Composition for fuel cell electrode and manufacturing method of fuel cell electrode using the same

Abstract

The present invention relates to a composition for forming a fuel cell electrode comprising a catalyst, a pore-forming agent, an ionomer, and a solvent, wherein the pore-forming agent comprises a sublimable compound, and a method for manufacturing a fuel cell electrode using said composition.

Description

Technology Field

[0001] The present invention relates to a composition for forming a fuel cell electrode and a method for manufacturing a fuel cell electrode using the same. More specifically, the invention relates to a composition for forming a fuel cell electrode and a method for manufacturing a fuel cell electrode using the same, which can improve the performance of a fuel cell by controlling the pore size and porosity within the electrode layer through the introduction of a sublimable pore-forming agent that can be easily removed during the electrode manufacturing process without a separate additional process. 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-based fuel materials like methanol, ethanol, and natural gas, into electrical energy. Due to their high energy efficiency and eco-friendly characteristics, including low pollutant emissions, they are gaining attention as a next-generation clean energy source capable of replacing fossil fuels.

[0003] These fuel cells have the advantage of being able to produce a wide range of outputs through a stack configuration formed by stacking unit cells, and are attracting attention as small and portable power sources because they exhibit an energy density 4 to 10 times that of small lithium batteries.

[0004] The stack that actually generates electricity in a fuel cell has a structure in which several to 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 anode (or fuel electrode) and a cathode (or air electrode) are formed on opposite sides 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 of the electrolyte. Among these, polymer electrolyte membrane fuel cells are gaining popularity as portable, automotive, and home power supply devices 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) that use hydrogen gas as fuel and direct methanol fuel cells (DMFCs) that use liquid methanol as fuel.

[0007] To summarize the reactions occurring in a polymer electrolyte fuel cell, first, when a fuel such as hydrogen gas is supplied to the anode, hydrogen ions (H₂) are produced at the anode through the oxidation reaction of hydrogen. + ) and electrons (e - ) is generated. The generated hydrogen ions are transferred to the reduction electrode through the polymer electrolyte membrane, and the generated electrons are transferred to the reduction electrode through the external circuit. At the reduction electrode, oxygen is supplied, and oxygen combines with hydrogen ions and electrons to produce water through the reduction reaction of oxygen.

[0008] Since polymer electrolyte membranes serve as a pathway for hydrogen ions generated at the anode to be transferred to the cathode, they must fundamentally possess excellent hydrogen ion conductivity. Furthermore, polymer electrolyte membranes must have excellent separation capabilities for separating hydrogen gas supplied to the anode from oxygen supplied to the cathode. In addition, they require excellent mechanical strength, dimensional stability, and chemical resistance, as well as characteristics such as low ohmic loss at high current densities.

[0009] In the above fuel cell system, the membrane electrode assembly (MEA) that substantially generates electricity has a structure in which an anode and a cathode are positioned with a polymer electrolyte membrane containing a hydrogen ion-conducting polymer in between, and each electrode mainly comprises a composition of a catalyst, an ionomer, a solvent, and additives, and preferably has a structure capable of effectively discharging water generated during the operation process while simultaneously supplying fuel within the fuel cell.

[0010] Japanese Patent Publication No. 2006-147371 discloses a method for obtaining an electrode layer having pores of different sizes and types formed thereon by sputtering platinum particles together with iron particles and then removing only the iron particles using hydrochloric acid to secure pores and porosity of a fuel cell electrode.

[0011] However, according to the above method, in order to remove iron particles, which are pore-forming materials included in the electrode-forming composition, a strong acid such as hydrochloric acid must be separately added, and there is also a problem that side reactions may occur between other components, such as catalysts or ionomers, included in the electrode-forming composition due to the strong acid such as hydrochloric acid. The problem to be solved

[0012] The objective of the present invention is to provide a composition for forming a fuel cell electrode that can optimize the pore size and porosity of the electrode layer of a fuel cell.

[0013] Another objective of the present invention is to provide a method for manufacturing a fuel cell electrode using the above-described composition for forming a fuel cell electrode. means of solving the problem

[0014] One embodiment of the present invention provides a composition for forming a fuel cell electrode comprising a catalyst, a pore-forming agent, and an ionomer, wherein the pore-forming agent comprises a sublimable compound.

[0015] The above pore-forming agent may include ammonium bicarbonate, menthol, naphthalene, maleic anhydride, salicylic acid, benzoic acid, or a combination thereof.

[0016] The mass ratio of the catalyst and the pore-forming agent in the above electrode-forming composition may be 1:0.1 to 1:2.

