KR100903612B1 - Membrane-electrode assembly for fuel cell and fuel cell system comprising same - Google Patents

Abstract

The present invention relates to a membrane-electrode assembly for a fuel cell and a fuel cell system including the same, wherein the membrane-electrode assembly for a fuel cell is formed of microfiber, and has a porous polymer support having fine pores and inside the micropores of the porous polymer support. A polymer electrolyte membrane including a hydrogen ion conductive polymer is positioned, and includes an anode electrode and a cathode electrode located on both sides of the polymer electrolyte membrane.

The polymer electrolyte membrane of the fuel cell membrane-electrode assembly of the present invention has excellent ion conductivity and excellent strength and can be formed in a thin thickness.

Microfiber, Pore, Polymer Electrolyte, Fuel Cell

Description

Membrane-electrode assembly for fuel cell and fuel cell system comprising same {MEMBRANE-ELECTRODE ASSEMBLY FOR FUEL CELL AND FUEL CELL SYSTEM COMPRISING SAME}

1 is a view schematically showing a process for producing a polymer electrolyte membrane of the present invention.

2 schematically illustrates the structure of a fuel cell system of the present invention;

Figure 3 is a graph showing the measurement of the film resistance of the polymer electrolyte membrane of Examples 1 to 2 and Comparative Example 1 of the present invention.

[Industrial use]

The present invention relates to a fuel cell membrane electrode assembly and a fuel cell system including the same, and more particularly, to a fuel cell membrane electrode assembly having excellent mechanical strength and a fuel cell system 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. This fuel cell is a clean energy source that can replace fossil energy, and has the advantage of generating a wide range of outputs by stacking unit cells, and having an energy density of 4-10 times that of a small lithium battery. It is attracting attention as a compact and mobile 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 "fuel electrode" or "oxidation electrode") and a cathode electrode (also called "air electrode" or "reduction electrode") with a polymer electrolyte membrane containing hydrogen ion conductive polymer therebetween. Has a structure in which

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, fuel is ionized by an oxidation reaction, and electrons are generated, and the generated electrons are oxidized according to an external circuit. Reaching the cathode, which is the pole, hydrogen ions pass through the polymer electrolyte membrane and are delivered to the cathode. 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.

It is an object of the present invention to provide a membrane-electrode assembly for a fuel cell with improved mechanical strength.

Another object of the present invention is to provide a fuel cell system capable of exhibiting high performance, including the membrane-electrode assembly.

In order to achieve the above object, the present invention includes a polymer electrolyte membrane formed of ultra-fine yarn, including a porous polymer support having fine pores and a hydrogen ion conductive polymer located inside the fine pores of the porous polymer support, the polymer electrolyte Provided is a membrane-electrode assembly for a fuel cell comprising an anode electrode and a cathode electrode located on both sides of the membrane.

The present invention also includes the membrane-electrode assembly and the separator, and includes at least one electricity generating unit for generating electricity through an electrochemical reaction between a fuel and an oxidant, a fuel supply unit supplying fuel to the electricity generating unit, and an oxidant Provided is a fuel cell system including an oxidant supply unit for supplying to a generator.

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

The present invention relates to a membrane-electrode assembly for a fuel cell, and to a membrane-electrode assembly including a polymer electrolyte membrane having excellent mechanical strength.

In a fuel cell, the membrane-electrode assembly is composed of a polymer electrolyte membrane, an anode electrode and a cathode electrode positioned on both sides of the polymer electrolyte membrane. The polymer electrolyte membrane is a polymer electrolyte membrane in which a conductive polymer is positioned in the pores of a porous polymer film. It is mainly used because it shows moderate mechanical strength.

However, in recent years, as the demand for polymer electrolyte membranes with higher porosity, excellent ion conductivity, and thin thickness while increasing the mechanical strength of polymer electrolyte membranes has been increased, studies on such polymer electrolyte membranes have been made. .

The polymer electrolyte membrane of the present invention can satisfy these requirements, and is formed of ultra-fine yarn, and includes a porous polymer support having micropores and an ion conductive polymer located inside the micropores of the porous polymer support.

