KR100759435B1 - Catalyst for fuel cell and membrane-electrode assembly for fuel cell - Google Patents

Abstract

A catalyst and a membrane-electrode assembly for a fuel cell, including the same are provided to improve an amount of a supported organic metal material and a degree of dispersion, thereby producing a fuel cell system with excellent performances. A catalyst for a fuel cell comprises a conductive carrier having an average pore size of 20-30 nm and an organic metal material supported on the carrier. Preferably, the conductive carrier is selected from the group consisting of carbon aerosol, mesoporous carbon and a combination thereof, and the organic metal material is selected from the group consisting of a compound represented by the formulae 1-4(wherein, M is Fe, Co, Ni or Cu) and a combination thereof. A membrane-electrode assembly includes a cathode comprising the catalyst, an anode comprising a platinum-based catalyst or the catalyst, which is opposed to the cathode, and a polymer electrolytic membrane disposed between the cathode and the anode.

Description

Catalysts for fuel cells and membrane-electrode assemblies for fuel cells including the same {CATALYST FOR FUEL CELL AND MEMBRANE-ELECTRODE ASSEMBLY FOR FUEL CELL}

1 is a schematic view showing the structure of the membrane-electrode assembly of the present invention.

2 is a schematic view showing a configuration of a fuel cell system of the present invention.

[Industrial use]

The present invention relates to a fuel cell catalyst and a fuel cell membrane-electrode assembly including the same, and more particularly, to a fuel cell catalyst having a high loading amount and a high dispersion and a fuel cell membrane-electrode assembly including the same.

[Prior art]

A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy.

Such a fuel cell is a clean energy source that can replace fossil energy, and has a merit of generating a wide range of output by stacking unit cells stacked, and 4-10 times more energy than a small lithium battery. Due to its density, it is attracting attention as a compact and portable portable power source.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC) and a direct oxidation fuel cell (Direct Oxidation Fuel Cell). When methanol is used as a fuel in the direct oxidation fuel cell, it is called a direct methanol fuel cell (DMFC).

The polymer electrolyte fuel cell has an advantage of having a high energy density and a high output, but requires attention to handling hydrogen gas and reforms fuel for reforming methane, methanol, natural gas, etc. to produce hydrogen as fuel gas. There is a problem that requires additional equipment such as a device.

On the other hand, the direct oxidation fuel cell has a lower energy density than the polymer electrolyte fuel cell, but it is easy to handle fuel and has a low operating temperature, so that it can be operated at room temperature, in particular, it does not require a fuel reformer.

In such fuel cell systems, the stack that substantially generates electricity comprises several unit cells consisting of a membrane-electrode assembly (MEA) and a separator (also called a bipolar plate). It has a structure laminated to several tens. The membrane-electrode assembly is called an anode electrode (also called a “fuel electrode” or an “oxidation electrode”) and a cathode electrode (also called “air electrode” or “reduction electrode”) with a polymer electrolyte membrane containing a hydrogen ion conductive polymer therebetween. ) Is located.

The principle of generating electricity in a fuel cell is that fuel is supplied to an anode electrode, which is a fuel electrode, adsorbed to a catalyst of the anode electrode, and the fuel is oxidized to generate hydrogen ions and electrons. Reaching the cathode electrode, hydrogen ions pass through the polymer electrolyte membrane and are delivered to the cathode electrode. An oxidant is supplied to the cathode, and the oxidant, hydrogen ions, and electrons react on the catalyst of the cathode to generate electricity while producing water.

The catalyst is generally used in various forms of platinum catalyst, one of which is widely used to support the platinum on the carbon carrier. However, since platinum is an expensive precious metal, an excessive amount cannot be used, and battery performance is limited. Therefore, studies on catalysts that can be used as catalysts for fuel cells instead of precious metals such as platinum are being actively conducted. One of them is a method of preparing a catalyst using an organometallic material, or it is difficult to produce a satisfactory high activity catalyst due to the large volume of the organic metal itself, which is difficult to support.

It is an object of the present invention to provide catalysts for high tack and highly dispersed fuel cells.

Another object of the present invention is to provide a membrane-electrode assembly for a fuel cell comprising the catalyst.

In order to achieve the above object, the present invention provides a catalyst for a fuel cell comprising a conductive carrier having a pore size of 20 to 30nm and an organometallic material supported on the carrier.

The invention also includes an anode electrode and a cathode electrode positioned opposite each other; And a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, wherein the cathode electrode includes the catalyst of the present invention. The anode electrode may include a platinum-based catalyst or may include the catalyst of the present invention.