[0017] The catalyst comprises a carrier and metal particles supported on the carrier, and

[0018] The above carrier is any one selected from the group consisting of graphite, Denka black, Ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanoballs, activated carbon, and combinations thereof, and

[0019] The metal particles may be any one selected from the group consisting of platinum, ruthenium, osmium, platinum-M alloy (wherein M is any one 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.

[0020] The above ionomer may be any one selected from the group consisting of fluorinated polymers, benzimidazole polymers, polyimide polymers, polyetherimide polymers, polyphenylene sulfide polymers, polysulfone polymers, polyethersulfone polymers, polyetherketone polymers, polyether-etherketone polymers, polyphenylquinoxaline polymers, and combinations thereof.

[0021] The above composition further comprises a solvent, and the solvent may be any one selected from the group consisting of water, methanol, ethanol, butanol, n-propanol, isopropanol, n-butyl acetate, ethylene glycol, dipropylene glycol, glycerol, and combinations thereof. However, to prevent catalyst ignition caused by organic solvents, it is preferable to sufficiently wet the catalyst with water to lower catalyst activity and then add another solvent. In addition, regarding the solvent used when preparing the pore-forming agent solution, it is preferable to select it by considering the solubility of the pore-forming agent used and the composition of the final electrode-forming composition.

[0022] Another embodiment of the present invention provides a method for manufacturing an electrode for a fuel cell, comprising the steps of: (1) mixing and dispersing a pore-forming agent and a solvent to prepare a pore-forming agent dispersion; (2) mixing and dispersing a catalyst, an ionomer, and a solvent, and mixing them with the pore-forming agent dispersion to prepare an electrode-forming composition; and (3) applying and drying the electrode-forming composition to manufacture an electrode, wherein the pore-forming agent comprises a sublimable compound.

[0023] In the step of preparing the pore-forming agent dispersion of (1) above, the mixing and dispersion may be performed using a high-shear disperser and a homomixer selected from each other.

[0024] In the step of preparing the electrode-forming composition of (2) above, the mixing and dispersion steps may be performed using a device selected from the group consisting of an ultrasonic grinder, a homomixer, a 3-roll mill, a resonant acoustic mixer, a paste mixer, a stirrer, a high-shear disperser, and combinations thereof.

[0025] The mass ratio of the catalyst and the pore-forming agent in the above electrode-forming composition may be 1:0.1 to 1:2.

[0026] The drying of the above-described electrode-forming composition can be carried out at a temperature of 60 to 100 ℃. Effects of the invention

[0027] According to the present invention, by introducing a sublimable pore-forming agent into a composition for forming a fuel cell electrode, the pore size and porosity of the fuel cell electrode layer can be controlled to facilitate fuel supply and discharge of generated water, thereby improving the performance of the fuel cell.

[0028] In addition, since the sublimable pore-forming agent included in the composition can be easily removed during the electrode drying process without additional processes during the process of forming an electrode using the above-mentioned fuel cell electrode forming composition, the performance of the fuel cell electrode and fuel cell manufactured thereby can be improved. Brief explanation of the drawing

[0029] FIG. 1 is a schematic cross-sectional view of a membrane-electrode assembly according to one embodiment of the present invention. FIG. 2 is a schematic diagram illustrating the overall configuration of a fuel cell according to one embodiment of the present invention. Figure 3 is an electron microscope image of the cross-section of the electrode layer prepared in Comparative Example 1 (Fig. 3(a)), Example 1 (Fig. 3(b)), Example 2 (Fig. 3(c)), and Example 3 (Fig. 3(d)). Specific details for implementing the invention

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

[0031] In the drawings, thicknesses have been enlarged to clearly represent various layers and regions, and the same reference numerals have been used for similar parts throughout the specification. When a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between. Conversely, when a part is described as being "immediately on" another part, it means that there is no other part in between.

[0032] A composition for forming a fuel cell electrode according to one embodiment is described below.

[0033] The present invention relates to a composition for forming a fuel cell electrode that can improve the performance of a fuel cell by controlling the pore size and porosity within an electrode layer by introducing a sublimable pore-forming agent that can be easily removed during the manufacturing process of the electrode without a separate additional process, and a method for manufacturing a fuel cell electrode using the same.

[0034] Specifically, a composition for forming a fuel cell electrode according to one embodiment comprises a catalyst, a pore-forming agent, and an ionomer.