The porous polymer support preferably has a porosity of 50 to 90%. If the porosity of the porous polymer support is less than 50%, the amount of ion-conducting polymer filled in the pores is low, resulting in a decrease in the ion conductivity of the prepared polymer electrolyte membrane, and when the porosity exceeds 90% It is not preferable because of the weak mechanical strength.

In addition, the thickness of the porous polymer support is preferably 5 to 50 µm, more preferably 10 to 25 µm. If the thickness of the porous polymer support is less than 5 μm, the mechanical strength of the polymer support is weak, and if it exceeds 50 μm, the membrane resistance of the polymer electrolyte membrane filled with the ion conductive polymer is large, which is not preferable.

The diameter of the ultrafine yarn is preferably 0.01 to 1 μm. If the diameter of the microfiber is less than 0.01 μm, the mechanical strength of the polymer support composed of the microfiber is low because of the low mechanical strength of the microfiber. ) Is more than 1 μm, so that uniform hydrogen ions are not transferred.

The porous polymer support may be 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, It is preferably formed of at least one hydrogen ion conductive polymer selected from polyether-etherketone-based polymer, polyphenylquinoxaline-based polymer or polystyrene-based polymer. More preferably poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), polyvinylidene fluoride, copolymer of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid group, defluorinated sulfide poly Ether ketones, aryl ketones, polystyrene, poly (2,2'-m-phenylene) -5,5'-bibenzimidazole (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole ) Or poly (2,5-benzimidazole) may be used at least one hydrogen ion conductive polymer.

The porous polymeric support of the present invention is prepared by a charge induced spinning process (electrospinning). Referring to this process in more detail with reference to FIG. 1, a solution, suspension or melt 1 of porous support forming material is placed inside the heater 7 and sprayed jet nozzles. Into this connected chamber (chamber) 3.

As the porous support forming material, a hydrogen ion conductive polymer may be used as described above. In addition, when the porous support forming material is used as a solution or a suspension, acetone, chloroform, ethanol, isopropanol, methanol, toluene, tetrahydrofuran, water, benzene, benzyl alcohol, 1,4-dioxane, propanol, carbon tetra Chloride, cyclohexane, cyclohexanone, methylene chloride, phenol, pyridine, trichloroethane, acetic acid, N-methylpyrrolidone, N, N-dimethylformamide, dimethylsulfoxide, N, N-dimethylacetamide, 1 -Methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, dimethyl carbonate, acetonitrile, N-methylmorpholine-N-oxide, butylene carbonate, 1,4-butylarolactone, diethyl carbonate, diethyl ether, 1,2-dimethoxyethane, ethylmethyl carbonate, methyl formate, 3-methyloxazolidin-2-one, methyl propionate, 2-methyltetrahydrofuran (2-methyletetrah ydrofurane) or sulfolane can be used.

Subsequently, when a high voltage of 1 to 1000 kV is applied to the solution or the melt, one jet is formed while the charged polymer solution is released. This results in an equilibrium of charged droplets hanging at the end of the capillary tube from the point that the electric force is equal to the surface tension at the surface of the solution or melt, and if the potential is increased, the charged droplets become unstable. As the jet is filled, a charged jet is formed.

In addition, since the electric force is greater than the surface tension, the filled jet is discharged in the direction of the grounded collecting screen 9 and dispersed to form a microfiber.

The ultrafine fibers are spun onto a releasing film placed on the matrix collecting screen while rotating the matrix collection screen with the motor 11. Subsequently, the release film is removed to obtain a porous polymer support.

Filling the ion conductive polymer in the porous polymer support prepared in the process is to immerse the porous polymer support in the ion conductive polymer solution, cast the ion conductive polymer solution on the porous polymer support or after the immersion process And casting the polymer solution on both surfaces of the obtained porous polymer support.

The ion conductive polymer solution includes a polymer having excellent hydrogen ion conductivity and a solvent. The polymer having excellent hydrogen ion conductivity may include a perfluoro polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer, a poly One or more hydrogen ion conductive polymers selected from ether ketone polymers, polyether-ether ketone polymers or polyphenylquinoxaline polymers may be used, and more preferably poly (perfluorosulfonic acid), poly (perfluoro Rocarboxylic acid), copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, defluorinated sulfide polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5 One or more hydrogen ion conductive polymers selected from '-bibenzimidazole (poly (2,2'-(m-phenylene) -5,5'-bibenzimidazole) or poly (2,5-benzimidazole) Can be used.

