KR20070013855A - Membrane/electrode assembly for fuel cell and fuel cell system comprising the same - Google Patents

Abstract

Provided are a membrane/electrode assembly for fuel cell which has excellent proton conducting property as well as improved heat resistance and physical properties, and a fuel cell comprising the same. The membrane/electrode assembly comprises anode and cathode electrodes(100,100') which are opposite to each other; and a polyelectrolyte membrane. The polyelectrolyte membrane comprises a polymer of formula 1. In the formula 1, at least one of X1 to X8 are functional radicals represented by formula 2, and n is an integer of 100-10000. In the formula 2, Y1 or Y2 is independently one element selected from the group consisting of halogen elements or hydrogen, n is an integer of 1-10, and n2 is an integer of 1-10. The fuel cell system comprises at least one electric generator, a fuel supply part for supplying a fuel to the electric generators, and an oxidizing agent supply part for supplying the oxidizing agent to the electric generators. The electric generators comprise the polyelectrolyte membrane, the membrane/electrode assembly positioned on both sides of the polyelectrolyte membrane, and a separator positioned on both sides of the membrane/electrode assembly. And the electric generators generate the electricity by electrochemical reaction of fuel and oxidizing agent.

Description

Membrane-electrode assembly for fuel cell and fuel cell comprising same TECHNICAL FIELD

1 is a schematic cross-sectional view of a membrane-electrode assembly for a fuel cell of the present invention.

2 is an exploded perspective view of a stack of a fuel cell system of the present invention.

[Industrial use]

The present invention relates to a fuel cell membrane-electrode assembly and a fuel cell including the same, and more particularly, to a fuel cell membrane-electrode assembly having excellent hydrogen ion conductivity and excellent heat resistance and mechanical properties, and a fuel cell including the same. .

[Private Technology]

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

The low temperature fuel cell may include a polymer electrolyte fuel cell (PEMFC) and a 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 is a clean energy source that can replace fossil energy, and has high power density and energy conversion efficiency, can be operated at room temperature, and can be miniaturized and encapsulated. It can be widely used in fields such as portable power supply and military equipment.

In general, a polymer electrolyte fuel cell using hydrogen as a fuel has advantages of high energy density and high output, but it is necessary to pay attention to the handling of hydrogen gas and methane, methanol, and natural gas to produce hydrogen as fuel gas. There is a problem in that an auxiliary facility such as a fuel reforming device for reforming the back is required.

On the other hand, direct oxidation fuel cells using liquid as fuel have lower energy density, lower output, and a larger amount of electrode catalyst than polymer electrolyte type due to the slow reaction rate. It is advantageous in that it is easy and the operating temperature is low and especially no fuel reformer is required.

In such fuel cell systems, the stack that substantially generates electricity may comprise several to tens of unit cells consisting of a membrane-electrode assembly (MEA) and a separator (or bipolar plate). It has a laminated structure. The membrane-electrode assembly is called an anode electrode (also called "fuel electrode" or "oxide electrode") and a cathode electrode (also called "air electrode" or "reduction electrode") with a polymer electrolyte membrane including a hydrogen ion conductive polymer therebetween. Has a bonded structure.

As the polymer electrolyte membrane serving as an electrolyte in the membrane-electrode assembly, a fluorine-based electrolyte membrane such as a perfluorosulfonic acid ionomer membrane is widely used.

However, the fluorine-based polymer electrolyte membrane has a problem of low hygroscopicity and inability to use at high temperatures.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a membrane-electrode assembly for a fuel cell having excellent hydrogen ion conductivity and excellent heat resistance and mechanical properties.

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

In order to achieve the above object, the present invention includes an anode and a cathode electrode located opposite each other and a polymer electrolyte membrane positioned between the anode and the cathode electrode,

The polymer electrolyte membrane provides a fuel cell membrane-electrode assembly including a polymer represented by the following Chemical Formula 1.

[Formula 1]

In the formula, X ₁ to X ₈ is selected from the group consisting of hydrogen and a functional group represented by the following formula (2), at least one of these is a functional group represented by the formula (2). n represents the degree of polymerization, where n is an integer in the range of 100 to 10000.

[Formula 2]

Wherein Y ₁ or Y ₂ are each independently selected from the group consisting of halogen elements and hydrogen, n 1 is an integer in the range of 1 to 10 and n 2 is an integer in the range of 1 to 10.

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

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

1 is a schematic cross-sectional view of a membrane-electrode assembly for a fuel cell of the present invention.

Referring to FIG. 1, the fuel cell membrane-electrode assembly 10 of the present invention includes the polymer electrolyte membrane 110 and the fuel cell electrodes 100 and 100 ′ respectively disposed on both surfaces of the polymer electrolyte membrane 110. Include. The electrode includes electrode substrates 102 and 102 'and catalyst layers 104 and 104' formed on the surface of the electrode substrate.

