 is a transmission electron microscope (TEM) photograph of plate-shaped porous silica used in an embodiment of the present invention.

[0026] [Figure 5] 4 is an optical microscope photograph of the surfaces of a first electrode layer and a second electrode layer manufactured according to an embodiment of the present invention.

[0027] [Figure 6] 1 shows the results of evaluating low humidification performance of membrane electrode assemblies (MEAs) manufactured according to examples and comparative examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] Although the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the disclosed embodiments.

[0029] A fuel cell membrane electrode assembly according to one aspect of the present invention is characterized in that the catalyst layer includes plate-shaped porous silica. The catalyst layer including plate-shaped porous silica may be formed on only one side of the polymer electrolyte membrane, or may be formed on both sides.

[0030] Figure 1 shows one shape of plate-shaped porous silica. Referring to Figure 1, a catalyst layer containing plate-shaped porous silica is positioned in contact with an electrolyte membrane and can effectively contain moisture through the pores of the silica, thereby suppressing moisture evaporation from the polymer electrolyte membrane. This helps the polymer electrolyte membrane and catalyst layer maintain appropriate humidity in a low-humidity environment, thereby maintaining excellent ionic conductivity.

[0031] The mesopores of the plate-shaped porous silica may be perpendicular to the plate shape (same direction as the thickness direction). When the pores are perpendicular to the plate shape, the pores are arranged perpendicular to the electrolyte membrane, facilitating mass transfer and further improving performance. When the pores are horizontal to the plate shape, the pores are arranged parallel to the electrolyte membrane during electrode formation, which is the same as existing mesoporous silica, hindering mass transfer and reducing performance.

[0032] The plate-like porous silica may be mesoporous silica, specifically, plate-like porous silica having pores with diameters of 2 to 40 nm, 4 to 30 nm, or 6 to 20 nm. If the pore diameter of the silica is less than 2 nm, the excessively small pores may make it difficult for water to penetrate, limiting ion transmission through the pores and possibly reducing the water-retaining properties of the porous silica. If the pore diameter of the silica is greater than 40 nm, water that penetrates into the pores may not remain in the pores for long and may easily evaporate, potentially resulting in little improvement in performance in low-humidity environments.

[0033] The size of the plate-like porous silica may be preferably 50 to 2000 nm, 100 to 1500 nm, 150 to 1000 nm, or 200 to 800 nm. Here, the size of the porous silica refers to the maximum length of the plate-like width. If the size of the porous silica is larger than this range, the catalyst and ionomer in the catalytic layer are not evenly dispersed and distributed due to the silica that does not participate in the chemical reaction in the catalytic layer, resulting in a decrease in content and a decrease in the chemical reaction efficiency of the catalytic layer. Furthermore, if the size of the porous silica is smaller than this range, the pores are not easily aligned perpendicular to the electrolyte membrane, resulting in a problem of impeded mass transfer.

[0034] The thickness of the plate-like porous silica may be preferably 30 to 300 nm, 40 to 250 nm, or 50 to 200 nm. If the thickness of the plate-like porous silica is thinner than this range, the porous silica structure may be easily damaged even by a weak physical external impact, and the damage may be the same as that of amorphous silica during dispersion. If the thickness of the plate-like porous silica is thicker than this range, the pores may be unnecessarily deep compared to the depth at which water can penetrate into the pores, and the porous silica may occupy an unnecessarily large volume in the catalytic layer, thereby reducing the efficiency of the catalytic layer.

[0035] Plate-shaped porous silica can be prepared using a conventional method for preparing porous silica, which involves hydrolysis, condensation, and calcination. However, a template for forming the plate-shaped structure, such as a block copolymer composed of an aqueous block and a hydrophilic block, can be used, and the template can be hydrolyzed with a silica precursor and an acidic catalyst. Examples of the block copolymer include Pluronic P123 and Pluronic F127. Examples of the silica precursor include, but are not limited to, tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, or mixtures thereof. Examples of the acidic catalyst include HCl, acetic acid, nitric acid, and sulfuric acid. The hydrolysis, condensation, and calcination conditions can be appropriately selected from conventional conditions by those skilled in the art, taking into account the reaction conditions and conditions.

