KR20080035293A - Electrode, membrane-electrode assembly for fuel cell, fuel cell, and method for preparing the same - Google Patents

Abstract

An electrode for a fuel cell, a method for preparing the electrode, a method for preparing a membrane electrode assembly by using the electrode, and a fuel cell containing the membrane electrode assembly are provided to promote the movement of the electricity generated at an electrode layer to the outside and to minimize the loss of a catalyst material. An electrode for a fuel cell comprises an active layer which comprises a catalyst material infiltrated in an electrically conductive porous polymer structure. Preferably the electrically conductive porous polymer structure has a membrane form having a thickness of 5-50 micrometers and comprises at least one selected from the group consisting of polyaniline, polypyrrole, polythiophene, polyacetylene, polyacene and a composite polymer comprising the materials.

Description

Electrode for fuel cell, membrane-electrode assembly, fuel cell and manufacturing method thereof {ELECTRODE, MEMBRANE-ELECTRODE ASSEMBLY FOR FUEL CELL, FUEL CELL, AND METHOD FOR PREPARING THE SAME}

1 is a schematic diagram of a polymer electrolyte fuel cell manufactured according to the present invention.

2 is a performance graph of the membrane electrode assembly prepared by Example 1 and Comparative Example 1.

The present invention relates to an electrode used in a fuel cell, a membrane-electrode assembly (MEA), a fuel cell, and a method of manufacturing the same. More specifically, the coating process can be simplified and the loss of catalyst ink can be minimized. An electrode, a membrane electrode assembly, and its manufacturing method are related.

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 or alkaline fuel cells, etc., depending on 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, electrolyte, and the like.

Among these, the polymer electrolyte fuel cell (PEMFC), which is being developed recently, has superior output characteristics compared to other fuel cells, has a low operating temperature, fast start-up and response characteristics, and is a mobile power source such as an automobile. Of course, it has a wide range of applications, such as distributed power supply for homes, public buildings and small power supply for electronic devices.

Polymer electrolyte fuel cells consist of a continuous composite of membrane electrode assemblies (MEAs), such as the heart of a fuel cell, and bipolar plates that collect and supply the generated electricity. Here, the membrane electrode assembly means a conjugate of an electrode in which an electrochemical catalytic reaction of fuel (aqueous methanol solution or hydrogen) and air occurs and a polymer membrane in which hydrogen ions are transferred.

The electrochemical reaction in a fuel cell consists of two separate reactions: the oxidation reaction at the anode and the reduction at the cathode. The anode and cathode are separated through the electrolyte. Methanol and water are supplied directly to the anode instead of hydrogen, and hydrogen ions generated during the oxidation of methanol move to the cathode along the polyelectrolyte and react with oxygen supplied to the cathode to generate electricity. do. The reaction that takes place is as follows.

_{Anode: CH 3 OH + H 2 O} → CO 2 + 6H + + 6e -

^{_{Cathode: 3 / 2O 2 + 5H +}} + 6e - → 3H 2 O

Total reaction: CH ₃ OH + 3 / 2O ₂ → CO ₂ + 3H ₂ O

The electrodes of a direct methanol fuel cell are typical diffusion electrodes. The electrode consists of two layers, an electrode diffusion layer (electrode support layer) and an active layer. The electrode diffusion layer is a layer that plays a role of support and fuel diffusion, and is made of carbon paper or carbon cloth. The active layer is a layer in which substantial electrochemical reaction occurs in contact with the polymer electrolyte membrane, and platinum particles as catalysts are dispersed in carbon particles or are composed of platinum or alloy black.

Electrode in the early stage of direct methanol fuel cell development was used by adding Pt-black to spray on carbon paper or carbon cloth used as diffusion layer to form an active layer and bonding it with electrolyte membrane by using heating compression method. However, the above method has a disadvantage in that the structure is not efficient because the interface resistance between the active layer and the electrolyte membrane is large, and catalyst catalysts penetrate into the diffusion layer and do not participate in the reaction.

In order to solve the above problems, methods for directly forming a catalyst layer on an electrolyte membrane, such as a decal process (US 6,391,486) and sputter deposition (US 6,171,721), have been proposed.

However, in the decal process, the active layer is formed separately, and then the active layer is bonded to the electrolyte membrane. However, the decal process requires a high temperature above the glass transition temperature of the electrolyte membrane and requires a separate pretreatment, which complicates the process. In addition, there is a disadvantage that the transfer of the active layer formed separately is not made properly.