Hereinafter, the present invention will be described in more detail.

The present invention uses an organometallic material as a catalytically active material. The organometallic material has a large volume, so that it is difficult to support a large amount in a carbon-based material such as Ketjen Black, which is generally used for a carrier, and the pores of the carrier are blocked. There was a problem.

In the present invention, a conductive carrier having a large pore size was used to solve this problem.

That is, the catalyst for a fuel cell of the present invention includes a conductive carrier having a pore size of 20 to 30 nm and an organometallic material supported on the conductive carrier.

In the conductive carrier of the present invention, when the pore size is smaller than 20 nm, a bulky organometallic material has a problem of blocking pores. When the pore size is larger than 30 nm, the surface area of the carrier is reduced or the density of the catalyst is maintained when the large pore and the large surface area are simultaneously maintained. There is a problem that the amount applied to the membrane-electrode assembly is reduced because it is low. Such a conductive carrier has a large pore size compared to a carbon carrier such as Ketjen Black and Vulcan X, which is used as a conventional carrier, having a pore size of about 5 nm, and thus can support a bulky organometallic material.

The conductive carrier may be selected from the group consisting of carbon aerogels, mesoporous carbon, and combinations thereof as the carbon-based material. In addition, the conductive carrier having such large pores can be manufactured using any method as long as the conductive carrier having the desired pores is prepared. Examples thereof include the following method. In the following description, resorcinol, sodium carbonate, formaldehyde, and water used to prepare a carrier are representative examples, but are not limited thereto.

Resorcinol, sodium carbonate, water, formaldehyde, and the mixture are mixed and stirred, and the obtained product is left to gel by leaving the gelled solution at a high temperature of 473K to 1273K, 5MPa to 30MPa. Under a high pressure of CO ₂ supercritical drying process to produce a carbonized aerogel (Carbonized Aerogel) powder carrier. In this process, an organic metal compound is supported on a carrier and then heat-treated to prepare a catalyst.

As the organometallic material, one or more selected from the group consisting of compounds represented by the following Chemical Formulas 1 to 4 may be used.

[Formula 1]

 [Formula 2]

(In Formula 1 or 2, M is Fe, Co, Ni or Cu)

[Formula 3]

[Formula 4]

 In the catalyst of the present invention, since the supported amount of the metal occupies 20 to 30% by weight of the total catalyst weight, it can be seen that it can be very highly supported compared to the conventional 10% by weight or less.

The catalyst of the present invention can be usefully used as a catalyst for a cathode electrode in a fuel cell or as a catalyst for all electrodes that are anode electrodes and cathode electrodes.

The membrane-electrode assembly for a fuel cell of the present invention comprising the catalyst of the present invention includes an anode electrode and a cathode electrode positioned opposite each other, and includes a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode.

The anode electrode and the cathode electrode include an electrode substrate and a catalyst layer formed on the electrode substrate. The cathode electrode may include the catalyst of the present invention, the anode catalyst may include a general platinum-based catalyst, and both the anode electrode and the cathode electrode may include the catalyst of the present invention.

When the anode electrode includes a common platinum-based catalyst, the catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy ((M is Ga, Ti, A catalyst selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Mo, W, Rh, Ru, and combinations thereof; Specific examples include Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / Co, Pt / Ru Or at least one selected from the group consisting of / W, Pt / Ru / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni, and Pt / Ru / Sn / W.

In addition, such a metal catalyst may be used as the metal catalyst (black) itself, or may be supported on a carrier. As the carrier, carbonaceous materials such as graphite, denka black, ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanoballs or activated carbon may be used, or alumina, silica, zirconia, Inorganic fine particles such as titania may be used, but carbon-based materials are generally used.

The catalyst layer may further include a binder resin for improving the adhesion of the catalyst layer and the transfer of hydrogen ions.

It is preferable to use a polymer resin having hydrogen ion conductivity as the binder resin, more preferably a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid group, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain. Any polymer resin which has can be used. Preferably, a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer, a polyether ketone polymer, a polyether One or more hydrogen ion conductive polymers selected from ether ketone polymers or polyphenylquinoxaline polymers, more preferably poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), Copolymers of tetrafluoroethylene with fluorovinyl ethers containing sulfonic acid groups, defluorinated sulfided polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5'-bibenzimidazole One containing at least one hydrogen ion conductive polymer selected from (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) or poly (2,5-benzimidazole) may be used.