[0035] In a fuel cell system, the membrane electrode assembly (MEA) that substantially generates electricity has a structure in which an anode and a cathode are positioned with a polymer electrolyte membrane containing a hydrogen ion-conducting polymer in between, and each electrode preferably comprises a composition mainly of a catalyst, an ionomer, a solvent, and additives, and has a structure capable of effectively discharging water generated during the operation process while simultaneously supplying fuel within the fuel cell.

[0036] To ensure smooth fuel supply and improve the efficiency of the electrochemical reaction in a fuel cell, it is desirable to use electrodes with small pore sizes and high porosity. However, if the pore size is excessively reduced, there is a problem in that water generated during the operation of the fuel cell cannot be effectively removed; conversely, if the pore size is excessively large, while the discharge of generated water can proceed smoothly, the overall porosity of the electrode decreases, leading to a problem of reduced fuel supply efficiency.

[0037] In this regard, the composition for forming a fuel cell electrode according to the present invention can improve the performance of a fuel cell by controlling the pore size and porosity of the electrode using a pore-forming agent during the process of forming the fuel cell electrode, and by introducing a pore-forming agent that can be easily removed during the manufacturing process of the electrode without a separate additional process.

[0038] The above-mentioned pore-forming agent is intended for creating pores and controlling porosity in a fuel cell electrode so as to facilitate fuel supply and discharge of generated water, and may refer to a material capable of forming pores and porosity in the electrode solely through a drying process of the electrode-forming composition without undergoing a separate process, as with pore-forming agents disclosed in prior art.

[0039] In one embodiment, the pore-forming agent may include a sublimable material, preferably a material capable of forming pores and porosity in an electrode by sublimating at a temperature of 60 to 100°C, specifically may include ammonium bicarbonate, menthol, naphthalene, maleic anhydride, salicylic acid, benzoic acid, or a combination thereof, and preferably may include ammonium bicarbonate as the pore-forming agent.

[0040] The above-mentioned pore-forming agent is included in a composition for forming fuel cell electrodes, and has the advantage of being able to form various pore sizes or porosity of fuel cell electrodes by varying the particle size through methods such as controlling the rotational speed of a dispersion device, such as a high-shear disperser, which will be described later.

[0041] In one embodiment, the mass ratio of the catalyst and the pore-forming agent in the electrode-forming composition may be 1:0.1 to 1:2, and preferably 1:0.2 to 1:1. If the content of the pore-forming agent is less than the above mass ratio, the effect of adding the pore-forming agent may be negligible, and if the mass ratio of the pore-forming agent exceeds the above mass ratio, there may be a problem in that the physical durability of the manufactured electrode layer is reduced due to excessive pore formation.

[0042] In one embodiment, the catalyst may comprise a carrier and metal particles supported on the carrier.

[0043] The above carrier may be a carbon-based material including, for example, graphite, Denka black, Ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanoballs, activated carbon, and combinations thereof. More specifically, the carbon-based carrier is most preferably selected from the group consisting of hollow carbon capsules (HCC), multimodal porous carbon (MPC), carbon nanotubes (CNT), carbon nanofibers (CNF), mesoporous carbon, graphene, high surface area high conductivity carbon black, and combinations thereof.

[0044] Any of the above metal particles that can participate in the reaction of a fuel cell and be used as a catalyst can be used, for example, platinum-based catalysts can be used.

[0045] As the platinum-based catalyst, any metal particle selected from the group consisting of platinum, ruthenium, osmium, platinum-M alloy (wherein M is any one 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.

[0046] The anode electrode and the cathode electrode of the fuel cell may use the same material as a catalyst, but more specific examples of the platinum-based catalyst may be any one selected from the group consisting of Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / Co, Pt / Ru / W, Pt / Ru / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni, and Pt / Ru / Sn / W.

[0047] At this time, the metal particles may be located on the surface of the carrier, or they may penetrate into the carrier while filling the internal pores of the carrier.

[0048] Any polymer resin having a cation exchange group selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphate groups, phosphonic acid groups, and derivatives thereof in a side chain can be used as the above ionomer.

[0049] In one embodiment, the ionomer may comprise one or more hydrogen ion-conducting polymers selected from fluorinated polymers, benzimidazole polymers, polyimide polymers, polyetherimide polymers, polyphenylene sulfide polymers, polysulfone polymers, polyethersulfone polymers, polyetherketone polymers, polyether-etherketone polymers, and polyphenylquinoxaline polymers; more specifically, the ionomer may comprise one or more hydrogen ion-conducting polymers selected from poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, sulfated polyetherketones, aryl ketones, poly(2,2'-m-phenylene)-5,5'-bibenzimidazole, and poly(2,5-benzimidazole). there is.