In the membrane-electrode assembly 10, the electrode 100 disposed on one surface of the polymer electrolyte membrane 110 is called an anode electrode (or a cathode electrode), and the electrode 100 ′ disposed on the other surface is called a cathode electrode ( Or anode electrode). The anode electrode generates an oxidation reaction that generates hydrogen ions and electrons from the fuel transferred through the electrode substrate to the catalyst layer, the polymer electrolyte membrane moves the hydrogen ions generated from the anode electrode to the cathode electrode, the cathode electrode through the polymer electrolyte membrane It generates a reduction reaction that generates water from the supplied hydrogen ions and the oxidant delivered to the catalyst layer through the electrode substrate.

In general, as the polymer electrolyte membrane, a fluorine-based electrolyte membrane such as a perfluorosulfonic acid ionomer membrane is used. However, the fluorine-based polymer electrolyte membrane has a hydrogen ion conductivity when -SO ₃ H is hydrated, but has a problem of low hygroscopicity and inability to use at high temperatures.

Accordingly, in the present invention, a polymer having a functional group having excellent hydrogen ion conductivity in a polyether ether ketone (PEEK) backbone, which is known to have excellent mechanical properties such as heat resistance, toughness, and chemical resistance, is used as a material of a polymer electrolyte membrane for fuel cells, thereby providing excellent heat resistance. In addition, the present invention provides a fuel cell membrane-electrode assembly having excellent hydrogen ion conductivity.

In the present invention, in order to increase the hydrogen ion conductivity of the polyether ether ketone (PEEK) polymer electrolyte membrane, a functional group represented by Formula 2 is introduced at at least one position of X ₁ to X ₈ of the polyether ether ketone (PEEK).

In the functional group of Formula 2, the sulfonic acid group (-SO ₃ H) has hydrogen ion conductivity, and the hydrogen ion conductivity may be increased by increasing the acidity of the sulfonic acid group. In the present invention, hydrogen ionic conductivity is improved by attaching a sulfonic acid group to the amide structure (-CONH) to increase the acidity.

In Formula 2, Y ₁ or Y ₂ are each independently one element selected from the group consisting of halogen elements or hydrogen, and among them, fluorine (F) or hydrogen (H) is preferable.

In Formula 2, n1 is an integer in the range of 1 to 10, preferably an integer in the range of 1 to 3, and more preferably 1 to 2.

In addition, n2 in the formula (2) is an integer in the range of 1 to 10, preferably an integer in the range of 1 to 3, more preferably 1 to 2.

Of the polymers having Formula 1, a polymer of Formula 3 may be preferably used.

[Formula 3]

Wherein n represents the degree of polymerization, where n is an integer in the range from 100 to 10000, and n is preferably an integer in the range from 1000 to 7000.

The polymer of the present invention can be prepared into a film by casting or electrospining to produce a polymer film.

A polymer membrane made of the polymer is placed between electrodes to prepare a membrane-electrode assembly. The electrode is a catalyst layer formed on the electrode substrate.

The catalyst layer comprises a so-called metal catalyst which catalyzes the related reaction (oxidation of fuel and reduction of oxidant), and includes platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or platinum -M alloy preferably comprises at least one catalyst selected from the group consisting of at least one transition metal selected from the group consisting of Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn It is more preferable to include at least one catalyst selected from among platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-cobalt alloy or platinum-nickel.

In general, as the metal catalyst, those supported on a carrier are used. The carrier may be carbon such as denka black, activated carbon, Ketjen black, acetylene black, graphite, or inorganic fine particles such as alumina, silica, titania, zirconia, or the like. 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 a 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.

The electrode substrate serves as a fuel diffusion layer that diffuses fuel or an oxidant and transfers electrons generated in the catalyst layer. Accordingly, the electrode substrate is made of a conductive material having electronic conductivity, and is preferably a carbon cloth, a carbon paper, a metal cloth, or the like.

A microporous layer may be further positioned between the electrode substrate and the catalyst layer for uniform diffusion of fuel or oxidant. The microporous layer (MPL) preferably comprises at least one conductive carbon selected from the group consisting of graphite, carbon nanotubes (CNT), fullerenes (C60), activated carbon, carbon nanohorn and carbon black.

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

Separators are disposed on both sides of the membrane-electrode assembly to supply fuel and oxidant to the catalyst layer, thereby forming at least one electricity generating unit for generating electricity through an electrochemical reaction between the fuel and the oxidant. At least one electricity generating unit is stacked to form a stack.

2 is an exploded perspective view of this stack.

Referring to FIG. 2, the stack 1 includes a membrane-electrode assembly 10 including the fuel cell electrode and a separator 20 disposed on both sides of the membrane-electrode assembly.

In the fuel cell system of the present invention, the fuel supply unit serves to supply the hydrogen-containing fuel to the electricity generator, and the oxidant supply unit serves to supply the oxidant to the electricity generator.