The hydrogen ion conductive polymer may replace H with Na, K, Li, Cs or tetrabutylammonium in an ion exchange group at the side chain end. In case of replacing H with Na in the side chain terminal ion exchanger, NaOH is substituted for the preparation of the catalyst composition, and tetrabutylammonium hydroxide is substituted for tetrabutylammonium, and K, Li or Cs may be substituted with appropriate compounds. It can be substituted using. Since this substitution method is well known in the art, detailed description thereof will be omitted.

The binder resin may be used in the form of a single substance or a mixture, and may also be optionally used with a nonconductive polymer for the purpose of further improving adhesion to the polymer electrolyte membrane. It is preferable to adjust the usage-amount so that it may be suitable for a purpose of use.

Examples of the nonconductive polymer include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoro alkylvinyl ether copolymer (PFA), and ethylene / tetrafluoro Ethylene / tetrafluoroethylene (ETFE), ethylenechlorotrifluoro-ethylene copolymer (ECTFE), polyvinylidene fluoride, copolymer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), dode At least one selected from the group consisting of silbenzenesulfonic acid and sorbitol is more preferred.

The electrode substrate plays a role of supporting the electrode and diffuses the fuel and the oxidant to the catalyst layer, thereby serving to easily access the fuel and the oxidant to the catalyst layer. A conductive substrate is used as the electrode substrate, and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (porous film or polymer composed of metal cloth in a fibrous state). It means that the metal film is formed on the surface of the cloth formed of fibers) may be used, but is not limited thereto.

In addition, it is preferable to use a water-repellent treatment with a fluorine-based resin as the electrode base material because it can prevent the reactant diffusion efficiency from being lowered by water generated when the fuel cell is driven. Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, and fluorinated ethylene propylene ( Fluorinated ethylene propylene), polychlorotrifluoroethylene or copolymers thereof can be used.

In addition, a microporous layer may be further included to enhance the reactant diffusion effect in the electrode substrate. These microporous layers are generally conductive powders having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotubes, carbon nanowires, and carbon nanohorns. -horn or carbon nano ring.

The microporous layer is prepared by coating a composition comprising a conductive powder, a binder resin and a solvent on the electrode substrate. The binder resin may be polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, alkoxy vinyl ether, polyvinyl alcohol, cellulose acetate Or copolymers thereof and the like can be preferably used. As the solvent, alcohols such as ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, etc. may be preferably used. The coating process may be screen printing, spray coating, or coating using a doctor blade according to the viscosity of the composition, but is not limited thereto.

The polymer electrolyte membrane is generally used as a polymer electrolyte membrane in a fuel cell, and any one made of a polymer resin having hydrogen ion conductivity may be used. Representative examples thereof include a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid group, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain.

Representative examples of the polymer resin include a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer and a polyether ketone It may include one or more selected from a polymer, a polyether-ether ketone-based polymer or a polyphenylquinoxaline-based polymer, more preferably poly (perfluorosulfonic acid) (generally marketed as Nafion), Poly (perfluorocarboxylic acid), copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, defluorinated sulfide polyether ketones, aryl ketones, poly (2,2'-m-phenylene) Or at least one selected from -5,5'-bibenzimidazole (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) or poly (2,5-benzimidazole) Can be.

In the hydrogen ion conductive group of the hydrogen ion conductive polymer, H may be substituted with Na, K, Li, Cs or tetrabutylammonium. In case of replacing H with Na in the side chain terminal ion exchanger, NaOH is substituted for the preparation of the catalyst composition, and tetrabutylammonium hydroxide is substituted for tetrabutylammonium, and K, Li or Cs may be substituted with appropriate compounds. It can be substituted using. Since this substitution method is well known in the art, detailed description thereof will be omitted.

The membrane-electrode assembly of the present invention is schematically shown in FIG. As shown in FIG. 1, the membrane-electrode assembly 20 of the present invention includes a polymer electrolyte membrane 25 and is located on both sides of the polymer electrolyte membrane 25, and a cathode electrode including the catalyst of the present invention. 21 and the anode electrode 22 is included.

The fuel cell system including the membrane-electrode assembly of the present invention includes at least one electricity generator, a fuel supply and an oxidant supply.

The electricity generating unit includes the membrane-electrode assembly and the separator (also referred to as bipolar plate), and serves to generate electricity through an electrochemical reaction between a fuel and an oxidant.

The fuel supply unit serves to supply fuel to the electricity generation unit, and the oxidant supply unit serves to supply an oxidant to the electricity generation unit. The fuel may be a hydrogen-containing fuel or a hydrocarbon fuel such as methanol, ethanol or propanol. Examples of the oxidant include air or oxygen.