[0050] The above-described polymer resin having hydrogen ion conductivity may substitute H with Na, K, Li, Cs, or tetrabutylammonium at the cation exchange group at the end of the side chain. When substituting H with Na at the ion exchange group at the end of the side chain, NaOH is used during the preparation of the catalyst composition; when substituting with tetrabutylammonium, tetrabutylammonium hydroxide is used for substitution; K, Li, or Cs may also be substituted using appropriate compounds. Since the above substitution method is widely known in the art, a detailed description thereof is omitted in this specification.

[0051] The above ionomer may be included in an amount of 20 to 50 parts by weight based on 100 parts by weight of solid content in a composition for forming a fuel cell electrode, for example, in an amount of 25 to 40 parts by weight. If the content of the above ionomer is less than 20 parts by weight, problems may occur in the formation of an ion conduction network of the fuel cell electrode, which may lead to a decrease in performance, and if it exceeds 50 parts by weight, a decrease in pores within the electrode and a decrease in water drainage ability may lead to an increase in resistance, which may result in a decrease in performance.

[0052] The above ionomer can be used in the form of a single substance or a mixture, and may also be optionally used in combination with a non-conductive compound to further enhance adhesion to the polymer electrolyte membrane. It is preferable to adjust the amount used to suit the intended purpose.

[0053] One or more of the above-mentioned non-conductive compounds may be used, 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.

[0054] In one embodiment, the composition for forming a fuel cell electrode may further include a solvent. The solvent may be any one selected from the group consisting of water, methanol, ethanol, butanol, n-propanol, isopropanol, n-butyl acetate, ethylene glycol, dipropylene glycol, glycerol, and combinations thereof, and is not limited to any type as long as it can effectively disperse a pore-forming agent included in the composition for forming a fuel cell electrode, but preferably, an aqueous solvent including water may be used.

[0055] The above solvent may be included in an amount of 50 to 95 parts by weight based on 100 parts by weight of the composition for forming a fuel cell electrode, for example, in an amount of 80 to 90 parts by weight. If the content of the solvent is 50 parts by weight or more, it prevents the viscosity of the catalyst composition from becoming too high, thereby preventing a decrease in the dispersion of catalyst particles and uneven formation of the catalyst layer; and if the content of the solvent is 95 parts by weight or less, it prevents the viscosity of the catalyst composition from becoming too low, thereby preventing the problem of the catalyst layer being thin and requiring repeated coating.

[0056] Another embodiment of the present invention provides a method for manufacturing an electrode for a fuel cell, comprising the steps of: preparing an electrode-forming composition comprising a catalyst, a pore-forming agent, and an ionomer; and applying and drying the electrode-forming composition to manufacture an electrode, wherein the pore-forming agent comprises a sublimable compound.

[0057] According to a method for manufacturing an electrode for a fuel cell according to one embodiment, since a sublimable pore-forming agent included in the composition can be easily removed during the electrode drying process without an additional process during the process of forming an electrode using the composition for forming a fuel cell electrode, there is an advantage in that the performance of the fuel cell electrode and the fuel cell manufactured thereby can be improved.

[0058] In the method for manufacturing an electrode for a fuel cell according to one embodiment, the description of the types of catalyst, pore-forming agent, ionomer, and solvent is as described above.

[0059] One embodiment of the present invention provides a method for manufacturing an electrode for a fuel cell, comprising: (1) a step of preparing a pore-forming agent dispersion by mixing and dispersing a pore-forming agent and a solvent; (2) a step of preparing an electrode-forming composition by mixing and dispersing a catalyst, an ionomer, and a solvent and mixing them with the prepared pore-forming agent dispersion; and (3) a step of manufacturing an electrode by applying and drying the electrode-forming composition, wherein the pore-forming agent comprises a sublimable compound.

[0060] In the step of preparing the pore-forming agent dispersion of (1) above, dispersion can be carried out using either a high-shear disperser or a homomixer, but any method capable of uniformly dispersing the pore-forming agent in a solvent can be used without limitation, and preferably, the pore-forming agent dispersion can be prepared using a high-shear disperser.

[0061] In the process of first preparing a dispersion of the above (1) pore-forming agent by adding and dispersing the pore-forming agent in a solvent, the particle size of the pore-forming agent can be controlled by adjusting the rotational speed through a device such as a high-shear disperser or a homomixer, and thereby there is an advantage in that the pore size and porosity of the electrode layer produced finally can be controlled.