Sputter deposition can improve the efficiency of the catalyst, but due to the crystalline characteristics of the Pt catalyst, a thin film is formed at a thickness of 1 μm or more, thereby preventing cation permeation. Therefore, only a very small amount of catalyst can be used, resulting in low power density. In addition, sputter deposition has a disadvantage in that it is impossible to obtain more than a certain level of output density. Due to the characteristics of the semiconductor process, it is manufactured in a high vacuum region, and thus is not suitable for mass production due to high production cost and long production time.

As described above, the conventional fuel cell catalyst manufactures a membrane electrode assembly by coating a catalyst ink including a catalyst component on both sides of a proton conductive polymer membrane, and is typically spray coating and die coating. This is mainly considered. Spray coating has a problem of loss of catalyst ink and low productivity when manufacturing a membrane electrode assembly, and die coating has a relatively good loss of catalyst ink, but has a problem of non-uniformity of coating layer.

Therefore, current membrane electrode assembly manufacturing technology has a lot of problems due to the complexity of the coating process and the loss of the catalyst ink is required to solve the problem.

In order to solve the above problems, the present invention is to impregnate the catalyst ink in the electroconductive porous polymer structure, and then adhered to the diffusion layer or the electrolyte membrane to prepare a membrane electrode assembly, a complex coating process can be omitted, It has also been found that the loss of catalyst ink can be minimized. In addition, it is possible to promote electron transfer in the active layer by using an electrically conductive porous polymer structure.

Accordingly, the present invention provides a fuel cell electrode, a method of manufacturing the electrode, a membrane electrode assembly having the electrode, a method of manufacturing the membrane electrode assembly, the catalyst material comprising an active layer impregnated in an electrically conductive porous polymer structure, And a fuel cell provided with the membrane electrode assembly.

The present invention provides an electrode for a fuel cell, characterized in that the catalytic material comprises an active layer impregnated in a porous polymer structure having electrical conductivity.

In addition, the present invention comprises a) preparing a catalyst ink by mixing a catalyst, an ionomer, and a dispersion solvent; b) a second step of impregnating the catalyst ink in the electrically conductive porous polymer structure; It provides a method for manufacturing an electrode for a fuel cell comprising a.

The present invention also provides a fuel cell membrane electrode assembly in which the electrode is attached to both surfaces of the electrolyte membrane.

In addition, the present invention comprises a) preparing a catalyst ink by mixing a catalyst, an ionomer, and a dispersion solvent; b) a second step of impregnating the catalyst ink in the electrically conductive porous polymer structure; c) a third step of adhering the catalyst-impregnated electrically conductive porous polymer structure to both sides of the hydrogen ion conductive polymer membrane; It provides a method for producing a membrane electrode assembly for a fuel cell comprising a.

In addition, the present invention comprises a) a first step of preparing a catalyst ink by mixing a catalyst, an ionomer and a dispersion solvent; b) a second step of impregnating the catalyst ink in the electrically conductive porous polymer structure; c) a third step of adhering the catalyst impregnated electroconductive porous polymer structure to the diffusion layer; And d) a fourth step of adhering the electrode prepared in the third step to both sides of the hydrogen ion conductive polymer film. It provides a method for producing a membrane electrode assembly for a fuel cell comprising a.

Moreover, this invention provides the fuel cell provided with said membrane electrode assembly.

Hereinafter, the present invention will be described in detail.

According to the present invention, instead of forming an active layer by coating a catalyst ink on a diffusion layer such as carbon paper or carbon cloth, or an electrolyte membrane by spray coating or die coating, in the manufacturing process of a fuel cell electrode and a membrane-electrode assembly in the related art, By manufacturing an active layer impregnated with a catalyst ink in a porous polymer structure and adhering to a diffusion layer or an electrolyte membrane, a fuel cell electrode and / or a membrane-electrode assembly are manufactured, thereby simplifying the process by eliminating a complicated coating process and coating. Characterized in that the loss of the catalyst ink generated in the process can be minimized. Furthermore, it is characterized by improving the electrical conductivity in the active layer through electrical conduction by the electrically conductive porous polymer structure.

<Fuel cell electrode>

The electrode for a fuel cell of the present invention is characterized in that it comprises an active layer in which a catalytic material is impregnated in an electrically conductive porous polymer structure, wherein the active layer is bonded to the diffusion layer to form an electrode, and the electrode and the electrolyte membrane are bonded to each other to form a membrane electrode assembly. (MEA) can be configured.

The electroconductive porous polymer structure used in the active layer serves as a support for supporting the electrode catalyst and ionomer, and thus can be used as a support for the catalyst layer in the conventional electrode, so that the electroconductive porous without the diffusion layer It is also possible to configure an electrode composed of only a polymer structure and a catalyst.