A schematic structure of the fuel cell system of the present invention is shown in FIG. 2, which will be described in more detail with reference to the following. Although the structure shown in FIG. 2 shows a system for supplying fuel and oxidant to an electric generator using a pump, the fuel cell system of the present invention is not limited to such a structure, and a fuel cell using a diffusion method without using a pump is shown. Of course, it can also be used for system architecture.

The fuel cell system 1 of the present invention includes at least one electricity generation unit 3 for generating electrical energy through an oxidation reaction of a fuel and a reduction reaction of an oxidant, a fuel supply unit 5 for supplying the fuel, And an oxidant supply unit 7 for supplying an oxidant to the electricity generation unit 3.

In addition, the fuel supply unit 5 for supplying the fuel may include a fuel tank 9 storing fuel and a fuel pump 11 connected to the fuel tank 9. The fuel pump 11 serves to discharge the fuel stored in the fuel tank 9 by a predetermined pumping force.

The oxidant supply unit 7 for supplying the oxidant to the electricity generating unit 3 includes at least one oxidant pump 13 for sucking the oxidant with a predetermined pumping force.

The electricity generator 3 is composed of a membrane-electrode assembly 17 for oxidizing and reducing a fuel and an oxidant, and a separator 19 and 19 'for supplying fuel and an oxidant to both sides of the membrane-electrode assembly. At least one of these electricity generating units 3 constitutes a stack 15.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

(Example 1)

1.6 g resorcinol and 0.03 g sodium carbonate were dissolved in 48 ml of distilled water. 2.2 ml of 37% formaldehyde was added to the solution, followed by addition of nitric acid to a pH of 6. The resulting solution was then gelled by standing at 85 ° C. for 5 days, after which 10 ml of acetone was added and left for 3 days. The carbon aerosol powder carrier was prepared through the CO ₂ supercritical drying process at a temperature of 773 K and a pressure of 7.6 MPa. The prepared carrier had an average pore size of about 20 nm.

A fuel cell catalyst was prepared by supporting 2.5 g of iron-phthalocyanine (M is Fe in Formula 1) dissolved in 200 cc of xylene in 1 g of the prepared carrier, followed by drying and heat treatment. In the prepared catalyst, the average pore size was about 20 nm and the metal loading was 22% by weight.

[Formula 1]

Since the carrier prepared according to Example 1 was very large compared to the Ketjen black carrier pore size of about 5 nm, which has a pore size of about 20 nm, it can be seen that the supporting amount and the dispersibility of the organic metal material are high, and thus this catalyst is used. It can be predicted that a fuel cell system having excellent performance can be obtained.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

The catalyst for a fuel cell of the present invention can provide a fuel cell system having excellent performance with high loading amount and dispersion degree of bulky organometallic material.

Claims (8)

Conductive carriers having an average pore size of 20 to 30 nm; And Organometallic material supported on the carrier Catalyst for fuel cell comprising a. The method of claim 1, The conductive carrier is a fuel cell catalyst selected from the group consisting of carbon aerosol, mesoporous carbon and combinations thereof. The method of claim 1, The organometallic material is a fuel cell catalyst that is selected from the compounds represented by the following formulas (1) to 4 and combinations thereof. [Formula 1]

[Formula 2]

 (In Formula 1 or 2, M is M is Fe, Co, Ni or Cu) [Formula 3]

[Formula 4]

An anode electrode and a cathode electrode located opposite each other; And A polymer electrolyte membrane positioned between the anode electrode and the cathode electrode Including, The cathode electrode Conductive carriers having a pore size of 20 to 30 nm; And Membrane-electrode assembly for a fuel cell comprising a catalyst comprising an organic metal material supported on the carrier. The method of claim 4, wherein The anode electrode is a fuel cell membrane-electrode assembly comprising a platinum-based catalyst. The method of claim 4, wherein The anode electrode A conductive carrier having a pore size of 20 to 30 nm and Membrane-electrode assembly for a fuel cell comprising a catalyst comprising an organic metal material supported on the carrier. The method according to claim 4 or 6, The conductive carrier is selected from the group consisting of carbon aerosol, mesoporous carbon, and combinations thereof. The method according to claim 4 or 6, The organometallic material is a fuel cell membrane-electrode assembly selected from the compounds represented by the following Chemical Formulas 1 to 4 and combinations thereof. [Formula 1]

[Formula 2]

 (In Formula 1 or 2, M is M is Fe, Co, Ni or Cu) [Formula 3]

[Formula 4]

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