[0062] In one embodiment, in the step of preparing the pore-forming agent dispersion of (1) above, the dispersion can be performed using a high-shear disperser at a rotational speed of 2,500 rpm to 7,000 rpm, and preferably at a rotational speed of 2,500 rpm to 4,500 rpm for 3 to 60 minutes. As the rotational speed increases, the size of the pore-forming agent particles decreases, and as the holding time increases, the distribution of the pore-forming agent particle size becomes more uniform. By adjusting the rotational speed and holding time, the pore size and porosity within the electrode layer can be easily controlled thereafter, thereby expecting a reduction in resistance of the fuel cell and an improvement in performance.

[0063] In the step of preparing the electrode-forming composition of (2) above, the mixing and dispersion steps may be performed using a method selected from the group consisting of an ultrasonic grinder, a homomixer, a 3-roll mill, a resonant acoustic mixer, a paste mixer, a stirrer, a high-shear disperser, and combinations thereof, but are not limited to this and may be used as long as the method can disperse uniformly.

[0064] In one embodiment, the mass ratio of the catalyst to the pore-forming agent in the electrode-forming composition may be 1:0.1 to 1:2, and preferably 1:0.2 to 1:1. If the content of the pore-forming agent is less than the above mass ratio, the effect of adding the pore-forming agent may be negligible, and if the mass ratio of the pore-forming agent exceeds the above mass ratio, there may be a problem in that the physical durability of the manufactured electrode layer is reduced due to excessive pore formation.

[0065] Next, (3) the electrode forming composition is applied and dried to manufacture an electrode.

[0066] Depending on the viscosity of the electrode forming composition, the above coating process may use a screen printing method, a spray coating method, a coating method using a doctor blade, a spray coating method, etc., but the present invention is not limited thereto.

[0067] In addition, the electrode may be applied with a thickness of 1 to 100 μm. If the thickness is less than 1 μm, the reaction area may be small and activity may decrease, and if it exceeds 100 μm, the travel distance of ions and electrons may increase and resistance may increase.

[0068] Meanwhile, after applying the electrode-forming composition, the electrode-forming composition may be optionally dried, and the drying process may involve drying at 60 to 100°C for 8 hours or more. If the drying temperature is below 60°C, the evaporation of the solvent is not smooth, so a sufficiently dried electrode may not be formed, and if it exceeds 100°C, there may be a risk of ignition of the catalyst and cracking of the electrode may occur. It is preferable to select the drying time under conditions where the solvent in the electrode layer can evaporate sufficiently.

[0069] According to another embodiment of the present invention, a membrane-electrode assembly for a fuel cell is provided, comprising an electrode prepared from the composition for forming the fuel cell electrode.

[0070] FIG. 1 is a cross-sectional view schematically illustrating the membrane-electrode assembly. Hereinafter, the membrane-electrode assembly will be described with reference to FIG. 1.

[0071] The above membrane-electrode assembly (150) comprises an anode electrode (110) and a cathode electrode (110) positioned opposite each other; and a polymer electrolyte membrane (130) positioned between the anode electrode (110) and the cathode electrode (110). In the above membrane-electrode assembly (150), the electrode disposed on one side of the polymer electrolyte membrane (130) and causing an oxidation reaction that generates hydrogen ions and electrons from fuel is called the anode electrode (110), and the electrode causing a reduction reaction that generates water from hydrogen ions supplied through the polymer electrolyte membrane (130) and the oxidizing agent of the electrode is called the cathode electrode (110).

[0072] At least one of the anode electrode (110) and the cathode electrode (110) may be a fuel cell electrode manufactured from the fuel cell electrode forming composition of the present invention described above.

[0073] The polymer electrolyte membrane (130) is a solid polymer electrolyte with a thickness of 10 to 200 μm and has the function of ion exchange for moving hydrogen ions generated at the anode electrode (110) to the cathode electrode (110).

[0074] The polymer electrolyte membrane (130) may be a hydrocarbon-based polymer electrolyte membrane, a fluorine-based polymer electrolyte membrane, and a mixture or copolymer of one or more of these.

[0075] The above hydrocarbon-based polymer electrolyte membrane may include a hydrocarbon-based polymer, and the polymer may be selected from styrene, imide, sulfone, phosphazene, ether-ether ketone, ethylene oxide, polyphenylene sulfide, or homopolymers or copolymers of aromatic groups 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.

[0076] More preferably, one or more selected from the group consisting of sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyetherketone, sulfonated polyetheretherketone, sulfonated polyaryrene ether ether ketone, sulfonated polyaryrene ether ether ketone, sulfonated polyaryrene ether sulfone, sulfonated polyaryrene ether benzimidazole, and a membrane into which an ion conductor has been introduced may be used as the suitable hydrocarbon membrane.

