KR20060019844A - A membrane electrode assembly for fuel cell and a fuel cell comprising the same - Google Patents

Abstract

The present invention relates to a fuel cell membrane / electrode assembly and a fuel cell including the same, wherein the membrane / electrode assembly comprises: an anode and a cathode electrode disposed to face each other; And a polymer electrolyte membrane positioned between the anode and the cathode electrode, wherein the polymer electrolyte membrane includes a porous glass material in which fine pores are formed.

According to the present invention, since the glass membrane having micropores is formed as the polymer electrolyte membrane of the fuel cell membrane / electrode assembly, there is no need for a separate humidifying device, thereby reducing the cost and space saving effect, while passing hydrogen ions through the micropores. Since it does not pass through and is used regardless of the type of fuel, there is an effect that can improve the efficiency of the fuel cell.

Fuel Cell, Polymer Electrolyte Membrane, Glass

Description

Membrane / electrode assembly for fuel cell and fuel cell comprising same {A MEMBRANE ELECTRODE ASSEMBLY FOR FUEL CELL AND A FUEL CELL COMPRISING THE SAME}

1 is a cross-sectional 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 10a: anode catalyst layer (anode)

10b: cathode catalyst layer (cathode) 15: polymer electrolyte membrane

20: membrane / electrode assembly

[Industrial use]

The present invention relates to a fuel cell membrane / electrode assembly and a fuel cell including the same, and more particularly, a fuel cell membrane / which does not pass fuel while passing hydrogen ions using porous glass as a polymer electrolyte membrane. It relates to an electrode assembly and a fuel cell comprising 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.

Fuel cells are classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, polymer electrolyte batteries, or alkaline fuel cells according to the type of electrolyte used. Each of these fuel cells operates on essentially the same principle, but differs in the type of fuel used, operating temperature, catalyst, and electrolyte.

Among these, polymer electrolyte fuel cells (PEMFCs), which are being developed recently, have much higher output characteristics, lower operating temperatures, faster start-up and pressure characteristics than other fuel cells, As well as transportable power supply, there is a wide range of applications such as distributed power supply such as homes, public buildings and small power supply such as for electronic devices.

The polymer electrolyte fuel cell as described above basically includes a stack, a reformer, a fuel tank, a fuel pump, and the like to construct a system. The stack forms the body of the fuel cell, and the fuel pump supplies the fuel in the fuel tank to the reformer. The reformer reforms the fuel to generate hydrogen gas and supplies the hydrogen gas to the stack. Accordingly, the polymer electrolyte fuel cell supplies fuel in a fuel tank to a reformer by operation of a fuel pump, reforms the fuel in the reformer to generate hydrogen gas, and electrochemically reacts the hydrogen gas and oxygen in a stack. Generates electrical energy.

On the other hand, the fuel cell may employ a direct methanol fuel cell (DMFC) method that can supply a liquid methanol fuel directly to the stack. Such a direct methanol fuel cell fuel cell, unlike the polymer electrolyte fuel cell, the reformer is excluded.

In such a fuel cell system, a stack that substantially generates electricity is composed of a number of unit cells consisting of a membrane / electrode assembly (MEA) and a separator (also called a bipolar plate). It has a stacked structure of several tens. The membrane / electrode assembly has a structure in which an anode electrode (also called "fuel electrode" or "oxide electrode") and a cathode electrode (also called "air electrode" or "reduction electrode") are attached with a polymer electrolyte membrane interposed therebetween. Have

1 is a view schematically showing an operating state of the fuel cell 1. In the fuel cell, the membrane / electrode assembly 20 includes a cathode catalyst layer 10a, a cathode catalyst layer 10b, and a polymer electrolyte membrane 15. Referring to FIG. 1, when hydrogen gas or fuel is supplied to the anode catalyst layer 10a, an electrochemical oxidation reaction occurs and ionizes to hydrogen ions H ⁺ and electrons e ⁻ . The ionized hydrogen ions move to the cathode catalyst layer 10b through the polymer electrolyte membrane 15 and electrons move through the anode catalyst layer 10a. Hydrogen ions transferred to the cathode catalyst layer 10b cause an electrochemical reduction reaction with oxygen supplied to the cathode catalyst layer 10b to generate heat of reaction and water, and electrical energy is generated by the movement of electrons. This electrochemical reaction can be represented by the following scheme.

Scheme 1

The ^{_{anode: H 2 → 2H + + 2e}} -

_{^{Cathode: 2H + + 1/2 O 2 +}} 2e - → H 2 O

The polymer membrane / electrode assembly is composed of a solid polymer electrolyte membrane and a carbon supported catalysts electrode layer. At this time, the polymer electrolyte membrane serving as an electrolyte may include Nafion (Nafion, a brand name of DuPont), Premion (Flemion, a brand name of Asahi Glass), Asifrex (Asiplex, a brand name of Asahi Chemical), and A perfluorosulfonate ionomer membrane such as Dow XUS (Dow XUS, Dow Chemical Co., Ltd.) electrolyte membrane is widely used, and the carbon-supported catalyst electrode layer is made of porous carbon paper or carbon. A carbon powder, in which fine catalyst particles such as platinum (Pt) or ruthenium (Ru), are supported on an electrode support such as carbon cloth, is used by bonding a waterproof binder.

