KR20060122160A - A membrane electrode assembly for fuel cell, a method for preparing the same and a fuel cell comprising the same - Google Patents

Abstract

Provided are a membrane electrode assembly for a fuel cell which is improved in the adhesive strength of an electrode and an electrolyte membrane, and its preparation method. The membrane electrode assembly comprises an anode and a cathode which are located so as to face each other; a polymer electrolyte membrane which is located between the anode and the cathode, wherein the anode, the cathode and the polymer electrolyte membrane comprise a poly(2,5-benzimidazole) polymer. Preferably the anode and the cathode comprise a metal catalyst comprising at least one selected from the group consisting of platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and an alloy of platinum and M, wherein M is at least one transition metal selected from Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn.

Description

Membrane-electrode assembly for fuel cell, method for manufacturing same, and fuel cell comprising same {A MEMBRANE ELECTRODE ASSEMBLY FOR FUEL CELL, A METHOD FOR PREPARING THE SAME AND A FUEL CELL COMPRISING THE SAME}

1 is a view schematically showing an operating state of a fuel cell including a polymer electrolyte membrane.

<Description of the symbols for the main parts of the drawings>

1: fuel cell 3: anode

5: cathode 7: polyelectrolyte membrane

[Industrial use]

The present invention relates to a membrane-electrode assembly for a fuel cell, a method for manufacturing the same, and a fuel cell including the same, and more particularly, for a fuel cell capable of improving operating efficiency and reliability of a fuel cell due to excellent adhesion between an electrode and an electrolyte membrane. Membrane-electrode assembly, a method of manufacturing the same and a fuel cell comprising the same.

[Prior art]

A fuel cell is an electrochemical cell in which free energy changes due to fuel oxidation are converted into electrical energy. In fuel cells, organic fuels such as methanol, formaldehyde or formic acid are oxidized to carbon dioxide at the anode and air or oxygen is reduced to water at the cathode. Because of the high specific energy of organic fuels (eg, the specific energy of methanol is 6232 wh / kg), fuel cells using organic fuels are extremely attractive both in installation and in portable applications.

Fuel cells are classified into alkali type, phosphoric acid type, molten carbonate, solid oxide, and polymer fuel cells according to the type of electrolyte used. Among the various types of fuel cells, the polymer electrolyte membrane fuel cell uses a polymer as an electrolyte, so there is no risk of corrosion or evaporation by the electrolyte, and a high current density per unit area can be obtained. Compared to fuel cells, its output characteristics are much higher and its operating temperature is low, so its development is actively promoted for use as a portable power source for automobiles, distributed power sources for homes and public buildings, and small power sources for electronic devices. It is becoming.

The fuel cell stack body, which forms the center of such a polymer fuel cell power generation system, is based on a solid electrolyte made of a proton-exchange membrane. It consists of a unit cell constructed by attaching by pressing, and the fuel cell power plant system can reach several W to several hundred kW by stacking these unit cells in several layers. Will be configured.

On the other hand, in the power generation system of the polymer fuel cell, the performance of the membrane / electrode assembly (MEA) has a great influence on the power generation characteristics. The polymer membrane electrode assembly is composed of a polymer electrolyte membrane (solid polymer electrolyte membrane) and a carbon supported catalyst electrode layer (carbon supported catalysts electrode layer), as the polymer electrolyte membrane Nafion (trade name manufactured by DuPont), Premion Perfluorosulfonic acid ionomer membranes such as (Flemion, trade name manufactured by Asahi Glass), Asifrex (Asiplex, trade name manufactured by Asahi Chemical), and Dow XUS (Dow XUS, trade name manufactured by Dow Chemical) Perfluorosulfonic acid ionomer membranes are widely used, and the carbon-supported catalyst electrode layer is formed of fine catalyst particles such as platinum (Pt) or ruthenium (Ru) on an electrode support such as porous carbon paper or carbon cloth. The supported carbon powder is used in combination with a water repellent binder.

The present invention is to solve the above-described problems, an object of the present invention is to improve the operating efficiency and reliability of the fuel cell by excellent adhesion between the electrode and the polymer electrolyte membrane, a fuel cell membrane-electrode assembly, a manufacturing method thereof and To provide a fuel cell comprising the same.