[0077] The above-mentioned fluorine-based polymer electrolyte membrane can be used without special limitations as long as it is a material having sufficient mechanical strength and high electrochemical stability to form a film as an ion-conducting membrane. Specific examples of fluorine-based polymer electrolyte membranes include perfluorosulfonic acid resin and copolymers of tetrafluoroethylene and fluorovinyl ether. The fluorovinyl ether moiety has the function of conducting hydrogen ions. The above-mentioned copolymer is commercially available as it is sold by DuPont under the trade name Nafion.

[0078] Meanwhile, the membrane-electrode assembly (150) may further include an interfacial adhesive layer (not shown) located between the polymer electrolyte membrane (130) and the electrode (110).

[0079] The above interface adhesive layer enables the membrane-electrode assembly (150) to have low hydrogen permeability without a decrease in hydrogen ion conductivity, improves the interfacial bonding between the electrode (110) and the polymer electrolyte membrane (130), thereby improving the durability of the membrane-electrode assembly (150) and improving the performance and durability of the membrane-electrode assembly (150) under high temperature / low humidity conditions. The above interface adhesive layer may be located on only one side of the polymer electrolyte membrane (130).

[0080] According to another embodiment of the present invention, a fuel cell comprising the membrane-electrode assembly is provided. FIG. 2 is a schematic diagram illustrating the overall configuration of the fuel cell.

[0081] Referring to FIG. 2 above, the fuel cell (200) includes a fuel supply unit (210) that supplies a mixed fuel in which fuel and water are mixed, 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 causing an electrochemical reaction between the reformed gas containing hydrogen gas supplied from the reforming unit (220) and an oxidizing agent supply unit (240) that supplies an oxidizing agent to the reforming unit (220) and the stack (230).

[0082] The stack (230) comprises a plurality of unit cells that generate electrical energy by inducing an oxidation / reduction reaction between a reforming gas containing hydrogen gas supplied from the reforming unit (220) and an oxidizing agent supplied from the oxidizing agent supply unit (240).

[0083] Each unit cell refers to a unit cell that generates electricity and includes a membrane-electrode assembly that oxidizes / reduces oxygen in an oxidant and a reforming gas containing hydrogen gas, and a separator (also called a bipolar plate, hereinafter referred to as a 'separator') for supplying the reforming gas containing hydrogen gas and the oxidant 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 located at the outermost side of the stack is specifically referred to as an end plate.

[0084] Among the above separator plates, the end plate is provided with a pipe-shaped first supply pipe (231) for injecting a reforming gas containing hydrogen gas supplied from the reforming unit (220) and a pipe-shaped second supply pipe (232) for injecting oxygen gas, and the other end plate is provided with a first discharge pipe (233) for discharging to the outside a reforming gas containing hydrogen gas that is finally unreacted and remaining in a plurality of unit cells, and a second discharge pipe (234) for discharging to the outside an oxidizing agent that is finally unreacted and remaining in the above unit cells.

[0086] Specific embodiments of the present invention are presented below. However, the embodiments described below are merely for the purpose of specifically illustrating or explaining the present invention and do not limit the present invention. Furthermore, details not described herein can be sufficiently technically inferred by a person skilled in the art, so their description is omitted.

[0088] [Preparation Example: Preparation of a composition for forming a fuel cell electrode]

[0089] Preparation Example 1

[0090] (1) 5 g of ammonium bicarbonate (Daejeong Hwakum Co.) and 45 ml of distilled water are added to a high-shear disperser L5M-A High Shear Mixer (Silverson Co.), and the mixture is dispersed for 10 minutes at a rotation speed of 2,500 rpm to prepare a pore-forming agent dispersion.

[0091] (2) 5 g of Pt / CB (Tanaka, TEC10E50E) as a catalyst, 10 g of Nafion D2021 (Dupont), a perfluorosulfonic acid polymer, as an ionomer, and 23 g of a solvent mixed with dipropylene glycol and distilled water in a 1:1 ratio were mixed, and the catalyst and ionomer were sufficiently dispersed for 1 hour using a 3-roll mill (EXAKT 50) so that they could be uniformly dispersed, and then sufficiently mixed with the prepared pore-forming agent dispersion to prepare a composition for forming a fuel cell electrode.

[0093] Preparation Example 2

[0094] A composition for forming a fuel cell electrode was prepared in the same manner as in Preparation Example 1, except that the rotation speed of the high-shear disperser was set to 4,500 rpm in the step of preparing the pore-forming agent dispersion in Preparation Example 1.