In order to solve the problems of the prior art as described above, an object of the present invention is to use a porous glass material as the material of the polymer electrolyte membrane, it is not necessary to install a separate humidifier, and solve the cross-over problem of methanol, etc. Irrespective of the present invention, there is provided a fuel cell membrane / electrode assembly having excellent fuel cell efficiency and a fuel cell including the same.

The present invention provides an anode and a cathode electrode facing each other to achieve the above object; And a polymer electrolyte membrane positioned between the anode and the cathode electrode, wherein the polymer electrolyte membrane includes a porous glassy material having fine pores.

In addition, the present invention comprises the steps of coating a catalyst slurry comprising a metal catalyst, a binder and a solvent on one surface of the gas diffusion layer is a carbon support to prepare a catalyst electrode; Processed by the sol-gel method to prepare a glass with micropores formed; And placing the catalyst electrode as an anode electrode and a cathode electrode, and placing the glass material having the micropores therebetween, followed by hot rolling to bond the catalyst electrode to the catalyst electrode.

The present invention also provides a membrane / electrode assembly; And a bipolar plate sandwiching the membrane / electrode assembly.

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

Conventional polymer electrolyte membranes are mainly formed of Nafion, which is a perfluoro-based polymer, but polymer membranes such as Nafion generate H ⁺ mobility when water molecules are moistened with -SO ₃ H. Therefore, the conventional method of manufacturing the membrane / electrode assembly used a method of placing the Nafion membrane between the anode and the cathode, bonding them with heat, and then supplying moisture to the electrode plate with a humidifier to moisturize the polymer membrane. However, in the above, in order to humidify the polymer electrolyte membrane, a humidifier must be provided separately. In addition, the perfluoro-based polymer may not be used at a temperature of 120 ° C. or higher, and is expensive, and there is a problem in that a humidification apparatus must be installed to meet humidification conditions for the above reason.

Recently, research has been made to use an aromatic thermosetting polymer as a polymer electrolyte membrane for a fuel cell. However, when methanol is used as a fuel, the cross-over problem of methanol is still not solved. There is a problem falling.

According to the present invention, glass is used as the polymer electrolyte membrane of the fuel cell membrane / electrode assembly, so that the polymer does not need to be humidified through a separate humidifier as in the prior art.

In addition, according to the present invention, micropores are formed in the glass, so that hydrogen ions generated in the membrane / electrode assembly pass through and are not passed through even when a fuel such as methanol is used. Therefore, the polymer electrolyte membrane of the present invention can be used without being limited to a kind of fuel. In addition, the polymer electrolyte membrane including the glassy microporous formed of the present invention is excellent in mechanical properties than when formed of a conventional polymer and can be used at a temperature of 120 ℃ or more.

In the polymer electrolyte membrane for a fuel cell of the present invention, the porous glass material in which the fine pores are formed is preferably contained in an amount of 10 to 100% by weight. That is, in the present invention, the glass may be used alone, or may be used by mixing with an ionic polymer.

The porous glass material in which the micropores are formed may include about 70% of silica as an inorganic oxide. Examples of the porous glassy material include soda lime silica, lead oxide-lead glass, boron silicate glass, and bentonite, which is a clay mineral produced by deterioration of glass particles. have.

In addition, it is preferable that the porous glass material in which the micropores are formed has a porosity of 0.1 to 40% by volume, more preferably 10 to 40% by volume.

It is preferable that the micropore size of the glassy microporous formed is 0.01 to 100 ㎛. In this case, when the glass micropore size is less than 0.01 μm, there is a problem in that the hydrogen conductivity is lowered.

The manufacturing method of the glass material used as the polymer electrolyte membrane for the fuel cell is not particularly limited, and may be preferably formed by processing the sol-gel method to form micropores.

It is preferable that the polymer electrolyte membrane prepared above has a thickness of 1 to 100 μm.

In addition, the present invention can be prepared a membrane / electrode assembly by a conventional method using the polymer electrolyte membrane prepared above. In a preferred embodiment, a catalyst slurry comprising a metal catalyst, a binder, and a solvent is coated on one surface of a gas diffusion layer serving as a carbon support to prepare a catalyst electrode, and after preparing a glass material in which micropores are formed by a sol-gel method, the catalyst electrode is an anode. A membrane / electrode assembly can be prepared by placing an electrode and a cathode on the glass substrate in which the micropores are formed, and hot-rolling them together.

Thus, the membrane / electrode assembly comprises an anode and a cathode electrode located opposite each other; And a porous glass material of the present invention located between the anode and the cathode as a polymer electrolyte membrane.

As the anode and the cathode serves as a catalyst layer, a catalyst slurry may be prepared by mixing a metal catalyst, a binder, and a solvent, which is a dispersion medium, and may be manufactured by coating and drying it on one surface of a carbon support.