As the solvent, water, methanol, ethanol, isopropyl alcohol, propanol, diethylene glycol, dipropylene glycol, ethylene glycol, propylene glycol or glycerol may be used.

In the membrane-electrode assembly including the polymer electrolyte membrane of the present invention, the anode electrode and the cathode electrode include a catalyst layer. The catalyst of this catalyst layer is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, At least one catalytic metal selected from the group consisting of Cu and Zn).

The polymer electrolyte membrane has an ion exchange function for transferring hydrogen ions generated in the catalyst layer of the anode electrode to the catalyst layer of the cathode electrode, and a polymer having excellent 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 groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups 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 at least one selected from a polymer, a polyether-etherketone-based polymer or a polyphenylquinoxaline-based polymer, 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 or at least one selected from (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) or poly (2,5-benzimidazole).

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). The metal film formed on the surface of the fabric formed of fibers (referred to as metalized polymer fiber) may be used, but is not limited thereto.

In addition, a microporous layer may be further included to enhance the gas diffusion effect in the electrode substrate. This microporous layer may generally comprise a conductive powder having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene or carbon nanotubes. The microporous layer is prepared by coating a composition comprising a conductive powder, a binder resin and a solvent on the gas diffusion layer. As the binder resin, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, cellulose acetate, and the like may be preferably used. The solvent may be ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, or the like. Alcohols, water, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone and the like can 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 fuel cell system of the present invention having the above-described configuration includes an electric generator, a fuel supply and an oxidant supply including the membrane-electrode assembly and separator of the present invention.

The electricity generation unit serves to generate electricity through an electrochemical reaction between a fuel and an oxidant, and the fuel supply unit supplies a fuel containing hydrogen or a hydrocarbon fuel such as methanol, ethanol or propanol to the electricity generation unit. The oxidant supply unit serves to supply an oxidant to the electricity generating unit.

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. Naturally, it can be used for system architecture.

 The fuel cell system 100 of the present invention includes a stack 17 having at least one electric generator 19 for generating electrical energy through an electrochemical reaction between a fuel and an oxidant, and a fuel supply unit for supplying the fuel. (11) and the oxidant supply part 5 which supplies an oxidant to the electricity generation part 19 is comprised.

In addition, the fuel supply unit 10 for supplying the fuel has a fuel tank 9 for storing fuel.

The oxidant supply unit 5 for supplying the oxidant to the electricity generating unit 19 is provided with at least one oxidant pump 13 for sucking the oxidant with a predetermined pumping force.

The electricity generating unit 19 is composed of a membrane-electrode assembly 21 for oxidizing and reducing a fuel and an oxidant, and separators 23 and 25 for supplying fuel and an oxidant to both sides of the membrane-electrode assembly.

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

(Example 1)

A porous support forming material prepared by dissolving polyvinylidene fluoride in acetone at a concentration of 5% by weight was injected into a chamber to which a spray jet nozzle of the structure shown in FIG. 1 was connected. Subsequently, the porous support forming material wool was maintained at 60 ° C. A high voltage of 10 kV was applied to the nozzle, the discharge rate of the melt of the porous support forming material at each needle was 180 mu l, the height between the known collecting screens was kept at 15 cm, and an aluminum plate was used as the known collecting screen.

Jets were formed from the melt, and the jets were spun onto a release film placed on the known collection screens while rotating a motorized known collection screen at a rate of 3 m / min. When the spinning process was completed, the release film was removed to prepare a porous polymer support. In the prepared polymer support membrane, the diameter of the ultrafine fibers was 0.2 μm, the porosity was 70%, and the thickness was 30 μm.

The porous polymer support was immersed in a Nafion (polyperfluorosulfonic acid) / H ₂ O / 2-propanol (Solution Technology Inc.) solution at a concentration of 5 wt% to prepare a polymer electrolyte membrane.