[0096] Preparation Example 3

[0097] A composition for forming a fuel cell electrode was prepared in the same manner as in Preparation Example 1, except that the rotation speed of the high-shear disperser was set to 6,500 rpm in the step of preparing the pore-forming agent dispersion in Preparation Example 1.

[0099] Comparative Manufacturing Example 1

[0100] A composition for forming a fuel cell electrode was prepared by mixing 5 g of Pt / CB (Tanaka, TEC10E50E) as a catalyst, 10 g of Nafion D2021 (Dupont), a perfluorosulfonic acid polymer, as an ionomer, 23 g of a solvent mixed with dipropylene glycol and distilled water in a 1:1 ratio, and 6.75 g of distilled water, and then using a 3-roll mill (EXAKT 50) to sufficiently disperse the catalyst and ionomer for 1 hour so that they could be uniformly dispersed.

[0102] [Example: Preparation of Membrane-Electrode Assembly]

[0103] The compositions for forming fuel cell electrodes prepared in each of the above Preparation Examples 1 to 3 and Comparative Preparation Example 1 were bar-coated onto a fluorinated ethylene propylene release film under conditions of a coating speed of 10 mm / s and a coating thickness of 100 μm, and then dried at 60 ℃ for 8 hours to prepare electrodes.

[0104] The above dried electrode was cut to the required size, aligned so that the electrode surface and the electrolyte membrane were in contact on both sides of a polymer electrolyte membrane (DuPont product; Nafion 212 Membrane), and then transferred by hot pressing under heat and pressure conditions of 140°C and 1 MPa for 5 minutes, followed by maintaining at room temperature for 1 minute, and the release film was peeled off to manufacture a membrane-electrode assembly.

[0106] [Experimental Example: Performance Evaluation of Membrane-Electrode Assembly]

[0107] Evaluation Experiment Example 1 Comparison of electrode layer pores depending on the presence or absence of pore-forming agent

[0108] For the electrodes prepared according to the above examples using the compositions of Comparative Preparation Example 1 and Preparation Examples 1 to 3, the pore distribution and porosity of the porous electrodes were measured via Mercury Porosity Measurement (MIP), and the results are shown in Table 1 below. An Autopore 9605 instrument was used for the measurement, and the prepared electrode layer sample was 1 x 5 cm 2Analysis was performed by injecting 10 EA, and only data with a pore diameter of 5 µm or less were used.

[0110] Average pore diameter (nm) Porosity (%) Comparative Example 1 41.11 37.84 Example 1 50.12 40.21 Example 2 47.35 39.32 Example 3 43.25 38.66

[0111] From Table 1 above, it was confirmed that the average pore diameter and porosity increased in the electrode layer prepared by introducing a pore-forming agent according to the present invention, and that the pore diameter and porosity could be controlled according to the rpm level of the high-shear disperser.

[0113] Evaluation Experiment Example 2 Comparison of fuel cell electrode layer thickness with and without pore-forming agent addition

[0114] Cross-sectional samples of the electrode layers of the membrane-electrode assemblies prepared in the above examples were observed using an electron microscope (S-3400N, Hitachi) and their thickness was measured. Figure 3 shows electron microscope images of the cross-sections of the electrode layers prepared in Comparative Example 1 (Fig. 3(a)), Example 1 (Fig. 3(b)), Example 2 (Fig. 3(c)), and Example 3 (Fig. 3(d)). In addition, the thickness of the upper cathode electrode layer was compared among the results, and the results are summarized in Table 2 below.

[0115] Electrode layer thickness (㎛) Comparative Example 1 8.58 Example 1 11.74 Example 2 10.95 Example 3 9.76

[0116] From Table 2, it can be seen that the electrode layer thickness increases slightly with the addition of a pore-forming agent, which is attributed to the influence of pore formation within the electrode layer.

[0118] Evaluation Experiment Example 3 Comparison of fuel cell performance and mass transfer resistance between samples

[0119] The output performance of the membrane-electrode assembly prepared in the above example was evaluated through IV measurement. Specifically, to verify the output performance under actual fuel cell operating conditions, hydrogen (100 %RH) and air (100 %RH) were supplied to the anode and cathode, respectively, at amounts corresponding to Stoichiometry 1.2 / 2.0 under conditions of 65°C using a fuel cell unit cell evaluation device (Scribner 850 fuel cell test system). The current density was measured at a voltage of 0.6V, and a higher result value indicates superior output performance.