In order to achieve the above object, an anode and a cathode electrode located opposite each other; It provides a membrane-electrode assembly for a fuel cell comprising a polymer electrolyte membrane positioned between the anode and the cathode electrode, wherein the anode and cathode electrode and the polymer electrolyte membrane comprises a poly (2,5-benzimidazole) polymer.

The present invention also provides a method for preparing a catalyst dispersion comprising mixing a metal catalyst, a poly (2,5-benzimidazole) polymer and a dispersion medium; Coating the catalyst dispersion on both sides of the poly (2,5-benzimidazole) polymer membrane; And calcining the coated polymer membrane and then hot rolling.

The present invention also provides a fuel cell comprising the membrane-electrode assembly.

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

FIG. 1 is a view schematically showing an operating state of a fuel cell 1 including an anode 3, a cathode 5, and a polymer electrolyte membrane 7. The anode 3 and the cathode 5 include a catalyst layer in which a metal catalyst participating in an electrochemical reaction is supported on carbon. In the fuel cell, hydrogen or fuel is supplied to the anode 3 and an oxidant is supplied to the cathode 5 to generate electricity by the electrochemical reaction of the anode and the cathode. That is, an oxidation reaction of hydrogen or organic fuel occurs at the anode 3 and a reduction reaction of oxidant occurs at the cathode 5 to generate a voltage difference between the two electrodes. Preferred examples of the oxidant are oxygen or air.

In the present invention, a poly (2,5-benzimidazole) polymer is used as the polymer electrolyte membrane, and the poly (2,5-benzimidazole) polymer is included in the anode and cathode electrode catalyst layers to improve adhesion between the electrode and the electrolyte membrane. Let's do it. Poly (2,5-benzimidazole) polymers are present in both the anode, cathode electrode and polymer electrolyte, thereby reducing the interfacial resistance that may occur at the interface between the electrode and the polymer electrolyte membrane, thereby making it firmly attached.

According to one embodiment of the invention, the catalyst and the poly (2,5-benzimidazole) polymer is preferably used in a weight ratio of 60 to 86: 40 to 14. When the content of the catalyst is lower than 60% by weight, the content of the catalyst is lowered, which may lower the efficiency of the fuel cell. When the content of the catalyst is higher than 86% by weight, the ion conductivity is lowered, which is not preferable.

The poly (2,5-benzimidazole) polymer is represented by the following formula (1).

[Formula 1]

In the above formula, n represents a degree of polymerization, but is not particularly limited, but is preferably in the range of 300 to 600. In addition, the polymer of Formula 1 preferably has a weight average molecular weight of 34800 to 69600.

Poly (2,5-benzimidazole) used in the present invention can be obtained by mixing 3,4-diaminobenzoic acid with a dehydrating agent as a monomer and then heating and polymerizing. The dehydrating agent may be preferably a solution containing P ₂ O ₅ and CX ₃ SO ₃ H (X is hydrogen or F). The 3,4-diaminobenzoic acid is preferably used after purification by reacting with a base or an acid before mixing with the dehydrating agent.

The membrane-electrode assembly of the present invention is prepared by coating a catalyst dispersion prepared by mixing a metal catalyst, a poly (2,5-benzimidazole) polymer and a dispersion medium on both sides of a polymer electrolyte membrane.

The metal catalyst may be platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu And at least one catalyst selected from the group consisting of Zn), platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum It is more preferred to include at least one catalyst selected from cobalt alloys or platinum-nickel.

The metal catalyst may also be supported on a carrier. As the carrier, carbon such as acetylene black or graphite may be used, or inorganic fine particles such as alumina, silica, zirconia, titania, or the like may be used. In the case of using the noble metal supported on the carrier as a catalyst, a commercially available commercially available product may be used, or the noble metal supported on the carrier may be prepared and used. Since the process of supporting the precious metal on the carrier is well known in the art, detailed descriptions thereof will be readily understood by those skilled in the art even if the detailed description is omitted.