[0036] 2 is a simplified diagram illustrating the structure of one embodiment of a fuel cell membrane electrode assembly 100 according to the present invention. Referring to FIG. 2, the pores of the plate-like porous silica 1 are preferably formed in a direction perpendicular to the plane of the electrolyte membrane 20 in the first catalyst layer 11 containing the silica 1. When the plate-like porous silica 1 is arranged so that the pores are perpendicular to the plane of the electrolyte membrane 20, the pores effectively absorb moisture discharged from the electrolyte membrane 20, facilitating mass transfer, and thereby more effectively maintaining a moist environment for the electrolyte membrane 20.

[0037] Although plate-shaped porous silica helps maintain a moist environment within the membrane electrode assembly in a low-humidity environment, it is not directly involved in the oxidation-reduction reaction of the catalyst layer or in hydrogen ion conduction, so it is important that it be present in an appropriate proportion within the catalyst layer. Specifically, the plate-shaped porous silica is preferably present in the first catalyst layer at 1 to 20 wt % of the total weight of the first catalyst layer. If the plate-shaped porous silica is present in the first catalyst layer at less than 1 wt %, the effect of the plate-shaped porous silica in maintaining a moist environment may be insignificant. If the plate-shaped porous silica is present in the first catalyst layer at more than 20 wt %, the oxidation-reduction reaction catalyzed by the catalyst layer may not occur sufficiently, which may reduce fuel cell efficiency.

[0038] The first catalytic layer containing plate-like porous silica contains an ionomer, and it is preferable that the ionomer content be higher than that of a typical catalytic layer that does not contain porous silica, in order to ensure smooth conduction of hydrogen ions. Specifically, the ionomer content of the first catalytic layer is preferably 34 to 40 wt% based on the total weight of the first catalytic layer. If the ionomer content in the first catalytic layer is higher than this range, it may hinder the supply of fuel to the platinum catalytic active sites, while if the ionomer content in the first catalytic layer is too low, it may hinder the ion transport ability of the catalytic layer.

[0039] The ionomer may include one or more ionomers selected from the group consisting of fluorine-based ionomers and hydrocarbon-based ionomers. The hydrocarbon-based ionomer may be any known hydrocarbon-based polymer, such as sulfonated derivatives of poly(arylene ether)s (SPAEs), poly(arylene sulfide)s (SPASs), polyimides (SPIs), polybenzimidazoles (PBIs), polyphenylenes (PPs), or polyether ether ketone (PEEK). The fluorine-based polymer may be any known fluorine-based polymer, such as perfluorinated sulfonic acid, polyvinylidene fluoride, hexafluoropropylene, trifluoroethylene, polytetrafluoroethylene, or a copolymer thereof.

[0040] However, the ionomer contained in the catalyst layer together with the plate-shaped porous silica preferably has an equivalent weight (EW) of 600 to 1200 for effective ion conductivity of the catalyst layer.

[0041] The thickness of the first catalytic layer containing the plate-like porous silica is preferably 0.2 to 5 μm. If the thickness of the first catalytic layer is thinner than 0.2 μm, the catalytic layer may be too thin to contain sufficient plate-like porous silica therein, and even if plate-like porous silica is contained therein, the chemical reaction in the catalytic layer may not occur sufficiently. Conversely, if the thickness of the first catalytic layer is thicker than 5 μm, the efficiency of the fuel cell may be improved by creating a moist environment due to the inclusion of the plate-like porous silica, but the volume occupied by the porous silica may prevent the catalytic chemical reaction from occurring, resulting in a greater decrease in efficiency.

[0042] Therefore, to further improve the efficiency of the catalyst layer, the first catalyst layer containing plate-like porous silica may be formed only in the area in contact with the polymer electrolyte membrane, and a structure in which a catalyst layer containing no or a smaller amount of porous silica is additionally laminated may be applied.

[0043] The first catalyst layer may be located between the second catalyst layer and the polymer electrolyte membrane. The second catalyst layer contains no or a small amount of plate-shaped porous silica, and it is preferable for the second catalyst layer to contain almost no or almost no plate-shaped porous silica from the perspective of cell performance. If the second catalyst layer contains plate-shaped porous silica, its content should be less than that of the first catalyst layer, and may be less than that of the first catalyst layer by at least 1 wt %, e.g., 1 to 20 wt %, specifically at least 5 wt %, and more specifically at least 10 wt %. Figure 2 shows a simplified view of a membrane electrode assembly 100 according to one embodiment of the present invention, in which a first catalyst layer 11 is formed on one side of a polymer electrolyte membrane 20, and a second catalyst layer 12 containing no or a small amount of plate-shaped porous silica is stacked on the first catalyst layer 11 to form a multilayer catalyst layer 10. Although FIG. 2 only shows a polymer electrolyte membrane having a catalyst layer 10 including a first catalyst layer 11 formed on one side, multiple catalyst layers may be formed on both sides of the polymer electrolyte membrane, and the catalyst layer 10 including the first catalyst layer 11 may be a cathode or an anode, and is not particularly limited.