[0120] An electrochemical analyzer (Biologic SP-200) was used to verify the electrochemical active area and mass transfer resistance. The mass transfer resistance was measured at a frequency range of 0.1 Hz to 10 kHz and 2,200 mA / cm² under the same temperature and fuel supply conditions as the output performance evaluation. 2 Experiments were conducted at current densities.

[0121] The evaluation results are shown in Table 3 below.

[0122] Battery Performance Evaluation (A / cm) 2 ) Mass transfer resistance Comparative Example 1 1.35 0.148 Example 1 1.48 0.101 Example 2 1.44 0.118 Example 3 1.41 0.127

[0123] From Table 3 above, it was confirmed that in Examples 1 to 3, in which a pore-forming agent was added according to the present invention, battery performance increased and mass transfer resistance decreased.

[0125] Although 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. Furthermore, various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the claims set forth below also fall within the scope of the present invention. Explanation of the symbols

[0126] 110: Anode electrode and cathode electrode 130: Polymer electrolyte membrane 150: Membrane-electrode assembly 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 unit

Claims

Claim 1 A composition for forming a fuel cell electrode, comprising a catalyst, a dispersion of a pore-forming agent in which a pore-forming agent is dispersed, and an ionomer, wherein the pore-forming agent comprises a sublimable compound that sublimes at a temperature of 60 to 70°C, wherein the sublimable compound comprises at least ammonium bicarbonate, wherein the dispersion of the pore-forming agent is dispersed using a high-shear disperser at a rotational speed of 2,500 rpm to 7,000 rpm, wherein the mass ratio of the catalyst to the pore-forming agent is 1:0.1 to 1:1, and wherein the ionomer is included in an amount of 20 to 50 parts by weight based on 100 parts by weight of solid content in the composition for forming a fuel cell electrode. Claim 2 A composition for forming a fuel cell electrode according to claim 1, wherein the pore-forming agent further comprises menthol, naphthalene, maleic anhydride, or a combination thereof. Claim 3 delete Claim 4 A composition for forming a fuel cell electrode according to claim 1, wherein the catalyst comprises a carrier and metal particles supported on the carrier, the carrier is any one selected from the group consisting of graphite, Denka black, Ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanoballs, activated carbon, and combinations thereof, and the metal particles are any one selected from the group consisting of platinum, ruthenium, osmium, platinum-M alloy (wherein M is any one 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. Claim 5 A composition for forming a fuel cell electrode according to claim 1, wherein the ionomer is any one selected from the group consisting of fluorinated polymers, benzimidazole polymers, polyimide polymers, polyetherimide polymers, polyphenylene sulfide polymers, polysulfone polymers, polyethersulfone polymers, polyetherketone polymers, polyether-etherketone polymers, polyphenylquinoxaline polymers, and combinations thereof. Claim 6 A composition for forming a fuel cell electrode according to claim 1, further comprising a solvent, wherein the solvent is any one selected from the group consisting of water, methanol, ethanol, butanol, n-propanol, isopropanol, n-butyl acetate, ethylene glycol, dipropylene glycol, glycerol, and combinations thereof. Claim 7 (1) a step of preparing a pore-forming agent dispersion by mixing and dispersing a pore-forming agent and a solvent; (2) a step of preparing an electrode-forming composition by dispersing a catalyst, an ionomer, and a solvent, and then mixing them with the pore-forming agent dispersion; A method for manufacturing an electrode for a fuel cell, comprising the step of (3) applying and drying the electrode-forming composition to manufacture an electrode, wherein in the step of preparing the pore-forming agent dispersion of (1), the dispersion is performed using a high-shear disperser at a rotational speed of 2,500 rpm to 7,000 rpm, the pore-forming agent comprises a sublimable compound that sublimes at a temperature of 60 to 70 ℃, the sublimable compound comprises at least ammonium bicarbonate, the mass ratio of the catalyst to the pore-forming agent is 1:0.1 to 1:1, and the ionomer is included in an amount of 20 to 50 parts by weight based on 100 parts by weight of solid content in the battery electrode-forming composition. Claim 8 delete Claim 9 delete Claim 10 delete Claim 11 A method for manufacturing an electrode for a fuel cell according to claim 7, wherein in the step of manufacturing the electrode-forming composition of (2) above, the mixing and dispersion steps are performed using a device selected from the group consisting of an ultrasonic grinder, a homomixer, a 3-roll mill, a resonant acoustic mixer, a paste mixer, a stirrer, a high-shear disperser, and combinations thereof. Claim 12 A method for manufacturing an electrode for a fuel cell according to claim 7, wherein the drying of the coated electrode-forming composition is carried out at a temperature of 60 to 100 ℃.

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