In the present invention, the porous polymer structure may have electrical conductivity. When the porous polymer structure has electrical conductivity, there is an advantage that may help smoothly flow electricity from the electrode layer to the outside. Non-limiting examples of the porous polymer structure having electrical conductivity include porous polyaniline-based, polypyrrole-based, polythiophene-based, polyacetylene-based, polyacene-based, and the like, and other organic or inorganic materials as long as they maintain electrical conductivity. Compound polymers are also possible.

Although the form of the electrically conductive porous polymer structure is not particularly limited, it is preferable to have flexibility. When the electrically conductive porous polymer structure has flexibility, it is easy to handle the impregnation process of the catalyst ink, and it may be applied to the electrolyte membrane or the diffusion layer. In the case of joining, there is an advantage in that bonding is easier, and in the present invention, it is preferable to have a film form in the range of 5 μm to 50 μm in thickness. There is a problem that impregnation becomes difficult.

In the present invention, the active layer included in the electrode is a form in which the catalyst is impregnated in the electrically conductive porous polymer structure, the electrically conductive porous polymer structure has pores in the porosity range of 60 ~ 90 vol%, the catalyst inside the pores It may be present, or may be present in the pores of all of the electrically conductive porous polymer structure, or only present in the pores of some of the electrically conductive porous polymer structure.

In addition, the catalyst may be present in the pores of the electrically conductive porous polymer structure, and may also exist by forming a layer on the outer surface of the electrically conductive porous polymer structure, and the presence of such a catalyst and the impregnation amount of the catalyst may be impregnated. It can be adjusted according to the method and impregnation conditions (eg, impregnation time, type of solvent, impregnation temperature, solid concentration of the catalyst ink, etc.).

In the present invention, the catalyst material is not particularly limited as long as it is known to those skilled in the art as a catalyst material that can be used for the oxidation / reduction electrode of the fuel cell, and may be platinum or a platinum-containing alloy, and non-limiting examples thereof include Pt, Pt / Ru, Pt / Pd, Pt / Au, Pt / Ag, Pt / Ir, Pt / Rh, Pt / Os and the like.

In addition, the catalyst material includes a form in which only particles of the catalyst material are attached, or a form in which particles of the catalyst material are attached to other carriers.

The electrode for a fuel cell according to the present invention may further include a diffusion layer, and carbon dioxide, carbon cloth, or the like may be used in the diffusion layer, and the reactants and the product may be sufficiently diffused to serve to smoothly react.

<Method of manufacturing electrode for fuel cell>

Since the manufacturing method of the electrode for a fuel cell of the present invention does not require a coating process unlike the manufacturing method of the electrode for a conventional fuel cell, unlike the conventional manufacturing method, the process can be simplified, and the catalyst ink generated in the coating process It is characterized by minimizing losses. In addition, it is possible to obtain an effect of increasing the conductivity in the active layer by using an electrically conductive porous structure. The method of the present invention may be based on a method of adhering an electroconductive porous polymer structure impregnated with a catalyst to a diffusion layer such as carbon paper. In this case, the method of adhesion may be performed by a method known to those skilled in the art, for example, a method of heating compression. You can. In addition, the electroconductive porous polymer structure impregnated with the catalyst may be used alone as an electrode without adhering to a support such as a diffusion layer.

Method for producing an electrode according to the present invention is as follows,

a) a first step of preparing a catalyst ink by mixing a catalyst, an ionomer, and a dispersion solvent; And

b) a second step of impregnating the catalyst ink in the electrically conductive porous polymer structure;

It may be to include.

As the dispersion solvent, those known to those skilled in the art can be used, which are commonly used in catalyst inks, and non-limiting examples thereof include alcohols such as distilled water, ethanol and isopropyl alcohol, and mixtures of distilled water and alcohol.

In the first step of a), the catalyst, ionomer, and dispersion solvent are uniformly mixed to prepare a catalyst ink, and additives may be included for uniform dispersion.

In the second step of b), the electroconductive porous polymer structure is impregnated with the catalyst ink prepared in the first step, and the method of impregnation dipping the electroconductive porous polymer structure into a bath in which the catalyst ink is contained, capillary force By using a dipping method in which the catalyst ink penetrates into the pores, or by using an ultrasonic wave to accelerate the penetration of the catalyst ink while using the above dipping method (sonification), etc. may be used. Methods can be used.

Meanwhile, after impregnating the catalyst ink in the porous polymer structure, it may be dried to remove the solvent, or may be dried after being adhered to the electrolyte membrane or the diffusion layer to remove the solvent.