As the dispersion medium, alcohol, water, dimethylacetamide (DMAc), dimethylformamide, dimethyl sulfoxide (DMSO), N-methylpyrrolidone, and tetrahydrofuran solvent may be preferably used. Alcohol, such as propyl alcohol, ethanol, n-propyl alcohol, butyl alcohol, etc. can be used preferably.

In the catalyst dispersion, the poly (2,5-benzimidazole) polymer does not exist in a dissolved state but exists in a dispersed state. The coating process may be a screen printing method, a spray coating method or a coating method using a doctor blade, a gravure coating method, a dip coating method, a silk screen method, a painting method, etc., depending on the viscosity of the dispersion, but is not limited thereto. Before carrying out the firing process, a process of drying the coated electrode in an inert gas atmosphere may be further performed. The firing step is preferably carried out at a temperature of 130 to 180 degrees, the firing time is preferably 2-3 minutes.

After the firing process, a film-electrode assembly is manufactured by a pressing method such as a hot rolling process or a rolling method. In the above process, the poly (2,5-benzimidazole) polymer present in the coating film may be gelled to firmly attach the electrode to the polymer film. In the present invention, both the electrode catalyst layer and the polymer membrane contain the same polymer so that the electrode catalyst layer can be continuously and uniformly well bonded to the polymer membrane.

In another embodiment of the present invention, the catalyst dispersion may be prepared by coating the electrode substrate. In this case, a metal catalyst, a poly (2,5-benzimidazole) polymer, and a dispersion medium are mixed to prepare a catalyst dispersion, and the catalyst dispersion is coated on one surface of an electrode substrate to produce an anode and a cathode, and the anode electrode and A membrane-electrode assembly is manufactured by placing a poly (2,5-benzimidazole) polymer film between the cathode electrodes, firing the same, and hot rolling.

The electrode substrate may be used by water repellent treatment with polytetrafluoroethylene (PTFE) or the like, and carbon paper or carbon cloth may be used, but is not limited thereto. The electrode substrate serves to support the polymer membrane electrode assembly and also to diffuse the reaction gas into the polymer membrane electrode assembly. The electrode substrate coated with the catalyst dispersion is bonded to the polymer electrolyte membrane, and then fired and hot rolled to prepare a membrane-electrode assembly. In addition, the catalyst may be prepared by coating the electrode substrate and then bonding the polymer electrolyte membrane.

The manufactured membrane-electrode assembly may be inserted between a gas flow channel and a bipolar plate on which a cooling channel is formed to manufacture a unit cell, and stacked to manufacture a stack, and then inserted between the two end plates to manufacture a fuel cell. Can be. Fuel cells can all be manufactured by conventional techniques in the art.

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: Preparation of membrane-electrode assembly and unit cell)

A catalyst dispersion was prepared by mixing 60 parts by weight of platinum-supported carbon powder (Pt / C), 40 parts by weight of poly (2,5-benzimidazole) polymer, and isopropyl alcohol with a dispersion medium. The catalyst dispersion was coated on both sides of a poly (2,5-benzimidazole) polymer electrolyte membrane, and the coated polymer membrane was calcined at 150 ° C. for 2 minutes and then hot rolled to prepare a membrane-electrode assembly.

The prepared membrane-electrode assembly is inserted between two gaskets, and then inserted into two bipolar plates in which a gas channel and a cooling channel of a predetermined shape are formed, and then compressed between copper end plates. The battery was prepared.

(Comparative Example 1)

A unit cell was manufactured in the same manner as in Example 1, except that Nafion (DuPont) was used instead of the poly (2,5-benzimidazole) polymer in Example 1.

The membrane-electrode assembly prepared according to Example 1 of the present invention showed that the bonding layer was uniform and robust. In addition, the voltage-current value was measured by operating at 60 degrees while supplying 50% humidified air and hydrogen to the anode and cathode of the unit cell. As a result, a voltage value improved by about 10% or more was compared with that of Comparative Example 1 using Nafion. Seemed.