The fuel cell system of the present invention can be employed in a phosphoric acid type, polymer electrolyte type, direct oxidation type and alkali type fuel cells, but is preferably employed in a polymer electrolyte type or direct type oxidation type fuel cell. Preferred examples of the direct oxidation fuel cell include a direct methanol fuel cell.

Hereinafter, preferred embodiments 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)

Example 1

A polyether ether ketone of Formula 3 having an average degree of polymerization of 5000 was dispersed in isopropyl alcohol and extruded to prepare a polymer film.

The polymer electrolyte membrane was placed between the cathode and the anode electrode and calcined at 100 ° C. for 1 minute, followed by hot rolling to prepare a membrane-electrode assembly. The cathode and the anode are prepared by coating a carbon slurry on a carbon paper, a catalyst slurry prepared by mixing a platinum catalyst (Pt / C) supported on carbon powder, a polyether ether ketone binder of Formula 3 having an average degree of polymerization of 5000, and an isopropyl alcohol solvent. It was. In this case, the catalyst amount of the catalyst layer was fixed at 0.4 mg / cm ² .

After inserting the prepared membrane-electrode assembly between the gasket (gasket), and inserted into the two separator gas channel channel and the cooling channel formed of a predetermined shape, and then compressed between the copper end (end) plate unit cell Prepared.

 Comparative Example 1

A membrane-electrode assembly and a unit cell were prepared in the same manner as in Example 1 except that perfluorosulfonic acid (Nafion 112) was used as the polymer electrolyte membrane.

As a result of evaluating the current density characteristics of the fuel cells prepared according to Example 1 and Comparative Example 1 while varying the temperature, the fuel cell of Example 1 was similar in current to the fuel cell of Comparative Example 1 at low temperature. It was confirmed that the density characteristics were shown, and at a high temperature, the current density characteristics were much better than those of the fuel cell of Comparative Example 1.

The membrane-electrode assembly of the present invention has excellent hydrogen ion conductivity, excellent heat resistance, can be used at high temperatures, and mechanical properties are also excellent.

Claims (12)

Anode and cathode electrodes positioned opposite one another; And It includes a polymer electrolyte membrane located between the anode and the cathode, The polymer electrolyte membrane is a fuel cell membrane-electrode assembly comprising a polymer represented by Formula 1 below: [Formula 1]

At least one of X ₁ to X ₈ of Formula 1 is a functional group represented by Formula 2, n is an integer in the range of 100 to 10000, [Formula 2]

In Formula 2, Y ₁ or Y ₂ are each independently an element selected from the group consisting of a halogen element or hydrogen, n1 is an integer in the range of 1 to 10, and n2 is in the range of 1 to 10. Integer. The membrane-electrode assembly of claim 1, wherein Y ₁ in Formula 2 is fluorine (F) or hydrogen (H). The membrane-electrode assembly of claim 1, wherein Y ₂ in Formula 2 is fluorine (F) or hydrogen (H).       The membrane-electrode assembly of claim 1, wherein in Formula 2, n1 is an integer ranging from 1 to 3. 3.       The membrane-electrode assembly of claim 1, wherein in Formula 2, n 2 is an integer in the range of 1 to 3. 3. The fuel cell of claim 1, wherein the anode and cathode electrodes include an electrode substrate and a catalyst layer, and the catalyst layer comprises at least one metal catalyst selected from the group consisting of platinum, ruthenium, osmium, and a platinum-transition metal alloy. Membrane-electrode assembly for batteries. According to claim 1, wherein the anode and the cathode electrode comprises an electrode base and a catalyst layer, the catalyst layer is one or more selected from the group consisting of platinum, ruthenium, osmium, and platinum-transition metal alloy supported on the carrier Membrane-electrode assembly for a fuel cell comprising a metal catalyst. The membrane-electrode assembly of claim 1, wherein the anode and cathode electrodes comprise an electrode substrate and a catalyst layer, and the electrode substrate is made of carbon paper or carbon cloth. The membrane-electrode assembly of claim 1, wherein the anode and cathode electrodes comprise an electrode substrate and a catalyst layer, and the electrode substrate further comprises a microporous layer (MPL). The method of claim 9, wherein the microporous layer (MPL) comprises at least one conductive carbon selected from the group consisting of graphite, carbon nanotubes (CNT), fullerenes (C60), activated carbon, carbon nanohorn and carbon black. Membrane-electrode assembly for fuel cell. A membrane-electrode assembly according to any one of claims 1 to 10 disposed on both sides of the polymer electrolyte membrane and the polymer electrolyte membrane, and a separator disposed on both sides of the membrane-electrode assembly, At least one electricity generating unit generating electricity through an electrochemical reaction; A fuel supply unit supplying the fuel to the electricity generation unit; And A fuel cell system comprising an oxidant supply unit for supplying the oxidant to the electricity generation unit. The fuel cell system of claim 11, wherein the fuel cell system is a polymer electrolyte type or a direct oxidation type.

Images