(Example 2)

The same procedure as in Example 1 was carried out except that a porous support forming material solution prepared by dissolving polystyrene in acetone solvent at a concentration of 7% by weight was used. In the prepared polymer support, the diameter of the ultrafine fibers was 0.5 μm, the porosity was 85%, and the thickness was 40 μm.

(Example 3)

The same procedure as in Example 1 was carried out except that a porous support forming material melt prepared by dissolving poly (2,5-benzimidazole) in a concentration of 3% by weight in N-methylpyrrolidone solvent was used. In the prepared polymer support membrane, the diameter of the ultrafine fibers was 0.5 μm, the porosity was 80%, and the thickness was 35 μm.

(Comparative Example 1)

A porous polytetrafluoroethylene membrane having a porosity of 50% and a thickness of 25 μm was applied to a solution of Nafion / H ₂ O / 2-propanol (Solution Technology Inc.) at a concentration of 5 wt% in the same manner as in Example 1. It was immersed.

The membrane resistances of the polymer electrolyte membranes prepared in Examples 1 and 2 and Comparative Example 1 were evaluated by the impedance method, and are shown in FIG. 3. That is, the resulting polymer electrolyte membrane was impregnated in 50 ° C. and 1M methanol, and then the hydrogen ion conductivity was measured. As a result, in Example 1, 0.18 Ohmcm ² and Example 2 obtained 0.13 Ohmcm ² , whereas in Comparative Example 1, a value of 0.31 Ohmcm ² was obtained. This result shows that the porous polymer supports of Examples 1 and 2 produced by the charge induced spinning process have high porosity, so that more ion conductive materials are present in the polymer electrolyte membrane, and they are well connected in three dimensions so that the ion transport passage is It means well formed.

The polymer electrolyte membrane of the fuel cell membrane-electrode assembly of the present invention has excellent ion conductivity and excellent strength and can be formed in a thin thickness.

Claims (10)

A polymer electrolyte membrane formed of ultra-fine yarn and including a porous polymer support having fine pores and a hydrogen ion conductive polymer located inside the micro pores of the porous polymer support; And Anode and cathode electrodes on both sides of the polymer electrolyte membrane Including; The porous polymer support has a porosity of 70 to 90%, Poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), polyvinylidene fluoride, copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, defluorinated sulfided polyether ketones, aryl Ketone, polystyrene, poly (2,2'-m-phenylene) -5,5'-bibenzimidazole (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole), poly ( 2,5-benzimidazole) and a combination thereof, wherein the membrane-electrode assembly for a fuel cell is formed of a hydrogen ion conductive polymer selected from the group consisting of. delete The membrane-electrode assembly of claim 1, wherein the porous polymer support has a thickness of 5 to 50 μm. The membrane-electrode assembly of claim 1, wherein the ultrafine yarn has a diameter of 0.01 to 1 μm. The membrane-electrode assembly of claim 1, wherein the porous polymer support is formed by a charge induced spinning process. A polymer electrolyte membrane formed of ultra-fine yarn and including a porous polymer support having fine pores and a hydrogen ion conductive polymer located inside the micro pores of the porous polymer support; And a membrane-electrode assembly and a separator including anode and cathode electrodes positioned on both sides of the polymer electrolyte membrane, the at least one electricity generating unit generating electricity through an electrochemical reaction between a fuel and an oxidant; A fuel supply unit supplying fuel to the electricity generation unit; And Oxidant supply unit for supplying an oxidant to the electricity generating unit Including; The porous polymer support has a porosity of 70 to 90%, Poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), polyvinylidene fluoride, copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, defluorinated sulfided polyether ketones, aryl Ketone, polystyrene, poly (2,2'-m-phenylene) -5,5'-bibenzimidazole (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole), poly ( 2,5-benzimidazole) and a combination thereof, the fuel cell system is formed of a hydrogen ion conductive polymer selected from the group consisting of. delete The fuel cell system of claim 6, wherein the porous polymer support has a thickness of 5 to 50 μm. The fuel cell system of claim 6, wherein the ultrafine yarn has a diameter of 0.01 to 1 μm. 7. The fuel cell system of claim 6, wherein the porous polymeric support is formed by a charge induced spinning process.

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