[0044] The plate-like porous silica further extends the hydrogen ion conduction path within the catalyst layer, and the porous structure of the silica allows the ionomer to penetrate into the silica pores, further facilitating hydrogen ion conduction. Therefore, in catalyst layer 10, the ionomer content of first catalyst layer 11 is preferably greater than that of second catalyst layer 12 to increase the bonding strength between the catalyst layer and the electrolyte membrane and to facilitate the ionomer's placement in the silica pores, but the present invention is not limited thereto.

[0045] The catalyst layer contains a catalyst, and any catalyst that participates in the cell reaction and can be used as a catalyst for a normal fuel cell can be used. Specifically, platinum-based metals can be preferably used.

[0046] Examples of platinum-based metals include platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), osmium (Os), platinum-M alloys (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), and tin. The platinum-based catalytic metal may include any one selected from the group consisting of platinum (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 technical field may be used without limitation.

[0047] 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.

[0048] 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.

[0049] Such a catalyst can be used as a catalyst black or can be supported on a carrier.

[0050] The support can be selected from carbon-based supports, porous inorganic oxides such as zirconia, alumina, titania, silica and ceria, and zeolites. The carbon-based support may be selected from graphite, super P, carbon fiber, carbon sheet, carbon black, Ketjen Black, Denka Black, acetylene black, carbon nanotube (CNT), carbon sphere, carbon ribbon, fullerene, activated carbon, carbon nanofiber, carbon nanowire, carbon nanoball, carbon nanohorn, carbon nanocage, carbon nanoring, ordered nano- / meso-porous carbon, carbon aerogel, mesoporous carbon, graphene, stabilized carbon, activated carbon, and combinations of one or more thereof, but is not limited thereto, and any support available in the art may be used without limitation.

[0051] The catalyst particles may be located on the surface of the support or may penetrate into the support, filling its internal pores.

[0052] When a precious metal supported on a carrier is used as a catalyst, a commercially available product may be used, or a catalyst prepared by supporting a precious metal on a carrier may be used. The process of supporting a precious metal on a carrier is widely known in the art, and therefore, even if a detailed description is omitted in this specification, it is easily understandable to those skilled in the art.

[0053] The catalyst particles may be contained in an amount of 20 wt % to 80 wt % based on the total weight of the catalyst layers 10 and 30. If the amount is less than 20 wt %, there is a problem of reduced activity, and if the amount is more than 80 wt %, there is a problem of reduced catalytic activity due to agglomeration of the catalyst particles, which reduces the active area.

[0054] In addition, the catalyst layers 10 and 30 may contain a binder to improve adhesion and promote hydrogen ion transport. It is preferable to use an ionomer having ion conductivity as the binder. The ionomer has been described above, so a repeated description will be omitted.

[0055] However, the ionomer may be used alone or in the form of a mixture, and may also be used selectively with a non-conductive compound to further improve adhesion to the polymer electrolyte membrane 50. The amount used is preferably adjusted to suit the intended use.

[0056] As the non-conductive compound, one or more selected from the group consisting of polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene (ETFE), ethylene chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer (pVdF-HFP), dodecylbenzenesulfonic acid, and sorbitol may be used.

[0057] The binder may be included in an amount of 20 wt % to 80 wt % of the total weight of the catalyst layers 10 and 30. If the binder content is less than 20 wt %, the generated ions may not be transported well, and if it exceeds 80 wt %, the pores may be insufficient to supply hydrogen or oxygen (air), and the active area for reaction may be reduced.

[0058] The electrode substrate may be a porous conductive substrate to facilitate the supply of hydrogen or oxygen. Typical examples include, but are not limited to, carbon paper, carbon cloth, carbon felt, or metal cloth (a porous film made of fibrous metal cloth or a metal film formed on the surface of a polymer fiber cloth). Furthermore, it is preferable to use electrode substrates 40, 40' that are water-repellent treated with a fluorine-based resin to prevent a decrease in reactant diffusion efficiency due to water generated during fuel cell operation. Examples of fluorine-based resins that can be used include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, fluorinated ethylene propylene, polychlorotrifluoroethylene, and copolymers thereof.