<Membrane Electrode Assembly for Fuel Cell>

As described above, the membrane electrode assembly for a fuel cell according to the present invention is characterized in that an electrode including an active layer in which a catalytic material is impregnated in an electrically conductive porous polymer structure is attached to both surfaces of an electrolyte membrane and functions as a fuel electrode and an air electrode. In addition, the diffusion layer may be further attached to the outer surface to which the electrolyte membrane and the electrode are attached, or the electrode may be formed of only the active layer without the diffusion layer.

Carbon paper, carbon cloth, and the like may be used for the diffusion layer that may be used in the membrane electrode assembly for fuel cell according to the present invention, and the reactants and the product may be sufficiently diffused to serve to smoothly react.

<Method for Manufacturing Membrane Electrode Assembly>

Method for producing a membrane electrode assembly according to the present invention is as follows,

a) a first step of preparing a catalyst ink by mixing a catalyst, an ionomer, and a dispersion solvent;

b) a second step of impregnating the catalyst ink in the electrically conductive porous polymer structure;

c) a third step of adhering the catalyst impregnated electrically conductive porous polymer structure to both sides of the hydrogen ion conductive polymer membrane; And

Optionally, d) a fourth step of adhering the diffusion layer to the outer surface of the membrane assembly prepared in the third step;

It may be to include.

In the present invention, a method of adhering the electroconductive porous polymer structure impregnated with the catalyst to both surfaces of the electrolyte membrane and then adhering the diffusion layer to the outer surface thereof may be used, and conversely, adhering the electroconductive porous polymer structure impregnated with the catalyst to the diffusion layer. The electrode layer may be prepared first, and then a method of adhering to both surfaces of the electrolyte membrane may be used such that the active layer faces the electrolyte membrane in the electrode layer. Of course, a method of not attaching the diffusion layer to the outer surface is also possible.

That is, according to another aspect of the manufacturing method of the membrane electrode assembly of the present invention,

a) a first step of preparing a catalyst ink by mixing a catalyst, an ionomer, and a dispersion solvent;

b) a second step of impregnating the catalyst ink in the electrically conductive porous polymer structure;

c) adhering the catalyst impregnated electrically conductive porous polymer structure to the diffusion layer; And

d) a fourth step of adhering the electrode prepared in the third step to both sides of the hydrogen ion conductive polymer film;

It may be to include.

At this time, the method of adhesion can use the method known to a person skilled in the art, and can be based on methods, such as a heating compression bonding.

<Fuel cell>

The fuel cell including the membrane electrode assembly may be manufactured by a method known to those skilled in the art except for using the electrode and the membrane-electrode assembly manufactured in the present invention.

In this case, the fuel cell using the electrode catalyst of the present invention may be a polymer electrolyte fuel cell and a direct liquid fuel cell employing an oxygen reduction reaction as a cathode reaction, but are not limited thereto. In particular, a direct methanol fuel cell, a direct formic acid fuel cell, a direct ethanol fuel cell or a direct dimethyl ether fuel cell is preferable.

Except for the electrode and membrane electrode assembly produced in the present invention, all the materials constituting the fuel cell may be any material used in conventional fuel cells known in the art.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited thereto.

Example 1

1-1. Electrode Fabrication Using Electroconductive Porous Polymer Structure

Polyaniline was polymerized on the porous polyethylene membrane to prepare an electrically conductive porous polymer structure coated with polyaniline.

Catalytic ink was prepared by stirring a mixed solvent of an electrode catalyst (Tanaka, 60 wt% Pt / carbon), Nafion ionomer, isopropyl alcohol, and water, and the size of 5 cm × 5 cm in a catalyst ink solution prepared at room temperature. After immersing the polymer structure, the ultrasonic wave was added to impregnate the catalyst ink in the pores and then dried.

The impregnation process was repeated until the desired amount of platinum coating (0.4 mg-Pt / cm ² ) was obtained.

1-2. Membrane electrode  Junction ( MEA ) Produce

After bonding the catalyst-impregnated polymer structure prepared in Example 1-1 to the diffusion layer by hot pressing, the Nafion electrolyte membrane was thermally and mechanically bonded between the prepared electrodes to prepare a membrane electrode assembly. An ion exchange membrane fuel cell was prepared.

Comparative Example 1

The electrode was prepared by mixing an electrode catalyst (Tanaka noble metal, 60 wt% Pt / carbon) with a Nafion ink having high hydrogen ion conductivity and applying a carbon electrode to a fuel electrode and an oxygen electrode. At this time, platinum loading on the side of the oxygen electrode was 0.4 mg-Pt / cm ² and platinum loading on the anode electrode was 0.4 mg-Pt / cm ² .