The catalyst layer includes a so-called metal catalyst that catalyzes the related reactions (oxidation of hydrogen and reduction of oxygen), and platinum group metals of the periodic table of elements, for example, Pt or Ru, transition metals such as Fe or Co, etc. may be used. Can be. Also generally, those supported on a carrier are used. As the carrier, carbon such as acetylene black or graphite may be used, or inorganic fine particles such as alumina or silica 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, even if detailed description thereof is omitted, it is easily understood by those skilled in the art. The metal catalyst used in the present invention is preferably selected from the group consisting of Pt / C, Pt / Ru, and Pt / Fe / Co.

The solvent used as the dispersion medium may be preferably an alcohol, alcohol, ether, ester, amide solvent, and the like, and specific examples thereof include isopropyl alcohol, butanol, dimethyl ketone, and the like.

In the present invention, the binder may be a fluorine-based polymer, a benzimidazole-based polymer, a ketone-based polymer, a polyether-based polymer, a polyester-based polymer, a polyamide-based polymer, a polyimide-based polymer, and the like. no.

As the carbon support serves as a gas diffusion layer, carbon paper or carbon cloth may be used, but is not limited thereto. The gas diffusion layer serves to support the fuel cell electrode and diffuses the reaction gas into the catalyst layer so that the reaction gas can be easily accessed to the catalyst layer. In addition, it is preferable to use a water repellent treatment of carbon paper or carbon cloth with a fluorine-based resin such as polytetrafluoroethylene as the gas diffusion layer to prevent the gas diffusion efficiency from being lowered by water generated when the fuel cell is driven. Do.

The prepared membrane / electrode assembly is inserted between a gas flow channel and a bipolar plate having a cooling channel to manufacture a unit cell, and a stack is manufactured by stacking the same. can do. Fuel cells can all be manufactured by conventional techniques in the art. The membrane / electrode assembly of the present invention can be applied to both low temperature humidification type, low temperature no humidification type, and high temperature no humidification type batteries.

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)

A glass substrate having a micropore size of 0.1 μm and a porosity of 10 vol% was formed to a thickness of 40 μm by the sol-gel method and used as a polymer electrolyte membrane for a fuel cell.

Then, after stacking the carbon paper on which platinum is deposited on both surfaces of the polymer electrolyte membrane prepared above, and pressurized 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 channel and a cooling channel of a predetermined shape are formed, and then compressed into a copper end plate. The battery was prepared.

(Comparative Example)

A poly (perfluorosulfonic acid) electrolyte membrane (Nafion ^™ , DuPont) having a thickness of 40 μm was used as the polymer electrolyte membrane for fuel cells.

Then, after stacking the carbon paper on which platinum is deposited on both surfaces of the polymer electrolyte membrane prepared above, and pressurized to prepare a membrane / electrode assembly. At this time, in order to maintain a humid state, a humidifier was connected to the membrane / electrode assembly.

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

Table 1 shows the results of operating hydrogen for 10 hours at a temperature of 80 ° C. for the unit cells prepared in Examples and Comparative Examples.

Voltage Current density (A / ㎠) Example Comparative example 0 0.93 0.91 0.2 0.87 0.82 0.6 0.54 0.51 0.8 0.43 0.42 One 0.34 0.31

In Table 1, the embodiment of the present invention is also excellent in performance, there is no fuel cross-over problem, in the case of the comparative example there is a problem that the fuel cross-over and the performance is also poor.

The polymer electrolyte membrane for a fuel cell of the present invention uses glass with fine pores, and thus does not require a separate humidifying device and the fuel does not pass, thereby solving the fuel cross-over problem and improving the efficiency of the fuel cell.

Claims (9)

Anode and cathode electrodes positioned opposite one another; And It includes a polymer electrolyte membrane located between the anode and the cathode, Wherein the polymer electrolyte membrane is a fuel cell membrane / electrode assembly comprising a fine glass pores formed. The fuel cell membrane / electrode assembly according to claim 1, wherein the fine pores have a glassy content of 10 to 100 wt%. The membrane / electrode assembly of claim 1, wherein the glassy microporous glass has a porosity of 0.1 to 40% by volume. The fuel cell membrane / electrode assembly according to claim 1, wherein the glass micropores having the micropores have a size of 0.01 to 100 µm. Preparing a catalyst electrode by coating a catalyst slurry including a metal catalyst, a binder, and a solvent on one surface of a gas diffusion layer serving as a carbon support; Processed by the sol-gel method to prepare a glass with micropores formed; And Joining the catalyst electrode as an anode electrode and a cathode electrode by placing the glass material having the micropores therebetween and then hot rolling the same. Method for producing a fuel cell membrane / electrode assembly comprising a. The method of manufacturing a fuel cell membrane / electrode assembly according to claim 5, wherein the fine pores have a glassy content of 10 to 100 wt%. 6. The method of claim 5, wherein the glassy microporous glass has a porosity of 0.1 to 40% by volume. The method of claim 5, wherein the micropore-formed glassy micropore size is 0.01 to 100 µm. A membrane / electrode assembly according to any one of claims 1 to 4; And And a bipolar plate sandwiching the membrane / electrode assembly.

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