[0059] The electrode substrate may further include a microporous layer for enhancing the reactant diffusion effect. The microporous layer may generally include a conductive powder having a small particle size, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotubes, carbon nanowires, carbon nanohorns, or carbon nanorings.

[0060] The microporous layer is produced by coating an electrode substrate with a composition containing a conductive powder, a binder resin, and a solvent. Examples of binder resins that can be used include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, alkoxy vinyl ether, polyvinyl alcohol, cellulose acetate, and copolymers thereof. Examples of solvents that can be used include alcohols such as ethanol, isopropyl alcohol, n-propyl alcohol, and butyl alcohol; water; dimethylacetamide; dimethyl sulfoxide; N-methylpyrrolidone; and tetrahydrofuran.

[0061] The coating process may be performed by, but is not limited to, a screen printing method, a spray coating method, or a coating method using a doctor blade, depending on the viscosity of the composition.

[0062] A fuel cell according to another embodiment of the present invention may include a membrane electrode assembly according to an embodiment of the present invention.

[0063] FIG. 3 is a schematic diagram showing the overall configuration of the fuel cell.

[0064] Referring to FIG. 3, the fuel cell 200 includes a fuel supply unit 210 that supplies a mixed fuel obtained by mixing fuel and water, a reformer 220 that reforms the mixed fuel to generate a reformed gas containing hydrogen gas, a stack 230 that generates electrical energy by electrochemically reacting the reformed gas containing hydrogen gas supplied from the reformer 220 with an oxidant, and an oxidant supply unit 240 that supplies the oxidant to the reformer 220 and the stack 230.

[0065] The stack 230 includes a plurality of unit cells that generate electrical energy by inducing an oxidation / reduction reaction between the reformed gas containing hydrogen gas supplied from the reforming unit 220 and the oxidant supplied from the oxidant supplying unit 240 .

[0066] Each unit cell refers to a unit cell that generates electricity and includes a membrane electrode assembly that oxidizes / reduces oxygen in the reformed gas containing hydrogen gas and the oxidant, and a separator plate (also called a bipolar plate, hereinafter referred to as "separator plate") that supplies the reformed gas containing hydrogen gas and the oxidant to the membrane electrode assembly. The separator plates are located on both sides of the membrane electrode assembly, with the membrane electrode assembly at the center. In this case, the separator plates located at the outermost sides of the stack are sometimes referred to as end plates.

[0067] One of the end plates of the separation plates has a first pipe-shaped supply pipe 231 for injecting the reformed gas containing hydrogen gas supplied from the reforming section 220, and a second pipe-shaped supply pipe 232 for injecting oxygen gas, and the other end plate has a first exhaust pipe 233 for discharging the reformed gas containing hydrogen gas that ultimately remains unreacted in the multiple unit cells to the outside, and a second exhaust pipe 234 for discharging the oxidant that ultimately remains unreacted in the unit cells to the outside.

[0068] In the fuel cell, except that a 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 generating unit are the same as those used in conventional fuel cells, and therefore detailed description thereof will be omitted in this specification.

[0069] Although the present invention may be embodied in many different forms, it is not intended to be limited to the embodiments set forth herein, and the present invention is not limited to the embodiments set forth herein.

[0070]

[0071] [Example 1]

[0072] 0.32 g of ZrOCl2·8HO and 2.0 g of Pluronic P123 were dissolved in a 2.0 M HCl aqueous solution, and then 4.2 g of TEOS (tetraethylorthosilicate) was added and hydrolysis was carried out for 30 minutes at 35°C. 1.0 g of TMB (trimethylbenzene) was then added to the mixed solution, and hydrolysis and condensation polymerization were carried out for 12 hours at 35°C. The mixture was then hydrothermally treated at 90°C for 5 hours and calcined at 550°C for 5 hours to produce plate-shaped mesopolis porous silica SBA.

[0073] A membrane electrode assembly was fabricated according to a conventional manufacturing method, except that the cathode was constructed using a first catalyst layer containing 5 wt% of the plate-shaped porous silica and a second catalyst layer containing no silica. The total thickness of the catalyst layers was 15 μm, and the thickness of the first catalyst layer was 3 μm. Nafion was used as the ionomer, and a platinum catalyst was used.