In the present invention, a poly (2,5-benzimidazole) polymer is used as the polymer electrolyte membrane, and the poly (2,5-benzimidazole) polymer is included in the anode and cathode electrode catalyst layers to improve adhesion between the electrode and the electrolyte membrane. It is possible to improve the operation efficiency and reliability of the fuel cell excellently. Poly (2,5-benzimidazole) polymer is present in both the anode, cathode electrode and polymer electrolyte, thereby reducing the interfacial resistance that may occur at the interface between the electrode and the polymer electrolyte membrane.

Claims (20)

Anode and cathode electrodes positioned opposite one another; It includes a polymer electrolyte membrane located between the anode and the cathode, The anode, cathode electrode and the polymer electrolyte membrane is a fuel cell membrane-electrode assembly comprising a poly (2,5-benzimidazole) polymer. The membrane-electrode assembly of claim 1, wherein the anode and the cathode comprise a catalyst layer comprising a metal catalyst and an electrode substrate. The method of claim 2, wherein the metal catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, A membrane-electrode assembly for a fuel cell, wherein the membrane is at least one catalyst selected from the group consisting of Co, Ni, Cu, and Zn). The membrane-electrode assembly of claim 1, wherein the poly (2,5-benzimidazole) polymer is represented by Formula 1 below: [Formula 1]

N represents the degree of polymerization. The membrane-electrode assembly of claim 1, wherein the poly (2,5-benzimidazole) polymer is prepared by polymerizing a 3,4-diaminobenzoic acid monomer. Preparing a catalyst dispersion by mixing a metal catalyst, a poly (2,5-benzimidazole) polymer and a dispersion medium; Coating the catalyst dispersion on both sides of the poly (2,5-benzimidazole) polymer membrane; And Firing the coated polymer membrane and then placing the electrode between the electrode substrates. The method of claim 6, wherein the metal catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, A method of manufacturing a membrane-electrode assembly for a fuel cell selected from the group consisting of one or more transition metals selected from the group consisting of Co, Ni, Cu and Zn. The method of claim 6, wherein the poly (2,5-benzimidazole) polymer is represented by Formula 1 below: [Formula 1]

N represents the degree of polymerization. The method of claim 6, wherein the poly (2,5-benzimidazole) polymer is prepared by polymerizing 3,4-diaminobenzoic acid mono. The method of claim 6, wherein the dispersion medium is at least one selected from the group consisting of alcohol, water, dimethylacetamide (DMAc), dimethylformamide, dimethyl sulfoxide (DMSO), N-methylpyrrolidone, and tetrahydrofue Method of manufacturing a membrane-electrode assembly for phosphorus fuel cells. The method of claim 6, further comprising drying the coated electrode in an inert gas atmosphere before performing the firing process. The method of claim 6, wherein the firing step is performed at a temperature of 130 to 180 degrees. Preparing a catalyst dispersion by mixing a metal catalyst, a poly (2,5-benzimidazole) polymer and a dispersion medium; Coating the catalyst dispersion on one surface of an electrode substrate to prepare an anode and a cathode; And A method of manufacturing a membrane-electrode assembly for fuel cell comprising the steps of placing and firing a poly (2,5-benzimidazole) polymer membrane between the anode electrode and the cathode electrode. The method of claim 13, wherein the metal catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Method of producing a membrane-electrode assembly for a fuel cell is selected from the group consisting of one or more transition metals selected from the group consisting of Co, Ni, Cu and Zn. The method of claim 13, wherein the poly (2,5-benzimidazole) polymer is represented by Chemical Formula 1 below: [Formula 1]

N represents the degree of polymerization. The method of claim 13, wherein the poly (2,5-benzimidazole) polymer is prepared by polymerizing a 3,4-diaminobenzoic acid monomer. The method of claim 13, wherein the dispersion medium is at least one selected from the group consisting of alcohol, water, dimethylacetamide (DMAc), dimethylformamide, dimethyl sulfoxide (DMSO), N-methylpyrrolidone, and tetrahydropu Method of manufacturing a membrane-electrode assembly for phosphorus fuel cells. The method of claim 13, further comprising drying the coated electrode in an inert gas atmosphere before performing the firing process. The method of claim 13, wherein the firing step is performed at a temperature of 130 to 180 degrees. The method of claim 13, wherein the electrode substrate is water-repellent carbon paper or carbon cloth.

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