Except for the electrode manufacturing process was carried out in the same manner as in Example 1 to prepare a membrane electrode assembly and a fuel cell comprising the same.

Experimental Example 1

Performance Evaluation of Fuel Cells

The performance test of the unit cell using the electrode catalyst prepared according to the present invention was carried out as follows.

Air and hydrogen at normal pressure were supplied to the positive electrode of the manufactured unit cell, and both air and hydrogen were used at 100% humidification condition. Thereafter, the current density was measured while varying the voltage across the unit cell, and is shown in FIG. 2.

As a result, the MEA of Example 1 showed a current density of 0.72 A / cm 2 at 0.65V, and from this, it was confirmed that the performance was superior to 0.62 A / cm 2 of the comparative example (see FIG. 2).

The present invention can omit the complicated coating process by impregnating the catalyst ink in the electroconductive porous polymer structure and then adhering it to the diffusion layer or the electrolyte membrane, and also controlling the process of impregnating the electroconductive porous polymer structure in the catalyst ink to control the catalyst. The amount of catalyst can be varied, so that the loss of catalyst ink can be minimized. And, by using the electrically conductive porous polymer structure, it is possible to facilitate the smooth movement of electricity generated in the electrode layer to the outside.

Claims (16)

A fuel cell electrode, characterized in that the catalyst material comprises an active layer impregnated in a porous polymer structure having electrical conductivity. The electrode of claim 1, wherein the electrically conductive porous polymer structure is in the form of a membrane having a thickness in the range of 5 to 50 µm. The method of claim 1, wherein the electrically conductive porous polymer structure comprises at least one selected from the group consisting of polyaniline-based, polypyrrole-based, polythiophene-based, polyacetylene-based, polyacene-based, and composite polymers containing the above materials. A fuel cell electrode, characterized in that. The electrode of claim 1, wherein the electrically conductive porous polymer structure has a porosity in the range of 60 vol% to 90 vol%. The fuel cell electrode as claimed in claim 1, wherein the catalyst material is present in the pores of all or part of the porous polymer structure. The electrode as claimed in claim 5, wherein the catalyst material is present not only inside the pores of the porous polymer structure but also forming a layer on the surface of the porous polymer structure. The method of claim 1, wherein the catalyst material is at least one selected from the group consisting of Pt, Pt / Ru, Pt / Pd, Pt / Au, Pt / Ag, Pt / Ir, Pt / Rh, and Pt / Os. A fuel cell electrode. The fuel cell electrode as claimed in claim 1, wherein the catalyst material is supported on the surface of another carrier particle, and the carrier particle on which the catalyst is supported is impregnated in the electrically conductive porous polymer structure. a) a first step of preparing a catalyst ink by mixing a catalyst, an ionomer, and a dispersion solvent; b) a second step of impregnating the catalyst ink in the electrically conductive porous polymer structure; Method for producing an electrode for a fuel cell comprising a. 10. The method according to claim 9, wherein the second step comprises dipping the electroconductive porous polymer structure into the catalyst ink. 10. The method of claim 9, wherein the second step comprises ultrasonically dipping the electroconductive porous polymer membrane into the catalyst ink. The membrane electrode assembly for fuel cells, wherein the electrode according to any one of claims 1 to 8 is attached to both surfaces of the electrolyte membrane. a) a first step of preparing a catalyst ink by mixing a catalyst, an ionomer, and a dispersion solvent; b) a second step of impregnating the catalyst ink in the electrically conductive porous polymer structure; c) a third step of adhering the catalyst-impregnated electrically conductive porous polymer structure to both sides of the hydrogen ion conductive polymer membrane; Method for producing a membrane electrode assembly for a fuel cell comprising a. The method of claim 13, further comprising: d) a fourth step of adhering the diffusion layer to the outer surface of the membrane assembly prepared in the third step; Method of producing a membrane electrode assembly for a fuel cell further comprises. a) a first step of preparing a catalyst ink by mixing a catalyst, an ionomer, and a dispersion solvent; b) a second step of impregnating the catalyst ink in the electrically conductive porous polymer structure; c) a third step of adhering the catalyst impregnated electroconductive porous polymer structure to the diffusion layer; And d) a fourth step of adhering the electrode prepared in the third step to both sides of the hydrogen ion conductive polymer film. Method for producing a membrane electrode assembly for a fuel cell comprising a. A fuel cell comprising the membrane electrode assembly according to claim 12.

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