[0074] Figure 5 shows optical microscope images of the surface of the first electrode layer (a) after formation and the surface of the second electrode layer (b) after formation of the first electrode layer in Example 1. Referring to Figure 1, if the plate-like porous silica is large after formation of the first electrode layer (a), the surface of the first electrode layer will have an uneven shape. In the uneven surface of the first electrode layer, the areas containing porous silica are high and the areas not containing porous silica are relatively low, and this uneven shape helps improve the performance and durability of the membrane electrode assembly.

[0075]

[0076] [Example 2]

[0077] A membrane electrode assembly was prepared in the same manner as in Example 1, except that the second catalyst layer was not used.

[0078]

[0079] [Comparative Example 1]

[0080] A membrane electrode assembly was prepared in the same manner as in Example 1, except that spherical silica (50 nm) was used for the first catalyst layer.

[0081]

[0082] Comparative Example 2

[0083] 2.0 g of Pluronic P123 was dissolved in a 2.0 M HCl aqueous solution, and 4.2 g of TEOS (tetraethylorthosilicate) was added. Hydrolysis and condensation polymerization were carried out at 35°C for 12 hours, followed by calcination at 550°C for 5 hours to produce conventional mesopolis silica (not plate-like).

[0084] A membrane electrode assembly was fabricated in the same manner as in Example 1, except that the conventional mesophorous silica prepared above was used for the first catalyst layer.

[0085]

[0086] Comparative Example 3

[0087] A membrane electrode assembly was manufactured in the same manner as in Example 1, except that the second catalyst layer contained 20 wt % of plate-shaped mesoporous silica.

[0088]

[0089] [Table 1]

[0090]

[0091] [Experimental example: Performance comparison of membrane electrode assemblies]

[0092] The performance of the membrane electrode assemblies according to the configurations in Table 1 in a low humidity environment (temperature: 80°C, humidity: RH 30%) was evaluated and is shown in Figure 6. Referring to Figure 6, in a low humidity environment, the voltage measured at the current density of Examples 1 and 2 was significantly higher than that of Comparative Examples 1, 2, and 3. In particular, Example 1, which includes the second electrode layer, showed excellent voltage even at the same current density, demonstrating the excellent effectiveness of the membrane electrode assemblies.

[0093]

[0094] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

[0095]

[0096] [Explanation of symbols]

[0097] 100: Membrane electrode assembly

[0098] 1: Plate-shaped porous silica

[0099] 10, 30: Electrode

[0100] 11: First catalyst layer 12: Second catalyst layer

[0101] 20:Polymer electrolyte membrane

[0102] 200: Fuel cell 210: Fuel supply section

[0103] 220: Reforming section 230: Stack

[0104] 231: 1st supply pipe 232: 2nd supply pipe

[0105] 233: 1st discharge pipe 234: 2nd discharge pipe

[0106] 240: Oxidant supply unit

Claims

1. a first catalyst layer containing plate-shaped porous silica, a second catalyst layer, and a polymer electrolyte membrane; The plate-like porous silica has pores with a diameter of 2 to 40 nm, a size of 50 to 2,000 nm, and a thickness of 30 to 300 nm; the second catalyst layer does not contain plate-like porous silica or contains a smaller amount of plate-like porous silica than the first catalyst layer; the first catalyst layer is located between the second catalyst layer and the polymer electrolyte membrane; A membrane electrode assembly for a fuel cell, comprising:

2. 2. The fuel cell membrane electrode assembly according to claim 1, wherein the plate-shaped porous silica includes mesopores in a shape perpendicular to the plate-shaped shape.

3. 2. The membrane electrode assembly for a fuel cell according to claim 1, wherein the plate-shaped porous silica in the first catalyst layer is contained in an amount of 1 to 20 wt % based on the total weight of the first catalyst layer.

4. 2. The membrane electrode assembly for a fuel cell according to claim 1, wherein the ionomer content of the first catalyst layer is 34 to 40 wt % based on the total weight of the first catalyst layer.

5. 2. The membrane electrode assembly for a fuel cell according to claim 1, wherein the thickness of the first catalyst layer is 0.2 to 5 [mu]m.

6. 10. The fuel cell membrane electrode assembly according to claim 1, wherein the ionomer content of the first catalyst layer is greater than the ionomer content of the second catalyst layer.

7. A fuel cell comprising the fuel cell membrane electrode assembly of claim 1.

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